BE1030848B1 - Steering system of a motor vehicle and method for operating a steering actuator unit of a motor vehicle in the event of a blockage of a steered wheel - Google Patents

Abstract

The present invention relates to a method for operating a steering actuator unit (9) of a motor vehicle comprising a steering actuator (5) and an electric motor (11), wherein the steering actuator (5) is driven by the electric motor (11) to convert a steering command into a steering movement of steerable wheels (4), and wherein, if a blockage of a steered wheel (4) is detected when the steering actuator (5) is driven, a maximum torque that can be provided by the electric motor (11) is reduced. The invention further relates to a steering system (1) for a motor vehicle with steerable wheels (4), comprising a steering handle (7) for specifying a steering command and a steering actuator unit (9) for converting a specified steering command into a steering movement of steerable wheels (4) of a motor vehicle, wherein the steering system (1) is designed to operate the steering actuator unit (9) according to an aforementioned method.

Description

Steering system of a motor vehicle and method for operating a steering actuator unit of a motor vehicle in the event of a blockage of a steered wheel

The invention relates to a method for operating a steering actuator unit of a motor vehicle according to the preamble of claim 1. Furthermore, the invention relates to a steering system for a motor vehicle with steerable wheels, comprising a steering handle for specifying a

steering command and a steering actuator unit for converting a given steering command into a

Steering movement of steerable wheels of a motor vehicle, whereby the steering system is

is trained to operate the steering actuator unit.

In the prior art, a steer-by-wire steering system and a method for steering motor vehicles are known from DE 10 2005 041 086 A1, which are intended to prevent overheating of the steering actuator when a steering angle of a steerable wheel cannot be achieved due to a blockage of the wheel. For this purpose, a predetermined steering angle for the steering actuator is

The angle of rotation is corrected if the steerable wheel is blocked. In addition, the

DE 10 2018 126 726 A1, how a blocking of a steerable wheel can be detected and that in this case a feedback is sent to the steering handle. In addition, the

Publications DE 102 61 001 A1, EP 3 702 245 A1, DE 10 2010 032 043 A1 and

EP 1 772 349 A2 deals with the problem of steering systems where a steered wheel is

obstacle, in particular a curb, in which case it is proposed to reduce the assist torque exerted on the wheels.

Against this background, it is an object of the present invention to provide a method for

To operate a steering actuator unit and to improve a steering system.

To solve this problem, a method for operating a steering actuator unit according to

Claim 1 and a steering system for a motor vehicle according to the subordinate

Claim 11 is proposed. Further advantageous embodiments of the invention are described in the dependent claims and the description and shown in the figures.

The proposed solution provides a method for operating a steering actuator unit of a

Motor vehicle comprising a steering actuator and an electric motor, wherein the steering actuator is used to convert a steering command into a steering movement of steerable wheels from the

Electric motor is driven, and in the event of a detected blockage of a steered wheel when driving the steering actuator, a maximum torque that can be provided by the electric motor

torque is reduced. Because the maximum torque available from the electric motor

Torque is reduced, the probability that due to the torque generated by the

Electric motor mechanical forces introduced into the steering system can cause damage to the

steering system, for example mechanical deformations, are advantageously reduced. In particular, the power provided by the electric motor in the blockage situation is

Torque reduced.

According to the invention, if a blockage of a steered wheel is detected when driving the

Steering actuator the maximum torque available from the electric motor to a

Safety limit value is reduced. In particular, the safety limit value is in an interval between 2 Nm (Nm: Newton meter) and 5 Nm, further in particular the

Maximum limit 3 Nm. The safety limit is advantageously set so that a torque provided by the electric motor is large enough to

Driving situation in which in particular no steered wheel is blocked, to convert a detected steering command into a steering movement of the steerable wheels. On the other hand, the safety limit value is advantageously set so that a torque provided by the electric motor is reduced in such a way that damage to the steering system, in particular damage to a

steering pinion, on a steering rack, on tie rods and/or on cross members.

The method according to the invention further provides that the electric motor for driving the

Steering actuator is operated in a normal mode such that the torque provided by the electric motor does not exceed a predetermined maximum limit, whereby the maximum limit is greater than the safety limit. The predetermined

The maximum limit value is advantageously below a torque that the

Electric motor could technically provide from its design. In particular, the

Maximum limit value in an interval between 4 Nm and 10 Nm, further in particular the

Maximum limit 6.5 Nm. This advantageously further protects the steering system against damage.

According to a further advantageous embodiment of the method, when a detected

Blockage of a steered wheel when driving the steering actuator, the maximum torque that can be provided by the electric motor continuously decreases from the maximum limit to the

Safety limit reduced. Advantageously, mechanical stress that has built up in the steering system due to the locked wheel is continuously reduced, which further improves protection of the steering system against damage.

According to the invention, when a blockage of a steered wheel is detected when the steering actuator is driven, the maximum torque that can be provided by the electric motor is

Torque is continuously increased from the safety limit to the maximum limit. Advantageously, the steering system is thereby further protected against damage. In particular, the reduction from the maximum limit to the

Safety limit and/or raising the safety limit to the

Maximum limit within a given adjustment period. The given

The adaptation time period is advantageously in an interval between 0.1 s (s: second) and 1.5. In particular, the predetermined adaptation time period is 0.5 s.

A particularly advantageous embodiment of the method provides that a blockage of a steered wheel is detected when the steering actuator is driven if a first

Torque threshold value for a torque provided by the electric motor is exceeded and/or a first speed threshold value for a speed of the electric motor is undershot. It has been shown that in this way a blocked steered wheel can advantageously be detected with a high degree of probability. In particular, it is provided that when the two aforementioned conditions are met, i.e. the first

Torque threshold exceeded and also a speed value of a speed of the

electric motor falls below the first speed threshold, a blockage of a steered

wheel is detected when driving the steering actuator. Advantageously, in one of the

A detection flag is set in the electronic control unit assigned to the steering actuator unit. The set detection flag advantageously signals a detected blockage of a steered wheel when driving the steering actuator.

According to an advantageous development of the method, a blockage of a steerable

wheel when driving the steering actuator if the first torque threshold is exceeded for a predetermined first safety period and/or if the first

speed threshold is exceeded for a predetermined second safety margin. The first

In particular, the safety period may be equal to the second safety period.

Due to the respective safety period, for the duration of which the torque threshold value or the speed threshold value must be exceeded according to this design variant, a blocked steered wheel is advantageously prevented with even higher

Reliability is recognized. A particular advantage is that the probability of incorrect detection of a blocked steered wheel is significantly reduced.

Measurement errors or other causes for a short-term exceedance or

Falling below the respective threshold value is advantageously filtered out by providing the safety margin. If, in this embodiment, the torque provided by the electric motor exceeds the

torque threshold and the engine speed falls below the speed threshold for a period of time that is shorter than the safety time period, then a blockage of a steered wheel when driving the steering actuator is advantageously not detected. The first safety time period is advantageously speed-dependent. The second

The safety time period is advantageously speed-dependent. In particular, it is intended that the respective safety time period is greater the higher a

The respective safety time period can also depend on other vehicle parameters and/or on a set

Driving program. Further specifications and dependencies for the respective

Safety time periods can also be advantageously implemented. In particular, it is provided that the safety time period lies in a time interval between 0.1 s and 5 s, more advantageously in a time interval between 0.2 s and 1.5 s. For a simplified

In particular, a constant safety period can also be provided. An advantageous value for a constant safety period is 0.5s.

An advantageous embodiment of the method provides that a blockage of a guided

wheel is detected when driving the steering actuator when a first torque threshold for a torque provided by the electric motor is exceeded and a first

Speed threshold for a speed of the electric motor is undershot, whereby the

The torque provided by the electric motor exceeds the first torque threshold at least for the

Duration of the predetermined first safety period must be exceeded.

According to a further advantageous embodiment of the method, a cancellation of a

Blockage of a steered wheel detected when driving the steering actuator if a second

torque threshold value for a torque provided by the electric motor is undershot and/or a second speed threshold value for a speed of the electric motor is exceeded. In particular, it is provided that a lifting of a blockage of a steered wheel when driving the steering actuator is detected when a second

Torque threshold value for a torque provided by the electric motor is undershot or a second speed threshold value for a speed of the electric motor is exceeded. In this way, it is advantageously possible to return to normal operation in which the torque provided by the electric motor is not limited to the

safety limit is reduced, in particular with a low probability that

Damage to the steering system can occur due to excessive engine torque. In particular, 5 it is intended that when a blockage of a steered wheel is detected during

Driving the steering actuator the detection flag in the steering actuator unit assigned

Control unit is deleted.

In particular, a third or fourth safety period can be specified for falling below or exceeding the respective threshold value, in particular to prevent an unwanted premature return to a

to prevent normal operation.

An advantageous design variant further provides that the first

Torque threshold is greater than the second torque threshold. In particular, it is provided that the first torque threshold is greater than the safety limit and the safety limit is greater than the second torque threshold. This design advantageously further prevents an unwanted premature return to normal operation.

Another design variant with an advantageously lower

Implementation effort, on the other hand, provides that the first torque threshold is equal to the second torque threshold and/or that the first speed threshold is equal to the second speed threshold.

In a further advantageous embodiment of the method, if a blockage of a steered wheel is detected when the steering actuator is driven, the power provided by the electric motor

Torque is limited by a torque limiter. For this purpose, appropriate hardware is provided, which in particular enables a mechanical limitation of the

torque is achieved.

According to a further embodiment of the method, a control signal for controlling the electric motor is specified in order to implement a steering command, wherein when a detected

If a steered wheel is blocked when driving the steering actuator, the torque that can be provided by the electric motor is limited by adjusting the control signal.

Advantageously, this provides a more cost-effective and weight-reduced design for

Limitation of the torque of the electric motor is provided.

The steering system for a motor vehicle with steerable wheels, which is further proposed to solve the problem mentioned above, comprises a steering handle for specifying a

steering command and a steering actuator unit for converting a given steering command into a

Steering movement of steerable wheels of a motor vehicle, wherein the steering system is designed to operate the steering actuator unit according to a method designed according to the invention.

In particular, the features described above can be implemented individually or in any combination. In particular, the steering actuator unit comprises a

Steering actuator and an electric motor, wherein the steering actuator is designed by means of the electric motor in particular to convert a steering command into a steering movement of the steerable wheels.

Furthermore, the steering system is in particular assigned an electronic control unit, wherein the control unit can in particular be included in the steering system.

Advantageously, the control unit is designed to control the steering actuator unit according to a method designed according to the invention. In particular, the steering system is designed to operate the steering actuator unit in such a way that the steering actuator is used to implement a

Steering command is converted into a steering movement of steerable wheels by the electric motor, wherein if a blockage of a steered wheel is detected when the steering actuator is driven, a maximum torque that can be provided by the electric motor is reduced.

Advantageously, the steering system also comprises sensor units for detecting a

electric motor and to detect a speed of the electric motor.

The control unit is advantageously designed to receive and evaluate the signals provided by the sensor units.

According to an advantageous embodiment, the steering system is a steer-by-wire steering system.

According to a further advantageous embodiment, the steering system is a

Rear wheel steering system.

Further advantageous details, features and design details of the invention are described in

The following is explained in more detail in connection with the embodiments shown in the figures (Fig.: Figure).

Fig.1 in a simplified perspective view an embodiment of a

Steering system designed according to the invention;

Fig. 2 shows an embodiment of a method according to the invention using a flow chart;

Fig. 3a is a diagrammatic representation of an exemplary torque signal curve when operating a steering actuator unit according to the invention; and

Fig. 3b is a diagrammatic representation of an exemplary steering angle signal curve when operating a steering actuator unit according to the invention as shown in Fig. 3a.

In Fig. 1, an embodiment of a steering system 1 designed according to the invention for a

Motor vehicle, wherein the steering system 1 is a steer-by-wire steering system. The steer-by-wire steering system 1 comprises a steering column with a steering shaft 2 and a feedback

Actuator 10. At one end of the steering shaft 2, a steering handle 7 designed as a steering wheel is arranged in a rotationally fixed manner. A driver can give a steering command via the steering handle 7. The

Feedback actuator 10 is designed, in particular, to convey a steering feel, a

torque or a steering resistance torque on the steering shaft 2, which a driver of the motor vehicle can perceive via the steering handle 7. The

Steering handle 7 can be rotated in the known manner to give a steering command to the

Steering shaft 2, which is detected by sensors. For this purpose, the steer-by-wire steering system 1 can in particular have an absolute angle sensor unit 15 assigned to the steering shaft 2, which is designed to detect a position of the steering handle 7 as a rotation angle and to

Control unit 16 of the steer-by-wire steering system 1. In Fig. 1, the

Control unit 16 and the steering system 1 associated sensor units 14, such as the

Absolute angle sensor unit 15, shown only schematically.

The control unit 16 is in particular an ECU (ECU: Electronic Control Unit) and is designed, taking into account the absolute angle sensor unit 15 provided

angle signal a control signal C1 for controlling a steering actuator unit 9 of the steer-by-

Wire steering system 1, in particular for controlling an electric motor 11 of the

Steering actuator unit 9. The steering actuator unit 9 is part of a steering gear 3 included in the steer-by-wire steering system 1, wherein the steering actuator unit 9 in this embodiment is a

Steering pinion 5 as a steering actuator and an electric motor 11 driving the steering pinion 5.

By appropriate control with a control signal assigned to the steering actuator unit 9

Control unit 16 provided control signal C1, the steering pinion 5 is used to implement a

Steering command into a steering movement of the steerable wheels 4 driven by the electric motor 11. In this embodiment, the steering actuator unit 9 acts by means of the

electric motor 11 via the steering pinion 5 onto a coupling element designed as a rack 6 and triggers a steering movement of the steerable wheels 4 of a motor vehicle, which

In particular, they are connected to the rack 6 via tie rods 8. The tie rods 8 themselves are connected in a known manner to a steered wheel 4 via steering knuckles.

The torque provided by the electric motor 11 to implement a steering command varies in particular depending on a resistance counteracting the steering movement of the steered wheels 4. The steering system 1 is designed to operate the steering actuator unit 9 in such a way that a blockage of a steered wheel 4, for example a blockage caused by a

Curb in the execution of a steering movement blocked wheel is detected, and in case of a detected blockage of a steered wheel 4 when driving the steering pinion 5 of the

Steering actuator unit 9 reduces a maximum torque that can be provided by the electric motor 11 to a safety limit value. To detect a blocked steered wheel 4, a first sensor unit 17, which detects a torque provided by the electric motor 11, and a second sensor unit 18, which detects a

Motor speed of the electric motor 11 is detected, provided sensor signals are evaluated by the control unit 16. If the evaluation shows that a signal provided by the electric motor 11

Torque exceeds a specified torque threshold and at the same time the

If the engine speed falls below a predetermined speed threshold, a blockage of a steered wheel 4 is detected when driving the steering pinion 5, and the

The torque provided by the electric motor is reduced to the specified safety limit.

The reduction of the electric motor 11 is reduced in this embodiment by a corresponding adjustment of the control signal C1. The reduction of the

The torque available from the electric motor 11 is cancelled again if an evaluation of the signals provided by the sensor units 17, 18 shows that either the

The torque provided by the electric motor 11 has fallen below the specified torque threshold or the motor speed of the electric motor 11 has exceeded the specified speed threshold.

Further possible design details for the method for operating the steering actuator unit 9 are explained below with reference to Fig. 2 to Fig. 3b.

Referring to Fig. 2, particular design details relating to the detection of a wheel blocked in a steering movement are explained and with reference to Fig. 3a and Fig. 3b

Design details for adjusting the torque provided or available by the electric motor.

In Fig. 2, a flow chart is shown that symbolically shows the detection of a

Blockage of a steered wheel when performing a steering movement is described. In this embodiment, the steps during a

Operating a steering system is carried out repeatedly. The method provides that in a step S1.1, a torque currently provided by the electric motor is detected by means of a sensor unit 17 for detecting a torque provided by the electric motor and transmitted to a control unit 16 assigned to the steering actuator unit.

In addition, in a further step S1.2, which can be carried out in particular at the same time as step S1.1, a sensor unit 18 is used to detect an engine speed of the

Electric motor, a current motor speed of the electric motor is detected and transmitted to the control unit 16.

The control unit 16 then checks in a step 2.11 whether the torque provided by the electric motor is greater than (>) or less than or equal to (<) a predetermined

Torque threshold Thr_T is then output for the respective output of the

Check block 61 returns a value of “true” or “false”. If the check shows that the provided

Torque has exceeded the specified torque threshold Thr_T, so that in

Fig. 2 at the left output of the test block 61 the value “true” is present and at the right

If the output of the test block 61 is “false”, a timer 60 starts and for a predetermined period of time T, in particular for 0.5 s, in a step S2.12 in a

Test block 62, which may actually be identical to test block 61, checks whether a torque currently provided by the electric motor continues to exceed the specified torque threshold Thr_T for the duration of the time period T or not. If the

Torque falls below the specified torque threshold Thr_T, the right

The output of test block 62 is “true” and otherwise “false”.

If the torque continues to exceed the specified torque threshold Thr_T, step S2.12 is repeated until the time period T has elapsed and, if the torque still exceeds the specified torque threshold Thr_T, a value "true" is output at the left output of the test block 62. Otherwise, the value "false" is present at the output.

In parallel, the control unit 16 checks in a step S2.2 whether the motor speed of the electric motor is greater than (>) or less than or equal to (<) a predetermined speed threshold value

Thr_R is. If the detected engine speed falls below the specified speed threshold

Thr_R or if this is equal to the specified speed threshold Thr_R, the

Test block 63 outputs the value “true” on the right and the value “false” on the left. If the

However, if the engine speed is above the specified speed threshold Thr_R, the value “true” is output on the left and the value “false” on the right.

The values output by the test blocks 61, 62, 63 are then fed to an OR operation 67 or an AND operation 68, as shown by way of example in Fig. 2, and the signals are subjected to a logical “OR” operation in a step S3.1 and in a

Step S3.2 is subjected to a logical “AND” operation. If either a detected

Torque is below the specified torque threshold Thr_T or the detected

Speed is above the specified speed threshold Thr_R, the OR

The value “true” is given in the link and a torque limit 70 is deactivated in a step S4.1. A control signal C1 determined by the control unit 16 for controlling the

The electric motor of the steering actuator unit is then output unchanged by the control unit 16. If, however, the torque provided by the electric motor exceeds the specified torque threshold value Thr_T for the specified time period T or longer and the speed of the electric motor also falls below the specified

Speed threshold Thr_R, the AND operation 68 returns the value “true” and the

Torque limitation 70 is activated in a step S4.2. The control signal C1 determined by the control unit 16 is then changed taking into account the torque limitation 70 in such a way that the changed control signal C1 controls the electric motor in such a way that the electric motor can provide a maximum torque that does not exceed a safety limit value, which is advantageously below the torque threshold Thr_T. A new

Torque threshold Thr_T is set, which is advantageously below the

Only when the torque limitation 70 is deactivated again is the previous torque threshold Thr_T, which is above the safety limit, specified again.

In a diagrammatic representation, Fig. 3a shows an exemplary course for a

The torque provided by the electric motor 20 is shown in Nm over time. Below is

Fig. 3b in another diagram an exemplary steering angle 21 of a joint

Wheel 4 of a motor vehicle is shown over time. The curves are greatly simplified and would actually show fluctuations.

In the period from 0 s to 2 s no steering command is given. The steering angle 21 is 0°.

The vehicle is driving straight ahead. Accordingly, no torque is specified by the electric motor. The electric motor for driving the steering actuator is operated in normal operation in such a way that the torque provided by the electric motor does not exceed a specified maximum limit value 24. From a point in time of 2 s, a

Steering angle 21 is implemented and the electric motor generates a torque 20 greater

Zero provided.

At the time t1, at which the steering actuator unit and thus also the electric motor are still operating in normal mode, in this embodiment a steered wheel encounters a

Curb. The steered wheel cannot move any further and is blocked, whereby due to the

Elasticity of the steering system, the torque 20 provided increases sharply. The torque exceeds a predetermined first

Torque threshold 26 and the engine speed falls below a specified

Speed threshold because the electric motor cannot continue to operate in the usual manner.

The steering angle 21 cannot be changed any further and a flag 29 is set, which signals the detection of a 20 blockage of a steered wheel when driving the steering actuator. Since the torque 20 exceeds a specified safety period, which is

Example is 0.5 s, remains unchanged and thus continues to meet the specified

torque threshold value, a blockage of a steered wheel is detected and the torque available from the electric motor is continuously reduced from the maximum limit value 24 to a safety limit value 22 starting at a time t3, which

embodiment corresponds approximately to half the maximum limit value 24.

As a result, the torque 20 provided decreases from a point in time t4 in accordance with the specified torque limit, so that the safety limit value 22 is not exceeded by the torque 20 provided. The theoretical course of the non-limited torque 20* is also shown in Fig. 3a. From a point in time t5, which is

Fig. 3a is 6 s, a steering angle in the opposite direction is specified. This causes the

Torque 20 below a predetermined second torque threshold 28 and the

Engine speed again exceeds the engine speed threshold, so that the cancellation of the

Blockage of the steered wheel is detected and flag 29 is deleted. The

The torque available from the electric motor is continuously increased from the safety limit value 22 to the maximum limit value 24.

The components shown in the figures and explained in connection with them

Embodiments serve to explain the invention and are not limitative of it.

List of reference symbols 1 Steering system 2 Steering shaft 3 Steering gear 4 Steerable wheel 5 Steering actuator 6 Rack 7 Steering handle 8 Tie rod 9 Steering actuator unit 10 Feedback actuator 11 Electric motor of the steering actuator unit (9) 14 Sensor units 15 Absolute angle sensor unit 16 Control unit 17 Sensor unit for detecting a torque provided by the electric motor (11) 18 Sensor unit for detecting a motor speed of the electric motor (11) 20 Torque provided by the electric motor (11) 20 20% non-limited torque (20) 21 Steering angle of a steered wheel (4) 22 Safety limit value 24 Maximum limit value for a torque that can be provided by the electric motor (11) 26 First torque threshold value 28 Second torque threshold value 29 Flag first safety time period 60 Timer 61 Test block torque 30 62 Test block torque 63 Test block speed 67 Or-link 68 And-link 70 Torque limitation

C1 Control signal for controlling the electric motor (11)

Claims (13)

Expectations 1. Method for operating a steering actuator unit (9) of a motor vehicle comprising a steering actuator (5) and an electric motor (11), wherein the steering actuator (5) is driven by the electric motor (11) to convert a steering command into a steering movement of steerable wheels (4), wherein when a blockage of a steered wheel (4) is detected when the steering actuator (5) is driven, a maximum torque that can be provided by the electric motor (11) is reduced to a safety limit value (22), and wherein the electric motor (11) for driving the steering actuator (5) is operated in normal operation such that the torque that can be provided by the electric motor (11) does not exceed a predetermined maximum limit value (24), wherein the maximum limit value (24) is greater than the safety limit value (22), characterized in that when a blockage of a steered wheel (4) is detected when the steering actuator (5) is driven, the maximum torque that can be provided by the electric motor (11) is continuously reduced from the Safety limit (22) is raised to the maximum limit (24). 2. Method according to claim 1, characterized in that when a blockage of a steered wheel (4) is detected when driving the steering actuator (5), the maximum torque that can be provided by the electric motor (11) is continuously reduced from the maximum limit value (24) to the safety limit value (22). 3. Method according to one of the preceding claims, characterized in that a blockage of a steered wheel (4) during driving of the steering actuator (5) is detected when a first torque threshold value (26) for a torque (20) provided by the electric motor (11) is exceeded and a first speed threshold value for a speed of the electric motor (11) is undershot. 4. Method according to claim 3, characterized in that a blockage of a steered wheel (4) during driving of the steering actuator (5) is detected if the first torque threshold value (26) is exceeded for a predetermined first safety period (30) and/or if the first speed threshold value is undershot for a predetermined second safety period. 5. Method according to one of the preceding claims, characterized in that a lifting of a blockage of a steered wheel (4) when driving the steering actuator (5) is detected when a second torque threshold value (26) for a torque (20) provided by the electric motor (11) is undershot or a second speed threshold value for a speed of the electric motor (11) is exceeded. 6. The method according to claim 5, characterized in that the first torque threshold value (26) is greater than the safety limit value (22) and the safety limit value (22) is greater than the second torque threshold value (28). 7. The method according to claim 5, characterized in that the first torque threshold value (26) is equal to the second torque threshold value (28). 8. Method according to claim 5 or claim 7, characterized in that the first speed threshold value is equal to the second speed threshold value. 9. Method according to one of the preceding claims, characterized in that when a blockage of a steered wheel (4) is detected when driving the steering actuator (5), the torque that can be provided by the electric motor (11) is limited by a torque limiter. 10. Method according to one of the preceding claims, characterized in that, in order to implement a steering command, a control signal (C1) for controlling the electric motor (11) is specified, wherein, in the event of a detected blockage of a steered wheel (4) when driving the steering actuator (5), the torque that can be provided by the electric motor (11) is limited by an adaptation of the control signal (C1). 11. Steering system (1) for a motor vehicle with steerable wheels (4), comprising a steering handle (7) for specifying a steering command and a steering actuator unit (9) for converting a predetermined steering command into a steering movement of steerable wheels (4) of a motor vehicle, characterized in that the steering system (1) is designed to operate the steering actuator unit (9) according to a method according to one of the preceding claims. 12. Steering system (1) according to claim 11, characterized in that the steering system (1) is a steer-by-wire steering system. 13. Steering system (1) according to claim 11 or claim 12, characterized in that the steering system (1) is a rear-wheel steering system.