GB2074519A - Steering mechanism for skid- steer vehicles - Google Patents

Abstract

Mechanism for steering a vehicle by causing the tracks or wheel sets of the vehicle to be driven at different speeds includes two epicyclic gear trains, the sun wheels (25 and 35) of which are mounted on a transverse shaft (24) which is driven by the vehicle engine. The planet wheels (26, 27 and 36, 37) of the respective gear trains are mounted on carriers (28 and 38) which are connected to respective drive shafts (4 and 5). The planet wheels are in mesh not only with their respective sun wheels, but also with internal teeth of respective ring gears (29 and 39). The ring gears (29 and 39) are provided with external teeth which mesh respectively with pinions (65 and 66) mounted on shafts (67 and 68) which are coupled by gear wheels (69 and 70). Means such as an electric motor 81 or a hydrostatic motor are provided for driving one of the shafts (67 and 68) to cause the ring gears (29 and 39) to rotate at equal variable speeds in opposite directions to cause turning of the vehicle. <IMAGE>

Description

SPECIFICATION Steering mechanism for skid-steer vehicles This invention relates to steering mechanism for skid-steer vehicles, which term is used herein to include track-laying vehicles steered by their tracks and also vehicles having a plurality of coupled driving wheels on each side of the vehicle and steered by changing the relative speed of the wheel sets on the two sides.

One known type of steering mechanism for a skid-steer vehicle includes a differential gear connected between the vehicle engine and the members driving the tracks or wheel sets. In such an arrangement, means are provided to apply a braking force to one or other of the tracks or wheel sets so that the speed of that track or wheel set decreases and the speed of the other track or wheel set increases. Any such arrangement is wasteful of power because at least some of the output of the vehicle engine is absorbed in the braking device.

Another type of steering arrangement for a skid-steer vehicle includes a clutch and brake between the engine and the right track or wheels, and a clutch and brake between the engine and the left track or wheels. Any such arrangement allows only straight ahead travel with power to both tracks or wheel sets. Only half the traction is available on turns and much of the remaining half is robbed to turn the vehicle itself on short turns.

Yet another type of steering arrangement for a skid-steer vehicle includes a continuously-variable speed drive to each track or wheel sets. Such arrangements are more efficient than those mentioned in the preceding paragraphs, but are very expensive and complicated.

It is an object of the present invention to provide a steering mechanism for a skid-steer vehicle which does not suffer from the disadvantages of the two types of mechanism referred to in the preceding paragraphs.

From one aspect the invention consists in a steering mechanism for a skid-steer vehicle comprising two epicyclic gear trains, wherein the sun wheels of the two trains are driven at the same speed, wherein the planet wheel carriers of the two trains drive respective ones of the tracks or wheel sets, and wherein means are provided to rotate the annuli of the two trains at equal variable speeds in opposite directions.

Preferably the two epicyclic gear trains are arranged coaxially, the two sun wheels being mounted at opposite ends of a single drive shaft or on two coaxial drive shafts constrained to rotate together. The drive shaft, or shafts, will normally be arranged transversely in the vehicle, and will be driven through a driving pinion and crown wheel.

Preferably each annul us is provided with external as well as internal teeth, and a respective pinion meshes with each of the external gears. The two pinions are mounted on shafts which are interconnected by a pair of gear wheels. Thus if one of the shafts rotates, it causes the other shaft to rotate in the opposite direction. The two pinions have the same number of teeth, and the two gear wheels provide a 1:1 ratio. Thus the two shafts are constrained to rotate at equal speeds.

It is to be understood that, assuming that there is resistance to movement of the tracks or wheel sets, the two annuli will be subjected to forces tending to rotate them in the same direction.

However, since they are coupled so that they can only rotate in opposite directions, they will remain stationary if the resistance to movement of the two tracks or wheel sets is the same.

To ensure that the vehicle may be caused to move in a straight path, means are provided to apply a braking force to one of the two shafts.

However, it is to be understood that this arrangement will not absorb power from the engine in the same way as the normal differential type of steering mechanism.

Means are also provided to rotate one of the shafts at a controlled rate. Preferably the torque required to cause this rotation is derived from the vehicle engine through an infinitely-variable drive system. This system may be, for example, a hydrostatic drive or an electromagnetic drive. In any case, it will be understood that the torque required to produce turning of the vehicle is low in comparison to the torque required to drive the vehicle. Thus the hydrostatic drive can be very much smaller than would be required if hydrostatic drives were provided between the vehicle engine and each track.

Alternatively the shaft may be rotated by a reversible d.c. electric motor powered by secondary batteries charged by the vehicle engine.

This system has the advantage that steering control is retained even in the event of engine failure.

Methods of performing the invention will now be described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a plan view of a track-laying vehicle incorporating a steering mechanism in accordance with the invention; Figure 2 is a cross-sectional view of the steering mechanism used in the vehicle illustrated in Figure 1 taken on the line 2:2 looking in the direction of the arrows; and Figure 3 is a plan view of a skid-steer wheeled vehicle incorporating a steering mechanism in accordance with the invention.

The vehicle illustrated in Figure 1 is a tracklaying tractor provided with a bull-dozer shovel, or the like, indicated diagrammatically at 1. The vehicle is driven by an engine which is located in the region designated by the reference numeral 2.

Bolted to the rear of the engine fly wheel housing is a gear box (not shown) which transmits engine power to a propeller shaft 3. This propeller shaft drives a pair of output shafts 4 and 5 through the steering mechanism 86. Each of the shafts 4 and 5 is coupled to a respective track driving sprocket 6 or 7. The track driven by the sprocket 7 is indicated at 8. The vehicle is provided with five pairs of wheels 9, each pair being independently sprung by means of torsion bars such as those illustrated at 10. The vehicle is steered by means of a steering wheel 11 which controls the drive to a shaft 1 2 which provides control input to the steering mechanism 6.

The steering mechanism, which is illustrated more particularly in Figure 2, includes a bevel pinion 22 secured on the end of the propeller shaft 3. The bevel pinion 22 meshes with a crown wheel 23 which is itself fixed to a transverse shaft 24. It is to be understood that the shaft 24 may in fact be constituted by two coaxial shafts each having a spline meshing with one half of the internal spline of the crown wheel. The crown wheel 23 and the shaft 24 are mounted in taper roller bearings 71 and 72 which are respectively secured in walls 73 and 74 of a housing 75. The transverse shaft 24 carries sun wheels 25 and 35 of two epicycle gear trains. Planet wheels of the respective gear trains are shown at 26, 27, 36 and 37.The two planet wheels 26 and 27 are rotatably mounted on a carrier 28, and the two planet wheels 36 and 37 are rotatably mounted on a carrier 38. The carrier 28 is connected to the drive shaft 4 which carries the sprocket 6. The drive shaft 4 is rotatable in taper roller bearings 41 and 42. The bearings 41 and 42 are carried in a member 43 which is bolted to a housing member 44 which is itself bolted to the housing 75.

Similarly, the carrier 38 is connected to the drive shaft 5 which carries the sprocket 7. The drive shaft 5 is rotatable in taper roller bearings 51 and 52. The bearings 51 and 52 are mounted in a member 53 which is bolted to a housing member 54 itself bolted to the housing 75. Preferably conventional coupling arrangements (not shown) are provided between the drive shafts 4 and 5 and the respective sprockets 6 and 7 to enable the sprockets to be separated from the steering mechanism.

The planet wheels 26 and 27 are in mesh not only with the sun wheel 25, but also with internal teeth of an annulus or ring gear 29. Similarly, the planet wheels 36 and 37 are in mesh not only with the sun wheel 35, but also with the internal teeth of an annulus 39. If the two annuli 29 and 39 were to be held stationary, rotation of the bevel gear 22 would cause the two shafts 4 and 5 to rotate at the same speed. Under these circumstances, the two epicyclic gear trains would act merely as reduction gears. However, in accordance with the invention, the two annuli 29 and 39 are rotatably mounted. For this purpose, they are carried on spiders 61 and 62 respectively, these spiders being rotatably mounted on bearings 63 and 64 respectively secured in the walls 73 and 74. In addition, the annuli 29 and 39 are provided with external teeth which mesh respectively with pinions 65 and 66.The pinion 65 is fixed to a shaft 67 and the pinion 66 is fixed to a shaft 68. These two shafts are coupled by means of a pair of gear wheels 69 and 70. These two gear wheels have the same number of teeth so that rotation of the shaft 68 causes equal and opposite rotation of the shaft 67. The shaft 67 is mounted in a bearing 76 carried by the housing 75, and a bearing 77 carried by the housing member 44. Similarly, the shaft 68 is rotatably mounted in a bearing 78 and a bearing 79 carried by the housing member 54.

The shaft 68 extends through the housing member 54 as the control shaft 12 which is connected to a reduction gear train 80. The input of this gear train is connected to the output shaft of a d.c. electric motor 81. The motor 81 is connected to a battery (not shown) through a control circuit (also not shown) coupled to the steering wheel 11. The control circuit enables the steering wheel 11 to cause rotation of the motor 81 in either direction. As the steering wheel is turned in one direction from a central position, the motor 81 is caused to rotate in one direction, and its speed is increased as the steering wheel 11 is turned further away from the central position.

Similarly, if the steering wheel is turned away from the central position in the opposite direction, the motor 81 is caused to rotate at an increasing velocity in the opposite direction.

As is already stated, rotation of the shaft 68 in one direction causes rotation of the shaft 67 in the opposite direction, and this produces equal and opposite speeds of rotation of the annuli 29 and 39. Thus rotation of the shaft 68 in one direction will increase the speed of rotation of the shaft 4 and decrease the speed of rotation of the shaft 5 assuming constant speed of rotation of the propeller shaft 3. Similarly rotation of the shaft 68 in the opposite direction will decrease the speed of rotation of the shaft 4 and increase the speed of rotation of the shaft 5. As is well-known, any difference in the speed of rotation of the two drive shafts 4 and 5 will cause the vehicle to change direction.If desired, the drive to the shaft 68 may be arranged so that is is possible to rotate the shaft at such a speed that it is effective not merely to reduce the speed of rotation of one of the drive shafts 4 and 5, but actually to cause this drive shaft to remain stationary or rotate in the opposite direction. Again, as is well-known, if the two shafts 4 and 5 rotate in opposite directions, very rapid turning of the vehicle may be produced.

The control system for the electric motor 81 preferably includes dynamic braking but, in addition, it should also include a separate electromagnetic brake operating to prevent rotation of the motor 81 when the steering wheel 11 is in the central position. Conveniently this braking system is controlled by a microswitch which is automatically closed when the steering wheel is in its central position.

Figure 3 of the drawings shows a vehicle generally similar to that illustrated in Figure 1 except that the tracks are replaced by three pairs of ground wheels 91,92, and 93. The wheels are carried on stub axles so that the wheels in each pair are rotabable independentiy. However, the three wheels on each side of the vehicle are respectively interconnected by chains so that all the wheels on one side rotate at the same speed.

Engine power is applied to the two sets of ground wheels through a steering mechanism 6 generally similar to that illustrated in Figure 2.

However, in this case, the control shaft 12 is driven by the vehicle engine through an infinitelyvariable hydrostatic drive system. As shown, the hydrostatic system consists of a fixed pump and a variable motor 94, the pump being driven by the vehicle engine. The variable motor is a swivelmounted axial piston motor which is controlled by the steering wheel of the vehicle so that rotation of the steering wheel in one direction causes increasing rotation of the shaft 1 2 in one direction, while rotation of the steering wheel in the opposite direction causes rotation of the shaft 12 in the opposite direction. When the steering wheel is in its central position, the hydrostatic system holds the shaft 12 stationary.

As in the case of the tracked vehicle illustrated in Figure 1, any difference in the speed of rotation of the two sets of ground wheels of the vehicle illustrated in Figure 3 will cause the vehicle to change direction.

Claims (17)

1. A steering mechanism for a skid-steer vehicle comprising two epicyclic gear trains, wherein the sun wheels of the two trains are driven at the same speed, wherein the planet wheel carriers of the two trains drive respective ones of the tracks or wheel sets, and wherein means are provided to rotate the annuli of the two trains at equal variable speeds in opposite directions.

2. A steering mechanism as claimed in Claim 1, wherein the two epicyclic gear trains are arranged coaxially, the two sun wheels being coupled to a single crown wheel driven by a bevel pinion.

3. A steering mechanism as claimed in Claim 2, wherein each annul us is provided with external as well as internal teeth, and a respective pinion meshes with the external teeth of each annulus.

4. A steering mechanism as claimed in Claim 3, wherein the two pinions are mounted on shafts which are interconnected by a pair of gear wheels so that rotation of one of the shafts causes the other shaft to rotate at the same speed in the opposite direction.

5. A steering mechanism as claimed in Claim 4, including means for applying a braking force to one of said two shafts.

6. A steering mechanism as claimed in Claim 4, including means for rotating one of said shafts at a controlled rate.

7. A steering mechanism as claimed in Claim 6, wherein said means for rotation is constituted by an infinitely-variable hydrostatic drive system deriving power from the vehicle engine.

8. A steering mechanism as claimed in Claim 6, wherein said means for rotation comprises an electric motor powered by a battery through a variable control system.

9. A steering mechanism for a skid-steer vehicle comprising: A) first and second sun wheels; B) bearing means for coaxially mounting said sun wheels; C) means for driving said sun wheels at the same speed; D) a set of first planet wheels rotatably mounted on a first carrier rotatable about the common axis of said sun wheels, each of said first planet wheels meshing with said first sun wheel; E) a set of second planet wheels rotatably mounted on a second carrier rotatable about the common axis of said sun wheels, each of said second planet wheels meshing with said second sun wheel; F) first and second output shafts driven respectively by said first and second carriers; G) a first annulus rotatable about the axis of said sun wheels, said first annulus having internal and external teeth, and said internal teeth meshing with said first planet wheels;; H) a second annulus rotatable about the axis of said sun wheels, said second annulus having internal and external teeth, and said internal teeth meshing with said second planet wheels; I) a first pinion meshing with the external teeth of said first annulus, and fixed to a first shaft; J) a second pinion meshing with the external teeth of said second annulus and fixed to a second shaft, said first and second shafts being coupled by means of gear wheels so that they are constrained to rotate at equal speeds in opposite directions; and K) reversible means for driving said first shaft.

10. A steering mechanism as claimed in Claim 9, wherein said reversible means comprises an infinitely-variable hydrostatic system powered by the vehicle engine.

11. A steering mechanism as claimed in Claim 9, wherein the reversible means comprises an electric motor powered by a battery through a variable control system.

12. A track-laying vehicle steered by its tracks and including a pair of track driving sprockets coupled to a vehicle engine through a steering mechanism as claimed in Claim 9.

1 3. A skid-steer wheeled vehicle having a plurality of coupled driving wheels on each side of the vehicle, said driving wheels being connected to a vehicle engine through a steering mechanism as claimed in Claim 9.

14. A steering mechanism for a skid-steer vehicle substantially as hereinbefore described with reference to, and as illustrated in, Figure 2 of the accompanying diagrammatic drawings.

1 5. A track-laying vehicle steered by its tracks substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 of the accompanying diagrammatic drawings and including a pair of track driving sprockets coupled to a vehicle engine through a steering mechanism substantially as hereinbefore described with reference to, and as illustrated in, Figure 2 of the accompanying diagrammatic drawings.

1 6. A skid-steer wheeled vehicle substantially as hereinbefore described with reference to, and as illustrated in, Figure 3 of the accompanying diagrammatic drawings, said vehicle having a plurality of coupled driving wheels on each side of the vehicle, and said driving wheels being connected to a vehicle engine through a steering mechanism substantially as hereinbefore described with reference to, and as illustrated in, Figure 2 of the accompanying diagrammatic drawings.

17. Any features of novelty, taken singly or in combination, of the embodiments of the invention as herein before described with reference to the accompanying diagrammatic drawings.