Vehicle for agricultural use - Patent Review 5039129

I claim:

1. An agricultural vehicle comprising a frame, a pair of ground wheels each having a hub on which the wheel rotates and a tire with a ground engaging periphery for supporting the frame in movement across the ground in a direction along an axis longitudinal of the frame, the wheels being spaced to respective sides of a center line of the vehicle, parallel to said longitudinal axis and a pair of suspension devices each for connecting a respective one of the ground wheels for flexible movement relative to the frame in a vertical direction to accommodate variations in ground height, each suspension device comprising a rigid axle member, means mounting the axle member on the frame for pivotal movement about a suspension axis fixed relative to the frame and extending substantially parallel to said longitudinal axis and located inwardly of the ground wheel, the axle member comprising a first portion extending in a substantially horizontal direction from said suspension axis to another end at a position closely adjacent said ground wheel, and a second portion rigidly coupled to the first portion and extending substantially vertically downwardly from the outer end to a lower end at the hub so that the hub is located downwardly and outwardly of the suspension axis, means mounting the hub on the lower end such that all force communicated to the hub from the ground passes into the second portion and from the second portion into the first portion, the hub providing rotation about a wheel axis at right angles to the longitudinal axis and fixed relative to said axle member such that vertical movement of said ground wheel about said suspension axis causes horizontal movement of said tire periphery at the ground in a direction at right angles to said suspension axis, and spring means connected between said frame and said axle member providing a spring resistance to upward movement of said axle member relative to the frame about said suspension axis.

2. The invention according to claim 1 wherein said spring means comprises gas spring means which includes one end which is expandable and compressible relative to another end thereof with said one end connected to said frame and to said other end connected to the axle member.

3. The invention according to claim 2 wherein said spring means consists of a single gas spring member.

4. The invention according to claim 1 wherein the horizontal portion includes means for adjusting the length thereof for adjusting the spacing between the ground wheels.

5. The invention according to claim 4 wherein each of the axle members comprises a receiving portion and an extension portion slidably mounted within the receiving portion such that an outer end of the extension portion can be moved to increase and decrease spacing thereof from a centre axis of the frame.

6. The invention according to claim 5 wherein the frame includes a channel member extending at right angles to said longitudinal axis and defining a horizontal upper web and a pair of depending sides, said axle member being mounted within the channel member for pivotal movement about a support pin bridging said side portions of said channel member, said spring means being connected between an under surface of said web and an upper surface of said axle member.

7. The invention according to claim 1 wherein the frame has a centre axis longitudinally thereof positioned midway between said ground wheels and wherein the suspension axis are arranged closely adjacent the centre axis.

8. The invention according to claim 1 wherein shock damping means for damping movement of the suspension device consists solely of said ground wheel and said axle member and the cooperating movement of the tire periphery on the ground.

9. The invention according to claim 1 wherein the axle member extends substantially at right angles to the longitudinal axis.

10. The invention according to claim 1 including a second pair of ground wheels, each of said second pair of ground wheels having a suspension device, said frame defining a front portion having one of said first and second pairs of ground wheels mounted thereon and a rear portion having the other of said first and second pairs of ground wheels mounted thereon, and pivot connection means connecting the front portion to the rear portion for pivotal movement about a vertical axis to provide an articulated steering system for said frame.

11. The invention according to claim 10 wherein the pivot connection means is arranged closer to the pair of ground wheels on the front portion than the pair of ground wheels on the rear portion and sufficiently close thereto to cause the steering action to take place substantially solely at the front pair of wheels.

12. The invention according to claim 11 wherein the rear pair of ground wheels is mounted on the frame for adjustable movement in a direction longitudinal of the frame.

13. The invention according to claim 10 wherein the frame includes a single beam extending along a central axis of the frame and wherein pivotal movement of the front portion of the frame relative to the rear portion of the frame takes place solely above said vertical steering axis.

14. An agricultural vehicle comprising a frame having a front frame portion and a rear frame portion, a front pair of ground wheels mounted on the front frame portion and a rear pair of ground wheels mounted on the rear frame portion, suspension means mounting the ground wheels on the frame for supporting the frame in movement across the ground in a direction along an axis longitudinal of the frame, an engine mounted on the frame providing motive power for driving at least one pair of the ground wheels, a load receiving section provided on the rear portion of the frame, and steering means comprising pivot connection means between the front frame portion and the rear frame portion and defining a vertical pivot axis, the pivot axis being arranged closer to the front pair of wheels than the rear pair of wheels.

15. The invention according to claim 14 wherein the pivot axis is arranged substantially immediately rearwardly of the front pair of wheels.

16. The invention according to claim 14 wherein the pivot axis is arranged to be spaced from the front pair of wheels by a distance such that in a steering action substantially only the front frame portion pivots about the vertical pivot axis.

17. The invention according to claim 14 wherein the pivot axis is arranged to be of the order of 18 inches rearwardly of a line joining the rotation axes of the front pair of wheels.

18. The invention according to claim 14 wherein the frame includes a single beam extending along a central axis of the frame and wherein pivotal movement of the front portion of the frame relative to the rear portion of the frame takes place solely about said vertical steering axis.

19. The invention according to claim 14 wherein the rear pair of ground wheels are mounted on the rear frame portion for adjustable movement in a direction longitudinal of the rear frame portion.

20. The invention according to claim 14 wherein each ground wheel is supported on the frame by an axle member comprising a receiving portion and an extension portion mounted within the receiving portion such that an outer end of the extension portion can be moved to increase and decrease spacing thereof from a centre axis of the frame.

21. The invention according to claim 20 wherein the frame includes a channel member extending at right angles to said longitudinal axis and defining a horizontal upper web and a pair of depending sides, said axle member being mounted within the channel member for pivotal movement about a support pin bridging said side portions of said suspension means comprising channel member, said spring means connected between an under surface of said web and an upper surface of said axle member.

22. A vehicle comprising a frame, a front pair of ground wheels mounted on the frame, a rear pair of ground wheels mounted on the frame, means mounting the ground wheels on the frame for supporting the frame in movement across the ground in a direction along an axis longitudinal of the frame, each of at least one pair of the ground wheels having a hydraulic motor mounted thereon for providing direct drive to the respective wheel, an engine having a main drive coupling at one end of the engine, a hydraulic pump driven by the main drive coupling of the engine for providing pressurized hydraulic fluid to the hydraulic motors, and means mounting the engine at one end of the frame with the main drive coupling and the hydraulic pump on that end of the engine which is adjacent said one end of the frame.

23. The invention according to claim 22 wherein the engine is mounted at the front end of the frame with the hydraulic pump forwardly of the engine.

24. The invention according to claim 23 wherein there is provided a cab rearwardly of the engine and a load section rearwardly of the cab.

25. The invention according to claim 22 wherein the frame includes a front portion having said one pair of ground wheels thereon and a rear portion having the other pair of ground wheels mounted thereon and pivot connection means connecting the front portion to the rear portion for pivotal movement about a vertical axis to provide an articulated steering system for said frame.

26. The invention according to claim 25 wherein the frame includes a single beam extending along a central axis of the frame and wherein pivotal movement of the front portion of the frame relative to the rear portion of the frame takes place solely about said vertical steering axis.

27. An agricultural vehicle comprising a frame having a front frame portion and a rear frame portion, a front pair of ground wheels mounted on the front frame portion and a rear pair of ground wheels mounted on the rear frame portion, spring suspension means mounting the ground wheels on the frame for supporting the frame in movement across the ground in a direction along an axis longitudinal of the frame, the spring suspension means allowing vertical movement of each ground wheel relative to the frame, an engine mounted on the frame providing motive power for driving at least one pair of the ground wheels, a load receiving section provided on the rear portion of the frame, and steering means comprising pivot connection means between the front frame portion and the rear frame portion and defining a vertical pivot axis, wherein the frame includes a single beam extending along a central axis of the frame and wherein pivotal movement of the front portion of the frame relative to the rear portion of the frame takes place solely about said vertical steering axis.

28. The invention according to claim 27 wherein the pivot axis is arranged to be spaced from the front pair of wheels by a distance such that in a steering action substantially only the front frame portion pivots about the vertical pivot axis.

29. The invention according to claim 27 wherein the pivot axis is arranged to be of the order of 18 inches rearwardly of a line joining the rotation axes of the front pair of wheels.

30. The invention according to claim 27 wherein each ground wheel is supported on the frame by an axle member comprising a receiving portion and an extension portion mounted within the receiving portion such that an outer end of the extension portion can be moved to increase and decrease spacing thereof from a centre axis of the frame.

31. The invention according to claim 27 wherein the frame includes a channel member extending at right angles to said longitudinal axis and defining a horizontal upper web and a pair of depending sides, said axle member being mounted within the channel member for pivotal movement about a support pin bridging said side portions of said suspension means comprising channel member, said spring means connected between an under surface of said web and an upper surface of said axle member.

Description Submit all comments and votes

RELATED APPLICATIONS

Attention is directed to related application Ser. No. 436,595 filed Nov. 15, 1989, and Ser. No. 437,087 filed Nov. 16, 1989, which are closely related to the present application and include disclosure of the same features shown herein but claim different aspects of the machine concerned.

BACKGROUND OF THE INVENTION

This invention relates to a vehicle which is particularly but not exclusively designed for use as an agricultural vehicle for transporting various loads across rough terrain in an agricultural process for example spraying liquid onto the ground or spreading of granular materials onto the ground.

Various designs of vehicle have previously been provided for example for use as field sprayers including three wheeled vehicles manufactured by Spray Coupe which comprise a self-propelled vehicle carrying the liquid to be sprayed together with a boom which defines the plurality of nozzles through which the liquid is sprayed. Vehicles of this type have a design of the frame and support system which has a number of disadvantages and cannot provide the suspension system nor the adjustability required for modern agricultural techniques and to accommodate high ground speeds required for modern vehicles of this type.

Other vehicles of this general type include large wheels with wide tires which provide suspension basically through the flexibility of the tire itself. While these vehicles can accommodate heavy loads and provide a satisfactory suspension, they of course cause significant damage to the ground or to the crop in view of the wide compressing action of the large tires.

Many designs of a vehicle of this type have a raised frame for high clearance and wheels mounted on vertical pivot coupling at the far corner of the frame. These designs do not lend themselves to an effective suspension system or to a steering system which will allow adjustment to the wheel spacing for row crop applications.

SUMMARY OF THE INVENTION

It is one object of the present invention therefore to provide a vehicle having a frame and wheel support system which enables the vehicle to carry out agricultural processes while cooperating more effectively with the crops and terrain.

It is a further object of the present invention to provide an improved suspension system for a vehicle of this type.

It is a further object of the present invention to provide a vehicle having an improved steering system.

It is a yet further object of the present invention to provide a vehicle which mounts the engine, frame and suspension system in a manner which allows ready access to the operating parts for service and repair.

According to the first aspect of the invention there is provided a vehicle comprising a frame, a pair of ground wheels each having a tire with a ground engaging periphery for supporting the frame in movement across the ground in a direction along an axis longitudinal of the frame, and a pair of suspension devices each for connecting a respective one of the ground wheels for flexible movement relative to the frame to accommodate variations in ground height, each suspension device comprising a rigid axle member, means mounting the axle member on the frame for pivotal movement about a suspension axis fixed relative to the frame and extending substantially parallel to said longitudinal axis, means mounting the ground wheel on the axle member for rotation about a wheel axis at right angles to the longitudinal axis and fixed relative to said axle member such that vertical movement of said ground wheel about said suspension axis causes horizontal movement of said tire periphery at the ground in a direction at right angles to said suspension axis, and spring means connected between said frame and said axle member providing a spring resistance to upward movement of said axle member relative to the frame about said suspension axis.

According to the second aspect of the invention there is provided a vehicle comprising a frame having a front frame portion and a rear frame portion, a front pair of ground wheels mounted on the front frame portion and a rear pair of ground wheels mounted on the rear frame portion, suspension means mounting the ground wheels on the frame for supporting the frame in movement across the ground in a direction along an axis longitudinal of the frame, an engine mounted on the frame providing motive power for driving at least one pair of the ground wheels, a load receiving section provided on the frame, and steering means comprising pivot connection means between the front frame portion and the rear frame portion and defining a vertical pivot axis, the pivot axis being arranged closer to the front pair of wheels than the rear pair of wheels.

According to the third aspect of the invention there is provided a vehicle comprising a frame, a front pair of ground wheels mounted on the frame, a rear pair of ground wheels mounted on the frame, suspension means mounting the ground wheels on the frame for supporting the frame in movement across the ground in a direction along an axis longitudinal of the frame, each of at least one pair of the ground wheels having a hydraulic motor mounted thereon for providing direct drive to the respective wheel, an engine having a main drive coupling at one end of the engine, a hydraulic pump driven by the main drive coupling of the engine for providing pressurized hydraulic fluid to the hydraulic motors, and means mounting the engine at one end of the frame with the main drive coupling and the hydraulic pump on that end of the engine which is adjacent said one end of the frame.

According to a fourth aspect of the invention there is provided a vehicle comprising a frame having a front frame portion and a rear frame portion, a front pair of ground wheels mounted on the front frame portion and a rear pair of ground wheels mounted on the rear frame portion, suspension means mounting the ground wheels on the frame for supporting the frame in movement across the ground in a direction along an axis longitudinal of the frame, an engine mounted on the frame providing motive power for driving at least one pair of the ground wheels, a load receiving section provided on the rear portion of the frame, and steering means comprising pivot connection means between the front frame portion and the rear frame portion and defining a vertical pivot axis, wherein the frame includes a single beam extending along a central axis of the frame and wherein pivotal movement of the front portion of the frame relative to the rear portion of the frame takes place solely about said vertical steering axis.

With the foregoing in view, and other advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, the invention is herein described by reference to the accompanying drawings forming a part hereof, which includes a description of the best mode known to the application and of the preferred typical embodiment of the principles of the present invention, in which:

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a field sprayer according to the invention.

FIG. 2 is a top plan view of FIG. 1.

FIG. 3 is a side elevational view of the sprayer of FIG. 1.

FIG. 4 is a top plan view of the frame, suspension and wheel arrangement of the sprayer of FIG. 1 with the cab tank and other parts removed.

FIG. 5 is a cross-sectional view along the lines 5--5 of FIG. 4.

FIG. 6 is a side elevational view of a forward end of the sprayer with much of the super structure of the sprayer shown only schematically.

FIG. 7 is a rear elevational view of a centre portion of the boom and boom control assembly.

FIG. 8 is a top plan view of a portion of the boom showing a spray shield arrangement omitted from FIG. 1 for convenience of illustration.

FIG. 9 is a cross sectional view along the lines 9--9 of FIG. 8 through one portion of the boom showing the spray shield arrangement.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

The drawings illustrate and the following description relates to a sprayer for spraying agricultural crops which is particularly adapted for modern spraying conditions and is sufficiently adaptable to accommodate many different crop conditions and requirements.

However many of the aspects of the sprayer are applicable to other types of vehicle which are designed for agricultural use for example spreaders of particulate material which also include a boom assembly. While the description herein is therefore particularly directed to the sprayer, it is not intended that the protection provided by this patent should be so limited and other types of vehicle are contemplated by the inventor in this matter.

The sprayer shown particularly in FIGS. 1, 2 and 3 comprises a central frame supporting the vehicle including an elongate beam and a pair of axle assemblies generally indicated at 10 and 11 which will be described in more detail hereinafter. Upon the frame and axle assembly is mounted an engine 13, a hydraulic pump system 14, a cab 15, a platform 16 supporting a load in this case a tank 17 for liquid to be sprayed and a boom generally indicated at 18.

Further details of the vehicle are visible in FIG. 1 many of which are not of major importance to the present invention for example a return hydraulic fluid reservoir 19, an engine cover 20 and the various instrumentation in the cab indicated at 21.

Turning therefore firstly to the frame and axle assembly shown best in FIGS. 4, 5 and 6, the main frame includes a front frame portion 22 and a rear frame portion 23. The rear frame portion comprises a central single elongate beam 24 in the form of square tube. The beam extends from the rear end 25 to a forward end 26 and is rigid and resistant to twisting. A support and stiffening element 27 is connected underneath the back end 26.

The rear axle assembly 11 comprises an inverted channel 11A with an upper web 28 and depending sides 29 and 30. A hole is cut through the sides 29 and 30 at the web 28 at a centre section of the channel to a depth of approximately half the depth of the sides 29 and 30 and a cross channel 28A is welded in place in the opening thus formed. The interior dimension of the cross channel is formed to accommodate the beam 24 which extends through the channel 28A thus formed in the channel 11A and is clamped to the cross channel 28A at portions 31 thereof which project outwardly from the sides 29 and 30 along the sides of the beam 24. The portions 31 are clamped to the beam by suitable bolt connections 32 which project through holes in the beam which are located at spaced positions along the length of the beam to accommodate different positions of the rear axle assembly 11 along the beam. Depending upon the load applied to the frame, therefore, the position of the rear axle assembly can be chosen so that the balance of the weight applied to the different wheels is optimized.

The sides 29 and 30 are substantially continuous along the length of the channel except that outermost lower corners 33 are chamfered. A channel iron 34 is welded across the open face of the channel to provide structural rigidity for the sides. Upstanding reinforcing webs can be welded on the upper surface of the web to provide structural strength transverse to the web adjacent its outermost ends.

The channels 11A and 10A are therefore rigidly coupled to the beam and form therewith a rigid frame structure longitudinal of the vehicle and transverse to the vehicle. The front axle assembly 10 is substantially equivalent to the rear axle assembly with the differences being described in detail hereinafter. The basic structure remains common however and therefore the same reference numerals are used in relation to the front axle assembly as shown in FIG. 4.

Two axle members 36 and 37 each supporting a respective ground wheel 38 are mounted on the channel for pivotal suspension movement relative thereto. Each axle member comprises a horizontal portion 39 which extends from an innermost end 40 pivotally connected to the channel by a pin 41 extending through the horizontal portion 39 and through the sides 29 and 30 of the channel. The pin 41 thus defines a pivot axis which is substantially immediately adjacent the centre axis of the vehicle defined at and the beam 24 positioned beneath the beam 24. The axis of the pivot pin 41 is parallel to the direction of movement to the vehicle and in a substantially horizontal plane so that the horizontal portion 39 of the axle member is confined to pivot about the pin 41 with the outer end thereof moving in a vertical plane. As shown in FIG. 5, the horizontal portion 39 extends outwardly at right angles to the centre axis of the vehicle and the horizontal portion is confined to move up and down in this vertical plane at right angles to the vehicle axis. As the pin 41 must resist twisting of the axle member 36 about a vertical axis and about an axis longitudinal to the axle member, the pin is coupled to the sides 29 and 30 by a pair of large bearings 41A bolted on the outer surfaces of the sides.

The horizontal portion 39 of the axle member is defined by an outer sleeve member 42 and an inner tubular member 43 which can slide in the sleeve member as best shown in FIG. 4 to increase and decrease the effective length of the horizontal portion. Adjustment of the length of the horizontal portion is obtained by a hydraulic cylinder 44 which is connected at one end to an outer surface of the sleeve member 42 and at the opposed end to an outer surface of the tubular portion 43. The length can be adjusted by initially driving the cylinder 44 outwardly to increase the amount of the tubular portion 43 extending out of the channel 42 and then reversing the action of the cylinder to draw the tubular portion 43 back into the channel up to engagement of a pin 45 with the end surface of the channel 42. The pin 45 can be located in a number of different holes 45A as shown. Thus in FIG. 4 the front axle assembly is shown in an extended position whereas the rear axle assembly is shown in a retracted position and it will be appreciated that each of the axle members can be extended individually to a required length depending upon circumstances. For example it is possible to extend the axle members on one side of the vehicle to a greater extent than that of the other side of the vehicle when running on a side of the hill.

The outer end of the tubular portion 43 is welded to a vertical tubular portion 46 which extends downwardly from the outer end to a hub 47 of the ground wheel 38. The extent of the vertical portion 46 is sufficient that the upper edge of the wheel is approximately at the same height as the underside of the horizontal portion thus raising the clearance of the frame of the vehicle to a height well above ground level to accommodate passing over crops which are already well grown. In practice the height of the clearance would be of the order of 48 to 96 inches depending upon the crops with which the sprayer is intended to be used. The wheel size and length of the member 46 can be altered accordingly.

Drive to the wheels 38 is provided by a hydraulic motor of conventional type mounted within the hub 47 schematically indicated at 48. Drive can be provided to all four wheels if required or to only two of the wheels depending upon known design parameters.

In a suspension action of the axle member relative to the fixed channel forming part of the frame, the axle member moves upwardly and downwardly as indicated by the arrow 49. Spring resistance to upward movement of the axle member is provided by a single gas spring 50 mounted on top of the horizontal portion at the outer end of the channel 42 and between the upper surface of the channel 42 and the under surface of the web 28 of the channel of the frame. Reinforcing flanges of the web 28 can be positioned at the gas spring 50 to accommodate the loads applied on the web 28 by the gas spring.

The gas spring is of a conventional type readily available from Goodyear or Firestone selected according to the loads to be accommodated. A gas spring of 6 inch travel will give a suspension movement at the wheel of the order of 12 inches.

The single gas spring has of course no shock damping properties and acts simply as a spring resistance to upward movement of the axle member. The single gas spring has the advantage relative to a conventional flexible metal spring that it has a substantially constant spring resistance over a relatively wide range rather than having an increasing spring resistance as is obtained by a conventional metallic spring arrangement. The design of the gas spring is not shown in detail as this is a commercially available item as described above.

The pivot axis for the axle member is arranged as close as possible to the centre axis of the vehicle. It will be appreciated from the geometry of FIG. 5 that vertical movement of the axle member along the line 49 will result in transverse movement of the wheel and particularly the lower most edge of the wheel in contact with the ground as indicated by the arrows 51. The positioning of the pivot axis of the axle member as close as possible to the centre of the vehicle minimizes this amount of movement. The height of the vertical portion increases the amount of movement so that in a practical arrangement in which the length of the horizontal portion is substantially equal to the height of the pivot axis from the bottom of the wheel, the amount of movement along the line 51 is equal to the movement 49. However the movement of the wheel and the flexing of the tire is used positively in this suspension design to provide the sole shock damping arrangement thus avoiding necessity for any other shock absorbing devices. The tire uses a conventional agricultural vehicle tire and the flexing of the tire and the movement of the tire relative to the ground can readily accommodate the movement necessary along the line 51.

This suspension arrangement has a number of significant advantages for agricultural vehicles.

1. It surprisingly provides a significant improvement in stability so that the vehicle can move over rough terrain at relatively high speeds of up to 15 miles an hour with the suspension system accommodating and accepting vigorous movements for example as provided by passage across a ditch.

2. The amount of roll of the vehicle from side to side is very limited which is of particular importance bearing in mind the high centre gravity of the load.

3. There is no torque effect on acceleration or deceleration of the vehicle. The torque effect occurs on acceleration on most suspension systems in that the suspension rises or lowers significantly as the vehicle accelerates from rest. This is due to a torquing of the suspension spring system which causes it to vary in length and thus lift or lower the vehicle and its load. In the case of a sprayer this is highly undesirable since if it occurs, the boom will drop vigorously toward the ground during startup or acceleration which will significantly alter the spray pattern.

4. The system will accommodate adjustment of the length of the axle member to vary the vehicle track Width for on-the-go adjustment. Variation of the track width is necessary to accommodate the various row widths of row crops and to accommodate the tram-line farming system in which repeated passes over the ground are carried out on the same wheel tracks to avoid damaging crops and to avoid the necessity to plant seeds on the intended wheel tracks.

Turning now to particularly FIGS. 6 and 4, the steering system for the vehicle is shown which is provided by an articulated steering system so that the front and rear axle assemblies 10 and 11 can be substantially identical. The front axle assembly 10 including the channel member 10A has mounted on the upper surface that is the upper surface of the web 28 a plate 120 which includes a front portion extending forwardly from the front surface of the channel 10A which is substantially equal to the width of the engine compartment. From a line across the front surface of the channel 10A, the plate 120 tapers rearwardly from both sides toward an apex rearwardly of the rear surface of the channel 10A. The apex terminates in a transverse edge 121 of the plate which is substantially equal in width to that of the beam 24. A second plate 122 is attached across the underside of the channel 10A and projects only rearwardly from the channel 10A and is shaped similarly to the rear part of the upper plate 120. The plates therefore define between them a space for receiving the front end of the beam 24 and the stiffening element 27. Both the beam 24 and the stiffening element 27 include a vertical opening for receiving a pin 123 passing through the plates and through the beam to define a single vertical axis at which the beam can pivot relative to the plates. Suitable bearings for the pin 123 are provided so that the steering action can take place without wear but the details of these are not shown. The pivot pin 123, therefore, provides a pivot axis which is of the order of 18 inches rearwardly of a line joining the rotation axis of the front pair of wheels. Thus the pivot axis is significantly closer to the front axle than to the rear axle and provides an articulated steering system so that the front axle and the front frame portion pivot about the steering axis relative to the rear axle and the rear frame portion. The positioning of the steering axis adjacent the front axle causes the vehicle to move in a steering action so that the front portion of the frame pivots about the pivot axis rather than the conventional articulated steering system in which both the front and rear portions tend to pivot equally about the pivot axis. This steering action of the front portion of the frame causes the vehicle to properly follow the required rows or tracks without a tendency of the steering system to cause crabbing of the vehicle out of the required line of travel.

Actuation of the steering system is provided by an hydraulic cylinder 55 coupled between a flange 55A mounted on the beam 24 and a suitable lug on the rear face of the axle assembly 10. Suitable hydraulic controls (not shown) are available to achieve the necessary accuracy of steering action.

The frame including the front channel 10A, the plates 120 and 122, the rear beam 24 and the rear channel 11A thus forms a substantially rigid structure which can pivot solely about the vertical steering pivot pin 123. There is no flexibility in the frame which allows any twisting of the frame either by twisting of the beams or by specifically provided universal couplings in the steering system. The movement of the wheels relative to the frame is accommodated solely by the suspension of the axle members. The front air springs are totally independent while a connection is made across the rear air springs to accommodate roll. This provides a vehicle which is highly stable with a very effective suspension action which can accommodate movement over agricultural terrain. At the same time the boom and the load described hereinafter are mounted on the stable rigid frame and thus are not exposed to twisting actions of the frame.