Steer-by-wire system and method for operating a steer-by-wire system in a normal operating mode and in a special operating mode

Abstract

The present invention relates to a method for operating a steer-by-wire system (1) for a motor vehicle, the steer-by-wire system (1) having a steering input device (2) by means of which a steering command can be specified and a steering gear (3) including a steering actuator (5) that can be driven by an electric motor (4) and a coupling element (6), wherein, in a normal operating mode that converts the steering command into steering motion of the steerable wheels (7) of the motor vehicle, a control signal (11) is sent to the electric motor (4) of the steering actuator (5), the electric motor (4) converting the received control signal (11) into mechanical motion of the steering actuator (5), wherein the steering actuator (5) acts on the coupling element (6), and wherein, in a special operating mode, the electric motor (4) operates in generator mode. Furthermore, the present invention relates to a steer-by-wire system (1) designed to operate according to such a method.

Description

Technical Field

[0001] This invention relates to a steer-by-wire system for motor vehicles, having a steering input device by means of which a steering command can be specified and a steering gear comprising a steering actuator and a coupling element. The steering actuator has an electric motor, wherein the electric motor of the steering actuator is designed to receive a control signal and convert the received control signal into mechanical motion of the steering actuator to convert the steering command into steering motion of the steerable wheels of the motor vehicle, wherein the steering actuator is designed to act on the coupling element to execute the steering command. Furthermore, this invention relates to a method for operating such a steer-by-wire system, wherein, in a normal operating mode for converting the steering command into steering motion of the steerable wheels of the motor vehicle, a control signal is sent to the electric motor of the steering actuator, the electric motor converting the received control signal into mechanical motion of the steering actuator, wherein the steering actuator acts on the coupling element. Background Technology

[0002] In a classic steering system for motor vehicles, a steering command introduced by the driver via a steering input device is transmitted to the steering gear via mechanical coupling, causing rotation of at least one steerable wheel corresponding to the steering command. It is known from the prior art, for example from EP 2 353 968 B1, that a classic steering system can be enhanced such that an electric motor supports the steering command input via the steering input device by means of an active connection with the steering system. This reduces the torque that must be applied by the driver of the motor vehicle to the steering input device to achieve a specific rotation of at least one steerable wheel. Nevertheless, even in the event of a motor failure, the mechanical connection between the steering input device and at least one steerable wheel ensures vehicle steering capability even in the event of an electronic problem.

[0003] From the prior art, steer-by-wire systems for motor vehicles are considered a further development of such electromechanical steering systems. Here, the mechanical coupling between the steering input device and the steering gear is eliminated. Instead, steering commands are detected by sensors and converted into electrical signals, which are then forwarded to an electric motor actively connected to the steering gear to cause rotation of at least one steerable wheel corresponding to the steering command. For example, DE 10 2018 115 329 A1 discloses such a steer-by-wire system. Steer-by-wire systems offer several advantages. For example, they require less installation space. Furthermore, the mechanical stress on the required components is less compared to those required in classical steering systems.

[0004] In addition to the advantages of such steer-by-wire systems, the mechanical decoupling between the steering input device and the steering gear creates new challenges requiring reliable solutions to ensure safe driving. To better address these challenges, many components of steer-by-wire systems are designed with redundancy to improve reliability. For example, WO 2019 / 154903 A1 describes an electromechanical steering system with a control unit featuring redundant design.

[0005] However, there is a growing need to improve the safety of operating steer-by-wire systems and to make steer-by-wire systems safer. In this context, one object of the present invention is to provide a method for operating a steer-by-wire system and a steer-by-wire system that improves the safety of motor vehicle drivers. Specifically, it aims to improve safety when the steering actuator of the steer-by-wire system no longer responds to a specified steering command. Summary of the Invention

[0006] To achieve this objective, a method for operating a steer-by-wire system for motor vehicles and a steer-by-wire system of the present invention are provided. Other advantageous embodiments of the invention are described in the specification and illustrated in the accompanying drawings.

[0007] The proposed solution provides a method for operating a steer-by-wire system for a motor vehicle, wherein the steer-by-wire system includes a steering input device by means of which steering commands can be specified, and a steering gear including a steering actuator and a coupling element, which can be driven by an electric motor. In a normal operating mode, where the steering commands are converted into steering motion of the steerable wheels of the motor vehicle, a control signal is sent to the electric motor of the steering actuator, which converts the received control signals into mechanical motion of the steering actuator. The steering actuator acts on the coupling element. Furthermore, the electric motor operates in a generator mode in a special operating mode. The special operating mode is specifically the operating mode of the steer-by-wire system when a serious fault and / or functional failure of the steer-by-wire system is detected. In particular, if the steering actuator of the steer-by-wire system no longer responds to the specified steering commands, i.e., the motor vehicle can no longer be steered by means of the steering input device of the steer-by-wire system, a serious fault or functional failure exists that leads to a change to the special operating mode. Because the electric motor of the steering actuator operates in generator mode under special operating conditions, it advantageously functions as an electric brake, limiting or damping the steering motion of the steerable wheels of the motor vehicle. This utilizes the active connection between the electric motor of the steering actuator and the steerable wheels of the motor vehicle. Therefore, the steering wheels are specifically arranged via tie rods on a rack on which the steering actuator can act. Adjusting the wheel angle of the steering wheels causes movement of the rack, which in turn causes movement of the steering actuator, which then acts on the electric motor. Due to the generator mode, kinetic energy is converted into electrical energy, thereby producing a braking or damping effect. Advantageously, the generated electrical energy and the resulting damping effect are proportional to the kinetic energy. In particular, uncontrolled "chattering" of at least one steering wheel can thus be prevented. Advantageously, an anti-rotation device is provided for the steerable wheels of the motor vehicle. Therefore, the motor vehicle can be advantageously controlled in an improved manner, and thus the motor vehicle can be stopped more safely. Advantageously, directional stability can be achieved until the motor vehicle comes to a complete stop.

[0008] Another advantageous embodiment provides a steer-by-wire system comprising front axle steering for adjusting the wheel steering angle of the front wheels of a motor vehicle and rear axle steering for adjusting the wheel steering angle of the rear wheels of the motor vehicle. If a severe functional impairment occurs in either the front or rear axle steering, rendering the associated wheels no longer steerable, the movement of the rack in the impaired steering is advantageously damped, particularly if the rack is free to move. Advantageously, this reduces the steering effect caused by the defective steering. In particular, a short-circuit circuit is provided for the electric motor of the steering actuator of the defective steering actuator, which is assigned to the control unit of the steer-by-wire system to generate another control signal for controlling the defective steering, wherein a phase of the electric motor is short-circuited by control using the other control signal, and thus damping the movement of the rack in the defective axle steering.

[0009] According to another aspect, damping of the steering motion of the damaged axle is generally provided, particularly to avoid undesirable external forced adjustment of the wheel steering angle of the wheel steerable by the damaged axle. Specifically, the steering motion of the damaged axle is advantageously damped when a wheel steering angle favorable to steering requirements is set. In particular, functional axle steering is used to achieve steering requirements. Advantageously, functional axle steering can be supported by targeted braking intervention, introduced drive torque, and / or other control interventions. Specifically, it is provided that, for damping, a significant damping torque is applied to the motor of the steering actuator of the steer-by-wire system, preferably by short-circuiting the electrical phases of the motor. The resulting damping force is advantageously used to maintain a constant wheel steering angle of the wheel steerable by the damaged axle, particularly in cases of defective front axle steering, to maintain a constant wheel steering angle of the front wheels, and especially to allow the vehicle to be steered by means of rear axle steering.

[0010] Advantageously, in a variation of this embodiment, the motor phase short-circuit control unit is activated, particularly by the driving condition determination device, and even more particularly by the vehicle dynamics control system, which advantageously detects the conditions of the vehicle and steers it after a steering failure affected by the fault. If additional damping is used, particularly by means of the motor phase short-circuit, the unintentional steering motion of the no longer particularly steerable wheels is advantageously braked by dynamic lateral forces, particularly by friction and the resulting damping. Advantageously, this effect can limit the disturbance response of the still effective steering, particularly the effective rear-wheel steering, where it is still possible to advantageously slow the steering by means of alternative steering with the brakes or drivetrain, and can advantageously be used purposefully. Thus, the controllability of the vehicle in the event of a steering system failure can be advantageously further improved. The proposed embodiment is particularly useful in cases of emergency braking or slow evasive maneuvers, during which the vehicle must remain in its lane despite a steering system defect. Advantageously, the control unit detects a fault in the electric steering actuator of the front axle and activates a phase short-circuit circuit on its electric servo motor, thereby advantageously fixing the wheel steering angle of the front wheels. The control unit then advantageously transmits reference position information to the rear axle steering based on the measured steering wheel position.

[0011] Specifically, it also provides a system where damping for defective axle steering and alternative steering functions operate in parallel, particularly through targeted braking of the vehicle's wheels and / or through steering of still-steering wheels that enable functional axle steering. In this case, the damping function is advantageously turned on and off in a targeted manner to indirectly adjust the desired wheel steering angle, thereby further improving steering control.

[0012] Specifically, it provides a method for braking a motor vehicle to a standstill using wheel-specific slip control. This allows for an improved deceleration process. If wheel-specific slip control is not feasible, it advantageously provides a method for using the braking potential of the wheel with the lowest braking potential as a braking reference value. This advantageously avoids wheel lock-up during braking, which would otherwise make the vehicle's path more difficult to control.

[0013] Furthermore, it is advantageously provided that when the generator mode is activated, all other steerable axes of the vehicle follow a reference trajectory to support the safe braking process.

[0014] An advantageous embodiment of this method provides that at least two phases of the electric motor of the steering actuator are electrically connected to each other. Advantageously, braking or damping effects can be achieved in this way.

[0015] Specifically, at least two phases of the motor are short-circuited to electrically connect them. The advantage of this short-circuiting is its relative simplicity and therefore cost-effectiveness. Furthermore, damping or braking effects can be achieved very quickly in this manner.

[0016] A particularly advantageous development provides that all phases of the motor are electrically connected to each other. In the event of a short circuit, all phases of the motor are then advantageously short-circuited. Advantageously, the fact that all phases of the motor are electrically connected to each other increases the damping or braking effect.

[0017] As another advantageous implementation, the motor is provided to operate in generator mode with maximum current consumption. Maximum current consumption refers to the technically possible maximum current consumption for the specific motor used. Because the motor operates in generator mode with maximum current consumption, the damping or braking effect of the motor is advantageously further increased.

[0018] According to another advantageous embodiment, the electricity generated in generator mode is stored in an energy storage device. Advantageously, the motor is therefore under lighter load, especially compared to a phase short circuit, and damage to the motor in generator mode can be better avoided. Furthermore, the electrical energy converted by the motor and supplied to the energy storage device can be used, particularly to supply power to other auxiliary systems when needed, such as for the safe parking of the vehicle. Specifically, an energy accumulator and / or capacitor is provided as the energy storage device.

[0019] Furthermore, it is advantageous to provide that the electricity generated in generator mode is converted into heat by means of an ohmic resistor. Advantageously, in this embodiment, there is no problem that the energy storage device cannot absorb further energy. In particular, in addition to the option of storing the generated electricity in an energy storage device, it is also possible to provide an option of converting the electricity generated by the motor into heat energy by means of an ohmic resistor.

[0020] In another advantageous embodiment of the method, the motor is cooled in generator mode, particularly when a phase short circuit is provided to the motor. This advantageously better prevents damage to the motor and the resulting failure of its damping or braking effect.

[0021] Specifically, it is provided that the electric motor operates in a special operating mode when a predefined serious abnormal condition has been detected. In this regard, the special operating mode is specifically an emergency operating mode. Specifically, such a serious abnormal condition exists if the steering actuator no longer responds to specified steering commands, particularly neither to steering commands given by the vehicle's control unit in the vehicle's automatic driving mode nor to steering commands given by the driver via the steering input device in the vehicle's manual or semi-manual driving modes, or fails to respond in the specified manner. If the steering command can still be specified by the control unit, or by the driver via the steering input device, then switching to the special operating mode should preferably be avoided unless other criteria for the existence of a serious abnormal condition are specifically met. This can specifically be the case where the vehicle has been involved in an accident but has not yet come to a stop.

[0022] To detect predefined severe abnormal states, at least one of the following states is advantageously evaluated: vehicle position, vehicle speed, vehicle tilt, expected path, vehicle impulse, steering actuator temperature, steering actuator torque, steering actuator rotational speed, steering input command torque, steering input command rotational direction, and steering input command rotational position. Specifically, the states are detected and evaluated continuously or at short intervals, particularly in the millisecond range. Evaluation is performed specifically to identify severe technical defects and / or accident situations and / or driver inaction (e.g., due to impaired consciousness) as predefined severe abnormal states with maximum certainty.

[0023] Another proposed steer-by-wire system for motor vehicles includes a steering input device and a steering gear by means of which steering commands can be specified. The steering gear includes a steering actuator with an electric motor and a coupling element. The electric motor of the steering actuator is designed to receive control signals to convert steering commands into steering motion of the steerable wheels of the motor vehicle, and to convert the received control signals into mechanical motion of the steering actuator. The steering actuator is designed to act on the coupling element to execute the steering commands. The steer-by-wire system is designed to operate according to a method designed according to the invention, wherein the method particularly has the features described individually or in combination above. Therefore, the electric motor of the steering actuator in the steer-by-wire system is particularly designed to operate in generator mode in a special operating mode of the steer-by-wire system, and is therefore particularly designed to dampen or brake the motion applied to the electric motor via the steering gear in the special operating mode. Thus, the steerable wheels of the motor vehicle are advantageously impeded by resistance, thereby preventing or at least reducing uncontrolled movement of the steerable wheels in abnormal conditions. The electric motor of the steer-by-wire system is particularly a synchronous motor, and particularly a permanent magnet synchronous motor. Specifically, the motor may be provided comprising multiple winding groups, each of which can be individually controlled via a corresponding phase. Preferably, the motor is designed such that it can operate in generator mode using individual winding groups and using all winding groups. Advantageously, the damping or braking effect of the motor can be controlled in this way in special operating modes. To obtain maximum braking effect, the motor advantageously operates in generator mode using all winding groups.

[0024] Specifically, a control unit is provided to be assigned to the electric motor of the steering actuator, wherein the control unit is designed to control the electric motor for operation of the steer-by-wire system. Advantageously, the steer-by-wire system includes this control unit. The control unit is particularly a suitably configured microcontroller unit. In particular, the control unit may be included in the power unit of the electric motor. Advantageously, the control unit is designed to put the electric motor into generator mode in special operating modes.

[0025] Further advantageously, the steering-by-wire system includes a circuit arrangement designed to electrically connect the phases of the motor to each other. Advantageously, for this purpose, the circuit arrangement includes controllable switching elements, particularly MOSFETs. In particular, it is further provided that the circuit arrangement is designed to electrically connect all phases of the motor to each other. Furthermore, it is particularly provided that the circuit arrangement is designed to short-circuit the phases of the motor, particularly all phases of the motor. In particular, it is provided that the phases of the various winding groups of the motor, particularly the phases of all winding groups of the motor, can be electrically connected to each other by means of the circuit arrangement.

[0026] Specifically, as a variation of the implementation for phase short circuit, a circuit arrangement is provided in which the phases of the motor are electrically connected to each other in a manner that allows the motor to operate in generator mode, and the generated electricity is supplied to an energy storage device and / or converted into heat energy by means of an ohmic resistor. Specifically, an energy storage device is provided, specifically a high-performance capacitor or an energy accumulator, which may be particularly included in a steering system by wire. Specifically, it can also be provided that the electricity generated by the motor in generator mode is supplied to the energy storage device of the motor vehicle.

[0027] Further advantageously, the circuit arrangement of the steer-by-wire system includes controllable switching elements connected to the phases of the motor. Advantageously, the control unit assigned to the motor is designed to control these switching elements to trigger a damping or braking effect of the motor in a special operating mode. In particular, it is provided that the switching elements are self-conducting semiconductor switching elements, especially self-conducting MOSFETs. Advantageously, severe abnormal conditions that prevent the supply of current to the gate terminals of the MOSFETs to block the current from the MOSFETs, which would otherwise cause the phases of the motor to become electrically connected to each other, especially in the event of a phase short circuit in the motor, are eliminated.

[0028] According to another advantageous embodiment of the steer-by-wire system, the electric motor includes a cooling device. The cooling device can be passive or active. Advantageously, in the event of a phase short circuit in the electric motor, the cooling device provides improved dissipation of heat generated in the electric motor.

[0029] Furthermore, a motor vehicle having a steer-by-wire system according to the invention is proposed, wherein the steer-by-wire system has the above-described features individually or in combination. Attached Figure Description

[0030] Combination Figures 1 to 3 The exemplary embodiments shown illustrate other advantageous details, features, and implementation details of the invention in more detail. In the accompanying drawings:

[0031] Figure 1 An exemplary embodiment of the steer-by-wire system according to the present invention is shown in a simplified perspective view;

[0032] Figure 2 An exemplary embodiment of the electric motor of the steer-by-wire system according to the present invention is shown in a simplified circuit diagram, the steer-by-wire system having a control unit and circuit arrangement; and

[0033] Figure 3 An exemplary embodiment of a method for operating a steering-by-wire system designed according to the present invention is illustrated in block diagram.

[0034] In different figures, the same parts are usually given the same reference numerals, and therefore sometimes only one of the figures is described together. Detailed Implementation

[0035] exist Figure 1 The diagram schematically illustrates an exemplary embodiment of a steer-by-wire system 1 designed according to the present invention. The steer-by-wire system 1 includes a steering column 9 having a steering shaft 91, wherein a steering input device 2 in the form of a steering wheel is non-rotatably arranged at one end of the steering shaft 91. The driver can specify a steering command by means of the steering input device 2. The steering input device 2 can be rotated in a known manner to introduce torque as a steering command into the steering shaft 91. Figure 1 Feedback actuators not explicitly specified in the text can provide steering resistance torque to transmit a natural steering feel.

[0036] Furthermore, the steer-by-wire system 1 in this exemplary embodiment includes a steering gear 3 having a steering actuator 5 in the form of a steering pinion and a coupling element 6 in the form of a rack. The steering actuator 5 includes an electric motor 4, which may be, in particular, a three-phase permanent magnet synchronous motor. The steering actuator 5 can be driven by the electric motor 4 to act on the coupling element 6 and trigger steering movement of a steerable wheel 7, which is specifically connected to the coupling element 6 via a tie rod 8. Each tie rod 8 is itself connected to the steering wheel 7 in a known manner via a steering knuckle.

[0037] In the normal operating mode of the online steering system Figure 1 A steering command detected by a sensor (not explicitly shown) is sent to control unit 10, specifically ECU (Electronic Control Unit), as the detected steering command 12. Control unit 10 generates a control signal 11 based specifically on the received detected steering command 12. Control signal 11 is sent to motor 4 of steering actuator 5 to convert the detected steering command 12 into steering motion of steerable wheel 7. Motor 4 then converts the received control signal 11 into rotational motion of steering actuator 5, which in turn converts this rotational motion into corresponding translational motion of coupling element 6, thereby causing adjustment of the steering angle of steerable wheel 7.

[0038] The electric motor 4 is also designed to operate in a generator mode, a special operating mode different from the normal operating mode. In this generator mode, the electric motor 4 does not guarantee the conversion of the control signal 11 into mechanical motion of the steering actuator 5, and therefore does not guarantee the steering motion of the steerable wheel 7. Instead, in generator mode, the electric motor 4 dampens the motion of the steerable wheel 7 applied externally to it. Therefore, normally, when the electric motor 4 is not controlled, the motion of the steering wheel 7 will cause longitudinal displacement of the rack-and-pinion coupling element 6, which in turn will cause rotation of the steering actuator 5 in the form of a steering pinion and rotation of the rotor of the electric motor 4. If the steering wheel 7 cannot be controlled, this will cause the steering wheel 7 to randomly change its steering angle without significant resistance, potentially leading to a safety-critical driving situation.

[0039] By operating the electric motor 4 in generator mode, this behavior is advantageously prevented or at least reduced, because in generator mode, the electric motor 4 functions similarly to a brake. Therefore, the rotational steering angle of the steerable wheel 7 can be advantageously maintained, particularly until the corresponding vehicle comes to a safe stop.

[0040] Alternatively or additionally, the steer-by-wire system 1 may include another steering actuator 51 having another motor 41, wherein the control unit 10 sends another control signal 111 to the other motor 41 of the other steering actuator 51 to adjust the steering angle of the steerable wheel 7 in a corresponding manner.

[0041] Figure 2 An exemplary embodiment for the control of the electric motor 4 is schematically shown in the figure. Figure 2 A circuit arrangement 14 is shown, comprising a control unit 10, an inverter 17 including three half-bridges, and a feedback branch 18. Phases 21, 22, and 23 of the motor 4 are controlled by means of the inverter 17, and the control unit 10 receives feedback regarding the current applied to the phases via the feedback branch 18. Furthermore, a circuit arrangement 15 is provided, designed to electrically connect phases 21, 22, and 23 of the motor 4 to each other. For this purpose, circuit arrangement 15 includes controllable switching elements 16, particularly self-conducting MOSFETs, connected to phases 21, 22, and 23 of the motor 4. Figure 2 The circuit arrangement 15 and the switching element 16 are shown only schematically.

[0042] With the aid of switching element 16, phases 21, 22, and 23 of motor 4 can be electrically short-circuited in a special operating mode. In an alternative embodiment, phases 21, 22, and 23 of motor 4 can be connected in a conductive manner that allows motor 4 to operate in generator mode, wherein the electrical energy generated in generator mode is supplied to an energy storage device for storing electrical energy, particularly a battery, or converted into heat energy by means of an ohmic resistor. The control of switching element 16 in circuit arrangement 15 is performed by means of control unit 10.

[0043] In this exemplary embodiment, the control unit 10 is also specifically designed to monitor whether a predefined serious abnormal state has occurred. To this end, the control unit 10 receives and evaluates a plurality of state signals 13 detected by sensors. These state signals may be provided, in particular, by means of other driver assistance systems, specifically by the ESP (Electronic Stability Program) system and / or the pre-collision system. The state signals 13 advantageously relate to the vehicle itself, particularly vehicle position, vehicle speed, vehicle tilt, predicted path and / or vehicle impulse, and the technology of the steer-by-wire system 1 (particularly the temperature of the steering actuator 5, the torque of the steering actuator 5, and / or the rotational speed of the steering actuator 5). These state signals 13 are advantageously compared with predefined variables, and these variables are checked to see if they are within specified intervals and / or do not exceed or fall below predefined thresholds. For other states, the following are advantageously checked: the detected steering command 12, particularly the torque of the steering input command 12, the direction of rotation of the steering input command 12, and / or the rotational position of the steering input command 12. If a predefined serious abnormal state is detected by evaluating the detected status signal 13 and the detected steering command 12, especially the lack of steering command when leaving the specified path, the steer-by-wire system 1 switches from the normal operating mode to a special operating mode. In the normal operating mode, the steering command is executed by the steer-by-wire system 1 in the usual manner. In the special operating mode, the electric motor 4 operates as a brake in generator mode.

[0044] Figure 3 The present invention provides a simplified exemplary embodiment of a method for operating a steer-by-wire system for a motor vehicle. The steer-by-wire system may specifically employ the method described in reference [reference text]. Figure 1The described form. In normal operating mode A, a specified steering command is detected, and a corresponding control signal for translating the detected steering command into steering motion of the steerable wheels of the motor vehicle is sent to the electric motor of the steering actuator of the steer-by-wire system. In normal operating mode A, the electric motor drives the steering actuator of the steer-by-wire system according to the received control signal, and the steering actuator adjusts the wheel steering angle of the steerable wheels of the motor vehicle via the coupling element of the steer-by-wire system. Normal operating mode A may include several operating modes, particularly a manual driving mode and an automatic driving mode. In manual driving mode, the driver specifies a steering command using a steering input device; in automatic driving mode, the vehicle is autonomously controlled without driver intervention in steering.

[0045] During normal operation mode A, continuously check for the presence of a serious emergency D. If this is not the case ( Figure 3 If the branch "No" is selected, the steer-by-wire system remains in normal operating mode A. On the other hand, if a serious abnormal state D is detected ( Figure 3 If the branch "is" in the code indicates that the steer-by-wire system switches to special operating mode B, the electric motor no longer drives the steering actuator; instead, the electric motor dampens the movement of the steering actuator in generator mode. However, at the same time, a continuous check is performed for serious abnormal conditions D. If the condition remains unchanged (…), the system will continue to operate in special mode B. Figure 3 If the branch "is" in the code, the steer-by-wire system remains in special operating mode B. Otherwise ( Figure 3 If the branch "No" is selected, the steer-by-wire system switches back to normal operating mode A. Specifically, it also allows for controlled stopping of the vehicle using other driver assistance systems if a serious abnormal condition D is detected. This special operating mode allows other driver assistance systems to better predict further driving conditions, enabling better preparation of passive safety systems such as airbags for potential collisions, thus better protecting vehicle occupants.

[0046] The exemplary embodiments shown and described in conjunction with the accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0047] List of reference numerals

[0048] 1. Steer-by-wire system

[0049] 2. Steering input device

[0050] 3. Steering gear

[0051] 4 Electric motor

[0052] 41 Electric motor

[0053] 5. Steering actuator

[0054] 51 Steering actuator

[0055] 6 Coupling Components

[0056] 7 Steering wheels

[0057] 8. Pull rod

[0058] 9. Steering column

[0059] 91 Steering Axle

[0060] 10 Control Unit

[0061] 11 Control Signals

[0062] 111 Control Signal

[0063] 12 steering commands detected

[0064] 13 Detected state signals

[0065] 14 Circuit Layout

[0066] 15 Circuit Layout

[0067] 16 Switching elements in circuit layout (15)

[0068] 17 Inverter

[0069] 18 Feedback Branches

[0070] 21, 22, 23 Phases of motor (4)

[0071] A Normal Operating Mode

[0072] B. Special Operation Mode

[0073] D. Severe Abnormal State

[0074] No serious abnormalities were detected.

[0075] Y detected a serious abnormal state.

Claims

1. A method for operating a steer-by-wire system (1) of a motor vehicle, the steer-by-wire system (1) having a steering input device (2) capable of specifying steering commands and a steering gear (3), the steering gear (3) comprising a steering actuator (5) driven by an electric motor (4) and a coupling element (6), wherein, In the normal operating mode (A) where steering commands are converted into steering motion of the steerable wheel (7) of a motor vehicle, a control signal (11) is sent to the motor (4) of the steering actuator (5), which converts the received control signal (11) into mechanical motion of the steering actuator (5), wherein the steering actuator (5) acts on the coupling element (6), characterized in that the motor (4) operates in generator mode in a special operating mode (B), and the motor (4) operating in generator mode acts as a motor brake to dampen the steering motion of the steerable wheel (7).

2. The method according to claim 1, characterized in that, In the generator mode, at least two phases (21, 22, 23) of the motor (4) are electrically connected to each other.

3. The method according to claim 2, characterized in that, The at least two phases (21, 22, 23) of the motor (4) are short-circuited to each other so as to electrically connect them to each other.

4. The method according to claim 2 or claim 3, characterized in that, All phases (21, 22, 23) of the motor (4) are electrically connected to each other.

5. The method according to any one of claims 1-3, characterized in that, The electric motor (4) operates at maximum current consumption in the generator mode.

6. The method according to any one of claims 1-3, characterized in that, The electricity generated in the generator mode is stored in an energy storage device.

7. The method according to any one of claims 1-3, characterized in that, The electricity generated in the generator mode is converted into heat by means of an ohmic resistor.

8. The method according to any one of claims 1-3, characterized in that, In the generator mode, the motor (4) is cooled.

9. The method according to any one of claims 1-3, characterized in that, When a predefined severe abnormal state (D) is detected, the motor (4) operates in the special operating mode (B).

10. The method according to claim 9, characterized in that, In order to detect the predefined severe abnormal state (D), at least one of the following states is evaluated: vehicle position, vehicle speed, vehicle tilt, expected path, vehicle impulse, temperature of the steering actuator (5), torque of the steering actuator (5), rotational speed of the steering actuator (5), torque of the steering input command, rotational direction of the steering input command, and rotational position of the steering input command.

11. A steer-by-wire system (1) for a motor vehicle, the steer-by-wire system (1) having a steering input device (2) by means of which a steering command can be specified and a steering gear (3), the steering gear (3) comprising a steering actuator (5) having an electric motor (4) and a coupling element (6), wherein, The motor (4) of the steering actuator (5) is designed to receive a control signal (11) and convert the received control signal (11) into mechanical motion of the steering actuator (5) so as to convert a steering command into steering motion of the steerable wheels (7) of the motor vehicle, wherein the steering actuator (5) is designed to act on the coupling element (6) to execute the steering command, characterized in that the steer-by-wire system (1) is designed to operate in accordance with the method according to any one of claims 1-10.

12. The steer-by-wire system (1) according to claim 11, characterized in that, The electric motor (4) is assigned a control unit (10), wherein the control unit (10) is designed to control the electric motor (4) to operate the steering-by-wire system (1).

13. The steer-by-wire system (1) according to claim 11 or claim 12, characterized in that... The circuit arrangement (15) is designed to electrically connect the phases (21, 22, 23) of the motor (4) to each other.

14. The steer-by-wire system (1) according to claim 13, characterized in that, The circuit arrangement (15) includes a controllable switching element (16) connected to the phases (21, 22, 23) of the motor (4).

15. The steer-by-wire system (1) according to claim 14, characterized in that, The switching element (16) is a self-conducting semiconductor switching element.

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