GB2135641A

GB2135641A - Motor vehicles such as tractors

Info

Publication number: GB2135641A
Application number: GB08405017A
Authority: GB
Inventors: Der Lely Cornelis Van
Original assignee: Texas Industries Inc
Current assignee: Texas Industries Inc
Priority date: 1983-02-28
Filing date: 1984-02-27
Publication date: 1984-09-05
Also published as: DE3406914A1; FR2541647B1; NL8300732A; GB2135641B; FR2541647A1; JPS6018462A; GB8616628D0; GB2177663B; GB2177663A; IT1173382B; IT8419803A0; GB8405017D0

Abstract

A tractor has, on each axle, inboard and outboard wheels (41, 42, 57, 58), which are provided with pneumatic tyres. The tyres of the inboard wheels (41, 58) are narrower than those of the outboard wheels (42, 57) and have a higher inflation pressure. The track width of the inboard wheels is approximately 150 cms. The provision of eight wheels as illustrated reduces pressure of the tractor on the ground when drawing e.g. a plough or harrow. The four outer wheels 42, 57 can be removed to enable the tractor to be used with the narrower tyre wheels 41, 58 in row cultures. The tractor is provided at the front and back with a lifting device 45, 72. Front and rear power take off shafts 26, 22 are drivable through a change-speed gearbox 18. The tractor wheels are driven by hydraulic motors 39 supplied by pumps 14, 15 driven by an engine 6. <IMAGE>

Description

SPECIFICATION Motor vehicles such as tractors This invention relates to motor vehicles and particularly, but not exclusively, to agricultural tractors.

Existing tractors have the disadvantage that there is no possibility of adapting the tractor both to work in a row cultures and on the field when drawing, for example, ploughs and harrows.

According to a first aspect of the present invention there is provided a motor vehicle comprising a frame, a power take-off shaft and a lifting device, the vehicle being provided with a wheel assembly comprising two wheels mounted on a common axle, these wheels having pneumatic tyres, one of which is narrower than the other.

Deterioration of the soil structure in the wheel track of the tractor is less significant in row cultures than in working on the field, where it is highly important to minimize the ground pressure of the tractor wheels with regard to the future growth of plants. By removing the wheels with the broader pneumatic tyres, the tractor can be used with the narrower pneumatic tyres with a narrow wheel track in row cultures. When the tractor is to be used on the field, the wheels with the broader pneumatic tyres can be used with the wheels with the narrower tyres so that a broad wheel track and a large contact surface between the wheels and the ground are obtained, it being thus ensured that the ground pressure is low. At least for the wheels having the broader tyres, lowpressure pneumatic tyres can be used so that the contact surface of the tractor with the ground is appreciably enlarged.

According to a second aspect of the present invention there is provided a motor vehicle comprising a frame, a power take-off shaft and a lifting device, the vehicle further comprising two narrow wheels disposed one on each side of the vehicle with a track width of about 1 50 cms.

According to a third aspect of the present invention there is provided a motor vehicle comprising a frame, a power take-off shaft and a lifting device, a hydraulic pump being provided at the front end of the vehicle for driving a wheel or wheels of the vehicle.

According to a fourth aspect of the present invention, there is provided a motor vehicle comprising a frame, a power take-off shaft disposed at the front of the vehicle and a lifting device, the power take-off shaft being drivable at more than one speed.

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: Figure 3 is a front view of the tractor of Figures 1 and 2; Figure 4 is a fragmentary view taken in the direction of the arrow IV in Figure 1; Figure 5 is a view taken in the direction of the arrow V in Figure 4; and Figure 6 corresponds to Figure 4 but shows a different configuration.

The tractor shown in the Figures comprises a frame 1 having a central hollow frame beam 2, the centreline of which lies in the vertical longitudinal central plane 3 of the tractor. The side walls at the front of the frame beam 2 are rigidly secured to two upwardly extending plates 4 which slope forwardly from bottom to top and are symmetrical about the plane 3. These plates are parallel to the plane 3 and at their top ends they rigidly embrace a frame beam 5 which projects forwardly away from them. The length of the frame beam 5 is about 25 to 30% of the length of the frame beam 2 and the beam is substantially horizontal and parallel to the frame beam 2. The plates 4 and the frame beam 5 constitute at the front of the tractor an extension of the frame beam 2 situated further from the ground than the beam 2 itself, thus providing a frame having a "goose neck" configuration.

At a relatively small distance above the top of the frame beam 2 and near the rear edges of the plates 4 there is a driving engine 6 of the tractor which is fastened to the frame beam 2. The engine 6 is preferably a Diesel engine having a power of about 60 kw. The engine 6 is disposed so that its crank shaft lies approximately in the plane 3. The crank shaft of the engine 6 protrudes both to the front and to the rear of the engine.

The end of the crank shaft emerging from the front of the engine is provided with a pulley 7, which is drivably connected by means of a chain or a belt with a pulley 8 disposed above the pulley 7 for driving a fan of a radiator 9 mounted in front of the engine 6, with respect to the normal intended direction of travel A of the tractor. The front end of the crank shaft of the engine 6 projects forwardly beyond the pulley 7, where it is provided with axial splines to engage an auxiliary shaft 10 provided with two universal joints.The front end of the auxiliary shaft 10 is coupled with an input shaft of a gear box 1 liThe auxiliary shaft 10 drives a gear wheel 12, mounted near the bottom of the gear box 1 which is drivably in mesh with two gear wheels 13, having the same pitch diameter as each other, disposed one on each side of the plane 3 and obliquely above the gear wheel 12. The rotary shafts of the two gear wheels 1 3 project forwardly through the front wall of the gear box 11 and constitute drive shafts for two hydraulic pumps 14 and 1 5 disposed side by side symmetrically about the plane 3. The pumps 14 and 15, as shown in the side elevation of Figure 1, are at the front of the tractor, in front of a vertical plane containing the rotary axes of front wheels 1 6 to be described later in this description.The gear box 11 rests on the top of the frame beam 6 and the pumps 14 and 15 are a short distance above the top of the frame beam 5.

The end of the crank shaft emerging from the rear of the engine 6 is coupled by an auxiliary shaft 1 7 provided with two universal joints with an input shaft of a change-speed gear box 18, which is supported, by a bearing housing 19, on the top of the frame beam 2 at a position about 25 to 35% of the way along the frame beam 2 from its rear end. The change-speed gear box 18 and the auxiliary shaft 17 are disposed symmetrically about the plane 3. On the rear wall of the change-speed gear box 1 8 is mounted a gear box 20 comprising a plurality of meshing gear wheels which are disposed vertically one below another and whose pitch circle diameter increases downwardly away from the output shaft of the gear box 18.The lowermost gear wheel of the gear box 20 has a rearwardly projecting output shaft which is coupled by a telescopic auxiliary shaft 21, provided with two universal joints, with a power take-off shaft 22 at the rear of the tractor.

An output shaft of the gear box 20 projects forwardly with respect to the direction A and corresponds to the lowermost gear wheel; this shaft is supported in the bearing housing 1 9 and extends forwardly beyond the bearing housing to be connected with an auxiliary shaft 23 having two universal joints. Like the power take-off shaft 21, the shaft 23 is symmetrical about the plane 3.

The auxiliary shaft 23 extends forwardly from the bearing housing 19 to a bearing 24 near the rear of the engine 6. The shaft 23 is coupled near the bearing 24 with a shaft 25 which is supported by the bearing 24 near the front of the tractor and projects forwardly to a position disposed, as viewed from the side, below the pumps 14 and 1 5, to form a front power take-off shaft 26. The shaft 25, the centre line of which lies in the plane 3, extends below the underside of the engine 6, above the top of the frame beam 2 and between the two plates 4. A substantially vertical plate 27 is welded to the front end of the frame beam 5 and extends at right angles to the plane 3, terminating some distance below the underside of the frame beam 5. The lower edge of the plate 27 is approximately the same height above the ground as the centreline of the frame beam 2.To the rear face of the plate 27 is welded a hollow beam 28, the centreline of which is at right angles to the plane 3 and which serves as a front axle.

The vertical rear face of the beam 28 is extended upwardly near the plane 3 in the form of a plate 29 parallel to the plate 27. The shaft 25 is a short distance above the top of the front axle 28 and is journalled in the plates 27 and 29.

A carrier 30 for rear wheels 31 of the tractor is pivotably journalled in the rear end of the frame beam 2 so as to turn about a horizontal pivotal axis lying in the plane 3 and coinciding substantially with the centreline of the frame beam 2. For this purpose the rear part 32 of the frame beam 2 receives a shaft 33 which projects for some distance from the rear end 32. This rearwardly projecting end of the shaft 33 is surrounded by a sleeve 34, the centreline of which coincides with that of the shaft 33 and which bears axially on the shaft 33 by means of end partitions. Two hollow beams 35 are welded to the two sides of the sleeve 34. The beams 35 are symmetrical with respect to the plane 3 in the position shown and are outwardly and rearwardly inclined from the front end of the sleeve 34.The two beams 35 are rigidly interconnected approximately midway along their length by a hollow beam 36 extending at right angles to the plane 3 in the position shown. The beam 36 and parts of the beams 35 form a triangular construction, as viewed on plan. The top of the beam 36 is provided midway along the length of the beam with a bearing 37 for supporting the auxiliary shaft 21 and the power take-off shaft 22.

Sleeves 38 are welded to the outermost rear ends of the two beams 35. The centre line of each of the sleeves 38 being, in the position shown, at right angles to the plane 3. The centrelines of the two sleeves 38 are aligned with each other. On the outer end of each sleeve 38 is fastened a hydraulic motor 39. The output shafts of the motors 39 are in line with each other and are at right angles to the plane 3. Each of the two hydraulic motors 39 is surrounded by a supporting element 40, which has (see Figure 2) the form of a truncated cone which tapers towards the outboard side of the tractor. The centreline of the cone coincides with that of the motors 39 and the sleeves 38.The larger end of the supporting element, which is directed towards the plane 3, is fastened to the rim of an inner rear wheel 41, whereas the smaller end of the supporting element 40 located on the outboard side can be fastened to the rim of an outer rear wheel 42. Each supporting element 40 is rigidly secured to the output shaft of the associated hydraulic motor 39. The two motors 39 of the rear wheels 41 can be driven by one of the pumps 14 or 1 5. Both the hydraulic pumps 14 and 1 5 and the hydrostatic motors 39 may be provided with means for controlling the fluid displacement to vary the speed of rotation of the output shaft of the motor 39 and hence of the wheels 16, 31.

This control of the fluid displacement of the motors 39 and the pumps 14, 15 can be performed from the driver's seat. The diameter of all of the wheels of the tractor is about 125 cms.

As can be seen in Figure 2, the inner wheels 41 are narrower than the outer wheels 42. Both the wheels 41 and 42 are provided with pneumatic tyres. The width of the pneumatic tyre of each inner rear wheel 41 is about 35 to 40 cms and the width of the pneumatic tyre of each outer rear wheel 42 is about 50 cms.

The inner rear wheels 41 are preferably provided with high-pressure tyres, whereas the outer rear wheels 42 are equipped with lowpressure tyres, which has the advantage that their ground contact surface is relatively large.

The wheel track of the two narrow inner rear wheels 41 is about 1 50 cms. The overall tyre width of a set of rear wheels 3 is, therefore, about 90 cms.

The front wheels 1 6 are designed in the same manner as the rear wheels 31 and they run in the same tracks. This means that the tractor stands on the ground with a total tyre width of 4x90=360 cms. For effective use of a tractor an overall tyre width of at least about 320 cms is considered to be necessary. The total tyre width of the tractor, which is about 360 cms, is therefore larger than the overall transport width of the tractor, which is about 300 cms.

On both sides of the plane 3, and a short distance from it, vertical supporting plates 43 are symmetrically welded to the tops of the beams 35 and 36, these plates extending upwardly and rearwardly from the beams 35, 36. The supporting plates 43 provide a bearing for a top arm 44 of a three-point lifting device 45 at the rear. Lugs 46 are fastened to the rear of the beam 36 symmetrically about the plane 3 to hold aligned pivotal shafts, about which lower lifting arms 47 of the three-point lifting device 45 are pivotable. The supporting plates 43 also support a sleeve 48 which extends parallel to the beam 36 and is symmetrical to the supporting plates 43.

The sleeve 48 projects from the outer sides of the supporting plates. The length of the sleeve 48 approximately corresponds to the distance between the rear ends of the lower lifting arms 47. At both ends the sleeve 48 carries a shaft about which a rearwardly extending arm 49 is pivotable, the arm 49 extending to the rear away from the sleeve 48. Each of the two arms 49 is provided near its rear end with a pivotal shaft about which a lifting arm 50 is pivotable, the lower end of which is pivotally connected with the lifting arm 47 on the same side of the tractor. The piston rod of a hydraulic cylinder 51 is pivotally connected to each of the two arms 49 at a position between its ends. The other end of the cylinder 51 is pivotally journalled in lugs 52 fastened to the rear wall of the beam 36.Thus the three-point lifting device 45 comprises for each arm 47 a separate hydraulic cylinder which can be actuated from the driver's seat and which can turn the associated lifting arm 47 of the lifting device by turning the arm 49 in its bearing in the supporting plates 43 by means of the associated arm 50. The two hydraulic cylinders 51 are preferably double-acting cylinders so that each lower lifting arm 47 can be forced both upwards and downwards.

As shown in the plan view of Figure 2, on one side of the plane 3 and on one side of the frame beam 2 there is a fuel tank 53 which is situated behind the engine 6 and supported by supports (not shown) on the frame beam 2. On the other side of the frame beam 2 there is a tank 54 for hydraulic fluid. The two tanks 53 and 54 extend approximately to the same vertical level as the underside of the frame beam 2. The distance between the underside of the frame beam 2 and the ground is about 60 cms.

The construction of the suspension and the steering means for the two pairs of front wheels 1 6 is shown in Figures 4 to 6. Both ends of the front axle beam 28 have fastened to them pivotal shafts 55, which serve as king pins. Each king pin 55 extends upwardly and may be slightly inclined to the rear from bottom to top. A fork-like fastening piece 56, which grips around the swivel shaft 55, supports a sleeve 38 for pivotal movement about the king pin 55. A hydrostatic motor 39 is rigidly secured to the outboard side of the sleeve 38. The output shaft of the motor 39 is fastened to a supporting element 40, which is in the form of a truncated cone and carries an outer front wheel 57 at its outboard end and an inner front wheel 58 at its inboard end.The dimensions of the front wheels 57, 58, the kind of pneumatic tyres and the relative arrangement of the front wheels 57 and 58 on both sides of the plane 3 are fully analogous to those of the rear wheels 41 and 42. Therefore, the outer front wheels 57 will run in the same tracks as the outer rear wheels 42 and the inner front wheels 58 will run in the same tracks as the inner rear wheels 41. With the front wheels the sleeves 38 are provided at the front with horizontal supports 59, which are forwardly and inwardly inclined when the front wheels are in the straight-ahead position.

At the end of each support 59 away from its sleeve 38 there is an upwardly extending pivotal shaft 60 which is parallel to the king pin 55 and about which a belt-crank 61 is pivotable. In the straight-ahead position of the front wheels 1 6 as shown in Figure 4, one arm of the bell-crank 61 is inclined inwardly and rearwardly away from the pivotal shaft 60, and the other arm extends forwardly and slightly inwardly, with respect to the direction A. The rearwardly and inwardly directed arm of the bell-crank 61 is rigidly connected to one end of a rod 62, the other end of which is pivotally connected by a pivotal shaft 62A, extending parallel to the pivotal shaft 60, to a substantially horizontal steering plate 63. In the straight-ahead position of the front wheels 16, the steering plate 63 is symmetrical to the plane 3.It has the shape of an isosceles triangle, the vertex of which is ahead of the pivotal shaft 60 with respect to the direction A.

Near the vertex the triangular steering plate 63 is pivotable about a pivotal shaft 64 which is parallel to the pivotal shaft 60 and is connected with the front free end of a substantially horizontal supporting plate 65, which is rigidly secured at its rear edge to the plate 27. The steering plate 63 is some distance below the plate 65 and between the two, the pivotal shaft 64, which is pivotable with respect to the supporting plate 65, has fastened to it a second steering plate 66 which also has the shape of an isosceles triangle. The second steering plate 66 extends to the rear away from the pivotal shaft 64 like the steering plate 63. Figure 6 shows that the steering plate 66 has the same shape as the steering plate 63, but the length of the two equal sides is about half the length of those of the steering plate 63. The steering plates 63 and 66 constitute a coupling member for the parts of the steering mechanism of the front wheels on both sides of the plane 3. Near the corners away from the vertex of the steering plate 66 there are pivotal shafts 67 which extend parallel to the pivotal shaft 60. The end of a hydraulic cylinder 68 is pivotable about each of the pivotal shafts 67. The end of the piston rod of the hydraulic cylinder 68 is pivotally connected to the forwardly protruding arm of the bell-crank 61 by a pivotable shaft 69 which also extends parallel to the pivotal shaft 60. As shown in Figure 4, in the straightahead position of the front wheels 1 6 the construction is fully symmetrical about the vertical longitudinal plane 3 of the tractor.

Steering of the front wheels 1 6 is performed by supplying hydraulic fluid to one of the doubleacting hydraulic cylinders 68 so that its piston rod is extended, while the other hydraulic cylinder is not energized and its piston rod is hydraulically blocked. In a position once fixed for the front wheels at least one of the cylinders 68 is hydraulically blocked. Figure 6 shows such a position, in which the front wheels 1 6 located on both sides of the tractor have turned about the associated king pins 55. Owing to the extension of one of the hydraulic cylinders 68 the steering plates 63 and 66, which are fixed together, are forced towards the side on which the extended hydraulic cylinder 68 is situated. Owing to the fixed length of the rod 62 the support 59 turns outwardly (to the left in Figure 6).The assembly comprising the sleeve 38, the hydraulic motor 39, the supporting element 40 and the associated front wheels 1 6 then turns out of the position shown in Figure 4 suitable for the straight-ahead travel through a maximum angle of at least about 750 in one direction and at least about 600 in the other direction so that the overall angle of turn of a front wheel is larger than 900; with the proportions of the illustrated embodiment the angle is at least about 1350. The quadrangular construction of the pivotal shafts 55, 60, 62A and 64 is fixed in any position of the front wheels with respect to the front axle 28 by the length of the cylinder 68 which can be hydraulically blocked in the chosed position of deflection.The determination of the shape of the quadrangular construction by means of the length of the cylinder 68 is thus obtained by the action of the triangular construction 69, 62A, 67, bearing in mind that the position of the pivotal shaft 64 with respect to the front axle 28 is fixed.

Therefore, by means of this steering mechanism of the front wheels 1 6 very large steering turns can be obtained, whereas nevertheless the axes of both front wheels invariably intersect approximately on the common wheel axis of the rear wheels 31. As a result of this construction, the tractor is very manoeuverable, which is epecially important on the headlands of a field to be worked or of a row culture so that little space is required at th.e headlands for performing bends, leaving a larger part of the available surface for cultivation.

Forwardly extending vertical plates 70 are welded to the front faces of the plates 27 and to the top face of the plate 65, these plates 70 being disposed symmetrically about the plane 3 and serving to receive a front lifting device 71. The lower lifting arms 72 of the lifting device 71 are pivotable together about a pivotal shaft 73 which extends at right angles to the plane 3 and is located, as shown in the side elevation of Figure 1, in front of the front axle 28, approximately at the same vertical level as the axes of the front wheels and substantially midway along a radius of the front wheels. From the pivotal shaft 73 the rigidly interconnected, lower lifting arms 73 are symmetrically inclined in a forward and outward direction with respect to the direction A on both sides of the plane 3.The two lower lifting arms 72 are tubular and are rigidly connected with one another near the pivotal shaft 73. As shown in the plan view of Figure 2, the lower lifting arms 72 have the shape of a V. On the sides facing the tractor the arms 72 have a fairly pointed end, in which the pivotal shaft 73 is journalled.

Approximately midway along their lengths, the arms 72 are rigidly interconnected by a tube 74 which is at right angles to the plane 3.

Approximately midway between the plane of symmetry 3 and each of the fastening points of the tube 73 to the arms 72, the top of the tube 73 is provided with fastening members formed by aligned pivotal shafts 75 which are normal to the plane 3, about which the ends of the piston rods of hydraulic lifting cylinders 76 are pivotable. The two hydraulic lifting cylinders 76 are symmetrically disposed on both sides of the plane 3. The other ends of the hydraulic lifting cylinders are fastened to the supporting plates 70 at their top edges by pivotal shafts 77 which are also normal to the plane 3 and are aligned with one another. At the front and top edges of the plates 70 a top rod 79 of the three-point lifting device 71 is pivotally fastened by a pivotal shaft 78 extending parallel to the pivotal shafts 77.The lower lifting arms 72 and the top. rod 79 are provided at their free ends with hook-like coupling members which open upwardly and downwardly respectively for attaching machines in the same manner as described for the rear lifting device 45.

These hook-like coupling members are formed by upwardly extending steel plates which are parallel to the direction A and are welded to the ends of the tubular arms 72.

The overall weight of the tractor is about 2500 kgs and at the coupling points there is a lifting power of about 4000 kgs for each lifting device; the overall length of the tractor is about 540 cms.

The driver's seat is situated in a cab 80 which extends-as shown in Figure 1-from the region above the leading part of the rear wheels up to approximately the rear of the front wheels. The engine 6, located between the axles of the front and rear wheels extends partly into the cab 80, as does the change-speed gear box 18 provided on one side with a control lever. All control members for the drive, the steering, the power take-off shafts and the lifting devices can be adjusted from the cab.

During operation the engine 6 drives the hydraulic pumps 14 and 15 through the auxiliary shaft 17 and the gear wheels 12 and 13, these pumps being coupled by hydraulic lines (not shown) with the four hydraulic motors 39 of the front and rear wheels. The fluid displacements of the pumps and the motors can be controlled from the cab. Through the auxiliary shaft 1 7 the engine 6 drives the change-speed gear box 18, which drives the rearwardly and forwardly extending auxiliary shafts 21 and 23 through the gear wheel systems in the gear box 20. The telescopic auxiliary shaft 21 drives the rear power take-off shaft 22. The auxiliary shaft 23 drives the shaft 25 and hence the front power take-off shaft 26.

The driver can control from his seat the transmission ratio between the auxiliary shaft 1 7 and the power take-off shafts 21, 23 by means of the change-speed gear box 18 provided with its control lever. The change-speed gear box 18, which may be designed like a simple, manual automobile gear box of an automobile, enables the setting of speeds of rotation of the power take-off shafts 22 and 26 of 1000, 770, 540 and 450 rev/min so as to obtain a great variety of speeds of one of the power take-off shafts relative to the travelling speed of the tractor, which is continuously variable.

The tractor is designed so that on uneven land all wheels have their maximum ground pressure.

For this purpose the rear wheels 31 arranged on both sides of the tractor on the beams 35 associated with the rear part of the frame are pivotable together about the horizontal pivotal shaft 33 extending in the direction A and fastened at the front to the front part of the frame, in particular, to the frame beam 2.

By the separate actuation of the lower lifting arms 47 of the rear lifting device 45 by the associated hydraulic cylinder 51, a high lifting power can be achieved and it is also possible to adjust accurately the height of one of the lifting arms 47 with respect to zve other lifting arm 47 from the cab 80, for example for setting a fertilizer dispenser in a horizontal position when the tractor is driving on slightly sloping land. In order to obtain a high lifting power of the lower lifting arms 72 of the front lifting device 71 two hydraulic cylinders 76 are provided so that the lifting power is transferred to the tractor on both sides of the plane 3.

The location of the engine 6 near the front wheels 1 6 and the disposition of the hydraulic pumps 14 and 1 5 above and in front of the front axle 28 provide a forward location of the centre of gravity of the tractor so that, when only the rear lifting device 45 is loaded by an implement (which will be the more usual case), the front wheels still exert sufficient force on the ground to transfer the driving torque to the ground. The outermost wheels 42 and 57 of the rear and front wheels respectively are releasably fastened to the supporting elements 40. When these outer wheels are removed, the tractor bears solely on the four inner wheels 41 and 58, which are provided with high-pressure tyres. In this case the tractor is appreciably narrower overall and the relatively narrow wheels 41, 58 permit of using the tractor in row cultures.When the tractor has to perform field work, for example harrowing, the outer wheels 42 and 57 are fitted so that at each corner the tractor is supported by a total tyre width of about 90 cms, the overall tyre width of the tractor being thus 360 cms, which exceeds the transport width of the tractor. Since the outer wheels 42, 57 are provided with low-pressure tyres, the ground contact surface of these tyres is comparatively large so that a low ground pressure is ensured which prevents deterioration of the soil structure. In this case the air pressure in the tyres of the wheels 41 and 58 may be slightly reduced so that also these tyres have a large ground contact surface.

Whilst various features of the tractor 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 described both individually and in various combinations.

Claims

1. A motor vehicle comprising a frame, a power take-off shaft and a lifting device, the vehicle being provided with a wheel assembly comprising two wheels mounted on a common axle, these wheels having pneumatic tyres, one of which is narrower than the other.

2. A motor vehicle as claimed in claim 1, in which a said wheel assembly is provided on both sides of the vehicle.

3. A motor vehicle as claimed in claim 1 or 2, in which a said wheel assembly is provided both on a front axle and on a rear axle of the vehicle.

4. A motor vehicle as claimed in any one of the preceding claims, in which the wheel having the narrower pneumatic tyre is arranged inboard of the wheel having the broader pneumatic tyre.

5. A motor vehicle as claimed in any one of the preceding claims, in which the broader pneumatic tyre is a low pressure tyre.

6. A motor vehicle as claimed in any one of the preceding claims, in which the narrower pneumatic tyre is a high-pressure tyre.

7. A motor vehicle as claimed in any one of the preceding claims, in which the wheel track of two narrower wheels arranged one on each side of the vehicle is about 1 50 cms.

8. A motor vehicle as claimed in any one of the preceding claims, in which the sum of the widths of the tyres of the vehicle exceeds the transport width of the vehicle.

9. A motor vehicle as claimed in claim 8, in which the sum of the widths of the tyres is four times about 90 cms.

10. A motor vehicle as claimed in any one of the preceding claims in which the sum of the widths of the tyres of the vehicle is more than about 320 cms.

11. A motor vehicle as claimed in any one of the preceding claims, in which the diameter of the wheels is about 125 cms.

12. A motor vehicle as claimed in any one of the preceding claims, which comprises eight tyres of substantially equal diameters.

13. A motor vehicle as claimed in any one of the preceding claims, in which the wheel assembly, or at least one of the wheel assemblies, is steerable as a unit.

14. A motor vehicle as claimed in any one of the preceding claims, in which a front axle of the vehicle has two wheels which are mounted for turning through about 900 about two king pins and which are drivable by hydraulic motors.

1 5. A motor vehicle comprising a frame, a power take-off shaft and a lifting device, the vehicle further comprising two narrow wheels disposed one on each side of the vehicle with a track width of about 1 50 cms.

16. A motor vehicle as claimed in claim 14 or 15, in which a steerable wheel can be turned by means of a quadrangular pivot structure to which a triangular pivot structure is coupled.

17. A motor vehicle as claimed in claim 1 6, in which the length of one of the sides of the triangular structure is variable.

18. A motor vehicle as claimed in claim 1 7, in which one of the sides of the triangular structure is constituted by a hydraulic cylinder which is actuable from a driver's seat of the vehicle.

1 9. A motor vehicle as claimed in any one of claims 16 to 18, in which the quadrangular and triangular structures of two steerable wheels are coupled with one another by a coupling member which is pivotable with respect to the front axle.

20. A motor vehicle as claimed in any one of the preceding claims, in which at least one wheel of the vehicle is drivable by a hydraulic motor which is fastened to a tubular member.

21. A motor vehicle as claimed in claim 20, in which the tubular member of a steerable wheel is pivotable about a king pin shaft.

22. A motor vehicle as claimed in any one of the preceding claims, in which at least one hydraulic pump is arranged at the front end of the vehicle for driving the wheels.

23. A motor vehicle comprising a frame, a power take-off shaft and a lifting device, a hydraulic pump being provided at the front end of the vehicle for driving a wheel or wheels of the vehicle.

24. A motor vehicle as claimed in claim 22 or 23, in which two hydraulic pumps are disposed approximately above a front axle of the vehicle.

25. A motor vehicle as claimed in claim 24, in which the pumps are disposed side by side and are drivable through gear wheel transmissions.

26. A motor vehicle as claimed in claim 24 or 25, in which the pumps drive four hydraulic wheel motors.

27. A motor vehicle as claimed in any one of the preceding claims, in which a power take-off shaft is provided at the front of the vehicle which can be driven at more than one speed.

28. A motor vehicle comprising a frame, a power take-off shaft disposed at the front of the vehicle and a lifting device, the power take-off shaft being drivable at more than one speed.

29. A motor vehicle as claimed in claim 27 or 28, in which the power take-off shaft is drivable at speeds of 1000, 770, 540 or 450 rev/min.

30. A motor vehicle as claimed in any one of claims 27 to 29, in which the power take-off shaft is drivable through a change-speed gear box actuable from a driver's seat of the vehicle.

31. A motor vehicle as claimed in claim 30, in which a power take-off shaft at the rear of the vehicle is also drivable from the change-speed gear box.

32. A motor vehicle as claimed in claim 30 or 31, in which the power take-off shaft, or at least one of them, is drivable through a gear wheel transmission provided between the change-speed gear box and the power take-off shaft.

33. A motor vehicle as claimed in any one of claims 30 to 32, in which the power take-off shaft, or at least one of them, is drivable by an auxiliary shaft, provided between the changespeed gear box and the power take-off shaft, which is provided with universal joints.

34. A motor vehicle as claimed in any one of the preceding claims, in which the tractor frame comprises a central frame beam which, towards the front of the vehicle, extends upwardly and then forwardly.

35. A motor vehicle as claimed in any one of the preceding claims, in which, near the rear, the frame comprises a pivotable part which is pivotable about a horizontal axis extending in the intended direction of travel of the vehicle, with respect to a front frame part.

36. A motor vehicle as claimed in claim 35, in which the pivotable part carries rear wheels.

37. A motor vehicle as claimed in any one of the preceding claims, in which the distance between the lowermost part of the frame and the ground is about 60 cms.

38. A motor vehicle as claimed in any one of the preceding claims, in which the weight is about 2500 kgs.

39. A motor vehicle as claimed in any one of the preceding claims, in which a lifting device is provided both at the front and at the rear of the vehicle.

40. A motor vehicle as claimed in any one of the preceding claims, in which the power of a driving engine of the vehicle is about 60 kw.

41. A motor vehicle as claimed in any one of the preceding claims, the length of which is about 540 cms.

42. A motor vehicle as claimed in any one of the preceding claims, in which the lifting power at coupling points for attaching implements is about 4000 kgs.

43. A motor vehicle as claimed in claim 42, in which the lifting device is provided with a plurality of lower lifting arms, each of which is connected to a respective hydraulic lifting cylinder.

44. A motor vehicle as claimed in any one of the preceding claims, in which the lifting device comprises two rigidly interconnected lifting arms.

45. A motor vehicle as claimed in claim 44, in which the lifting arms are arranged in a V-shaped fashion.

46. A motor vehicle as claimed in claim 45, in which the lifting arms diverge in the direction towards their free ends.

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

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