WO2002060741A1

WO2002060741A1 - Steering system for non-guided vehicles

Info

Publication number: WO2002060741A1
Application number: PCT/EP2001/015157
Authority: WO
Inventors: Reinhold Schneckenburger; Hubert Bohner
Original assignee: Daimlerchrysler Ag
Priority date: 2001-01-19
Filing date: 2001-12-20
Publication date: 2002-08-08
Also published as: DE10102244A1

Abstract

The invention relates to a "Steer by wire" steering system which stimulates a steering stop on the steering wheel (15) by means of a manual force actuator (18) when the maximum steering adjustment of the wheel (1) is achieved.

Description

Steering system for non-track vehicles

The invention relates to a steering system for non-track-bound vehicles, with

a sensor device actuated by a steering handle, in particular a steering handwheel, for a steering angle setpoint,

- a steering unit controlling the steered vehicle wheels,

a further transmitter device for a steering angle actual value, which detects the steering angles of the steered vehicle wheels,

- A controlled system regulating the control unit as a function of a target / actual value comparison of the steering angle and

- A manual power actuator, which applies forces to the steering handle in order to simulate a forced coupling of the steering handle and the steered vehicle wheels and / or reaction forces caused by the condition of a roadway.

Steering systems of this type, in which the “steer by wire” concept is implemented, are known in principle. Due to the fact that at least during normal operation there is no forced coupling between the steered vehicle wheels and the steering handle, steering or disturbing forces acting on the steered vehicle wheels cannot easily be noticed by the driver In particular, the driver cannot recognize when the steered vehicle wheels have reached their steering stop, that is to say that they have reached a maximum predetermined steering adjustment in relation to the straight-ahead position.

US Pat. No. 5,347,458 discloses a steering system that is intended for non-track-bound vehicles and operates according to the “steer by wire” concept, which has a manual power actuator in order to simulate forces on the steering handle which act on the steered vehicle wheels. In this way, the driver is given a steering feeling which essentially corresponds to the steering feeling which arises in a steering system with a positive coupling between the steering handle and the steered vehicle wheels.

The object of the invention is to ensure optimal control of the manual power actuator when the steered vehicle wheels reach a maximum steering adjustment compared to the straight-ahead position.

This object is achieved in that the manual power controller simulates a steering stop when reaching such a maximum steering adjustment.

In this context, provision is preferably made to trigger the simulation of a steering stop by signals from the actual value transmitter device.

The invention is based on the general idea of providing only a “virtual” steering stop for steer-by-wire operation and dispensing with fixed end stops for the steering handle. This also takes into account the fact that changing transmission ratios during steer-by-wire operation can occur between the actuating strokes of the steering handle and the steering angle changes of the steered vehicle wheels and, accordingly, the maximum possible or permissible steering angle of the steered vehicle wheels can be achieved with different positions of the steering handle.

Due to the preferably provided triggering of the simulation of the steering stop by means of the actual value transmitter device, which can directly and precisely “recognize” the reaching of a final steering angle value, a situation-appropriate simulation of the steering stop is ensured with comparatively simple means even if the steering angle setpoint is next to one of the position portion of the steering handle also depends on the includes drive parameters of the vehicle dependent portion or can include, as is known for example from DE 195 46 943 Cl.

In this context, it can be provided in particular that the portion of the steering angle setpoint which is dependent on the position of the steering handle is additively and / or multiplicatively superimposed on a setpoint portion which is dependent on the driving state of the vehicle, in particular the driving speed and / or on the state of the roadway. In simple terms, this is largely equivalent to the fact that the transmission ratio between the actuating stroke of the steering handle and the steering angle change caused by the actuating unit can change depending on parameters, in particular depending on the driving speed of the vehicle.

According to a particularly expedient embodiment of the invention, it can be provided that the actuating unit is switched off when an end value of the steering adjustment is reached or that it is only allowed to work with a reduced force in the direction exceeding the respective end value.

This takes into account the fact that the “virtual” steering stop provided for the steering handle in the invention can have a certain flexibility or elasticity and, accordingly, with extreme actuation of the steering handle, a steering angle setpoint could be generated which corresponds to a steering angle beyond the maximum achievable steering angle This is equivalent to the fact that a permanent setpoint / actual value deviation occurs in such an operating phase, the actuating unit being driven to reduce the setpoint / actual value deviation with maximum power without a further change in the steering angle being possible.

There is also the possibility of a mechanical and / or hydraulic positive coupling between the steering handle (15) and manufacture the steered vehicle wheels when the maximum steering adjustment is reached. In particular, the manual power actuator can be deactivated again when the mechanical and / or hydraulic positive coupling between the steering handle and the steered vehicle wheels is produced. This design makes it possible to dimension the manual power actuator “small”, ie the maximum torque that the manual power actuator must be able to generate can be selected to be low, for example in the range of 8-15 numbers. However, the driver is then able to apply a higher torque Apply the steering handle so that it could turn the steering handle beyond the steering stop simulated by the manual power actuator Since, in this embodiment of the invention, a continuously mechanical and / or hydraulic connection is established between the steering handle and the steered vehicle wheels, the steering handle cannot be deflected any further when the vehicle wheels have reached their limit stop in terms of design. The manual power actuator can therefore be made compact with low power.

The mechanical and / or hydraulic positive coupling between the steering handle and the steered vehicle wheels is expediently produced when a comparison variable correlating with the torque generated by the manual power actuator exceeds a predefinable threshold value. The moment itself can also serve as a comparison variable. If the manual force actuator is formed by an electric motor, the comparison variable can e.g. serve the current consumption of the electric motor or the electrical power consumed by the electric motor.

Otherwise, with regard to further preferred features of the invention, reference is made to the claims and the following explanation of the drawing, on the basis of which a particularly preferred embodiment of the invention is described in more detail.

It shows Fig. 1 is a schematic representation of a steering system of the type specified and Fig. 2 is an exemplary representation of the manual power control.

According to FIG. 1, a vehicle (not shown in more detail) has steerable front wheels 1 which are coupled via tie rods 2 to the piston rod 3 of a double-acting hydraulic piston-cylinder unit 4 for joint steering adjustment. The two sides of the piston-cylinder unit 4 are connected via hydraulic lines 5 and 6 to a control valve 7, which is otherwise connected via line 8 to the pressure side of a hydraulic pump 9 and via line 10 to a relatively unpressurized hydraulic reservoir 11 that the suction side of the hydraulic pump 9 is also connected.

A normally open shut-off valve 12 is arranged between the hydraulic lines 5 and 6. Otherwise, pressure transmitters 13 and 14 are provided on the hydraulic lines 5 and 6 for detecting the respective hydraulic pressure.

A steering handwheel 15 is connected via a steering shaft 16 on the one hand to a rotary angle sensor 17 and on the other hand to a manual power actuator 18. The manual power actuator 18 can be designed as an electric motor, which can oppose a rotatable adjustment of the steering handwheel 15 with an adjustable or controllable torque; the corresponding regulation or control is explained further below. The strength of this torque can be detected by means of a torque meter 19 and set using a control arrangement.

An electronic control circuit 20 provided as a control arrangement has a setpoint computer 21 which on the input side with the rotary angle sensor 17 and preferably also with further sensors (not shown) for vehicle-side operating parameters, such as driving speed, lateral acceleration and / or yaw rate, and / or with the driver actuated sensors is connected, for example with command devices, for example in the form of switches, for setting a "sporty" or a "comfort-oriented" operating behavior.

The setpoint computer 21 determines from the signals of the rotary angle sensor 17 actuated by the steering handwheel 15 and the other sensors a steering angle setpoint value which is dependent on the rotary position of the rotary angle transmitter 17 and thus on the rotary position of the steering handwheel 15 and which is variable as a function of parameters. Actual value generator 22 is compared, which is assigned to the piston rod 3 in the example shown.

In normal operation, the control circuit 20 keeps the shut-off valve 12 closed and controls the electromagnetically actuated control valve 7 as a function of the target / actual value comparison of the steering angle, so that when the pump 9 is operating, a more or less large one between the two sides of the piston-cylinder unit 4 hydraulic pressure difference occurs and the piston-cylinder unit 4 acts on the steerable wheels 1 with controllable steering force. In this way, the steered front wheels 1, on the one hand, perform steering movements analogous to the rotational movements of the steering handwheel 15 on the driver's side. On the other hand, vehicle dynamics parameters can also be taken into account by the setpoint computer 21, so that automatic steering corrections for stabilizing the vehicle are possible if necessary. In any case, the setpoint computer 21 can vary the transmission ratio between the change in the steering angle of the wheels 1 and the change in the angle of rotation of the steering handwheel 15 by taking into account parameters of the driving operation or the driving state, in particular the driving speed and the state of the roadway.

Furthermore, the control circuit 20 regulates or controls the manual power actuator 18. The manual power actuator 18 is also intended to simulate a steering stop when the steered wheels 1 reach the maximum design steering angle to the left or right.

Based on the parameter-dependent steering angle setpoint specification by the setpoint computer 21, the steered vehicle wheels 1 can reach their maximum steering deflection at fundamentally different rotational positions of the steering handwheel 15, i.e. no fixed rotary stops can be assigned to the steering handwheel 15.

2, the control circuit 20 has a circuit 23, which receives the signals from the actual value transmitter 22 and specifies a moment o, which increases substantially proportionally with small steering angles α near the straight-ahead position with increasing deviation from the straight-ahead position and with larger steering angles α in amount remains essentially the same.

The signal M ₀ is passed on to a summing circuit 24.

Another circuit 25 also receives the signals of the actual value transmitter 22 and determines a torque M _a therefrom which has the value zero on both sides of the straight-ahead position up to steering angles α of large magnitude. Only when the steering angles α reach the proximity of the design limit angles or come close to the limit angles, does M _A assume large values.

The signal M _A is also fed to the summing circuit 24.

In addition, the signal M _A passes through a differentiator 26 and a downstream amplifier 27, which is connected on the output side to the summing circuit 24.

In addition, the summation circuit 24 can be connected on the input side to further circuits 28 which, for example, receive the signals from the pressure transmitters 13 and 14 and an additional torque M _z depending on the size and direction of the Specify pressure transducers 13 and 14 determined pressure difference. This signal M _z is also fed to the summing circuit 24.

The signals supplied are additively linked by the summing circuit 24. The output signal output by the summing circuit controls a driver circuit 29, which in turn actuates the manual power actuator 18 in such a way that it opposes a driver-side rotary adjustment of the steering handwheel 15 to a resistance analogous to the signal sum of the input signals at the summing circuit 24, a steering stop being simulated when the Wheels 1 reach their maximum steering angle α to the right or left. The differentiator 26 gives the driver the feeling of a progressively hardening and damped stop.

The manual power actuator 18 thus acts similarly to a controllable brake, the resistance felt by the driver also being dependent on the rotational speed of the steering handwheel 15.

If a torque meter 19 is arranged between the steering handwheel 15 and the manual power actuator 18 in order to record the actual torque transmitted between the steering handwheel 15 and the manual power actuator 18, the driver circuit 29 can be controlled in the sense of a regulation, i.e. the output signal of the summing circuit 24 is processed as a setpoint for the steering resistance which can be felt on the steering handwheel 15, while the output signal of the torque meter 19, when the steering handwheel 15 is actuated, reproduces the actual value of the steering resistance which can be felt on the steering handwheel 15. The driver circuit 29 is then controlled in such a way that the target / actual value deviation is minimized.

According to a preferred embodiment of the invention, the signals of the actual value transmitter 22 can also be used for a special control of the control valve 7, such that the piston-cylinder unit 4 can generate no or only reduced forces when in the respective steering direction constructively possible maximum steering deflection is reached. As soon as the actual value transmitter 22 "reports" that the maximum steering deflection in one steering direction has been reached or has almost been reached, the control valve 7 can be reset to the vicinity of its neutral central position and can only be adjusted from this position to those positions in which the in Forces of the piston-cylinder unit 4 acting in the direction of the aforementioned maximum steering deflection are further reduced or forces are generated in the opposite direction.

For this purpose, the output signals of the circuit 25 can optionally be used and fed to a comparator circuit 30. As soon as the output signal M _A exceeds a tolerance range T adapted to the maximum possible steering deflections upwards or downwards, the control valve 7 is reset to the neutral central position.

The result of this is that the piston-cylinder unit 4 is unable to exert any significant forces in the direction exceeding the maximum steering angle in the region of a maximum steering deflection.

Here, the fact is taken into account that the steering handwheel 15 can be rotated by the driver into a position in which the setpoint calculator 21 determines a steering angle setpoint that is greater than the maximum achievable steering angle despite the simulation of a steering stop by the manual power actuator 18. In such a case, the control circuit 20 can no longer correct the target / actual value deviation of the steering angle. On the other hand, the control circuit 20 would control the control valve 7 without the measures described above such that the piston-cylinder unit 4 attempts to generate very high forces in a direction exceeding the respective maximum steering angle. This would lead to undesirably high loads on the steering system. In a further embodiment, a mechanical and / or hydraulic positive coupling can be produced between the steering handwheel 15 and the steerable vehicle wheels 1 if the vehicle wheels 1 are in the range of their maximum adjustable steering angle to the left or right. This forced coupling prevents the driver from moving the steering handwheel beyond the simulated steering stop and thereby changing the relative position between the steering handwheel 15 and the steerable vehicle wheels, which would result in a permanent offset. This would have the consequence that when the vehicle is traveling straight ahead, the steering handwheel would not assume its neutral position, but rather the position rotated relative to the neutral position. This problem can be avoided by means of the forced coupling when the steering stop is reached. As soon as the vehicle wheels 1 reach their maximum steering angle, this cannot be deflected any further because of the mechanical and / or hydraulic connection to the steering handwheel 15.

When the mechanical and / or hydraulic positive coupling is produced, the manual force actuator 18 formed by the electric motor can be switched off. This relieves the load on the electric motor and protects it from damage.

The mechanical and / or hydraulic positive coupling is produced when a comparison variable correlating with the torque generated by the manual power actuator exceeds a predetermined threshold value. The torque measured by the torque meter 19, which acts between the steering handwheel 15 and the manual force actuator 18, can serve as a comparison variable, for example. As an alternative to this, there is also the possibility of using the motor current or the electrical power as a comparison signal, which is supplied to the electric motor forming the manual power actuator.

As soon as the comparison signal exceeds the threshold value, the mechanical and / or hydraulic positive coupling is concluded. This can be achieved, for example, by closing a clutch in the steering linkage or switching valves, so that a hydraulic operative connection is created between the steering handwheel 15 and the piston-cylinder unit 4. Steering systems of this type with a mechanical or hydraulic fallback level are known per se.

It goes without saying that the threshold value can have a constant value, but can in principle be set as desired. For example, it can also depend on parameters such as vehicle speed.

In a preferred embodiment, the mechanical and / or hydraulic positive coupling is activated when the torque generated by the manual power actuator 18 exceeds a threshold value of approximately 10-15 Nm. The electrical power or current consumption of the electric motor 18 associated with this threshold value can also serve as a comparison signal.

In a departure from the illustrated embodiment, the hydraulic piston-cylinder unit 4 can also be replaced by other, e.g. electrical or pneumatic actuating units can be replaced, in which case 7 adapted control elements are to be provided instead of the control valve.

In the event of an emergency, additional actuating units and controls to ensure redundancies, which are not shown in normal operation, are generally arranged. If necessary, a normally opened mechanical or hydraulic forced coupling between the steering handwheel 15 and the steered wheels 1 can also be present.

If, in the event of an emergency, a further actuating unit or the forced coupling for controlling the steered wheels 1 are switched on, the shut-off valve 12 is opened automatically. In the embodiment shown above, it can additionally or alternatively be provided to determine the torque M _A as a function of the signals from the rotary angle sensor 17 and / or as a function of the signals from the setpoint computer 21. The value of M _{A then} increases in terms of amount if the angle of rotation of the steering handwheel 15 and / or the calculated steering angle setpoint exceeds a limit value 2 ^{* in} terms of amount.

In the event that a fault should occur during steer-by-wire operation, an “emergency level” (not shown) can be automatically switched on, for example an inactive mechanical coupling between steering handwheel 15 and that is ineffective in steer-by-wire operation by opening a clutch steered vehicle wheels, at the same time the shut-off valve 12 falls into its open state in order to avoid undesirable effects of the disturbed steer-by-wire system on the emergency control of the steered vehicle wheels 1 via said positive coupling.

Claims

claims

1. Steering system for non-track vehicles, with

a transmitter device (17, 21) actuated by a steering handle, in particular a steering handwheel (15), for a steering angle setpoint,

- A steering unit (4) controlling a steered vehicle wheels (1),

- a further transmitter device (22), which detects the steering angle of the steered vehicle wheels (1), for an actual steering angle value,

- One of the control unit (4) depending on a setpoint-actual value comparison of the steering angle regulating system (20)

- A manual power actuator (18) which applies forces to the steering handle (15) in order to simulate a forced coupling of the steering handle (15) and steered vehicle wheels (1) and / or reaction forces caused by the condition of a roadway, characterized in that the manual power actuator ( 18) simulates a steering stop when a maximum steering adjustment of the steerable wheels (1) is reached.

2. Steering system according to claim 1, d a d u r c h g e k e n n z e i c h n e t that signals of the actual value transmitter device (22) trigger directly or indirectly a signal for the simulation of the steering stop.

3. Steering system according to claim 1 or 2, characterized in that signals from a sensor (17) detecting the position of the steering handle (15) and / or a setpoint computer (21) for the steering angle trigger a signal for the simulation of the steering stop directly or indirectly.

4. Steering system according to claim 2, d a d u r c h g e k e n n z e i c h n e t that the actual value transmitter device (22) limit switch or separate signal transmitter for steering angle end positions of the steered vehicle wheels (1).

5. Steering system according to one of claims 1 to 4, that the control unit (4) switches off when a maximum steering adjustment of the steered vehicle wheels (1) is reached.

6. Steering system according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that the actuator (4) when reaching a maximum steering adjustment of the steered vehicle wheels (1) can only work with reduced force in the respective maximum steering adjustment in the direction exceeding.

7. Steering system according to one of claims 1 to 6, that a mechanical and / or hydraulic positive coupling is produced between the steering handle (15) and the steered vehicle wheels (1) when the maximum steering adjustment is reached.

8. Steering system according to claim 7, characterized in that the mechanical and / or hydraulic positive coupling between the steering handle (15) and the steered vehicle wheels (1) is then produced when one with the hand power adjuster (18) generated torque correlating comparison variable exceeds a predeterminable threshold value.

9. Steering system according to claim 7 or 8, d a d u r c h g e k e n n z e i c h n t that the manual power actuator (18) is deactivated when the mechanical and / or hydraulic positive coupling between the steering handle (15) and the steered vehicle wheels (1).

10. Steering system according to one of claims 1 to 9, d a d u r c h g e k e n n z e i c h n e t that the steering angle setpoint device (17,21) works parameter-dependent.

11. Steering system according to one of claims 1 to 10, characterized in that a summing circuit (24) is provided for controlling the manual power actuator (18), which processes at least a first signal (Mo) and a second signal (M _A ) additively, the the first signal represents a steering resistance to be specified and the second signal represents additional forces when the maximum possible steering deflection of the steered vehicle wheels (1) is reached.

12. Steering system according to one of claims 1 to 11, that the control system (20) actuates the manual power actuator (18) and / or the actuating unit (4) as a function of the parameters.

13. Steering system according to one of claims 1 to 12, so that the manual power actuator (18) can be controlled, at least when simulating the steering stop, also as a function of the actuating speed of the steering handle (15) to simulate a damped stop.

14. Steering system according to one of claims 1 to 13, characterized in that the manual power actuator (18) can be controlled as a function of forces which are active between the actuating unit (4) and the steered vehicle wheels (1).

15. Steering system according to claim 14, so that a hydraulic actuating unit (4) is provided and the forces between the actuating unit (4) and the steered vehicle wheels (1) are detected with pressure transmitters (13, 14).

16. Steering system according to one of claims 1 to 15, so that the simulation of the steering stop can be switched between “comfort-oriented” and “sporty” on the driver side.