GB2250246A

GB2250246A - Wheeled motor vehicle with contra-rotating drive shafts, eg four-wheel-drive vehicle

Info

Publication number: GB2250246A
Application number: GB9025864A
Authority: GB
Inventors: David Bryan Marshall
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1990-11-28
Filing date: 1990-11-28
Publication date: 1992-06-03
Anticipated expiration: 2010-11-28
Also published as: GB9025864D0; GB2250246B

Abstract

A wheeled motor vehicle has a body structure (20), an engine (1), a transmission (3, 4, 5) and two or more drive shafts (5, 7), the engine and transmission forming a rigid unit (1, 2, 3, 4, 5) and being mounted to the body structure (20) and the driveshafts (6, 7) transmitting drive between the transmission (3, 4, 5) and the wheels, wherein at least two driveshafts (6, 7) have their axes of rotation approximately parallel with each other and contra rotate during transmission of drive to cancel out torque reaction between engine and body structure. <IMAGE>

Description

A WHEELED MOTOR VEHICLE This invention relates to wheeled motor vehicles.

In the study of the effects on vehicle occupants of noise, vibration and harshness ("NVH") generated in the vehicle by engine and transmission operation it has long been appreciated that transmission of NVH from an engine/transmission unit into the vehicle body structure, whence it is sensed by the occupants, is dependant upon the stiffness of flexible mounts to mount the engine/transmission unit to the body structure; the stiffer the mount the more NVH is transmitted. Four wheel drive vehicles which have very low gear ratios and with consequent high transmission of reaction torque between engine/gearbox unit and body structure need very stiff flexible mounts to react the torque without allowing excessive relative movement between engine/transmission unit and body structure.These very stiff mounts result in correspondingly high transmission of NVH from the engine/transmission unit into the body structure in such vehicles. High NVH in a vehicle is both unpleasant and fatiguing for vehicle occupants and can thus be a safety risk to the driver.

It is an object of the invention to reduce NVH transmission in four wheel drive vehicles.

According to one aspect of the invention there is provided a wheeled motor vehicle having a body structure, and engine, a transmission and a plurality of driveshafts, the engine and transmission forming a rigid unit and being mounted to the body structure and the driveshafts transmitting drive between the transmission and the wheels, wherein at least two driveshafts have their axes of rotation parallel with each other to within 200 and contra rotate during transmission of drive.

With this arrangement torque reaction between, on the one hand, the engine/transmission unit and, on the other hand the vehicle body structure, is reduced to the extent that torque reaction is cancelled through the transmission between one driveshaft and another. Lighter construction can be achieved for those parts of the body structure and engine/transmission unit to which mounts or mounting the engine/transmission to the body structure are connected.

The engine/transmission unit is preferably mounted to the body structure by flexible mounts.

Flexible mounts of reduced stiffness may therefore be used, resulting in lower transmission of NVH between engine/transmission unit and body structure.

Preferably, at least two driveshafts have their axes of rotation parallel to within 150, more preferably to within 100 and most preferably substantially parallel.

The closer the axes of rotation of the driveshafts come to parallelism the more torque reaction from the driveshafts can be cancelled out through the transmission, and any tendency of the engine/transmission unit to be rotated by torque reaction can be correspondingly reduced.

In one embodiment the motor vehicle may have two driveshafts and, during transmission of drive, the torque carried by each driveshaft may be substantially the same.

With such an arrangement the net torque reaction experienced by the engine/transmission unit will be substantially zero so long as the driveshafts remain substantially parallel. The torque reaction suffered where non parallel shafts are used will be the torque reacted from each driveshaft multiplied by the cosine of the angle between the driveshafts, and will consequently be of small magnitude.

Preferably the motor vehicle has a spaced pair of driven axles, the transmission including a differential having a drive input and a pair of driven outputs, the differential being positioned between the driven axles and each said driveshaft taking drive from a said output to an axle.

The torque carried by each driveshaft is therefore rendered substantially the same by this convenient means and the advantaye of the invention is obtained without major modification to known layouts of drive components in four wheel drive vehicles.

The engine and at least part of the transmission may extend in line longitudinally of the vehicle with at least the differential extending transversely of the vehicle from said part of the transmission, each driveshaft extending longitudinally of the vehicle and having a universal joint positioned therealong and being radially separated from the other driveshaft, said positioning and radial separation being adjusted to minimise the distance of each universal joint from a nodal line of vibration of the engine transmission unit which vibration is transverse to the longitudinal axis of the vehicle and is induced during operation of the engine/transmission unit.

Such an arrangement of engine and transmission, with part of the transmission extending transversely of the vehicle from another part of the transmission, tends to 'skew' round a nodal line of transverse vibration of the type known as 'engine beaming' from a direction transversely of the vehicle to a direction angled from the transverse direction. A closer correspondence between the nodal line and the positioning of the universal joints is therefore allowed with the arrangement described and reduced vibration is thus induced in the drive train, further reducing the incidence of NVH in the vehicle.

The two driven outputs from the differential are conventionally co-axial and one of the driveshafts may have its axis radially displaced from the output from which it takes drive, drive being transmitted by a geared connection between output and driveshaft.

This arrangement provides a simple method for achieving contra rotation of the driveshafts and at the same time a radial separation of the driveshaft axes. The distance of radial separation may be adjustable according to the size of gears used.

The invention will now be described by way of example with reference to the accompanying drawing of which: Figure 1 is a schematic three quarters rear perspective view of a vehicle according to the invention, Figure 2 is a schematic plan view of a prior art engine, gearbox, range change box and centre differential, and Figure 3 shows the unit of Figure 2 modified according to the invention in which the centre differential has drive taken from one output via a geared connection to one driveshaft.

Components having the same function in all the figures of the drawing have been given identical reference numerals for ease of understanding.

Figure 1 shows a vehicle having a body structure 20, and an engine 1 connected via a bellhousing 2 to a transmission comprising a gearbox 3 and a range change box 4, the engine, bellhousing, gearbox and range change box extending in line longitudinally of the vehicle. The engine 1 and range change box 4 are mounted to the body structure 20 by flexible mounts 21. Extending from the range change box 4, transversely of the vehicle, is a differential 5 . The differential 5 has a casing 9 which rotatably supports a forward driveshaft 6 and a rear driveshaft 7, said driveshafts having axes radially separated from one another. The forward driveshaft 6 includes a universal joint 8 positioned therealong in proximity to the casing 9. The rear driveshaft 7 similarly includes a universal joint 10.

The forward driveshaft 8 drives a front axle 11 for the vehicle via a forward axle differential 12 and the rear driveshaft 7 drives a rear axle 13 via a rear axle differential 14.

It will be seen by the arrows in Figure 1 that when the front and rear axles 11, 13 rotate in a clockwise direction that the driveshafts 6, 7 rotate in opposite directions from one another. The driveshafts 6, 7 have parallel axes and therefore driving torque which the engine/gearbox/range change box/differential unit reacts with the body structure 20 to which it is mounted is zero.

Referring to Figures 2 and 3, a unit (hereafter called an 'overall unit') comprising an engine 1, bellhousing 2, gearbox 3, range change box 4 and differential 5 is shown.

Also shown are a front nodal line A and rear nodal line B of transverse vibration of the overall unit.

Such transverse vibration is known as 'engine beaming' and occurs because the relatively large masses of the engine 1 on the one hand and the gearboxes 3, 4 and differential 5 on the other hand are separated by the relatively flexible bellhousing 2. A transverse vibration having a large amplitude in the region of the bellhousing and much reduced amplitude in the region of the engine and the gearboxes and differential therefore occurs. As the differential 5 extends transversely from the range change box 4 the rear nodal line is 'skewed' round at an angle from the transverse direction.

As the universal joints 8, 10 are on and near respectively the rear nodal line B, transference of engine beaming vibration through them into either the axles 11, 13 or the body structure 20 of the vehicle is kept to a minimum.

It will be observed that the forward universal joint 8 lies on the rear nodal line B in both figures, but that the rear universal joint 10 lies considerably closer to the rear nodal line B for the embodiment according to the invention shown in Figure 3 in which the driveshafts 6, 7 have axes radially separated from each other.

It will be appreciated that, within limits, any desired radial separation of the driveshafts may be obtained to optimise positioning of the universal joints.

It will also be appreciated that the configuration of engine, gearboxes and differential may be varied as desired and, so long as these are all in unit with one another there will be zero or little torque transfer into a body of the vehicle when a layout according to the invention is employed.

Similarly, the driveshafts may have axes radially separated from one another or may be co-axial, with no effect on the torque transfer to the body structure of the vehicle during transmission of drive.

Claims

1. A wheeled motor vehicle having a body structure, an engine, a transmission and a plurality of driveshafts, the engine and transmission forming a rigid unit and being mounted to the body structure and the driveshafts transmitting drive between the transmission and the wheels, wherein at least two driveshafts have their axes of rotation parallel with each other to within 200 and contra rotate during transmission of drive.

2. A wheeled motor vehicle as in claim 1, wherein the engine/transmission unit is mounted to the body structure by flexible mounts.

3. A wheeled motor vehicle as in claim 1 or 2, wherein said at least two driveshafts have their axes of rotation parallel to within 150.

4. A wheeled motor vehicle as in claim 1, 2 or 3, having two driveshafts wherein, during transmission of drive, the torque carried by each driveshaft is substantially the same.

5. A wheeled motor vehicle as in claim 4 having a spaced pair of driven axles, the transmission including a differential having a drive input and a pair of driven outputs, the differential being positioned between the driven axles and each said driveshaft taking drive from a said output to an axle.

6. A wheeled motor vehicle as in claim 5, wherein the engine and at least part of the transmission extend in line longitudinally of the vehicle with at least the differential extending transversely of the vehicle from said part of the transmission, each driveshaft extending longitudinally of the vehicle and having a universal joint position therealong and being radially separated from the other driveshaft, said positioning and radial separation being adjusted to minimise the distance of each universal joint from a nodal line of vibration of the engine/transmission unit which vibration is transverse to the longitudinal axis of the vehicle and is induced during operation of the engine/transmission unit.

7. A wheeled motor vehicle as in claim 6, wherein the two driven outputs from the differential are co-axial, one of the driveshafts having its axis radially displaced from the output from which it takes drive, drive being transmitted by a geared connection between output and dr iveshaft.

8. A wheeled motor vehicle substantially as described herein with reference to the accompanying drawing.