GB2304659A

GB2304659A - A power train for a four-wheel drive motor vehicle

Info

Publication number: GB2304659A
Application number: GB9618590A
Authority: GB
Inventors: David Charles Nesbitt; David John Tickle; Clive David Woolmer
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1995-09-05
Filing date: 1996-09-04
Publication date: 1997-03-26
Anticipated expiration: 2016-09-04
Also published as: GB2304659B; GB9518056D0; GB9618590D0; GB2304659A8

Abstract

In a motor vehicle having a pair of front wheels 12, 13 and a pair of rear wheels 14, 15, a power train includes a longitudinally mounted engine 26 adjacent one end of the vehicle, a longitudinally mounted change speed transmission 28 spaced from and drivingly connected to the engine through an input propshaft 31, front and rear differentials 17 and 19 and a transfer transmission 29 mounted with the change speed transmission and drivingly connected to the differentials through front and rear propshafts 34, 35. The change speed transmission 28 has its output shaft parallel to its input shaft and may be substantially identical to the type of gearbox used in transverse-engine front-wheel drive vehicles.

Description

A Power Train For A Motor Vehicle The invention relates to power trains for motor vehicles, particularly for four wheel drive vehicles having longitudinally mounted engines.

Known power trains of this type typically comprise a change speed transmission mounted axially in line with the engine and a transfer transmission which is either mounted directly to the change speed transmission to drive front and rear differentials through propshafts axially offset from the engine and the change speed transmission or a separate unit which is spaced from the change speed transmission and connected to it through a short universally jointed propshaft.

Front wheel drive cars with transverse engine and transmissions have been increasingly popular since 1960.

Since then most drive lines have comprised a change speed transmission mounted in line with the engine, an input shaft of the transmission being axially aligned with the engine and an output shaft being parallel to and spaced from the input shaft with the input shaft and the output shaft both extending from the change speed transmission at the same end. The output shaft has a gear which directly drives a gear mounted on a differential cage of a differential mounted to the rear of the change speed transmission, this having drive shafts directly connected to the front wheels.The change speed unit used in the conventional type of four wheel drive power train described above was usually able to use a casing, rotary drive components and selector components substantially identical to those produced for the change speed transmission used for the conventional front engine rear wheel drive motor vehicle where the change speed transmission was directly connected to a rear axle through a longitudinal propshaft.

The production of new designs of change speed transmission for such conventional drive arrangements is becoming increasingly rare as change speed transmissions are designed and developed for the large numbers of vehicles now produced with transverse engines.

One attempt to use a change speed transmission of the type common to front wheel drive vehicles in a four wheel drive longitudinal engine layout is shown in GB-A-2035930.

However with this arrangement the engine is set too far back in the vehicle and the front propshaft is too short to allow for appropriate vehicle refinement and adequate service life of the propshaft universal joints.

According to the present invention there is provided a power train for a motor vehicle having a pair of front wheels and a pair of rear wheels and comprising an engine which in use is mounted longitudinally in the vehicle adjacent one end thereof, a change speed transmission spaced from and drivingly connected to the engine through an input propshaft which in use is mounted longitudinally in the vehicle between the axis of the front wheels and the axis of the rear wheels, a main drive clutch or coupling device mounted on the engine and coupled to the input propshaft to drive the input propshaft at or substantially at engine speed, a front differential disposed in use between the front wheels and drivingly connected thereto and a rear differential disposed in use between the rear wheels and drivingly connected thereto and a transfer transmission mounted in unit with the change speed transmission and drivingly connecting to the front differential through a front propshaft and to the rear differential through a rear propshaft.

Typically, the main drive clutch or coupling comprises a friction clutch or torque converter mounted on or used in place of the engine flywheel. By using a flywheel and clutch or a torque converter mounted directly on the engine, the unit comprising the change speed transmission and the transfer transmission can have a smaller profile which allows underfloor installation, even in a relatively small sports/utility type vehicle.

Preferably the change speed transmission comprises an input shaft connected to the input propshaft and an output shaft parallel to and spaced from the input shaft, the input shaft and the output shaft both extending from the change speed transmission at the same end thereof. This allows the change speed transmission to include a casing, rotary drive components and selector components substantially identical to those produced for a change speed transmission used in a front wheel drive motor vehicle having an engine mounted transversely in the vehicle.

The change speed transmission may include pairs of gears on the input and output shafts which are selectively connected by dog clutches, syncromesh clutches or by friction clutches. Control may be manual, semi-automatic or automatic. Alternatively the change speed transmission may be an automatic transmission employing epicyclic gear trains whose ratios are controlled by friction brakes and/or clutches or may be any kind of continuously variable transmission (CVT) unit. Transmissions of all of the above types have been developed for use in front wheel drive vehicles with transverse engines and are all appropriate for use in the present invention.

Other aspects of the invention will be apparent from the appended claims and from the examples contained in the following description which is with reference to the accompanying drawings in which: Fig.1 is a diagrammatic side elevation of a motor vehicle incorporating a power train according to the invention; Fig.2 is a plan view based on Fig.l showing the power train and wheels; Fig.3 is a longitudinal cross-section of a change speed transmission and a transfer transmission shown in Figs.l and 2; Fig.4 is a view similar to Fig.3 showing a first modified transfer transmission; Fig.5 is a view similar to Fig.3 showing a second modified transfer transmission; Fig.6 is a view similar to Fig.3 showing a third modified transfer transmission; Fig.7 is a view similar to Fig.3 showing a fourth modified transfer transmission;; Fig.8 is a cross-section of a known type of automatic transmission for a front engine, front wheel drive vehicle; Fig.9 is a view similar to Fig.3 showing an automatic type change speed transmission of the kind shown in Fig.8; and Fig.10 is a cross section of a known type of dual-mass flywheel of suitable for use with the invention.

In Figs.l and 2 a motor vehicle 11 includes a pair of front wheels 12, 13 and a pair of rear wheels 14, 15. The front wheels 12, 13 are carried by a front axle 16 having a differential 17. Similarly rear wheels 14, 15 are carried by a rear axle 18 having a differential 19. The front axle 17 is suspended from a vehicle chassis 21 by means of leading links 22 and coil springs 23. The rear axle 18 is suspended from the chassis by means of trailing links 24 and air springs 25.

The front and rear axles 16, 18 form part of a power train which also includes an engine 26, a flywheel and a main drive friction clutch mounted on the engine crankshaft and covered by a bell housing 27. Also included in the power train are a change speed transmission 28 and a transfer transmission 29 mounted in unit with the change speed transmission. The change speed transmission 28 and the transfer transmission 29 are mounted spaced from and independently of the engine 26, the change speed transmission being drivingly connected to the engine by an input propshaft 31 having universal joints 32 and 33 at each end. The transfer transmission 29 is drivingly connected to the front differential 17 through a front propshaft 34 and to the rear differential 19 through a rear propshaft 35.

Fig.3 shows the change speed transmission 28 and the transfer transmission 29 in more detail. The change speed transmission 28 has a housing which comprises a main casing 36 and an end plate 37. Similarly the transfer transmission 29 includes a housing comprising a main casing 38 and the end plate 37 which it shares with the change speed transmission 28. The rotating components of the change speed transmission 28 include an input shaft 39 and an output shaft 41 parallel to and spaced from the input shaft. The input shaft 39 and the output shaft 41 both extend from the change speed transmission at the same end thereof, i.e. through the end plate 37, in the direction of the engine 26.

The change speed transmission 28 comprises first, second, third, fourth and fifth forward ratio constant mesh gear trains, 42, 43, 44, 45 and 46 respectively, and a reverse gear train 47 which is engaged by moving a reverse idler gear 48 into mesh. In a manner conventional in general arrangement drawings of transmissions, the reverse idler gear 48 is shown with its axis displaced from the plane of its true axis.

The forward gears are selected by operating syncromesh clutches by means of a conventional selector mechanism (not shown) . The input shaft 39 is journalled in the main casing 36 of the change speed transmission 28 and in the end plate 37 and has splines 49 drivingly connecting it to an input adapter shaft 51 which is journalled in the main casing 38 of the transfer transmission 29 and has a flange 52 to connect it to the rear universal joint 33 of the input propshaft 31.

The output shaft 41 of the change speed transmission 28 is journalled in the main casing 36 of the change speed transmission, in the end plate 37 and in the main casing 38 of the transfer transmission 29 and drives a lubricating oil pump 50. This output shaft 41 also acts as the input shaft for the transfer transmission 29, the driving gears of two pairs of output gear trains 53 and 54 being mounted on the output shaft 41 and selectable by a syncromesh mechanism 55 to give a high range output (gear train 53) or a low range output (gear train 54). The driven gears of the gear trains 53 and 54 form part of the input member of an intermediate differential 56, which as shown in Fig.3 is of the Torsen (Trade Mark) limited slip type.

The outputs of the intermediate differential 56 are connected to flanged stub shafts 57 and 58 which are connected to the front propshaft 34 and the rear propshaft 35 respectively.

In the first modification shown in Fig. 4 the high and low range output gear trains 53 and 53 are replaced by toothed belt drives 53A and 54A.

In the second modification shown in Fig.5 the high range and low range output gear trains 53 and 54 are replaced by a single driving output gear 59 which meshes with an output driven gear 61 which is the annulus of an epicyclic gear train 62 providing two ratios for High range and Low range operation.

In a third modification shown in Fig.6 an epicyclic gear train 62B similar to gear train 62 shown in Fig.5 is used with a toothed belt drive 63.

In the fourth modification shown in Fig.7 the intermediate differential 56D is a spur gear type with slip controlled by a hydraulically actuated multiplate clutch 72. The input shaft is modified to extend through the casing 38D of the transfer transmission and through an end cover plate 68 and has splines 51D for connection to the input propshaft 31. The stub shafts 57D and 58D also have splines for connection to the front and rear propshafts 35 and 35.

It will be appreciated that other types of differential may be used, preferably a limited slip type or a locking type which may be controlled internally, externally under the control of the driver or by other means.

The change speed transmission 28 may be controlled by a conventional gear shift lever and appropriate linkage or may be controlled by actuators under automatic or semiautomatic control.

In place of the five speed syncromesh type of transmission shown there may be substituted other types of transmission packaged for an input shaft and an output shaft parallel and spaced from each other and projecting from the same side of the transmission. Such alternatives include known types of continuously variable transmissions (CVTs), e.g. belt and expanding pulley types or toroidal types such as Torotrak (Trade Mark), and automatic transmissions employing friction clutches or brakes.

Fig.8 shows a conventional automatic transmission 65 for a front engine front wheel drive vehicle and which employs friction clutches and brakes and a torque converter 66 mounted on the engine crankshaft. The output of the automatic transmission 65 is by a gear train 67, an output jackshaft 68 and a differential 69.

Fig.9 shows how the conventional automatic transmission 65 can be used in the present invention. The torque converter 66A is mounted within the bell housing 27B and pipes 69 connect the torque converter with the automatic transmission 65B which replaces the syncromesh type change speed transmission 28 shown in Figs.3 to 6. A muff coupling 71 to connect the pipes 69 to the rotating components of the torque converter 66C is incorporated in the bell housing 27C. The transfer transmission 29C is similar to the transfer transmission 29 shown in Fig.3, the output jackshaft 68C incorporating the driving gears for the output gear trains 53C and 54C.

As described above, the change speed transmission and the transfer transmission are integrated to a large extent and, in the syncromesh transmissions shown in Figs.3 to 7, use a common lubricating oil system. The main casing 36, the input shaft 39 and all the gear wheels and parts of the syncromesh mechanism associated with the gear trains 42, 43, 44, 45, 46 and 47 are all common to or substantially identical to a "parent" transmission produced for a front wheel drive motor vehicle having an engine mounted transversely in the vehicle, the output shaft in the parent transmission normally driving a differential connected to output shafts which drive the front wheels.This greatly reduces the number of components which are specific to the change speed transmission 28 and allows for a considerable cost reduction since transverse engine front wheel drive cars are produced in very large numbers whereas four wheel drive vehicles have a relatively low production volume.

Similarly, the main casing and all the gear wheels and brakes and clutches and control mechanism of the automatic transmission 65c are all common to or substantially identical to those produced for the parent automatic transmission 65 shown in Fig.8.

The extent to which the change speed transmission can retain commonality with its parent transmission for the transverse engine front wheel drive vehicle will depend on the detailed construction of the parent transmission and the requirements of convenience and manufacturing capacity.

However, it is envisaged that for most known constructions it will be possible to retain the same degree of commonality as outlined above and in some cases even more.

For example, the whole of the casing of the change speed transmission may be suitable for retention and the transfer transmission be adapted to fit or the output shaft of the parent change speed transmission may be adapted by forming a splined end in place of the usual output gear. In this case the transfer transmission can use a separate input shaft which couples to the change speed transmission output shaft in a similar manner to the input adapter shaft 51.

As shown in Figs.l and 2 the front and rear propshafts 34 and 35 are of substantially equal length which helps to reduce any vibration and harshness caused or exacerbated by the use of excessively short propshafts and increases the service life of the universal joints. By positioning the change speed transmission 28 substantially mid-way between the axles 16 and 18 the polar moment of inertia of the vehicle is reduced and the various components of the drive train can be packaged to provide good ground clearance without undue difficulty By spacing the change speed transmission and the transfer transmission 28 and 29 from the engine 26 and bell housing 27 there is greater space available for the packaging of engine auxiliaries, particularly exhaust components.In particular, a catalytic converter can be positioned close to the engine, i.e. with only a short intermediate length of pipe, so that it can reach its operational temperature much sooner than if it is positioned further from the engine. A further advantage is that the mountings for the engine are required to absorb engine torque only. However, in a modification (not shown), the bell housing and the casing of the transfer transmission are connected by a tubular housing which surrounds the input propshaft and which eliminates the need for universal joints.

The spacing of the change speed transmission from the clutch is contrary to conventional teaching which requires that the inertias of the rotating components from the syncromesh back to the clutch driven plate should be as low as possible, these components having to rapidly increase or decrease their rotational speed during a gear change under the action of the syncromesh clutches. However, by careful selection of advanced materials and design, these inertias can be kept to an acceptable level. For example by using a twin-mass flywheel as exemplified by Fig.10 the clutch driven plate does not require torsional damping springs.

The input propshaft 31 can be of low mass composite material and at least one of the universal joints 32 or 33 can be a lightweight flexible disc-type coupling. Since the universal joints 32 or 33 do not have to accommodate large angular misalignments, other simple types of universal joint may be used, e.g. a shaft with a barrelled spline formation engaging straight internal splines. such a joint has the advantage of accommodating longitudinal movements between the engine and the change speed transmission.

Although conventional beam axles are shown, the invention is equally applicable to vehicles with independent suspensions or other suspensions of the kind in which the axle differential is not wholly part of the unsprung mass. Whilst the transfer transmissions shown are all of the two speed ratio High/Low range-change type, the invention may be used with a single speed ratio transfer transmission.

Claims

1. A power train for a motor vehicle having a pair of front wheels and a pair of rear wheels and comprising an engine which in use is mounted longitudinally in the vehicle adjacent one end thereof, a change speed transmission spaced from and drivingly connected to the engine through an input propshaft which in use is mounted longitudinally in the vehicle between the axis of the front wheels and the axis of the rear wheels, a main drive clutch or coupling device mounted on the engine and coupled to the input propshaft to drive the input propshaft at or substantially at engine speed, a front differential disposed in use between the front wheels and drivingly connected thereto and a rear differential disposed in use between the rear wheels and drivingly connected thereto and a transfer transmission mounted in unit with the change speed transmission and drivingly connecting to the front differential through a front propshaft and to the rear differential through a rear propshaft.

2. A power train according to Claim 1 wherein the change speed transmission comprises an input shaft connected to the input propshaft and an output shaft parallel to and spaced from the input shaft, the input shaft and the output shaft both extending from the change speed transmission at the same end thereof.

3. A power train according to Claim 2 wherein the change speed transmission includes a casing, rotary drive components and selector components substantially identical to those produced for a change speed transmission used in a front wheel drive motor vehicle having an engine mounted transversely in the vehicle.

4. A power train according to any preceding claim wherein the change speed transmission and the transfer transmission are integrated and share common components.

5. A power train according to any preceding claim wherein the change speed transmission and the transfer transmission are mounted independently of the engine.

6. A power train according to any of Claims 1 to 4 wherein the bell housing and the casing of the transfer transmission are connected by a tubular housing which surrounds the input propshaft.

7. A power train according to any preceding claim wherein the input propshaft has a universal joint at each end.

8. A power train according to any preceding claim wherein the change speed transmission is in use mounted substantially midway between the front and rear differentials.

9. A power train according to any preceding claim wherein the front and rear propshafts are of substantially equal length.

10. A motor vehicle incorporating a power train as claimed in any preceding claim.

11. A motor vehicle incorporating a power train substantially as described herein with reference to Figs.l to 3 or modified as described with reference to Figs.4 to 7 or Fig.9 of the accompanying drawings.

12. A power train for a motor vehicle having a pair of front wheels and a pair of rear wheels and substantially as described herein with reference to Figs.1 to 3 or modified as described with reference to Figs.4 to 7 or Fig.9 of the accompanying drawings.