EP1725791A1

EP1725791A1 - Gear selector and transmission

Info

Publication number: EP1725791A1
Application number: EP05717905A
Authority: EP
Inventors: John Pius Burke
Original assignee: Ricardo UK Ltd
Current assignee: Ricardo UK Ltd
Priority date: 2004-03-05
Filing date: 2005-03-04
Publication date: 2006-11-29
Also published as: WO2005085683A1; GB0405094D0

Abstract

Ar gear selector includes hollow telescopic shafts (31, 32), the respective ends of which are adapted for connection to selector hubs of a gear transmission. The shafts (31, 32) may be hollow, and have apertures (39) which align to allow lubricant to spray from the interior onto a selected pair of gears. Novel transmission layouts are also described.

Description

Gear Selector and Transmission

This invention relates to improvements in gear selectors for gear transmissions, especially twin clutch transmissions.

A twin clutch transmission generally comprises a manual multi-speed gear set in which the drive to individual gear pairs is alternately through one of two clutches. The 'odd' ratios (e.g. first and third) are driven through one clutch, whilst the even ratios (e.g. second and fourth) are driven through another clutch. Additional ratios can be added if necessary.

This arrangement permits pre-selection of one adjacent ratio so that a 'hot' gear shift is obtained by disengaging one clutch as the other is engaged.

Provided that engagement and disengagement of the clutches is carefully controlled it is possible to achieve a very rapid ratio change whilst applying a continuing drive force to the transmission output shaft.

This kind of transmission is conceptually relatively simple, and permits the use of conventional gears and other components of a manual transmission to produce a semi or fully automatic transmission.

A known six speed twin clutch transmission has co-axial input shafts driving 'odd' and 'even' input gear clusters. Twin layshafts carry constant mesh output gears, and conventional synchromesh hubs for engaging the required output gears to the respective layshaft. Such an arrangement provides a short but relatively wide transmission, well suited to front wheel drive vehicles in which space between the driving wheels is restricted by steering and suspension arrangements.

According to a first aspect of the invention there is provided a shift actuator for a gear transmission, the actuator having an actuating axis and comprising a housing defining a plurality of adjacent fluid chambers about said axis and a plurality of fluid members one in each fluid chamber and reciprocally movable longitudinally of said axis from a respective mid position to two respective end positions, the actuator further comprising a plurality of telescopic shafts reciprocal along said axis, one each connected to a respective fluid member, and the distal end of each shaft being adapted for connection to a gear selector.

In a preferred embodiment two shafts are provided, the inner shaft protruding from the outer shaft, and each shaft having a selector fork protruding at one side for engagement with the ring of a synchromesh coupling. By this means two concentric shafts can engage four loose gear with the shaft on which the gears rotate. By placing the fluid chambers together and preferably at one end, the hydraulic connections are simplified.

Preferably the fluid chambers are adapted to hydraulic fluid under pressure, and the fluid members are pistons reciprocal in respective bores of the chambers. Alternatively the fluid members may comprise diaphragms.

The fluid members may be returned to the centre position by resilient means, but in the preferred embodiment incorporate hydraulic centring whereby the centre position is assured by application of pressure to both sides.

In the preferred embodiment the inner telescopic member defines a fluid pathway, the outer telescopic member having apertures in the wall thereof, one said apertures being aligned with said pathway in the end position of one respective actuator and the centre position of the other respective actuator. Such an arrangement may be used to direct a jet of fluid under pressure from within the telescopic members to the exterior thereof.

The telescopic members may further include anti-rotation means to prevent relative rotation with respect to each other, and relative rotation with respect to said housing.

In the preferred embodiment the actuator further includes a tubular member fixed relative to said housing and engaging the distal end of the innermost shaft. Preferably the tubular member engages the innermost shaft internally. Such an arrangement both provides a distal end support for the actuator, and permits respective apertures to be aligned for providing a jet of fluid in the end positions of the inner telescopic member.

In a transmission assembly the housing may be mounted at one end, and the tubular member at the other end, so that the actuator extends along the full length of the layshaft.

In a preferred embodiment, the inner ram is tubular; this arrangement reduces inertia and manufacturing cost, and provides the fluid pathway via apertures in the wall thereof. However the inner ram could be solid, and define passageways for providing fluid to apertures of a tubular outer ram.

The apertures permit fluid to be sprayed on gear pairs which are driving, and allows both lubrications and cooling.

In a second aspect, the invention comprises a twin clutch gear transmission having a shift actuator according to the first aspect, the distal end of each ram being connected to a double acting gear selector hub of the transmission.

Preferably the transmission has twin layshafts, and two of said actuators are provided, one each in association with each layshaft.

In a preferred embodiment the transmission has an input shaft axis and two parallel layshaft axes, the actuators being located within a boundary defined by radii of the input shaft axis and passing through each layshaft axis. Preferably the actuators are provided side by side about a radius substantially bisecting said radii.

The transmission may further include one or more fluid passageways aligned with one or more external apertures of the outer telescopic ram and adapted to direct fluid to gears of the transmission. Such passageways may comprise pipes mounted in the transmission casing and directed to spray fluid at the leading edge of a gear pair, so as to cool and lubricate the gear teeth immediately prior engagement thereof. Said pipes may be grouped as a spray bar assembly in any suitable and convenient manner.

In a third aspect, the invention comprises a fluid component assembly for a twin clutch gear transmission, the assembly comprising a substantially tubular housing having one end adapted for attachment to an engine and the other end adapted for attachment to a gear set, and the tubular housing having a wall transverse to the axis thereof, the wall being adapted on one side to support a twin clutch pack for rotation, and on the other side to support a fluid valve block, whereby in use the valve block lies between the clutch pack and gear set.

Such an arrangement is compact, and provides for a fluid component sub-assembly for connection to a gear set sub-assembly, to the intent that each sub-assembly may be manufactured and/or tested in a separate facility.

Preferably the transverse wall is a partition wall, and is substantially to the centre of said tubular housing. In a preferred embodiment said wall defines with said valve block a plurality of fluid passageways for directing fluid under pressure within said transmission. The transverse wall includes necessary aperture for output shafts of the clutch pack.

In a preferred embodiment said transverse wall has on the engine side a collar projecting from said aperture and co-axial therewith, the collar being adapted to support the clutch pack casing for rotation, and including fluid passageways therein for supplying fluid under pressure to said clutch pack.

Preferably said transverse wall is further adapted for mounting of an oil pump thereon on the gear set side. Said wall may further be adapted for mounting of one or more actuators thereon. In this arrangement the transverse wall provides fluid connection between the valve block, pump, actuator(s) and clutch pack in use. In a fourth aspect the fluid component casing includes a pump assembled thereto, and further includes an aperture for a pump drive shaft whereby the pump is on one side of the wall, and the drive is provided on the other side. Such an arrangement ensures a well supported pump drive bearing and convenient gear drive connection to the clutch pack or outer input shaft.

The casing may further include the valve block, clutch pack and or shift actuator(s) as a sub-assembly.

Such a sub-assembly can be conveniently tested as a unit for fluid integrity and performance before connection to the gear set.

According to a fifth aspect, the invention comprises a m dular twin clutch transmission comprising a gear module having a housing and including gears, input shafts and layshaft assembled thereto, and a hydraulic module comprising a housing and having twin clutch pack, pump and valve block assembled thereto whereby the modules are adapted for assembly and testing at locations remote from each other.

The modular transmission may further include a final drive module comprising a housing having final drive gears assembled thereto.

In a sixth aspect, the invention comprises a transmission assembly having a transmission axis, and sequentially along said axis a clutch and a gear transmission, wherein said assembly has a final drive including opposite co-axial output shafts extending transversely of said axis, the final drive including on one side of said axis a crown wheel and pinion, and on the other side of said axis a differential gear.

Preferably the transmission assembly is a twin clutch, twin layshaft transmission, and in the preferred embodiment the axis of said output shafts is between said clutch and gear transmission. Other aspects of the invention will be apparent from the following description of preferred embodiments shown by way of example in the accompanying drawings in which :- Fig. 1 is a developed plan view of a schematic twin clutch transmission according to one aspect of the invention;

Fig. 2 is a schematic end view of the transmission of Fig. 1 showing the true relationship of input shafts and layshafts;

Fig. 3 is a schematic longitudinal section through an actuator according to the invention;

Fig. 4 is a schematic axial section through a hydraulic module of the invention;

Figs. 5-8 show several similar transmission having a common gear module.

With reference to the drawings, Fig. 1 illustrates schematically a seven speed twin clutch transmission according to the invention.

An input shaft 11 drives the casing of a conventional twin multi plate wet clutch 12 from which extends concentric output shafts 13,14. The centre shaft 13 is fast with input gears of the Odd' ratios 1,3,5,7, whilst the hollow shaft 14 is fast with the 'even' ratios 2,4,6, and a reverse ratio comprising idler 15 and output gear 16. Reverse ratio will not be further described, but is conventional.

Twin layshafts 17,18 receive the loose output gears of the individual ratios as illustrated, which are grouped in pairs so that four synchromesh dog clutches 19 are shiftable to the left and to the right to engage each of the seven forward and one reverse ratio, as required. Each layshaft drives an output shaft 20 via gear train 21. Partition walls 22-25 of the transmission support the various shafts and act as a casing for the transmission.

The valve block 26 and oil pump 27 are provided between the twin clutch 12 and the gears, as illustrated, and will be further described below.

Fig. 1 illustrates the transmission as a developed plan. Fig. 2 is a schematic cross-section showing the approximate location of respective shafts of a typical transmission, and some representative gears.

The input shafts 13,14 and layshafts 17,18 are arranged at the apices of triangle. Conventionally the input shafts are at the top. Reverse gear idler 15 and output gear are shown by a solid line, whereas second ratio gears '2' and the first ratio layshaft gear T are shown in dotted outline. It will be readily appreciated that a mechanism for shifting the synchromesh hubs 19 can be mounted in the space around the layshaft, but for packaging purposes the region on either side of the second rather input gear (represented by actuator 30A) , or between and below the layshafts (represented by actuator 30B) is advantageous.

A shift actuator 30 according to the invention is illustrated in Fig. 3, and comprises concentric shafts 31,32 as illustrated, each being reciprocated in use by a respective double acting piston 33,34 at one end. The inner shaft 31 is hollow, and supported at the end remote from the pistons by a stub shaft 35 projecting from a wall 36 of the gearbox casing.

Attached to each of the shafts 31,32 is a respective shift fork 37,38 which couples conventionally with a respective synchromesh hub on one of the transmission layshafts 17,18.

In use the forks 37,38 may be shifted to the left and to the right by introducing hydraulic fluid under pressure to the appropriate side of the respective piston 33,34, and shifted back to the centre position by, for example releasing fluid on the pressurized side and allowing the fork to return under a resilient load. Alternatively, as illustrated, the piston may centralize under hydraulic pressure applied to both sides.

Typical locations for a shift actuator are illustrated in Fig. 2 and marked by reference numerals 30A and 3 OB. It will be appreciated that one such actuator is required for each layshaft 17,18, and that both actuators could be housed in the transmission adjacently between and below the layshafts.

As mentioned above, the inner shaft 31 is hollow and slides within and relative to the outer shaft 32. The stub shaft 35 slides within the inner shaft 31. Apertures 39 are provided in the respective shafts, and are aligned in pairs when a fork is shifted to the left or to the right. Thus when both forks 37,38 are in the neutral condition, as illustrated, no layshaft gears are engaged with a layshaft, and no apertures are aligned.

When however one of the forks is shifted, a pair of aperture become aligned as illustrated by arrows 40, and permit hydraulic fluid under pressure within the inner shaft

31 to spray out. In this way the apertures may be aligned to spray lubricant on the gear ratio which is engaged and is transmitting drive through the transmission. This spray can both cool the gears and reduce friction, so providing transmission efficiency. It will be appreciated that the arrangement is particularly effective since fluid is sprayed only on the gears of the ratio(s) which are engaged at any time.

Fluid under pressure can be introduced into the inner shaft 31 in any suitable manner, but is typically via the ends.

The preferred embodiment arranges the dual pistons immediately adjacent the input end of the transmission, and thus next to the valve block 26 and pump 27. This arrangement minimizes hydraulic path length, and avoids long passages by which fluid under pressure is supplied to the piston chambers, and to the inner shaft 31 for lubrication.

For maximum effect, lubrication oil should be sprayed on the gears from the leading side so as to the immediately drawn into the tooth contact region. For packaging purposes the shift actuator may however be located on the trailing side of the gears. In that case a suitable static duct or multiple duct spray bar can be provided, and mounted on an internal wall of the transmission, to take fluid from the outlet aperture of the actuator 30 to the required location. In use such a duct comprises a simple pipe 41 having an inlet end 42 in sliding contact with the outer surface of the respective shaft 31,32, and the outlet end 43 pointing at the leading side of the respective gear set. Such a pipe is illustrated by way of example in Fig. 2 showing a path from actuator 30B. Plainly actuator 30A could for example spray oil directly into the leading side of second speed gears '2'.

Fig. 4 illustrates modularity of one aspect of the invention. A front housing 50 connects on engine 51 to that part 52 of a twin clutch transmission which houses the gears. Within the housing is a partition wall 22, on the engine side of which is located the twin clutch assembly, and on the gearbox side of which is located the valve block and oil pump. On the engine side of the partition wall is mounted a collar 53 which surrounds the input shafts of the gearbox (not illustrated).

This engagement has a number of advantages. Firstly the gear set and gear casing can be manufactured separately from the remainder of the transmission. This means that a production facility for manual transmissions can without difficulty produce the gear set assembly and ship it to an assembly location. No change to this facility needs to be made in order to accommodate production and assembly of hydraulic components.

The associated advantage is that the hydraulic components, particularly the valve block can be produced and tested and assembled in a conventional facility adapted to the appropriate standards.

Furthermore the partition wall 22 not only provides a convenient mounting surface for the valve block and pump, but can also provide the necessary fluid pathways to the wet clutch pack, and to the piston end of the shift actuators 30. It will be understood that the shift actuators can, if required form part of this 'hydraulic' sub-assembly and be mounted directly with respect to the partition wall. On the engine side the collar 53 both supports the clutch housing for rotation thereon, and provides internal fluid pathways for clutch actuation and lubrication.

The valve block 26 typically comprises an electro-hydraulic unit having a plurality of hydraulic passageways and valves, and an electronic control module thereon. The control module is mounted to the exterior of the valve block, on the gear transmission side, and communicates with the vehicle electrical system via a multi-terminal connector on the top surface of the front housing 50. This arrangement ensures that hydraulic and electrical testing of the sub-assembly can be completed prior to shipping to a final assembly facility.

Thus all of the hydraulic components can be contained together, fluid pathways are short and speed and efficiency of transmission operation is improved. By grouping components in this manner, the number of hydraulic connections is also reduced, thus mitigating the problem of obtaining leak tight connections.

Figs. 5-8 illustrate modularity of a transmission according to the invention.

In Fig. 5 a conventional rear drive transmission is illustrated (as shown in Fig. 1) in which a gear set 60 has on the front side a hydraulic assembly 61 comprising clutch pack 62, valve block 63, pump 64 and other hydraulic components. On the rear side is a transfer gear set 65 and a single propeller shaft 66 as output. A partition wall 67 is provided in the hydraulic assembly on which the major hydraulic components are mounted.

In Fig. 6 a front drive assembly has opposite drive shafts 71, a gear set 60 as in Fig. 5, and an end plate 72. Two partition walls 73,74 respectively mount the clutch pack and valve block/pump. A crown wheel 75 is provided at one side, and a differential gear 76 at the other side. In this arrangement the layshafts are coupled at the clutch end to a pinion for driving connection to the crown wheel. Drive is transmitted to the differential carrier across the transmission, and above or below the input shafts. Output from the differential gear is conventional. This arrangement is particularly space-efficient since the crown wheel and differential gear are provided on either side of the input shafts rather than comprising a combined assembly on one side. Thus the transmission protrudes minimally on both sides, and is substantially symmetrical.

Fig. 7 is similar to Fig. 5 but has an integrated rear axle 77 with opposite drive shafts 78.

Fig. 8 is similar to Fig. 7 but has a bolt-on transaxle 79, also with opposite drive shafts 78.

The inventions are not limited to the examples illustrated and described herein, but extend to all variants encompassed by the claims appended hereto.

Claims

Claims 1. A shift actuator (30) for a gear transmission, the actuator (30) having an actuating axis and comprising a housing defining a plurality of adjacent fluid chambers about said axis and a plurality of fluid members (33,34) one in each fluid chamber and

> reciprocally movable longitudinally of said axis from a respective mid position to two respective end positions, the actuator (30) further comprising a plurality of telescopic shafts (31,32) reciprocal along said axis, one each connected to a respective fluid member (23,24), and the distal end of each shaft (31,33) being adapted for connection to a gear selector.

2. An actuator according to claim 1 wherein two shafts are provided, the inner shaft (31) protruding from the outer shaft (32) and each shaft having a selector fork (37,38) at one side for engagement with the ring of a synchromesh coupling of a manual gear transmission.

3. An actuator according to claim 1 or claim 2 wherein said fluid chambers are adjacent.

4. An actuator according to claim 3 wherein said fluid chambers are side by side on said axis.

5. An actuator according to claim 4 wherein the fluid chamber of said inner shaft (31) is axially outboard of the fluid chamber of said outer shaft (32).

6. An actuator according to any preceding claim wherein said fluid chambers are adapted to hydraulic fluid and define respective bores, and the fluid members are pistons (33,34) reciprocal in said bores.

7. An actuator according to claim 6 wherein the innermost telescopic shaft defines a hydraulic fluid pathway.

8. An actuator according to claim 7 wherein said telescopic shafts (31,32) are hollow.

9. An actuator according to claim 8 wherein inner and outer shafts (31,32) having apertures (39) in the respective walls thereof, and said apertures (39) being adapted to be in register at the end positions of one piston (34) and a mid position of the other piston (33).

10. An actuator according to any of claim 8 or claim 9 and further including a tubular member (35) in which the free end of said inner shaft (31) is relatively slidable, said tubular member (35) and inner shaft having apertures (39) in the respective walls thereof, and said apertures (39) being adapted to be in register at the end positions of the piston (34) of said inner shaft.