GB2132145A

GB2132145A - Motor vehicles such as tractors

Info

Publication number: GB2132145A
Application number: GB08332885A
Authority: GB
Inventors: Der Lely Cornelis Van
Original assignee: Texas Industries Inc
Current assignee: Texas Industries Inc
Priority date: 1982-12-17
Filing date: 1983-12-09
Publication date: 1984-07-04
Also published as: DE3345317A1; NL8204875A; FR2537938B1; FR2537938A1; GB2132145B; GB8332885D0; IT1168742B; IT8324229A0

Abstract

An agricultural tractor has front and rearwheels (35,40), all of which are driven by an engine (14). Drive is transmitted through a differential in a housing (17) which splits the power between the wheels on the two sides of the tractor. Further differentials (41) split the power between the front and rear wheels on each side. The three differentials are provided in a common transverse assembly. A drivable, spiked ground engaging roller may be provided for extra traction. There may be eight wheels each of diameter about 1 metre and carrying wide tyres for low ground pressure. The track of the inner wheels is preferably about 1.5m and that of the outer wheels 2.5m. The weight distribution may be about 2 DIVIDED 3 at the front to 1 DIVIDED 3 at the rear. The cab may have a flat floor at a level above that of the tops of the rear wheels and above a gear box. <IMAGE>

Description

SPECIFICATION Motor vehicles such as tractors This invention relates to motor vehicles and particularly, although not exclusively, to tractors or similar vehicles for agricultural purposes.

Tractors having drivable wheels arranged one behind the other frequently have the disadvantage that, when making sharp turns, the wheels are not uniformly driven. This gives rise to deterioration of the soil structure.

According to a first aspect of the present invention there is provided a motor vehicle comprising front and rear wheels, a respective differential drive being provided between a front wheel and a rear wheel on each side of the vehicle.

According to a second aspect of the present invention there is provided a motor vehicle comprising front and rear wheels and at least, three differential drives provided in a common shaft assembly extending transversely of the normal intended direction of operative travel of the vehicle.

According to a third aspect of the present invention there is provided a motor vehicle comprising front and rear wheels, a drivable ground-engagable roller being provided between the front and rear wheels.

According to a fourth aspect of the present invention there is provided a motor vehicle comprising front and rear wheels, the diameter of a front wheel and of a rear wheel being about 100cms and about two thirds of the vehicle weight being supported by the front wheels.

According to a fifth aspect of the present invention there is provided a motor vehicle comprising front and rear wheels and a driver's cab, the floor of which is flat, is located at a higher level than the tops of the rear wheels and is disposed above a gear box of the vehicle.

According to a sixth aspect of the present invention there is provided a motor vehicle comprising front and rear wheels, four of the wheels having a track width of about 250 cms and four others of the wheels having a track width of about 150cms.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a side view of a tractor; Figure 2 is a plan view of the tractor of Figure 1 taken in the direction of the arrow II, the tractor cab being omitted for the sake of clarity; Figure 3 is a front view of the tractor taken in the direction of the arrow Ill in Figure 1; Figure 4 is a plan view of the tractor frame taken on the line IV-IV in Figure 1; and Figure 5 is a side view of another embodiment of a tractor.

The frame 1 of the tractor, which is shown separately in Figure 4 for the sake of clarity, is symmetrical about the vertical longitudinal central plane 2 of the tractor and comprises two parallel, spaced pipes or tubes 3 which are substantially horizontal or slope slightly upwards from the rear to the front, with respect to the intended direction A of travel of the tractor.

The tubes 3 form part of the front part of the tractor. The tubes 3 are interconnected both at their front and rear ends by plates 4 and 5 which extend substantially vertically and parallel to each other at right angles to the plane 2. Between the rear portions of the tubes 3 there is a circular tube 6, the centreline of which lies in the plane 2. The tube 6 is supported with respect to the two tubes 3 by the hindmost plate 5, with respect to the direction A, and by a plate 7 located some distance ahead of, and parallel to, the plate 5. The plate 7, like the plates 4 and 5, is rigidly connected to the tubes 3. The distance between the plates 5 and 7 is about 30% of the length of each of the two tubes 3.The plates 5 and 7 have each a circular opening in which a bearing bushing 8 and 9 respectively is mounted, these bearing bushings supporting the tube 6 in a pivotal manner so that it can turn about its centreline with respect to the assembly of the tubes 3 and the plates 4, Sand 7. The plate 7 and the bearing bushing 9 are arranged near the front of the tube 6. The tube 6 extends beyond the rear ends of the two tubes 3 and beyond the plate 5 for a distance which is about 20 to 25% of the length of each of the tubes 3. A transverse beam 10 is rigidly secured to the rear end of the tube 6. The transverse beam 10 is hollow and preferably has a square cross-section. The rear end of the tube 6 is welded to a front face of the transverse beam 10 and the junction is reinforced by means of supporting plates 11.The transverse beam 10 has a centreline at right angles to the centreline of the tube 6. The length of the transverse beam 10 is about 80 to 85% of the overall length of each of the tubes 3. In the position shown, the transverse beam 10 is symmetrical about the plane 2. Wheel carriers 12 are fastened to the transverse beam 10 near its ends.

These wheel carriers 12 are welded to a rear face of the transverse beam 10, with respect to the direction A. The wheel carriers 12 preferably have a hollow square cross-section, and have a centreline parallel to the plane 2.

Figures 1 and 5 show that the centrelines of the parallel wheel carriers 12 are parallel to upper and lower faces of the beam 10, these faces being included to the parallel centre lines of the tubes 3 and 6. The wheel carriers 12 slope downwards to the rear away from the beam 10. The centrelines of the wheel carriers 12 are at an angle of about 155 to the centrelines of the tubes 3 and 6 in the embodiment shown in Figure 1 and at an angle of about 165 in the embodiment shown in Figure 5. The length of each of the two wheel carriers 12 measured parallel to the plane 2 is about 15 to 20% of the length of each of the tubes 3. Each of the two wheel carriers 12 is provided at its rear end with a closing plate 13 having a portion at right angles to the centreline of the carrier 12 and rigidly fastened to the associated wheel carrier 12.

As shown in Figures 1 and 5, a driving engine 14 is fastened at the front ends of the tubes 3, which preferably have a hollow, square section. The engine 14 is provided at the front with a cooling device 15 and a ventilator 16. The engine 14 is disposed symmetrically about the plane 2. The output shaft of the driving engine emerges from the rear of the engine and constitutes an input shaft of an assembly 17 comprising a change-speed and a differential mechanism disposed in a casing situated behind the driving engine 14 and also supported by the two tubes 3. The change-speed gear box forming part of the assembly 17 is situated at the front of the assembly and directly adjoins the rear of the engine 14, and the differential gear is located at the rear of the assembly.The driving engine 14 and the assembly 17 extend from a position at the front ends of the tubes 3 along about 65 to 70% of the length of the tubes 3.

To one side of the housing of the assembly 17 is fastened a housing of gear wheel transmission 18, which can be driven from the change-speed gear at a speed of rotation proportional to the speed of rotation of the drivable wheels of the tractor. The gear wheel transmission 18 has, at the rear with respect to the direction A, two output shafts 19 and 20, the speed of rotation of which, in operation, is proportional to that of the drivable wheels of the tractor or to the travelling speed respectively.

From the rear side of the assembly 17 emerges an output shaft 21, the speed of rotation of which is proportional to that of the driving engine 14. The centreline of the output shaft 21 lies in the plane 2.

The housing of the assembly 17 has near the rear and on both sides embossed parts 22 comprising part of the differential gear of the assembly 17. To each of the two embossed parts 22 is rigidly secured a carrying tube 23 and 24 respectively. The centrelines of the carrying tubes 23 and 24 are in line and extend at right angles to the plane 2. The carrying tubes 23 and 24 constitute supports and bearings for drive shafts disposed in them, and these shafts are drivable from the differential gear of the assembly 17 at a speed of rotation proportional to that of the driven wheels of the tractor or to the travelling speed respectively.

On both sides of the plane 2, on the top of each of the carrying tubes 23 and 24, there are supports 25, the top faces of which are provided with elastic elements 27 supporting the underside of a cab 27 near its front end. The distance between the two supports 25 is about 50 to 55% of the length of each of the tubes 3. The rear ends of each of the tubes 3 are provided at the top with a support 28 which is substantially vertical like the supports 25. At the top of the two supports 28 there is fastened a carrier 29 which is normal to the plane 2. The top face of the substantially horizontal carrier 29 and the top ends of the supports 25 are located in the same horizontal plane or in a plane inclined slightly upwards in the direction A.The top of the carrier 29 is also provided with elastic elements 26 which are spaced from the plane 2 by the same distance as the elements 26 on the supports 25. The elastic elements 26 on the carrier 29 support the underside of the cab 27 near its rear end. Viewed on plan, the rear boundary line of the carrier 29 approximately coincides with the plane 5.

Between the rear of the driving engine 14 and the front of the cab 27 there is a fuel tank 30 which extends between the top of the assembly 17 and a position at the same level as the top of the driving engine 14.

At a place situated about 20% of the way along the length of the tubes 3 from the front ends of said tubes there is a wheel carrier 31 which is fastened to the top faces of the tubes 3 so as to be normal to the plane 2, viewed on plan. The wheel carrier 31 is preferably constructed in the form of a hollow, square-section beam disposed symmetrically about the plane 2. The two outermost parts of the wheel carrier 31 have centre lines normal to the plane 2 (Figure 3). These outermost parts are connected to innermost parts which are inclined downwards and inwards, as viewed in the front view of Figure 3, and which in turn are connected near the pipes 3 to a central part normal to the plane 2, the lower face of the central part being fastened to the top faces of the tubes 3. The central part passes below the driving engine 14.The two outermost ends of the wheel carrier 31 are disposed substantially in the same vertical plane parallel to the plane 2 as each of the outermost ends of the carrying tubes 23 and 24 respectively. Housings of gearwheel transmissions 32 are fastened to each of the two ends of the wheel carrier 31. The underside of each of the housings of the gear wheel transmissions 32 is provided with a tubular swivel shaft or king pin 33, which is inclined downwards and forwards away from the associated gear wheel transmission 32. Each king pin 33 is pivotable about its centreline with respect to the associated gear wheel transmission 32. Each king pin 33 is rigidly secured at its lower end to a housing 34 of a gear wheel transmission having aligned output shafts which are normal to the plane 2 in the position shown in the Figures.These output shafts of the gear wheel transmissions 34 constitute drive shafts of front wheels 35 which are arranged in pairs on both sides of the associated king pins 33 and gear wheel transmissions 34. The housing of the gear wheel transmission 34 provides the bearing of the ground wheels 35 located on each side.

A gear wheel transmission 1Q is rigidly secured to the top of the transverse beam 10, near each end. An input shaft 37 of each gear wheel transmission projects to the front and is horizontal or slopes upwardly towards the front. A tube 38 is rigidly secured to the rear of each gear wheel transmission 36, this tube 38 being at a distance above and parallel to the adjacent wheel carrier 12. The rear end of each tube 38 is rigidly secured to the front of a gear box 39 which is fastened to the rear face of the adjacent closing plate 13 and extends upwards from that closing plate. Drive to the input shaft of each gear wheel transmission 36 is transmitted through the gear wheel transmission to a drive shaft located coaxially within the tube 38; this drive shaft consti tutus an input shaft for the gear box 39. Each gear box 39 has two aligned output shafts which project from opposite sides of the box and are parallel to the transverse beam 10. These output shafts serve as drive shafts of rear wheels 40 disposed on opposite sides of the gear box 39 and of the associated wheel carrier 12. The four rear wheels 40, like the four front wheels 35, are arranged in pairs so that the plane of symmetry of each pair of rear wheels 40 coincides with the plane of symmetry of the corresponding pair of front wheels 35.

The carrying tubes 23 and 24 accommodate output shafts of the differential gear of the assembly 17. The housing of a differential gear 41 is rigidly secured to the outermost end of each of the carrying tubes 23,24. The shafts journalled in the carrying tubes 23 and 24 also constitute input shafts of the two differential gears 41. Each of the two differential gears 41 has a substantially horizontal output shaft 42 directed to the front with respect to the direction A and an output shaft 43 which projects to the rear.

The shafts 41 and 42 are aligned with each other.

Viewed from the side, three aligned, coupled differential gears are thus arranged between the front and rear wheels.

The gear wheel transmissions 32 of the respective pairs of front wheels 35 have at the rear side substantially horizontal input shafts 44 directed to the rear. On each side of the plane 2, the input shafts 37 and 44 and the output shafts 42, 43 are located substantially in the same vertical planes parallel to the plane 2. Each forwardly projecting output shaft 43 of the differential gear 41 and the respective rearwardly directed input shaft 44 of the gear wheel transmission 32 are intercoupled by an intermediate shaft 45 having two universal joints in order to compensate for any structurally desired vertical or lateral differences.Each rearwardly projecting output shaft 43 of the differential gear 41 and the respective fowardly projecting input shaft of the gear wheel transmission 36 for driving the rear wheels 40 are coupled by means of an intermediate shaft 46, which is also provided with universal joints for the same reasons. On each side of the tractor the differential gear 41 and the associated intermediate shafts 45 and 46 are covered by a hood 47 which abuts the underside of the cab 27 and comprising a panel located above these parts and a downwardly extending panel connected to the outboard side of the first panel. The hood 47 serves as a foot board giving access to the cab and it serves at the same time as a mudguard.

The drive shafts of the rear wheels 40 and the centrelines of the wheel carriers 12 are parallel to a common upwardly sloping plane. The diameters of the front wheels 35 (which are preferably provided with low-pressure pneumatic tyres) and those of the rear wheels 40 are equal to each other. in the embodiment shown in Figures 1 to 4, this diameter is about 90 cms, and in the embodiment of Figure 5 it is about 100 cms. The axial width of each wheel is about 40 cms. The distance between the central vertical planes of the outermost rear wheels and front wheels respectively is about 200 to 270 cms, preferably about 250 cms. The distance between the central vertical planes of the inner rear wheels and front wheels respectively is about 120 to 160 cms, preferably 150 cms.

Pivotal shafts 48 are provided at, or slightly ahead of, a position substantially midway between front and rear wheel axles. As is shown in Figure 1, this pivotal shaft 48 is journalled respectively in the two pipes 3, and their centrelines are aligned with each other. A respective carrier 49 is pivotable about each of the two pivotal shafts 48. The carriers 49 extend downwards and rearwardly in the operational position of Figure 1 away from their pivotal shafts 48.

The rear end of each carrier is rigidly secured to a supporting beam 50 which is normal to the plane 2.

Viewed on plan, the supports 49 are directly adjacent the outer faces of the pipes 3. The supporting beam 50 is symmetrical about the plane 2.

The length of the supporting beam 50 is about 4.5 times the distance between the outboard faces of the tubes 3 and is substantially the same as that of the carrier 29 (Figure 2). The outer ends of the supporting beam 50 lie substantially in a plane containing the outermost boundary surfaces of the front and rear inner wheels 35 and 40. These ends of the supporting beam 50 are provided with rigidly secured supporting plates 51 which extend rearwardly and, in operation, downwardly and support near their rear ends a shaft 52, which is at right angles to the plane 2. A tube 53 is rigidly secured to the shaft 52 so as to be coaxial with the shaft. A large numer of plates 54 are secured to the tube 53, these plates 54 being arranged in a row at short distances from one another.The plates 54, as shown in Figure 1, are provided with pointed extensions or spikes; preferably there are eight spikes on each plate.

On the top face of the supporting beam 50 and at a position directly behind the output shaft 19 of the gear wheel transmission 18, there is a gear wheel transmission 55 having a forwardly projecting input shaft 56. The gear wheel transmission 55 has an output shaft extending parallel to the supporting beam 50 away from the housing of the gear wheel transmission towards the nearer end of the supporting beam 50. This output shaft is supported within a tubular support 57. The tubular support 57 carries, at its end adjacent the end of the supporting beam 50, a housing 58 of a gear wheel or chain transmission 58 (Figures 1 and 2), which transmits driving movement of the output shaft of the gear wheel transmission 55 to one end of the shaft 52.The shaft 52, the tube 53 surrounding it, and the spiked plates 54 constitute a drivable roller of the tractor which is disposed between front and rear wheels. The shaft 52 of the roller is positioned at a distance from the axes of the rear wheels 40 which is about 30% of the total distance between the axes of the front and rear wheels. This disposition of the drivable roller ensures that it does not interfere with implements to be attached to the tractor, mainly near the rear and/or front wheels.

On the top face of the transverse beam 10 there are supports 60 which are rigidly secured to the beam at equal distances from the middle of the beam 10. These supports 60 slope upwardly and to the rear away from the transverse beam 10. Near their top ends, the supports 60 hold a tubular shaft 61, which is parallel to the transverse beam 10 and is provided at its ends disposed outboard of the supports 60 with carriers 62. These carriers 62 are rigidly secured to the shaft 61 and project to the rear away from it. An arm 63 of variable length is pivoted to the rear end of each carrier 63 and extends downwardly away from the carrier 62. The arm 63 is pivotally connected at its lower end to a lower lifting arm 64 of a three-point lifting device 65 arranged at the rear of the tractor.The pivotal connection between each arm 63 and the respective lower lifting arm 64 is substantially midway along the length of the lower lifting arm 64. Supports 66 are rigidly secured to the top face of the transverse beam 10 between the two supports 60 and at short equal distances from the middle of the beam 10. These supports 66 extend upwardly above the shaft 61, which is additionally supported by them. At the top ends of the supports 66 there is a shaft 67 which extends parallel to the transverse beam 10. The front end of an upper lifting arm 68 is pivotable about the shaft 67. The top lifting arm 68 is preferably in the form of a hydraulic ram, the piston rod of which extends to the rear, and is provided with a coupling point 69 in the form of a hook which opens downwardly. The hydraulic ram forming the upper lifting arm 68 can be actuated from the cab 27.At their rear ends the lower lifting arms 64 are provided with hook-like coupling members 7 which open upwardly. Near the pivotal shaft between each arm 63 and the associated carrier 62, another pivotal shaft pivotally connects the carrier 62 to the end of a piston rod of a hydraulic ram 71, the other end of which is pivotally connected to a lug secured to the rear face of the transverse beam 10. The two hydraulic rams 71 can both be acutuated from the cab 27.

Apart from the two rearwardly projecting output shafts 19 and 20, the gear wheel transmission 18 has a forwardly projecting output shaft substantially in line with the shaft 20. This output shaft is supported in a tubular carrier 72 extending from the housing of the gear wheel transmission 18 to a position near the front end of the driving engine 14 (Figure 2). At the front, the carrier 72 holding the forwardly projecting output shaft of the gear wheel transmission 18 meets a gear box 73, which - as will be apparent from Figure 3 - slopes downwardly from the front end of the tubular carrier 72 towards the plane 2. The gear box 73 comprises a gearwheel transmission which transmits driving movement of the output shaft in the carrier 72 to an output shaft of the gear box 73 situated near the plane 2 and projecting forwardly.This output shaft constitutes a power take-off shaft 74, which like the output shafts 19 and 20, is drivable at a speed proportional to the travel speed of the tractor The gear box 73 also receives a drive shaft projecting from the front of the engine 14, this shaft driving an output shaft of a separate gear wheel set inside the gear box 73. This output shaft constitutes a front power take-off shaft 75 of the tractor, which can bs driven at a speed proportional to the speed of the engine.

The output shaft 21 of the differential gear, which shaft is located in the plane 2, is extended rearwardly by an intermediate shaft 76 provided with universal joints to be connected to a rear power take-off shaft 77, which is located by a support 78 on the top face of the transverse beam 10. The intermediate shaft 76 is a telescopic shaft. The power take-off shaft 77 is situated in the plane 2 in the illustrated position of the tractor shown. Another support 78 is fastened to the top face of the transverse beam 10 on one side of the plane 2, between one of the supports 60 and one of the supports 66. This latter support 78 supports a rear power take-off shaft 79 of the tractor. The power take-off shaft 79 is coupled with the output shaft 20 ofthe gearwheel transmission 18 by means of a telescopic intermediate shaft 80 having a pair of universal joints.The input shaft 56 of the gear wheel transmission 55 for the drivable roller 59 is drivably coupled with the output shaft 19 of the gear wheel transmission 18 by means of a telescopic intermediate shaft 81 having universal joints.

As shown in Figure 3, the plate 4 fastened to the front end of the pipes 3 has a number of holes 82 for attaching a detachable three-point lifting device to the front of the tractor.

Each of the two king pins 33 has rigidly fastened to it an extension arm 83 at a position close to the underside of the corresponding gearwheel transmission 32. The arm 83 extends inwardly from the associated king pin 33 and is provided at its inner end with an upwardly directed pivotal shaft or a ball joint by means of which a substantially straight steering rod 84 is pivotally connected to the extension arms. From its extension arm 83, each steering rod 84 extends to the rear, the rearmost end being fastened to a corner of a triangular steering plate 85 which is symmetrical about the plane 2 in the straight-ahead position of the front wheels 35.The steering rods 84 are connected by upwardly extending pivotal shafts or ball joints with the rear corners of the steering plate 85, whilst the front corner of the steering plate 85, which is located in the plane 2, is pivotally connected by an upwardly extending pivotal shaft 86 with the two pipes 3. The centreline of the pivotal shaft 86 has a fixed position with respect to the frame 1. The steering plate 85 can be turned from the cab 27 by means of a hydraulic ram (not shown) with respect to the frame 1 about the pivotal shaft 86 as a result of which the two pairs of front wheels 35 can turn about the centrelines of the king pins 33 in a manner such that at least one of the pair of front wheels 35 can turn at a maximum through about 90 from the position shown in Figure 2.The steering plate 85 is located about midway between the rotary axes of the front and rear wheels 35 and 40.

The front of the cab 27 is disposed behind the rear of the engine 14, and the rear of the cab is disposed approximately at the same position along the length of the tractor as the front of each rear wheel 40. The floor of the cab 27 slopes slightly to the rear with respect to the top of the frame 1.

The overall effective width of the drivable roller 59 is - as indicated in Figure 2 - larger than the distance between the inner front and rear wheels 35. The end faces of the effective part of the drivable roller 59 may extend up to planes parallel to the plane 2 and containing the centrelines of the wheel carriers 12.

The pivotal shafts 48 about which the roller 59 is pivotable are parallel to, and approximately midway between, the rotary axes of the front and rear wheels.

Two hydraulic rams 87 are pivotally connected with the underside of the beam 29 at equal distances from the plane 2. Each ram 87 can turn about a pivotal shaft 88 normal to the plane 2. The lower end of the piston rod of each hydraulic ram 87 is pivotally mounted on the top face of the supporting beam 50 of the roller 59 by means of a pivotal shaft 89 parallel to the pivotal shaft 88. The two hydraulic rams 87 can be actuated form the cab 27.

During operation, the drivable front wheels 35 and the drivable rear wheels 40 are driven as follows.

The rear output shaft of the driving engine 14 drives the drive shafts in the carrying tubes 23 and 24 through the change-speed gear of the assembly 17 (which can be actuated from the cab and which may be a hydrostatic torque converter or a manually operated gear box) and the differential gear of the assembly 17. The drive shafts in the carrying tubes 23 and 24 constitute input shafts of the differentials 41.The output shafts 42 drive the input shafts of the gear wheel transmissions 32 through the intermediate shafts 45. The gear wheel transmissions 32 comprise bevel gear wheels and constitute an orthogonal transmission, the output shafts of which are coaxial with the king pins 33. These downwardly directed output shafts drive the front wheels 35 on both sides of the housings 34 through the orthogonal transmissions in those housings.

The rear output shafts 43 of the differential gears 41 drive the input shafts 37 of the gear wheel transmissions 36 through the intermediate shafts 46.

The output shafts in the tubes 38 drive the pairs of rear wheels 40 located on both sides of the gear boxes 39. In this way advantageous drive through bends and also a compact drive from one shaft which branches to the front and rear wheels are obtained. Owing to the differential gear in the assembly 17 the driven front and rear wheels on one side of the plane 2 may, on an average, have a speed of rotation differing from that on the other side 2, whilst each of the two differential gears 41 ensure that the driven front wheels 35 may have a speed of rotation differing from that of the driven rear wheels on the same side of the plane 2.The latter feature is particularly important when the centre of the turn of the tractor as a whole with respect to the ground is nearer the rear wheels than the front wheels on the same side of the plane 2, which often occurs when negotiating a sharp bend. Then, of course, a difference in the average speed of rotation of the front and rear wheels on one side of the plane 2 occurs with respect to that of the wheels on the other side of the plane 2. Under heavy soil conditions it is often a disadvantage that the propelling force exerted by the tractor on the ground is limited by the behaviour of the wheels relative to the ground. Then the proportion of the maximum available engine power or driving torque applied to the wheels must remain low so that, despite the higher available engine power, no higher propelling force can be obtained for the attached implements (for example a plough).

By providing the drivable roller 59 it is possible to ensure that at least part of the further engine power available for one or more power take-off shafts can provide an additional propelling force because the spikes 54 of the roller 59 can penetrate deep into the ground and can thus exert an appreciable traction force on the tractor and on the implements coupled to it, which force is added to the driving torque of the (slipping) wheels. Because the power take-off shaft power of the tractor is utilized, the desired propelling force is less dependent, if at all, on the condition of the soil as compared with the force that can be exerted through the wheels.The drivable roller 59 is coupled to the frame 1 by quickly releasable members such as the easily removable pivotal shafts 48 with the frame and by means of the quickly releasable pivotal shafts 89 with the piston rods of the draulic rams 87. The input shaft 56 of the gear wheel transmission 55 is coupled through the intermediate shaft 81 with the output shaft 19, which can be driven with a speed of rotation proportional to that of the wheels 35 and 40. The transmission ratio of the gear wheel transmission 55 is such that the effective peripheral speed of the roller 59 is equal to that of the wheels 35 and 40 (assuming no slip) or slightly higher. From the cab 27 the driver can press the roller 59 into the ground by actuating the hydraulic rams 87, the rollerturning downwards about the pivotal shafts 48.If the roller drive is not required, the driver can lift the roller into an inoperative position above the ground.

The front and rear power take-off shafts 75 and 77 can be driven at a speed proportional to that of the engine and they serve to drive implements attached to the front and rear lifting devices respectively. The front power take-off shaft 74 and the rear power take-off shaft 79, which can be driven at speeds proportional to the travel speed, can drive implements hitched to the front and rear three-point lifting devices respectively by means of propelling members comparable to the roller 59 but having, for example, the form of a soil cultivator. In this way it is possible to utilize the power available at the power take-off shafts for obtaining a still higher additional traction force than that of the roller 59.

During operation the four rear wheels 40 and the transverse beam 10 can turn together as a unit about the centreline of the tube 6 with respect to the tubes 3, which support the rest of the tractor including the front wheels 35. This ensures that, even on uneven soil, all of the wheels constantly have a uniform ground pressure.

The distribution of the tractor weight is such that about two thirds of the weight is supported by the front wheels and one third by the rear wheels. Since the tractor has eight wheels preferably provided with low-pressure tyres having a broad contact surface on the ground, the tractor weight is distributed over a large surface so that the pressure exerted on the ground by the wheels is relatively low and consequently deterioration of the ground structure is avoided for a major part. When it is not required to use eight wheels, the outermost front wheels 35 and the inner rear wheels 40 or the inner front wheels 35 and the outermost rear wheels 40 can be removed so that the remaining wheels do not run in the same tracks as each other. This again serves to minimize deterioration of the soil structure in each track.

The width of the cab 27 is about equal to the distance between the outer side walls of the inner front wheels. The floor of the cab, which is complete ly flat, is higher than the top of the rear wheels and disposed at least partly above the top of the housing of the assembly 17 of the change-speed and differentrial gears.

The embodiment of Figure 5 shows in principle the same design of tractor. The front and rear wheels have a diameter of about 100 cms. In the embodi ment of Figure 5, the obtuse angle between the wheel carriers 12 and the tubes 3 and 6 is larger than in the preceding emboidment so that a separate gear wheel transmission 36 between the intermediate shafts 46 and the gear boxes 39 is not required, its function being performed bythe rear universal joints of the intermediate shafts 46.

Whilst various features of the tractors that have been described, and that are illustrated in the drawings, will be set forth in the following claims as inventive features, it is to be noted that the invention is not necessarily limited to these features and that it encompasses all of the features that have been describd both individually and in various combinations.

Claims

1. A motor vehicle comprising front and rear wheels, a respective differential drive being provided between a front wheel and a rear wheel on each side of the vehicle.

2. A motor vehicle as claimed in claim 1, in which each differential drive is situated at one end of a drivable shaft assembly extending transversely of the normal intended direction of operative travel of the vehicle.

3. A motor vehicle as claimed in claim 1 or 2, in which at least one front wheel and at least one rear wheel disposed on one side of the tractor can be driven from the differential drive.

4. A motor vehicle as claimed in claim 3, in which the front and rear wheels on each side of the vehicle can be driven by means of an intermediate shaft provided with universal joints fom the respective differential drive.

5. A motor vehicle as claimed in claim 4, in which the intermediate shaft is telescopically extensible.

6. A motor vehicle as claimed in claim 4 or 5, in which the intermediate shafts lie in a vertical plane which is substantially parallel to the normal intended direction of operative travel of the vehicle.

7. A motor vehicle as claimed in any one of claims 4 to 6, in which four intermediate shafts are provided for driving the front and rear wheels.

8. A motor vehicle as claimed in any one of the preceding claims, in which the two differential drives are drivable from a third differential drive.

9. A motor vehicle as claimed in any one of the preceding claims, in which at least three differential drives are provided in a common shaft assembly extending transversely of the normal intended direction of operative travel of the vehicle.

10. A motor vehicle comprising front and rear wheels and at least three differential drives provided in a common shaft assembly extending transversely of the normal intended direction of operative travel of the vehicle.

11. A motor vehicle as claimed in claim 9 or 10, in which the common shaft assembly is situated between the rotary axes of the front and rear wheels.

12. A motor vehicle as claimed in claim 2 or in any one of claims 9 to 11, in which the shaft assembly has a stationary position relative to the tractor frame.

13. A motor vehicle as claimed in claim 2 or in any one of claims 9 to 12, in which the shaft assembly is drivable at a speed proportional to the travelling speed of the vehicle.

14. A motor vehicle as claimed in any one of the preceding claims, in which the rear wheels are pivotable about an axis extending in the normal intended direction of operative travel of the vehicle relatively to a change-speed gear box coupled with a driving engine of the vehicle.

15. A motor vehicle as claimed in any one of the preceding claims, in which a gear box coupled with a driving engine of the vehicle comprises a continuously variable change-speed device.

16. A motor vehicle as claimed in any one of claims 1 to 14, in which a gear box coupled with a driving engine of the vehicle comprises a stepwise variable change-speed device.

17. A motor vehicle as claimed in any one of claims 14 to 16, in which the housing of the gear box comprises a differential drive by means of which both a front wheel and a rear wheel can be driven.

18. A motor vehicle as claimed in any one of the preceding claims, in which the driving engine is disposed in front of the change-speed gear box and is disposed mainly above the front wheels.

19. A motor vehicle as claimed in any one of the preceding claims, in which a drivable groundengaging roller is disposed between a front wheel and a rear wheel.

20. A motor vehicle comprising front and rear wheels, a drivable ground-engagable roller being provided between the front and rear wheels.

21. A motor vehicle as claimed in claim 19 or 20, in which the roller is provided with sharp extensions for penetrating the soil.

22. A motor vehicle as claimed in any one of claims 19 to 21, in which the roller is drivable about an axis extending transversely of the normal intended direction of operative travel of the vehicle.

23. A motor vehicle as claimed in any one of claims 19 to 22, in which the roller is hydraulically displaceable upwardly and downwardly relatively to the remainder of the vehicle.

24. A motor vehicle as claimed in any one of claims 19 to 23, in which the roller is releasably connnected to a further part of the vehicle by means of a quick-action connector, for example, a pin.

25. A motor vehicle as claimed in claim 23 when appendant to claim 24, in which the roller is releasably connected to a hydraulic ram by means of a quick-action connector, for example a pin.

26. A motor vehicle as claimed in any one of claims 19 to 25, in which the effective width of the roller is larger than the distance between the most adjacent rear wheels arranged on opposite sides of the vertical longitudinal central plane of the vehicle.

27. A motor vehicle as claimed in any one of claims 19 to 26, in which the roller is disposed below the tractor frame and near the rear wheels.

28. A motor vehicle as claimed in any one of claims 19 to 27, in which the roller is pivotable about a pivotal axis disposed approximately midway along the length of the vehicle.

29. A motor vehicle as claimed in any one of claims 19 to 28, in which the roller is drivable by means of a power take-off shaft of the vehicle, which can be driven at a speed proportional to the travelling speed of the vehicle.

30. A motor vehicle as claimed in any one of the preceding claims, in which the diameter of a front wheel and that of a rear wheel is about 100 cms and in which about two thirds of the vehicle weight is supported by the front wheels.

31. A motor vehicle comprising front and rear wheels, the diameter of a front wheel and of a rear wheel being about 100 cms and about two thirds of the vehicle weight being supported by the front wheels.

32. A motor vehicle as claimed in any one of the preceding claims, in which four front wheels and four rear wheels are provided.

33. A motor vehicle as claimed in any one of the preceding claims, in which the width of a wheel is about 40 cms.

34. A motor vehicle as claimed in any one of the preceding claims, in which all of the wheels of the vehicle are drivable.

35. A motor vehicle as claimed in any one of the preceding claims, in which steerable wheels are provided which can be turned in at least one direction through approximately 90 .

36. A motor vehicle as claimed in claim 35, in which the steerable wheels can be turned by means of a steering plate which is located to the rear of the steerable wheels.

37. A motor vehicle as claimed in claim 36, in which the steering plate is connected with each of the steerable wheels by a steering rod which extends approximately in the normal intended direction of operative travel of the vehicle.

38. A motor vehicle as claimed in any one of the preceding claims, in which a driver's cab is provided, the floor of which is flat, is located at a higher level than the top of each rear wheel, and is disposed above a change-speed gear box of the vehicle.

39. A motor vehicle comprising front and rear wheels and a driver's cab, the floor of which is flat, is located at a higher level than the tops of the rear wheels, and is disposed above a gear box of the vehicle.

40. A motor vehicle as claimed in claim 38 or 39, in which the cab floor slopes slightly downwards from front to rear.

41. A motor vehicle as claimed in any one of the preceding claims, in which a side plate is provided along at least one side of the cab to serve as a foot board and a mudguard.

42. A motor vehicle as claimed in any one of the preceding claims, in which the vehicle comprises four wheels having a track width of about 250 cms and four further wheels having a track width of about 150 cms.

43. A motor vehicle comprising front and rear wheels, four of the wheels having a track width of about 250 cms and four others of the wheels having a track width of about 150 cms.

44. A motor vehicle as claimed in any one of the preceding claims, in which at least one power take-off shaft is provided which is drivable at a speed proportional to the travel speed of the vehicle and in which at least one power take-off shaft is provided which is drivable at a speed proportional to the engine speed.

45. A motor vehicle as claimed in claim 44, in which the power take-off shafts are arranged both at the front and the rear of the vehicle.

46. A motor vehicle as claimed in any one of the preceding claims, in which a lifting device is provided at the rear and implement attachment facilities are provided at the front.

47. A motor vehicle as claimed in any one of the preceding claims, in which a three-point lifting device is provided, the top rod of which comprises a hydraulic ram.

48. A motor vehicle as claimed in any one of the preceding claims, in which the power of the driving engine is aout 60 KW.

49. A motor vehicle as claimed in any one of the preceding claims, which is an agricultural vehicle.

50. A motor vehicle as claimed in claim 49, which is a tractor.

51. A tractor substantially as described herein with reference to, and as shown in, the accompanying drawings.