GB2270506A

GB2270506A - Adjustment of the steering response of a road vehicle

Info

Publication number: GB2270506A
Application number: GB9219458A
Authority: GB
Inventors: John Phillip Tomlinson
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-09-15
Filing date: 1992-09-15
Publication date: 1994-03-16
Anticipated expiration: 2012-09-15
Also published as: GB9219458D0; GB2270506B

Abstract

A road vehicle used to simulate unfavourable steering conditions provided with means for steering the rear wheels in a manner responsive to a demand signal comprises one or more castors 19 rotatable about a vertical axis and lowerable by a hydraulic ram 15 to raise a road wheel from content with the road surface. This arrangement allows large defections of the rear steering to occur in response to specific demand while otherwise retaining the normal vehicle construction and handling characteristics, irrespective of the vehicle size and weight. <IMAGE>

Description

MEANS FOR ADJUSTMENT OF THE STEERING RESPONSE OF A ROAD VEHICLE This invention relates to means for adjustment of the steering response of a road vehicle. This adjustment is for simulation of desired steering conditions. Such means could be used in a vehicle for training drivers in driving techniques such as skid control.

A vehicle for this purpose is described in US Patent No. 4967859. In this vehicle, front and rear wheels are each mounted on steering racks. The driven wheels are the front wheels, which are controlled through two alternative pinion shafts, each disengageable by a clutch.

One shaft leads to the steering wheel for normal steering control, the other leads to an auxiliary motor which drives the steering rack according to a demand signal. This demand signal is determined by the position of the steering rack and by the steering conditions which are to be simulated.

To simulate skids effectively, it is necessary also to steer the undriven wheels, here the back wheels.

Under normal conditions, the back wheels are locked straight ahead. However, when the vehicle is to simulate a skid, the rear steering rack is driven by a second auxiliary motor in a direction determined by a demand signal. Depending on the nature of the demand signal, the Wheels can be steered to the straight ahead position, or with positive or negative dependence on the position of the steering wheel.

Such an arrangement poses considerable difficulties in the adaption of an existing vehicle to a training vehicle incorporating such a system. Conventional front drive vehicles are not designed to allow for the possibility of steering of the rear wheels. Typically, such vehicles can be adapted to give of the order of 80 of movement; greater movement could only be achieved by complete vehicle redesign or major structural modification.

This system of skid simulation is thus prohibitively expensive to use on the majority of road vehicles.

Accordingly, the invention provides means for adjustment of the steering response of a road vehicle for simulation of desired steering conditions, comprising: extension means fixed at one end to the mounting of a road wheel, and having at the other end thereof a castor, said castor having a mounting capable of rotation about an axis which is substantially vertical in use; detection means for detecting when a steering input to a steering system of the vehicle is in excess of a predetermined angular value; whereby when the steering input is detected to be in excess of said predetermined angular value, said extension means extends so as to lift the road wheel clear of the ground, the ground being then in contact with the castor.

Desirably, there should be two such extension means, each being associated with one of the rear, undriven, wheels. Advantageously, the extension means is a hydraulic ram. It is also desirable for the castor to be rotatable through a full 3600. A desirable mounting position to the road wheel assembly is to the wheel post.

It is also desirable that the means be connected to the wheel axle by means of a bearing.

A specific embodiment of the invention is described below, by way of example, with reference to the accompanying drawing, in which: Figure 1 shows a schematic view of a means according to the invention.

Figure 1 shows a schematic diagram of the means alone, parts of a conventional vehicle not being shown.

The lifting means itself is a hydraulic ram 15, hydraulically powered through inputs 16 and 17. The ram is fixed at position 18 to the top of a wheel post of the vehicle. The wheel post carries the wheel stub axle and the brake drum or disk. This mounting maintains the suspension movement of the vehicle, as the attachment is to the wheel post rather than to the vehicle body itself.

The ram is connected at its other end to the top plate of a castor thrust bearing 14, which is capable of 360C movement about its vertical axis. The bottom plate of the thrust bearing is attached to the offset castor 19.

The top plate of the thrust bearing is also attached by an arm 12 to a pivot bearing 13 which is mounted around the vehicle axle.

When the vehicle is being driven normally, ram 15 is powered to an up position. The castor does not then contact the ground and does not influence the drive of the vehicle. However, when a skid is to be simulated, this means may come into operation. It is desirable for small steering angles of the rear wheels to be achieved by allowing for a limited steering angle of the rear wheels themselves. Preferably, the rear wheels are configured to allow possibly 50 of movement.

The control means for the rear wheel steering can be similar to that described in US Patent No. 4967859. The steering rack can be driven by an electric motor as in the US Patent. The motion of the rack is then determined by a demand signal with positive, negative or zero dependence on the steering wheel motion, and by a sensor determining the position of the rack. The difference demand signals can be preset and provided through a control unit used by an instructor. Alternatively, the steering rack of US Patent No. 4967859 could be replaced by providing steering control of each rear wheel through a hydraulic ram responsive to similar signals. In this case the position of wheels would need to be sensed, rather than positions of the rack.

The maximum steering response available to the rear wheels leads to a predetermined angular value which the steering wheels cannot exceed. If the demand signals indicate that the steering rack should provide turn beyond this value, then the lifting means of the invention has to be brought into position. For a normal car 50 would be a suitable maximum steering response angle, though the invention could still be employed even with a 0 angle.

When the rear wheels are required to steer through an angle greater than the maximum steering response available to them, then the hydraulic ram is activated.

The ram extends downwards, until the castor comes into contact with the ground and lifts the associated road wheel clear of it. This enables extremely rapid spins to be achieved by the vehicle, as the spin is no longer restricted by the inability of the rear wheels to turn more than 80 away from the straight ahead position.

Precise control of the lifting means enables skids to be simulated very accurately. The rate of lift can be varied from one side to the other, this variation being dependent on the steering direction. This simulates the body roll forces of an actual skid. Variation of the speed of lift with vehicle speed can be used to give a progressive breakaway at slow speed, or a more rapid breakaway at higher speed.

The system of the invention is highly advantageous for the teaching and practising of skid control. A skid can be averted by a faster reaction by the driver; a fast corrective lock in the direction of the slide will place the front of the vehicle in line with the rear, thus aligning the castors with the driving wheels.

The castor could then be again lifted by the hydraulic ram 15. A rapid skid can thus be satisfactorily simulated, and major adjustment to the test vehicle is not required to achieve it.

Claims

1. A road vehicle provided with steerable front and rear wheels mounted upon axles, responsive to a steering input transmitted from a steering wheel through a steering mechanism, provided with one or more castors capable of rotation about an approximately vertical axis, and hydraulic cylinder, valve and control means to effect the lowering of one or more of said castors by applying a force with respect to an adjacent one of said axles to displace a road wheel from contact with the road surface.

2. A road wheel as claimed above wherein said control means effects the lowering of said castors in the event that the steering input applied to said rear wheels exceeds their available mechanical movement.

3. A road vehicle according to claim 1 whereby said control means effects the lowering of one of said castors in order to create a simulated body roll of the vehicle about a horizontal axis.