GB2074513A - Vehicle axle assembly - Google Patents

Abstract

In an axle assembly, for improving the stability of a vehicle, notably for maintaining ground clearance of the vehicle chassis when it is necessary to increase the diameter of the steerable ground wheels, two axle shafts (6, 7) which are fixed respectively to two steerable wheels (3, 4) through the intermediary of articulation joints (11, 12), the axle shafts are each inclined downwards to define an angle ( alpha ) with a straight line (17) joining together the joints (11, 12) and the centres of the wheels (3, 4). The axle assembly can be used with advantage for conversion of a vehicle from two-wheel drive to four- wheel drive, in particular for tractors. <IMAGE>

Description

SPECIFICATION Vehicle axle assembly The present invention relates to an axle assembly for a vehicle with four driving wheels.

Axle assemblies are known for use in rotationally driving the guiding wheels of fourwheel drive vehicles, that is to say vehicles such as cross-country vehicles or tractors which comprise a front driving axle equipped with guiding wheels and at least one rear driving axle.

In the known arrangements these driving axles extend horizontally on the vehicle chassis and are generally mounted to turn, at least over a portion of their length, in a casing connected to the chassis. They are rotationally driven from the engine of the vehicle or from the mechanism driving the rear axle through the intermediary of a drive mechanism, usually a differential which is also housed in the casing. Designs for such vehicles are, for example, disclosed in United States patent specification No. 3 400 777 and the specification of published German Application No.

2001 975.

It is also known that vehicles initially equipped with driving wheels only at the rear may be converted into four-wheel drive vehicles. A modification of this type, intended for a tractor, forms the basis of, for example, published German Application No. 2 405 71 8. In the majority of cases the conversion is relatively. easy to carry out due to the fact that, considered overall, it is only necessary to fit to the vehicle chassis the casing of the driving axle and, for the rotational drive of the latter, to add the necessary transmission equipment and/or to modify the transmission equipment with which the vehicle to be converted is fitted.This relative ease of fitting out moreover constitutes a strong commercial argument for the designer who, at the initial design stage for a new model of a two-wheel drive vehicle, can allow for the fact that a conversion of this vehicle into a four-wheel drive vehicle may well be subsequently required by the user.

For certain vehicles with four driving wheels, in particular those in which the front guiding wheels are of smaller diameter than the rear wheels, as is frequently the case with tractors, the search for improved traction leads to fitting the front guide wheels with tyres of larger dimensions or, where applicable, of fitting wheels of a larger diameter.

This modification becomes more necessary in the case of tractors originally fitted with drive wheels only at the rear and already converted or to be converted into tractors with four drive wheels. In these tractors, in fact, and notably for the purpose of reducing wheel base and facilitating steering, the front wheels are generally of a considerably smaller diameter than the rear wheels and, by comparison with the latter, are frequently equipped with tyres which differ both in form and dimensions.

Such a modification nevertheless is accompanied by the disadvantage of raising the front part of the vehicle so that its chassis is no longer horizontal. It follows that the connection between this chassis and the various items of equipment intended to be fitted to the vehicle is also modified, which can give rise to serious difficulties when the equipment should be drawn and/or pushed in a horizontal plane. Similarly, when front-mounted tools such as front loaders are used, they may not even be able to touch the ground. Moreover, there is a risk that this raising of the chassis and, consequently, of the drive axle of the guiding wheels together with its driving mechanism, may result, when travelling over uneven ground or steep slopes, in poor stability of the vehicle, the centre of gravity of which is now higher.

There is accordingly a need for a drive axle of the aforementioned type for a vehicle with four driving wheels, which enables the stability of the vehicle to be improved, and the clearance from the ground designed for the vehicle chassis to be maintained, when it is necessary to increase the diameter of the guiding wheels for the purpose of obtaining better traction.

According to the present invention there is provided an axle assembly for a four-wheel drive vehicle, comprising two axle shafts drivable in conjunction by drive transmission means and each coupled by a universal joint to a respective steerable ground wheel, the axle shafts being so inclined downwardly from the joints as to each extend at an angle to a straight line passing through the joints and the wheel centres.

Two embodiments of the invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic front view, partially in section, of a portion of a vehicle equipped with an axle assembly constructed according to a first embodiment of the invention, Fig. 2 is a plan view of the axle assembly of Fig.

1,and Fig. 3 is a schematic front viaw, partially in section and to a larger scale than Fig. 1, of an axle assembly constructed according to a second embodiment of the invention.

Referring now to the drawings, in Fig. 1 there is shown a chassis 1 of a vehicle with four drive wheels, such as a tractor. An axle-box or casing 2 is connected by means (not shown) for example in an oscillating manner and/or by means of springs to the base 1.1. of the forward part of the chassis 1. The driving axle, for rotationally driving the two front guiding wheels 3 and 4 of the tractor, is composed of a central part-axle 5 and two lateral part-axles 6 and 7. The central part-axle 5 is rotatably mounted in the central portion 2.1 of the axle-box 2 and is rotationally driven through the intermediary of a differential drive mechanism (not shown) from a drive shaft 8 (Fig. 2).The part-axles 6 and 7 are connected at their ends 6.1 and 7.1, to the ends 5.1 and 5.2, respectively of the central part-axle 5 by means of articulation devices 9 and 10, such as cardan joints. At their ends 6.2 and 7.2, the lateral part-axles 6 and 7 are connected, through the intermediary of articulation devices 11 and 12 such as cardan joints, to driving stubaxles 1 3 and 14 associated with, respectively, the wheels 3 and 4.

Ends 2.2 and 2.3 of the axle-box 2 each have an upper and a lower arm pivotally engaging between analogous arms of a respective one of tubular hubs 1 5 and 16, in which the stub axles 13 and 14 of the wheels 3 and 4 are respectively centred. The orientation of the hubs 15 and 16 with respect to the axle-box 2 and, consequently, the steering of the wheels 3 and 4 is carried out from a steering installation (not shown).

Fig. 1 shows that, from the articulation devices 11 and 1 2 which connect them to the stub axles 13 and 14, the part-axles 6 and 7 are inclined downwards and each define an angle of the same value a with a notional straight line 1 7 joining together the articulation devices 11 and 12, in other words, the centres of the wheels 3 and 4.

These wheels are thus raised with respect to the position which they would have adopted if the driving axle had extended horizontally at the level of the central part-axie 5.

As a result of the fact that it enables the position of the drive mechanism to be lowered with respect to the wheel stub axles, such an arrangement offers an advantage in the case where improved stability is desired for the tractor.

It is particularly advantageous when in the case of a tractor which is in service orto be converted, it is necessary to equip the guiding wheels with tyres of larger dimensions or, if applicable, to fit wheels of larger diameter. In this case, not only can the ground clearance of the chassis 1 be maintained, that is to say the later can remain horizontal, but also the initial centre of gravity of the tractor can also be maintained or lowered, which contributes to maintaining and even improving the stability of the thus modified tractor.

From Fig. 2, which shows diagrammatically, from above, the driving axle of Fig. 1, it is apparent that the two part-axles 6 and 7 are also inclined forwards in the direction of travel of the tractor and that they each form an angle !3 with the line 17 joining together the articulation devices 11 and 12 of the stub axles of the wheels 3 and 4.

Such a measure, which is already known for vehicles equipped with a front driving axle for the purpose of improving the steering of the wheels, has the drawback of moving the centre of gravity of the vehicle forwards, which may be dangerous in the case of a tractor that is required to travel on steep terrain. Due to the fact that it results in a slight lowering of the position of the drive mechanism, notably the differential mechanism, the downward inciination of the two lateral partaxles 6 and 7 enables the aforementioned drawback to be at least partly counteracted.

In the embodiment of the invention shown in Fig. 3, reference 33 denotes the chassis of a tractor with four driving wheels. An axle-box or casing 1 8 is connected by means (not shown), for example, in an oscillating manner and/or by means of springs to the base 33.1 of the front portion of the chassis 33. The axle-box 1 8 has two end portions 18.1 and 18.2, which each possess an upper arm and a lower arm pivotally engaged between analogous arms of a non-rotatable tubular hub 19 or 20, in which a driving stub axle 21 or 22 of one of two forward guiding wheels 23 and 24 of the tractor is centred. The orientation of the tubular hubs 1 9 and 20 with respect to the axle--box 1 8 is controlled from a steering mechanism (not shown).

The driving axle for rotationally driving the guiding wheels 23 and 24 is composed of two half-axles 25 and 26. At their ends 25.1 and 26.1, the haif-axles 25 and 26 are connected to the stub" axles 21 and 22, respectively, of the corresponding wheels 23 and 24 by means of articulation devices 27 and 28, such as cardan joints. The free ends 25.2 and 26.2 of the halfaxles 25 and 26 are connected together by means of an articulation device 29, such as a cardan joint, disposed on the axis of the tractor. One of the halfaxles 26 is rotationally driven by a differential drive mechanism 30 housed in a compartment 1 8.3 of the axle-box 1 8 and the toothed driving wheel 31 of this mechanism is driven by a rotatable drive shaft and drive pinion (not shown).

From the articulation devices 27 and 28 which connect them to the stub axles 21 and 22 of the wheels 23 and 24, the two half-axles are inclined downwards and each define an angle a of the same value with a notional straight line 32 joining together the articulation devices 27 and 28 and the centres of the wheels 23 and 24.

Such an embodiment of the axle shaft, which necessitates the use of a single articulation device, is relatively simple to construct and has an advantageous capital cost.

In the two forms of embodiment shown, the part-axles under consideration form the subject of an arrangement which is symmetrical about the axis of the vehicle. It is self-evident that the respective angles which they make with the straight line joining together the articulation devices which connected them to the wheels could be different. Similarly, instead of being simple articulations as shown, the articulation devices could be double cardan joints. It is equally self-evident that, instead of being composed of several parts 18, 1 8.1 and 18.2, the axle-box 18 could be of monobloc construction.

Claims (6)

1. A axle assembly for a four-wheel drive vehicle, comprising two axle shafts drivable in conjunction by drive transmission means and each coupled by a universal joint to a respective steerable ground wheel, the axle shafts being so inclined downwardly from the joints as to each extend at an angle to a straight line passing through the joints and the wheel centres.

2. An axle assembly as claimed in claim 1, wherein the axle shafts are interconnected at ends thereof remote from said joints by a Cardan joint, one of the axis shafts being provided with means couplable to the drive transmission means.

3. An axle assembly as claimed in either claim 1 or claim 2, wherein the axle shafts are so inclined forwardly from the joints as to each extend at an angle to the straight line.

4. An axle assembly for a four-wheel drive vehicle, substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

5. An axle assembly for a four-wheel drive vehicle, substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

6. A four-wheel drive vehicle provided with an axle assembly as claimed in any one of the preceding claims.