Method for operating an electromechanical steering system, electromechanical steering system and motor vehicle

Abstract

The present invention relates to a method for operating an electromechanical steering system (1) of a motor vehicle (2). According to the method, a communication fault between a first control device (7) and a second control device (9) is first detected, and the first control device (7) applies a predefined excitation pattern to an electric motor (3), which is then detected by the second control device (9). In this way, communication between the first control device (7) and the second control device (9) is ensured even in the event of a communication link (6) failure. The invention further relates to an electromechanical steering system (1) for a motor vehicle (2) and a motor vehicle (2).

Description

[0001] The present invention relates to a method for operating an electromechanical steering system of a motor vehicle. Furthermore, the invention relates to an electromechanical steering system for a motor vehicle and to a motor vehicle.

[0002] In addition to the familiar mechanical components of a steering system, electromechanical steering systems feature a so-called "power pack," which includes an electric motor (actuator) for adjusting the steering angle and a control unit (ECU) for selectively operating the electric motor. The control unit is connected to the electric motor via a control cable.

[0003] High-availability electromechanical steering systems must meet strict, specific technical specifications (ASIL D according to ISO 26262) to ensure predefined operational reliability and particularly high availability. For example, it is stipulated that high-availability electromechanical steering systems must have redundant control devices, each with at least one control line. The individual control devices and the associated control line of such redundant control systems are also referred to as a "redundancy path" within the scope of the invention. By providing at least two redundancy paths, continued operation of the steering system via the other redundancy path is highly likely even if one of the redundancy paths fails.

[0004] To meet the stringent requirements of the regulations, an uncoordinated operating state of both redundancy paths must be reliably excluded. For example, a false detection of the failure of one of the redundancy paths could lead to both redundancy paths entering uncoordinated operation, potentially working against each other. This is counteracted by a configuration in which each redundancy path can determine the state of the other redundancy path with the appropriate integrity (ASIL D).

[0005] Typically, both redundancy paths are connected to each other via an inter-ECU bus for this purpose. Status information can be exchanged between the redundancy paths via the inter-ECU bus, so that the control device of one redundancy path knows the status of the other redundancy path. Such a redundant steering system is known, for example, from document DE 10 2018 108 597 A1. Document DE 10 2020 207 196 A1 describes a method for operating a redundant steering system in which control variables from the respective redundancy paths are generated, averaged, and then integrated into a common target control variable. This is intended to prevent the two redundancy paths from interacting with each other. Further methods for operating electromechanical steering systems as well as electromechanical steering systems are known from the documents DE 11 2020 005 705 T5 and US 2013 / 0 320 905 A1.

[0006] Known inter-ECU bus implementations have the disadvantage that the probability of failure in the inter-ECU bus communication is too high to guarantee the required integrity (ASIL D). This can be improved by redundant state detection of the redundancy paths. To ensure redundant state detection, the inter-ECU buses used for transmitting the state data are usually also designed redundantly, so that if one of the inter-ECU buses fails, communication can take place via the other inter-ECU bus. However, this leads to significantly higher hardware and assembly costs.

[0007] It is therefore an object of the present invention to eliminate, or at least partially eliminate, the disadvantages described above in an electromechanical steering system. In particular, the object of the present invention is to provide a method for operating an electromechanical steering system and an electromechanical steering system for a motor vehicle that, in a simple and cost-effective manner, prevent the redundancy paths from interacting with each other in the event of a disruption in the intra-system communication between the redundancy paths.

[0008] The above object is achieved by the independent patent claims. Accordingly, the object is achieved by a method for operating an electromechanical steering system of a motor vehicle having the features of independent claim 1, by an electromechanical steering system having the features of the independent claim 9, and by a motor vehicle having the features of the independent claim 10. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the steering system according to the invention and the motor vehicle according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is and can always be made to each other.

[0009] According to a first aspect of the invention, the object is achieved by a method for operating an electromechanical steering system of a motor vehicle. The steering system comprises an electric motor for setting a steering angle, a first redundancy path for controlling the electric motor in an active operating state, and a second redundancy path for controlling the electric motor in an active operating state in the event of failure of the first redundancy path and for remaining in a passive operating state when the first redundancy path controls the electric motor. The first redundancy path comprises a first control device and a first control line. The second redundancy path comprises a second control device and a second control line. Communication between the first control device and the second control device is possible via a communication connection of the steering system. The method comprises: - Detecting the occurrence of a communication fault in the communication conducted via the communication link between the first control device and the second control device by the first control device when the first control device is functioning as intended, and / or the second control device when the second control device is functioning as intended, - Imposing a predefined excitation pattern on the electric motor by the first control device and operating the first control device in the active operating state when the first control device is functioning as intended and has detected the communication fault, - detecting the excitation pattern by the second control device and operating the second control device in the passive operating state when the second control device functions as intended, - Operating the second control device in the active operating state when the second control device is functioning as intended, has detected the communication fault and has not detected an excitation pattern.

[0010] The electromechanical steering system with which the method according to the invention is implemented can have the same components and the same structure as a conventional electromechanical steering system with redundancy paths. The electromechanical steering system has the electric motor for adjusting the steering angle. According to the invention, multiple electric motors can also be provided, so that if one electric motor fails, the steering angle can still be adjusted by the other electric motor in emergency operation.

[0011] To control the electric motor, the electromechanical steering system has the first redundancy path. The first redundancy path has the first control device and the first control line. The first control device is preferably electrically coupled to the electric motor via the first control line, so that the electric motor can be controlled by the first control device. The operating state in which the first redundancy path controls the electric motor is referred to as the active operating state.

[0012] In the event that the first redundancy path fails, for example due to an electronic defect in the first control device, damage to the first control line, or the like, the electromechanical steering system has the second redundancy path for controlling the electric motor. The second redundancy path has the second control device and the second control line. The second control device is preferably electrically coupled to the electric motor via the second control line, such that the electric motor can be controlled by the second control device. The operating state in which the second redundancy path controls the electric motor is also referred to as the active operating state. The second redundancy path is designed to remain in a passive operating state when the first redundancy path is in the active operating state and thus controls the electric motor.In the context of the invention, a passive operating state is understood to mean, for example, a standby mode, i.e., an operating state in which the electric motor is not controlled. This prevents both redundancy paths from controlling the electric motor simultaneously and thus potentially resulting in opposing controls.

[0013] To prevent both redundancy paths from being in the active operating state simultaneously, the electromechanical steering system has the communication connection. The communication connection is designed to provide a communication path for communication between the first control device and the second control device. The communication connection can be designed, for example, as an inter-ECU bus or the like. Via the communication connection, the first control device can, for example, indicate to the second control device that the first control device is in the active operating state, so that no intervention in the steering by the second control device is required and the second control device can therefore remain in the passive operating state.Communication via the communication connection can, for example, be unidirectional, in particular from the first controller to the second control device. Feedback from the second control device is not absolutely necessary. However, bidirectional communication via the communication device can also be provided, for example feedback from the second control device to the first control device to indicate that the second control device has detected the communication from the first control device and remains in the passive operating state. Furthermore, it can be provided that status information is exchanged between the control devices via the communication connection, in particular at regular intervals, so that, for example, the possible failure of one of the two control devices and thus the presence of a potentially critical operating state of the steering system can be detected more quickly.

[0014] The triggering boundary condition of the method according to the invention is a communication disruption in the communication conducted between the first control device and the second control device via the communication connection. Within the scope of the invention, a communication disruption is understood to mean that the communication between the control devices no longer functions properly, for example, a complete loss of communication. A communication disruption can have several causes, such as a defect in the first control device, the communication connection, the second control device, a power supply disruption to one of the control devices, or the like.

[0015] The occurrence of the communication fault is initially detected by the control devices that are functioning as intended. Within the scope of the invention, the intended functioning of a control device means that the respective control device is free of defects and thus meets the requirements of the active operating state and of communication via the communication connections. If the control device is unable to control the electric motor as specified or to conduct the predefined communication, the respective control device is not functioning as intended. Preferably, the occurrence of the communication fault is detected by both control devices if both control devices are functioning as intended.

[0016] If the first control device is functioning as intended and has detected the occurrence of the communication disruption, the first control device applies the predefined excitation pattern to the electric motor and operates the electric motor in the active operating state. A predefined excitation pattern is understood to mean a predefined operation of the electric motor that differs from the usual operation of the electric motor, for example, in a signal amplitude, signal frequency, signal duration, signal sequence, signal modulation, or the like. The predefined excitation pattern is preferably determined in such a way that any influence on the steering is marginal and imperceptible to a driver of the motor vehicle. In this way, an unintentional steering movement of the motor vehicle due to the predefined excitation pattern is avoided.Furthermore, the excitation pattern is preferably selected in such a way that clear detection is ensured in the case of superpositioned excitation, for example an additional control of the electric motor for targeted steering of the motor vehicle.

[0017] If the second control device functions as intended, the second control device detects the applied excitation pattern and then remains in the passive operating state, since the control of the electric motor is carried out by the first control device. The excitation pattern can be detected, for example, via the electromagnetic coupling of the second control device to the electric motor.

[0018] If the second control device is not functioning as intended and is therefore defective, the second control device is also not ready to control the electric motor and is therefore also in a passive operating state. This initially poses no problem for the operation of the electromechanical steering system, since the first control device is already in the active operating state, thus ensuring the steering of the motor vehicle.

[0019] If the first control device is not functioning as intended and is therefore defective, the first control device will not apply a predefined excitation pattern to the electric motor. If the second control device is also functioning as intended, the second control device detects the occurrence of the communication fault and that no predefined excitation pattern was applied to the electric motor by the first control device. In this case, the second control device concludes that the first control device is defective and switches to the active operating state for operating the steering system.

[0020] A method according to the invention for operating an electromechanical steering system of a motor vehicle has the advantage over conventional methods that an appropriate response of the steering system to a defect in the first control device, the second control device, and the communication line is ensured using simple means and in a cost-effective manner. Consequently, safe continued operation of the steering system is always ensured. In the event of a failure of the first control device, further steering of the motor vehicle is carried out by the second control device. In the event of a failure of the communication line, further steering of the motor vehicle is carried out by the first control device. In the event of a failure of the second control device, further steering of the motor vehicle is carried out by the first control device. This also makes it possible to dispense with the redundancy of communication lines.As a result, the operational reliability of the electromechanical steering system is advantageously improved compared to conventional steering systems while reducing manufacturing costs.

[0021] According to a preferred further development of the invention, in a method for operating an electromechanical steering system of a motor vehicle, it can be provided that the second control device imposes an excitation pattern on the electric motor in the active operating state, wherein the first control device is operated in the passive operating state upon receiving the excitation pattern. To further reduce the risk of the first control device and the second control device being operated simultaneously in the active operating state, for example, if imposition of the predefined excitation pattern by the first control device is prevented, it can be provided according to the invention that the second control device also imposes the excitation pattern, which can then be received by the first control device.The first control device then switches to the passive operating state to prevent simultaneous operation of the electric motor by the first control device and the second control device. This has the advantage of further improving the operational reliability of the electromechanical steering system with simple means and in a cost-effective manner, while reducing manufacturing costs.

[0022] According to the invention, it is preferred that the excitation pattern is detected via a position sensor arranged on the electric motor. Relative movements of a rotor of the electric motor to a stator of the electric motor can be detected via the position sensor. The relative movements can, for example, comprise an alternation of the direction of rotation of the rotor. When the excitation pattern is superimposed on a steering action of the electric motor, the relative movement can also comprise a periodic change in the rotational speed of the rotor, wherein the excitation pattern is preferably designed to be smaller than a steering action for changing a steering angle by 1°. The excitation pattern is thus designed in such a way that reliable detection of the excitation pattern via the position sensor is ensured even during a steering movement of the steering system.This has the advantage that the operational reliability of the electromechanical steering system is further improved using simple means and in a cost-effective manner while reducing manufacturing costs.

[0023] More preferably, the excitation pattern comprises a sinusoidal oscillation. The sinusoidal oscillation is easy to generate and easy to detect. Furthermore, a sinusoidal oscillation differs slightly from a normal steering action for steering the motor vehicle, ensuring reliable detection of the excitation pattern even during a steering movement of the steering system. A particularly characteristic design of the excitation pattern thus ensures a particularly high probability of detecting the excitation pattern even during steering operation. This has the advantage of further improving the operational reliability of the electromechanical steering system using simple means and in a cost-effective manner, while reducing manufacturing costs.

[0024] In a particularly preferred embodiment of the invention, a method can be provided in which the sinusoidal oscillation has a predefined frequency or frequency sequence and / or amplitude or amplitude sequence. A predefined frequency is understood in particular to mean a constant frequency within the scope of the invention, for example 50 Hz. A frequency sequence is understood in particular to mean a constant change in frequency, a sudden change in frequency, or a change in frequency with different rates of change. For example, the frequency can be increased in a gradual, sudden, progressive, degressive, or discontinuous manner from 50 Hz to 100 Hz. A predefined amplitude is understood in particular to mean a constant amplitude within the scope of the invention.In the context of the invention, an amplitude sequence is understood to mean, in particular, a constant change in amplitude, a sudden change in amplitude, or a change in amplitude with different rates of change. For example, the amplitude can be increased gradually, abruptly, progressively, degressively, or discontinuously. A particularly characteristic design of the excitation pattern ensures a particularly high probability of detecting the excitation pattern, even during steering operation. This has the advantage of further improving the operational reliability of the electromechanical steering system with simple means and in a cost-effective manner, while reducing manufacturing costs.

[0025] Preferably, the electromechanical steering system is operated in emergency mode after the communication fault has been detected. Emergency mode can be understood, for example, as operation of the steering system in which the stress on the steering system is reduced compared to normal operation of the steering system. This can be achieved, for example, by operating the electric motor with a reduced torque, a reduced speed, a reduced steering angle, or the like. Emergency mode reduces the probability of failure of other components of the steering system that are still functioning as intended. This has the advantage that the operational reliability of the electromechanical steering system is further improved using simple means and in a cost-effective manner, while reducing manufacturing costs.

[0026] According to a preferred embodiment of the invention, a method can be provided in which the electromechanical steering system, in emergency operation, causes an engine of the motor vehicle to operate at a limited power to drive the motor vehicle, wherein the limited power is lower than the possible power of the engine in normal operation. For example, the control device in the active operating state transmits via a communication interface to an engine control device of the motor vehicle that the steering system is in emergency operation. This causes the engine control device to limit the maximum power of the engine, so that, for example, a maximum acceleration and / or maximum speed of the motor vehicle are limited compared to normal operation.By limiting the vehicle's driving dynamics in this way, lower forces can be transferred to the steering system, thus reducing the load on the steering system. Furthermore, the steering system's operation in emergency mode is improved, as the demands on the steering system are reduced at reduced acceleration and speed. This has the advantage of further improving the operational reliability of the electromechanical steering system using simple and cost-effective means while reducing manufacturing costs.

[0027] Particularly preferably, after the communication fault has been detected, the electromechanical steering system issues a warning to a passenger of the motor vehicle. The warning can be issued, for example, via a specially provided warning light or a display on a display device, for example, on the screen of an on-board computer or the like. The warning can also comprise an image, text, or the like. Preferably, the warning includes a request to a driver of the motor vehicle to manually assume control of the motor vehicle. This has the advantage that the operational reliability of the electromechanical steering system is further improved using simple means and in a cost-effective manner, while reducing manufacturing costs.

[0028] According to a second aspect of the invention, this object is achieved by an electromechanical steering system for a motor vehicle. The electromechanical steering system can have the same components and the same structure as a conventional electromechanical steering system with redundancy paths. The electromechanical steering system has an electric motor for adjusting the steering angle. According to the invention, multiple electric motors can also be provided, so that if one electric motor fails, the steering angle can still be adjusted by the other electric motor in emergency operation.

[0029] To control the electric motor, the electromechanical steering system has the first redundancy path. The first redundancy path has the first control device and the first control line. The first control device is preferably electrically coupled to the electric motor via the first control line, so that the electric motor can be controlled by the first control device. The operating state in which the first redundancy path controls the electric motor is referred to as the active operating state.

[0030] In the event that the first redundancy path fails, for example due to an electronic defect in the first control device, damage to the first control line, or the like, the electromechanical steering system has the second redundancy path for controlling the electric motor. The second redundancy path has the second control device and the second control line. The second control device is preferably electrically coupled to the electric motor via the second control line, such that the electric motor can be controlled by the second control device. The operating state in which the second redundancy path controls the electric motor is also referred to as the active operating state. The second redundancy path is designed to remain in a passive operating state when the first redundancy path is in the active operating state and thus controls the electric motor.In the context of the invention, a passive operating state is understood to mean, for example, a standby mode, i.e., an operating state in which the electric motor is not controlled. This prevents both redundancy paths from controlling the electric motor simultaneously and thus potentially resulting in opposing controls.

[0031] To prevent both redundancy paths from being in the active operating state simultaneously, the electromechanical steering system has the communication connection. The communication connection is designed to provide a communication path for communication between the first control device and the second control device. The communication connection can be designed, for example, as an inter-ECU bus or the like. Via the communication connection, the first control device can, for example, indicate to the second control device that the first control device is in the active operating state, so that no intervention in the steering by the second control device is required and the second control device can therefore remain in the passive operating state.Communication via the communication connection can, for example, be unidirectional, in particular from the first controller to the second control device. Feedback from the second control device is not absolutely necessary. However, bidirectional communication via the communication device can also be provided, for example feedback from the second control device to the first control device to indicate that the second control device has detected the communication from the first control device and remains in the passive operating state. Furthermore, it can be provided that status information is exchanged between the control devices via the communication connection, in particular at regular intervals, so that, for example, the possible failure of one of the two control devices and thus the presence of a potentially critical operating state of the steering system can be detected more quickly.

[0032] According to the invention, the electromechanical steering system is designed to implement the method according to the invention and thus differs from conventional electromechanical steering systems. This difference can be manifested, for example, in appropriate programming of the control devices. Furthermore, the first control device is designed to detect the communication fault and apply the predefined excitation pattern to the electric motor. The second control device is designed to detect the communication fault and detect the predefined excitation pattern applied to the electric motor.

[0033] The electromechanical steering system according to the invention provides all the advantages already described for a method for operating an electromechanical steering system according to the first aspect of the invention. Accordingly, the electromechanical steering system according to the invention has the advantage over conventional electromechanical steering systems that an appropriate response of the steering system to a defect in the first control device, the second control device, and the communication line is ensured using simple means and in a cost-effective manner. Consequently, safe continued operation of the steering system is always ensured. In the event of a failure of the first control device, further steering of the motor vehicle is carried out by the second control device. In the event of a failure of the communication line, further steering of the motor vehicle is carried out by the first control device.If the second control device fails, the vehicle continues to be steered by the first control device. This eliminates the need for redundant communication lines. Consequently, the operational reliability of the electromechanical steering system is advantageously improved compared to conventional steering systems, while reducing manufacturing costs.

[0034] According to a third aspect of the invention, the object is achieved by a motor vehicle. The motor vehicle has a drive system for driving the motor vehicle and a braking system for braking the motor vehicle. According to the invention, the motor vehicle has an electromechanical steering system according to the invention. The motor vehicle is preferably designed for autonomous driving. Further preferably, the drive system, the braking system, and the steering system are networked in a communicative manner, for example, via a central vehicle control device of the motor vehicle.

[0035] The motor vehicle according to the invention provides all the advantages already described for a method for operating an electromechanical steering system according to the first aspect of the invention and for an electromechanical 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 an appropriate response of the steering system to a defect in the first control device, the second control device, and the communication line is ensured using simple means and in a cost-effective manner. Consequently, safe continued operation of the steering system is always ensured. In the event of a failure of the first control device, further steering of the motor vehicle is carried out by the second control device.If the communication line fails, the vehicle continues to be steered by the first control device. If the second control device fails, the vehicle continues to be steered by the first control device. This also eliminates the need for redundancy of communication lines. Consequently, the operational reliability of the electromechanical steering system is advantageously improved compared to conventional steering systems, while reducing manufacturing costs.

[0036] A method according to the invention for operating an electromechanical steering system of a motor vehicle, an electromechanical steering system according to the invention, and a motor vehicle according to the invention are explained in more detail below with reference to drawings. They each show schematically: Fig. 1 shows a circuit diagram of an electromechanical steering system according to the state of the art, Fig. 2 shows a circuit diagram of an electromechanical steering system according to a preferred embodiment of the invention, Fig. 3 shows a side view of a preferred embodiment of a motor vehicle according to the invention, and Fig. 4 shows a flow chart of a preferred embodiment of a method according to the invention.

[0037] Elements with the same function and mode of action are listed in the Fig. 1 to 4 are each provided with the same reference numerals.

[0038] In Fig. 1 schematically illustrates a circuit diagram of an electromechanical steering system 1 according to the prior art. The electromechanical steering system 1 comprises an electric motor 3 for setting a steering angle, a first redundancy path 4 for operating the electric motor 3 in an active operating state, and a second redundancy path 5 for operating the electric motor 3 in an active operating state.

[0039] The first redundancy path 4 has a first control device 7, which is coupled to a first power supply 14 of the first redundancy path 4 via a first control line 8 of the first redundancy path 4 and to the electric motor 3 via the first power supply 14. Thus, the power supply to the electric motor 3 can be specifically controlled by the first control device 7. Furthermore, the first redundancy path 4 has a position sensor 11 for detecting a rotor position of a rotor of the electric motor 3.

[0040] The second redundancy path 5 has a second control device 9, which is coupled to a second power supply 15 of the second redundancy path 5 via a second control line 10 of the second redundancy path 5 and to the electric motor 3 via the second power supply 15. Thus, the power supply to the electric motor 3 can be specifically controlled by the second control device 9. The second redundancy path 5 also has a position sensor 11 for detecting the rotor position of the rotor of the electric motor 3.

[0041] To ensure that either only the first redundancy path 4 or only the second redundancy path 5 controls the electric motor 3, the steering system 1 of the prior art has multiple communication connections 6 between the first control device 7 and the second control device 9. If one of the communication connections 6 fails, communication is ensured via the other communication connections 6. Such a system requires a high level of assembly effort and high material costs and is therefore very cost-intensive.

[0042] Fig. Figure 2 shows a schematic circuit diagram of an electromechanical steering system 1 according to a preferred embodiment of the invention. The electromechanical steering system 1 has an electric motor 3 for setting a steering angle, a first redundancy path 4 for operating the electric motor 3 in an active operating state, and a second redundancy path 5 for operating the electric motor 3 in an active operating state.

[0043] The first redundancy path 4 has a first control device 7, which is coupled to a first power supply 14 of the first redundancy path 4 via a first control line 8 of the first redundancy path 4 and to the electric motor 3 via the first power supply 14. Thus, the power supply to the electric motor 3 can be specifically controlled by the first control device 7. Furthermore, the first redundancy path 4 has a position sensor 11 for detecting a rotor position of a rotor of the electric motor 3.

[0044] The second redundancy path 5 has a second control device 9, which is coupled to a second power supply 15 of the second redundancy path 5 via a second control line 10 of the second redundancy path 5 and to the electric motor 3 via the second power supply 15. Thus, the power supply to the electric motor 3 can be specifically controlled by the second control device 9. The second redundancy path 5 also has a position sensor 11 for detecting the rotor position of the rotor of the electric motor 3.

[0045] To ensure that either only the first redundancy path 4 or only the second redundancy path 5 controls the electric motor 3, a communication connection 6 is provided between the first control device 7 and the second control device 9. The first control device 7 and the second control device 9 are also configured to detect a communication disruption in the communication conducted via the communication connection 6. The cause of such a communication disruption can be, for example, a defect in the first control device 7, the second control device 9, or the communication connection 6.

[0046] Furthermore, the first control device 7 is designed to impose the predefined excitation pattern on the electric motor 3 upon detecting such a communication disruption. The second control device 9 is designed to detect the predefined excitation pattern imprinted on the electric motor 3 upon detecting such a communication disruption. In this way, a backup communication connection is created that is independent of the communication connection 6, via which it can also be ensured that, depending on the current state of health of the steering system 1, only the first redundancy path 4 or only the second redundancy path 5 controls the electric motor 3. Thus, opposing control of the electric motor 3 by the first redundancy path 4 and the second redundancy path 5 is avoided.

[0047] In Fig. Figure 3 shows a schematic side view of a preferred embodiment of a motor vehicle 2 according to the invention. The motor vehicle 2 has a drive system 12 for driving the motor vehicle 2, a braking system 13 for braking the motor vehicle 2, and an electromechanical steering system 1 according to the invention for steering the motor vehicle 2.

[0048] Fig.4 shows a preferred embodiment of a method according to the invention schematically in a flow diagram. The method is carried out with a steering system 1 according to the invention, in which, in this example, damage to the communication link 6 occurs. The first control device 7 is in an active operating state and controls the electric motor 3. The second control device 9 is in a passive operating state in which no control of the electric motor 3 takes place. In a first method action 100, the first control device 7 and the second control device 9 determine the occurrence of the communication disruption between the first control device 7 and the second control device 9 caused by the damage to the communication link 6. This can be done, for example, by not receiving any responses to requests sent via the communication link 6.

[0049] In a second method action 200, the first control device 7 imprints the predefined excitation pattern on the electric motor 3. The predefined excitation pattern is designed in such a way that it differs significantly from a conventional control of the electric motor 3. In a third method action 300, the second control device 9 detects the imposed excitation pattern, for example, by evaluating a magnetic field of the electric motor 3, by detecting a rotor position of a rotor of the electric motor 3 via the position sensor 11, or the like, and remains in the passive operating state, while the first control device 7 remains in the active operating state and controls the electric motor 3. List of reference symbols 1 steering system 2 motor vehicles 3 electric motor 4 first redundancy path 5 second redundancy path 6 Communication connection 7 first control device 8 first control line 9 second control device 10 second control line 11 Position sensor 12 Drive system 13 Braking system 14 first power supply 15 second power supply 100 first procedural action 200 second procedural action 300 third procedural action

Claims

[1] A method for operating an electromechanical steering system (1) of a motor vehicle (2), wherein the steering system (1) comprises an electric motor (3) for setting a steering angle, a first redundancy path (4) for controlling the electric motor (3) in an active operating state, a second redundancy path (5) for controlling the electric motor (3) in an active operating state in the event of failure of the first redundancy path (4) and for remaining in a passive operating state when the first redundancy path (4) controls the electric motor (3), and a communication connection (6), wherein the first redundancy path (4) comprises a first control device (7) and a first control line (8), wherein the second redundancy path (5) comprises a second control device (9) and a second control line (10), wherein communication between the first control device (7) and the second control device (9) can be carried out via the communication connection (6),the method comprising: - Detecting the occurrence of a communication fault in the communication conducted via the communication link (6) between the first control device (7) and the second control device (9) by the first control device (7) when the first control device (7) is functioning as intended, and / or the second control device (9) when the second control device (9) is functioning as intended, - Imposing a predefined excitation pattern on the electric motor (3) by the first control device (7) and operating the first control device (7) in the active operating state when the first control device (7) is functioning as intended and has detected the communication fault, - detecting the excitation pattern by the second control device (9) and operating the second control device (9) in the passive operating state when the second control device (9) functions as intended, - Operating the second control device (9) in the active operating state when the second control device (9) is functioning as intended, has detected the communication fault and has not detected any excitation pattern. [2] Method according to claim 1, characterized by that the second control device (9) impresses an excitation pattern on the electric motor (3) in the active operating state, wherein the first control device (7) is operated in the passive operating state upon receiving the excitation pattern. [3] Method according to claim 1 or 2, characterized by that the excitation pattern is detected via a position sensor (11) arranged on the electric motor (3). [4] Method according to one of the preceding claims, characterized by that the excitation pattern has a sinusoidal oscillation. [5] Method according to claim 4, characterized by that the sinusoidal wave has a predefined frequency or frequency sequence and / or amplitude or amplitude sequence. [6] Method according to one of the preceding claims, characterized by that the electromechanical steering system (1) is operated in emergency mode after the communication fault has been detected. [7] Method according to claim 6, characterized by that the electromechanical steering system (1) in emergency operation causes an engine of the motor vehicle (2) to operate to drive the motor vehicle (2) with a limited power, wherein the limited power is lower than a possible power of the engine in normal operation. [8] Method according to one of the preceding claims, characterized bythat after the communication fault has been detected, a warning is issued by the electromechanical steering system (1) to an occupant of the motor vehicle (2). [9] An electromechanical steering system (1) for a motor vehicle (2), comprising an electric motor (3) for setting a steering angle, a first redundancy path (4) for controlling the electric motor (3) in an active operating state, a second redundancy path (5) for controlling the electric motor (3) in an active operating state upon failure of the first redundancy path (4) and for remaining in a passive operating state when the first redundancy path (4) controls the electric motor (3), and a communication connection (6), wherein the first redundancy path (4) has a first control device (7) and a first control line (8), wherein the second redundancy path (5) has a second control device (9) and a second control line (10), wherein communication between the first control device (7) and the second control device (9) can be carried out via the communication connection (6), characterized bythat the electromechanical steering system (1) is designed to carry out a method according to one of the preceding claims. [10] Motor vehicle (2), comprising a drive system (12) for driving the motor vehicle (2) and a braking system (13) for braking the motor vehicle (2), characterized by that the motor vehicle (2) has an electromechanical steering system (1) according to claim 9.

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