TRACK-LAYING VEHICLE

Abstract: A belt tensioning mechanism (31) is provided for use with a vehicle (10) having an axle (20) pivotably connected to a frame (14) of the vehicle with inextensible belts (26, 28) entrained about wheel assemblies (22, 24, 22′, 24′) mounted on either side of the vehicle for transmitting tractive effort to the earth. An axle (20) is connected to a frame (14) by a swivel bearing (36) being slidably disposed on a pin (34), such that, the axle (20) moves longitudinally relative to the frame (14) while still being able to swivel about the pin (34). Further­ more, an adjusting mechanism (42) is provided to produce the force necessary to sufficiently tension the belts (26, 28) to provide frictional drive between the belts (26, 28) and the drive wheel assemblies (24, 24′).

Description: TRACK-LAYING VEHICLE This invention relates to track-laying vehicles, such as tractors or equipment, using track as opposed to wheels for providing both ground support and tractive effort. Work vehicles, as opposed to vehicles for personnel transport, are generally intended to push or pull other equipment or earth, or carry a load. Consequently, these vehicles require high tractive forces between the vehicle and the terrain over which the vehicle is travelling. When using track belt to increase tractive force, a high load must be generated in the belt in order to minimize slippage between the track belts and the drive wheels. Various types of tensioning mechanisms have been suggested for use on track-laying vehicles with track belts to tension each track belt independently. For example, US-A-245267l discloses one arrangment in which are pair of wheels are slidable on longitudinal side members of a vehicle frame and are interconnected by a pivotal link which is acted upon by a central jack to urge the one pair of wheels away from another pair of wheels and hence tension belts entrained about the wheels. However, this arrangement is complex and liable to jamming, cannot accommodate uneven ground, and it would be preferred to use a single axle extending across the vehicle. US-A-1401625 discloses a vehicle of a kind, hereinafter referred to as of the kind described, having a frame with a central, vertical longitudinal plane; an axis connected to the frame at one end of the vehicle and extending thereacross through the plane; a first pair of wheel assemblies rotatably mounted on opposite ends of the axle independently of the frame; a second pair of driving wheel assemblies rotatably mounted on opposite sides of the frame at the other end of the vehicle; and first and second tracks entrained about the wheel assemblies on respective sides of the vehicle. However, the particular vehicle described is a small garden tractor including a sprocket drive for a track chain, rather than relying on friction to provide a belt drive, and it ultizes a complex and bulky mechanism to provide tensioning of the track and further provide recoil when objects pass between the sprocket drive and the track. When attempting to utilize apparatus of this type in large industrial vehicles, the components would be unreasonably large and bulky thus prohibiting their practical use. In accordance with the invention, a vehicle of the kind described is characterised in that the tracks are substantially inextensible belts; in that there are means for universally swivelling the axle relatively to the frame and for enabling the axle to slide longitudinally of the frame; and in that there are means for adjusting the position of the axle relatively to the frame to maintain a predetermined tension in the belts while permitting the swivelling and longitudinal movement of the axle. The present invention thus provides a tensioning mechanism which allows the axle to swivel about a locus relatively to the frame and further allows the axle to move longitudinally relatively to the frame for absorbing any motions created by one end of the axle moving in a longitudinal direction. Furthermore, the tensioning mechanism is compact while still having the ability to produce high forces for tensioning the belts. The entire mechanism utilized for tensioning and swivelling of the axle may be relatively simple in construction and does not require large bulky components. This arrangement provides the high forces necessary for tensioning the belts while still allowing the axle to move relatively to the frame whenever an object such as a rock, limb or board passes between the belt and the wheels. An example of a vehicle constructed in accordance with the invention is illustrated in the accompanying drawings, in which: Figure 1 is a side elevation; Figure 2 is a front elevation; and, Figure 3 is a plan view showing a portion of the vehicle and partly in section on the line Ill-Ill in Figure 2. Referring now to the drawings and more particularly to Figure 1 and 2, a work vehicle 10 is shown having a chassis 12 and a frame 14 which constitutes a portion of the chassis 12. The frame defines a longitudinal axis 16 and a vertical plane 18 centrally disposed along the longitudinal axis 16. The vehicle includes an axle 20 connected to a front portion of the frame 14 and has a first pair of wheel assemblies 22,22' rotatably connected to opposite ends of the axle 20. A second pair of wheel assemblies 24,24' are respectively connected to opposite sides of a rear portion of the frame 14. First and second inextensible belts 26,28 are respectively entrained about the wheel assemblies 22,24,22',24' on each side of the vehicle 10. A bogie system 30 is rotatably connected to the frame 14 on each side of the vehicle 10 and in load sharing contact with the respective belts 26,28 to share the loads being placed on the belts from the load of the vehicle as it negotiates the terrain. Referring now to Fig. 3, a belt tensioning mechanism 31 is illustrated which more clearly shows an embodiment of the present invention. A means 32 is provided for connecting the axle 20 to the frame 14 so that the axle 20 is free to swivel and to slide longitudinally relative to the frame. The connecting means 32 includes a pin 34 connected to the frame 14 parallel to the longitudinal axis 16 and along the centrally disposed plane 18. The connecting means 32 also includes a swivel bearing 36 connected to the axle 20 and slidably disposed on the pin 34. The swivel bearing 36 includes a race 37 secured to the axle 20 by a snap ring 38 and a spherical bearing member 39 defining a bore 40 adapted to slidably mount on the pin 34. A means 42 is provided for adjusting the axle 20 relative to the frame 14 to maintain at least a predetermined tension on the first and second belts 26,28, while permitting the stiling and longitudinal movements of the axle 20. The adjusting means 42 includes a force generating mechanism 44 connected between the frame 14 and the axle 20. The force generating mechanism 44 ildes a jack mechanism 45 pivotably connected at one end to the frame 14 along the centrally disposed plane lo. The jack mechanism 45 includes a pivot pin 46, se as a bolt, dowell, etc., connected to the frame 14 along the centrally disposed plane 18 longitudinally remote from and in axial alignment with the pin 34. The jack mechanism 45 also includes a force transmitting member 48 pivotably mounted on the pivot pin 46 and a pair of jack assemblies 50. Each of the jack assemblies 50 has a rod end portion 52 and a head end portion 54. Each of the jack assemblies 50 further includes a housing 56 and a rod 58 connected to a piston 60 which is slidably disposed in the housing 56. The head end portion 54 is generally defined by the housing 56 while the rod end portion 52 is generally defined by the rod 58. The housing 56 of each jack assembly 50 defines first and second ports 62,64 respectively in communication with head and rod end pressure chambers 66,68 which are separated by the piston 60. The housing 56 of each jack assembly is connected to opposite ends of the force transmitting member 48 while the rod 58 of each jack assembly 50 slidably extends through the force transmitting member 48 at the location of the connection with the housing 56. The force generating mechanism 44 also includes a force transfer mechanism 69, such as, a pair of force transmitting arms 70 each respectively connected to opposite ends of the axle 20 by respective pin joints, one shown at 72. The other end of each of the force transmitting arms 70 is connected to the rod 58 of each of the jack assemblies 50 by locking nuts 73 in a known manner. The arms 70 each respectively has a surface 74 in sliding contact with the opposite ends of the force transmitting member 48. A plurality of retainers 76 are secured to the member 48 and adapted to maintain the sliding and alignment relationship between the surface 74 of the arms 70 and the opposite ends of the member 48. Additionally, the force generating mechanism 44 includes a means 78 for aligning each of the first pair of wheel assemblies 22,22' relative to the belts 26,28. The alignment means 78 includes a pair of spindles 80 each pivotally connected to the opposite ends of the axle 20 at the respective pin joint 72 and a pair of adjusting assemblies 82 each being connected between the respective spindle 80 and the associated one of the force transmitting arms 70. The adjusting assembly 82 includes a first bracket 84 secured to the other end of the spindle 80 and a second bracket 86 secured to the arm-70 with an adjustable fastener member 88 connected between the brackets 84,86. As shown, the fastener member 88 is a bolt and nut, but it is recognized that the fastener member 88 could be replaced with other known adjustable fastening means. Each of the spindles 80 has the respective wheel assembly 22/22' rotatably connected to one end thereof. The force generating mechanism 4 additionally includes a source of pressurized fluid, such as a pump 90, which draws fluid from a tank 92 in a conventional manner and delivers presssurized fluid to a switching valve 94 through a conduit 96. A pair of conduits 98,100 respectively connect the switching valve 94 to the inlet ports 64,62 of the jack assemblies 50. The switching valve 94 is connected to the tank 92 in a conventional manner by a conduit 102 and may be actuated either manually, electrically or hydraulically. A relief valve 104 is connected to the conduit 96 and adapted to control the pressure in the conduit 96 to a predetermined maximum level. From a review of the Figs. and the above description, it is readily apparent that numerous modifications and/or combination of elements could be combined without departing from the essence of the invention. For example, various forts of hydraulic circuits could be utilized to extend and/or retract the cylinder disclosed herein without departing from the essence of the invention. industrial A#p1icability In the use of work vehicles of this type, the belt tensioning mechanism 31 as shown in the various embodiments herein is necessary to provide the high tensions in the belt to prevent slippage between the drive wheels 24,24' and the first and second belts 26,28. The tensioning mechanism 31 must generate sufficient tension in each of the belts 26,28 so that there is a satisfactory frictional driving force between the drive wheels 24,24' and the respective belt 26/28. For example, in one vehicle having a gross weight of 115.7 kN (26,000 lbs.) and a belt width of 61 cm (25 inches), an initial tension of 44.5 kN (10,000 lbs.) in each of the belts operated successfully. It is recognized that different size belts would vary in total force needed in the belt to maintain the frictional driving force between the belts 26,28 and the respective wheel assemblies. Furthermore, it is necessary to provide recoil of one side of the axle 20 in the event an object such as rock, limb, board, etc. passes between one of the belts 26/28 and the respective wheel assembly 22/24,Z#'/241. referring more specifically to the operation of the embodiment shown in Fig. 3, fluid pressure fron the pump 90 is directed to the pressure chc..bers 68 of the jack assemblies 50 generating a force on the piston 60 which is transferred through the rod 58 and the arms 70 to the axle 20. The bore 40 of the spherical bearing member 39 allows the axle 20 to slide relative to the pin 34. Consequently, the force transali.ted to the axle 20 is further transferred through the spindles 80 to the pair of wheel assemblies 22,22' and tensions the first and second belts 26,28. The relief valve 104 controls the maximum pressure in the pressure chambers 68 and consequently controls the tension in the belts 26,28. When a foreign object passes between, for example, the belt 28 and the wheel assembly 22', the spindle 80 that is connected to the wheel assembly 22' moves towards the second wheel assembly 24'. It is recognized that if pneumatic tires are being use in the wheel assembly 22' that the tires will take a portion of the recoil and in many cases will be sufficient to absorb all of the recoil needed. In the event that the spindle 80 which is connected to the axle 20 moves towards the second wheel assembly 24', the axle 20 pivots about the other wheel assembly 22 and slides relative to the pin 34 without inducing any bending moments in the axle 20. Simultaneously therewith the arm 70 slides along t#e surface 74 relative to one end of the force transmitting Ifiesber 48 causing extension of the rod 58 relative to the horsing 56 against the bias of the pressure in the pressure chamber 68. The fluid displaced in the pressure chamber 68 as a result of the movement of the rod 58 is forced out the port 64 to the tank 92 through the conduit 98, the switching valve 94 and the relief valve 104. Since the setting of the pressure relief valve 04 has not changed, the force on the axle 20 through the arm 70 does not change with the above-noted movement. As the foreign object moves out fro between the belt and wheel assembly, the axle 20 re. rns to its original position by fluid under pressure entering the pressure chamber 68 causing movement of the piston 68, rod 5±, arm 70f and axle 20. The swivel bearing 36 further allows the axle 20 to pivot about the pin 34 in the event one of the wheel assemblies 22,22' runs over a raised object on the ground. The force transmitting member 48 pivots about the pivot pin 46 thus allowing the jack assemblies 50 and arms 70 to pivot simultaneously with any pivoting movement of the axle 20 about the pin 34. In the event that tensioning of the belts 26,28 cause relative misalignment of the rotating axis of the wheel assemblies 22,22', the adjusting assemblies 82 are adjusted in order to move the wheel assembly 22/22' about the pivot point 72 to realign the respective wheel assembly 22/22'. If it is desirable to change one or both of the belts 26,28, the switching valve 94 is moved to its other position thus directing pressurized fluid to the pressure chambers 66 of the jack assemblies 50. The pistons 60 and associated rods 58 resulting in the axle 20 moving along the pin 34 towards the second pair of wheel assemblies 24,24'. After the new belt(s) have been installed, the switching valve 94 is returned to the original position thus directing the pressurized fluid into the pressure chambers 68 of the jack assemblies 50 to tension the belts as previously described. In view of the foregoing, it is readily apparent that the belt tensioning mechanism 31 shown and described in the various ernbodiments provides a simple mechanism having the ability to provide zilch tensioning forces in the belts 26,28 while still allowing the axle 20 of the vehicle 1G to swivel and slide in a longitudinal direction relative to the frame 14 of the vehicle 10 to compensate for recoil action of one of the wheel assemblies 22,22' relative to the other.

Claims: CLAIMS 1. A vehicle (10) having a frame (14) with a central, vertical longitudinal plane (18); an axle (20) connected to the frame at one end of the vehicle and extending thereacross through the plane, a first pair of wheel assemblies (22,22') rotatably mounted on opposite ends of the axle independently of the frame; a second pair of driving wheel assemblies (24,24') rotatably mounted on opposite sides of the frame at the other end of the vehicle; and first and second tracks (26,28) entrained about the wheel assemblies on respective sides of the vehicle; characterised in that the tracks are substantially inextensible belts (26,28); in that there are means (32) for universally swivelling the axle (20) relatively to the frame (14) and for enabling the axle to slide longitudinally of the frame; and in that there are means (42) for adjusting the position of the axle (20) relatively to the frame (14) to maintain a predetermined tension in the belts while permitting the swivelling and longitudinal movement of the axle. 2. A vehicle according to claim 1, wherein the swivel means (32) includes a pin (34) and a universally swivelling bearing (36) slidably mounted on the pin (34), one of the pin (34) and the swivel bearing (36) being secured to the axle (20) at a point midway between the ends of the axle (20) and the other 6f the pin (34) and swivel bearing (36) being secured to the frame (20) at the one end of the frame in the'central plane (18). 3. A vehiclevaccording to claim 2, wherein the pin (34) is attached'. to the frame (14) and the swivel bearing (36) is attached to the axle (20). 4. A vehicle according to claim 2 or claim 3, wherein the adjusting means (42) includes a force generating mechanism (44) connected between the frame (14) and the axle (20) and being adapted to move the axle (20) relatively to the frame (14) to establish the predetermined tension in the first and second belts (36,28). 5. A vehicle according to claim 4, wherein the force generating mechanism (44) includes a jack mechanism (45) pivotably connected at one end to the frame (14) and extending along the central plane (18) and a force transfer mechanism (69) connected to opposite ends of the axle (20) and operatively connected to the other end of the jack mechanism (45). 6. A vehicle according to claim 5, wherein the jack mechanism (45) includes a pivot pin (46) connected to the frame (14) along the central plane (18) longitudinally remote from and in axial alignment with the pin (34), a force transmitting member (48) pivotably mounted on the pivot pin (46) and a pair of jack assemblies (50) each respectively connected between opposite ends of the force transmitting member (48) and the force transfer mechanism (69). 7. A vehicle according to claim 6, wherein the force transfer mechanism (69) includes a pair of force transmitting arms (70) each connected between one of the jack assemblies (50) and one of the ends of the axle (20). 8. A vehicle according to claim 7, wherein each of the jack assemblies (50) includes a rod end portion (52) and a head end portion (54) with one of the end portions (52,54) of the jack assemblies (50) being connected to the opposite ends of the force transmitting member (48) and the other of the end portions (52,54) of the jack assemblies (50) being connected to the respective force transmitting arms (70). 9. A vehicle according to any one of claims 6 to 8, wherein each of the jack assemblies (50) is arranged to generate at least a predetermined force on the axle (20) for tensioning the first and second belts (26,28) and is independently movable in response to one end of the axle (20) moving longitudinally relatively to the frame {14) while maintaining at least the predetermined tension in the first and second belts (26,28). 10. A vehicle according to any one of claims 4 to 9, wherein the force generating mechanism (44) includes means (78) for aligning each of the first pair of wheel assemblies (22,22') relatively to the respective belt (26,28) so that the wheel assemblies are maintained in alignment with the belts. 11. A vehicle according to claim 10, when dependent at least on claim 7, wherein each of the force transmitting arms (70) is pivotally connected to the axle (20) by a pin joint (72) and the aligning means (78) includes a pair of spindles (80) pivotably connected to the respective end of the axle (20) and having the respective wheel assembly (22,22') rotatably mounted on one end of each spindle (80), and a pair of adjusting assemblies (82) connected between the respective spindle (80) and the respective force transmitting arm (70). 12. A vehicle according to claim 11, wherein each of the spindles (80) is connected at one end to the axle (20) at the respective pin joint (72) and each of the adjusting assemblies (82) is connected to the other end of the respective spindle (80). 13. A vehicle according at least to claim 6, wherein the pair of jack assemblies (50) are operative selectively to retract the axle (20) and the first pair of wheel assemblies (22,22') towards the second pair of wheel assemblies (24,24') so that the first and second belts (26,28) may be changed.

Inventors: SATZLER, RONALD L.
Applicants: CATERPILLAR INC.
Application year: 1985
Main classification: B62D55
IPC codes: B62D55, E02F9