GB2159110A - Drive line for four wheel drive vehicle - Google Patents

Abstract

A driveline for a four-wheel drive vehicle, having a prime mover 2 and two propeller shafts 9 and 10 connected to drive front- and rear-wheels, comprises two identical continuously- variable-ratio transmissions of the belt and sheave type mounted in parallel with common rotating parts coaxial. Each input sheave 7 and 8 is driven by the prime mover output shaft. Each output sheave drives a respective propeller shaft; and a belt coupling the input and the output sheave. A differential gear unit 1 connects the prime mover output shaft and the input sheaves to ensure equal torque input to the sheaves from the prime mover. The two propellor shafts may be locked to avoid wheelspin using a locking clutch 11. <IMAGE>

Description

SPECIFICATION Driveline for a four-wheel-drive vehicle This invention relates to drivelines for vehicles in which all four wheels may be driven, and in particular to such drivelines in which the gear ratio is continuously variable.

Continuously variable ratio transmissions are well known, and those of the belt and sheave type have been used successfully in two wheel drive passenger cars. An example of this type of transmission is described in European Patent Application 4130, and comprises input and output sheaves or pulleys with a belt gripped so as to transmit a torque from input to output, and means to adjust the gear ratio steplessly between the two by shifting the radial position of the gripping point of the belt, usually on both sheaves. This arrangement is compact but has a limited torque- transmitting capability. It has been proposed to use two identical transmissions of this type in parallel in a rearwheel- drive car to obtain higher torques, each transmission driving a different rear wheel.In this arrangement, a differential gear shares the input torque equally between the transmissions, to avoid overloading either of the belts. However, this arrangement is not suitable for a four-wheel-drive vehicle, where the problems of high torque and providing drive to all wheels have to be met.

The invention consists in a driveline for a fourwheel-drive vehicle having a prime mover and two propeller shafts connected to drive front- and rearwheels respectively, the driveline comprising: two substantially identical continuously-variable-ratio transmissions of the belt and sheave type mounted in parallel with common rotating parts coaxial, each having an input sheave adapted to be driven by the prime mover output shaft, an output sheave adapted to drive a respective propeller shaft, and a belt coupling the two sheaves; and a differential gear unit connecting the prime mover output shaft and the input sheaves to ensure equal torque input to the sheaves from the prime mover.

Preferably, the prime mover output shaft and the propeller shafts are parallel and spaced apart, and substantially perpendicular to both of the belts. In a preferred embodiment, the differential gear unit is mounted coaxially between the input sheaves and has a cage driven by the prime mover output shaft, and two outputs connected to respective input sheaves. In one example, for permanent four wheel drive, the output sheaves are linked by a locking clutch which is selectively operable to ensure that the two propeller shafts maintain substantially equal speeds. In an alternative example, the output sheaves are connected permanently together and to one propeller shaft, and the two propeller shafts are selectively connected together by a locking clutch, thereby providing optional two- or four-wheel drive.

For high- and low-ranges of gear ratios, one or both output sheaves may be geared to the corresponding propeller shaft by way of a two-speed gear set, such as a lockable epicyclic gear.

In order that the invention may be better understood, some embodiments will now be discribed with reference to the accompanying drawings, wherein: Figure 1 is a diagram of a driveline in accordance with a first preferred embodiment of the invention, suitable for four wheel drive; Figure 2 shows a second preferred embodiment, suitable for two- or four-wheel drive; Figure 3 is a diagram of the output portion for just one axle of a driveline according to a third embodiment; and Figure 4 shows the output portion of a driveline according to a fourth embodiment.

In the arrangement shown diagrammatically in Figure 1, a differential gear 1, 5, 6, is used to ensure that each belt/sheave assembly 7, 8 carries equal torque. The differential cage 1 is driven from the prime mover, which may be a petrol engine 2, via a starting device 3 and a forward/reverse gear 4. Each output 5 (6) from the differential drives one belt/sheave unit 7 (8) and the output sheave 13 (12) of each belt/sheave unit drives a respective output shaft 9 (10) which drives the axles through propel ler shafts (not shown). At all times, therefore, equal torques are transmitted via the belt/sheave units to respective axles.

In order to effect a locking action and thereby avoid the risk of wheelspin, a locking clutch 11 is operable to connect the two output shafts 9, 10 together. The differential still ensures equal torque distribution to the belt/sheave units but the locking clutch downstream of the latter ensures that one propeller shaft cannot speed up relative to the other.

An automatic electronic control system (not shown) of conventional design responds to vehicle parameters and driver demands to control the gear ratios of each belt/sheave unit independently.

A further arrangement which gives optional twoor four-wheel drive is shown in Figure 2. Here, the output sheaves 12, 13 are permanently connected together and to one output shaft 14. The locking clutch 15 is then operated to engage the other output shaft.

A second range of gear ratios may be provided by the arrangement of Figure 3, for instance for off road use. A two-speed gear set, which in this example is a simple epicyclic unit 17, 18, 22, connects one of the output sheaves 16 to its propeller shaft 21. The output sheave 16 drives the sun gear 17 of the epicyclic gear set, whose annulus 18 is fixed to the gearbox casing. A sliding sleeve 19 carrying teeth 20 is splined to the corresponding output shaft 21 and engages either the sun gear 17, for high ratios (high regime) or the planet carrier 22, for low ratios (low regime).

This two-speed arrangement may be used on just one of the output sheaves, using the basic configuration of Figure 2. Where the Figure 1 basic configuration is used, however, two such arrangements are required, one at each output sheave 9, 10; this provides four wheel drive with torque sharing to the axles in low regime.

Where torque sharing to the axles is not required in low regime, the arrangement of Figure 4 may be used. In this embodiment, there are three dog clutches A, B and C. Clutch A is the same as the two-speed gearset of Figure 3. Clutch B has the same function as clutch 11 in Figure 1 and selectively connects the two output sheaves 24, 25 together. Clutch C connects one output shaft 26 either to its output sheave 25 or to the other output shaft 27.

For high regime operation, clutch A is moved rightwards connecting output sheave 24 to output shaft 27. Clutch B is disengaged and clutch C is moved rightwards connecting output sheave 25 to output shaft 26. To effect the differential locking action described above, clutch B may be engaged by leftwards movement to connect the two output sheaves 20, 25 together.

To engage low ratio, clutch B is engaged as above, clutch C is then moved leftwards to connect both output shafts 26, 27 together and finally clutch A is moved leftwards to connect carrier 28 to output shaft 27. The clutches must be operated in this sequence.

The result of the sequence of operation is that the two output sheaves 24, 25 locked together by Clutch B drive the sun wheel 29 of the epicyclic, the planet carrier 28 of which drives the two output shafts 26, 27 which are locked together by clutch C.

The locking clutches in all figures have been shown as dog clutches. Any suitable clutch can be used e.g. friction clutches operated by independent means.

In the event that dog clutches are used, when the shift from high to low ratio or vice versa is made, there will be a significant speed difference between the dogs unless the vehicle is moving very slowly. To avoid this, a feature can be included in the control system of the belt/sheave assemblies whereby when a shift of ratio range is initiated by the driver, the control system senses the speeds of the dogs about to be engaged and adjusts the belt/sheave units to match the dog speeds exactly.

In addition, if required, conventional baulk ring type synchromesh units can be installed between pairs of dogs to ensure that engagement cannot take place until the speeds of the dogs are matched.

Claims (13)

1. A driveline for a four-wheel drive vehicle having a prime mover and two propeller shafts connected to drive front- and rear-wheels respectively, the driveline comprising: two substantially identical continuously-variable-ratio transmissions of the belt and sheave type mounted in parallel with common rotating parts coaxial, each having an input sheave adapted to be driven by the prime mover output shaft, an output sheave adapted to drive a respective propeller shaft, and a belt coupling the two sheaves; and a differential gear unit connecting the prime mover output shaft and the input sheaves to ensure equal torque input to the sheaves from the prime mover.

2. A driveline according to Claim 1, wherein the prime mover output shaft and the propeller shafts are parallel and spaced apart, and substantially perpendicular to both of the belts.

3. A driveline according to Claim 1 or Claim 2, wherein the differential gear unit is mounted coaxially between the input sheaves and has a cage driven by the prime mover output shaft, and two outputs connected to respective input sheaves.

4. A driveline according to Claim 1, 2 or 3, wherein the output sheaves are linked by a locking clutch which is selectively operable to ensure that the two propeller shafts maintain substantially equal speeds.

5. A driveline according to Claim 1, 2 or 3, wherein the output sheaves are connected permanently together and to one propeller shaft, and the two propeller shafts are selectably connected together by a locking clutch, thereby providing optional two- or four-wheel drive.

6. A driveline according to any of Claims 1 to 4, wherein at least one output sheave is geared to its propeller shaft by way of a two-speed gearset to provide alternative ranges of gear ratios.

7. A driveline according to Claim 5, wherein only one output sheave is geared to its propeller shaft by way of a two-speed gearset to provide alternative ranges of gear ratios.

8. A driveline according to Claim 6 or 7, wherein the or each two-speed gearset comprises a simple epicyclic gear coaxial with the respective propeller shaft, the gearset being lockable for direct drive.

9. A driveline according to Claim 4, wherein one output sheave is geared to its propeller shaft by way of a two-speed gearset, and further comprising a two-position clutch for connecting the other propeller shaft selectively either to the said propeller shaft for low regime or to the other output sheave for high regime operation.

10. A driveline according to Claim 9, wherein the two-speed gearset comprises a simple epicyclic gear having a sun gear integral with the output sheave, a planet carrier connectable to the said propeller shaft and an annul us anchored to the transmission casing.

11. A four-wheel drive vehicle having a prime mover, front- and rear-wheels, and a driveline in accordance with any preceding claim.

12. A driveline for a four-wheel drive vehicle substantially as described herein with reference to the accompanying drawings.

13. A four-wheel drive vehicle having a driveline substantially as described herein with reference to the accompanying drawings.