GB2114519A - Steering arrangements for vehicles - Google Patents

Abstract

A steering arrangement for a vehicle having two sets of steered wheels comprises a two lever steering assembly (20, 21) in which the two levers (20 and 21) are interconnected by a pivotal mounting (10). Retainer means (27) having two operational modes are provided; A four wheel steer operational mode where the two levers are locked to provide an effectively rigid lever assembly to enable the two sets of wheels to be steered in unison and a two wheel steer operational mode where the levers are released such that one lever can pivot with respect to the other lever, to permit one set of wheels to be steered independently of the other. <IMAGE>

Description

SPECIFICATION Steering arrangements for vehicles This invention relates to steering arrangements for vehicles In particular, although not exclusively, the invention relates to steering arrangements for vehicles having at least two sets of wheels capable of being steered, such vehicles are commonly referred to as four wheel steer vehicles and frequently are used in underground mine installations where the vehicles are required to negotiate roadway junctions.

In one known four wheel steer vehicle the two axles associated with the two sets of wheels, respectively, are linked by a longitudinally extending linkage to ensure that all the four wheels steer in unison. One problem encountered when operating on steep gradients is that the vehicles can slide sideways into the side of the roadway and in such circumstances attempts to steer away from contact with the roadway side are found abortive due to the rear wheels attempting to steer towards the roadway side as the front wheels are steered away from the roadway side.

An object of the present invention is to provide a steering arrangement for a four wheel steer vehicle which tends to reduce or eliminate the above mentioned problem.

According to the present invention a steering arrangement for a vehicle having two sets of steerable wheels comprises a two lever steering assem bly in which the two levers are interconnected by a pivotal mounting, two links for steerably connecting the two levers to the two sets of wheels, respective ly, and retainer means having two alternative operation modes in one mode of which the two levers are locked to provide an effectively rigid lever component and in the other mode of which the two levers can pivot with respect to each other about the pivotal mounting under the action of two rams, in use, one operational mode of the retainer means enabling the two sets of wheels to be steered in unison and in the other operational mode enabling one set of wheels to be steered independently of the other set of wheels.

Preferably, the retainer means comprises hyd raulically actuated detent means.

Advantageously, the hydraulically activated detent means are urged by hydraulic pressure towards one operational mode and by resilient means towards the other operational mode.

Preferably, the locked effectively rigid lever com ponent is capable of pivotal movement about the pivotal mounting.

Advantageously, the locked effectively rigid lever component is urged to pivot about the pivotal mounting by one of said two rams.

Preferably, valve means are provided tending to hydraulically lock the other of said two rams.

Conveniently, the steering arrangement compris yes two steering control units, means being provided to ensure that at any one time only one steering control unit is operable to steer the vehicle.

The present invention also provides a vehicle having two sets of steerable wheels and a steering arrangement substantially as defined above.

By way of example, one embodiment of the present invention will be described with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically a prior known steering arrangement for a four wheel steer vehicle; Figure2 shows a plan detail of a steering arrangement constructed in accordance with the present invention; Figure 3 shows an incomplete longitudinal sectional view through the detail of Figure 2; and Figure 4 shows a hydraulic circuit diagram for a steering arrangement constructed in accordance with the present invention.

Figure 1 shows diagrammatically to steering arrangement for a conventional four wheel steer vehicle on which the four steerable wheels 1,2,3 and 4 are arranged in two sets 1 and 2, and 3 and 4.

Each wheel is rotatably mounted on a cranked bracket 5 with the two brackets 5 in each set of wheels linked by two cross links 6. A further cranked bracket 7 pivotally connects the adjacent ends of each pair of cross links 6 to a longitudinally extending link 8 which, in turn, are pivotally connected to a rigid lever 9 pivotally supported to the vehicle chassis at pivotal mounting 10 and to a double acting ram 11 at mounting 12. The cranked brackets 5 and 7 are pivotally mounted to the vehicle chassis at mountings 13 and 14, respectively, and the cross links 6 are pivotally connected to the cranked brackets 5 and 7 by mountings 15 and 16 respectively. The longitudinally extending links 8 are pivotally connected to the cranked brackets 7 and to the lever 9 by pivotal connections 17 and 18, respectively.The two connections 18 are an equal distance from the mounting 10. Thus in operation of the prior known four wheel steering arrangement timing the steering wheel (not shown) adjusted the extension of ram 11 to pivot the lever 9 about the pivotal mounting 10 to vary the setting of the links 6 and 8 and cranked brackets 5 and 7 to steer the four wheels 1,2,3 and 4 in unison. Thus, the four wheel steer vehicle lent itself to use in underground mines where relatively tight bends have to be negotiated.

As previously mentioned in the introduction to this specification such a known vehicle suffers from the disadvantage that should the vehicle slide sideways to contact a roadway side it is not possible to steer the vehicle away from the roadway side. It will be appreciated that because the four wheels are steered in unison as one set of wheels is turned to try and steer the vehicle away from the roadway side the other set of wheels simultaneously is turned tending to steer the vehicle towards the roadway side.

The above problem tends to be overcome or reduced by the steering arrangement constructed in accordance with the present invention. Such a construction now is described with reference to Figures 2, 3 and 4 of the drawings.

Figures 2 and 3 show a two lever steering assembly which replaces the rigid lever 9 of the conventional steering arrangement of Figure 1. The steering assembly comprises two levers 20 and 21 pivotally interconnected by the pivotal mounting 10 which as in the previously described embodiment is fixedly mounted to the vehicle chassis. Both the levers 20 and 21 are pivotally connected by mountings 18 to the two longitudinally extending links 8 also referred to in the description of the conventionally known steering arrangement, the pivot pins being omitted on Figure 3. Double acting rams 22 and 23 are provided for urging the levers 20 and 21 about the pivotal mounting 10, the rams being pivotally connected to the associated lever by mountings 18.The pivot pins from the mountings 18 are omitted on Figure 3 and the piston rods of the rams are indicated by reference numbers 24 and 25, respectively.

Retainer means having two alternative operational modes are provided on the levers 20 and 21. In one operational mode the retainer means locks the two levers 20 and 21 to provide an effectively rigid lever component 20, 21 which in use operates in the same manner as the rigid lever 9 of the conventional four wheel steer vehicle shown in Figure 1. In the other operational mode the retainer means releases the two levers 20 and 21 which, thereby, are allowed to pivot relatively to one another under the action of the associated ram 22 or 23. In this second operational mode the steering arrangement permits one set of wheels to be steered independently of the other set of wheels.

The retainer means comprises a single acting hydraulic ram 27 mounted on the lever 20 and having a piston rod 28 movable within its cylinder 29 under the action offluid pressure against the action of resilient means constituted by a coiled spring 30 such that the tapered end 31 of the piston rod is urged towards the other lever 21. The arrangement is such that when the two levers are in a preselected aligned position the tapered end 31 of the piston rod engages in a hole 32 provided in a bush 40 in the lever 21 to lock the two levers to form an effectively rigid lever component. As shown in Figure 2 the lever 21 is provided with two outwardly extending curved abutment wings 50 for abutment by the tapered end 31 of the activated piston rod when the two levers 20 and 21 are out of the preselected aligned position.Once the ram 27 is activated by hydraulic pressure to extend the piston rod the tapered end slidably abuts one or other of the abutmentwings. Upon relative pivotal movement of the two levers towards the preselected aligned position the tapered end slides along the abutment wing until the hole 32 is engaged by the piston rod.

Thus, further relative movement of the two levers is prevented until the hydraulic ram 27 is de-activated and the piston rod retracted under the actional of the spring 30.

A seal is provided to prevent leakage of pressure fluid from the ram 27. Pressure fluid is fed to the ram via an inlet port 41. It should be noted that in Figure 2 the retainer means are shown in the operational mode in which the two elvers 20 and 21 are permitted to pivot relatively to one another, ie the tapered end 31 of the piston rod 28 is disengaged from the hole 32 under the action of the resilient bias. In Figure 3 the two levers 20 and 21 are shown in the preselected algined position with the retainer means activated i.nto the operational mode in which hydraulic pressure fed to the ram 27 is retaining the tapered end 31 ofthe piston rod 28 engaged within the tapered hole 32.

Figure 4 shows the hydraulic circuit diagram for the embodiment of the steering arrangement previously discussed with reference to Figures 2 and 3.

In Figure 4 the rams 22,23 and 27 are shown.

The hydraulic circuit diagram shows a steering arrangement for a double ended vehicle having a driving cab at each end of the vehicle. A selector valve 50 is provided to select which of the two steering control units 51 or52 is operable to steer the vehicle at any one time. The valve is provided a manually operable handle 53.

Each of the steering control units 51, 52 comprise a steering unit 54, 55 having a distributor valve and a rotary meter. Atypical steering unit is commercially obtainable, as for example, a Danfoss steering unit type OSPA or OSPB. Each steering unit 54 or 55 is mounted on the associated steering wheel column with the steering wheel shaft 56, 57 extending into the steering unit such that when the steering wheel is actuated, the distributor valve directs pressure fluid fed to the unit from a pump 58, via the rotary meter, to one or other cylinder port 59 or 60 depending upon the direction of rotation of the steering wheel. The rotary meter ensures that the volume of pressure fluid supplied to each cylinder port is proportional to the angular rotation of the steering wheel.If the supply of pressure fluid fed to the inlet port 61 from the pump 58 ie manual steering of the vehicle is maintained. An outlet port 62 is provided to feed excess supply of pressure fluid back to tank.

From the outlet ports 59, 60 pressure fluid is fed via flow control valves 65 to associated inlet ports 63,64 of the previously discussed double acting rams 22, 23. The flow control valves 65 are pilot operated against resilient loading by fluid pressure fed from the previously mentioned selector valve 50.

The valves 65 provide means for ensuring that at any one time only the desired steering control unit can be operated to steer the vehicle. In Figure 4 the valves 65 associated with the steering control unit 52 are shown in the operational mode determined by the resilient bias without being fed with pilot fluid.

Each set of inlet ports 63, 64 also is connected to a pilot operated flow control valve 70 provided to ensure that when the steering arrangement take up a two wheel steer mode hydraulic ram associated with the set of none steered wheels is hydraulically locked in position. A selector valve 71 is provided in each driving cab to selectwhethertwo or four wheels steer drive arrangement is desired. In Figure 4 both the selector valves 71 are shown in the two wheel steer mode with both rams 22, 23 hydraulically locked in position.

In operation, the vehicle driver operates cab selector valve 50 to select which cab is to be at the front of the vehicle, ie which cab is to be the driving cab. In Figure 4, the valve 50 is shown feeding pilot fluid pressure to actuate the pilot operated flow control valves 65 associated with the steering control unit 52 which thereby prohibits the control unit being used to steer the vehicle. Thus, steering control unit 51 is selected as the control unit in the driving cab. In addition, the driver actuates valve 71 to select the four wheel steer mode such that pressure fluid is fed via valve 50 to actuate the ram 27 of retainer means to lock the levers 20,21 to provide an effectively rigid lever component.

Pressure fluid is fed from the steering pump 58 via inlet port 61 to one or other of the outlet ports 59,60 or 62 depending upon the operational position of the steering wheel. If the driver wishes to steer the vehicle in a direction such that the piston rod 24 of ram 22 needs to be extended he will turn the steering wheel such that pressure fluid is fed to inlet port 63 of the ram. The ram extension is dependent upon the amount of pressure fluid fed to the ram, which in turn, is dependent upon the amount the steering wheel is turned.

A similar operational procedure occurs if the driver turns the steering wheel in the opposite direction, pressure fluid then being fed to the inlet port 64 of the double acting ram 24.

As the retainer means is actuated to lock the levers 20 and 21 to provide an effectively rigid lever component the vehicle is steered much as a conventional four wheel steered vehicle. The inlet ports 63, 64 of the ram 23 currently associated with the rear steering control unit 52 are connected to tank via the associated pilot operated valve 70 which is in the opposite operational mode to that shown in Figure 4.

Thus, the piston rod 25 of ram 23 is free to move and plays no part in the steering.

Should the driver desire to steer the vehicle as a two wheel steer vehicle then he actuates the valve 71 to cut off pilot fluid from the valve 70 which thereby moves under its spring loading into the position as shown in Figure 4, the connections to the two ports 63 and 64 of the ram 23 are effectively closed to hydraulically lock the ram in the previously set desired operational position. At the same time pressure fluid is exhausted from the ram 27 permitting the tapered end 31 of the piston rod 28 to move under its spring loading 30 to disengage the hole 32.

Thus, the retainer means releases the two levers 20, 21,from the locked effectively rigid condition permitting the lever 20 to pivot about the pivotal mounting 10 under the action of the ram 22, the lever 20 pivoting with respect to the lever 21 which is held in the previously mentioned preselected desired position by the hydraulically locked ram 23.

The steering operation is similar to that previously described except only the leading set of wheels are steered by turning the steering wheel.

It will be understood that if the vehicle slides while negotiating a steep gradient such that the stationary vehicle body finishes in contact with the roadway side prohibiting any vehicle movement in a direction towards the roadway side, the operator can steer away from the side by first placing the control in four wheel steer mode and applying full lock to the steering wheel such that the rear set of wheels are directed away from the roadway side, the vehicle remaining stationary throughout the steering adjustments. Once the rear wheels are directed away from the roadway side the driver switches the steering mode to two wheel steer thus hydraulically locking the rear wheels in the preset direction away from the roadway side. With the vehicle steering control in the two wheel steer mode the driver steers the front wheels into a direction away from the roadway side.

When started the vehicle drives away from the roadway side with both sets of wheels directed away from the roadway side.

Once the vehicle is clear of the roadway side the driver operates the steering control into the four wheel steer mode the valve 71 feeding pilot fluid to the flow control valve 70 which thereby connects the ram connections 63 and 64 to tank permitting movement of the ram 23 with the lever 21. Simultaneously, the ram 27 of the retainer means is activated to move the piston rod against the spring loading 30 such that the tapered end 31 is caused to abut one or other of the flanged wings 80. Upon pivotal movement of the lever 20 about the pivotal mounting 10 the levers 20 and 21 reach an aligned position when the tapered end 31 engages the hole 32 to lock the two levers 20 and 21 to provide an effectively rigid lever component. Thereafter, until the valve 71 is re-activated the vehicle steers a conventional four wheel steer vehicle.

Claims (9)

1. A steering arrangement for a vehicle having two sets of steerable wheels, comprising a two lever steering assembly in which the two levers are interconnected buy a pivotal mounting, two links for steerably connecting the two levers to the two sets of wheels, respectively, and retainer means having two alternative operational modes in one mode of which the two levers are locked to provide an effectively rigid lever component and in the other mode of which the two levers can pivot with respect to each other about the pivotal mounting under the action of two rams, in use, one operational mode of the retainer means enabling the two sets of wheels to be steered in unison and in the other operational mode enabling one set of wheels to be steered independently of the other set of wheels.

2. An arrangement as claimed in claim 1, in which the retainer means comprises hydraulically actuated detent means.

3. An arrangement as claimed in claim 2, in which the hydraulically actuated detent means are urged by hydraulic pressure towards one operational mode and by resilient means towards the other operational mode.

4. An arrangement as claimed in claim 1, 2 or 3, in which the locked effectively rigid lever component is capable of pivotal movement about the pivotal mounting.

5. An arrangement as claimed in claim 4, in which the locked effectively rigid lever component is urged to pivot about the pivotal mounting by one of said two rams.

6. An arrangement as claimed in claim 5, in which valve means are provided tending to hydraulically lock the other of said two rams.

7. An arrangement as claimed in any one of the preceding claims, in which the steering arrangement comprises two steering control units, means being provided to ensure that at any one time only one steering control unit is operable to steer the vehicle.

8. A steering arrangement for a vehicle having two sets of steerable wheels, substantially as described herein and substantially as shown in the accompanying drawings.

9. Avehicle comprising two sets of steerable wheels and a steering arrangement as claimed in any one of the preceding claims.