Steering system for non track-bound motor vehicles

The invention relates to a steering system for non-track-bound motor vehicles, with a driver-operated steering handle, eg steering wheel, a steering actuator for steering adjustment of steerable vehicle wheels, a steering angle setpoint generator which can be actuated with the steering handle, a steering angle actual value transmitter which can be actuated with the steerable vehicle wheels, a control arrangement constantly controlling for malfunction and controlling the steering actuator as a function of a comparison of the nominal and actual values ​​of the steering angle and a cooperating sensor system and a mechanical or hydraulic positive coupling arranged between the steering handle and the steerable vehicle wheels; which is opened when the control arrangement works correctly or remains open (ineffective normal state) and is automatically closed in case of faulty control arrangement (effective special state).

Such steering systems, according to the concept <img file="EP0985591A2_D0001.tif" />Steer by wire "are basically known and will be developed for future motor vehicles. These systems offer the fundamental advantage that they are suitable for a wide variety of vehicles, at least in terms of the control arrangement and the associated sensors without constructive modifications. By appropriate programming, on the one hand, virtually any transmission ratio between the control stroke of the steering handle and the steering angle change of the steered vehicle wheels can be realized. In addition, it is possible to connect the control arrangement with additional sensors to preset parameters, eg Crosswind influences, to be considered automatically or auszuregeln.

In order to be able to ensure the required degree of safety in the case of system errors, it is provided that, when an error occurs in the control arrangement or in case of failure of signals to be evaluated by the control system, automatically a mode of operation for abnormal operation or To switch on emergency operation. In this mode of operation, a forced coupling between the steering handle and steered vehicle wheels is provided, so that the steering system works in principle like a conventional steering, although the usual conventional steering mechanical steering column optionally replaced by other mechanical system or by hydraulic systems, especially hydrostatic systems can be.

The object of the invention is now to show advantageous measures in a steering system of the type specified in terms of reliability of the system.

This object is achieved according to the invention that the (effectively switched) positive coupling has a predetermined elasticity and cause effective relative coupling between steering angle setpoint generator and steering angle feedback with effective positive coupling between the steering handle and steered vehicle wheels transferable forces and moments, and that the steering system in a special state (effective switched positive coupling) works with sufficient residual function of the control system and sensors as power steering, in that the control arrangement controls the steering actuator analogously to the amount and direction of the relative displacement detectable from the signals from the steering angle setpoint generator and the steering angle actual value generator for generating a servo force with a transmitted force or Moments diminishing direction controls.

The invention is based on the general idea to reduce when applied forced coupling the applied by the driver hand forces on the steering handle as far as possible and to operate the steering system analogous to a conventional power steering. In this context, the control arrangement is intended to control the steering actuator for generating a servo force reducing the hand forces. Here, the invention exploits the fact that the switched-in emergency forced coupling between the steering handle and steered vehicle wheels due to elastic compliances of the coupling elements or Media may have a corresponding elastic compliance, with the result that between the steering handle side end and Entrance and the steered vehicle wheels associated end or Output of the positive coupling during transmission of forces and moments more or less large relative movements occur, leading to corresponding relative adjustments between the steering angle setpoint and Lenkwinkelistwertgeber. In the invention, the abovementioned desired and actual value encoders are now used in the special state of the steering system for detecting these relative adjustments and thus for detecting the transmitted forces and moments.

So while setpoint and actual value in the normal state of the steering system for determining the target-actual value deviation of the steering angle, they are used in the special state to determine the transmitted forces between the steering handle and steered vehicle wheels and moments. Due to this dual function of setpoint and actual value transmitter, the comfort of a conventional power steering system can be made possible without additional sensors for special operation.

It is only necessary to design the control arrangement so that it detects the present directly upon switching on the positive coupling relative positions of the setpoint and actual value. Since no forces or moments between steered vehicle wheels and steering handle are transmitted immediately at the time of switching on the positive coupling, the aforementioned relative position is characteristic of an unstrained forced coupling.

A particular advantage of the invention is that the technical design of the forced coupling can be arbitrary. For the feasibility of the invention, it is of minor importance, whether a forced coupling via mechanical elements or hydraulically. In the former case, the elastic deformability of the mechanical elements is utilized. In the second case, the elastic compliance of the walls of the hydraulic lines and the compressibility of the hydraulic medium is used.

Moreover, with regard to preferred features of the invention to the claims and the following explanation of the drawing, reference is made to the particularly preferred embodiments.

It shows<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>a circuit diagram-like representation of a first embodiment,</dd><dt>Fig. 2</dt><dd>a corresponding representation of a second embodiment and</dd><dt>Fig. 3</dt><dd>a corresponding representation of another embodiment of the invention.</dd></dl>

In the example shown in Fig. 1 has a motor vehicle not shown in detail steerable front wheels 1, which are coupled to each other via steering rods 2 and a rod 3 steerable.

The rod 3 forms the piston rod of two mutually parallel piston-cylinder units 4 and 5, which are each designed as double-acting units.

The piston-cylinder unit 4 is coupled via two hydraulic lines 6 and 7 with the two piston working spaces of a double-acting piston-cylinder unit 8, whose pistons are mechanically positively coupled with a steering wheel 9. The pistons of the unit 8 move to the right or left, when the steering wheel is rotated clockwise or counterclockwise. Upon displacement of the piston of the piston-cylinder unit 8, the steering wheel is rotated accordingly.

Moreover, the steering wheel 9 is drivingly connected to a self-locking electric motor 10, which is able to work as a pure force generator with the motor shaft held and its purpose will be explained below.

Between the hydraulic lines 6 and 7, a normally closed shut-off valve 11 is arranged, which can be switched by energizing its solenoid against the force of a return spring from the closed position shown in its open position and automatically switching off the solenoid acting on the electric current from the return spring in the illustrated Closing position brought or held in this position.

The piston-cylinder unit 5 is connected via hydraulic lines 12 and 13 with two terminals of a control valve 14, which via two further connections with a relatively pressureless hydraulic reservoir 15 and a hydraulic pressure source, in the example shown, a hydraulic pressure accumulator 16 and pumps 17 and 18, connected is. The accumulator 16 can by means of the pump 17 and be recharged another pump 18. Both pumps 17 and 18 are secured by check valves 19 against return from the pressure to its suction side and connected to the suction side of the reservoir 15. The pump 17 is driven by an electric motor 20. The pump 18 is connectable via a switchable coupling 21 to the motor 22 of the motor vehicle.

Between the hydraulic lines 12 and 13, a normally open shut-off valve 23 is arranged, which can be brought by electrical energization of its actuating magnet against the force of a return spring from the illustrated Offfenlage in its closed position or held in this closed position.

An electronic control and control arrangement 24 is connected on the input side to a transmitter 25 for the actual value of the steering angle of the front wheels 1. This encoder 25 can cooperate, for example, with the rod 3, which executes an adjustment stroke that is analogous to the steering angle when the wheels 1 are being adjusted.

In addition, the input side of the control and control assembly 24 is connected to a operated by the steering wheel 9 encoder 26 for the target value of the steering angle.

In addition, the input side of the control and regulation arrangement is connected to a torque sensor 27, which detects the transmitted between the steering wheel 9 and the electric motor 10 forces or moments.

Finally, a plurality of pressure sensors 28, 29 and 30 are connected to the input side of the control and control arrangement 24, the signals of which reproduce the hydraulic pressures in the hydraulic lines 6 and 7 or 12 and 13 or the pressure at the pressure input of the control valve 14.

On the output side, the regulating and control arrangement 24 is connected to the actuating magnets of the shut-off valves 11 and 23 and of the control valve 14. In addition, the electric motors 10 and 20 and the clutch 21 are controlled by the output of the control and regulating arrangement.

The steering system of Fig. 1 functions as follows:

In normal operation, the switching valves 11 and 23 are brought by the control and control assembly 24 by energizing the aforementioned valves 11 and 23 associated actuating magnets in the layers, not shown, and held in these positions. Accordingly, the piston-cylinder unit 4 is hydraulically decoupled from the piston-cylinder unit 8 and the steering wheel 9.

On the other hand, the pressure difference between the two piston working spaces of the piston-cylinder unit 5 is controlled by actuation of the control valve 14, in the following manner:

The control and control arrangement 24 detects via the encoder 25, the actual value of the steering angle of the front wheels. 1 About the actuated by the steering wheel encoder 26, the control and control assembly 24 receives the target value of the steering angle. The control solenoids of the control valve 14 are then controlled in accordance with a target / actual value comparison carried out by control and control arrangement 24. If no desired actual value deviation is present, the control valve 14 remains in the illustrated central position, in which the piston-cylinder unit 5 is hydraulically freewheeled and connected to the reservoir 15, while the pressure accumulator 16, which in response to the signal the pressure sensor 30 via the pump 17 or 18, if necessary, is constantly recharged, compared to the piston-cylinder unit 5 is shut off. If a setpoint-actual value deviation occurs, the control valve 14 is shifted from the illustrated center position to the right or left, depending on the direction of the target-actual value deviation, so that in each case a piston working chamber of the piston-cylinder unit 5 is controllably connected to the pressure port of the control valve 14 and the other piston working space of the unit 5 with the reservoir 15 and the piston-cylinder unit 5, a controllable pressure difference is effective, with the result that the piston-cylinder unit 5 generates a control force in a direction predetermined by the direction of the nominal-actual value deviation of the steering angle. In this way, a setpoint-actual value deviation of the steering angle is corrected for a short time, and the front wheels 1 follow the steering adjustment of the steering handwheel 9.

From the signals of the pressure sensors 29 and / or from the electrical voltages and currents to the solenoid of the control valve 14, the controller and control assembly 24 can determine the effective pressure difference on the piston-cylinder unit 5 directly or indirectly, the measure with the between the steering wheels 1 and the piston-cylinder unit 5 transmitted forces or Moments is correlated. In correlation to these forces is determined by the control and control assembly 24, a target value for a hand wheel 9 sensible hand force and adjusted by appropriate control of the electric motor 10, the torque sensor 27, the effective between the electric motor 10 and steering wheel 9 forces or Moments and thus the actual value of the manual force detected. As a result, therefore, the motor 10 is regulated as a function of a desired-actual value comparison for the hand forces. In this way, the driver on the steering wheel 9 receives a haptic feedback between the vehicle steering wheels 1 and the piston-cylinder unit 5 effective forces.

The control and regulation arrangement 24 constantly monitors itself for correct function. In addition, the signals of the donors and sensors 25 to 30 connected to the input side of the regulation and control arrangement 24 are constantly checked for plausibility. If a system error is detected, the solenoid of the shut-off valve 11 is de-energized, with the result that the shut-off valve 11 in the in Fig. 1 shown closed position switches and the piston-cylinder units 4 and 8 and thus the steerable front wheels 1 and the steering wheel 9 are positively coupled together hydraulically.

As far as a sufficient residual function of the control and control arrangement 24 and the sensor system cooperating therewith is provided, the steering system according to the invention operates with the forced coupling switched on in the manner of a conventional power steering system. This means that the control and regulating arrangement 24 controls the control valve 14 as a function of the forces and moments transmitted between steering wheel 9 and steered vehicle wheels 1, such that the piston-cylinder unit 5 generates a force to be applied to the steering wheel 9 manual force-reducing servo force ,

For detecting the transmitted between steering wheel 9 and steered vehicle wheels 1 forces and moments is in the example of FIG. 1 exploited the elasticity of the hydraulic coupling between the piston-cylinder units 4 and 8. Due to the compressibility of the hydraulic medium and the elastic compliance of the walls of the hydraulic lines 6 and 7 and the cylinder of the piston-cylinder units 4 and 8 occurs between the steering wheel 9 and steered vehicle wheels 1 a more or less large elastic compliance, with the result that between steering wheel 9 and steered vehicle wheels 1 relative movements can occur which deviates from the transmission ratio of the drive connection between steering wheel 9 and steered vehicle wheels 1.

These relative movements can be determined from the signals of the setpoint and actual value encoders 25 and 26, when the control and control arrangement 24, the relative positions of the two sensors 25 and 26 when switching the hydraulic forced coupling between the steering wheel 9 and steered vehicle wheels. 1 <img file="EP0985591A2_D0002.tif" />knows ", at the time of switching on the Zangkopplung is a practically force-free state of the forced coupling before. Due to the design-dictated ratio between rotational movements of the steering wheel 9 and steering movements of the wheels 1 can then control and control arrangement for each detected from the signals of the sensor 26 rotational position of the steering wheel 9 an expected steering position of the steered vehicle wheels 1 and to determine a corresponding expected signal of the sensor 25. If then the actual signal of the sensor 25 deviates in one or the other direction from the expected signal, this is equivalent to the fact that between the steering wheel 9 and steered vehicle wheels 1, a corresponding force or a corresponding moment is transmitted in one direction or the other. Thus, then the control and control assembly 24 by appropriate adjustment of the control valve 14, the piston-cylinder unit 5 hydraulically control such that this unit 5 generates a respective steering maneuver of the driver assisting servo.

The embodiment shown in Fig. 2 differs from the arrangement of FIG. 1 essentially in that the piston-cylinder unit 6 is replaced by a hydrostatic, reversible pump 31, can be exchanged with the hydraulic medium between the hydraulic lines 6 and 7 , This pump 31 is on the one hand forcibly coupled to the electric motor 10 and on the other hand with the steering wheel 9.

In addition, another reversible and preferably also hydrostatic pump 32, the hydraulic lines 12 and 13 connect. To drive this pump is an electric motor 33, which is actuated by the control and regulation arrangement 24.

The operation of the embodiment of FIG. 2 is consistent with the operation of the embodiment of FIG. 1 as far as possible.

When the switching valve 11 assumes its closed position, the hydrostatic pump 31 and the piston-cylinder unit 4 and thus the steerable vehicle wheels 1 and the steering wheel 9 are positively coupled together.

This positive coupling is then made when the control and control assembly 24 should detect a malfunction in the steering system. As far as a malfunction in parts of the hydraulic system of the piston-cylinder unit 5 is present or appears possible in such a case, the power supply of the magnet of the changeover valve 23 is automatically switched off, so that the changeover valve 23 in the in Fig. 2 shown open position switches and the piston-cylinder unit 5 is hydraulically switched to freewheel under all circumstances.

In normal operation, ie If the control and control arrangement 24 does not detect any malfunction, the changeover valves 11 and 23 of the control and control arrangement 23 in each case in their in Fig. 2 Not shown positions held. The electric motor 33 is then controlled by the control and regulation arrangement as a function of a setpoint-actual value comparison of the steering angle, ie in response to the difference between the signals of the encoder 25 and 26, operated in one or the other direction with more or less large force, so that the piston-cylinder unit 5 transmits a corresponding actuating force to the steered wheels 1.

Also in the embodiment of FIG. 2 the control and regulation arrangement 24 can in turn determine from the signals of the sensors 25 and 26 with forced coupling of steering wheel 9 and steered vehicle wheels the forces and moments transmitted between steering wheel 9 and steered vehicle wheels 1 and depending on this drive the electric motor 33 in such a way, that it produces a force which is analogous to the aforementioned forces and moments, the then hydraulically transmitted via the driven by the electric motor 33 pump 32 and the hydraulic lines 12 and 13 to the piston-cylinder unit 5 and thus steering action as a servo power.

The embodiment shown in Fig. 3 initially differs from the embodiments described above in that for emergency a mechanical drive between steering wheel 9 and steered vehicle wheels 1 is provided.

In the example shown, the rod 3 is arranged as a rack, which meshes with a pinion 40, which in turn is mechanically connected via a spring loaded in the closing direction of the coupling 41 and a subsequent shaft 42 to the steering wheel 9. The clutch 41 can be opened by a servomotor 43 against the force of its closing spring to separate the mechanical drive between steered vehicle wheels and steering wheel 9. The shaft 42 is further drivingly connected to the self-locking electric motor 10 (self-locking). Between the steering wheel 9 and the shaft 42 and the electric motor 10 and the shaft 42 each torque sensors 44 and 45 are arranged.

The pinion 40 is connected to the sensor 25 designed as an angle sensor for determining the actual steering angle value. The shaft 42 is connected to the steering wheel 9 with the also formed as an angle sensor encoder 26, which serves as a steering angle setpoint generator in normal operation.

Moreover, the rod 3 in turn forms the piston rod of the piston-cylinder unit 5, which in turn can be actuated according to the arrangement of FIG. 1 or 2.

In normal operation, the servo motor 43 of the clutch 41 is constantly energized by the control and control assembly 24, such that it holds the clutch 41 against the force of its closing suspension. In addition, the control and control arrangement 24 actuates the piston-cylinder unit 5 or the unit 5 controlling elements such that a possible difference between the steering angle command value supplied by the encoder 26 and the steering angle feedback value supplied by the encoder 25 is compensated by the forces generated by the unit 5. For this purpose, reference is made to the comments on FIGS. 1 and 2 directed.

In case of system failure, the servo motor 43 is switched off by the control and control assembly 24, so that the clutch 41 closes and steering wheel 9 and steered vehicle wheels 1 are positively coupled together.

Also in the example of FIG. 3 occurs between the steering wheel 9 and steered vehicle wheels 1 when the positive coupling is switched on a more or less large elastic compliance, which is based in particular on the torsional elasticity of the shaft parts between the pinion 40 and steering wheel 9. Thus, the control and regulating arrangement 24 in turn from the signals of the sensors 25 and 26 determine the transmitted between steering wheel 9 and steered vehicle wheels 1 forces and moments and depending on the actuating force of the steering actuator, in the case of FIG. 3 a piston-cylinder unit 5, control.

Notwithstanding the drawings illustrated embodiments, the torque sensors 27 and 44 also steering hand wheel side of the unit 8 and the pump 31 and the drive connection between the motor 10 and shaft 42 may be arranged.

Should when switching on the Nofallbetriebes, ie When the forced coupling between steering wheel 9 and steered vehicle wheels 1 of the electric motor 10 still generate a torque, its influence on the signal difference between the signals of the angle sensors 25 and 26 can be computationally compensated, so that in the result alone caused by hand signals signal difference between the sensors 25 and 26 is used to control a servo generated with the unit 5 and / or with the electric motor 10. For this computational compensation can eg stored empirical values ​​for the dependence of the aforementioned signal difference on the forces and moments acting between steering wheel 9 and steered vehicle wheels 1 are taken into account.