GB2062140A - Planetary transmission with coaxial hydraulic actuator - Google Patents

Abstract

A transmission for an automotive vehicle, in which rotational power is input to a carrier 12 of a planetary gear mechanism and is taken out from the ring gear 17. An engagement member 21, coaxial with and rotationally coupled to the sun gear 16, may be frictionally engaged either to the ring gear 17 or to the transmission casing 7, and is driven between these two positions by a piston member 34 coaxial with and axially coupled to it, but rotationally free with respect to it, which is formed as a disk 36 with a hub 35 projecting from its center, the hub being connected to the engagement member 21 so as to be axially fixed thereto but rotationally free with respect thereto. An annular fluid pressure chamber 41 is defined around and coaxial with the hub 35, between the casing 7 and the piston member 34, on one side of the piston member. Selective supply of fluid pressure to the annular chamber 41 drives the engagement member 21 between its positions, whereby the transmission provides either a direct coupled stage or a stage providing increase of rotational speed. A disk spring 46 biases piston member 34 to the right (as shown in the drawing) and a one-way clutch 19 avoids overspeeding of the ring gear 17. <IMAGE>

Description

SPECIFICATION Planetary transmission with coaxial hydraulic actuator The present invention relates to a transmission for an automotive vehicle, such as an automobile or the like, and more particularly relates to a transmission device incorporating a planetary mechanism, which may be used as an overdrive transmission device, or alternatively as a subtransmission device coupled to a main transmission device, in which shifting between two different transmission speed stages is performed by a fluid pressure actuator.

There is a known transmission device for automotive vehicles, which comprises (a) a main transmission device, which is a manual gear selection type transmission device which can be manually selected between a plurality, usually three or more, transmission stages; and (b) an overdrive or subtransmission device, which is a planetary gear type transmission device provided either before or after the main transmission device in the power train, and which can be selected between a high speed stage and a low speed stage. In most cases the low speed stage is a directly connected stage, and the high speed stage is a speed-increasing stage. Therefore, by the selective operation of the subtransmission, in addition to the operation of the main transmission, a greater number of speed stages may be attained than if only the main transmission were provided.

Further, there is a known type of such a subtransmission device, which incorporates a planetary gear mechanism comprising a sun gear, a ring gear, and a plurality of planetary pinions meshed between the sun gear and the ring gear, wherein rotational power is input to the carrier of the planetary gear mechanism and is taken out from the ring gear of the planetary gear mechanism, and wherein the planetary gear mechanism is selected between said two speed stages by either (a) rotationally coupling the sun gear to the ring gear, in order to provide a direct transmission stage, or (b) rotationally coupling the sun gear to the housing of the transmission, in order to provide an increasing speed stage.

This rotational coupling has been performed by a frictional engagement member, rotationally fixed to the sun gear, which is axially displaceable with respect to the casing of the transmission between a first position wherein it frictionally engages with the ring gear, and a second position wherein it frictionally engages with the casing. Heretofore, such a frictional engagement member has been moved between its two positions by a sliding member which is axially fixed to the frictional engagement member but is able to rotate with respect thereto, said sliding member being axially driven to and fro by a fluid pressure actuator such as a cylinder-piston device mounted asymmetrically with respect to the axis of the planetary gear mechanism.Thereby, by controlling the supply of fluid pressure such as oil pressure to the fluid pressure actuator, via the sliding member the frictional engagement member may be driven between its two positions.

In general in automotive vehicles it is required to reduce the weight of the transmission system as much as possible, especially in small automobiles, and especially in front wheel drive automobiles such as front engine front drive automobiles. Because a two stage transmission device such as the one outlined above which includes a main manually selectable gear transmission device and a subtransmission device tends as a matter of course to be heavier than a simple one stage transmission device, the construction of the subtransmission device is particularly required to be as light as possible.

Further, because especially in a front engine front drive automobile the mounting space available for fitting such a transmission tends to be limited, it is also very important that such a subtransmission device for a so-called FF automobile should be as small as possible, and particularly that its axial dimension should be minimized. However, in the above outlined construction for such a subtransmission device, in which the frictional engagement member is driven by a sliding member which is in turn driven by an asymmetrically located cyiinder piston device, the total axial dimension has been somewhat large, and accordingly it has not been able to make such a transmission as small as could be desired.

According to the present invention, there is provided a transmission for an automotive vehicle, comprising: a casing; a sun gear; a carrier; a plurality of planetary pinions rotatably mounted on the carrier and meshed with the sun gear; a ring gear meshed with the planetary pinions; an engagement member coaxial with and connected to the sun gear so as to be rotationally fixed thereto and axially displaceable with respect to the casing between a first position wherein it is frictionally engaged to the ring gear and a second position wherein it is frictionally engaged to the casing; a piston member coaxial with the engagement member, and comprising a disk and a hub projecting from the center of the disk on its one side, the hub being connected to the engagement member so as to be axially fixed thereto and so as to be rotationally free with respect thereto, an annular fluid pressure chamber being defined around and coaxial with the hub by the cooperation of the casing and the piston member on said one side thereof; and a means for biasing the piston member in the direction to reduce the volume of said annular fluid chamber; selective supply of fluid pressure to said fluid pressure chamber driving the engagement member between its said positions; whereby the ratio of the rotational speed of the ring gear to that of the carrier may be set to either unity or a value greater than unity.

According to such a structure, since the member which corresponds directly to the sliding member in the above outlined conventional prior art devices is itself the piston of the hydraulic fluid pressure actuator, thereby the axial dimension of the device is much reduced, and also the total number of parts of the device is reduced, resulting in a smaller, lighter, and more reliable device, which is easier to manufacture. Further, because the piston of the hydraulic actuator is coaxial with the planetary gear mechanism, as a matter of course the diameter of this hydraulic fluid pressure actuator, i.e., of the aforesaid annular fluid pressure chamber, may be made large, and may be comparable with the diameter of the planetary gear mechanism as a whole.This provides a much increased effective cross sectional area for the hydraulic fluid pressure actuator, as compared to that available with a conventional fluid pressure actuator of the sort that could be fitted in practice to the end of a sliding member as described above.

Further, according to a detailed characteristic of the present invention, the connection between the hub of the- piston member and the frictional engagement member may be provided by a bearing, such as a ball bearing, whose outer race is directly constituted by the inner circumferential surface of the hub of the piston member.

According to such a construction, since no separate outer race for the bearing is provided, the radial dimension of the connecting construction between the engagement member and the piston member may be made smaller than if an outer race were provided separately and pressed into the hub of the piston member or the like. This simple construction also is effective in reducing the overall weight of the device, and in reducing its complexity, thereby increasing its service life and the ease of manufacture thereof.

Therefore an advantage of this invention is that is makes it possible to provide a transmission device for automotive vehicles such as automobiles, which may be used as a subtransmission device in combination with a main transmission, of the general structure outlined above as incorporating a planetary gear mechanism and a frictional engagement member, in which the construction and arrangement of the fluid pressure actuator, and the connection of this actuator to the frictional engagement member, are improved so as to reduce the number of parts in, and the weight of, the transmission device.

A further advantage of the present invention is that it makes it possible to provide such a transmission device in which the axial dimension has been reduced as compared with the above outlined conventional prior arts.

A further advantage of the present invention is that it makes it possible to provide such a transmission device in which, because of the reduction of the number of parts, reliability is increased and ease of construction is enhanced.

A further advantage of the present invention is that it makes it possible to provide such a transmission device in which the effective cross sectional area of the fluid pressure actuator is greater than is easily available in the above outlined prior art devices, so that accordingly the device may operate with a lower level of operating hydraulic fluid pressure.

The present invention will now be shown and described with reference to a preferred embodiment thereof, and with reference to the illustrative drawing. It should be clearly understood, however, that the description of the embodiment, and the drawing, are given purely for the purposes of explanation and exemplification only, and are not 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 drawing, the sole figure is a longitudinal sectional view, showing the essential parts of a preferred embodiment of the transmission for an automotive vehicle according to the present invention, which is in fact being used as a subtransmission coupled to a main manually operated transmission which is only partially shown.

A first preferred embodiment of the transmission for an automotive vehicle according to the present invention will now be described, with reference to the appended drawing.

In the drawing, the reference numeral 1 indicates a left hand part of the casing of a main transmission device of an automobile. The shown embodiment of the transmission according to the present invention is in fact, in the construction shown in the drawing, being used as a subtransmission coupled to a main transmission device which is manually shiftable between a plurality of speed stages. However, this main transmission device is not fully shown in the drawing, nor will it be fully described herein, because an understanding of the operation thereof is irrelevant with regard to the principles of the present invention.

The main transmission casing 1 supports, via a ball bearing 2, a tubular intermediate shaft 3, which projects a little to the left in the drawing out of the left hand side of the main casing 1. Further, the main casing 1 supports, via a ball bearing 4, a power output shaft 5, one end of which, again, projects a little to the left in the drawing out of the left hand side of the main casing 1. Within the main transmission casing 1 the intermediate shaft 3 and the output shaft 5 are parallel, and are selectably rotationally connectable to one another with various gearing ratios by manually engaged gears or the like, which are not shown. Further, the power output shaft 5 is rotationally coupled, at a part thereof not shown in the drawing, to a differential device which provides power to the road wheels of the automobile.

Through the center of the intermediate shaft 3, and coaxial therewith, there passes an input shaft 6. The input shaft 6 is rotatable within the intermediate shaft 3 on plain bearings. The right hand end in the drawing, not shown, of the input shaft 6 is connected to the power output shaft of an internal combustion engine which drives the automobile to which this transmission system is fitted, and the left hand end in the drawing of the power input shaft 6 projects out from the end of the intermediate shaft 3 for a certain distance and is rotatably supported by a plain bearing 8, which is mounted in a rear casing 7 which is the casing of the transmission according to the present invention.

The rear casing 7 is attached to the left hand side in the drawing of the main casing 1 by fixing means which are not shown. When these fixing means are disengaged, the rear casing 7 may be removed in the left hand direction in the drawing from the main casing 1, along with the transmission according to the present invention, and will leave projecting from the main casing 1 only the end of the power output shaft 5, the end of the intermediate shaft 3, and projecting from this the end of the power input shaft 6, all three of which shafts have splines formed thereon, as will be explained later.Accordingly, in applications for the main transmission device incorporating the main casing 1 in which it is not required to provide any subtransmission such as the transmission according to the present invention shown in the drawing, it will be relatively easy to mount a simple connecting member between the splines on the intermediate shaft 3 and the splines on the power input shaft 6 which projects out therefrom, in order fixedly to couple these two shafts together so as to utilize the main transmission device incorporating the main casing 1 by itself.

This has a useful meaning with regard to flexibility of design and production of various different models of automobile.

On the portion of the power input shaft 6 which protrudes out from the end of the intermediate shaft 3, and which is closer to the end of the intermediate shaft 3, there are formed some splines, and to the left of these splines in the drawing the power input shaft 6 is smooth. Upon this smooth end portion of the input shaft 6 there is mounted, via plain bearings 1 1, a sun gear 10 which is formed with a hub extension 9 protruding leftwards from it in the drawing. Thus, the sun gear 10 is rotatably supported upon the power input shaft 6.

The sun gear 10 is also axially slidable on the plain bearings 11 for a certain distance to the left and the right in the drawing on the input shaft 6.

On the aforesaid splined portion of the power input shaft 6 near to the end of the intermediate shaft 3, there is mounted a carrier 12 which has internal splines, so that the carrier 12 is rotationally fixed to the power input shaft 6. The carrier 12 is fitted with pinion shafts 14, one of which is shown in the drawing, and is penetrated into a hole in the carrier 1 2 and is fixed therein by an engagement pin 12'. The pinion shaft 14 rotatably supports, via a needle bearing 15, a planetary pinion 16. In fact, in the shown embodiment, there are provided several pinion shafts such as 14, and several planetary pinions such as 1 6, though only one of them is shown in the drawing. On the end of the pinion shaft 14 remote from the carrier 12 there is mounted a cover 13.The planetary pinion 1 6 is meshed with the sun gear 10, and, when the carrier 12 rotates with respect to the sun gear 10, performs planetary motion around the sun gear 10 in a per se well known fashion.

To the aforesaid splines on the end of the intermediate shaft 3 there is engaged a connecting member 18, which is thereby rotationally coupled to the intermediate shaft 3. A ring gear 1 7 is mounted on the connecting member 18, and the inside of this ring gear 17 is meshed with the planetary pinion 1 6. Accordingly, the ring gear 1 7 is rotationally coupled to the intermediate shaft 3. Between the carrier 12 of the planetary pinion 1 6 and this connecting member 1 8 there is mounted a one way clutch 1 9.

This one way clutch 1 9 is so constructed as to connect the carrier 12 rotationally to the connecting member 18, i.e. to the ring gear 17, when the carrier 1 2 attempts to rotate at a higher speed in the normal direction of rotation provided by the engine of the automobile, than the connecting member 18.

On the outer circumference of the ring gear 1 7 there is formed a conical clutch facing 20. A brake member 27, which is formed as a disk 31 and a ring 28 mounted to the outer circumference of the disk, is fixed by a bolt 30 (actually a plurality of bolts 30 are provided but only one is shown in the drawing) to the rear casing 7. The disk 31 has a central hole. The inner circumferential surface of the ring 28 is formed as a conical brake facing 29 opposing the conical clutch facing 20 formed on the ring gear 1 7 with a certain gap therebetween.

A frictional engagement member 21 is formed of three parts: a tubular hub portion 22, a disk portion 21 attached to the right hand end in the drawing of the hub 22 and extending outward therefrom, and a cone portion 24 extending in the right hand direction in the drawing from the outer circumference of the disk portion 21, and projecting between the conical clutch facing 20 and the conical brake facing 29. On the inner circumference of the cone portion 24 there is attached an annular clutch pad 25, and on the outer circumference of the cone portion 24 there is attached an annular brake pad 26. The hub portion 22 of the frictional engagement member 21 is supported on the hub extension 9 of the sun gear 10, and is rotationally connected thereto by splines.

In the shown embodiment, the frictional engagement member 21 is also axially fixed to the sun gear 10. Because the sun gear 10 is axially movable through a certain range along the smooth end portion of the power input shaft 6, as mentioned above, thereby the frictional engagement member 21 is axially displaceable between a first position, to the right in the drawing, wherein the annular clutch pad 25 engages the conical clutch facing 20 formed on the ring gear 17, and accordingly the sun gear 10, the frictional engagement member 21, and the ring gear 1 7 are all rotationally coupled together, and a second position, to the left in the drawing, wherein the annular brake pad 26 engages with the conical brake facing 29 formed on the brake member 27, and accordingly the sun gear 10 and the frictional engagement member 21 are rotationally coupled to the rear casing 7, via the brake member 27, so as not to rotate.

The arrangements for displacing the frictional engagement member 21 between its aforesaid first and second positions will now be described.

On the outer circumference of the hub portion 22 of the frictional engagement member 21 there is fitted an inner race 33. Running in this inner race 33 there are provided a plurality of balls 37. A piston member 34 is formed of a disk 36 with a hole through its center, and a hub portion 35 protruding in the right hand direction in the drawing from the inner circumference of the disk 36. An outer race, engaged with the balls 37, is directly cut on the inner surface of the hub portion 35. This outer race, the balls 37, and the inner race 33, together constitute a ball bearing 32, which engages the piston member 34 to the frictional engagement member 21 in such a fashion that these members are axially fixed with respect to one another, but are rotationally free with respect to one another.

The disk portion 36 of the piston member 34 is fitted into a circular hole formed in the inner side of the left hand end in the drawing of the rear casing 7, and a fluid seal is positively ensured between these two members by a seal member 42 mounted in an outer groove on the disk portion 36 of the piston member 34. The outer circumference of the hub portion 35 of the piston member 34 is engaged with the inner circumference of the central hole pierced through the disk portion 31 of the brake member 27, and further between these two members there is mounted a seal member 43, which is seated in a circumferential groove formed on the aforesaid inner circumferential surface of the central hole through the disk member 31, and which positively ensures a fluid seal against the hub portion 35.

Accordingly, an annular chamber 41 is defined around the hub portion 35 of the piston member 34, by the cooperation of the rear casing 7 and the piston member 34, on the right hand side in the drawing of the disk portion 36. This annular chamber 41 is sealed by the seal members 42 and 43, and constitutes an actuating fluid pressure chamber for driving the piston member 34. In order to prevent rotational movement between the piston member 34 and the rear casing 7, without hindering axial movement of the piston member 34 within the rear casing 7, an indexing pin 44 is mounted in a hole in the disk portion 36 of the piston member 34, and its end protrudes across the pressure chamber 41 and its tip is projected into a hole 45 formed in the disk portion 31 of the brake member 27.Accordingly, as this pin 44 slides in and out of the hole 45, the piston member 34 can move axially to and fro within the rear casing 7, increasing and decreasing the size of the annular fluid pressure chamber 41 ,freely, but cannot rotate with respect to the rear casing 7.

On the left hand side in the drawing of the piston member 34, between the disk portion 36 and the rear casing 7, there is fitted an annular disk spring 46, which urges the piston member 34 and, connected thereto, the frictional engagement member 21 to the right in the drawing, i.e. urges the frictional engagement member 21 to its said first position wherein it is frictionally engaged to the ring gear 17. Further, hydraulic fluid pressure is supplied to the annular fluid pressure chamber 41, via passages 50 and 51 formed in the rear casing 7, under the control of a switching system, not shown in the drawing, from a rotary hydraulic fluid pressure pump 47.This pump 47 comprises an outer rotor 49 which is fixed to the rear casing 7, and an inner rotor 48 which is, via splines, drivingly engaged to the left hand end of the power output shaft 5 which projects out from the main casing 1, as described above.

The transmission according to the shown first embodiment of the present invention operates as follows. When no hydraulic fluid pressure is supplied to the annular fluid pressure chamber 41, then the piston member 34 is biased to the right in the drawing under the resilient force of the disk spring 46, and accordingly the frictional engagement member 21 is also biased to the right in the drawing, i.e., towards its first position wherein, via the clutch pad 25, its cone portion 24 is frictionally engaged to the conical clutch facing 20 formed on the ring gear 17. In this state, therefore, the sun gear 10 and the ring gear 1 7 are rotationally coupled to one another, and accordingly the planetary gear mechanism as a whole, including the carrier 12 and the connecting member 1 8 is in a locked state.Accordingly, the power input shaft 6, which issplined to the carrier 12, is rotationally coupled to the intermediate shaft 3, which is splined to the connecting member 1 8. Accordingly, input power transmitted by the rotation of the crankshaft of the internal combustion engine (not shown) to the power input shaft 6 is directly transmitted to the intermediate shaft 3, without change of the rotational speed thereof. Thence, of course, via the main transmission device which is not shown, this rotational power is transmitted to the power output shaft 5, but this is not strictly relevant to the present invention. This state of the transmission according to the present invention is the directly connecting stage, wherein no increase of rotational speed is provided thereby.

On the other hand, when a specified value of hydraulic fluid pressure is supplied to the annular fluid pressure chamber 41, then the pressure exerted on the right hand side of the disk portion, 36 of the piston member 34 drives the piston member 34 to the left in the drawing, against the biasing action of the disk spring 46, and the frictional engagement member 21 is also moved to the left in the drawing, because it is coupled to the piston member 34 by the bearing 32, and cannot be moved with respect thereto in the axial direction.As a matter of fact, in this embodiment, because the frictional engagement member 21 is also axially fixed to the tubular extension 9 of the sun gear 10, the sun gear 10 also moves a little to the left in the drawing at this time, by the sliding of the plain bearings 11 on the power input shaft 6, with respect to the outer casing 7; but this does not substantially affect the condition of meshing between the sun gear 10 and the planetary pinions 1 6. However, the movement of the frictional engagement member 21 to the left in the drawing disengages the conical clutch pad 25 from the conical clutch facing 20 formed on the ring gear 17, and engages the conical brake pad 26 with the conical brake facing 29 of the brake member 27, thus stopping the rotation of the frictional engagement member 21, and, accordingly, stopping the rotation of the sun gear 10, because the sun gear 10 is rotationally fixed to the frictional engagement member 21 and thereby to the rear casing 7.Accordingly, in this state, the rotation of the power input shaft 6 provided by the action of the internal combustion engine (not shown) is transmitted, via the splined portion thereof, to the carrier 12 which carries the planetary pinions 16, and in a per se well known way is transmitted to the ring gear 1 7 at an increased rotational speed, i.e., at a reduction gearing ratio smaller than unity. That is to say, the ring gear 1 7 rotates faster than does the power input shaft 6, and accordingly the connecting member 18, which is connected to the ring gear 17, and the intermediate shaft 3, which is splined to the connecting member 1 8 likewise rotate at a high rotational speed than does the input shaft 6.

Thus, the shown embodiment of the transmission according to the present invention provides its socalled speed increasing stage.

Accordingly, by the selective supply of hydraulic fluid pressure to the annular fluid pressure chamber 41, the frictional engagement member 21 may be driven between its first and its second positions, and, according to this, the transmission according to the present invention provides either the direct connection stage, or the speed increasing stage. This is accomplished, as explained above, with a very compact construction, which is much more economical of space than prior art constructions.

By the shown construction in which the outer race of the bearing 32 is directly provided by the inner part of the hub portion 35 of the piston member 34, the radial dimension of the connecting structure between the piston member 34 and the frictional engagement member 21 may be much reduced, thereby lightening the construction. Further, because the number of parts in the construction is reduced, it is easier and cheaper to make, and more reliable in service.

In the shown embodiment axial displacement of the frictional engagement member 21 has been possible, although in fact this frictional engagement member 21 is axially as well as rotationally coupled to the sun gear 10, by the fact that the sun gear 10 is axially displaceable within the rear casing 7 to a certain extent, by sliding along the power input shaft 6 on the plain bearings 11. However, in a different construction, the sun gear 10 could be axially fixed within the rear casing 7, and the frictional engagement member 21 could be axially slidable with respect thereto, as on splines or the like. Such a construction would be quite within the scope of the present invention.

Although the present invention has been shown and described with reference to a preferred embodiment thereof, and in terms of the illustrative drawing, 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 any particular 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 embodiment, or of the drawing, but soiely by the scope of the appended claims, which follow.

Claims (8)

1. A transmission for an automotive vehicle, comprising: a casing; a sun gear; a carrier; a plurality of planetary pinions rotatably mounted on the carrier and meshed with the sun gear; a ring gear meshed with the planetary pinions; an engagement member coaxial with and connected to the sun gear so as to be rotationally fixed thereto and axially displaceable with respect to the casing between a first position wherein it is frictionally engaged to the ring gear and a second position wherein it is frictionally engaged to the casing;; a piston member coaxial with the engagement member, and comprising a disk and a hub projecting from the center of the disk on its one side, the hub being connected to the engagement member so as to be axially fixed thereto and so as to be rotationally free with respect thereto, an annular fluid pressure chamber being defined around and coaxial with the hub by the cooperation of the casing and the piston member on said one side thereof; and a means for biasing the piston member in the direction to reduce the volume of said annular fluid pressure chamber; selective supply of fluid pressure to said fluid pressure chamber driving the engagement member between its said positions; whereby the ratio between the rotational speed of the ring gear to that of the carrier may be set to either unity or a value greater than unity.

2. A transmission according to claim 1 , further comprising a bearing structure which connects the hub of the piston member to the engagement member, the outer race of said bearing structure being provided by said hub.

3. A transmission according to claim 1, wherein the biasing means urges the engagement member towards its first position, and supply of fluid pressure to said annular fluid pressure chamber urges the engagement member towards its second position.

4. A transmission according to any of claims 1-3, further comprising a means for engaging the piston member to the casing so that the piston member is rotationally fixed to the casing, but is axially free with respect to the casing.

5. A transmission according to any of claims 1-3, wherein the engagement member is axially fixed to the sun gear, and the sun gear is axially displaceable with respect to the casing.

6. A transmission according to any of claims 1-3, wherein the engagement member is axially displaceable with respect to the sun gear, and the sun gear is axially fixed with respect to the casing.

7. A transmission for an automotive vehicle, the transmission being substantially as hereinbefore described, with reference to, and as illustrated in, the accompanying drawings.

8. An automotive vehicle including a transmission as claimed in any preceding claim.