TRACK-TYPE VEHICLE HAVING STEERABLE WHEELS

Technical Field

This invention relates to track-type work vehicles and more particularly to a track-type vehicle having steerable wheels and a weight distributing apparatus for distributing the vehicle weight between the track assemblies and the wheels.

Background Art

A large percentage of agricultural work vehicles are supported and propelled by four or more wheels on front and rear axles. In work conditions requiring low ground pressure and increased traction, as many as four additional wheels are added to the conventional four wheels. As an alternative to the four wheel agricultural vehicles, self-laying track-type work vehicles are often employed because they offer excellent traction and low ground pressure. Work vehicles having either metal chain track or elastomeric belt track are available. Although track-type work vehicles offer many advantages over wheel type vehicles, sharp turning of the track-type vehicles can disturb soil and vegetation. This is due to the large amount of ground contact offered by the track assemblies, such ground contact causing a shearing action during turning operations. One type of a vehicle having a track structure and steerable wheels is disclosed in U.S. Patent No. 1,455,906 issued to W. C. Cox on May 22, 1923. In this patent a motor vehicle is equipped with an endless track structure at the rear of the vehicle and conventional steerable wheels at

the front of the vehicle. Cushioning means are provided in the track sections to cushion the movement of the vehicle wheels upon their respective tracks. A hand wheel is disposed in proximity to the seat of the drive to adjust the tracks.

Another type of traction apparatus is disclosed in U.S. Patent No. 2,057,211, issued to A. T. Shere on October 13, 1936. This patent discloses a track-laying type tractor having track-type structure at the rear and wheels at the front. Various other modifications are disclosed for converting an automobile into a crawler type tractor. This particular type of conversion would appear impractical in view of the different design requirements between automobiles and tractors.

The present invention is directed toward overcoming one or more of the problems as set forth above.

Disclosure of the Invention

In one aspect of the present invention, a track-type vehicle has a main frame, an axle, and first and second steerable wheels. First and second endless track assemblies are positioned on each lateral side of the frame. First and second steering cylinders are connected between the axle and a respective steerable wheel. The vehicle further includes a source of pressurized fluid, a weight distributing cylinder, and means for controlling the pressure of the pressurized fluid to the cylinder. Additional means measure the angle of steer of the steerable wheels, and the control means are activated in response to the steer angle.

Prior art vehicles which are utilized in agricultural work operations are often equipped with

wheels at the front and rear of the vehicle, such wheels serving to support and propel the vehicle. Wheel type vehicles, however, tend to cause undesirable soil compaction, and their use is somewhat limited in soft or wet soil conditions. Track-type vehicles provide greater traction in wet soil conditions and minimum soil compaction due to low ground pressure. However, track-type vehicles are generally more difficult to turn and manipulate and cause shearing action with the soil during turning.

The subject invention provides a track-type vehicle having steerable wheels and a weight management apparatus for changing the ground pressure applied by the steerable wheels and the track assemblies.

Brief Description of the Drawings

Fig. 1 is a diagrammatic side elevational view of a vehicle incorporating the subject invention; Fig. 2 is a diagrammatic plan view partly in section of the frame structure, the steerable wheels, and the track assemblies of the subject invention; Fig. 3 is a diagrammatic plan view on an enlarged scale of the rear portion of the subject vehicle showing the rear axle, the tie rod, and steering angle measuring apparatus;

Fig. 4 is a diagrammatic rear elevational view, taken generally along the lines 4-4 of Fig. 3; Fig. 5 is a diagrammatic sectional view taken generally along the lines 5-5 of Fig. 4;

Fig. 6 is a diagrammatic side elevational view, on an enlarged scale, of a portion of the structure shown in Fig. 1, and showing the weight distributing cylinder and its connection between the first and second auxiliary frames;

Fig. 7 is a diagrammatic plan view, on an enlarged scale, of a portion of the structure shown in Fig. 2 , and showing the track roller frame and a supporting assembly; Fig. 8 is a diagrammatic illustration of a chart showing a steer angle plotted against ground pressure under the steerable wheels;

Fig. 9 is a diagrammatic side elevational view, on an enlarged scale, of the lateral adjusting mechanism;

Fig. 10 is a schematic illustration of a hydraulic circuit for the subject invention.

Fig. 11 is a diagrammatic side elevational view or a portion of the drive wheel and belt showing the drive lugs, taken generally from the area marked 11 from Fig. 1; and

Fig. 12 is a diagrammatic enlarged sectional view of the drive wheel, belt, and drive lugs, taken generally from the area marked 12 in Fig. 2.

Best Mode for Carrying Out the Invention

Referring to the drawings, a track-type vehicle 10, such as a harvesting machine 10, has a main frame 12, an axle 14, and first and second steerable wheels 16,18 connected to the axle 14. The vehicle 10 further includes first and second endless track assemblies 20,22, with one track assembly positioned on each lateral side of the main frame 12. A source 24 of pressurized fluid includes a fluid pump 26 and a fluid reservoir 28. The pressurized fluid is used to operate various fluid devices on the vehicle 10, including a weight distributing cylinder 30 which is connected between the vehicle frame 12 and the axle 14. A control means 32, such as a pressure control valve 34, controls the

pressure of pressurized fluid to the cylinder 30. A measuring means 36 measures the angle of steer of the steerable wheels 16,18 and produces a signal in response to the steer angle. The measuring means 36 includes a link 38 having first and second ends 40,42 and first and second swivel joints 44,46 connected to the respective first and second ends 40,42. The first swivel joint 44 connects the link 38 to a tie rod 48 and the second swivel joint 46 connects the link 38 to a transducer 50, such as a electrical potentiometer 50. It is recognized that other types of mechanical and hydraulic sensors could be used.

The tie rod 48 has first and second ends 52,54 which are connected to respective first and second steerable wheels 16,18. The tie rod therefore follows the motion of the wheels 16,18 as they turn, and the link 38 also moves with the tie rod 48. The steerable wheels 16,18 are turned by first and second steering cylinders 45,47, which are controlled by a conventional hydraulic circuit and a steering wheel (not shown) in the operator's compartment 49. Each steering cylinder 45,47 has a first end portion 51 connected to the axle 14 and a second end portion 53 connected to one of the wheels 16,18. Since the second end 42 of the link 38 is connected to the transducer 50 by the second swivel joint 46, motion of the link 38 activates the transducer 50. The transducer 50 produces a signal which is directly proportional to the angle of steer of the wheels 16,18. This signal is relayed to the pressure control valve 34 which then generates a control signal which activates the control valve 34. The pressure supplied by the control valve 34 is varied as a function of the steer angle of the wheels 16,18. The control valve 34 therefore controls the pressure of the fluid in the

weight distributing cylinder 30, and the degree of pressurization is a function of the magnitude of the control signal and the steer angle of the wheels 16,18. Pressurization of the weight distributing cylinder 30 distributes the weight of the vehicle 10 between the track assemblies 20,22 and the steerable wheels 16,18. The more pressure applied to the cylinder 30, the more weight is shifted to the steerable wheels from the track assemblies 20,22. As the weight is shifted, the front portions 56 of the track assemblies 20,22 carry more weight and the rear portions 58 of the track assemblies carry less weight. As more of the weight is shifted to the front portions 56 of the track assemblies 20,22, the rear portions 58 of the track assemblies 20,22 are raised off of the ground. With particular reference to Fig. 8, the line 59 on the chart represents the steer angle plotted against the ground pressure under the steerable wheels in a steer right maneuver of the vehicle 10. The line 61 is the same as the line 59 in a steer left maneuver. The line 63 represents some minimum amount of ground pressure on the steerable wheels at a 0 degree steer angle. With particular reference to Fig. 2, 3, 4, and 6, the vehicle 10 includes first and second auxiliary frame assemblies 60,62 which are pivotally connected by a pivot pin 64. The first frame assembly is securely connected, as by welding, or by bolts 66 to the main frame 12 of the vehicle 10. The second frame assembly 62 has a first end portion 68 which is pivotally connected to the axle 14 by a pivot pin 70. A first bracket 72 is connected to the first auxiliary frame 60 and a second bracket 74 is connected to the second auxiliary frame 62. The weight distributing

cylinder 30 has a first end portion 76 connected to the first bracket 72 and a second end portion 78 connected to the second bracket 74. The second auxiliary frame 62 includes first, second, and third mounting plates 80,82,84, with the first plate having a plurality of mounting holes 86. The second bracket 74 is connectable to the first mounting plate 80 using selected ones of the mounting holes 86. By mounting the second bracket 74 at various positions on the mounting plate 80, the rear portions 58 of the track assemblies 20,22 can be raised off the ground to various levels. The axle 14 is pivotally connected to the first end portion 68 of the second frame assembly 62 by the second and third mounting plates 82,84. The vehicle 10 includes a power generating means 88, such as an engine 88, a transmission 90, first and second drive shafts 92,94, and first and second final drive assemblies 96,98. Each of the track assemblies 20,22 includes a drive wheel 100 and a track roller frame structure 102. The drive wheels 100 are powered by the engine 88 through the transmission 90, the drive shafts 92,94 and the final drive assemblies 96,98. Each of the track roller frame structures 102 includes a first end portion 104 which is connected to a respective drive wheel 100, and a middle portion 106 which is connected to the vehicle main frame 12. The middle portion 106 of each track roller frame structure 102 is connected to the main frame 12 by a supporting assembly 108. Each of the supporting assemblies 108 includes a mounting portion 110, an extension plate 112, a plurality of ribs 114, and a reinforcing plate 116. The mounting portion 110 rigidly connects the supporting assembly 108 to the vehicle main frame 12. The supporting assembly 108 includes a lateral

adjust ent mechanism 118, including a threaded rod 120, an L-shaped plate 122 positioned on the rod 120, and first and second nuts 124,126 threaded onto the rod 120. The first leg 128 of the L-shaped plate 122 is adapted to be secured to the track roller frame structure 102 by a plurality of bolts 130 and the second leg 132 of the L-shaped plate 122 is positioned on the threaded rod 120. The first and second nuts 124,126 are threaded onto the threaded rod 120 with the second leg 132 adapted to be clamped between the nuts 124,126. The bolts 130 also clamp the extension plate 112 to the track roller frame structure 102 with the extension plate 112 being sandwiched between the L-shaped plate 122 and the track roller frame structure 102. The bolts 130 pass through first and second slots 129,131 in the extension plate 112. The reinforcing plate 116 has a slot 134 for receiving a portion of the rod 120. Once positioned within the slot 134 the rod 120 is connected, as by welding, to the reinforcing plate.

The lateral adjustment mechanism 118 is used to make small lateral adjustments of the track roller frame 120 with respect to the remainder of the vehicle 10. The track assemblies 20,22 are preferably belted type track assemblies having an endless elastomeric belt 136 encircling the drive wheel 100, an idler wheel 138, and a plurality of guide rollers 140. Each of the guide wheels 100 includes first and second wheel portions 142,144 which are connected together by a plurality of bolts 146 to form a groove 148 therebetween. The belt 136 has a plurality of guide blocks 150 formed on the inner surface 148, with the groove 148 adapted to guide the belt 146 by the guide blocks 150. In order to prevent excessive wear and

heat buildup from frictional contact between the guide blocks 150 proper belt alignment is essential.

To change the alignment of the belt 136, moving the track roller frame toward the vehicle, the bolts 130 are loosened, the second nut 126 is loosened from engagement with the second leg 132, and the first nut 124 is tightened further onto the threaded rod 120. Since the bolts 130 are within the slots 129,131 the L-shaped plate 122 and the track roller frame 102 can move relative to the extension plate 112. Once the lateral adjustment has been made, the second nut 126 is re-tightened against the second leg 132 and the bolts 130 are re-tightened against the extension plate 122. Changing the alignment of the belt 136 in the opposite direction, the same procedure is followed, except the first nut 124 is first loosened and the second nut is tightened. Alignment of the belt 136 can be changed about one or two degrees. The alignment procedure is simplified if the track roller frame 102 is suspended off the ground in some manner.

Each of the drive wheels 100 includes a plurality of resilient drive lugs 152 connected to the circumferential surface 154 of the drive wheels 100. The drive lugs 152 frictionally contact the inner surface 156 of the drive belt 136 and frictionally rotate the belt 136 to propel the vehicle 10.

With particular reference to Figures 1 and 10, the tension between the drive wheel 100 and the belt 136 is established and maintained by a hydraulic cylinder 158 which is powered by the fluid pump 26. The head end portion 160 of the cylinder 158 is connected to the track roller frame 102 and the rod end portion 162 of the cylinder 158 is connected to the idler wheel 138 by an arm 164. By pressurizing the head end portion 160, the drive wheel 100 and the

idler wheel 138 are pushed apart to tension the drive belt 136. Pressure to the cylinder 158 is controlled by a control valve 166 and an adjustable control switch 168. The hydraulic cylinder 158 also provides recoil for the track assembly 20. When debris or foreign material becomes trapped between the inner surface 156 and the drive wheel 100, fluid is forced out of the head end portion 160 of the cylinder 158, across a relief portion of the control valve 166, into a drain line 170, and back to the reservoir 28. Once the debris has been expelled, an accumulator 172 provides flow and pressure to the head end portion 160 to extend the idler wheel 138 sufficient to keep the belt tight. A rod locking mechanism 174 is adapted to lock the rod 176 of the hydraulic cylinder 158 in position when the vehicle 10 is shut down and the pump 26 is no longer providing pressurized fluid. The rod locking mechanism 174 automatically locks onto the rod 176 in the absence of hydraulic pressurized fluid. This prevents release of the tension between the belt 136 and the drive wheel 100 when the vehicle 10 is not being operated.

Industrial Applicability With reference to the drawings, the subject track-type vehicle 10 with steerable wheels 16,18 is particularly useful as an agricultural vehicle, such as a combine harvesting vehicle. The track assemblies 20,22 provide good traction and low ground pressure, and the steerable wheels 16,18 provide the primary steering function for the vehicle 10.

The weight management apparatus 29, including the weight management cylinder 29, controls the amount of ground pressure applied to the steerable wheels 16,18 and to the track assemblies 20,222. When

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the steering cylinders 45,47 are activated to turn the wheels 16,18, the tie rod 48 follows the motion of the wheels 16,18. The link 38, which is connected at a first end 38 to the tie rod 48 and at a second end to the transducer 50, also follows the motion of the wheels 16,18. The transducer 50 produces a signal, which is proportional to the angle of steer of the wheels 16,18, to the modulatable control valve 34. The control valve 34 sends pressurized fluid to the weight distributing cylinder 30, which is connected between the vehicle main frame 12 and the axle 14. The cylinder 30 pushes down on the axle and steerable wheels 16,18 and lifts up on rear portion 58 of the track assemblies 20,22. Lifting up on rear portion 50 of the track assemblies 20,22 reduces the contact pressure of the track assemblies 20,22 with the ground and provides easier steering of the vehicle 10. The amount of lifting force applied to the rear portion 50 of the track assemblies 20,22 is a direct function of the steer angle of the steerable wheels 16,18. As the steering cylinders 45,47 return the wheels 16,18 to a straight position, the signal produced by the transducer 50 is removed from the control valve 34 and the control valve 34 returns to a preset minimum pressure position. The track assemblies 20,22 then return to their previous contact position with the ground until the steerable wheels 16,18 area gain turned by the steering cylinders 47,49. Lifting up on the rear portion 58 of the track assemblies 20,22 shifts the weight of the vehicle 10 to the steerable wheels 16,18 and to the front portion 56 of the track assemblies 20,22.

Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosure, and the appended claims.