GB2158022A - Automatic or manual power assisted steering - Google Patents

Abstract

A power assisted steering system incorporating a working piston (4) for actuating the steering linkage can be optionally switched between manually controlled power steering using mechanical adjustment of the spool valve (11) and automatically controlled steering utilising an electric signal generated in response to deviation from a desired position. The electric signal is used to control an electrohydraulic control valve (33, 34) which in turn controls the spool valve (11) and the working piston (4), eg by control of the fluid pressure on the end faces (26, 27) of the spool valve (11). The electric signals are generated by an antenna (100) monitoring a field, generated by a buried cable (104) and sensor (110) monitoring the angle of lock of the steering linkage. <IMAGE>

Description

SPECIFICATION Steering arrangement for vehicles The invention relates to a steering arrangement for vehicles which can be switched optionally to either manual or automatic transverse steering. Such an arrangement being known for example from an informative publication by the West German Federal Minister for Research and Technology: Short-haul Traffic Research, 1982, Pages 49-54.

A current-carrying leader cable is set into the road surface for the purpose of the automatic transverse steering of vehicles which is effected electronially, the course of this leader cable representing the desired path which the vehicle is intended to follow.

An electromagnetic field is built up around this current-carrying conductor as represented by the leader cable, the strength of this field decreasing as the distance from the conductor increases. It is possible to obtain from the quantity of current induced in sensing coils fixed to the vehicle a signal which is proportional to this distance and from which the transverse position of the vehicle relative to the leader cable can be calculated. The antenna signals -- which correspond to transvers position signals-from the antenna arrangement composed of sensing coils are processed together with a series of vehicle performance data, such as driving speed, the instantaneous degree of steering lock, and other values and, if necessary, a control signal can be calculated therefrom.The control signal service to vary the steering angle deflection in order that the preset desired path may be followed. According to a hydraulic circuit diagram in the publication already mentioned, the electric control signal is transmitted to an electrohydraulic control valve (EHC valve) which, when detuned, connects one side of a working piston to the return flow and the other side to the pressure supply. The working piston forms part of a control cylinder which, at least indirectly, pivots the wheels for an appropriate steering manoeuvre. A completely independent power steering is provided for the convention manual steering operation.During electronically controlled transverse steering operation the working cylinder which is normally integrated in the steering gear housing of the power steering system is rendered inoperative by preventing a build-up of pressure in the cylinder chambers by means of an open bypass. On the other hand, during manual steering the valve situated in the bypass remains closed Therefore, apart from the steering gear for manual operation, there is provided a further separate steering gear for transverse steering comprising an independent control cylinder and a control valve. The technical expenditure required for the additional hydraulic system is therefore considerable; also, fitting space is required to enable mounting of the hydraulic systems which create considerable additional weight.A further disadvantage is that, in the event of transverse steering operation, the steering cannot in an emergency be effected simply by manual operation of the steering wheel by the driver, but the by-pass valve must first be switched over.

A similarly costly hydraulic system is also provided as the steering gear according to U.S. Patent Specification 2424288. In this case, however, transverse steering is achieved by optical tracking of a bright or luminous continous guide strip on the roadway.

The problem underlying the invention is to simplify the hydraulic system, and thereby to create a smaller construction and save weight.

According to the invention there is provided a steering arrangement for vehicle which can be switched optionally to either manual steering or automatic transverse steering, comprising a hydraulic power steering gear including a working cylinder by means of which a power steering gear driven element connected to the steering linkage can be adjustably driven with power assistance, pressure actuation of the working piston during manual steering being controlled by mechanical adjustment of the control spool of a control valve, and further comprising a tansverse position controller which is operative during automatic transverse steering of the vehicle and which, depending on the variation or deviation of the actual transverse position of the vehicle from a desired transverse position, generates, an electric signal of appropriate magnitude which serves to control an electrohydraulic control valve (EHC valve) which, in turn, controls at least indirectly the pressure applied to an actuatorforthe automatic adjustment of the steering gear, wherein also during electronically controlled transverse steering, the working cylinder associated with the power steering gear serves as the actuator for the automatic adjustment of the steering gear and the electrohydraulic control valve is used for the hydraulic control of the other control valve.

The working cylinder which is connected in the power steering system for manual steering now serves as a steering cylinder even during electronically operated transverse steering. This is achieved because during both manual steering and track guided operation, the associated control valve serves to regulate the hydraulic flow from and to the working cylinder. During transverse steering operation the position of the control spool of the control valve is controlled hydraulically by the end faces of the spool valve being subjected to forces which correspond to the steering manoeuvre. The control of the flow of pressure medium to the end faces of the spool valve is effected by an electrohydraulic pilot valve which is detuned according to the output signals of an electronic controller which transmits control signals corresponding to the course of the desired path.Since only low pressures are to be controlled by the pilot valve, it can be dimensioned accordingly. Moreover, the weight and fitting space required for a further working cylinder are saved.

It is also advantageous that the hydraulic circuit of steering arrangements which are also designed originally only for manual steering can be simply converted in order to serve also as the hydraulic system for tracked operation by electronically operated transverse steering. Moreover, it is advantageous that security against malfunction is considerably increased when using a hydraulic system which is already well proved hitherto. It is advantageous, furthermore, that in an emergency the driver can immediately take over the steering function without further measures by simply gripping the steering wheel and overcoming the force acting on the control valve.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawing, the simple figure shows a hydraulic circuit diagram of a power steering gear, together with axial sections through the steering gear and the associated control valve, and with an electrohydraulic control valve which is represented by circuit diagram symbols and which receives it control pulses from a control circuit (represented by a functional diagram) for electronic transverse steering.

The power steering 1 has a steering gear housing 2 which is at the same time designed in the form of a slave cylinder 3 for a working piston 4. The working piston 4 separates two working chambers 5,6 which are connected to a control valve 11 through connections 7,8 and pressure medium lines 9, 10. The control spool 13 of the control valve 11, which is integrated in the steering gear housing 2 and the axis of which extends at right angles to the direction of extension of the steering shaft 14, has na annular groove 12 in which engages the steering guide 16 which is integral with the steering nut 15. The steering nut 15 is mounted so as to be capable of a spiral movement on the steering worm 17 by means of a recirculating ball system 18. The steering shaft 14 is mounted rotatably, byt axially non-slidably in the steering gear housing 2.The steering nut 15 is movable in an axial direction of movement relative to the steering worm 17 only simultaneously with the working piston 4, and a toothed rack section 19 which is also guided on the steering spindle 14. On its circumference the toothed rack section 19 has a toothed rack profile 20 cooperating with a toothed sector 21 which is non-rotatably connected to the drop arm 22. The connection 50 of the control valve 11 is permanently connected to a pressure medium pump 23 which is operated by the driving engine of the motor vehicle. The connections 51 and 52 of the control 11 serve as return posts for the pressure medium coming from the pressure medium pump 23 or from the working chambers 5,6 of the slave cylinder 3. The connections 51 and 52 are connected to a common return line 70 which leads to the return reservoir 31.Through the connections 53 and 54 of the control valve 11 the pressure medium can pass via the lines 9,10 to the connections 7,8 of the slave cylinder 3 and to the working chambers 5,6. The connections 51 and 58 lead to the end chambers 24, 25 in the valve housing, into which chambers the end faces 26,27 of the control spool 13 project. The connections 57 and 58 are interconnected through lines 71 and 72 and 73 including two fixed throttles 28 and 29. Also, in the area between the fixed throttles 28, 29, the line 73 has a connection leading to the return line 70. Seen in the direction of flow, the branch line is followed by a pressure regulating valve 30 which serves to preload the return stream of pressure medium in the section of line lying ahead.

Irrespective of the volumetric flow, the valve maintains a constant hydraulic pressure in the corresponding line section of the return line 70 unless the 2/2-way valve 32 is opened in a bypass 74 leading to the pressure regulating valve 30. The end chambers 24,25 are each connected to a pilot valve 34 also via lines 75,76 without constant throttles 28, 29 being interposed. In addition, the lines 75 and 76 can be disconnected by a 4/2-way valve 33. A return line 77 leads directly to the return reservoir 31 from the pilot valve 34, an electrohydraulic control valve.

The control valve 11 and the pilot valve 34 are preferably in the form of throttling directional control valves.

They operate for example according to the principle of the open centre each having four control edges. In addition to a central neutral position, there are an infinite number of intermediate control positions having a variable throttling effect. This means therefore that, depending on requirements, throttle points in corresponding lines are each opened or closed to a greater or smaller extent in opposite directions, thereby causing a throttling action or an increase in the volumetric flow and thus regulation of the working pressures after the throttle points.

The control spool 13 of the control valve 11 is centered in a cental neutral position buy a pretensioned centering spring 37. The various control positions of the electrohydraulic pilot valve 34 are created by the electric control pulses of the control circuit for the electronic tranverse steering. The electronic control circuit consists, in its essential components, of an antenna arrangement 100, for example coils, in which a field strength signal, which is dependent on the distance from the instantaneous transverse position of the vehicle, is generated and transmitted to a controller 101.Laid below the road surface 103 is a current-carrying leader cable 104 which defines a desired path and which generates the electromagnetic field and indicated by several concentric lines 105 of constant field strenght.The sensing element 110 which is in the form of a pin 110, comes into contact with a cam 111 rigidly connected to the drop arm 22 and is intended to indicate that the instantaneous actual angle of steering lock is measured continuously. The direction in which measuring and control signals are transmitted is represented by continuous lines with arrows between the individual control elements. The control signal from the controller 101 is amplified in an amplifier 106 and compared with the actual angle of lock in a comparator 107. If the desired angle and the actual angle differ, an appropriate control position is created by an electromagnet of the pilot valve 34.

During manual operation the directional control valve 33, as indicated, closes the passage through the lines 75 and 76. In this case the directional control valve 32 is opened. If the pretensioning of the spring 37 is overcome, the control spool 13 of the control valve 11 is move mechanically out of its neutral position by turning the steering wheel. If the spool valve 13 is deflected to the left, for example, the stream of pressure medium, which immediately flows back to the return line via connections 51 and 52 when the spool valve is in the neutral position, can flow via connection 50 from the pressure medium pump 23 to the connection 54 and from there into the working chamber 5. On the other hand, the passage cross-section is diminished from connection 50 to connection 53, as is the passage leading via the connection 52 to the return reservoir 31.On the other hand, the throttle cross-sections in the passage from connection 53 to connection 51 are opened further so that the pressure medium can flow freely out of the working chamber 6 of the slave cylinder 3 to the return reservoir 31. Because of the pressure difference the working piston 4 is displaced to the right, corresponding to an angle of lock to the right. After the desired angle of lock has been reached, a further flow of pressure medium and the maintenance of the pressure difference in the working piston 4 are no longer necessary, and the spool valve 13 again returns to its neutral central position since a force is no longer exerted at its forked end via the steering guide 15. Only if the steering is operated in the reverse direction is the spool valve 13 deflected into the opposite control position if power assistance is required.

Alternatively, it is now also possible for the vehicle steering to be electronically controlled. In this case the detuning of the spool valve 13 is not effected by torques applied to the steering wheel, whereby the spool valve 13 is detuned by the steering guide 16.

First, the directional control valves 32 and 33 are to be switched over so that the pressure medium delivered by the pressure medium pump 23 must flow back to the return reservoir 70 via the pilot valve 34. The pressure medium delivered by the pressure medium pump 23 flows firstly through the connections 51 and 52 into the line 70 which is connected through the constant throttles 28 and 29 to the lines 71 and 72 leading to the end chambers 25 and 26.

Depending on the control position of the pilot valve 34, the pressure medium is accumulated in varying amounts in the lines 75 and 76 so that a pressure difference can be built up in the end chambers 25 and 26. As a result of this pressure difference an axial force is exerted on the spool valve 13 detuning this valve so that the working chambers 5 and 6 of the slave cylinder 3 are subjected to difference pressures. By regulating the size of the pressure difference at the spool valve 13, the slave cylinder 3 of the power steering 1 can therefore be used for the steering operation during automatic transverse steering. However, for this purpose it is necessary for the return valve flow through the lines 75 and 76 to be reduced or increased appropriately in opposite direction by means of the pilot valve 34.Equal amounts of pressure medium can flow through both lines 75 and 76 only in a neutral position. In this case the instantaneous angle of steering lock is not changed. The electrohydraulic pilot valve 34 converts an electric analog input signal into a similar fluidic analog output signal. The electric control signal originated from the comparator 107 of the electronic control circuit, and is transmitted to the electromagnets of the pilot valve 34 via electric lines which are shown disconnected. The control unit 101 is for example a microprocessor which processes all the necessary measured values and determines therefrom a desired angle signal which is conveyed to the comparator 107 via the amplifier 106. If the desired angle differs from the actual angle, then an appropriate control signal is transmitted from the comparator 107. In special cases it may be necessary to switch over to manual steering as quickly as possible. This can be simply achieved by the driver gripping the steering wheel and applying to the wheel a torque of such magnitude that the force introduced onto the spool valve 13 by the steering guide is greaterthant the force of the pressure originating from the pressure difference at the end face.

Claims (6)

1. A steering arrangement for vehicles which can be switched optionally to either manual steering or automatic transverse steering, comprising a hydraulic power steeing gear including a working clyinderby means of which a power steering gear driven element connected to the steering linkage can be adjustably driven with power assistance, pressure actuation of the working piston during manual steering being controlled by mechanical adjustment of the control spool of a control valve, and further comprising a transverse position controller which is operative during automatic transverse steering of the vehicle and which, depending on the variation or deviation of the actual transverse position of the vehicle from a desired transverse position, generates, an electric signal of appropriate magnitude which serves to control an electrohydrualic control valve (EHS valve) which, in turn controls at least indirectly the pressure applied to an actuator for the automatic adjustment of the steering gear, wherein also during electronically controlled transverse steering, the working cylinder associated with the power steering gear serves as the actuator for the automatic adjustment of the steering gear and the electrohydraulic control valve is used for the hydraulic control of the other control valve.

2. An arrangement according to Claim 1, wherein the end faces of the control valve can be pressureactuated.

3. An arrangement according to Claim 1 or Claim 2, wherein the end chambers of the control valve, on the one hand, are each connected to a common pressure medium supply lying between constant throttles, and, on the other hand, are each connected to a return reservoir via throttling cross-sections of the electrohydraulic control valve which are adjustable in opposite directions.

4. An arrangement according to Claim 3, wherein the return flow of pressure medium in the control valve is accumulated in a line section of the return line by means of a presure control valve, and this line section acts as a common pressure medium delivery source.

5. An arrangement according to Claim 3 to Claim 4, wherein the lines for manual steering which lead to the electrohydraulic control valve can be disconnected by means of a pilot valve.

6. A steering arrangement for vehicles, substan tially as hereinbefore described and with reference to the accompanying drawings.