GB2180511A

GB2180511A - Four-wheel steering system for vehicles

Info

Publication number: GB2180511A
Application number: GB08621002A
Authority: GB
Inventors: Rodney Holmes
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-08-29
Filing date: 1986-08-29
Publication date: 1987-04-01
Also published as: GB8521469D0; GB8621002D0

Abstract

A four wheel steering system incorporates a torque shaft (22) inter-connecting a first, front wheel steering rack (18) and a rear wheel steering rack (26), via pinions at each end of the shaft. The system includes a speed sensing transducer (58) that actuates a latch (84) in a rear steering rack (26) when a vehicle reaches a speed above a predetermined value, to fix the rear axle to provide conventional front wheel steering, upon the wheel reaching a straight-ahead position. A slipping clutch arrangement (32) can be positioned between the shaft (22) and the rear axle, to provide a smooth engagement of the rear gear, and resilient means can be incorporated therein, or in the shaft (22) to store energy provided, e.g. on driving away from a kerb, when the rear wheel adjacent the kerb is allowed to deflect from its "normal" turned position. <IMAGE>

Description

SPECIFICATION Improvements in or relating to vehicle steering assemblies The present invention concerns improvements in or relating to vehicle steering assemblies, especially but not exclusively steering assemblies for small passenger and light commercial vehicles.

The use of many small passenger and light commercial vehicles in heavily congested areas, for example inner cities, parking areas, loading and unloading areas, is hindered by the relatively large turning circle of the vehicle.

For example, the turning circle required by London taxi cabs is 7.6m (25 feet) and whereas certain vehicles approach this turning circle most have turning circles of around 10.7m (35 feet). Often the turning circle cannot be improved without complicated and expensive engineering modification and it is an object of the present invention to provide a steering assembly which will give an improved turning circle but which is relatively cheap and reliable.

According to the present invention there is provided a steering assembly including a first rack and pinion steering gear for altering the steering angle of a pair of front wheels of a vehicle and a second rack and pinion steering gear for altering the steering angle of a pair of rear wheels of the vehicle, the first and second gears being connected together by a torque shaft rotatable by an auxiliary pinion meshing with the rack of the first gear.

Preferably the auxiliary pinion of the first gear has a greater diameter and number of teeth than the main pinion thereof so that the angular movement of the rear steerable wheels is less than the angular movement of the front steerable wheels. Conveniently the rear wheels may move through half the angle through which the front wheels move.

Preferably the torque shaft connected between the first and second gears incorporates one or more universal joints. Preferably the torque shaft has at least one section which will crush on impact.

Preferably means are provided for disengaging the second steering gear from the torque shaft. The means may comprise a solenoidoperated latch. The solenoid operated latch may be energized by a transducer sensing the vehicle's speed so that at a speed above a predetermined value the latch is disengaged to enable the rear steerable wheels to return to the true fore-and-aft direction at which stage it re-engages to lock the rear steerable wheels in this fore-and-aft direction.

Alternatively the disengaging means may comprise a hydraulically operated latch. Such a latch may be in contact with the rack of the second steering gear at all times, and means may be provided for the latch to move freely along said rack. The hydraulic system operating the latch may be actuated by a transducer sensing the vehicle speed so that at a speed above a predetermined value the latch is pressurized against the rear steering rack and when the rack returns to the true fore-and-aft direction the latch will engage the rack.

Preferably a mercury or pendulum switch is provided in series with the speed sensing transducer to prevent disengagement of the latch from said rack when the vehicle slows below said predetermined value at a rate greater than a predetermined de-accelaration, for example in the case of an emergency stop.

Preferably a slipping clutch is incorporated between the torque shaft and the second gear to facilitate smooth engagement and disengagement of the second gear.

Preferably a resilient connection in the form, for example, of a Bendix spring or an assembly of Bendix springs is incorporated in the connection between the torque shaft and the second gear so that when the rear wheels engage a lateral obstacle, for example a kerb, they deflect, the deflecting force being stored in the resilient means whereby on removal of the obstacle the wheels can return to the set steering angle.

Preferably said resilient means are utilised also to return the rear steered wheels to their correct steering angle with respect to the front steered wheels when the latch means are engaged after the vehicle returns to or below the said predetermined speed.

In a modification a rotation absorbing assembly is incorporated in the torque shaft, the assembly comprising first and second helically splined means of opposite hands engaged with corresponding splined means on the ends of the shaft into which the assembly is interposed, spring means being provided to bias the ends of the shaft away from each other.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 shows diagrammatically a plan of a vehicle steering assembly; Fig. 2 shows diagrammatically a front rack and pinion gear thereof; Fig. 3 shows a rotation absorbing assembly for incorporation in a torque shaft of the steering assembly; Fig. 4 shows diagrammatically a plan of a modified vehicle steering assembly; Fig. 5 shows a cross-sectional view of part of the assembly of Fig. 4; and Fig. 6 shows a perspective view of another part of the assembly of Fig. 4.

A four wheeled vehicle comprises a pair of front wheels 10 and a pair of rear wheels 12.

The front wheels 10 or the rear wheels 12 or both wheels 10 and 12 may be driven and the suspension means for the wheels may take any conventional form.

The front wheels 10 are steered in a conventional manner by a first rack and pinion steering gear 14 illustrated more clearly in Fig.

2. The assembly comprises a main or input pinion 16 connected to the steering column or power steering output shaft, a double-sided rack 18 and a second or auxiliary pinion 20 so mounted and of such dimensions that it rotates in a direction opposite to the main pinion 16 in a ratio of 2:1, that is for every two revolutions of the main pinion 16 the auxiliary pinion rotates once. The auxiliary pinion 20 is connected to a torque shaft 22 to transmit its rotation to a pinion 24 of a second rack and pinion steering gear which, in the embodiment illustrated, is mounted in front of the tubular rear axle 28 of the vehicle, the rear axle being provided with end inserts supporting swivel pin mounted stub axles (not shown).

It will be realised, therefore, that with a steering assembly of the type described above the turning circle of the vehicle can be considerably reduced. The arrangement is simple in its construction and consequently reliable and involves relatively little modification to an existing design of vehicle especially if that vehicle incorporates rack and pinion steering.

It is estimated that the handling of a vehicle and certainly its manoeuvrabiity will be considerably enhanced at lower speed and that at higher speed the rear steering assembly will not make any appreciable difference in normal handling.

In a modification, however, means are provided for disengaging the means for steering the rear wheels. It is envisaged that it is unlikely that the vehicle will be required to perform tight manoeuvres at speeds in excess of 12 m.p.h. and therefore automatic means are provided for disengaging the rear steering at and above this speed. Manual disengaging means may also be provided.

The automatic means comprise a speed sensitive transducer which, on reaching the predetermined speed, gives a signal which operates a solenoid latch 30 operable on the rear rack. On disengagement of the latch the self-centring castor action of the rear steering assembly causes the rear wheels to be returned to the true fore-and-aft direction at which stage the latch re-engages to lock the wheels in this position. To permit this movement a slipping clutch arrangement 32 is provided on the torque shaft 22 at or near its connection to the pinion 24 of the second steering gear. This clutch is actuated on operation of the latch actuating means so that when the predetermined speed has been reached and exceeded no drive is transmitted from the torque shaft 22 to the rear rack and pinion steering gear.

On returning to the predetermined speed and continuing at speeds beneath it, it is desirable that the rear wheels become steerable again and it will be realised that it is important that they return to a position where they are "in phase" with the front wheels. In other words if the front wheels are angled at 202 to the left, on re-engagement the rear wheels should be angled at 10' to the right. To achieve this a resilient assembly is incorporated in the torque shaft 22, the assembly comprising, for example, a pair of Bendix spring assemblies (not shown) similar to those incorporated in starter motors.The arrangement is such that when the rear steering wheels 1 2 move to the fore-and-aft position when the latch means is disengaged, the restoring force is stored in one or other of the Bendix springs so that on re-engagement of the latch means 30 and 32 the spring force is released to move the wheels back to a direction in phase with the front wheels.

The resilient assembly can be incorporated in the overall assembly in such a manner that problems which could be experienced by a four-wheel steer vehicle pulling away from a kerb can be obviated. Clearly in a normal situation the steered front wheels "drag" the unsteered rear wheels away from the kerb, the vehicle pivotting about a line normal to its rear axle. When all four wheels are steered in the manner described above the rear of the vehicle will tend to move towards the kerb and if precautions are not taken it may mount the kerb. The assembly of Bendix springs overcomes this problem by allowing the rear steered wheels to deflect on encountering a lateral obstacle, for example a kerb, and storing the deflecting force in the springs until the obstacle is cleared whereat the wheels return to the original position.

Various modifications can be made without departing from the scope of the invention. For example, the means for transmitting torque from the auxiliary pinion of the first rack and pinion steering gear to the pinion of the second gear may be modified. They may comprise, for example, hydraulic or electric transmission means.

A modification which dispenses with the need for the Bendix spring arrangement described above and the speed sensitive transducer and clutch means comprises a rotation absorbing assembly incorporated in the torque shaft 22. The assembly comprises a first helically splined shaft section 40 and a second helically splined section 42 the angle of the helix in the second section being opposite to that in the first. The sections 40, 42 are separated by a collar 44 and the hollow ends of the shaft 22 into which the arrangement is to be interposed are provided with corresponding helical splines, the shaft including also a telescopic arrangement (not shown).

Two similarly rated helical coil springs 46, 48 are arranged over the splined sections 40, 42 with their ends abutting the facing faces of the end of the shaft 22 and the collar 44.

In operation, if the rear wheels have not to be steered in accordance with a steering deflection of the front wheels, for example on hitting a kerb, rotation of the section of the shaft 22 connected to the first rack will result in relative movement between the splined assemblies 40, 42 and the shaft and will cause either the section 40 or the section 42 to move into the shaft end depending upon the direction of relative rotation between the shaft sections. This movement will of course be accompanied by an elongation of the telescopic connection in the shaft 22 and will take place against the restoring action of the respective coil spring 46 (48). When the obstacle is removed the energy stored in the coil spring will return the arrangement to the original position with the front wheels "in phase" with the rear wheels.

It will be realised that by careful choice of spring ratings and the castor effect of the rear wheel steering assembly it is preferable to ensure that at above a predetermined speed rotational movement of the front section of the shaft, imparted to it by the first rack and pinion means, will be absorbed in the assembly described above and will not be transmitted to the rear steerable wheels. Thus the need for the speed sensor solenoid and clutch is eliminated.

A further modification is shown in Figures 4 to 6, illustrating an assembly used with a power assisted steering system for disengaging the means for steering the rear wheels.

The system includes a hydraulic circuit with a reservoir 50 and a pump 52. The output of the pump is connected to a front steering rack 18 of a conventional type and a spool valve 56. The valve 56 is actuated by a speed sensing transducer 58 through a mercury or pendulum switch 60 and a relay 62.

A first output 64 of the valve 56 connects with the return feed 66 from the front steering rack 18 to the reservoir 50. A second output 68 of the valve 56 connects by a pipe 70 to a rack latch assembly 72 hereinafter to be described, mounted on a rear steering rack 26. A relief valve 74 is provided on the spool valve 56 connecting with the first output 64.

A connection with the second output 68 and the rack latch assembly 72 is usable for applying pressure to the rack latch assembly 72, and for fluid returning therefrom.

The rack latch assembly 72 as shown in Fig. 5, comprises a cylindrical housing 76 with an open end 78, mounted on the casing 80 of the rear steering rack 26 by a bolted plate 82. Movably mounted within the housing 76 is a latch 84 with a first end 86 thereof away from the closed end 88 of the casing 76, being tapered with a ball bearing 90 mounted on the apex thereof. Fixed on a second end of the latch 90 remote from the opening 78 of the casing 76 is a spool valve 94. The latch 84 is urged into a first position 96 substantially within the casing 76 but with the first end 86 protruding therefrom by a retaining spring 98 connected between the latch 84 and the closed end 88 of the casing 76. An end 100 of the pipe 70 remote from the valve 56 connects with the casing 76 at a location adjacent to the spool valve 94 of the latch 84 when in said first position 96.

Fig. 6 shows a section of the rear steering rack 26. A through hole 102 is provided substantially centrally of the rack 26 of a size to provide a sliding fit for the latch 96 therein.

The hole 102 has a lining 104 of a suitable hardened material. A longitudinal groove 106 is provided on the surface of the steering rack 26, the groove being radial with the hole 102.

When the latch 84 is in the first position 96 the ball bearing 90 is located to run along the groove 106. When the spool valve 56 is switched it provides pressure in the pipe 70, this pressure acting through the spool valve 94 onto the latch 84 in a direction towards the steering rack 26. When the steering rack 26 is moved into a position such that the hole 102 is aligned with the latch 84 the latch 84 is pushed into the hole to occupy a second position 108 with the tapered end 86 thereof resting on an insert 110 on the rack casing 80, the rear steering rack 26 is then locked with the rear wheels in the true fore-and-aft direction. Mounted on the closed end 88 of the casing is a micro-switch 112 connected to a warning light 114 which may be located within the vehicle.The microswitch 112 is actuated by compression of the spring 98 when the latch 84 is in the first position 96 providing an indication that the four wheel steering is in operation.

In use, upon starting the vehicle the light 114 will be luminated to indicate that the four wheel steering is in operation. The latch 84 will be held in the first position 96 by a retaining spring 98. The four wheel steering will continue to operate as the car moves off.

When a predetermined speed is reached, for example, 12 m.p.h. the transducer 58 will actuate the relay 62 switching the spool switch 56 providing pressure in the pipe 70 acting on the latch 84. When the hole 102 in the rear steering rack 26 is aligned with the latch 84 the latch will be forced into the hole 102 into the second position 108, locking the rear steering rack 26 and extinguishing the light 114.

When the vehicle slows below said predetermined speed the reverse procedure will take place with the retaining spring 98, upon removal of pressure in the pipe 70, pulling the latch 84 out of the hole 102 into the first position 96 illuminating the light 114. However, if the slowing down occurs at a rate greater than a predetermined acceleration, for example in the case of an emergency stop, the mercury or pendulum switch 60 will open, stopping the transducer 58 from switching the spool valve 56.

It will be appreciated that this assembly can be used when the front rack and pinion is not power assisted.

Claims

1. A steering assembly including a first steering gear for altering the steering angle of a pair of front wheels of a vehicle and a second steering gear for altering the steering angle of a pair of rear wheels of the vehicle, the first and second gears being connected together by a torque shaft rotatable by an auxiliary pinion meshing with the rack of the first gear.

2. An assembly as claimed in claim 1, in which the auxiliary pinion of the first gear has a greater diameter and number of teeth than the main pinion thereof so that the angular movement of the rear steerable wheels is less than the angular movement of the front steerable wheels.

3. An assembly as claimed in claim 2, in which the rear wheels move through half the angle through which the front wheels move.

4. An assembly as claimed in any of claims 1 to 3, in which the torque shaft connected between the first and second gears incorporates one or more universal joints.

5. An assembly as claimed in any of the preceding claims, in which the torque shaft has at least one section which will crush on impact.

6. An assembly as claimed in any one of the preceding claims, in which means are provided for disengaging the second steering gear from the torque shaft.

7. An assembly as claimed in claim 6, in which the disengaging means comprises a solenoid-operated latch.

8. An assembly as claimed in claim 7, in which the disengaging means comprises a soienoid-operated latch.

9. An assembly as claimed in claim 8, in which the latch is energized by a transducer sensing the vehicle's speed so that at a speed above a predetermined value the latch is disengaged to enable the rear steerable wheels to return to the true fore-and-aft direction at which stage it re-engages to lock the rear steerable wheels in this fore-and-aft direction.

10. An assembly as claimed in claim 7, in which the disengaging means comprises an hydraulically operated latch.

11. An assembly as claimed in claim 10, in which the latch is in contact with the rack of the second steering at all times.

12. An assembly as claimed in claim 11, in which means are provided for the latch to move freely along at least a part of said rack.

13. An assembly as claimed in claim 12, in which the free movement means comprises a ball bearing mounted on the latch and a corresponding groove provided on said rack.

14. An assembly as claimed in any one of claims 11 to 13, in which the hydraulic system operating the latch is actuated by a transducer sensing the vehicle's speed so that at a speed above a predetermined value the latch is pressurised against said rack, and when the rack returns to the true fore-and-aft direction the latch engages with said rack.

15. An assembly as claimed in claim 9 or 14 in which means are provided in series with the transducer to prevent disengagement of the latch from said rack when a vehicle slows below said predetermined value at a rate greater than a predetermined de-acceleration.

16. An assembly as claimed in claim 15, in which the disengagement prevention means is a mercury switch.

17. An assembly as claimed in claim 15, in which the disengagement prevention means is a pendulum switch.

18. An assembly as claimed in any of claims 6 to 17, in which, a slipping clutch is incorporated between the torque shaft and the gear to facilitate smooth engagement and disengagement of the second gear.

19. An assembly as claimed in claim 6, in which manual disengaging means are provided.

20. An assembly as claimed in any of the preceding claims, in which a resilient connection is incorporated in the connection between the torque shaft and the second gear so that when the rear wheels engage a lateral obstacle, for example a kerb, they deflect, the deflecting force being stored in the resilient means whereby on removal of the obstacle the wheels can return to the set steering angle.

21. An assembly as claimed in claim 20, in which the resilient connection is a Bendix spring.

22. An assembly as claimed in claim 20, in which the resilient connection is an assembly of Bendix springs.

23. An assembly as claimed in any of claims 20 to 22 when dependent on at least claim 7, in which said resilient means are utilised also to return the rear steered wheels to their correct steering angle with respect to the front steered wheels when the latch means are engaged after the vehicle returns to or below the said predetermined speed.

24. An assembly as claimed in any of claims 6 to 23, in which means are provided to indicate when the disengaging means is in use.

25. An assembly as claimed in claim 24, in which the indication means includes a lamp within the vehicle.

26. An assembly as claimed in any of claims 1 to 6, in which a rotation absorbing assembly is incorporated in the torque shaft, whereby above a predetermined speed of a vehicle rotational movement of a front section of a shaft will be absorbed in said absorbing assembly.

27. An assembly as claimed in claim 26, in which said absorbing assembly comprises first and second helically splined means of opposite hands engaged with corresponding splined means on the ends of the shaft into which the assembly is interposed, spring means being provided to bias the ends of the shaft away from each other, whereby when the rear wheels of the vehicle engage a lateral obstacle, they deflect, the deflecting force being absorbed in said absorbing assembly whereby on removal of the obstacle the wheels can return to the set steering angle.

28. A steering assembly substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

29. A steering assembly substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

30. A steering assembly substantially as hereinbefore described with reference to Figures 4, 5 and 6 of the accompanying drawings.

31. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.