DE102024205002A1 - Method for operating a steering system of a motor vehicle, steering system and motor vehicle - Google Patents

Abstract

The present invention relates to a method for operating a steering system (1) of a motor vehicle (2). According to the method, over-rotation of a steering wheel (3) of the steering system (1) is detected, a counter-torque is provided by a feedback actuator (5) of the steering system (1), a steering wheel torque applied to the steering wheel (3) by a driver of the motor vehicle (2) is monitored, and the counter-torque is adapted to the steering wheel torque in such a way that a damped return of the steering wheel angle to the programmed end stop occurs. The invention further relates to a steering system (1) for a motor vehicle (2) and to a motor vehicle (2).

Description

The present invention relates to a method for operating a steering system of a motor vehicle. The invention further relates to a steering system for a motor vehicle and to a motor vehicle with a steering system.

Steer-by-wire steering systems for motor vehicles are known in which the steering wheel is mechanically decoupled from the steering gear. A steering angle sensor is provided to detect the steering wheel angle. A control device controls a steering actuator according to the detected steering wheel angle to steer the motor vehicle. Such a steer-by-wire steering system is described, for example, in the document JP 2022 022 847 A known.

To ensure the most realistic steering experience possible, steer-by-wire systems typically feature a feedback actuator designed to generate torque on the steering wheel based on the torque acting on the actuator. Driving over a road surface irregularity thus provides direct haptic feedback to the driver.

To limit the steering range of the steering wheel, steer-by-wire systems can have a programmed end stop. The feedback actuator is designed to provide a particularly high counter-torque at the end stop, so that oversteering beyond the end stop is only possible by overcoming the torque that the feedback actuator can apply. Therefore, steer-by-wire systems have a weakness in the event of oversteering beyond the end stop.

The document DE 10 2021 210 041 A1 Disclosing a steer-by-wire steering system for a motor vehicle, in which a temporary shift of the end stop is provided to remedy this weakness, whereby no steering angle adjustment of the vehicle's wheels is made by the steering actuator in a range between the new end stop and the old end stop. Alternatively, it is also proposed to adjust the transmission ratio between the steering wheel angle and the steering actuator's steering angle to the new end stop. A disadvantage of these solutions is that either a free-running steering wheel or a change in the steering actuator's behavior is achieved. This can impair driving comfort. A similar steer-by-wire steering system is described in the document DE 10 2018 208 726 A1 known.

Known steer-by-wire steering systems have the disadvantage that if the programmed end stop is exceeded, the feedback actuator provides a particularly high counter-torque, which can cause the steering wheel to snap back when the driver releases steering force. In other steer-by-wire systems, where no such return to the normal steering wheel angle occurs, the ratio between the steering angle determined by the steering actuator and the steering wheel itself is altered, potentially impairing vehicle control for several seconds. This can compromise the safety of the vehicle's occupants and other road users.

It is therefore an object of the present invention to eliminate, or at least partially eliminate, the disadvantages of a steering system described above. In particular, it is an object of the present invention to provide a method for operating a steering system of a motor vehicle, a steering system for a motor vehicle, and a motor vehicle with a steering system, which in a simple and cost-effective manner reduce the impairment of the safety of the motor vehicle when the programmed end stop is exceeded and thus increase the safety of the steering system.

The aforementioned problem is solved by the claims. Accordingly, the problem is solved by a method for operating a steering system of a motor vehicle with the features of independent claim 1, by a steering system for a motor vehicle with the features of dependent claim 9, and by a motor vehicle with a steering system with the features of dependent claim 10. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawings. Features and details described in connection with the method for operating a steering system of a motor vehicle according to the invention naturally also apply in connection with the steering system and the motor vehicle according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always makes, or can make, reciprocal references.

• - Ermitteln eines Überdrehens eines Lenkrads des Lenksystems über einen vordefinierten programmierten Endanschlag des Lenkrads durch eine Winkelermittlungsvorrichtung des Lenksystems,
• - Bereitstellen eines Gegenmoments durch einen Feedback-Aktuator des Lenksystems zum Zurückstellen eines Lenkradwinkels des Lenkrads in Richtung des programmierten Endanschlags,
• - Überwachen eines von einem Fahrer des Kraftfahrzeugs auf das Lenkrad aufgebrachten Lenkradmoments durch eine Momentenermittlungsvorrichtung des Lenksystems, und
• - Anpassen des Gegenmoments an das Lenkradmoment durch den Feedback-Aktuator derart, dass eine gedämpfte Rückstellung des Lenkradwinkels zum programmierten Endanschlag hin erfolgt, wenn das Lenkradmoment kleiner ist als ein maximal verfügbares Gegenmoment des Feedback-Aktuators.

According to a first aspect of the invention, the problem is solved by a method for operating a steering system of a motor vehicle. The method comprises:

• - Detecting over-rotation of a steering wheel in the steering system via a predefined per gram-shaped end stop of the steering wheel by an angle detection device of the steering system,
• - Providing a counter-torque through a feedback actuator of the steering system to return a steering wheel angle to the programmed end stop,
• - Monitoring of a steering wheel torque applied to the steering wheel by a driver of the motor vehicle by means of a torque measuring device of the steering system, and
• - Adjusting the counter-torque to the steering wheel torque by the feedback actuator in such a way that a damped return of the steering wheel angle to the programmed end stop occurs when the steering wheel torque is smaller than a maximum available counter-torque of the feedback actuator.

The method according to the invention is preferably carried out on a steer-by-wire steering system. The steering system comprises the steering wheel for receiving a steering command from the driver of the motor vehicle, the angle detection device for determining the steering wheel angle, a steering actuator for steering the wheels of the motor vehicle depending on the steering wheel angle, and the feedback actuator for selectively providing torque at the steering wheel. Preferably, the steering system includes a torque detection device for monitoring the steering wheel torque applied to the steering wheel by the driver of the motor vehicle. More preferably, the steering system includes a control device for controlling the steering actuator depending on the steering wheel angle. According to the invention, the torque detection device can also be implemented by the control device in conjunction with the angle detection device. A return movement of the steering wheel caused by the feedback actuator can be detected by the angle detection device and is comparable to the control of the feedback actuator. From this, the steering wheel torque applied to the steering wheel by the driver can be determined. The steering system is preferably designed symmetrically such that the steering system behaves analogously between steering to the left and steering to the right.

The steering system is initially preferably operated in a normal driving situation. In this driving situation, the steering wheel angle is arranged within a working range between two predefined programmed end stops. The programmed end stops are preferably adapted to the steering capability of the vehicle's wheels. Within the scope of the invention, a programmed end stop is understood to be a virtual end stop which, due to the lack of a direct mechanical coupling between the wheels and the steering wheel, must be indicated by the feedback actuator so that the driver of the vehicle can better recognize when the steering angle corresponding to the virtual end stop has been reached. By moving the steering wheel within the working range, a corresponding adjustment of the steering angle of the wheels can thus be effected. The steering wheel angle is preferably continuously detected by the angle detection device.

If the programmed end stop is exceeded, the steering angles of the wheels can no longer follow the steering wheel angle due to a mechanical configuration of the steering system. The wheels are therefore preferably steered at the maximum achievable steering angle. The angle detection device detects when the programmed end stop is exceeded. This can occur, for example, when the steering wheel torque applied by the driver is greater than the counter-torque of the feedback actuator.

To indicate the programmed end stop and thus the steering wheel's exit from its operating range, the feedback actuator provides the counter-torque. A counter-torque is a torque that opposes the steering wheel torque applied by the driver when over-rotating the wheel. Outside the operating range, the counter-torque therefore acts as a restoring torque, intended to return the steering wheel to its operating range.

The torque detection device preferably continuously monitors the steering wheel torque applied by the driver. Only when the steering wheel torque applied by the driver is less than the maximum available counter-torque of the feedback actuator can the steering wheel angle return to its operating range. Within the scope of the invention, the maximum available counter-torque is understood to be the counter-torque for which the feedback actuator is designed to generate at most [value missing in original text]. The feedback actuator adjusts the counter-torque to the steering wheel torque in such a way that the return of the steering wheel angle to the programmed end stop is damped. Damping means, for example, that a sudden or jerky return is avoided. The steering wheel is thus preferably returned to its operating range smoothly and efficiently. A PID controller or similar device is preferably used for this purpose.

An inventive method for operating a motor vehicle's steering system has the advantage over conventional methods that user comfort and operational reliability of the steering system are improved in a simple and cost-effective manner. By allowing the programmed end stop to be overturned, the feedback actuator can be designed to be relatively small and therefore cost-effective. By precisely adjusting the counter-torque to the steering wheel torque, the steering wheel's return behavior to the working range is significantly improved compared to known steering systems, as a jerky or abrupt return of the steering wheel to the working range is effectively prevented.

According to a preferred embodiment of the invention, a method for operating a steering system can be provided that the angle detection device detects the driver's movement towards the programmed end stop before the steering wheel angle is exceeded, with the feedback actuator increasing the counter-torque as the steering wheel angle approaches the programmed end stop. Thus, the steering system recognizes that the steering wheel angle is approaching the programmed end stop and operates the feedback actuator in such a way that the driver of the vehicle, who is operating the steering wheel, can also better perceive the approach of the steering wheel angle to the programmed end stop. The closer the steering wheel angle in the operating range comes to the programmed end stop, the greater the counter-torque generated by the feedback actuator, so that the driver can better estimate the distance of the steering wheel angle from the programmed end stop based on the magnitude of the counter-torque. This has the advantage that the ease of use and operational reliability of the steering system are further improved in a simple and cost-effective manner.

According to the invention, it is preferred that the increase in counter-torque occurs from a predefined first steering wheel angle. The first steering wheel angle is located within the working range. The first steering wheel angle is positioned between a neutral position within the working range, in which the wheels are steered for straight-ahead driving and which preferably has the same distance to both virtual end stops, and one of the virtual end stops. Preferably, the first steering wheel angle is located midway between the neutral position and the virtual end stop. It is particularly preferred that the first steering wheel angle is positioned closer to the virtual end stop than to the neutral position. When steering within the working range between the neutral position and the first steering wheel angle, the counter-torque can thus be constant or follow a conventional characteristic. Within the scope of the invention, a conventional characteristic of the counter-torque is understood to mean a defined dependence of the counter-torque on other driving parameters, such as vehicle speed, road surface conditions, or the like. Upon reaching the first steering wheel angle and continuing to steer towards the virtual end stop, the counter-torque is increased. According to the invention, this increase can also be superimposed on the conventional characteristic of the counter-torque. This has the advantage that the ease of use and operational safety of the steering system can be further improved in a simple and cost-effective manner.

Preferably, the counter-torque is increased progressively with decreasing distance to the pre-programmed end stop. This means that the increase in counter-torque is relatively small at a relatively large distance to the programmed end stop, while the increase is relatively large at a relatively small distance. This progressive increase in counter-torque makes the approach of the programmed end stop more perceptible to the driver. Furthermore, the mechanical stress on the feedback actuator can be reduced, as a significantly lower counter-torque is provided in the vicinity of the steering wheel's neutral position than at the edges of the operating range near the programmed end stops. This has the advantage of further improving the ease of use and operational reliability of the steering system in a simple and cost-effective manner.

In a particularly preferred embodiment of the invention, a method may be provided such that the feedback actuator supplies the maximum available counter-torque at the programmed end stop before the programmed end stop is exceeded. By providing the maximum available counter-torque, the steering system design presents the driver with the maximum possible steering resistance, so that the driver clearly feels the exceeding of the programmed end stop. After the exceeding of the end stop, the maximum available counter-torque is preferably provided as long as the steering wheel torque applied by the driver is higher than the maximum available counter-torque. When the steering wheel torque is again less than the maximum available counter-torque, the counter-torque is reduced such that the damped return of the steering wheel angle to the programmed end stop is achieved. ten end stop. This has the advantage that the ease of use and operational reliability of the steering system are further improved in a simple and cost-effective manner.

Preferably, the damped return of the steering wheel angle to the programmed end stop occurs until the steering wheel angle corresponds to the programmed end stop. In other words, the steering wheel is brought into a steering position that is at the edge of its working range. A further requirement for this is that the steering torque applied by the driver is less than the maximum available counter-torque of the feedback actuator. By returning to the working range, a steering wheel position is provided in which turning the steering wheel towards the neutral position again results in an adjustment of the steering angle of the wheels. This has the advantage that the ease of use and operational reliability of the steering system are further improved in a simple and cost-effective manner.

According to a preferred embodiment of the invention, the steering system outputs a signal to the driver of the motor vehicle when the predefined end stop is exceeded. According to the invention, the signal strength can increase and/or change with increasing degree of over-rotation, for example, by increased intensity, increased amplitude, altered frequency, or the like. The signal can be output, for example, as a haptic signal, a visual signal, and/or an acoustic signal. The haptic signal can, for example, be a vibration applied to the steering wheel. The haptic signal can be generated, for example, by the feedback actuator. The visual signal can be generated, for example, by a warning light on the vehicle's instrument panel, a vehicle display, a head-up display, a light on the steering wheel, the vehicle's ambient lighting, or the like. The acoustic signal can be generated, for example, by a loudspeaker in the vehicle or the like. The acoustic signal can be output, for example, as a tone, a sequence of tones, a multi-tone signal, an announcement, or the like. A signal provides the driver and any passengers with clear feedback that the programmed end stop has been exceeded. This allows the driver to reduce steering effort and actively steer back into the steering system's working range, particularly with the support of the feedback actuator. This has the advantage of further improving the ease of use and operational safety of the steering system in a simple and cost-effective manner.

The counter-torque in the oversteered steering range is preferably provided in a pulsating or oscillating manner. The counter-torque can be provided, for example, in the form of a sinusoidal oscillation, a sawtooth oscillation, a combined oscillation, or the like, whereby a zero crossing is preferably avoided to prevent excessive oversteering by the driver. The amplitude of the oscillation is preferably relatively flat compared to the counter-torque. By providing the counter-torque in this way, it is possible to ensure that the steering wheel, in the oversteered state, performs oscillating movements, which can prompt the driver to reduce the steering torque and steer back towards the neutral position. This has the advantage that the ease of use and operational reliability of the steering system are further improved in a simple and cost-effective manner.

According to a second aspect of the invention, the problem is solved by a steering system for a motor vehicle. The steering system comprises a steering wheel for receiving a steering command from a driver of the motor vehicle, an angle detection device for determining the steering wheel angle, a steering actuator for steering the wheels of the motor vehicle depending on the steering wheel angle, and a feedback actuator for selectively providing torque at the steering wheel. According to the invention, the steering system is configured to carry out a method according to the invention for operating a steering system of a motor vehicle.

The steering system according to the invention is designed as a steer-by-wire system. The steering wheel is designed to receive steering commands from the driver of the motor vehicle. The angle detection device is designed to determine the steering wheel angle. A rotation of the steering wheel from a neutral position towards one of the two programmed end stops can be quantitatively detected by the angle detection device. The steering actuator is designed to steer the wheels of the motor vehicle depending on the steering wheel angle. For this purpose, the steering actuator is preferably communicatively coupled to a control device of the steering system. The control device is designed to detect the determined steering wheel angle, generate a control command for the steering actuator from this, and forward it to the steering actuator. Preferably, the steering system has a further detection device for determining the current steering angle.

The feedback actuator is designed to selectively provide torque at the steering wheel. This can be, for example, the counter-torque that opposes the steering wheel torque applied by the driver. Other types of torque can be, for example, simulated torques that would have been transmitted from the road to the steering wheel in an identical driving situation with a mechanical steering system. Preferably, the steering system includes a torque detection device for monitoring the steering wheel torque applied by the driver. According to the invention, the torque detection device can also be implemented by the control device in conjunction with the angle detection device and/or by the feedback actuator. A return movement of the steering wheel caused by the feedback actuator can be detected by the angle detection device and is comparable to the control of the feedback actuator. From this, the steering wheel torque applied by the driver can be determined. The steering system is preferably designed symmetrically such that the steering system behaves analogously when steering to the left and when steering to the right.

The steering system according to the invention offers all the advantages already described in relation to a method for operating a motor vehicle steering system according to the first aspect of the invention. Accordingly, the steering system according to the invention has the advantage over conventional steering systems that user comfort and operational reliability are improved in a simple and cost-effective manner. By allowing the steering wheel to be turned beyond the programmed end stop, the feedback actuator can be designed to be relatively small and therefore cost-effective. By precisely adjusting the counter-torque to the steering wheel torque, the return behavior of the steering wheel to the working range is significantly improved compared to known steering systems, as a jerky or abrupt return of the steering wheel to the working range is effectively prevented.

According to a third aspect of the invention, the problem is solved by a motor vehicle. The motor vehicle has a drive system for propelling the motor vehicle and a braking system for braking the motor vehicle. According to the invention, the motor vehicle has a steering system according to the invention.

The motor vehicle according to the invention offers all the advantages already described for a method for operating a steering system of a motor vehicle according to the first aspect of the invention and for a steering system for a motor vehicle according to the second aspect of the invention. Accordingly, the motor vehicle according to the invention has the advantage over conventional motor vehicles that ease of use and operational reliability of the steering system are improved in a simple and cost-effective manner. By allowing the programmed end stop to be overturned, the feedback actuator can be designed to be relatively small and therefore cost-effective. By specifically adjusting the counter-torque to the steering wheel torque, the return behavior of the steering wheel to the working range is significantly improved compared to known steering systems, as a jerky or abrupt return of the steering wheel to the working range is effectively prevented.

• 1 in einer perspektivischen Ansicht eine bevorzugte Ausführungsform eines erfindungsgemäßen Lenksystems,
• 2 in einer Seitenansicht eine bevorzugte Ausführungsform eines erfindungsgemäßen Kraftfahrzeugs, und
• 3 in einem Ablaufdiagramm eine bevorzugte Ausführungsform eines erfindungsgemäßen Verfahrens.

A method according to the invention for operating a steering system of a motor vehicle, a steering system according to the invention for a motor vehicle, and a motor vehicle according to the invention are explained in more detail below with reference to the drawings. The drawings schematically show:

• 1 in a perspective view a preferred embodiment of a steering system according to the invention,
• 2 a preferred embodiment of a motor vehicle according to the invention in a side view, and
• 3 A preferred embodiment of a method according to the invention is shown in a flowchart.

Elements with the same function and mode of operation are in the 1 to 3 each provided with the same reference numerals.

1 Figure 1 schematically shows a preferred embodiment of a steering system 1 according to the invention in a perspective view. The steering system 1 comprises a steering wheel 3, which is mechanically coupled to an angle detection device 4 for determining the steering wheel angle of the steering wheel 3 and to a feedback actuator 5. The angle detection device 4 quantitatively determines the steering wheel 3 being actuated by the driver or its current position. The feedback actuator 5 is designed to apply a torque, such as a counter-torque to a steering wheel torque applied by the driver or feedback of forces and torques acting on the steering system 1 from the road surface.

The feedback actuator 5 is also designed as a torque measuring device 6 to to quantitatively measure the steering torque applied by the driver. For adjusting the steering angle of wheels 8 (see...) 2 The steering system 1 has a steering actuator 7. The steering actuator 7 is coupled to the feedback actuator 5 via a control line 11. A control device of the steering system 1 (not shown) can, for example, be arranged on the feedback actuator 5 and coupled to the control line 11 and the feedback actuator 5.

In 2 A preferred embodiment of a motor vehicle 2 according to the invention is shown schematically in a side view. The motor vehicle 2 has a drive system 9 for propelling itself. The drive system 9 can, for example, be configured as an internal combustion engine, hybrid, or electric drive system 9. The drive system 9 can be configured to drive two or four wheels 8 of the motor vehicle 2. The motor vehicle 2 has a braking system 10 for braking itself. The braking system 10 is configured to brake the wheels 8. Furthermore, the motor vehicle 2 has a steering system 1 according to the invention.

3 Figure 1 schematically shows a preferred embodiment of a method according to the invention for operating a steering system 1 of a motor vehicle 2 in a flowchart. In a first process step 100, the angle detection device 4 of the steering system 1 determines that the steering wheel 3 of the steering system 1 has been turned beyond its predefined programmed end stop. The steering wheel 3 thus has a steering angle that lies outside a normal operating range of the steering wheel 3. This over-turning is caused by a steering torque applied to the steering wheel 3 by the driver of the motor vehicle 2.

In a second process action 200, the feedback actuator 5 provides a counter-torque to the steering wheel torque, which thus acts in the direction of the programmed end stop. The counter-torque therefore acts in a direction that returns the steering wheel angle of the steering wheel 3 to the programmed end stop. In this way, further over-rotation of the steering wheel 3 is to be prevented.

In a third procedural step 300, the torque measuring device 6 of the steering system 1 monitors the steering wheel torque applied to the steering wheel 3 by the driver of the motor vehicle 2. Monitoring the steering wheel torque is important in case the steering wheel torque decreases again, especially if the driver abruptly reduces the steering wheel torque or briefly releases the steering wheel 3.

If the steering wheel torque is less than the maximum available counter-torque of the feedback actuator 5, the feedback actuator 5, in a fourth process action 400, adjusts the counter-torque to the steering wheel torque such that a damped return of the steering wheel angle to the programmed end stop occurs. The counter-torque is thus only slightly greater than the steering wheel torque, so that a snapping back of the steering wheel 3 into the working range of the steering wheel 3 is prevented.

Reference symbol list

1

Steering system

2

motor vehicle

3

steering wheel

4

Angle measuring device

5

Feedback actuator

6

Torque measuring device

7

Steering actuator

8

wheel

9

drive system

10

Braking system

11

Control line

100

first procedural action

200

second procedural action

300

third procedural action

400

fourth procedural action

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• JP 2022 022 847 A [0002]
• DE 10 2021 210 041 A1 [0005]
• DE 10 2018 208 726 A1 [0005]

Claims (10)

A method for operating a steering system (1) of a motor vehicle (2), comprising: - Detecting an over-rotation of the steering wheel (3) of the steering system (1) beyond a predefined programmed end stop of the steering wheel (3) by means of an angle detection device (4) of the steering system (1), - Providing a counter-torque by means of a feedback actuator (5) of the steering system (1) to return a steering wheel angle of the steering wheel (3) to the programmed end stop, - Monitoring a steering wheel torque applied to the steering wheel (3) by a driver of the motor vehicle (2) by means of a torque detection device (6) of the steering system (1), and - Adjusting the counter-torque to the steering wheel torque by means of the feedback actuator (5) such that a damped return of the steering wheel angle to the programmed end stop occurs when the steering wheel torque is less than a maximum available counter-torque of the feedback actuator (5). Procedure according to Claim 1 , characterized in that the angle determination device (4) detects that the programmed end stop is being turned by the driver before the programmed end stop is overturned, wherein the feedback actuator (5) increases the counter-torque as the steering wheel angle gets closer to the end stop. Procedure according to Claim 2 , characterized in that the increase of the counter-torque occurs from a predefined first steering wheel angle. Procedure according to Claim 2 or 3 characterized in that the increase of the counter-torque occurs progressively with decreasing distance to the pre-programmed end stop. Method according to one of the preceding claims, characterized in that the feedback actuator (5) provides the maximum available counter-torque at the programmed end stop before the programmed end stop is over-rotated. Method according to one of the preceding claims, characterized in that the damped return of the steering wheel angle to the programmed end stop takes place until the steering wheel angle corresponds to the programmed end stop. Method according to one of the preceding claims, characterized in that the steering system (1) sends a signal to the driver of the motor vehicle (2) when the predefined end stop is exceeded. Method according to one of the preceding claims, characterized in that the counter-torque in the oversteered steering range is provided in a pulsating or oscillating manner. Steering system (1) for a motor vehicle (2), comprising a steering wheel (3) for receiving a steering command from a driver of the motor vehicle (2), an angle detection device (4) for determining a steering wheel angle of the steering wheel (3), a steering actuator (7) for steering wheels (8) of the motor vehicle (2) depending on the steering wheel angle and a feedback actuator (5) for selectively providing a torque at the steering wheel (3), characterized in that the steering system (1) is configured to carry out a method according to one of the preceding claims. Motor vehicle (2), comprising a drive system (9) for propelling the motor vehicle (2) and a braking system (10) for braking the motor vehicle (2), characterized in that the motor vehicle (2) has a steering system (1) for selectively steering the motor vehicle (2) in a direction of travel. Claim 9 exhibits.