GB2154961A

GB2154961A - Improvements in or relating to vehicle axle arrangements

Info

Publication number: GB2154961A
Application number: GB08501089A
Authority: GB
Inventors: Pier Carlo Boffelli
Original assignee: Baruffaldi Frizioni SpA
Current assignee: Baruffaldi Frizioni SpA
Priority date: 1984-01-27
Filing date: 1985-01-16
Publication date: 1985-09-18
Also published as: IT8419344A0; GB8501098D0; IT1173156B; GB8501089D0; DE3502524A1; FR2558779A1; GB2154961B

Abstract

An axle arrangement for leading wheels of a vehicle, preferably an off-road vehicle, in which a shaft (13), powered by a driving shaft (8) through a bevel gear pair (12a, 12b), can couple with axleshafts (14a, 14b) carrying the leading wheels by means of independent operable clutches (15a, 15b). Means are provided to engage and disengage one or both of the clutches automatically, depending on the conditions of the terrain and the path followed by the vehicle. <IMAGE>

Description

SPECIFICATION Improvements in or relating to vehicle axle arrangements This invention relates to an axle arrangement for a vehicle.

Vehicles used off the road, or on terrain with poor grip, especially tractors for agricultural use, require, in the-event of loss of grip by the rear driving wheels, drive to be applied also to the leading wheels, usually the front wheels, to enable the vehicle to move forward even under difficult conditions. A known construction provides a shaft connected to a gearbox by means of a clutch or the like, which operates a front steering axle, equipped with its own differential unit, which in turn must be of a lockable or self-locking type, all of which is very complicated and costly.

An object of the present invention is to provide an axle for leading wheels in which a lockable differential is not required to ensure drive on one or both of the wheels even under conditions where the terrain offers poor grip and enable bends to be turned correctly on hard terrain, allowing the wheels that follow paths with different radii to turn at different speeds.

An additional object of the present invention is to provide a-front driving axle for a vehicle which usually applies drive to both wheels, to boost the normal drive applied to the rear wheels and can be applied to just one of the front wheels during the bend, or to neither, when driving on-a road for instance.

According to the present invention, there is provided an axle arrangement for a vehicle, the axle arrangement comprising a driven shaft, two independently-operable clutches to couple said shaft with respective axle shafts intended to carry the vehicle wheels, manually-operable and automatically-operable control devices to provide engagement and disengagement of said clutches, and sensors arranged to be sensitive to the movement of the wheels and the path followed by the vehicle and capable of operating said automatic control device in relation to preestablished running requirements to engage or disengage one or both of said clutches as appropriate.

The clutches can be friction- or clawclutches, provided with remote control devices and the remote control devices can be electromagnetic, hydraulic or mechanical, depending on-the use requirements of the vehicle to which the axle is to be fitted and on the relative mechanical dimensions.

In a preferred embodiment of the invention, the clutches can be electromagnetic clutches, each having a fixed coil which forms one piece with the external axle box, this coil acting on a ring, or keeper, to cause a group of clutch discs to be pressed against the ring, these discs alternately forming one piece with the driven shaft and one of the axleshafts carrying the wheels, the clutches being disengaged, and the corresponding wheels free to run, when the coils are not electrically energised.The clutches can be retained engaged during normal running and temporarily disengaged, the or each automatic control device being operated by or interlocked with a steering device of the vehicle and controlling the disengagement of the clutch connecting one of the axleshafts to the driven shaft whilst turning a bend; in particular, it is appropriate that the or each automatic control device is operated by the steering device of the vehicle to disengage the clutch relating to that of the axleshafts carrying the wheel on the outside of the curve described by the vehicle.

In addition to the or each automatic control device, there is also a manual device to provide the independent engagement and disengagement of one or both of the clutches.

The axle can also comprise sensors which detect the speed and/or differences in speed of the vehicle's rear driving wheels, fitted with a differential device, these sensors acting on the or each automatic control device, causing the clutches to engage when the rear wheels exceed preestablished speeds or differences in speed, or skidding of the wheels themselves.

With any one of the clutches envisaged it is appropriate, should there be a failure in the supply of power to the or each control device for accidental reasons, that the clutches remain in the disengaged position. The clutches may also be disengaged by means of a manual control, making both shafts of the axle idle, particularly for road-use; furthermore, the clutches may be engaged by means of a manual control and by overriding the or each automatic control device, achieving the drive constantly on both wheels of the axle, particularly for off-road-use, on terrain which is uneven or has limited grip.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a general diagram of an agricultural tractor fitted with a front axle arrangement according to the invention; Figure 2 is a sectional view of part of the front axle; Figure 3 is a wiring diagram for the operation of the axle and associated components; Figure 4 is a diagram showing the behaviour of a vehicle fitted with the present axle a device on a bend with a tight radius; and Figures 5 and 6 are similar to Figure 4 but show respective bends of increasing radius.

Figure 1 shows a vehicle 1 such as an agricultural tractor intended to be usable away from a road, the vehicle having an engine 2 linked, by means of a gear and clutch unit 3 and a shaft 4, to a rear axle 5 carrying a pair of driving wheels 6.

In order to facilitate correct turning through bends the rear axle 5 includes a differential 7, possibly of a lockable or self-locking type for off-road-use.

From the gear and clutch unit 3 leads also a driving shaft 8, which drives a front axle 9 carrying a pair of steering wheels 1 Oa, 1 Ob.

The front axle 9 comprises an outer casing 11, housing inside a pair of bevel gears 1 2 comprising a pinion 1 2a and a crown wheel 12b, the latter carrying a driven shaft 1 3.

The driven shaft 1 3 is connected to two axleshafts 1 4a and 1 4b by means of a pair of clutches 15a and 15b contained in the casing 11. A preferred embodiment of the invention is illustrated in Figure 2 in detail, envisaging the use of clutches 15a, 15b which are electromagnetically operable.

As shown in Figure 2, the end of the shaft 8 carries the pinion 1 2a and is supported by a roller bearing 1 6 inside a tubular casing 16a, in its turn supported by the framework of the vehicle, in a known manner, not illustrated.

The casing 11 has side portions 11 a and 11 b, inside which are respective coils 1 7a and 1 7b of the electromagnetic clutches 15a and 15b, and bearings 1 8 of the driven shaft 13, carrying the crown wheel 12b. At each end of the shaft 1 3 is a crown 1 9, which has external toothing 19a, with which the relative internal toothing of clutch discs 20 mesh, the latter being arranged alternately with clutch discs 21, their external toothing being meshed with internal toothing 22 of a flange element 23, to which one of the axleshafts 14a, 1 4b is connected, by means of a splined section 24.

Around each coil 1 7a and 1 7b is a magnetic core 25, forming one piece with the shaft 13, with a small air gap in between. The core 25 has annular openings 26,- and similar annular openings 27 are made in the clutch discs 20 and 21. The magnetic flux produced by the coils 1 7 can be closed by keepers 28 of ferromagnetic material, which each have internal toothing and can slide on the toothing 19a, in such a way that the keepers 28 press the clutch discs 20 and 21 together and against the cores 25, thus transmitting motion of the driven shaft 1 3 to the axleshafts 1 4a and 14b.

When there is no electrical power supply to the coils 17, the clutch discs 20 and 21 move apart, leaving the axleshafts 1 4a and 1 4b free.

This embodiment is particularly economical in construction since the maximum force is exerted by the coil 1 7 to enable transmission by friction between the discs 20 and 21 of the drive torque applied to the axleshafts. This torque must be applied when the airgap is at a minimum, that is, when the discs 20 and 21 are in contact with each other and with the core 25, which can surround the coil 1 7 with the minimum of free space, restricted only by machining tolerances.

In this manner a vehicle is created with a four-wheel drive, in which the drive on the front wheels, by operating the clutches 1 5, may be disengaged for both wheels and also disengaged for just one of them, enabling bends to be turned without requiring differential devices which would have to be equipped with a lock. Disengagement of the clutch relating to one of the wheels may be controlled automatically, to correspond with the steering of the vehicle, by means of a device shown schematically in Figure 3.

As illustrated a pair of switches 29 and 30 is installed on the steering S of the vehicle, these being opened when steering to the right and left respectively, by means of cams connected to the steering device. When activated, the switches 29, 30 open the feeding circuit of the right and left coils 17b, 1 7a respectively, so that the wheel on the outside of the bend is made free during steering. There are also other switches 31 and 32, normally open, positioned on the respective feeding circuits ofthe coils 1 7b and 17a, and a switch 33, normally closed, which precedes the switches 29 and 30.

These devices, should it be desirable to override the automatic operation controlled by the steering device, make it possible to engage and disengage the clutches 15 as re quires.

In fact, by opening all three switches, 31, 32 and 33, the drive is disengaged at all times on both wheels of the front axle, for road-use for instance, where such drive is not required. Closing one or both switches 31 and 32, while 33 stays open, also makes it possible to engage the drive on one br both of the front wheels, irrespective of the path followed, at the driver's command The above-mentioned switches, 31, 32 and 33, may be independent and operated manually so as to enable the driver to select the most suitable drive conditions for the terrain being covered; alternatively, the switches may be interdependent and also equipped with automatic controls, operated, for instance, by devices that detect the speed or differences in speed of the rear wheels so that if one of the wheels skids, the front drive is applied to the wheel on the opposite side, which is more likely to be on solid ground, or to both. This automatic system, when it does not detect significant differences in the rotational speed of the rear wheels, due to one of them suddenly losing grip, may also automatically disengage the drive on the front wheels, with considerable savings in power.

Behaviour on bends is illustrated in Figures 4, 5 and 6, which schematically show an offroad vehicle, such as an agricultural tractor, with the rear axle 5 and rear wheels 6 and the front steering axle 9, carrying the front wheels 10a and lOb.

Figure 4 shows the vehicle on a bend with a comparatively small radius, R1, referring to the trajectory described by the centreline of the rear axle 5 of the vehicle, equipped with a conventional differential which may be lockable. As shown in the Figure, the inner front wheel lOa describes an arc with a radius R2, greater than R,. Under conditions of perfect grip to the terrain, therefore, the wheel 1 0a is required to turn with a tip speed greater than the average traversing speed of the vehicle on the bend, corresponding to the movement along the arc with a radius R1.

Figure 5 shows the diagram of a mediumradius bend in which the front wheel 1 Oa describes an arc with a radius R2', essentially the same as radius R,' described by the centreline of the rear axle 5.

In this case, with perfect grip on the ground, the tip speed of the inner front wheel 1 0a coincides with the average speed of advance, these speeds being relative to the movement along the same arc of the circle, with radius R,' = R2'.

In Figure 6, in the case of a bend with a wide radius R,", the inner front wheel 10a must travel on an arc with a radius R2", smaller than R11,, and must therefore rotate with a tip speed lower than the average speed of advance of the vehicle along the arc with radius R1", but essentially little different from the latter speed, given the small difference between R," and R2' .

The outer front wheel 1 Ob advances, in the three cases illustrated, along the arcs with radius R3, R3', R3" respectively, which are always greater than the corresponding middle radius R1, R1', R," and it therefore has a tip speed greater than the average speed of advance of the vehicle. Since the transmission of the motion to the front wheels, envisaged for correct running in a straight line, causes the front wheel to rotate with a tip speed that corresponds to the average traversing speed of the vehicle, which on a bend is an average between the two speeds of the rear wheels, connected together by means of a differential, if the drive is applied beforehand to the front wheel on the inside of the bend, in theory the bend can only be turned correctly in cases similar to that given in Figure 5.On wider bends this inner front wheel 1 0a will rotate at a slightly higher speed than the optimum speed. whereas on tighter bends the wheel 1 Oa will travel at a slower speed than the theoretical value.

Such differences, however, are fairly limited and completely negligible in off-road running, on rough ground, particularly when the ground moves and is uneven and contact of the wheels with the terrain is interrupted.

In the case of particularly tight bends, however, where the reduced speed of the inner driving front wheel acts as a brake on the movement, the drive on this wheel may be disengaged, leaving it free; the drive on this wheel may be reapplied, however, should the rear wheel lose grip, in other words when the front wheel can provide its own contribution to the drive around the bend.

This disengagement can also be operated automatically, for bends with a radius less than an appropriate value, by means of electrical controls- applied, for example, to the steering of the vehicle and automatic control devices, similar to those described previously, may be used to reapply the drive to the front wheels. A simple embodiment of a front driving axle is provided which also lends itself to many possibilities of operation, both manual and automatic, to select the most appropriate drive conditions for each type of terrain. In some applications it is also possible to use the present axle arrangement also for rear axles, in this case too eliminating the conventional differential device.

In this case, the clutches relating to the outer rear wheel and the inner front wheel, having speeds that are not too different, may be engaged at the same time, as can be determined from Figures 4, 5 and 6.

The present axle arrangement has been described with reference to cases in which it is disadvantageous, in the event of an anomaly, for the drive to remain engaged on both wheels of the front axle; in cases where this would be preferable, however, clutches of a different type could be used, usually kept engaged, by means of a spring for instance, and disengaged via a control.

Many variants can be made to that described above, especially as regards the adaptation to the various possible types of clutch, friction or claw, which can be used.

For example, in the case of clutches controlled hydraulically, a hydraulic or electrohydraulic circuit would be required, which carries out the same operations as the electrical circuit described above, and the same would apply to mechanically-controlled clutches, for which various connections could be used having the same purpose.

Claims

1. An axle arrangement for a vehicle, the axle arrangement comprising a driven shaft, two independently-operable clutches to couple said shaft with respective axle shafts intended to carry the vehicle wheels, manually-operable and automatically-operable control devices to provide engagement and disengagement of said clutches, and sensors arranged to be sensitive to the movement of the wheels and the path followed by the vehicle and capable of operating said automatic control device in relation to pre-established running requirements to engage or disengage one or both of said clutches as appropriate.

2. An axle arrangement according to claim 1, wherein said clutches are friction clutches equipped with remote control devices.

3. An axle arrangement according to claim 1, wherein said clutches are claw clutches equipped with remote control devices

4. An axle arrangement according to claim 2 or 3, wherein said remote control devices are electromagnetic, hydraulic or mechanical devices.

5. An axle arrangement according to claim 1, 2 or 3 wherein each said clutch is electromagnetically-operated, each having a fixed coil, a ring or keeper on which said coil acts when energised, a group of clutch discs between said coil and said ring or keeper and arranged to be pressed against said ring or keeper, alternate discs being connected to said driven shaft and one of said axleshafts respectively, said clutches thereby being disengaged, and the corresponding wheels free, when said coils are not electrically energised.

6. An axle arrangement according to any one of the preceding claims, wherein means are provided to retain said clutches engaged during normal running and temporarily disengage them, said automatic control device being operable by or interlockable to a steering device of the vehicle and controlling the disengagement of the clutch connecting one of said axleshafts to said driven shaft when thevehicle is travelling through a bend

7. An axle arrangement according to claim 6, wherein said automatic control device is operable by the steering device of the vehicle to disengage the clutch relating to that of said axleshafts which is intended to carry the wheel on the outside of the curve described by the vehicle.

8. An axle arrangement according to any one of the preceding claims and further comprising manual devices to operate independently the engagement and disengagement of one or both of said clutches.

9. An axle arrangement according to any one of the preceding claims, wherein it is intended to be the front axle of a vehicle and further comprising sensors which are intended to detect the speed and/or differences in speed of a vehicle's rear driving wheels having a rear axle, fitted with a differential device, these sensors acting- on said automatic control devices to cause said clutches to engage when said rear wheels exceed pre-established speeds or differences in speed or skidding of the wheels themselves.

1 0. An axle arrangement according to any one of the preceding claims, wherein in the event of a failure of said automatic control device, said clutches remain in the disengaged condition.

11. An axle arrangement according to any one of the preceding claims, wherein a manual control is provided to overridingly disengage said clutches to cause both axleshafts to idle.

12. An axle arrangement according to any one of the preceding claims, wherein a manual control is provided to override said automatic control device to engage said clutches to achieve constant drive on both wheels of the axle.

1 3. An axle arrangement, substantially as hereinbefore described with reference to the accompanying drawings.

14. A vehicle such as a tractor having a front axle incorporating an axle arrangement according to any one of the preceding claims.

1 5. A vehicle such as a tractor having a rear axle incorporating an axle arrangement according to any one of claims 1 to 1 3.