GB2050974A

GB2050974A - A steering device for a vehicle comprising hydraulic power-assisted steering facilities

Info

Publication number: GB2050974A
Application number: GB8012643A
Authority: GB
Original assignee: STILL GmbH
Current assignee: STILL GmbH
Priority date: 1979-04-19
Filing date: 1980-04-17
Publication date: 1981-01-14
Also published as: FR2454397B1; IT8021439A0; IT1141454B; DE2915890A1; FR2454397A1; GB2050974B

Abstract

A steering column 11 of a vehicle is connected to a meter 12 which measures the torque produced in said column when a steering correction is made. The meter is connected to a voltage-pulse converter which is connected to an arrangement which supplies to an electric motor 21 a voltage whose mean value is proportional to the measured torque. The motor drives a pump 15 which is connected to a double-acting hydraulic cylinder 6 whose piston 7, when displaced along the cylinder, effects appropriate alteration of the attitudes of the steerable wheels. The pump can be connected directly to said cylinder or can be connected via a steering valve 13 to said cylinder. Either the steering valve determines flow of pressure medium and hence direction of piston displacement, or voltage polarity determines direction of rotation of motor and hence direction of piston displacement. <IMAGE>

Description

SPECIFICATION A steering device for a vehicle comprising hydraulic power-assisted steering facilities The present invention relates to a steering device for a vehicle comprising hydraulic power-assisted steering facilities.

More particularly, the invention concerns a device for a battery-driven vehicle, preferably a fork-lift truck, comprising a steering wheel attached to a steering column, and comprising hydraulic powerassisted steering facilities which include a pressure medium pump, a steering valve controlled by means of the steering wheel and a steering cylinder which is fed via the steering valve from the pressure medium pump, the pressure medium pump being driven by a battery-fed electric motor for the power-assisted steering, said device possessing a power-measuring apparatus which is linked to the steering device and which is connected to the circuit of the electric motor and switches the latter on and off in dependence upon the power to be measured, and is connected to a force dependent upon the magnitude of the measured power.

In a device of this kind known from German Offenlegungsschrift No. 14 80 205, the steering wheel is connected to a metering or dosing pump which produces a flow which actuates the steering valve, wherein the flow produced by the pressure medium pump is fed via the steering valve to the steering cylinder. The apparatus which measures the power consists of a pressure meter arranged in the two conveyor pipelines ofthe metering or dosing pump.

This device is fairly elaborate and expensive because it comprises a dosing pump, a steering valve dependent upon the flow produced by the dosing pump, and pressure meters which convertthe pressure into an electric signal.

The principal aim of the invention is to provide a hydraulic power-assisted steering device which withdraws energy from the electric battery only on the occasion of power-assisted steering being required and only to the extent necessary for power-assisted steering and which comprises only a small number of simple, cheap control components.

For the realisation of this aim, in accordance with the present invention, a torque meter is provided which emits an electric voltage signal and which measures the power in the steering column, said torque meter being connected to a voltage-pulse converter which is, in turn, connected to a device which supplies the electric motor for the powerassisted steering with a voltage whose mean value is proportional to the steering torque, and being connected to a corresponding circuit system comprising an energy source.

The voltage-puise converter may consist of a voltage-pulse width-modulator.

The device which controls the current supply of the electric motor for the power-assisted steering may consist of a transistor end stage of a thyristor circuit.

A device which measures a steering torque in a steering column and converts it into an electric signal is already known (see German Offen legungssch rift No. 26 58697 and the corresponding United Kingdom Patent Specification No. 1,558,653) in a form in which the steering column is divided and the two parts thereof are linked by an elastic coupling, a fixed magnet being arranged on one part of the steering column and a differential magnetoresistive sensor being arranged opposite it on the other part of the steering column.However, it is also conceivable to replace a differential magnetoresistive sensor of this kind and which comprises a permanent magnet by a different control means, for example by arranging a light source on one part of the steering column, and supplying the light stream emanating from the light source to a light-senstive element, for example a photo-cell or a photo-resistor which emits the electric voltage signal, said voltage signal being dependent upon the relative rotation of the two steering column components (pending Patent Application No. 7933492). This dependency can be produced, for example, by the light source and the photo-resistor both being arranged on one and the same part of the steering column and a displaceable diaphragm which can be inserted between light source and photo-resistor being connected to the other part of the steering column, or by the light source being arranged on the one part of the steering column and the photo-resistor on the other part.

However, steering-assistance facilities are also known, which are operated electrically or by a pressure medium, which comprise a switching device which switches on the steering-assistance facilities when the steering wheel is operated, which switching device comprises a gear ring composed of magnetic material which is attached to the steering column and rotates together with the latter and opposite the teeth of which there is arranged an inductive sensor which emits a signal when a tooth of the gear ring moves past it, which signal is fed to a control circuit comprising a delay device which switches on the steering-assistance facilities each time a sensor signal occurs (see German Offenlegungsschrift No. 26 59 437). Thus, in this known device, the steering-assistance facilites are switched on with each rotary movement of the steering wheel irrespectively of the required power.

The aim which the present invention sets out to achieve may be realised, exploiting the general principal of the invention as a consequential development thereof, by another embodiment in which the steering valve is also dispensed with. In this case, the current strength or pulse density and the current direction of the current flowing towards the electric motor for the power-assisted steering is controlled in dependence upon the steering torque which occurs in the steering column and upon the direction of this torque, the pressure medium pump driven by this electric motor being directly connected by its two terminals to the two terminals of the steering cylinder, and expediently the pressure medium pump consisting of a compressor pump which blocks the connection between the two terminals in the rest state.An arrangement of this kind is advantageous in that, whenever the electric motor for the power-assisted steering is in operation, it drives the pressure medium pump and conveys a flow which is proportional to the speed of the electric motor to one side of the steering cylinder for such time as the electric motor is in operation; that is to say, the steered wheels of the vehicle are increasingly deflected towards a wider angle of traverse for such time as force is exerted on the steering wheel. In such a case, the speed of traverse is proportional to the exerted force. If the wheels are to be returned to their straight-ahead attitudes, a steering torque must be exerted on the steering wheel in the opposite direction in the usual fashion.It is possible to fix the lower part of the steering column so that a steering movement is exerted upon the steering wheel only to the extent necessary to produce a steering power-dependent electric signal. Thus, it is merely a question of producing a steering force on the steering wheel and it is this steering force which controls the steering movement. The extent of the angular movement of the steering wheel about its axis of rotation necessary to produce the electric voltage signal is expediently selected by means of an elastic linking element which is most pleasant or acceptable for the driver from the ergonomic-physiological standpoint.

A deviation from the conventional system consists in that, when travelling round bends having a uniform radius, the steering wheel remains powerless (i.e. without steering force applied thereto) in the normal position.

The present invention will now be more particularly described with reference to the accompanying drawing which schematically illustrates an exemplary embodiment of the invention.

In the drawing, two vehicle wheels 1 which are to be steered have been shown in solid lines in their straight-ahead attitudes and in dash-dotted lines in one of the two possible extreme attitudes thereof governed by the steering lock. Each wheel 1 is mounted on a steering stub axle 2 which can be pivoted about a king pin 3 which itself is mounted in the frame of the vehicle (not shown). Track rods 4 are articulated at their inboard ends (disposed approximately on the median plane of the vehicle) to a steer ing core 5 which is itself mounted in pivotal fashion in the vehicle frame (not shown) to which a hydraulic steering cylinder 6 is also attached.A piston 7 divides the cylinder 6 into two pressure chambers and is displaceable in said cylinder and is connected to one end of a piston rod 8 whose other end is connected to a steering lever 9 on one side of the vehicle, the steering lever 9 being rigidly connected to the stub axle 2. The outboard end of each track rod 4 is articulated to a steering lever 9.

A steering wheel 10 is permanently connected to a steering column 11 in which is arranged a torque meter 12 which is capable of emitting an electric voltage signal. The steering column 11 is connected to a steering valve 13 which is connected to a conveyor pipeline 14 of a pressure medium pump 15 and to a return pipeline 16 which leads to a tank 17. Also connected to said valve 13 are two pipelines 18 and 19 which lead to the respective two pressure chambers of the steering cylinder 6. The pump 15 is driven via a shaft 20 by an electric motor 21 which is operable to provide power-assisted steering and which is connected via two wires or cables 22 and 23 to a circuit 24. Said circuit is itself connected via a wire or cable 25 to an electric storage battery 26 and is supplied via a line system 27 with the electric voltage signal from the torque meter 12.

The torque meter is connected to a voltage-pulse converter which, in turn, is connected to a device which supplies the electric motor 21 with a voltage whose mean value is proportional to the steering torque. Said converter is also connected to a circuit which includes the battery 26. The converter preferably is a voltage-pulse width-modulator. The current supply for the electric motor 21 is controlled by a high-powertransistor or a thyristor switching arrangement.

The mode of operation is as follows: when no force is exerted on the steering wheel 10 and the steering valve 13 occupies its closed position, the lines 18 and 19 are closed and consequently the piston 7 is held stationary in the steering cylinder 6 and thus the steerable wheels 1 are held in their desired steering lock attitudes. If a steering correction is to be made, a force must firstly be exerted upon the steering wheel 10 which produces a torque in the steering column 11 this torque is measured by the torque meter 12 which supplies the circuit 24 with a signal via the line system 27 with the outcome that the electric motor 21 is connected to a voltage whose magnitude (mean value) corresponds or is proportional to the torque in the steering column 11.The electric motor 21 drives the pump 15 at the appropriate speed, and the pump conveys pressure via the pipeline 14 to the steering valve 13 which, as a result of the operation of the steering wheel 10, has been actuated in such manner that either the line 14 is connected to the line 18 and the line 19 is connected to the line 16,orthe line 14 is connected to the line 19 and the line 18 is connected to the line 16. As a result, the pressurised medium is conveyed from the pump 15 into the pressure chamber on one side of the piston 7 and medium is exhausted or drawn from the other pressure chamber of the steering cylinder 6; consequently, the piston 7 is displaced along the cylinder 6 and thus the steering lock attitudes of the wheels 1 are modified until no further force is exerted upon the steering wheel 10. When no further force is exerted on the steering wheel 10, the steering valve 13 closes again.

It will be appreciated that no steering force will be exerted on or applied to the steering wheel 10 when the steering angle of the steerable wheels 1 is not altered; that is to say, if a curve having a constant radius of curvature is being negotiated, no steering force will need to be applied to the steering wheel 10, in just the same way as no steering force is applied to said steering wheel 10 during straightahead travel of the vehicle.

Referring again briefly to an alternative embodiment, already described, in which the steering valve 13 is omitted, said alternative embodiment differs from that which is illustrated in Figure 1 only in that the free end of the steering column 11 is absolutely fixed or clamped in the vehicle, in that the pipeline 14 is connected directly to the pipeline 18, and in that one end of the pipeline 16 is connected directly to the pipeline 19 whereas the other end of said pipeline 16 is connected directly to the pump 15. The housing of the pump 15 is connected to the tank 17 by another pipeline provided for that purpose. The ability of the steering wheel 10 to be operated for steering purposes is provided by the elastic deformation of the elastic element in the torque meter 12.

An appropriate signal is triggered in the latter.

Claims

1. A steering device for a vehicle having hydraulic power-assisted steering facilities, said device comprising a pressure medium pump; a steering valve controlled by means of a steering wheel which is attached to a steering column; a steering cylinder connected to said pump by way of said steering valve; said pump being driven by a battery-powered electric motor; a torque meter being provided for measuring the torque produced in the steering column, said torque meter emitting an electric voltage signal which is applied to a voltage-pulse converter which is in turn connected to an arrangement which supplies the electric motor with a voltage whose mean value is proportional to the measured torque in the steering column.

2. A steering device for a vehicle having hydraulic power-assisted steering facilities, said device comprising a pressure medium pump; a doubleacting steering cylinder; said pump being driven by a battery-powered electric motor; a torque meter being provided for measuring the torque produced in a steering column of said vehicle, said torque meter emitting an electric voltage signal which is applied to a voltage-pulse converter which is in turn connected to an arrangement which supplies the electric motor witch a voltage whose mean value is proportional to the measured torque in the steering column; the voltage polarity which determines the direction of rotation of the electric motor and thus the pumping direction of the pump is dependent upon the direction of the turning force which is arbitrarily exerted upon a steering wheel attached to said steering column; said pump being directly connected to each of the pressure chambers of said double-acting steering cylinder.

3. A steering device as claimed in Claim 1 or Claim 2, wherein said arrangement includes a semiconductor output stage.

4. A steering device as claimed in Claim 3, wherein said stage is constituted by a high powered transistor.

5. A steering device as claimed in Claim 3, wherein said stage consists of a thyristor switching arrangement.

6. A steering device as claimed in Claim 1 or Claim 2, wherein said characterised arrangement contains a thyristor circuit.

7. A steering device as claimed in any one of the preceding Claims, wherein the voltage-pulse converter is a voltage-pulse width-modulator.

8. A steering device as claimed in Claim 2 or in any Claim appended to Claim 2, wherein the pressure medium pump is a positive-displacement pump which blocks its connection in the rest state thereof.

9. A steering device for a vehicle having hydraulic power-assisted steering facilities, constructed, arranged and operable substantially as hereinbefore described with reference to and as illustrated in the accompanying diagrammatic drawing.

10. A steering device as claimed in Claim 2, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to the accompanying diagrammatic drawing.

11. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described.