GB2473340A

GB2473340A - Gearbox having aligned input and output shafts

Info

Publication number: GB2473340A
Application number: GB1014724A
Authority: GB
Inventors: Anthony Richard Fitch
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-09-05
Filing date: 2010-09-06
Publication date: 2011-03-09
Anticipated expiration: 2030-09-06
Also published as: GB0915570D0; GB201014724D0; GB2473340B

Abstract

A gearbox having power input shaft 3 and an output shaft 6 aligned therewith, connection means 15 for directly interconnecting adjacent end portions of the two shafts 3 and 6, a plurality of gears 8 ,22, 27, 7 arranged in a gear train and also capable of interconnecting the input and output shafts 3 and 6, and synchromesh self shifting clutch 21 operable between the input shaft 3 and one gear 8 of said plurality of gears to connect the input shaft to said one gear 8, another of said gears 7 being connectable to the output shaft through a synchroniser hub 133 , and control means 25, 125, 150, for selectively connecting the input shaft 3 to the output shaft 6 either directly through the connection means 15 or indirectly through the gear train. Said one gear 8 is in the form of a coaxial hollow cylinder having gear teeth 9 on its outer surface and which is free to rotate relative to said shafts 3 and 6, said cylinder housing the clutch 21 and the connection means 15. The gearbox is preferably used as a retro fit overdrive to provide a cruising gear ration in vehicle applications.

Description

A GEARBOX

FIELD OF THE INVENTION

This invention relates to a gearbox which can be used as a stand-alone unit, for example in marine applications, or which may be used as supplementary gearbox, and in particular to a gearbox which can be used in conjunction with an existing gearbox to provide a cruising gear, sometimes referred to as an overdrive.

BACKGROUND TO THE INVENTION

The existing gearbox can be either a manual gearbox or an automatic gearbox, typically providing four or five discrete gear ratios determining the rate of rotation of the driving wheels for a given engine speed.

The requirement for a cruising gear, or overdrive, for motor vehicles has long been established. A cruising gear will reduce the engine speed at a given road speed, and so will reduce the fuel consumption and engine wear of the vehicle, both of which can give long term cost savings to the vehicle owner or user.

One prior art device is an overdrive unit which could be fitted to the output of a conventional * * gearbox and provide a higher ratio gear for reduced engine speed when cruising. Whilst many overdrive units have been made and fitted to vehicles they are relatively mechanically complex, inefficient and expensive. Because of their relative complexity the retro fitment of an overdrive unit to an existing vehicle is rare, and most overdrive units have been fitted as original equipment.

In addition, the torque. which can be transmitted by an overdrive unit is limited, and so overdrive units are typically used only on smaller vehicles such as passenger cars and light vans. Larger, e.g. commercial, vehicles have not been able to benefit from the fitment of an overdrive unit.

Commercial vehicles in particular could benefit from a cruising gear, since the gear ratios of their gearboxes are typically chosen to suit the vehicle when it is fully loaded, and yet the vehicle will oftenbe used either empty or only partially loaded. When the vehicle is being operated empty or partially loaded the engine speed will be higher than necessary, resulting in unnecessary fatigue to the vehicle and also perhaps to its driver whilst the fuel consumption will be higher than if a cruising gear was available on the vehicle.

Overdrive units have recently become less commonplace, and have been largely replaced by the vehicle manufacturers fitting one or more additional gears into the gearbox, so as to provide one or more higher cruising gears. However, the fitment of additional gears cannot be undertaken as a retro fit, and if the owner of an existing vehicle wishes to benefit from the advantages of a higher cruising gear it is necessary to purchase and fit a new gearbox containing the additional gear(s). The immediate cost penalty of the new gearbox will often outweigh the long-term cost savings associated therewith, so that the fitment of a new gearbox is not often undertaken. Instead, a vehicle which does not have a cruising gear will typically continue to be used despite the ongoing cost penalty.

In WO 2007/028986, the present applicant describes a gearbox which may be used as a supplementary gearbox which can give a vehicle a cruising gear and yet which is suited to retro-fitment to an existing vehicicle. This gearbox has a power input shaft and an output shaft aligned with the input shaft, connection means for directly interconnecting adjacent end portions of the two shafts, a plurality of gears arranged in a gear train and also capable of interconnecting the input and output shafts, and synchromesh self shifting clutch operable between the input shaft and one of said plurality of gears to connect the input shaft to said one gear, and control means for selectively connecting the input shaft to the output shaft either directly through the connection means or indirectly through the gear train.

The present Invention is an improvement to the gcarbox described in WO 2007/028986

Statements of Invention

According to the present invention there is. provided a gearbox having a main power input shaft and an output shaft aligned with the input shaft, connection means for directly interconnecting adjacent end portions of the two shafts, a plurality of gears arranged in a gear train and also capable of interconnecting the input and output shafts, and synchromesh self shifting clutch operable between the input shaft and one of said plurality of gears to connect the input shaft to said one gear, another of said gears being connectable to the output shaft through a synchroniser hub, and control means for selectively connecting the input shaft to the output shaft either directly through the connection means or indirectly through the gear train. *0

The gearbox may be used as a supplementary gearbox for fitment into the drive train of a vehicle utilizing a propeller shaft between the power source and the final drive.

The term "vehicle" includes boats as well as land motor vehicles.

* The main input shaft may be connected to a supplementary input shaft to which it may be connected and disconnected by means of an integral clutch.

Such a gearbox provides at least two different gear ratios. The gearbox can be made to transmit a large torque and so can be made suitable for commercial vehicles. Use of the gearbox as a supplementary gearbox will not require the replacement of the existing gearbox so that its initial cost should not outweigh the long-term cost saving it offers.

When used as a supplementary gearbox, the gear box is located downstream of the main drive line clutch unit of the vehicle but activation of the main clutch may not be required when gear ratios in the supplementary gearbox are changed as the latter employs a synchro self shifting clutch (SSS) principle and ratchet and pawl gear alignment.

Preferably, said one gear is in the form of a hollow cylinder having gear teeth on its outer surface and which is coaxial with the input and output shafts and free to rotate relative to said shafts, said cylinder housing the SSS clutch mechanisms and the connection means.

Preferably the gear teeth on the cylinder mesh with a sliding gear being axially slideable on a third shaft parallel to the input and output shafts and being the second gear in said gear train. * A cruising gear is rotatably mounted on the parallel shaft and meshes with said output gear which is rotatably mounted on the output shaft. The synchroniser hub is rotationally fast with the output shaft but axially slidable thereon to engage a synchroniser device mounted on the output gear.

The cylinder has internal gear teeth at its input shaft end and a piston coaxial with and slideable on the output shaft, the piston being movable axially relative to the cylinder. The sliding gear is in constant mesh with the external gear teeth on the cylinder, and has a friction brake which in use holds the cylinder stationary. The sliding gear has dog teeth at its output end which are engageable with reciprocal dog teeth on the cruising gear only when the piston has disconnected the collar from the input shaft.

The cruising gear preferably has a diameter less than the output gear, thus ensuring that for one revolution of the cruising gear the output gear rotates faster providing a rotational speed of the output shaft greater than that of the input shaft.

The piston may be axially moved by an actuator, preferably an electrical actuator.

Preferably the connection means is an axially slideable collar which is coaxial to said shafts and is connected to the piston, the piston also being connected to the sliding gear meshed with the cylinder, so that movement of both sliding collar and sliding gear is simultaneous.

The slidingcollar has internal splines that co-operate with like splines on the input and output shafts and is free to axially slide along the input and output shafts. Alignment of the teeth and the grooves on engagement is achieved by a ratchet and pawl device which aligns the internal and external splines. When the input shafts is engaged and connected directly to the output shaft, the collar interconnects both the input and output shafts providing direct in-line connection.

The synchromesh slide being permanently engaged on the input shaft is always rotating at the same speed as the input shaft and when the cylinder is stationary, the pawl on the synchromesh slide is not engaged with the ratchet on the inside of the cylinder and the gear teeth on the slider are not enmeshed with the internal teeth on the cylinder.

When the sliding gear moves towards the cruising gear, brake means acting on the cylinder is released and the cylinder rotation increases from stationary, until with the sliding gear and the cruising gear engaged with the output shaft and the collar disengaged from the input shaft, the cylinder increases rotation up to the same speed as the input shaft and the pawl on the synchromesh slide engages with the ratchet on the inside of the cylinder bringing the respective gear teeth into alignment and the synchromesh slide moves to engage its gear teeth with those on the inside of the cylinder. By this means, the input shaft is connected to the cylinder which drives the output shaft via the sliding gear, cruising gear and output gear.

Accordingly, drive is communicated from the input shaft to the output shaft solely by enmeshing gear train, and does not rely. upon a friction component as do conventional overdrive units. The torque which can be transmitted by the supplementary gearbox is therefore dependant upon the size and strength of the gears, which can be manufactured to transmit desired torque, for example those loads associated with commercial vehicles.

One cruising gear should be suitable for the vast majority of applications. The use of only two gear ratios makes controlling the gearbox easier for the driver of the vehicle since it can be controlled by a simple two-position switch or the like. The supplementary gearbox can of course contain more gears so as to provide more than two different gear trains and ratios between the input shaft and the output shaft. However it will be appreciated that the mechanical complexity will increase as more gears are added.

Preferably, in use the supplementary gearbox is controlled by electrical control means so that the operation of an on/off switch by the driver/operator causes the supplementary gearbox to engage direct mode or cruising mode respectively without any interface with the vehicle's existing gearbox or clutch.

The supplementary gearbox may have control means which receive a signal from the existing gearbox; the control means for example being adapted to prevent operation of the cruising gear unless the existing gearbox is already in either of the two highest gears in the gear range.

Since the tOrque required to be transmitted by the supplementary gearbox will be lower when the existing gearbox is in top gear, such an embodiment may enable the gears of the supplementary gearbox to be made smaller and lighter for a given vehicle since they would never be required to transmit the torque available with the lower gears of the existing gearbox.

Description of the Drawings

The invention will be described by way of Example only and with reference the following drawings in which: Fig. 1 is a longitudinal section through a second gearbox also according to the present invention, Fig. 2 is a section on the line 11-1! of Fig.1, Fig. 3 is a second longitudinal part section through the gearbox showing the actuation means, and Fig. 4 is section showing the provision of a reverse gear.

Detailed Description of the Invention

The gearbox is similar to the gearbox described in WO 2007/028986 and the contents of which are hereby incorporated into the present specification.

With reference now to Figures 1 & 2, there is shown a gear box 10 having a main gearbox input shaft 3 is arranged downstream of a supplementary input shaft 103 having an input flange 102 for connection to a power source, for example a motor vehicle gearbox output shaft, or a drive flange from a power unit such as an internal combustion engine. The use of the supplementary input 103 enables the gearbox to handle large torque loads.

The supplementary input shaft 103 can be connected and disconnected from the main input shaft 3 by means of a SSS clutch 104 mounted in an extension 105 of the gearbox casing 1.

The clutch 104 has a slide 111 with internal helical splines 134 mounted on external helical splines on the supplementary input shaft 103. The slide 111 has a ratchet 135 at the input end and gear teeth 113 at the output end. At the input end of this clutch assembly 104 is a pawl 112 on a sliding carrier 136 attached to an arm 138 connected to the clutch electrical actuator 139 which can move the pawl carrier 136 axially backwards and forwards inside a hollow cylindrical end portion 140 of the second input shaft 3. The hollow end portion 140 houses internal gear teeth 132 with a circular recess 141 formed within the teeth 132 for supporting the inner end 103A of the input shaft 103.

When the pawl carrier 136 is moved towards the main input shaft 3, the pawl 112 engages with the ratchet 135 to align the gear teeth 113 with the main input shaft gear teeth 132 and the carrier 136 continues axial movement until gear teeth 113 are engaged with gear teeth 132 to provide connection between the supplementary input shaft 103 and the main input shaft 3.

To disconnect the supplementary input shaft 103 from the main shaft 3, the clutch actuator 139 moves the pawl carrier 136 towards the input end of the clutch assembly 104 pulling the slide 111 away from the input shaft 3 so that the gear teeth 113 on the slide 111 disengage from the internal gear teeth 132 on the second input shaft 3.

The main input shaft 3 is axially aligned with an output shaft 6 having an output flange 5 for connection to a drive shaft to vehicle drive wheels, in the case of a motorvehicle. The inner end portions of the shafts 3 & 6 are located within a cylinder 8 which is axially fast and rotatable about the shafts. The output shaft 6 has an output gear 7 rotatably mounted on thereon adjacent the inside of the casing 1. A coaxial collar 15 is mounted on the adjacent end portions of the two shafts 3 & 6 within the cylinder 8. The cylinder 8 has external gear teeth 9 which in use mesh on one side with an idler gear 22. rotatable and axially slidable on a parallel shaft 20 mounted on the main gearbox casing I. Further idler gears (not shown) may act as balance gears to hold the cylinder 8 steady and in some circumstances two or more balance gears may be used additionally to the sliding idler gear 22. A cruising gear 27 is rotatably mounted on the other end of the shaft 20 and is permanently meshed with the output gear 7. . The cylinder 8 also houses a synchro-self-shifting (SSS) clutch 21 the operation of which is well known. The SSS clutch 21 comprises a slide 11 mounted on a threaded portion 34 of the shaft 3. The slide 11 has outwardly projecting ratchet teeth 35 thereon which are engagable with a pawl 12 mounted on the cylinder 8. The other end Of the slider 11 has gear teeth 13 which are engagable with internal gear teeth 110 on the cylinder 8. The arrangement is such that when the pawl 12 engages a ratchet tooth 35, the gear teeth 13 are aligned to mesh with the gear teeth 110.

With reference to Fig. 3 an electrical actuator 125 is mounted on the outside of the casing 1 and is connected to a worm drive 124. A disc 123 is mounted on the worm drive 124 for movement backwards and forwards thereon. The disc 123 engages with a flange 143 on a piston 19 which is slideably mounted on the output shaft 6. The piston 19 passes through one end of the cylinder 8 to engage with the annular collar 15 slideably mounted on the adjacent inner end portions of the two shafts 3 & 6. Said inner portions are splined and the collar 15 has co-operating internal splines and is axially moveable over the splined end portions. The collar 15 is shown in Fig. I connectingthe input shaft 3 and output shaft 6 in free rotation: The disc 123 also engages an annular flange 128 on the sliding gear 22. The sliding gear 22 has a friction brake surface at one end which is engagable with friction pads 137 fixed on the inside of the casing 1. The sliding gear 22 has dog teeth 129 at the other end which are * reciprocal to dog teeth 1 31 on the cruising gear 27. When the dog teeth 129 are engaged with the dog teeth 131, the sliding gear 22 is rotationally fast with the cruising gear 27.

The collar 15 in the cylinder 8 has a paw! 18 thereon which is engagable with ratchet gear teeth 17 on the main input shaft 3. The arrangement being that on axial movement of the collar 15, the pawl 18 engages the ratchet teeth 17 to align the reciprocal splines before the collar 15 engages the splines on the input shaft 3.

The piston 19 is rotationally fast with the output shaft 6 and axially slidable along splines formed on the output shaft 6 and is provided with a synchromesh hub 133 having a thrust bearing 140 adjacent the pistion 19 and dog teeth 25 and a conical synchronizer ring 26 on its side adjacent the output gear 7. In an alternative arrangement the synchroniser ring cound be mounted on the piston. The synchroniser ring 26 is engagable with a cone clutch 28 on the adjacent side of the output gear 27 and the dog teeth 25 on the synchromesh hub 133 are engagab!e with co-operating dog teeth 29 on the output hub 7.

As shown in Fig I, when the gearbox is in direct drive mode., the collar 15 is connecting the main input shaft 3 direct!y to the output shaft 6. The cylinder 8 is stationary being indirectly restrained by the brake 137 acting on the sliding gear 22. The SSS clutch slide 11 is rotating freely on the ratchet and pawl 12, 35, as the rotational speed of the cylinder (zero) is less than the input shaft. The cruising gear 27 is engaged with the output gear 7 in free rotation. The actuators 139 and 125 are connected to a control unit 150 operated through a driver operable switch 151. . . To move from direct drive mode to cruising mode The two input shafts 103 &3 are disengaged by the clutch electrical actuator 139 moving the pawl carrier 136 towards the input end of the clutch assembly 104 and pulling the clutch synchro slide 134 so that the gear teeth 113 on the clutch synchro slide disengage from the internal gear teeth 132 in the end portion 140 of the second input shaft 3.

The actuator 125 is caused to turn the worm drive 124 in one rotational direction, for example anti-clockwise, and the disc 123 is moved away from the actuator 125. The disc 123 moves the sliding gear 22 towards the cruising gear 27 and simultaneously the disc 123 moves the piston 19 away from the cylinder 8 pulling the collar 15 back along the output shaft 6. The movement of the sliding gear 22 releases the friction brake 137 and the cylinder 8 is able to rotate freely. The rightwards movement of the sliding gear 22 causes the dog teeth 129 on the sliding gear 22 move into engagement with the dog teeth 131 on the stationary cruising gear 27. The rotation of the cruising gear 27 is now transmitted through the sliding gear 22 to the cylinder 8 which begins to rotate.

The rightwards movement, as shown, of the collar 15 also disengages the collar 15 from the main input shaft 3. When the input and output shafts 3 & 6 are disengaged the sliding gear 22 is fast with the cruising gear 27. Simultaneously, the piston 19 rightwards abutting the thrust bearing 140 and moving the synchromesh hub 133 rightwards. The synchroniser ring 26 and cone clutch 28 come into contact and further movement of the hub 18 causes to the dog teeth 25 on the hub 133 to align with and engage with the dog teeth 29 on the output gear 27.

When the rotational speed of the cylinder 8 equals the rotational speed of the output/input shaft 3 & 6, the pawl 12 will engage with the ratchet gear 35 on the synchromesh slide 11.

With the ratchet gear and pawl 35 & 12 engaged, the synchromesh gear teeth 13 will be in alignment with the internal gear teeth 10 on the cylinder 8 and the synchromesh slide 11 will move along the screw threaded portion 34 to engage with the cylinder 8. The cylinder 8 is now rotationally fast with the main input shaft 3.

The output shaft 6 is now driven via the cylinder 8, sliding gear 22, cruising gear 27 and output gear 7. The rotation speed of the output shaft 6 is now faster than that of the input shaft 3. The relative speeds of the shafts depend upon the number of teeth on the cylinder 8, sliding gear 22, and output gear 7.

The clutch actuator 139 is energized to push the pawl carrier 136 along the primary input shaft 103 towards the other input shaft 3. The pawl 112 engages with the ratchet 135 to align the gear teeth 113 with the gear teeth 132 and the travel continues until the input shaft 103, clutch synchro slide 111 and main input shaft 3 are fast as one shaft.

To move from cruising mode to direct drive mode The two input shafts 103 &3 are disengaged by the clutch electrical actuator 139 moving the pawl carrier 136 towards the input end of the clutch assembly 104 and pulling the clutch synchro slide 134 so that the gear teeth 113 on the clutch synchro slide disengage from the internal gear teeth 132 in the end portion 140 of the second input shaft..

When the main input shaft 3 has been disengaged and is in free rotation, the actuator 125 turns the worm drive 124 in the reverse direction of rotation, in this case clockwise, and the disc 123 begins to move the piston 19 and synchroniser hub 133 back towards the cylinder 8.

This disengages the dog teeth 25 from the dog teeth 29 on the hub 7. The piston 19 engaging the flange 128 on the sliding gear 22 also moves the sliding gear 22 away from the cruising gear 27. Simultaneously, the movement of the piston 19 is pushing the collar 15 along the output shaft 6 towards the main input shaft 3 with the output shaft 6 still rotating at a faster rotational speed than the disconnected main input shaft 3. The continuing axial travel of the collar 15 brings the pawl 18 on the collar 15 into engagement with the ratchet gear 17 on the main input shaft 3. When the ratchet and pawl 18 & 117 are engaged, the inner splines on the collar 15 and the splines on the main input shaft 3 and output shaft 6 are in alignment and the collar 15 moves smoothly onto the input shaft 3, so that the collar 15 re-connects the second input shaft 3 and the output shaft 6.

The simultaneous travel of the sliding gear 22 disengages the sliding gear 22 from the cruising gear 27. The travel is stopped when the friction brake 137 on the casing I engages the sliding gear. With the sliding gear 22 stationary, the rotation of the cylinder 8 also ceases.' The rotation speed of the secondary input shaft 3 is now faster than the rotation speed of the cylinder 8 so the synchromesh slide 11 rotates along the helical splines 34 taking the gear teeth 13 out of engagement with the internal gear teeth 10 on the cylinder 8. The input shaft 3 and the output shaft 6 are now connected in line by the collar 15 with the synchromesh slide disengaged and the cylinder 8 and sliding gear 22 stationary.

With reference now to Fig.5, there is shown a section through a gearbox which is substantially the same as the gearbox shown in Figs 2-4, excepting that the gear box is NOT intended for use as a supplementary gearbox and may be used in conjunction with marine engines. In this case the cruising gear 27 does not mesh directly with the output gear 7. The gear box is provided with a transfer gear 155 which meshes with both the cruising gear 127 and the output gear 7 so as to reverse the direction of rotation of the output shaft 6 when the actuator 125 is operated, as an alternative to overdrive.

Claims

Claims 1. A gearbox having a main power input shaft and an output shaft aligned with the input shaft, connection means for directly interconnecting adjacent end portions of the two shafts, a plurality of gears arranged in a gear train and also capable of interconnecting the input and output shafts, and synchromesh self shifting clutch operable between the input shaft and one of said plurality of gears to connect the input shaft to said one gear, another of said gears being connectable to the output shaft through a synchroniser hub, and control means for selectively connecting the input shaft to the output shaft either directly through the * connection means or. indirectly through the gear train.
2 A gearbox as claimed in Claim I wherein the synchroniser hub is rotationally fast with the output shaft but axially slidable thereon to engage a synchroniser device mounted on the * output gear.
3. A gear box as claimed in Claim 2, wherein the said gears include a sliding gear being axially slideable on a third shaft parallel to the input and output shafts and being the second gear in said gear train, a cruising gear is rotatably mounted on the parallel shaft and which meshes with an output gear which is rotatably mounted on the output shaft, the output gear being connectable to the output shaft through the synchroniser hub which is fast to the output shaft.
4. A gearbox as claimed in any one of Claims I to 3 wherein said one gear is in the form of a hollow cyUnder having gear teeth on its outer surface and which is coaxial with the input and output shafts and free to rotate relative to said shafts,, said cylinder housing the SSS clutch mechanisms and the connection means and the gear teeth on the outer surface of said hub mesh with the second gear, the cylinder also having internal gear teeth at its input shaft end and accommodating a coaxial piston slidable on the output shaft to move the synchroniser hub axially into engagement with the output gear.
5. A gear box as claimed in Claim 4, wherein a thrust bearing is provided between the synchroniser hub and the piston.
6. A gearbox as claimed in Claim 4 or Claim 5 wherein the synchroniser hub is attached to the piston.7. A gear box as claimed in claim 5 or Claim 6 wherein the connection means is an axially slideable collar which is coaxial to said shafts and is connected to the piston, the piston also being connected to the sliding gear meshed with the cylinder, so that movement of the sliding gear is linked to the movement of the synchroniser hub.
7. A gearbox as claimed in Claim 6 wherein the piston is moved axially by an actuator, preferably an electrical actuator.
8. A gearbox as claimed in any one of Claims I to 6 wherein the main input shaft is.connected to a supplementary input shaft to which it is connected and disconnected by means of an integral clutch.