Controlling a steer-by-wire steering system

1. A steer-by-wire steering system for a motor vehicle, comprising:

an electronically controllable steering actuator configured to act on steered wheels of the vehicle,

an actuation unit,

a feedback actuator configured such that a user request for a steering angle from a steering input means outputs a feedback signal to the steering input means as a reaction to the request and a driving state of the motor vehicle,

a signal transmission configured to transfer the request to the actuation unit,

wherein the actuation unit is configured to actuate the steering actuator to transform the request into a deflection of the steered wheels, and

a feedback actuator monitor unit configured to detect a malfunction of the feedback actuator as a fault situation,

wherein the system is configured to operate in the fault situation according to the following method:

continuously reducing to zero the feedback signal to the steering input means within a first time period, and

one or more of:

reducing the signal transmission, and

interrupting the signal transmission for a second time period, and

only including the request which is transferred in the signal transmission as a reduced variable in the transformation for determining the change in the deflection of the wheels, and

omitting the request which is transferred in the signal transmission, for the second time period, from the transformation for determining the change in the deflection of the wheels.

2. The system of claim 1 , further comprising:

one or more of:

measuring and storing a vehicle velocity, and

measuring and storing the steered angle of the steered wheels, and

measuring and storing a position of the steering actuator, and

measuring or estimating a force of the steering actuator, wherein the force of the steering actuator is stored,

wherein the stored values are stored for a third time period, and

actuating the steering actuator on the basis of one or more of the stored vehicle velocity, the stored steered angle, the stored position of the steering actuator, and the stored or estimated force of the steering actuator.

3. The system of claim 1 , wherein the second time period is shorter than the first time period.

4. The system of claim 1 , including actuating, by means of the actuation unit, the feedback actuator after the expiry of the first time period.

5. The system of claim 1 , wherein the driving state of the motor vehicle corresponds to cornering.

6. The system of claim 1 , further comprising:

determining a defined steering angle status based on a steering angle and a steering angle speed applied by the user during travel,

transmitting the defined steering angle status to the actuation unit, and

actuating the steering actuator based on the defined steering angle status.

7. The system of claim 6 , including:

determining, when in the fault situation, one or more of the feedback signal, the user request on the basis of the steering angle status which is determined before the fault situation, the measured vehicle velocity, the measured steered angle of the measured position of the steering actuator, and the measured or estimated force of the steering actuator.

8. A steer-by-wire steering system for a motor vehicle, comprising:

an electronically controllable steering actuator configured to act on steered wheels of the motor vehicle,

an actuation unit,

a feedback actuator configured such that a user request for a steering angle can be applied by a user using a steering input means, and which outputs a feedback signal to the steering input means as a reaction to the request and a driving state of the motor vehicle,

a signal transmission device configured to transfer the request to the actuation unit,

wherein the actuation unit is configured to actuate the steering actuator in order to transform the request into a deflection of the steered wheels,

wherein a feedback actuator monitor unit configured to monitor the feedback actuator and detect a malfunction of the feedback actuator as a fault situation,

wherein the feedback actuator monitor unit is configured to reduce, in the fault situation, the feedback signal to the steering input means continuously to zero within a first time period, and one or more of:

reduce the signal transmission between the steering input means and the steering actuator, and

interrupt the signal transmission for a second time period, and

transmit the driver's request, transferred in the signal transmission, only as a reduced variable, and

transmit the driver's request, transferred in the signal transmission, into the transformation for determining the change in the deflection of the wheels in the actuation unit.

9. The steer-by-wire steering system of claim 8 , wherein the steering actuator acts on the steered wheels with a rack-and-pinion steering gear.