GB2122710A

GB2122710A - Actuation system for transmission clutch providing engagement pressure controllable according to clutch slip speed

Info

Publication number: GB2122710A
Application number: GB08311040A
Authority: GB
Inventors: Hiroshi Ito; Shigemichi Yamada
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1982-06-22
Filing date: 1983-04-22
Publication date: 1984-01-18
Also published as: JPS58225226A; GB8311040D0

Abstract

A clutch in a transmission includes a first member and a second member which are selectively pressed together in order to engage said clutch by friction between them. When it is required to engage the clutch, then this is performed by an actuation system which includes a variable pressure type actuator 44 (or 96) which selectively thus presses the first and second members together, and which can perform the pressing action with a pressing force which is controllable to vary over a range. The actuation system also includes a control system which controls the actuator, and means 142, 144 for detecting the rotational speed of said first member and the rotational speed of said second member. The control system functions so as to cause the actuator to thus press the first and second member together in such a fashion as to cause the pressing force between them to be varied according to the relative rotational speed between said first member and said second member. The two actuators 44, 96 control respective alternative input clutches between an engine and a change-speed gear, each clutch being used in alternate gear ratios. <IMAGE>

Description

SPECIFICATION Actuation system for transmission clutch providing engagement pressure controllable according to clutch slip speed The present invention relates to an actuation system for a clutch for a transmission of a vehicle, and more particularly relates to an actuation system for such a transmission clutch which can be operated automatically and which yet can provide smooth and accurate engagement of speed stages of the transmission, both during starting of the vehicle off from rest and during shifting between transmission speed stages during motion.

In a transmission which includes one or more clutches, such a clutch typically includes a first member which is pushed against a second member in order to mutually rotationally engage together two initially mutually rotating elements of the transmission. For example, in a particular first example of clutch construction, in the case that it is desired to rotationally engage a flywheel to a shaft axially opposed to it, said flywheel and said shaft being currently in the state of being rotated at different rotational speeds, then a clutch disk rotationally coupled to the shaft but axially free to move to a certain extent is pushed by a clutch pressure plate rotationally coupled to the flywheel against a friction face formed on the flywheel, which is axially fixed in position, and, by the compressed sandwiching of the clutch disk between the clutch plate which is being axially pushed and the flywheel, both of which are rotating with respect to said clutch disk, according to the action of dynamic friction therebetween a mutual torque or couple is generated between the shaft and the flywheel in the relative rotational direction to bring their absolute rotational speeds to be the same, in other words in the relative rotational direction to bring their relative rotational speed to zero. When this has happened, in other words when the dynamic frictional action has brought the flywheel and the shaft to rotate at the same rotational speed, then the above described clutch parts are all by their sandwiching together securely rotationally engaged together by static friction.The clutch plate is typically driven in the axial direction by a spring engaged thereto which is pushable via a clutch release bearing by a fork or the like. Such a fork may be manually driven by the foot of a vehicle operator pushing a clutch pedal, or may be power driven by an actuator, in the case of the transmission being an automatic transmission, for example. In a second exemplary form of construction, the clutch includes two sets of friction plates which are alternately interleaved together, the inner peripheries of the plates of one of said sets of said friction plates being connected to a first one of the rotating elements whose rotation is to be brought to be the same (for instance to a shaft) and the outer peripheries of the other of said sets of said friction plates being connected to the other one of said elements (for instance via a clutch casing to a ring gear).A piston which may be exemplarily driven by hydraulic pressure selectively axially squeezes together the two mutually interleaved sets of friction plates, being backed by some axially fixed member. Thus, again, in order to mutually rotationally engage together the two mutually rotating elements of the transmission, a first element (a one of the first set of friction plates) is pushed against a second element (an opposing one of the second set of friction plates).In a similar way to the first type of construction, by the compressed sandwiching of the one set of friction plates between the other set of friction plates, all of which are being axially pushed together and are rotating with respect to one another, according to the action of dynamic friction therebetween a mutual torque or couple is generated between the first and the second rotating elements in the relative rotational direction to bring their absolute rotational speeds to be the same, in other words in the relative rotational direction to bring their relative rotational speed to zero.When this has happened, in other words when the dynamic frictional action has brought the first and the second set of clutch plates to rotate at the same rotational speed, then the above described clutch parts are again all by their sandwiching together securely rotationally engaged together by static friction.

Now, a clutch of either of the above described types is used nowadays not only in the case of a vehicle which is equipped with a manual transmission, in which case the clutch is typically manually actuated, but may also be used in an automatic transmission, in which case the clutch is actuated automatically by the operation of an automatic transmission control system, either electrically or mechanically or hydraulically. In more detail, in fact, there exist types of automatic transmission nowadays in which the engagement of all the speed stages is mediated by the engagement and disengagement of a plurality of clutches of the two above outlined kinds.In other words, a gear transmission mechanism of the automatic transmission incorporates said plurality of clutches, and according to automatically performed selective engagement of various ones of said plurality of clutches the gear transmission mechanism is caused to provide its various speed stages. In this case, the shifting of the gear transmission mechanism between one and another of the speed stages is of course performed by altering the engagement pattern of the plurality of clutches, i.e. at least sometimes by engaging one or more of the clutches.Further, it is known for such an automatic transmission to be used in a vehicle as directly coupled to the crankshaft of the internal combustion engine thereof, without the interposition of any fluid coupling or torque converter therebetween. in this case, the torque shock cushioning effect of the fluid coupling or torque converter when thus shifting between speed stages of the transmission is not available, and also of course the action of the fluid coupling or torque converter in starting off the vehicle from rest (either forwards or backwards) is not available.In such a system, when the vehicle is to be started off from rest, one (or possibly more than one) of the clutches of the transmission is gradually and smoothly automatically engaged, so as when engaged to provide the pattern of clutch engagement appropriate to either the first or the reverse speed stage of the transmission, according to rising of the revolution speed of the engine as for example caused by depression of the accelerator pedal of the vehicle, and as this clutch is gradually automatically engaged the vehicle is moved away from rest in the first or the reverse speed stage, in a manner similar to that which occurs when a manual clutch is smoothly manually engaged, but in this case automatically controlled.In fact, the clutch which the one which is thus engaged in order to shift the vehicle off from rest is more usually one of the above mentioned first type, with a clutch disk member which is pressed against a pressure surface formed on the flywheel of the internal combustion engine; this is in consideration of the larger diameter typically required for such a moving off from rest type clutch due to the large torque which it must smoothly transmit.

Now, in order to provide smooth shifting between speed stages in a transmission, as well as in order to provide smooth moving off from rest in the case of a transmission system of the above mentioned type in which no fluid coupling or fluid torque converter is utilized, the engagement of a clutch should be smooth and should not cause any substantial torque shock or snatching or vibration in the rotation of the two rotating members the rotation of which is being clutched together. The quicker the speed stages are shifted between, or the quicker the vehicle is moved away from rest, the more danger exists of such torque shock, snatching, or vibration.

Conventionally, in order to reduce such torque shock during the engagement of a clutch which is hydraulically actuated by the supply of a hydraulic fluid pressure to a pressure chamber thereof, it has been practiced to provide a hydraulic fluid accumulator as connected to an intermediate portion of the conduit that supplies said actuating hydraulic fluid pressure to the pressure chamber of the clutch. This accumulator may for example be of a cylinder-piston type.Thereby when, from the situation in which no actuating hydraulic fluid pressure is being supplied via said conduit to engage the clutch, such engaging actuating hydraulic fluid pressure starts to be supplied, the speed of the rise of said actuating hydraulic fluid pressure from zero is greatly cushioned by the fluid absorbing action of the accumulator, and the actuating pressure for the clutch rises much more slowly and smoothly.

This method of causing the clutch to be smoothly engaged over a certain time period by the provision of a hydraulic fluid accumulator is partially effective, but in practice is far from perfect. First, it is extremely difficult to sufficiently reduce the transmission torque shock and snatching in this way, and to do so in any case requires the provision of a very large and bulky and heavy accumulator, which has serious negative consequences for transmission design, especially in the case of a transmission which must be compact and light, as for example a transmission for a front transversely mounted engine front wheel drive type vehicle. Next, a particular cause of such torque shock or vibration, i.e., of so called "clutch judder", is as follows.

When the two rotating members are first rotating at a considerable relative rotational speed and the clutch action is first occurring, with the first and the second member of the clutch being first pushed together as explained above, then the rotational torque exerted by each of the rotating members on the other is determined according to the product of the force pushing the first and the second clutch member together and the dynamic or moving coefficient of friction between them (or rather typically between facings provided on at least one of them; in any case, between their mutually moving engaging surfaces).On the other hand, as the rotational speeds of the two rotating members come closer and closer to one another, so that the rotating members start to come to rest with respect to one another, at a certain critical relative rotational speed (which will be hereinafter referred to as such) the friction between the mutually moving engaging surfaces of the first and second clutch member transits from being dynamic or moving friction to being static friction the coefficient of which is usually substantially greater than the coefficient of dynamic friction.

Since this happens before the relative rotational speed of the first and the second clutch members has become completely zero, a sudden increase of the torque exerted by each of the rotating members on the other is abruptly caused at this time. This clutch connection shock or transmission clutch biting shock can become unacceptably great, deteriorating the driving feeling of the vehicle, damaging the parts of the transmission including the clutch itself, and perhaps even causing premature failure of the transmission as a whole. If as outlined above no fluid coupling or torque converter is provided to the transmission, then these torque shocks are not cushioned and are accordingly felt even more severely. And, as will be easily understood, this so called clutch biting shock is not substantially cushioned by the provision of a hydraulic fluid accumulator in the conduit leading actuating hydraulic fluid pressure to the pressure chamber of the clutch, in the case of a hydraulically actuated clutch, because the clutch biting shock is not actually due to too sudden or rapid engagement of the clutch, but is due to the difference between the static and dynamic frictional coefficients as explained above.

Another consideration relating to the engagement of a clutch is that the load, frictional force, heat, and stress generated in the various members of the clutch is generally the greater the greater is the relative rotational speed of the members whose rotation is being brought to be the same, and is also generally the greater the greater is the pressure with which the clutch is actuated. In order to preserve the service life of the clutch mechanism as a whole the load, frictional force, heat, and strain generated in the members of the clutch must be kept within acceptable limits, since otherwise the mechanism will quickly be deteriorated and will suffer an unacceptable loss of clutching function.Now, in the case that the clutch is manually operated by the foot of a vehicle operator pushing on a clutch pedal, or the like, then an almost unconscious feedback relating to the back pressure from the clutch pedal operates to help to ensure that not too rough an action is exerted, in other words that a slick and smooth clutch engagement action is available, at least in the case of a skilled vehicle operator who is in mental tune with the operation of the machinery; but, in the case that the engagement of the clutch is performed mechanically by the action of an actuator, then the unconscious yet subtle regulatory action of human operation and touch is not available, and in the prior art it has been a real problem to secure smooth and slick clutch action for engaging speed stages of the transmission, and for starting the vehicle off from rest, without running the risk that the first and second clutch members should be pushed too strongly together, thus causing the clutch to be abruptly and over violently engaged, and thus causing "clutch judder" and possibly damaging the various parts of the clutch by generating too much heat and frictional stress therein as well as deteriorating the operational feeling of the transmission, or even in the case of starting the vehicle off from rest stalling the engine thereof, nor running the counterpart risk that by pushing the first and second clutch members too weakly together the clutch engagement action should be performed so slowly that steady buildup of frictional heat in the clutch parts by causing too much clutch slippage should similarly damage the clutch.

The difficulty of regulating this clutch engagement action is made the greater, because the clutch is operated in a wide range of operational conditions, with regard to rotational speeds of the two members thereof, load being transmitted thereby, and the like; and also because over the service life of the clutch the various operational constants thereof such as the thickness of the lining or linings thereof, the strength of springs thereof, and so on, alter substantially.

Accordingly, it is the primary object of the present invention to provide an actuation system for a transmission clutch, which can operate the clutch by a mechanicai system, in a satisfactory manner.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch by pushing two elements of it together, without causing over violent and abrupt such pushing.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch by pushing two elements of it together, without causing over gentle and weak such pushing.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch without causing torque shock.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch without causing snatching of the clutch.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch without causing clutch judder.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch without causing clutch biting shock.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch without causing stalling of the engine of the vehicle to which the transmission is fitted, during moving of the vehicle away from rest.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch in such a way as to aid with smooth shifting between the speed stages of the transmission during vehicle motion.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch in such a way as to aid with smooth moving away from rest of the vehicle.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch by pushing two elements of it together, while taking account of the difference between the coefficients of static and of dynamic friction between these two members.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which engages the clutch positively and effectually without generating any undue load or stress in the members thereof.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which engages the clutch positively and effectually without generating any undue heat or frictional force in the members thereof.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which engages the clutch positively and effectually without allowing too much or too little clutch slippage.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which engages the clutch positively and effectually without damaging the members thereof.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which engages the clutch positively and effectually without damaging other parts of the transmission by this engagement action.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which keeps the clutch operating over a satisfactory service life thereof.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which operates the clutch mechanically without producing any substantial risk of early and sudden failure thereof.

It is a further object of the present invention to provide an actuation system for a transmission clutch, which provides slick and smooth clutch operation.

It is a yet further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch by pushing together two members thereof, in which the strength of the pushing of said members is modulated according to which phase of clutching action is currently in progress.

It is a yet further object of the present invention to provide an actuation system for a transmission clutch, which mechanically operates the clutch by pushing together two members thereof, in which the strength of the pushing of said members is modulated according to the current relative rotational speed of the two members whose rotation is being brought to be the same.

It is a yet further object of the present invention to provide such an actuation system for a transmission clutch, which takes account of the various different possible operational conditions under which the clutch must work.

It is a yet further object of the present invention to provide such an actuation system for a transmission clutch, which mechanically operates the clutch by pushing together two members thereof, and which takes account of the range of various different possible rotational speeds between said two members under which the clutch must work.

It is a yet further object of the present invention to provide such an actuation system for a transmission clutch, which takes account of the possible wear on the members of the clutch.

It is a yet further object of the present invention to provide an actuation system for a transmission clutch, which does not involve the provision of any bulky hydraulic fluid accumulator for cushioning the engagement of the clutch.

It is a yet further object of the present invention to provide an actuation system for a transmission clutch, which is light.

It is a yet further object of the present invention to provide an actuation system for a transmission clutch, which is compact.

It is a yet further object of the present invention to provide an actuation system for a transmission clutch, which is particularly suitable for incorporation into a vehicle of the front transversely mounted engine front wheel drive type.

According to the most general aspect of the present invention, these and other objects are accomplished by, for a transmission clutch comprising a first member and a second member which are selectively pressed together in order to engage said clutch by friction between them: an actuation system, comprising: (a) an actuator which selectively presses said first member and said second member together, and which can perform said pressing action with a pressing force which is controllable to vary over a range; (b) means for detecting the rotational speed of said first member and the rotational speed of said second member; and (c) a control system which controls said actuator, so as to cause said actuator to thus press said first member and said second member together, in such a fashion as to cause the pressing force by which said first member and said second member are pressed together to be varied according to the relative rotational speed between said first member and said second member.

According to such a structure, the actuator presses the first and second members together under the control of the control system which is taking account of the actual rotational speed between these members, during the processive engagement of the clutch, and thus the engagement of the clutch can be very smoothly accomplished by this delicate form of control.

Thus over violent and abrupt such pressing, or over gentle and weak such pressing, can be avoided; and thus the clutch can be mechanically operated without causing torque shock, or snatching of the clutch. Clutch judder and clutch biting shock are accordingly avoided. Further, the clutch can be mechanically operated to shift the vehicle off from rest, without any danger of causing stalling of the engine of the vehicle to which the transmission is fitted, and can be mechanically operated during shifting of the transmission between speed stages in such a way as to aid with smooth such shifting, during vehicle motion. The clutch can be engaged positively and effectually without generating any undue load or stress in the members thereof, and without generating any undue heat or frictional force, by not allowing too much or too little clutch slippage.

Thus the clutch can be engaged effectually without damaging the members thereof, and without damaging other parts of the transmission by this engagement action; and thereby this clutch actuation system can keep the clutch operating over a satisfactory service life thereof, without producing any substantial risk of early and sudden failure thereof. Slick and smooth clutch operation of the clutch are provided, and account is taken of the various different possible operational conditions under which the clutch must work, and of the range of various different possible rotational speeds between said two members under which the clutch must work.This is done without the provision of any bulky hydraulic fluid accumulator for cushioning the engagement of the clutch, and accordingly the resulting transmission is light and is compact and further is particularly suitable for incorporation into a vehicle of the front transversely mounted engine front wheel drive type.

The present invention will now be shown and described with reference to two preferred embodiments thereof, and with reference to the illustrative drawings. It should be clearly understood, however, that the description of the embodiments, and the drawings, are all of them given purely for the purposes of explanation and exemplification only, and are none of them intended to be limitative of the scope of the present invention in any way, since the scope of the present invention is to be defined solely by the legitimate and proper scope of the appended claims.In the drawings, like parts and features are denoted by like reference symbols in the various figures thereof, and: Fig. 1 is a detailed longitudinal sectional constructional view of a transmission mechanism which utilizes two clutches which are actuated by the two preferred embodiments of the clutch actuation system according to the present invention, this particular transmission in fact incorporating two power transmission systems to each of which one of said clutches relates; Fig. 2 is a schematic skeleton structural view of the transmission mechanism shown in Fig. 1; Fig. 3 is a schematic view, in part block diagrammatical form, showing part of a combination eiectric/hydraulic control system for the transmission, and elements associated therewith;; Fig. 4 is a set of two graphs illustrating the operation of the transmission control system shown in Figs. 1 through 3 with respect to the operation of the first preferred embodiment of the clutch actuation system according to the present invention, as it is used in its mode of moving the vehicle off from rest, in both of which time is shown along the horizontal axis, and in which, respectively, relative rotational speed of two members whose rotational speed is brought to be equal by a clutch, and pressure between two members of said clutch which are pressed together to frictionally engage said clutch, are shown along the vertical axes; and Fig. 5 is a similar set of two graphs illustrating the operation of the transmission control system shown in Figs. 1 through 3 with respect to the operation of the second preferred embodiment of the clutch actuation system according to the present invention, as it is used in its mode of shifting between vehicle speed stages (actually the first and the second speed stages), in both of which time is shown along the horizontal axis, and in which, respectively, relative rotational speed of two members whose rotational speed is brought to be equal by a clutch, and pressure between two members of two clutches which are pressed together to frictionally engage said two clutches, are shown along the vertical axes.

The present invention will now be described with reference to the two preferred embodiments thereof, and with reference to the appended drawings. Fig. 1 shows a transmission mechanism incorporating two preferred embodiments of the clutch actuation system according to the present invention in a detailed longitudinai cross sectional view. In this figure, the reference numeral 1 generally denotes a multiple clutching mechanism, and 2 generally denotes a gear transmission mechanism.

A first hollow driving gear wheel shaft 3 is rotatable mounted in the transmission casing 52 via a bearing 53, extending horizontally across the upper portion of the casing 52 in the figure ("left", "right", "up", and "down" will be used in the sense of the relevant figure hereinafter), and a second substantially solid driving gear wheel shaft 4 is coaxially rotatably mounted within and extending through the tubular space inside the first hollow driving gear wheel shaft 3 on bearings which are not shown in the figure, with the left and right ends of the second driving gear wheel shaft 4 each protruding out from the left and right ends of said first driving gear wheel shaft 3 for a certain distance, the left end of said second solid driving gear wheel shaft 4 being rotatably supported from the transmission casing 52 by another bearing 54.In parallel with the coaxial first and second driving gear wheel shafts 3 and 4 and displaced downwards therefrom there is provided a driven gear wheel shaft 10, which is rotatably supported from the transmission casing 52 by bearings 55 and 56.

On the driven gear wheel shaft 10 there are rotatably mounted, in order from the right to the left in Fig. 1, a first speed driven gear wheel 11, a third speed driven gear wheel 13, a second speed driven gear wheel 12, and a fourth speed driven gear wheel 1 4. On the first driving gear wheel shaft 3 there are fixedly mounted, in order from the right to the left in Fig. 1, a first speed driving gear wheel 5, a reverse speed driving gear wheel 7, and a third speed driving gear wheel 6. On the portion of the second driving gear wheel shaft 4 which projects outwards to the left from the left hand end of the first driving gear wheel shaft 3 there are fixedly mounted, in order from the right to the left in Fig. 1, a second speed driving gear wheel 8 and a fourth speed driving gear wheel 9.

The first speed driving gear wheel 5 is in constant mesh with the first speed driven gear wheel 11; the second speed driving gear wheel 8 is in constant mesh with the second speed driven gear wheel 12; the third speed driving gear wheel 6 is in constant mesh with the third speed driven gear wheel 13; and the fourth speed driving gear wheel 9 is in constant mesh with the fourth speed driven gearwheel 14.

Between the first speed driven gear wheel 11 and the third speed driven gear wheel 13 on the driven gear wheel shaft 10 there is fitted a firstthird synchronizer 16, which performs the function of synchronizing engagement of the first speed stage and of the third speed stage, as will be understood hereinafter. This first-third synchronizer 16 is of a per se well known sort, in fact being an inertia lock type Borg Warner synchromesh device.The first-third synchronizer 1 6 comprises a hub 1 6a which is fixedly mounted on the driven gear wheel shaft 10, a first speed cone member 1 6b and synchronizer ring 1 6d associated with the first speed driven gear wheel 11 and a third speed cone member 1 sic and synchronizer ring 1 sue associated with the third speed driven gear wheel 13, and a first-third synchronizer sleeve 1 6f and locking key 1 69. The function of this first-third synchronizer 16 is to rotationally couple either the first speed driven gear wheel 11 or the third speed driven gear wheel 13 or neither of them to the driven gear wheel shaft 10, according respectively as the firstthird synchronizer sleeve 1 6f is slid to the right, to the left, or is allowed to remain at its intermediate position. On the outside of the first-third synchronizer sleeve 1 6f there is formed a reverse speed driven gear wheel 18, the action of which will be explained later. which is substantially coplanar with the reverse speed driving gear wheel 7 on the first driving gear wheel shaft 3.

Between the second speed driven gear wheel 12 and the fourth speed driven gear wheel 14 on the driven gear wheel shaft 10 there is fitted a second-fourth synchronizer 17, which performs the function of synchronizing engagement of the second speed stage and of the fourth speed stage, as will be understood hereinafter. This secondfourth synchronizer 1 7 is also of a per se well known sort, in fact also being an inertia lock type Borg Warner synchromesh device.The secondfourth synchronizer 1 7 comprises a hub 1 7a which is fixedly mounted on the driven gear wheel shaft 10, a second speed cone member 1 7b and synchronizer ring 1 7d associated with the second speed driven gear wheel 12 and a fourth speed cone member 1 7c and synchronizer ring 1 7e associated with the fourth speed driven gear wheel 14, and a second-fourth synchronizer sleeve 1 7f and locking key 1 79. The function of this second-fourth synchronizer 1 7 is to rotationally couple either the second speed driven gear wheel 1 2 or the fourth speed driven gear wheel 14 or neither of them to the driven gear wheel shaft 10, respectively according to the second-fourth synchronizer sleeve 1 7f is slid to the right, to the left, or is allowed to remain at its intermediate position.

On the right hand end portion of the driven gear wheel shaft 10 there is also fixedly mounted a power output gear wheel 15, which is in constant mesh with a differential power input ring gear 86 of a differential gear mechanism 85, which is of a per se well known sort. The differential gear mechanism 85 comprises a bevel gear wheel case 92 to which said power input ring gear 86 is fixed so as to rotate said bevel gear wheel case 92, and perpendicular to the rotational axis of the bevel gear wheel case 92 there is fixed a bevel gear wheel shaft 91, on which there are rotatably mounted a pair of bevel gear wheels 87 and 88.

Also supported rotatably by the casing of the differential gear mechanism 85 as coaxial with the rotational axis of the bevel gear wheel case 92 there are provided left and right power output shafts 93 and 94, to the inner ends of which there are fixed bevel gear wheels 89 and 90, respectively. These bevel gear wheels 89 and 90 are each in constant mesh with both of the bevel gear wheels 87 and 88. The operation of such a differential mechanism as this differential gear mechanism 85 is per se well known.

Finally, on a reverse idler gear wheel shaft 19 which is supported as parallel to the first and second driving gear wheel shafts 1 and 2 and the driven gear wheel shaft 10 there is rotatably and slidably mounted a reverse idler gear wheel 20.

Neither the reverse idler gear wheel shaft 1 9 nor the reverse idler gear wheel 20 can be seen in Fig. 1 because they are hidden by other members, but there are schematically shown in Fig. 2.

Arrangements which will be described in detail hereinafter are provided for shifting this reverse idler gear wheel 20 to and fro in the left and right directions on the reverse idler gear wheel shaft 19; and, when the reverse idler gear wheel 20 is in its most rightwards position on the reverse idler gear wheel shaft 19, said reverse idler gear wheel 20 does not mesh with any other gear wheels and is therefore free to rotate; but, when the reverse idler gear wheel 20 is in its most leftwards position on the reverse idler gear wheel shaft 19, said reverse idler gear wheel 20 meshes with the reverse speed driving gear wheel 7 and with the reverse speed driven gear wheel 1 8 formed on the outside of the first-third synchronizer sleeve 1 6f, so as to provide a reverse speed stage, as will be explained later.

The multiple clutching mechanism 1 is provided within a clutch housing 21, and its power input member 23 is in fact the flywheel of an internal combustion engine not shown in the figure which is used to power the vehicle to which this transmission is fitted. The rotational axis of the power output member of this internal combustion engine is of course coincident with the rotational axis of the first and second driving gear wheel shafts 3 and 4. Between this engine flywheel 23 and the first hollow driving gear wheel shaft 3 there is provided a selectively engageable first clutch assembly 200, and between this engine flywheel 23 and the portion of the second solid driving gear wheel shaft 4 which protrudes from the right hand end of said hollow driving gear wheel shaft 3 there is provided a selectively engageable second clutch assembly 201. This right hand end of the protruding portion of the second solid driving gear wheel shaft 4 and the hub portion oftheflywheel 23 are mutually supported by a bearing 24. Thus, according to selective engagement of the first and the second clutch assemblies 200 and 201, either the first driving gear wheel shaft 3 or the second driving gear wheel shaft 4 or neither of them can be powered from said internal combustion engine, so as to be rotated thereby. These functions of selective engagement of the first and second clutch assemblies 200 and 201 are performed by first and second preferred embodiments of the clutch actuation system according to the present invention, as will be explained in detail hereinafter.

The details of the construction of the first clutch assembly 200, which in fact is the one of the two clutch assemblies 200 and 201 which is required to transmit the greater torque and which accordingly is the one of the larger radius, and which is the one of the two clutch assemblies which is actuated by the first preferred embodiment of the clutch actuation system according to the present invention as will be seen shortly, are as follows, The face of the flywheel 23 facing towards the transmission 2 is formed with a flat annular frictional engagement surface 25. A clutch cover 27 is bolted to this right hand face of the flywheel 23 by means of a plurality of bolts 26, only one of which can be seen in Fig. 1.An annular pressure plate member 28 is fitted within the clutch cover 27 as movable along the axial line of the first driving gear wheel shaft 3, so as to oppose the frictional engagement surface 25. A plate or diaphragm spring 30 which is formed as an annulus is provided between the clutch cover 27 and the clutch plate member 28: in detail, a radially intermediate annular portion of the spring 30 is flexibly connected to the clutch cover 27 by a plurality of pin type fasteners 29, only one of which can be seen in Fig. 1 but which in fact are provided in a plurality as spaced around said radially intermediate annular portion, and the radially outer annular portion of the spring 30 is flexibly connected to the clutch plate member 28 by a plurality of spring type fasteners 28a, again only one of which can be seen in Fig. 1 but which in fact are again provided in a plurality as spaced around said radially outer annular portion.

A clutch disk assembly 35 is provided between the clutch plate member 28 and the opposing annularfrictional engagement surface 25 of the flywheel 23. This clutch disk assembly 35 comprises a hub member 36 which is rotationally connected by splines to the first driving gear wheel shaft 3, an annular disk plate 38 which is sandwiched between the annular frictional engagement surface 25 of the flywheel 23 and the opposing annular pressure surface 28b of the clutch plate member 28, and a torsional or annular type shock absorber assembly 39 of a per se well known kind which connected the disk plate 38 and the hub member 36 with a certain amount of rotational resilience therebetween.Both the sides of the annular disk plate 38 are faced with high friction type clutch linings 37, so as to have a good frictional effect against the opposing frictional surfaces 28b and 25.

The radially inner portion of the plate spring 30 is formed as a tubular member which is axially drivingly connected with a clutch driving fork 34, via a clutch release bearing 31 which allows relative rotational movement but prevents relative axial motion therebetween and which is slidably mounted on a sleeve member 33 which is fitted over the first hollow driving gear wheel shaft 3 and which is fixed to the transmission casing 21 by a plurality of boits 32 only one of which can be seen in Fig. 1.Only one end of the clutch driving fork 34 can be seen in Fig. 1, but in fact this fork 34 is formed as a bar type member, an intermediate portion of which is pivoted to the transmission casing 52, and the other end of which is drivingly connected to the piston of a hydraulic actuator 95 which will be described later with reference to the schematic diagram of Fig. 3.

Thus, when the hydraulic fluid pressure chamber 96 of the hydraulic actuator 95 is not supplied with pressurized hydraulic fluid and thus does not drive said not shown other end of this clutch fork member 34, then the radially central portion of the plate spring 30 is not driven thereby in the rightwards direction in Fig. 1, and thus the spring action of the spring 30, by levering in a circular pivoting fashion around the pin type fasteners 29 according to the resilient action of the spring 30, causes its outer peripheral portion to be strongly impelied in the rightwards direction and to press, via the spring type fasteners 28a, the clutch pressure plate member 28 towards the opposing frictional engagement face 25 of the flywheel 23.In this operational mode, the annular disk plate 38 is tightly clamped between the opposing frictional surfaces 28b and 25 of the clutch plate member 28 and the flywheel 23 and is frictionally coupled thereto: and thereby the first driving gear wheel shaft 3 is rotationally powered from the internal combustion engine (not shown).

On the other hand, when the hydraulic fluid pressure chamber 96 of the hydraulic actuator 95 is supplied with pressurized hydraulic fluid and thus drives the other end of this clutch fork member 34, then the radially central portion of the spring 30 is driven thereby in the rightwards direction in Fig. 1, and this overcomes the spring action of the spring 30 by levering this spring 30 in a circular pivoting fashion around the pin type fasteners 29, thus causing its outer peripheral portion to be moved in the leftwards direction and thus to cease to press the clutch pressure plate member 28 towards the opposing frictional engagement face 25 of the flywheel 23.In this operational mode, the annular disk plate 38 is not substantially squeezed between the respective opposing frictional surfaces 28b and 25 of the clutch plate member 28 and the flywheel 23, and accordingly is free to rotate with respect thereto; and thereby the first driving gear wheel shaft 3 is not substantially rotationally powered from the internal combustion engine.

The details of the construction of the second clutch assembly 201, which in fact is the one of the two clutch assemblies 200 and 201 which is required to transmit the lesser torque and which accordingly is the one of the smaller radius, and which is the one of the two clutch assemblies which is actuated by the second preferred embodiment of the clutch actuation system according to the present invention as will be seen shortly, are as follows.

The inner portion of the flywheel 23 is formed with a cylindrical cavity, facing towards the transmission 2, which has a cylindrical inner surface 40. This cavity is substantially pressure sealed in the rightwards direction in the figure by the cooperation of the second driving gear wheel shaft 4 and the radially inner portion of the flywheel 23, optionally with the interposition of a seal member therebetween. A clutch plate member 42 is fitted into the open left end of this cavity so as substantially to close it, and the inner or right hand surface of this clutch plate member 42 is formed as a flat annular frictional engagement surface 41.A piston member 43 is fitted within the cavity of the flywheel 23 as movable along the axial line of the second driving gear wheel shaft 4, and is slidably and rotatably and pressure sealingly engaged, optionally with the interposition of a seal member therebetween, over the end portion of said second driving gear wheel shaft 4, so that the left hand side of the piston member 43 opposes the frictional engagement surface 41 of the clutch plate member 42. The outer cylindrical surface of the piston member 43 slides on the inner cylindrical surface 40 of the cavity in the flywheel 23 in a pressure sealed fashion, optionally with the interposition of a seal member therebetween.

Thus a pressure chamber 44 is defined to the right of the piston member 43, between it and the flywheel 23. A clutch disk assembly 45 is provided between the piston member 43 and the opposing frictional engagement surface 41 of the clutch plate member 42. This clutch disk assembly 45 comprises a hub member 46 which is rotationally connected by splines to the second driving gear wheel shaft 4, an annular disk plate 48 which is sandwiched between the annular frictional engagement surface 41 of the clutch plate member 42 and the opposing pressure surface of the piston member 43, and a torsional or annular type shock absorber assembly 49 of a per se well known kind which connects the disk plate 48 and the hub member 46 with a certain amount of rotational resilience therebetween.Both the sides of the annular disk plate 48 are faced with high friction type clutch linings 47, so as to have a good frictional effect against the frictional engagement surfaces opposing them. A return spring 50 is fitted between the piston member 43 and the opposing frictional engagement surface 41 of the clutch plate member 42, radially outwards of the annular disk plate 48, so as to bias these members away from one another and so as to tend to decrease the size of the pressure chamber 44. And a hydraulic fluid conduit 51 is formed through the center of the second driving gear wheel shaft 4 and opens to the pressure chamber 44, for selectively supplying pressurized hydraulic fluid to said pressure chamber 44.

Thus, when the hydraulic fluid pressure chamber 44 is not supplied with pressurized hydraulic fluid via the conduit 51 and thus does not drive the piston member 43 to the left, then under the biasing action of the return spring 50 the piston member 43 is impelled in the rightwards direction and thus is not pressed towards the opposing frictional engagement face 41 of the clutch plate member 42. In this operational mode, the annular disk plate 48 is not substantially squeezed between the frictional surface 41 of the clutch plate member 42 and the piston member 43, and accordingly is free to rotate with respect thereto; and thereby the second driving gear wheel shaft 4 is not substantially rotationally powered from the internal combustion engine (not shown).On the other hand, when the hydraulic fluid pressure chamber 44 is supplied with pressurized hydraulic fluid of greater pressure value than a predetermined value via the conduit 51 and thus the piston member 43 is driven to the left, this overcomes the spring action of the spring 50, and in this operational mode the annular disk plate 48 is tightly clamped between the opposing frictional surface 41 of the clutch plate member 42 and the piston member 43, and accordingly is frictionally coupled thereto; and thereby the second driving gear wheel shaft 4 is rotationally powered from the internal combustion engine.

Thus, it will be particularly noted that the functional operations of the first and second clutching assemblies 200 and 201 are opposite: whereas the first clutching assembly 200 is engaged so as to transmit engine rotational power to the first driving gear wheel shaft 3 when its pressure chamber (the chamber 96) is not supplied with hydraulic fluid pressure, and is disengaged so as not to transmit engine rotational power to the first driving gear wheel shaft 3 when its pressure chamber is supplied with hydraulic fluid pressure, by contrast the second clutching assembly 201 is engaged so as to transmit engine rotational power to the second driving gear wheel shaft 4 when its pressure chamber (the chamber 44) is supplied with hydraulic fluid pressure, and is disengaged so as not to transmit engine rotational power to the second driving gear wheel shaft 4 when its pressure chamber is not supplied with hydraulic fluid pressure.

Parallel to the first and second driving gear wheel shafts 3 and 4 and the driven gear wheel shaft 10 there are slidably supported in an upper portion of the transmission casing 52 first and second selector fork shafts 58 and 59. On the first selector fork shaft 58 there is fixedly mounted a first selector fork 60, which can only be partly seen in the sectional view of Fig. 1, and which is engaged with the sleeve 1 Sf of the first-third synchronizer 1 6 so as selectively to drive said synchronizer sleeve 16f in the left and right directions, along the axial direction of the synchronizer. Likewise, on the second selector fork shaft 59 there is fixedly mounted a second selector fork 61, which also can only be partly seen in the sectional view of Fig. 1, and which is engaged with the sleeve 1 7f of the second-fourth synchronizer 1 7 so as selectively to drive said synchronizer sleeve 1 7f in the left and right directions, along the axial direction of the synchronizer.Further, on this second selector fork shaft 59 there is also slidably mounted a reverse speed selector fork 57, which also can only be partly seen in the sectional view of Fig. 1, and which is engaged with the reverse idler gear wheel 20, so as selectively to drive said reverse idler gear wheel 20 in the left and right directions along the axial direction of the reverse idler gear wheel shaft 19, so as selectively to mesh said reverse idler gear wheel 20 with the reverse speed driving gear wheel 7 and with the reverse speed driven gear wheel 1 8 formed on the outside of the first-third synchronizer sleeve 1 6f, in order to provide the reverse speed stage.On a left end portion of the first selector fork shaft 58 where it is slidably fitted through a hole in the transmission casing 52 there are formed three axially spaced apart click stop grooves or indentations 62, 63, and 64, and according to the axial position of the first selector fork shaft 58 one or another of these three click stop grooves 62, 63, and 64 is engaged with a ball not shown in the figure which is fitted into a hole in the side of said hole in the transmission casing 52 and which is biased against the side of the shaft 58 by a spring or the like; and similarly on a left end portion of the second selector fork shaft 59 where it is slidably fitted through a hole in the transmission casing 52 there are formed three axially spaced apart click stop grooves or indentations 65, 66, and 67, and according to the axial position of the second selector fork shaft 59 one or another of these three click stop grooves 65, 66, and 67 is engaged with a ball not shown in the figure which is fitted into a hole in the side of said hole in the transmission casing 52 and which is biased against the side of the shaft 59 by a spring or the like.

By means of this click stop mechanism, the first selector fork shaft 58 can be shifted between a central or neutral position in which its said ball is engaged with its central clip stop groove 62, a rightwardly shifted position in which its said ball is engaged with its said left click stop groove 63, and a leftwardly shifted position in which its said ball is engaged with its said right click stop groove 64; and when said first selector fork shaft 58 is in any one of its said three positions it is retained therein with a certain holding force by the above described click stop mechanism.Similarly, the second selector fork shaft 59 can be shifted between a central or neutral position in which its said ball is engaged with its said central click stop groove 65, a rightwardly shifted position in which its said ball is engaged with its said left click stop groove 66, and a leftwardly shifted position in which its said ball is engaged with its said right click stop groove 67; and when said second selector fork shaft 59 is in any one of its said three positions it is similarly retained therein with a certain holding force by the above described click stop mechanism.When the first selector fork shaft 58 is in its said central or neutral position, then the first selector fork 60 positions the sleeve 1 6f of the first-third synchronizer 16 to its intermediate position in which neither the first speed driven gear wheel 11 nor the third speed driven gear wheel 1 3 is rotationally coupled by the first-third synchronizer 1 6 to the driven gear wheel shaft 10.

When the first selector fork shaft 58 is in its said rightwardly shifted position, then the first selector fork 60 positions the sleeve 1 6f of the first-third synchronizer 1 6 to its rightwardly shifted position.

in which the first speed driven gear wheel 11 is rotationally coupled by the first-third synchronizer 16 to the driven gear wheel shaft 10. On the other hand, when the first selector fork shaft 58 is in its said leftwardly shifted position, then the first selector fork 60 positions the sleeve 1 6f of the first-third synchronizer 1 6 to its leftwardly shifted position in which the third speed driven gear wheel 1 3 is rotationally coupled by the first-third synchronizer 16 to the driven gear wheel shaft 10.

Similarly, when the second selector fork shaft 59 is in its said central or neutral position, then the second selector fork 61 positions the sleeve 1 7f of the second-fourth synchronizer 1 7 to its intermediate position in which neither the second speed driven gear wheel 12 nor the fourth speed driven gear wheel 14 is rotationally coupled by the second-fourth synchronizer 1 7 to the driven gear wheel shaft 1 0. When the second selector fork shaft 59 is in its said rightwardly shifted position, then the second selector fork 61 positions the sleeve 1 7f of the second-fourth synchronizer 1 7 to its rightwardly shifted position in which the second speed driven gear wheel 1 2 is rotationally coupled by the second-fourth synchronizer 1 7 to the driven gear wheel shaft 10. On the other hand, when the second selector fork shaft 59 is in its said leftwardly shifted position, then the second selector fork 61 positions the sleeve 1 7f of the second-fourth synchronizer 1 7 to its leftwardly shifted position in which the fourth speed driven gear wheel 14 is rotationally coupled by the second-fourth synchronizer 17 to the driven gear wheel shaft 10.

The first and second selector fork shafts 58 and 59 and the reverse speed selector fork 57 are driven between their positions explained above by hydraulic drive mechanisms which will now be described.

On the left hand end of the transmission casing 52 there is fitted an end cover 70, through which there are pierced two holes which oppose the left hand ends of the first and second selector fork shafts 58 and 59, which are formed with notch shapes. To this end cover 70 are fixed the casings of first and second hydraulic actuators 68 and 69.

Within the casing of the first hydraulic actuator 68 there is slidably fitted a first piston member 71, the right hand end of which protrudes from the casing and is formed with a notch shape which is drivingly engaged with the notch shape formed on the left hand end of the first selector fork shaft 58, so as to push and pull it. Pressure chambers 72 and 73 are respectively defined to the left and the right of this piston member 71 within the casing of the hydraulic actuator, and opposing compression coil springs 74 and 75 respectively mounted within the pressure chamber 72 and the pressure chamber 73 bias this piston member 71 together with the first selector fork shaft 58 respectively to the right and the left in Fig. 1.Similarly, within the casing of the second hydraulic actuator 69 there is slidably fitted a second piston member 76, the right hand end of which protrudes from the casing and is formed with a notch shape which is drivingly engaged with the notch shape formed on the left hand end of the second selector fork shaft 59, so as to push and pull it. Pressure chambers 77 and 78 are respectively defined to the left and the right of this piston member 76 within the casing of the hydraulic actuator, and opposing compression coil springs 79 and 80 respectively mounted within the pressure chamber 77 and the pressure chamber 78 bias this piston member 76 together with the second selector fork shaft 59 respectively to the right and the left in Fig. 1.To the pressure chambers 73, 74, 77, and 78 there are respectively communicated hydraulic fluid conduits 122,120, 121,and 123.

Thus, when pressurized hydraulic fluid is supplied neither to the pressure chamber 72 of the first hydraulic actuator 68 via the hydraulic fluid conduit 120 nor to its pressure chamber 73 via the hydraulic fluid conduit 122, then under the biasing actions of the compression coil springs 74 and 75 the piston member 71 thereof is shifted so as to position the first selector fork shaft 58 to its central or neutral position, in which its said ball is engaged with its said central click stop groove 62, and in which the first selector fork 60 positions the sleeve 16f of the first-third synchronizer 1 6 to its intermediate position in which neither the first speed driven gear wheel 11 nor the third speed driven gear wheel 1 3 is rotationally coupled by the first-third synchronizer 16 to the driven gear wheel shaft 10.When pressurized hydraulic fluid is supplied via the hydraulic fluid conduit 1 20 to the pressure chamber 72 of the first hydraulic actuator 68, then with the aid of the biasing action of the compression coil spring 74 and against the biasing action of the compression coil spring 75 which is overcome the piston member 71 thereof is shifted to the right, with a shifting force which is greater the greater is the magnitude of the pressure of such supplied hydraulic fluid, so as to position the first selector fork shaft 58 to its said rightwardly shifted position, in which its said ball is engaged with its said left click stop groove 63, and in which the first selector fork 60 positions the sleeve 1 6f of the first-third synchronizer 1 6 to its said rightwardly shifted position in which the first speed driven gear wheel 11 is rotationally coupled by the first-third synchronizer 1 6 to the driven gear wheel shaft 1 0. On the other hand, when pressurized hydraulic fluid is supplied via the hydraulic fluid conduit 122 to the pressure chamber 73 of the first hydraulic actuator 68, then with the aid of the biasing action of the compression coil spring.75 and against the biasing action of the compression coil spring 74 which is overcome the piston member 71 thereof is shifted to the left, again with a shifting force which is greater the greater is the magnitude of the pressure of such supplied hydraulic fluid, so as to position the first selector fork shaft 58 to its said leftwardly shifted position, in which its said ball is engaged with its said right click stop groove 64, and in which the first selector fork 60 positions the sleeve 1 6f of the first-third synchronizer 1 6 to its said leftwardly shifted position in which the third speed driven gear wheel 1 3 is rotationally coupled by the first-third synchronizer 1 6 to the driven gear wheel shaft 10.

Similarly, when pressurized hydraulic fluid is supplied neither to the pressure chamber 77 of the second hydraulic actuator 69 via the hydraulic fluid conduit 121 nor to its pressure chamber 78 via the hydraulic fluid conduit 123, then under the biasing actions of the compression coil springs 79 and 80 the piston member 76 thereof is shifted so as to position the second selector fork shaft 59 to its central or neutral position, in which its said ball is engaged with its said central click stop groove 65, and in which the second selector fork 61 positions the sleeve 1 7f of the second-fourth synchronizer 1 7 to its intermediate position in which neither the second speed driven gear wheel 12 nor the fourth speed driven gear wheel 14 is rotationally coupled by the second-fourth synchronizer 1 7 to the driven gear wheel shaft 10.

When pressurized hydraulic fluid is supplied via the hydraulic fluid conduit 121 to the pressure chamber 77 of the second hydraulic actuator 69, then with the aid of the biasing action of the compression coil spring 79 and against the biasing action of the compression coil spring 80 which is overcome the piston member 76 thereof is shifted to the right, with a shifting force which is greater the greater is the magnitude of the pressure of such supplied hydraulic fluid, so as to position the second selector fork shaft 59 to its said rightwardly shifted position, in which its said ball is engaged with its said left click stop groove 66, and in which the second selector fork 61 positions the sleeve 1 7f of the second-fourth synchronizer 1 7 to its said rightwardly shifted position in which the second speed driven gear wheel 1 2 is rotationally coupled by the secondfourth synchronizer 17 to the driven gear wheel shaft 10.On the other hand, when pressurized hydraulic fluid is supplied via the hydraulic fluid conduit 1 23 to the pressure chamber 78 of the second hydraulic actuator 69, then with the aid of the biasing action of the compression coil spring 80 and against the biasing action of the compression coil spring 79 which is overcome the piston member 76 thereof is shifted to the left, again with a shifting force which is greater the greater is the magnitude of the pressure of such supplied hydraulic fluid, so as to position the second selector fork shaft 59 to its said leftwardly shifted position, in which its said ball is engaged with its said right click stop groove 67, and in which the second selector fork 61 positions the sleeve 1 7f of the second-fourth synchronizer 17 to its said leftwardly shifted position in which the fourth speed driven gear wheel 14 is rotationally coupled by the second-fourth synchronizer 17 to the driven gear wheel shaft 10.

Finally, the reverse speed selector fork 57 is selectively driven to and fro to the left and right in Fig. 1 by a hydraulic actuator 81, which is not shown in Fig. 1 but is shown in Fig. 3. When the pressure chamber 83 of this hydraulic actuator 81 is not supplied with pressurized hydraulic fluid, then by the biasing action of a compression coil spring 84 the piston 82 is driven to the right in Fig. 3, and via a linkage which is not shown this piston 82 thereby shifts the reverse speed selector fork 57 in the rightwards direction in Fig. 1, so as to disengage the reverse idler gear wheel 20 from the reverse speed driving gear wheel 7 and from the reverse speed driven gear wheel 1 8 formed on the outside of the first-third synchronizer sleeve 16f. On the other hand, when the pressure chamber 83 of this hydraulic actuator 81 is supplied with pressurized hydraulic fluid, then against the biasing action of the compression coil spring 84 which is overcome the piston 82 is driven to the left in Fig. 3, and via the aforesaid linkage the piston 82 thereby shifts the reverse speed selector fork 57 in the Ieftwards direction in Fig. 1 , so as to mesh the reverse idler gear wheel 20 with the reverse speed driving gear wheel 7 and with the reverse speed driven gear wheel 18, so as to provide the reverse speed stage.

Now, referring to Fig. 3, the arrangements for providing selective engagement and disengagement of the first and second clutch assemblies 200 and 201 by selectively providing supply of hydraulic fluid pressure to the pressure chambers 44 and 96, and for moving the selector forks 57, 60 and 61 by selectively providing supply of hydraulic fluid pressure to the pressure chambers 83, 72, 73, 77, and 78, will be described.

A hydraulic fluid pump 100 sucks up hydraulic fluid from a pan 101, and the pressure of this hydraulic fluid is regulated to a line hydraulic fluid pressure by a line pressure regulation valve 102 of a per se well known sort. From this line pressure regulation valve 102, via a hydraulic fluid conduit 103, and then via hydraulic fluid conduits 104, 105, 106, 107, 108, 109, and 110 respectively, hydraulic fluid at substantially line pressure is led to input ports designated as "a" of seven electromagnetic fluid switching valves, which are respectively designated as 111, 112, 113, 114, 115, 116, and 117, and which are only schematically shown because they are per se well known.These electromagnetic fluid switching valves are all of substantially identical construction and function, and each of them has three ports designated as "a", "b", and "c", and functions as follows: when its solenoid (not shown) is supplied with actuating electrical energy then its port "a" is communicated to its port "b" while its port "c" is not communicated to any other port, and on the other hand when its solenoid is not supplied with actuating electrical energy then its port "b" is communicated to its port "c" while its port "a" is not communicated to any other port.Thus, when the solenoid of each of these electromagnetic fluid switching valves 111 through 11 7 is supplied with an electrical pulse signal with a certain duty ratio, the effective fluid flow resistance between its port "a" and its port "b" varies according to the duty ratio of said certain pulse signal, being the less the greater is said duty ratio; and correspondingly the effective fluid flow resistance between its port "b" and its port "c" also varies according to the duty ratio of said certain pulse signal, being the greater the greater is said duty ratio. The ports "c" of the electromagnetic fluid switching valves 111, 112, 113,114,115,116,and 117areall communicated via drain hydraulic fluid conduits 125,126,127,128,129, 130, and 131 respectively to the hydraulic fluid pan 101.

Now, the other connections of the five electromagnetic fluid switching valves 113 through 11 7 are as follows. The port "b" of the electromagnetic fluid switching valve 113 is communicated via the previously mentioned hydraulic fluid conduit 120 to the pressure chamber 72 of the first hydraulic actuator 68 which is for driving the first selector fork shaft 58, the first selector fork 60, and thereby the firstthird selector sleeve 1 6f of the first-third synchronizer 1 6 rightwards, i.e. for engaging the first speed stage.The port "b" of the electromagnetic fluid switching valve 114 is communicated via the previously mentioned hydraulic fluid conduit 121 to the pressure chamber 77 of the second hydraulic actuator 69 which is for driving the second selector fork shaft 59, the second selector fork 61, and thereby the second-fourth selector sleeve 1 7f of the secondfourth synchronizer 1 7 rightwards, i.e. for engaging the second speed stage.The port "b" of the electromagnetic fluid switching valve 11 5 is communicated via the previously mentioned hydraulic fluid conduit 122 to the pressure chamber 73 of the first hydraulic actuator 68 which is for driving the first selector fork shaft 58, the first selector fork 60, and thereby the firstthird selector sleeve 1 6f of the first-third synchronizer 16 Ieftwards, i.e. for engaging the third speed stage.The port "b" of the electromagnetic fluid switching valve 11 6 is communicated via the previously mentioned hydraulic fluid conduit 123 to the pressure chamber 78 of the second hydraulic actuator 69 which is for driving the second selector fork shaft 59, the second selector fork 61, and thereby the second-fourth selector sleeve 1 7f of the secondfourth synchronizer 1 7 leftwards, i.e. for engaging the fourth speed stage. Finally, the port "b" of the electromagnetic fluid switching valve 11 7 is communicated via a hydraulic fluid conduit 124 to the pressure chamber 83 of the aforementioned hydraulic actuator 81 which is for driving the reverse speed selector fork 57 and the reverse idler gear wheel 20 in the leftwards direction, i.e.

for engaging the reverse speed stage.

On the other hand, the other connections of the two electromagnetic fluid switching valves 111 and 12 are as follows. The port "b" of the electromagnetic fluid switching valve 111 is communicated via a hydraulic fluid conduit 11 8 to the pressure chamber 96 of the hydraulic actuator 95 for the clutch fork member 34 of the first clutch assembly 200. The port "b" of the electromagnetic fluid switching valve 11 2 is communicated via a hydraulic fluid conduit 11 9 and via the previously mentioned hydraulic fluid conduit 51 formed through the center of the second driving gear wheel shaft 4 to the pressure chamber 44 of the second clutch assembly 201.

The selective supply of electrical energy, i.e. of pulse signals of various duty ratios, to the solenoids of each of the seven electromagnetic fluid switching valves 111,112,113,114,115, 116, and 11 7 is performed from an electrical control device 140, the internal construction of which will not be explained in detail here because it is generally per se well known and conventional, and because the particular features thereof which are specific to the shown preferred embodiment will be easily supplemented by one of ordinary skill in the electronic and programming arts, based upon the functional disclosures in this specification.In the shown preferred embodiment, this electrical control device 140 may comprise a microprocessor and one or more pulse signal generators controlled by said microprocessor which can generate pulse signals of any desired duty ratio within a certain range, and also may comprise a muitiplexer or the like for directing said pulse signals to one or more of the solenoids of the seven electromagnetic fluid switching valves 111,112,113,114,115,116,and117.1nmany cases, the electrical control device 140 receives information relating to the operational conditions of the transmission system shown in Fig. 2 and the operational conditions of the vehicle in which said transmission system is incorporated and the requirements of the operator thereof from: a throttle opening amount sensor 141 which produces an electrical output signal representative of the current throttle opening amount of the engine (not shown) of the vehicle, i.e. of the current value of the load on said engine; a vehicle speed sensor 142 which produces an electrical output signal representative of the current value of the road speed of the vehicle; a shift position sensor 143 which produces an electrical output signal representative of the desired transmission range or speed stage which is currently manually selected by the driver of the vehicle; and an engine rpm sensor 144 which produces an electrical output signal representative of the current value of the rotational speed of the engine (not shown) of the vehicle.Based upon this and possibly other information, the electrical control device 140 decides which speed stage of the transmission mechanism shown in Fig. 1 should currently be engaged or should be shifted to, by appropriate shifting of the first and second synchronizer sleeves 1 6f and 1 7f and by appropriate engagement of the first and second clutching assemblies 200 and 201 as will be explained later, and outputs suitable electrical pulse signals to one or more of the solenoids of the seven electromagnetic fluid switching valves 111, 112, 113,114,115,116,and117forcausingtheshift forks SO, 61, and 57 and the first and second clutch assemblies 200 and 201 to be moved and engaged as explained in the appropriate part of the description given below with respect to the operation of the transmission system in each of its speed stages and with respect to the shifting between said speed stages.

In actual detail, the electrical control device 140, during the process of engaging a speed stage or of preparing to do so by shifting a one of the first-third and the second-fourth synchronizer sleeves 1 6f and 1 7f to the left or to the right of Fig. 1, and during the process of engaging or disengaging a one of the first and second clutching assemblies 200 and 201, may output to the solenoid of a particular one or more of the seven electromagnetic fluid switching valves 111, 112,113,114,115, 116, and 117 notasimple ON/OFF signal but instead a pulse signal of a certain duty ratio, so as to cause said one of the electromagnetic switching valves to supply a hydraulic fluid pressure which is neither zero nor line pressure but intermediate therebetween from its port "b" to its associated one of the pressure chambers 96, 44, 72, 77, 73, 78, and 82 via the associated one of the hydraulic fluid conduits 118 through 124. Thus, during the ON time periods of this pulse signal said pressure chamber is communicated via the port "b" of said electromagnetic fluid switching valve to the port "a" thereof so as to receive supply of line hydraulic fluid pressure; but on the other hand during the OFF time periods of said pulse signal said pressure chamber is communicated via the port "b" of said electromagnetic fluid switching valve to the port "c" thereof so as to be drained.

Therefore, the greater is the duty ratio of this pulse signal supplied to the solenoid of the electromagnetic fluid switching valve, the greater is the balance value of the hydraulic fluid pressure which is thus caused to be present in said pressure chamber, from a zero pressure value in said pressure chamber when said duty ratio is zero up to a line pressure value in said pressure chamber when said duty ratio is unity. In this way, the electrical control device 140 can control the pressure value in any of the pressure chambers 96,44, 72, 77, 73, 78, and 82 to be substantially any desired pressure value from substantially zero up to substantially line pressure, i.e. to be any desired value in a particular range. However, this function of supplying a particular desired hydraulic fluid pressure value intermediate between zero and line pressure to the various pressure chambers is only used during the transient process of shifting between speed stages of the transmission for better and smoother engagement of the synchronizer sleeves and the clutch assemblies 200 and 201, and at ail other times either zero or line pressure is supplied to each of the pressure chambers, i.e. only either an ON signal or an OFF signal is supplied to each of the electromagnetic switching valves. The matter of this transient intermediate pressure supply to the first and second clutching assemblies 200 and 201, during starting off of the vehicle from rest, and during shifting between speed stages of the transmission, is in fact essential to the principles of the present invention.

The engagement conditions of each of the first and second clutch assemblies 200 and 201 , the positions of the first-third synchronizer sleeve 1 6f of the first-third synchronizer 16 and of the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 17, and the position of the reverse idler gear wheel 20 on the reverse idler gear wheel shaft 19, will now be explained, during the engagement of each of the speed stages which can be provided by the transmission mechanism shown in Fig. 1 and explained above, i.e. during the engagement of the neutral speed stage, the reverse speed stage, and the first through the fourth forward speed stages; and also the sequences of shifting and of engagement and disengagement operations of these means which are employed in the various possible operations of shifting between these speed stages in this full automatic mode will be generally explained. In this connection, the transmission is assumed to be in a drive or "D" range, in which the control device 1 40 can select any of the four speed stages which the gear transmission mechanism can provide for being provided by the transmission; and the selection of exactly which of these four speed stages should be currently engaged is decided upon by the electrical control device 140, based upon said vehicle operational parameters, in a per se well known way for automatic transmission control, as for example based upon predetermined transmission shifting patterns stored in a memory of the electrical control device 140, and this matter will not be particularly further discussed herein because it is per se conventional.

First, when the engine of the vehicle is not being operated and the vehicle is not moving, then no hydraulic fluid pressure is being generated by the pump 100 and hence of course no hydraulic fluid pressure is being supplied to any of the pressure chambers 96, 44, 72, 77, 73, 78, and 82. Especially, because no hydraulic fluid is being supplied to the pressure chamber 96 of the actuator 95 the first clutch assembly 200 is engaged, and because no hydraulic fluid pressure is being supplied to the chamber 44 the second clutch assembly 201 is disengaged. Next, when the engine is started, during vehicle operation in the parking and in the neutral speed stage, i.e.

when the engine is being operated but the vehicle is not moving, the operation is that the first-third synchronizer sleeve 1 6f of the first-third synchronizer 1 6 and the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 1 7 are both positioned to their central or intermediate positions, by supply of an OFF electrical signal by the electrical control device 140 to all of the electromagnetic fluid switching valves 11 3, 114, 115, and 116, which accordingly causes the pressure chambers 72, 73, 77, and 78 of the first and second hydraulic actuators 68 and 69 to be all drained; and the first and second clutch assemblies 200 and 201 are both likewise disengaged, by supply of an ON electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 111 , which causes the pressure chamber 96 of the actuator 95 of the first clutching assembly 200 to be supplied with line pressure, and by supply of an OFF electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 11 2, which causes the pressure chamber 44 of the second clutching assembly 201 to be drained and to be supplied with substantially zero pressure, although in fact the engagement condition of the second clutch assembly 201 is irrelevant.

Next, when it is desired to engage the first speed stage from the neutral speed stage, and to move the vehicle away from rest, first as a preparatory step, by supply of an ON electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 113, which causes the pressure chamber 72 of the first hydraulic actuator 68 to be supplied with line pressure via the hydraulic fluid conduit 120, the first-third synchronizer sleeve 16f of the first-third synchronizer 16 is shifted to its rightwards position so as to rotationally engage the first speed driven gear wheel 11 with the driven gear wheel shaft 10, but at this time no drive will be transferred by this rotational engagement because the first clutch assembly 200 is still disengaged, since still the electrical control device 140 is supplying to the electromagnetic fluid switching valve 111 a ON electrical signal, i.e. an electrical signal of pulse ratio unity. Then, in order to actually engage this first speed stage, and to move the vehicle away from rest, the following action takes place: the accelerator pedal of the vehicle is depressed, and when, as determined by the electrical control device 140, the rotational speed of the engine as signalled from the engine rpm sensor 144 becomes higher than a predetermined value which is sufficient for starting the vehicle off from rest, then the first clutch assembly 200 is gradually engaged, by gradual decrease of the pulse ratio of the electrical signal supplied by the electrical control device 140 to the electromagnetic fluid switching valve 111 from the aforesaid unity value to an eventual value of zero, which causes the pressure chamber 96 of the hydraulic actuator 95 to be supplied with a hydraulic fluid pressure which gradually increases from zero up to line pressure.This will cause the vehicle to move away smoothly from rest, as the first clutch assembly 200 is progressively engaged, and to be operated in the first speed stage. Now, the exact details of this engagement process for the first clutch assembly 200, which are related to the gist of the present invention, will be explained in more detail in the part of this specification towards its end, with particular reference to the graphs shown in Fig. 4. The important point, as will be seen hereinafter, is that during the process of engagement of the first clutch assembly 200 the electrical control device 140 detects the relative rotational speed between the members thereof which are being engaged, i.e.

between the flywheel 23 and the clutch disk assembly 35, and control the engagement pressure between said members by controlling the pressure supplied to the pressure chamber 96 of the actuator 95 for the first clutch assembly 200 by controlling the value of the duty ratio of the pulse signal supplied to the electromagnetic fluid switching valve 111, in a feedback manner, so as most properly to engage the first clutch assembly 200.

So, during steady vehicle operation in the first forward speed stage, the first-third synchronizer sleeve 16f of the first-third synchronizer 1 6 is positioned to its rightwards position, so as to rotationally engage the first speed driven gear wheel 11 with the driven gear wheel shaft 10, and the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 17 is positioned to its central or intermediate position, and the first clutch assembly 200 is kept engaged while the engagement condition of the second clutch assembly 201 is irrelevant, by supply of an ON electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 11 3, and by supply of OFF electrical signals by the electrical control device 140 to the electromagnetic fluid switch valves 111, 112, 114,115,116,and 117,whichcausesthe pressure chamber 72 of the first hydraulic actuator 68 to be supplied with line pressure, while the pressure chambers 73, 77, 78, 82, 96, and 44 are not supplied with any substantial pressures. Thus rotational power is transmitted from the crankshaft (not shown) of the internal combustion engine (also not shown) via the fiywheel 23 and via the first clutch assembly 200 to the first driving gear wheel shaft 3, whence it is transmitted through the first speed driving gear wheel 5 to the first speed driven gear wheel 11 constantly meshed therewith, whence said drive is transmitted to the driven gear wheel shaft 10 to which said first speed driven gear wheel 11 is currently engaged by the first-third synchronizer 1 6, whence it is output via the power output gear wheel 1 5 to the differential gear mechanism 85.

However, when it is desired to shift up to the second speed stage from the first speed stage, as a preparatory step first it is ensured that the second clutch assembly 201 is disengaged, i.e.

that an OFF electrical signal is being sent by the electrical control device 140 in the electromagnetic fluid switching valve 112, and then, by supply of an ON electrical signal by the electrical control device 1 40 to the electromagnetic fluid switching valve 114, which causes the pressure chamber 77 of the second hydraulic actuator 69 to be supplied with line pressure, the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 17 is shifted to its rightwards position, so as to rotationally engage the second speed driven gear wheel 1 2 with the driven gear wheel shaft 10, but at this time no drive will be transferred by this rotational engagement because the second clutch assembly 201 is disengaged.Then, in order to actually engage this second speed stage, i.e. to perform the upshift, which as stated earlier is done when the electrical control device 140 decides that the appropriate time has come to do so based upon various vehicle operational parameters, then the first clutch assembly 200 is gradually disengaged, by gradual increase of the pulse ratio of the electrical signal supplied by the electrical control device 140 to the electromagnetic fluid switching valve 111 from the aforesaid zero value to an eventual value of unity, which causes the pressure chamber 96 of the hydraulic actuator 95 to be supplied with a hydraulic fluid pressure which gradually decreases from line pressure down to zero; and simultaneously the second clutch assembly 201 is gradually engaged, by gradual increase of the pulse ratio of the electrical signal supplied by the electrical control device 140 to the electromagnetic fluid switching valve 112 from the aforesaid zero value to an eventual value of unity, which causes the pressure chamber 44 of the second clutch assembly 201 to be supplied with a hydraulic fluid pressure which gradually increases from zero up to line pressure.

A good mutual timing is maintained during this switching over of engagement conditions, as will be explained hereinafter. Now, the exact details of this process of disengagement for the first clutch assembly 200 and of engagement of the second clutch assembly 201, which are related to the gist of the present invention, will be explained in more detail in the part of this specification towards its end, with particular reference to the graphs shown in Fig. 5.The important point, as will be seen hereinafter, is that during the process of engagement of the second clutch assembly 201 the electrical control device 140 detects the relative rotational speed between the members thereof which are being engaged, i.e. between the flywheel 23 and the clutch disk assembly 34, and controls the engagement pressure between said members by controlling the pressure supplied to the pressure chamber 44 of the second clutch assembly 201 by controlling the value of the duty ratio of the pulse signal supplied to the electromagnetic fluid switching valve 112, in a feedback manner, so as most properly to engage the second clutch assembly 201. After full disengagement of the first clutch assembly 200 and full engagement of the second clutch assembly 201, these conditions are maintained, by supply of an ON electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 111 , which causes the pressure chamber 96 of the actuator 95 of the first clutching assembly 200 to be supplied with line pressure, and by supply of an ON electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 112, which causes the pressure chamber 44 of the second clutching assembly 201 to be also supplied with line pressure.Later, at a convenient time, the first-third synchronizer sleeve 1 6f of the first-third synchronizer 1 6 is brought back to its neutral or intermediate position, by supply of an OFF electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 11 3, which causes the pressure chamber 72 of the first hydraulic actuator 68 to be supplied with substantially zero pressure, and thereafter the first clutch assembly 200 is kept disengaged.

Thus, during vehicle operation in the second forward speed stage, the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 1 7 is positioned to its rightwards position, so as to rotationally engage the second speed driven gear wheel 12 with the driven gear wheel shaft 10, and the first-third synchronizer sleeve 1 6f of the first-third synchronizer 1 6 is positioned to its central or intermediate position, and the second clutch assembly 201 is kept engaged while the first clutch assembly 200 is kept disengaged, by supply of ON electrical signals by the electrical control device 140 to the electromagnetic fluid switching valves 111, 112 and 114, and by supply of OFF electrical signals by the electrical control device 140 to the electromagnetic fluid switching valves 11 3, 11 5, 11 6, and 117, which causes the pressure chamber 77 of the second hydraulic actuator 69, the pressure chamber 96 of the actuator 95 of the first clutching assembly 200, and the pressure chamber 44 of the second clutching assembly 201 to be supplied with line pressure, while the pressure chambers 72, 73, 78, and 82 are not supplied with any substantial pressures.Thus rotational power is transmitted from the crankshaft of the internal combustion engine via the flywheel 23 and via the second clutch assembly 201 to the second driving gear wheel shaft 4, whence it is transmitted through the second speed driving gear wheel 8 to the second speed driven gear wheel 12 constantly meshed therewith, whence said drive is transmitted to the driven gear wheel shaft 10 to which said second speed driven gear wheel 12 is currently engaged, whence it is output via the power output gear wheel 1 5 to the differential gear mechanism 85.

However, when it is desired to shift up to the third speed stage from the second speed stage, or alternatively down to the first speed stage, respectively, first as a preparatory step, by supply of an ON electrical signal by the electrical control device 140 to either the electromagnetic fluid switching valve 11 5 or the electromagnetic fluid switching valve 113, which causes respectively either the pressure chamber 73 or the pressure chamber 72 of the first hydraulic actuator 68 to be supplied with line pressure, the first-third synchronizer sleeve 1 6f of the first-third synchronizer 1 6 is shifted respectively either to its Ieftwards or to its rightwards position, so as to rotationally engage either the third speed driven gear wheel 1 3 or the first speed driven gear wheel 11 with the driven gear wheel shaft 10, but at this time no drive will be transferred by this rotational engagement because the first clutch assembly 200 is still disengaged. Then, in order to actually engage respectively either the third or the first speed stage, i.e. to perform the respective upshift or downshift, the first clutch assembly 200 is engaged and the second clutch assembly 201 is disengaged, again with a good mutual timing being maintained during this switching over of engagement conditions, by switching over of the engagement conditions of these two clutching assemblies 200 and 201 in a fashion similar to that discussed above (but reversed) with reference to the shifting from the first to the second speed stage and illustrated in Fig. 5, by the operation of the electrical control device 140 in its alteration of the pulse ratios of the signals sent to the electromagnetic fluid switching valves 111 and 11 2. These new engagement conditions of the clutch assemblies 200 and 201 are maintained hereafter during the engagement of the new speed stage, by supply of an OFF electrical signal by the electrical control device 1 40 to the electromagnetic fluid switching valve 111, which causes the pressure chamber 96 of the actuator 95 of the first clutching assembly 200 to be supplied with substantially zero pressure, and by supply of an OFF electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 112, which causes the pressure chamber 44 of the second clutching assembly 201 to be also supplied with substantially zero pressure.Later, at a convenient time, the secondfourth synchronizer sleeve 1 7f of the secondfourth synchronizer 1 7 is brought back to its neutral or intermediate position, by supply of an OFF electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 114, which causes the pressure chamber 77 of the second hydraulic actuator 69 to be supplied with substantially zero pressure, and thereafter the engagement condition of the second clutch assembly 201 becomes irrelevant.

Thus, during vehicle operation in the third forward speed stage, the first-third synchronizer sleeve 16f of the first-third synchronizer 1 6 is positioned to its leftwards position, so as to rotationally engage the third speed driven gear wheel 1 3 with the driven gear wheel shaft 10, and the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 1 7 is positioned to its central or intermediate position, and the first clutch assembly 200 is kept engaged while the second clutch assembly 201 is kept disengaged, by supply of an ON electrical signal by the electrical control device 1 40 to the electromagnetic fluid switching valve 11 5, and by supply of OFF electrical signals by the electrical control device 1 40 to the electromagnetic fluid switching valves 111,112,113,114,1 16, and 11 7, which causes the pressure chamber 73 of the first hydraulic actuator 68 to be supplied with line pressure, while the pressure chambers 72, 73, 78, 82, 96, and 44 are not supplied with any substantial pressures.Thus rotational power is transmitted from the crankshaft of the internal combustion engine via the flywheel 23 and via the first clutch assembly 200 to the first driving gear wheel shaft 3, whence it is transmitted through the third speed driving gear wheel 6 to the third speed driven gear wheel 13 constantly meshed therewith, whence said drive is transmitted to the driven gear wheel shaft 10 to which said third speed driven gear wheel 1 3 is currently engaged, whence it is output via the power output gear wheel 1 5 to the differential gear mechanism 85.

However, when it is desired to shift up to the fourth speed stage from the third speed stage, or alternatively down to the second speed stage, respectively as a preparatory step first it is ensured that the second clutch assembly 201 is disengaged, and then by supply of an ON electrical signal by the electrical control device 140 to either the electromagnetic fluid switching valve 1 1 6 or the electromagnetic fluid switching valve 114, which causes respectively either the pressure chamber 78 or the pressure chamber 77 of the second hydraulic actuator 69 to be supplied with line pressure, the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 1 7 is shifted respectively either to its leftwards or to its rightwards position, so as to rotationally engage either the fourth speed driven gear wheel 14 or the second speed driven gear wheel 12 with the driven gear wheel shaft 10, but at this time no drive will be transferred by this rotational engagement because the second clutch assembly 201 is disengaged. Then, in order to actually engage respectively either the fourth or the second speed stage, i.e. to perform the respective upshift or downshift, the second clutch assembly 201 is engaged and the first clutch assembly 200 is disengaged, by switching over of the engagement conditions of these two clutching assemblies 200 and 201 in a fashion similar to that discussed above with reference to the shifting from the first to the second speed stage and illustrated in Fig. 5, with a good mutual timing being assured between these switchovers of engagement condition by the operation of the electrical control device 140 in its alteration of the pulse ratios of the signals sent to the electromagnetic fluid switching valves 111 and 112. These new engagement conditions of the clutch assemblies 200 and 201 are maintained hereafter during the engagement of the new speed stage, by supply of an ON electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 111 , which causes the pressure chamber 96 of the actuator 95 of the first clutching assembly 200 to be supplied with line pressure, and by supply of an ON electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 112, which causes the pressure chamber 44 of the second clutching assembly 201 to be also supplied with line pressure. Later, at a convenient time, the first-third synchronizer sleeve 1 6f of the first-third synchronizer 16 is brought back to its neutral or intermediate position, and thereafter the first clutch assembly 200 is kept disengaged.

Thus, during vehicle operation in the fourth forward speed stage, the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 1 7 is positioned to its leftwards position, so as to rotationally engage the fourth speed driven gear wheel 14 with the driven gear wheel shaft 10, and the first-third synchronizer sleeve 1 6f of the first-third synchronizer 1 6 is positioned to its central or intermediate position, and the second clutch assembly 201 is kept engaged while the first clutch assembly 200 is kept disengaged, by supply of ON electrical signals by the electrical control device 140 to the electromagnetic fluid switching valves 111, 11 2 and 116, and by supply of OFF electrical signals by the electrical control device 140 to the electromagnetic fluid switching valves 11 3, 114, 115, and 117, which causes the pressure chamber 78 of the second hydraulic actuator 69, the pressure chamber 96 of the actuator 95 of the first clutching assembly 200, and the pressure chamber 44 of the second clutching assembly 201 to be supplied with line pressure, while the pressure chambers 72, 73, 77, and 82 are not supplied with any substantial pressures.Thus rotational power is transmitted from the crankshaft of the internal combustion engine via the flywheel 23 and via the second clutch assembly 201 to the second driving gear wheel shaft 4, whence it is transmitted through the fourth speed speed driving gear wheel 9 to the second speed driven gear wheel 14 constantly meshed therewith, whence said drive is transmitted to the driven gear wheel shaft 10 to which said fourth speed driven gear wheel 14 is currently engaged, whence it is output via the power output gear wheel 1 5 to the differential gear mechanism 85. However, when it is desired to shift down to the third speed stage, first as a preparatory step, by supply of an ON electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 11 5, which causes the pressure chamber 73 of the first hydraulic actuator 68 to be supplied with line pressure, the first-third synchronizer sleeve 16f of the first-third synchronizer 16 is shifted to its Ieftwards position, so as to rotationally engage the third speed driven gear wheel 13 with the driven gear wheel shaft 10, but at this time no drive will be transferred by this rotational engagement because the first clutch assembly 200 is disengaged. Then, in order to actually engage the third speed stage, i.e. to perform the downshift, the first clutch assembly 200 is engaged and the second clutch assembly 201 is disengaged, again with a good mutual timing being maintained during this switching over of engagement conditions, by switching over of the engagement conditions of these two clutching assemblies 200 and 201 in a fashion similar to that discussed above (but reversed) with reference to the shifting from the first to the second speed stage and illustrated in Fig. 5, by the operation of the electrical control device 140 in its alteration of the pulse ratios of the signals sent to the electromagnetic fluid switching valves 111 and 11 2. These new engagement conditions of the clutch assemblies 200 and 201 are maintained hereafter during the engagement of the new speed stage, by supply of an OFF electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 111, which causes the pressure chamber 96 of the actuator 95 of the first clutching assembly 200 to be supplied with substantially zero pressure, and by supply of an OFF electrical signal by the electrical control device 140 to the electromagnetic fluid switching valve 112, which causes the pressure chamber 44 of the second clutching assembly 201 to be also supplied with substantially zero pressure.Later, at a convenient time, the secondfourth synchronizer sleeve 1 7f of the secondfourth synchronizer 1 7 is brought back to its neutral or intermediate position, and thereafter the engagement condition of the second clutch assembly 201 becomes irrelevant.

Finally, in order to move the vehicle off from rest in the rearwards direction, i.e. for vehicle operation in the reverse speed stage, while the vehicle is at rest and while both the first and the second clutch assemblies 200 and 201 are disengaged, by supply from the electrical control device 140 of an ON electrical signal to the electromagnetic fluid switching valve 111 and of an OFF electrical signal to the electromagnetic fluid switching valve 112 in a fashion similar to that explained above, the first-third synchronizer sleeve 1 6f of the first-third synchronizer 1 6 and of the second-fourth synchronizer sleeve 1 7f of the second-fourth synchronizer 1 7 are both positioned to their central or intermediate positions, and the reverse idler gear wheel 20 is shifted to the left in Figs. 1 and 2 along the axial direction of the reverse idler gear wheel shaft 19, so as to mesh with the reverse speed driving gear wheel 7 and with the reverse speed driven gear wheel 1 8 formed on the outside of the first-third synchronizer sleeve 1 6f. Next, in order to actually engage this reverse speed stage, and to move the vehicle away from rest backwards, the following action takes place: the accelerator pedal of the vehicle is depressed, and when, as determined by the electrical control device 140, the rotational speed of the engine as signalled from the engine rpm sensor 144 becomes higher than a predetermined value which is sufficient for starting the vehicle off from rest backwards, then, in a similar manner to that described earlier with respect to moving the vehicle off from rest forwards the first clutch assembly 200 is gradually engaged, by gradual decrease of the pulse ratio of the electrical signal supplied by the electrical control device 140 to the electromagnetic fluid switching valve 111 from the aforesaid unity value to an eventual value of zero, which causes the pressure chamber 96 of the hydraulic actuator 95 to be supplied with a hydraulic fluid pressure which gradually increases from zero up to line pressure.This will cause the vehicle to move smoothly from rest, as the first clutch assembly 200 is progressively engaged, and to be operated in the reverse speed stage. The details of this engagement process for the first clutch assembly 200, which are related to the gist of the present invention, are substantially the same as those with respect to starting off in the first forward speed stage, as explained in more detail in the part of this specification towards its end, with particular reference to the graphs shown in Fig. 4. Again, the important point, as will be seen hereinafter, is that during the process of engagement of the first clutch assembly 200 the electrical control device 140 detects the relative rotational speed between the members thereof which are being engaged, i.e.

between the flywheel 23 and the clutch disk assembly 35, and control the engagement pressure between said members by controlling the pressure supplied to the pressure chamber 96 of the actuator 95 for the first clutch assembly 200 by controlling the value of the duty ratio of the pulse signal supplied to the electromagnet fluid switching valve 111, in a feedback manner, so as most properly to engage the first clutch assembly 200.

So, during steady vehicle operation in the reverse speed stage, the first clutch assembly 200 is engaged while the second clutch assembly 201 is disengaged, by supply of an ON electrical signal by the electrical control device 1 40 to the electromagnetic fluid switching valve 11 7, and by supply of OFF electrical signals by the electrical control devices 140 to the electromagnetic fluid switching valves 111,112,113,114,115, and 116, which causes the pressure chamber 82 of the hydraulic actuator 81 for the reverse speed stage to be supplied with line pressure, while the pressure chambers 72, 73, 77, 78, 96, and 44 are not supplied with any substantial pressures.Thus at this time rotational power is transmitted from the crankshaft of the internal combustion engine via the flywheel 23 and via the first clutch assembly 200 to the first driving gear wheel shaft 3, whence it is transmitted through the reverse speed driving gear wheel 7 and the reverse idler gear wheel 20 and the reverse speed driven gear wheel 1 8 to the driven gear wheel shaft 10, whence it is output via the power output gear wheel 1 5 to the differential gear mechanism 85, now in a reverse rotational sense to the previous forward driving one, since one more gear wheel, the reverse idler gear wheel 20, is present in the rotational force transmission path.

Now, referring to the graphs shown in Figs. 4 and 5, the particular principle of the present invention will be explained. In all of these four graphs, time is shown along the horizontal axis, and: in the upper ones of these graphs in Fig. 4 and Fig.

5 respectively the lines A and A' respectively show the relative rotational speed between the two members of the first clutch assembly 200 which are selectively engaged together by the action of said clutch assembly 200 (i.e. the flywheel 23 and the clutch disk assembly 35) and the relative rotational speed between the two members of the second clutch assembly 201 which are selectively engaged together by the action of said clutch assembly 201 (i.e. the flywheel 23 and the clutch disk assembly 45) is shown along the vertical axis; while in the lower ones of these graphs respectively the line B shows the actual value of the pressure between the two frictionally engaged members of the first clutch assembly 200, and the lines B and C respectively show the actual values of the pressures between the two frictionally engaged members of both these first and second clutch assemblies 200 and 201 respectively, said pressures being controlled by suitable control of the electrical control device 140 of the pulse ratios of the signals respectively supplied to the electromagnetic fluid switching valves 111 and 112, are shown along the vertical axis. The graphs in Fig. 4 are applicable to the case of starting the vehicle off from rest, either forwards or backwards direction; and the graphs in Fig. 5 are applicable to the case of shifting between speed stages of the transmission during motion of the vehicle.

In the case of starting the vehicle off from rest by engaging the first clutching assembly 200 while the synchronizers 16 and 1 7 are in their positions for operating the first speed stage and the second clutching assembly 201 is kept in the disengaged state as explained above, i.e. when in this case it is desired to synchronize the relative rotation of the two members (the flywheel 23 and the clutch disk assembly 35) of this first clutch assembly 200, then the electrical control device 1 40 does not suddenly start outputting an electrical signal of pulse ratio zero to the electromagnetic switching valve 111, so as to suddenly and abruptly start supplying zero line hydraulic fluid pressure to the pressure chamber 96 so as forcibly to suddenly and abruptly engage said first clutch assembly 200; on the contrary, the electrical control device 140 outputs an electrical signal to said electromagnetic switching valve 111 so controlled, in a per se well known in the control art type of feedback manner, relative to the relative rotational speed between the two mutually rotating members of said first clutch assembly 200 as shown by the line A in the upper graph of Fig. 4 (in which the time point at the origin represents the start of shifting off from rest action) and as computed by the electrical control device 140 based upon the signal from the engine rpm sensor 144 (taking into account the fact that the vehicle speed is currently zero), that the pressure between the frictionally engaged members of said first clutching assembly 200 as controlled by the hydraulic fluid pressure supplied to said pressure chamber 96 of said actuator 95 thereof varies with respect to time and with respect to said mutual rotational speed of said members as shown by the line B in the lower graph of Fig. 4.In particular, in this first preferred embodiment of the clutch actuation system according to the present invention, the pressure between the frictionally engaged members (the flywheel 23 and the clutch disk assembly 35) of the first clutch assembly 200 is increased with time as the relative rotational speed between these members drops below a certain predetermined threshold value NS1, and then the pressure between the clutch members is steadily decreased as shown by the notched shape in the line B of Fig. 4 until the relative rotational speed between the clutch members reaches precisely zero, at which time the pressure between the clutch members is abruptly increased to a higher or steady engagement value to firmly engage the first clutch assembly 200 in the stationary engagement mode.This threshold relative rotational speed NS1 is the relative rotational speed between the two members of the first clutch assembly 200 at which the dynamic friction between them starts to become static friction as their relative rotational speed drops, and at which accordingly the danger of clutch judder due to increase of frictional coefficient between these members starts to occur, as explained earlier. Accordingly, the provision of the notched shape in the line B of Fig. 4 serves effectively to prevent clutch judder during starting of the vehicle away from rest, and to prevent possibly damaging the various parts of the first clutch assembly 200 by generating too much heat and frictional stress therein as well as deteriorating the operational feeling of the transmission, or even stalling the engine.This graph of Fig. 4 is also applicable to the case of starting the vehicle off from rest in the reverse speed stage.

In the case of shifting the transmission from the first speed stage to the second speed stage by disengaging the first clutching assembly 200 and engaging the second clutching assembly 201 while the synchronizers 16 and 1 7 are in their positions for operating the first speed stage and the second speed stage as explained above, i.e.

when in this case it is desired to synchronize the relative rotation of the two members (the flywheel 23 and the clutch disk assembly 45) of this second clutch assembly 201, then again the electrical control device 1 40 does not suddenly start outputting an electrical signal of pulse ratio zero to the electromagnetic switching valve 112, so as to suddenly and abruptly start supplying line hydraulic fluid pressure to the pressure chamber 44 so as forcibly to suddenly and abruptly engage said second clutch assembly 201; on the contrary, the electrical control device 140 outputs an electrical signal to said electromagnetic switching valve 112 so controlled, in a per se well known in the control art type of feedback manner, relative to the relative rotational speed between the two mutually rotating members of said second clutch assembly 201 as shown by the line A' in the upper graph of Fig. 5 (in which the time point at the origin represents the start of speed stage shifting action) and as computed by the electrical control device 140 based upon the signal from the engine rpm sensor 144 and the vehicle road speed sensor 142 (based upon the fact that the synchronizer sleeve 1 7f is in its position for engaging the second speed stage), that the pressure between the frictionally engaged members of said second clutching assembly 201 as controlled by the hydraulic fluid pressure supplied to said pressure chamber 44 thereof varies with respect to time and with respect to said mutual rotational speed of said members as shown by the line C in the lower graph of Fig. 5, while at the same time outputting an electrical signal to the electromagnetic switching valve 11 so controlled that the pressure between the frictionally engaged members of the first clutch assembly 200 varies with respect to time and with respect to said mutually rotational speed of said members as shown by the line B in the lower graph of Fig. 5.In particular, in this second preferred embodiment of the clutch actuation system according to the present invention, the pressure between the frictionally engaged members (the flywheel 23 and the clutch disk assembly 45) of the second clutch assembly 201 is increased with time as the relative rotational speed of these members decreases, until the relative rotational speed between these members drops below a certain predetermined threshold value NS2, and then the pressure between the clutch members is abruptly decreased as shown by the notched shape in the line B of Fig. 5 and is maintained substantially constant until the relative rotational speed between the clutch members reaches precisely zero, at which time the pressure between the clutch members is abruptly increased to a high or steady engagement value to firmly engage the second clutch assembly 201 in the stationary engagement mode. This threshold relative rotational speed NS2 is again the relative rotational speed between the two members of the second clutch assembly 201 at which the dynamic friction between them starts to become static friction as their relative rotational speed drops, and at which accordingly the danger of clutch judder due to increase of frictional coefficient between these members starts to occur, as explained earlier.Accordingly, the provision of the notched shape in the line B of Fig. 5 serves effectively to prevent clutch judder during shifting of the transmission from the first speed stage to the second speed stage, and to prevent possibly damaging the various parts of the second clutch assembly 201 by generating too much heat and frictional stress therein as well as deteriorating the operational feeling of the transmission. These graphs of Fig. 5, mutatis mutandis, are also applicable to the cases of shifting the transmission between other speed stages thereof, either upshifting or downshifting, as outlined earlier in this specification.

Thus, according to both of the two shown preferred embodiments of the clutch actuation system according to the present invention, it is seen that there is provided an actuation system for a transmission clutch, which operates the clutch automatically by a mechanical system in a satisfactory manner, by pushing two elements of it together, without causing over violent and abrupt such pushing, or over gentle and weak such pushing. Thus the clutch is mechanically operated without causing torque shock, or snatching of the clutch. Clutch judder and clutch biting shock are accordingly avoided.Further, the clutch is mechanically operated to shift the vehicle off from rest, without any danger of causing stalling of the engine of the vehicle to which the transmission is fitted, and is mechanically operated during shifting of the transmission between speed stages in such a way as to aid with smooth shifting, during vehicle motion. This is done by mechanically operating the clutch by pushing two elements of it together, while taking account of the difference between the coefficients of static and of dynamic friction between these two members. Thereby the clutch is engaged positively and effectually without generating any undue load or stress in the members thereof, and without generating any undue heat or frictional force, by not allowing too much or too little clutch slippage.Thus the clutch is engaged effectually without damaging the members thereof, and without damaging other parts of the transmission by this engagement action; and thereby this clutch actuation system keeps the clutch operating over a satisfactory service life thereof, without producing any substantial risk of early and sudden failure thereof.

Slick and smooth clutch operation of the clutch are provided by pushing together two members thereof, in such a way that the strength of the pushing of said members is modulated according to which phase of clutching action is currently in progress, i.e. according to the current relative rotational speed of the two members whose rotation is being brought to be the same. Thereby account is taken of the various different possible operational conditions under which the clutch must work, and of the range of various different possible rotational speeds between said two members under which the clutch must work. Also possible wear on the members of the clutch is taken account of.This is done without the provision of any bulky hydraulic fluid accumulator for cushioning the engagement of the clutch, and accordingly the resulting transmission is light and is compact and further is particularly suitable for incorporation into a vehicle of the front transversely mounted engine front wheel drive type.

Although the present invention has been shown and described with reference to a preferred embodiment thereof, and in terms of the illustrative drawings, it should not be considered as limited thereby. Various possible modifications, omissions, and alterations could be conceived of by one skilled in the art to the form and the content of this preferred embodiment, without departing from the scope of the present invention.

Therefore it is desired that the scope of the present invention, and of the protection sought to be granted by Letters Patent, should be defined not by any of the perhaps purely fortuitous details of the shown preferred embodiment, or of the drawings, but solely by the scope of the appended claims, which follow.

Claims

1. For a transmission clutch comprising a first member and a second member which are selectively pressed together in order to engage said clutch by friction between them: an actuation system, comprising: (a) an actuator which selectively presses said first member and said second member together, and which can perform said pressing action with a pressing force which is controllable to vary over a range; (b) means for detecting the rotational speed of said first member and the rotational speed of said second member; and (c) a control system which controls said actuator, so as to cause said actuator to thus press said first member and said second member together, in such a fashion as to cause the pressing force by which said first member and said second member are pressed together to be varied according to the relative rotational speed between said first member and said second member.

2. A transmission clutch actuation system according to claim 1, wherein said control system controls said actuator so as to cause said actuator to press said first and said second member together in such a fashion as to cause the pressing force by which said second member is pressed against said first member to increase smoothly and monotonically during the process of engagement of said clutch, until the relative rotational speed between said first member and said second member drops to a certain predetermined value.

3. A transmission clutch actuation system according to claim 2, wherein as the relative rotational speed between said first member and said second member drops from said certain predetermined value down to zero said pressing force by which said second member is pressed against said first member is steadily and monotonically decreased.

4. A transmission clutch actuation system according to claim 2, wherein as the relative rotational speed between said first member and said second member drops below said certain predetermined value said pressing force by which said second member is pressed against said first member is abruptly decreased to a certain pressing force value.

5. A transmission clutch actuation system according to claim 4, wherein as the relative rotational speed between said first member and said second member drops from said certain predetermined value down to zero said pressing force by which said second member is pressed against said first member is kept substantially constant at said certain pressing force value.

6. A transmission clutch actuation system according to any one of claims 1 through 5, wherein said actuator is a hydraulic actuator that is actuated by supply of an actuating hydraulic fluid pressure thereto and provides a pressing force between said second member and said first member related to the pressure value of said actuating hydraulic fluid pressure, and wherein said control system supplies said actuating hydraulic fluid pressure to said actuator.

7. A transmission clutch actuating system according to claim 6, wherein said control system comprises an electromagnetic valve that supplies said actuating hydraulic fluid pressure to said actuator and an electrical control device that controls said electromagnetic valve.

8. A transmission clutch actuation system according to claim 7, wherein said electromagnetic valve is a two mode type valve which according to supply or non supply of electrical energy thereto either provides supply of substantially a line hydraulic fluid pressure to said actuator or provides supply of substantially zero pressure value to said actuator, and wherein said electrical control device supplies an electrical pulse signal of a certain duty ratio to said electromagnetic valve.

9. A transmission clutch actuation system according to claim 8, wherein the duty ratio of said pulse signal, during the process of synchronization of the relative rotational speeds of said transmission elements, is varied by said electrical control device, between a first extreme duty ratio value which causes said electromagnetic valve to supply substantially a zero pressure value substantially continuously to said actuator at one extremity of the process of engagement of said clutch, through to a second extreme duty ratio value which causes said electromagnetic valve to supply substantially said line hydraulic fluid pressure substantially continuously to said actuator at the other extremity of the process of engagement of said clutch.

10. A transmission clutch actuation system according to any one of claims 2 through 5, wherein said certain predetermined value of relative rotational speed between said first member and said second member is substantially the value of said relative rotational speed at which the dynamic friction between said members starts to become static friction.

11. A transmission clutch actuation system substantially as herein described with reference to, and as illustrated in, the accompanying drawings.

12. A transmission clutch having an actuator system as claimed in any preceding Claim.