Method for operating a steering device

Abstract

Method for operating a steering device comprising at least one electric motor (10) which is intended to provide a steering torque in normal operation, wherein at least one status parameter correlated with an operation of the electric motor (10) (S E ) is monitored and in at least one operating state in which the status parameter (S E ) assumes an error value correlated with a fault and / or a malfunction of the electric motor (10), a shutdown process of the electric motor (10) is triggered, during which the electric motor (10) is switched off for a defined period of time (t D , t D ' is delayed, whereby the status parameter (S E ) during the time period (t D , t D ' changes are checked or monitored, and in the event that the status parameter (S) E ) during the time period (t D , t D ' assumes a normal value that deviates from the error value, normal operation continues, whereby the duration of the time interval (t) D , t D ' adapted to the type of fault and / or malfunction of the electric motor (10), and wherein the duration is at least twice as long as a fault tolerance time and / or fault response time correlated with the fault and / or malfunction of the electric motor (10) and is at most 300 ms.

Description

State of the art

[0001] The invention relates to a method for operating a steering device. Furthermore, the invention relates to a control unit with a computing unit for implementing such a method, as well as to a steering device with a computing unit for implementing such a method.

[0002] From the prior art, such as DE 10 2012 105 143 A1 and / or WO 2005 / 061 304 A1, steering systems with electric motors in the form of servo motors are known, wherein in at least one operating state in which an error correlated with the electric motor is determined, a switch-off process of the electric motor is triggered, in which the electric motor is braked to a standstill by a corresponding control of power electronics.

[0003] However, complete braking of the electric motor is generally only necessary in the case of serious and / or persistent errors, but not in the case of temporary errors and / or malfunctions of the electric motor. Such temporary errors and / or malfunctions can be caused, in particular, by short-term operating fluctuations and / or external influences, such as low outside temperatures in combination with voltage fluctuations and / or corresponding EMC influences while simultaneously requiring high steering dynamics. These can lead to the electric motor being completely braked, even though such complete braking may not be necessary for the safe operation of the steering system.

[0004] In this context, for example, EP 1 621 445 A2 discloses an electrically assisted steering system having an electric motor and a method for operating the electrically assisted steering system, wherein operation of the electric motor is monitored and, in at least one operating state in which an error and / or malfunction of a steering component, such as the electric motor, occurs, a shutdown process of the electric motor is triggered, during which an assistance torque provided by the electric motor is reduced. If the error and / or malfunction disappears, the assistance torque is increased again, wherein the assistance torque is set to an average value in a first step and is continuously increased to an initial value in a second step, such that normal operation continues.

[0005] Furthermore, DE 10 2012 105 143 A1 discloses a steering system that safely transfers the power steering system to a fault state when a serious fault occurs. To this end, the power assistance is deactivated within a specified period of time upon detection of the serious fault in the electronic power steering system.

[0006] Based on this, the object of the invention is, in particular, to provide a method for operating a steering device with improved robustness properties. This object is achieved by the features of claims 1, 10, and 11, while advantageous embodiments and further developments of the invention can be found in the subclaims. Disclosure of the invention

[0007] The invention is based on a method for operating a steering device which comprises at least one electric motor which, in normal operation, is provided for providing a steering torque, wherein at least one status parameter correlated with operation of the electric motor is monitored and, in at least one operating state in which the status parameter assumes an error value correlated with an error, in particular a temporary error, and / or a malfunction, in particular a temporary error, of the electric motor, a switch-off process of the electric motor is triggered, in which the electric motor, in particular a movement of the electric motor and in particular a rotor element of the electric motor, is delayed for a defined period of time, in particular without irreversibly switching off the electric motor.

[0008] In the present case, the status parameter is checked for changes or monitored for changes during the period, in particular once or advantageously repeatedly, and in the event that the status parameter assumes a normal value during the period that deviates from the error value and in particular correlates with normal operation, normal operation is continued. In particular, in at least one method step in which an error and / or malfunction of the electric motor is determined, depending on the error and / or malfunction, the status parameter is set to the error value and a switch is made to a shutdown operating mode in which the shutdown process of the electric motor is carried out, in particular without irreversibly switching off the electric motor. In addition, in particular in the

[0009] If the status parameter assumes the normal value during the time period, the system switches from the shutdown operating mode back to a normal operating mode, in which normal operation continues. Advantageously, the time period is also provided to delay an actual error response and / or a, in particular, final, shutdown of the electric motor. This configuration can, in particular, increase robustness, particularly in the case of time-critical errors and / or malfunctions, and achieve particularly flexible and / or robust error handling. In particular, it is possible to reversibly return from a shutdown process to active normal operation, whereby a fault tolerance time and / or fault response time can advantageously be flexibly adapted.In particular, this allows for a response to the fault and / or malfunction of the electric motor within a very short time, especially without immediately shutting down the electric motor completely. Furthermore, the sensitivity of the steering system to external interference can be advantageously reduced and / or operational reliability increased.

[0010] In this context, a "steering device" should be understood to mean at least one part, in particular a subassembly, of a steering system, in particular of a vehicle and preferably of a motor vehicle. In particular, the steering device can also comprise the entire steering system. In addition, the steering device can comprise further components and / or assemblies, such as at least one control unit, advantageously designed as a steering control unit, at least one power electronics unit, preferably designed as an inverter unit and / or output stage, for controlling the electric motor, and / or at least one sensor unit for detecting the error and / or malfunction of the electric motor and / or for detecting the status parameter. Furthermore, the electric motor is designed in particular as a brushless motor and advantageously as an asynchronous motor or as a permanently excited synchronous motor.The electric motor can, in particular, be part of an electric power steering system and, in particular, be provided for generating and / or providing electric steering assistance. Alternatively or additionally, the electric motor can be part of an electric superimposed steering system and / or external power steering system and, in particular, be provided for generating and / or providing a variable transmission ratio. Furthermore, "a fault and / or malfunction of the electric motor" should be understood to mean, in particular, a fault and / or malfunction of the electric motor itself and / or of a peripheral assembly interacting with the electric motor, such as a power supply, and a resulting malfunction of the electric motor and / or of the operation of the electric motor.Advantageously, the error and / or malfunction has a fault tolerance time and / or fault reaction time, in particular a time in which an error reaction must be initiated or completed, of less than 100 ms or less than 20 ms. Furthermore, a "status parameter" should be understood in particular as a parameter that is correlated with a current status, in particular operating status, of the electric motor. In particular, at least based on the status parameter, it is possible to infer an error and / or a malfunction of the electric motor and / or a peripheral module interacting with the electric motor and / or to detect an error and / or a malfunction of the electric motor and / or a peripheral module interacting with the electric motor.In particular, the status parameter comprises at least two status values, in particular a normal value in which no error and / or malfunction of the electric motor can be detected, and an error value in which an error and / or malfunction of the electric motor can be detected. In this context, the status parameter can be configured, for example, as a status variable and / or status indicator.

[0011] In addition, the steering device comprises, in particular, a computing unit designed to carry out the method for operating the steering device. A "computing unit" in this context is understood to mean, in particular, an electronic unit having an information input, an information processing unit, and an information output. Advantageously, the computing unit further comprises at least one processor, at least one memory, at least one input and / or output means, at least one operating program, at least one control routine, at least one calculation routine, at least one detection routine, and / or at least one shutdown routine.In particular, the computing unit is designed to trigger a shutdown of the electric motor and to delay the electric motor for a defined period of time, advantageously by controlling the power electronics, in at least one operating state in which the status parameter assumes an error value correlated with an error and / or malfunction of the electric motor. Furthermore, the computing unit is designed to check or monitor the status parameter for changes during the period of time and, in the event that the status parameter assumes a normal value that deviates from the error value during the period of time, to continue normal operation.Advantageously, the computing unit is also provided to determine an error correlated with the electric motor and / or a malfunction correlated with the electric motor and, depending on the absence or presence of the error and / or malfunction, to set the status parameter to the normal value or the error value. Preferably, the computing unit is further integrated into a control unit, in particular of the vehicle or preferably of the steering device. "Provided" should be understood in particular to mean specially programmed, designed and / or equipped. The fact that an object is provided for a specific function should be understood in particular to mean that the object fulfills and / or executes this specific function in at least one application and / or operating state.

[0012] Furthermore, it is proposed that a power electronics unit, in particular the power electronics already mentioned above, is controlled for controlling the electric motor during the switch-off process in such a way that, advantageously during the entire time period, an active deceleration of the electric motor is achieved, in particular by means of a phase short circuit, whereby in particular an advantageously simple and / or rapid deceleration of the electric motor can be achieved.

[0013] Furthermore, it is proposed that if the status parameter has the error value throughout the entire period, the electric motor is switched off, in particular completely. Particularly preferably, to switch off the electric motor, power switches of a power electronics system, in particular of the aforementioned power electronics, are activated to control the electric motor in such a way that an electrical connection to the electric motor is interrupted. Preferably, all power switches of the power electronics system are opened for this purpose. This allows a complete and / or irreversible shutdown of the electric motor, particularly in the case of a serious and / or persistent fault.

[0014] The error and / or malfunction could, for example, correspond to a blocking of the electric motor and / or be linked to a voltage spike in a vehicle's electrical system. However, according to a particularly preferred embodiment, it is proposed that the error and / or malfunction be correlated with an unintentional steering movement caused by the electric motor. This advantageously allows particularly time-critical errors and / or malfunctions in the form of unintentional steering movements, in particular with a fault tolerance time and / or fault response time of less than 20 ms, to be handled flexibly and reliably.

[0015] In the present case, the time period has a, in particular maximum, duration of at most 300 ms and preferably of at most 100 ms. The duration of the time period is adapted to a type of error and / or malfunction. Furthermore, the, in particular maximum, duration is at least twice and preferably at least four times longer than the fault tolerance time and / or fault reaction time correlated with the error and / or malfunction of the electric motor. Furthermore, the, in particular maximum, duration of the time period and / or a duration of the delay of the electric motor is shorter than an average reaction time of a vehicle driver, which is approximately 350 ms. As a result, the shutdown process can be designed to be particularly advantageously unobtrusive, so that it is not or hardly perceptible, in particular by a vehicle driver. In addition, operational safety and / or driving comfort can be further increased.

[0016] Furthermore, it is proposed that the status parameter be determined by means of a cyclical diagnosis, in which the presence and / or absence of the error and / or fault is checked at regular intervals, such as every 10 ms or every 1 ms. This allows for a particularly simple and / or precise determination of the status parameter.

[0017] In a further embodiment, it is proposed that an error counter be used to determine the status parameter, wherein the status parameter is set to the error value depending on a first numerical value of the error counter and to the normal value depending on a second numerical value of the error counter. In particular, in this context, the status parameter can be set to the error value if the error counter has the first numerical value and set to the normal value if the error counter has the second numerical value. Preferably, the error counter can, for example, be reset, in particular set to zero, if two consecutive diagnoses and / or measurements, in which in particular the presence and / or absence of the error and / or malfunction is determined, are different. The error counter is advantageously integrated into the control unit and / or the computing unit.This can further increase robustness and / or operational reliability.

[0018] Furthermore, it is proposed that the status parameter is set to the error value if the error and / or the fault is determined in at least two, advantageously at least four, preferably at least eight, preferably at least twelve and particularly preferably at least sixteen, consecutive diagnoses and / or measurements, and / or is set to the normal value if the error and / or the fault cannot be determined in at least two, advantageously at least four, preferably at least eight, preferably at least twelve and particularly preferably at least sixteen, consecutive diagnoses and / or measurements.In particular, the status parameter is set to the error value if the first numerical value has a value of at least two, advantageously at least four, preferably at least eight, preferably at least twelve, and particularly preferably at least sixteen, and / or set to the normal value if the second numerical value has a value of at least two, advantageously at least four, preferably at least eight, preferably at least twelve, and particularly preferably at least sixteen. This can, in particular, increase diagnostic accuracy and improve detection of the error and / or fault.

[0019] A particularly high degree of flexibility can also be achieved when the error counter exhibits hysteresis behavior and the first numerical value and the second numerical value are different from each other. In this context, the status parameter can, for example, be set to the error value if the error and / or fault is detected in eight or ten consecutive diagnoses and / or measurements, and set to the normal value if the error and / or fault cannot be detected in four or six consecutive diagnoses and / or measurements.

[0020] The method, the control unit, and the steering device are not intended to be limited to the application and embodiment described above. In particular, the method, the control unit, and the steering device may have a number of individual elements, components, and units that differs from the number stated herein to fulfill a functionality described herein. Drawings

[0021] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an exemplary embodiment of the invention. The drawings, the description, and the claims contain numerous aspects of the invention. Those skilled in the art will expediently consider these aspects individually and combine them into useful further combinations.

[0022] They show: Fig. 1 an exemplary steering system with a steering device in a simplified representation, Fig. 2 a control circuit and an electric motor of the steering device in a schematic representation, Fig. 3 an exemplary signal flow diagram of a method for operating the steering device and Fig. 4a-b show exemplary diagrams of a steering torque of the electric motor in different operating states. Description of the embodiment

[0023] Fig. 1 shows an exemplary steering system 26 in a perspective view. In the present case, the steering system 26 is designed as an electrically assisted steering system and accordingly has an electric auxiliary power assistance in the form of a power steering system. Furthermore, the steering system 26 is intended for use in a vehicle (not shown), in particular a motor vehicle. In an installed state, the steering system 26 has an operative connection to vehicle wheels 28 of the vehicle and is intended to influence a direction of travel of the vehicle. Alternatively or additionally, however, it is also conceivable to design a steering system with an electric superimposed steering system and / or external power steering. In addition, a steering system could in principle also be designed as a steer-by-wire steering system.

[0024] The steering system 26 comprises a steering device. The steering device comprises a steering handle 30, in the present case embodied as a steering wheel, for applying a manual steering torque, a steering gear 32, embodied as a rack and pinion steering gear, for example, which is provided to convert a steering command at the steering handle 30 into a steering movement of the vehicle wheels 28, and a steering shaft 34 for connecting, in particular mechanically, the steering handle 30 to the steering gear 32. Furthermore, the steering device comprises an electrically configured assistance unit 36 ​​for generating and / or providing electric steering assistance. The assistance unit 36 ​​is provided to introduce a steering torque, in particular in the form of an assistance torque, into the steering gear 32 and to assist the manual steering torque, in particular applied by the driver.Alternatively, a steering handle could also be designed as a steering lever and / or steering ball or the like. A steering device and / or a steering system could also, in principle, be free of a steering handle, for example, in a purely autonomously driving vehicle. Furthermore, a steering shaft could also only temporarily connect a steering handle to a steering gear, such as in a vehicle with autonomous driving and / or a steer-by-wire steering system with a mechanical fallback. In the latter case, the steering device and / or the steering system can also be free of a support unit and instead comprise at least one steering actuator.

[0025] The steering device further comprises an electric motor 10. In the present case, the electric motor 10 is designed as a synchronous motor, in particular a permanent magnet motor. The electric motor 10 is also designed as a multi-phase electric motor, in the present case, for example, a three-phase electric motor. The electric motor 10 is part of the assistance unit 36 ​​and is provided in particular for generating the electric steering assistance. In normal operation, the electric motor 10 is provided to provide the steering torque, in particular in the form of the assistance torque. Alternatively, an electric motor could also perform a function other than a steering assistance function. In this context, the electric motor could, for example, be part of an electric superimposed steering system and / or power steering system. Furthermore, the electric motor could also be part of a steering actuator, particularly in a steer-by-wire steering system.

[0026] Furthermore, the steering device has at least one sensor unit 38. The sensor unit 38 is arranged in a region of the electric motor 10 and is provided for the detection, in particular contactless, of at least one operating signal of the electric motor 10. In the present case, the sensor unit 38 is designed, for example, as a rotor position sensor and is provided for detecting an operating signal in the form of a rotor position signal of the electric motor 10. Furthermore, the sensor unit 38 is provided in the present case for the direct and / or indirect detection of an error and / or a malfunction of the electric motor 10. In principle, however, it is also conceivable to dispense with a sensor unit entirely. In addition, a sensor unit could be designed as an angle sensor that differs from a rotor position sensor.Furthermore, a fault and / or malfunction of an electric motor could also be detected and / or determined by an assembly of a steering device that differs from a sensor unit.

[0027] Furthermore, the steering device has a control unit 22. The control unit 22 is designed as a steering control unit. The control unit 22 has an operative connection with the sensor unit 38 and the electric motor 10. The control unit 22 is provided to receive the operating signal from the sensor unit 38. Furthermore, the control unit 22 is provided to control the electric motor 10 and thus, in particular, to adjust the steering torque, in particular as a function of the operating signal.

[0028] For this purpose, the control unit 22 comprises a computing unit 24. The computing unit 24 comprises at least one processor (not shown), for example in the form of a microprocessor, and at least one operating memory (not shown). In the present case, the computing unit 24 also has at least two different operating modes, in particular a normal operating mode and a switch-off operating mode. In the normal operating mode, the computing unit 24 is provided for setting the steering torque in the form of the assistance torque, and in the switch-off operating mode for decelerating and advantageously braking the electric motor 10. For this purpose, the computing unit 24 comprises at least one operating program stored in the operating memory, comprising at least one calculation routine, at least one control routine, at least one detection routine, and at least one switch-off routine.

[0029] In addition, the control unit 22 comprises a known power electronics 14 for controlling the electric motor 10 (see Fig. 2). The power electronics 14 has an operative connection to the computing unit 24 and is connected downstream of it in terms of control technology. In addition, the power electronics 14 has an operative connection to the electric motor 10. The power electronics 14 is designed as an inverter unit and / or as an output stage and, in the present case, comprises a plurality of inverters 40, in particular identically designed to one another, with one of the inverters 40 being assigned to each phase of the electric motor 10. Each of the inverters 40 comprises two power switches 16, 18, in particular identically designed to one another, in particular a high-side power switch 16 and a low-side power switch 18. Each of the inverters 40 is provided to convert a pulsating rectified voltage from an energy source (not shown) into a phase current and to supply it to the electric motor 10, in particular to exactly one phase of the electric motor 10.In principle, power electronics could also be designed separately and / or separately from a control unit.

[0030] In addition, the steering device can comprise further components and / or assemblies, such as at least one further sensor unit (not shown) for detecting a steering angle and / or for detecting other vehicle and / or environmental parameters.

[0031] During operation of the electric motor 10 in a vehicle, various types of errors can occur. On the one hand, serious and / or persistent errors can occur, requiring the electric motor 10 to be transferred to a safe operating state and switched off. On the other hand, temporary errors and / or malfunctions can occur, which can be caused in particular by short-term operating fluctuations and / or external influences, such as low outside temperatures in combination with voltage fluctuations and / or by corresponding EMC influences with a simultaneous requirement for high steering dynamics. In the latter case, a complete shutdown of the electric motor 10 may be dispensed with if the error and / or malfunction disappears before the complete shutdown, although a required maximum fault tolerance time and / or fault response time must be taken into account at the same time.

[0032] In order to achieve flexible error handling, particularly in these cases, while simultaneously ensuring the highest possible robustness, an exemplary method for operating the steering device is explained below. In the present case, the computing unit 24 is provided to execute the method and, for this purpose, has, in particular, a computer program with corresponding program code means.

[0033] Fig. 3 shows an exemplary signal flow diagram of the method for operating the steering device.

[0034] A first block 42 indicates the normal operating mode, in which the electric motor 10 is operated in normal operation and is intended to provide the steering torque. Furthermore, a status parameter S correlated with the operation of the electric motor 10 is E monitored. The status parameter S Eis designed, for example, as a status variable and / or status indicator of the electric motor 10 and has at least two status values, in particular a normal value in which no error and / or no malfunction of the electric motor 10 can be determined, and an error value in which an error and / or a malfunction of the electric motor 10 can be determined. Consequently, if an error and / or a malfunction correlated with the electric motor 10 is determined, the status parameter S E set to the error value.

[0035] In an operating state in which the status parameter S E assumes the error value, in particular correlated with the error and / or malfunction of the electric motor 10 (S E== 1), the system switches from normal operating mode to shutdown operating mode, and a shutdown process of the electric motor 10 is triggered. In the present case, the error and / or malfunction is correlated in particular with an unintentional steering movement caused by the electric motor 10, in particular a so-called "self-steering movement," and has a fault tolerance time and / or error reaction time of less than 20 ms, which means that the error and / or malfunction of the electric motor 10 must be responded to within a very short time. In principle, however, an error and / or malfunction could also correspond to a blocking of the electric motor 10. In this case, the fault tolerance time and / or error reaction time is in particular less than 150 ms and advantageously less than 100 ms.

[0036] A second block 44 indicates the shutdown operating mode in which the shutdown process of the electric motor 10 is carried out, wherein the electric motor 10 is switched off for a defined period of time t D , tD' For deceleration, the power electronics 14 are controlled in such a way that an active deceleration of the electric motor 10 is achieved by means of a phase short circuit. The time period t D , tD' is intended to delay an actual error reaction and / or a, in particular, final, shutdown of the electric motor 10 and has a duration of at most 250 ms, in the present case in particular of at most 100 ms, whereby the deceleration of the electric motor 10 is not or hardly perceptible to a vehicle driver. In addition, the duration of the period t D , tD' adapted to the type of error and / or malfunction of the electric motor 10 and, in the present case, at least four times longer than the fault tolerance time and / or fault reaction time, in particular correlated with the error and / or malfunction of the electric motor 10. During the time period t D , tD' the status parameter S E repeatedly checked for changes or monitored for changes. In this case, during the period t D , tD' checked whether the error and / or malfunction can still be determined. If the error and / or malfunction correlated with the electric motor 10 is detected during the time period t D , tD' can no longer be determined, the status parameter S E set to the normal value.

[0037] In case the status parameter S E during the period t D , tD' assumes the normal value, which in particular deviates from the error value and in particular correlates with normal operation (S E == 0), the shutdown mode is switched back to normal mode, and normal operation is continued. Consequently, the presented method makes it possible to reversibly return from the shutdown process to active normal operation while simultaneously meeting specified safety goals, in particular a required maximum fault tolerance time and / or fault response time.

[0038] In case the status parameter S E during the entire period t D , tD' has the error value (S E == 1), at the end of the time period t D , tD' changed from the shutdown mode to a fault mode.

[0039] A third block 46 indicates the fault operating mode, in which the electric motor 10 is shut down. In the present case, to shut down the electric motor 10, the power switches 16, 18 of the power electronics 14 are controlled in such a way that an electrical connection to the electric motor 10 is interrupted by opening all power switches 16, 18 of the power electronics 14. In this case, the electric motor 10 is advantageously switched off irreversibly, and the control unit 22 and / or the steering device are placed in a fail-safe state or, advantageously, a fail-operational state. Alternatively or additionally, an electric motor could also be switched off by means of a mechanical blocking device.

[0040] According to an advantageous further training, the status parameter S Efurther determined by means of an error counter 20, in particular integrated into the computing unit 24, and by means of a cyclical diagnosis, wherein the presence and / or absence of the error and / or fault is checked at regular intervals, advantageously every 1 ms. The status parameter S E is set to the error value depending on a first numerical value of the error counter and to the normal value depending on a second numerical value of the error counter. In addition, the error counter 20 is reset, in particular, to zero, if two consecutive diagnoses are different. In principle, an error counter could also be reset in any other way, for example, if four consecutive diagnoses are different and / or based on time.

[0041] Furthermore, the error counter 20 exhibits a hysteresis behavior, so that the first numerical value and the second numerical value are different from each other. In this case, the status parameter S E For example, it can be set to the error value if the error and / or malfunction is identified in eight consecutive diagnoses, and to the normal value if the error and / or malfunction cannot be identified in four consecutive diagnoses. This allows the exemplary error and / or malfunction, such as the unintentional steering movement, to be reliably detected within 8 ms, and a specified maximum error tolerance time and / or error response time of less than 20 ms can be maintained. Alternatively, such hysteresis behavior could also be dispensed with.

[0042] In the Fig. 4a and Fig. 4b shows exemplary diagrams of a provided steering torque of the electric motor 10 in different operating states.

[0043] Fig. 4a shows the electric motor 10 in a first operating state. A first time interval t1 corresponds to the normal operating mode, in which the electric motor 10 is operated in normal operation and is intended to provide the steering torque. At a first time T1, a particularly temporary error and / or a particularly temporary malfunction of the electric motor 10 occurs. In a subsequent second time interval t2, the error and / or malfunction is determined using the cyclic diagnosis and the error counter 20. An error reaction, in the form of a change to the shutdown operating mode, is initiated at a second time T2, at which the error counter 20 has the first numerical value and consequently the status parameter S Eis set to the error value. The second time point T2 is followed by the time period t D so that the electric motor 10 is decelerated. At the same time, during the time period t D the status parameter S E However, it is repeatedly checked or monitored for changes. Since the status parameter S E in this case during the period t D and in particular at a third time T3 is set to the normal value by the error counter 20, the shutdown mode is switched back to the normal mode and normal operation is continued

[0044] Fig. 4b shows the electric motor 10 in a second operating state. Another first time interval t1' corresponds to the normal operating mode, in which the electric motor 10 is operated in normal operation and is intended to provide the steering torque. At a further first time T1' a particularly serious and / or persistent error and / or a particularly serious and / or persistent malfunction of the electric motor 10 occurs. In a subsequent second time interval t2' The error and / or fault is determined using the cyclic diagnosis and the error counter 20. An error reaction, in the form of a change to the shutdown operating mode, is triggered at a second time T2' initiated, at which the error counter 20 has the first numerical value and consequently the status parameter S E is set to the error value. At the second time T2' closes the time period tD' so that the electric motor 10 is decelerated. Since the status parameter S E in this case during the entire period tD' has the error value, at the end of the time period tD' and in particular at a further third point in time T3' changed from the shutdown operating mode to the fault operating mode and the electric motor 10 is switched off.

Claims

[1] Method for operating a steering device which comprises at least one electric motor (10) which is provided in normal operation to provide a steering torque, wherein at least one status parameter (S E ) and in at least one operating state in which the status parameter (S E ) assumes an error value correlated with an error and / or a malfunction of the electric motor (10), a shutdown process of the electric motor (10) is triggered, in which the electric motor (10) is switched off for a defined period of time (t D , tD' is delayed, whereby the status parameter (S E ) during the period (t D , tD' is checked or monitored for changes and in case the status parameter (S E ) during the period (t D , tD' assumes a normal value that differs from the error value, normal operation is continued, whereby the duration of the time period (t D , tD' is adapted to the type of error and / or malfunction of the electric motor (10), and wherein the time duration is at least twice longer than a fault tolerance time and / or fault reaction time correlated with the error and / or malfunction of the electric motor (10) and is at most 300 ms. [2] Method according to claim 1, characterized by that a power electronics unit (14) for controlling the electric motor (10) is controlled during the switch-off process in such a way that an active deceleration of the electric motor (10) is achieved, in particular by means of a phase short circuit. [3] Method according to claim 1 or 2, characterized by that in case the status parameter (S E ) during the entire period (t D, tD' has the error value, the electric motor (10) is switched off, wherein in order to switch off the electric motor (10) power switches (16, 18) of a power electronics unit (14) for controlling the electric motor (10) are controlled in such a way that an electrical connection to the electric motor (10) is interrupted. [4] Method according to one of the preceding claims, characterized by that the electric motor (10) is decelerated during the switch-off process in such a way that the steering torque remains constant over the entire time period (t D , tD' is reduced linearly. [5] Method according to one of the preceding claims, characterized by that the error and / or malfunction is correlated with an unwanted steering movement caused by the electric motor (10). [6] Method according to one of the preceding claims, characterized by that the status parameter (S E) is determined by means of a cyclical diagnosis in which the presence of the error and / or fault is checked at regular intervals. [7] Method according to claim 6, characterized by that to determine the status parameter (S E ) an error counter (20) is used, wherein the status parameter (S E ) is set to the error value depending on a first numerical value of the error counter (20) and to the normal value depending on a second numerical value of the error counter (20). [8] Method according to claim 7, characterized by that the status parameter (S E ) is set to the error value if the error and / or fault is detected in at least two consecutive diagnoses, and / or is set to the normal value if the error and / or fault cannot be detected in at least two consecutive diagnoses. [9] Method according to claim 7 or 8, characterized bythat the error counter (20) has a hysteresis behavior and the first numerical value and the second numerical value are different from each other. [10] Control unit (22), in particular steering control unit, with a computing unit (24) for carrying out a method according to one of the preceding claims. [11] Steering device with at least one electric motor (10) and with a computing unit (24) for carrying out a method according to one of claims 1 to 9.

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