Control device and method for operating an electric motor, in particular an electric motor of a steering system

Abstract

A control device (10) for operating an electric motor (12), in particular an electric motor (12) of a steering system (14), is proposed, comprising power electronics (16), a primary driver unit (18) arranged for driving and controlling the power electronics (16) in normal operating conditions, and a secondary driver unit (20) connected in parallel to the primary driver unit (18) and arranged for driving and controlling the power electronics (16) in at least one error operating condition in which a fault and / or failure of the primary driver unit (18) occurs, the primary driver unit (18) and the secondary driver unit (20) each having an integrated tri-state function (22, 24), the secondary driver unit (20) being in a high impedance state in the normal operating condition.

Description

[Technical Field]

[0001] The present invention relates to a control device for operating an electric motor, in particular an electric motor of a steering system, and in particular to a method for operating an electric motor using such a control device, and also to an actuator assembly comprising such a control device and a steering system comprising such an actuator assembly. [Background technology]

[0002] The prior art is known for control devices for operating electric motors that include multiple driver units in the form of half-bridge drivers and / or gate drivers, where the driver units may be configured to drive various or individual power electronics. In the latter case, the driver units can be used, for example, to fulfill redundancy requirements, so that even in the event of an error, the drive control of the power electronics can be achieved and thus the operation of the electric motor can be maintained. However, if multiple driver units are connected in parallel and configured to drive the same power electronics, it is necessary to prevent or at least reduce the current flow from the primary and / or active driver units to the secondary and / or passive driver units during operation. In known control devices, for example, additional switches and / or resistors are used for this purpose. However, these known measures lead to a decrease in power efficiency and result in additional effort and costs. Summary of the Invention [Problem to be solved by the invention]

[0003] Starting from this, the object of the present invention is to provide a control device and a method for operating an electric motor which have improved properties, in particular with regard to efficiency. This object is achieved by the characterizing parts of claims 1, 6, 7 and 8, whereas preferred embodiments and developments of the invention can be read from the dependent claims. [Means for solving the problem]

[0004] Disclosure of the Invention A control device for operating an electric motor, in particular an electric motor of a steering system, is proposed, comprising power electronics, a primary driver unit arranged to drive and control the power electronics in a normal operating state, and a secondary driver unit connected in parallel to the primary driver unit and arranged to drive and control the power electronics in at least one error operating state in which a fault and / or failure of the primary driver unit occurs, wherein the primary driver unit and the secondary driver unit each have an integrated tri-state function, and the secondary driver unit is in a high-impedance state in the normal operating state. Furthermore, the primary driver unit is in an active state in the normal operating state. Therefore, in the present invention, the primary driver unit is active and the secondary driver unit is passive and / or inactive in the normal operating state. The secondary driver unit, in particular, in the present invention, is arranged to replace the primary driver unit in an error operating state. Therefore, preferably, in the error operating state, the primary driver unit is in a high-impedance state and the secondary driver unit is in an active state. Therefore, in the error operating state, the primary driver unit is passive and / or inactive, and the secondary driver unit is active. For switching and / or interchanging between the primary and secondary driver units, the control device may preferably comprise a switching unit in the form of a computing unit. This embodiment allows for improved efficiency, in particular power efficiency, control efficiency, energy efficiency, structural space efficiency, component efficiency and / or cost efficiency. Also, preferably, the availability of the control device can be increased. Furthermore, in particular, the computing costs can be minimized and / or the control algorithms can be simplified.

[0005] In this context, a "control device" is understood to mean at least a part, particularly a subassembly, of an actuator assembly, preferably at least a part of a steering system, that is provided for controlling the operation of at least one electric motor of the actuator assembly in at least one operating state. The electric motor is preferably configured as a servo motor, preferably as a brushless motor, and particularly preferably as an asynchronous motor or a permanently excited synchronous motor. Preferably, the electric motor here is part of the electric-assisted steering function and is provided in particular for generating electric steering assistance. The electric motor here can be configured, for example, as a 6-, 9-, or 12-phase electric motor. However, it is preferably proposed that the electric motor be configured as a three-phase electric motor. Furthermore, power electronics, configured as an inverter unit, in particular as an output stage and / or a B6 bridge circuit, are provided for power supply and / or energization of the electric motor.

[0006] Furthermore, the term "driver unit" should be understood to mean an at least partially electrically and / or electronically configured unit electrically connected to the power electronics, in particular to a control terminal of at least one power switch of the power electronics, for controlling the at least one power switch, in particular for providing a control voltage and / or a control current for the at least one power switch. Preferably, the driver unit is configured to drive all power switches of the power electronics. Preferably, the driver unit is configured here as a half-bridge driver and / or a gate driver. Furthermore, the primary driver unit is preferably configured as a master driver unit, whereas the secondary driver unit is configured as a slave driver unit. The primary driver unit and the secondary driver unit are configured redundantly and preferably identically to each other. Particularly preferably, the primary driver unit and / or the secondary driver unit are configured as an integrated electronic circuit. Preferably, the primary driver unit is configured to set the motor torque of the electric motor and preferably the auxiliary torque of the electric motor, in normal operating conditions, in particular by controlling the power electronics. The secondary driver unit has an operative connection relationship with the primary driver unit and is provided to replace the primary driver unit, particularly in an error operating state, and take over control of the power electronics and therefore the operation of the electric motor. Preferably, the primary driver unit in a normal operating state and the secondary driver unit in an error operating state use at least partially identical and / or comparable, particularly existing, assemblies and connection lines for controlling the power electronics, and are provided to drive and control the same power switches and therefore operate the same phases of the electric motor. Furthermore, the primary driver unit and the secondary driver unit are preferably capable of operating independently of each other.In particular, the primary driver unit is provided here exclusively for driving the power electronics in normal operating conditions, thereby changing and / or varying the motor moment of the electric motor and preferably the assist moment of the electric motor. The secondary driver unit is preferably provided exclusively for driving the power electronics in error operating conditions, thereby changing and / or varying the motor moment of the electric motor and preferably the assist moment of the electric motor. The phrase "the driver unit has a tri-state function" should be understood to mean, in particular, that the output of the driver unit, in particular connected to the power electronics, can assume at least three different states, where a first state corresponds to an active state, a second state corresponds to an inactive state, and a third state corresponds to a high-impedance state or "high-Z" state. For this purpose, the driver unit may, for example, have corresponding function units and / or function electronics. The expression "the driver unit has an integrated tri-state function" should be understood to mean, in particular, that the tri-state function or a functional unit and / or functional electronics coupled thereto are configured as an integrated electronic circuit together with the drive control electronics of the driver unit. Therefore, in particular, the tri-state function is not realized via external wiring. Furthermore, "fault and / or failure of the primary driver unit" should be understood to mean, in particular, fault and / or failure of the primary driver unit itself and / or a peripheral assembly cooperating with the primary driver unit, such as an energy supply, and should also be understood to mean a failure of the primary driver unit caused thereby.

[0007] Furthermore, the term "switching unit" should be understood to mean, in particular, an electrically and / or electronically configured unit that is electrically connected to the primary driver unit and / or the secondary driver unit and that is provided for changing, in at least one operating state, the state of an output of the primary driver unit, in particular connected to the power electronics of the primary driver unit, and / or the state of a further output of the secondary driver unit, in particular connected to the power electronics of the secondary driver unit, by means of a switching signal. The output of the primary driver unit and / or the further output of the secondary driver unit can be switched here, in particular, between an active state, an inactive state, and a high-impedance state or "high-Z" state depending on the switching signal. Furthermore, the term "computing unit" should be understood to mean, in particular, an electrical and / or electronic unit having an information input, an information processing section, and an information output. Preferably, the computing unit further comprises at least one processor, for example in the form of a microprocessor, at least one operating memory, at least one input means and / or output means, and at least one operating program. "Provided" should be understood to mean, inter alia, specially programmed, designed and / or configured. That an object is provided for a given function should be understood to mean, inter alia, that the object satisfies and / or performs this given function, at least in use and / or in operation.

[0008] The tri-state function of the primary driver unit can be controlled, for example, via a corresponding software configuration or software configuration bit. However, it is preferably proposed that the primary driver unit has a control pin for controlling the tri-state function of the primary driver unit. In particular, the control pin is used here to switch the output of the primary driver unit. Preferably, a switching unit, in particular a calculation unit, is electrically connected to the control pin, in particular so that the state of the primary driver unit can be changed using a switching signal. In this way, a particularly simple control of the tri-state function of the primary driver unit can be achieved.

[0009] Furthermore, the tri-state function of the secondary driver unit can be controlled via a corresponding software configuration or software configuration bit. However, according to a preferred embodiment, it is proposed that the secondary driver unit has an additional control pin for controlling the tri-state function of the secondary driver unit. In particular, this additional control pin is used here for switching an additional output of the secondary driver unit. Preferably, a switching unit, in particular a calculation unit, is electrically connected to the additional control pin, in particular so that the state of the secondary driver unit can be changed using a switching signal. This makes it possible to achieve a particularly simple control of the tri-state function of the secondary driver unit.

[0010] The control device may include a separate switching unit for switching and / or interchanging between the primary driver unit and the secondary driver unit, and a monitoring unit configured separately from the switching unit for monitoring the operation of the primary driver unit in normal operating conditions. However, according to a particularly preferred embodiment, it is proposed that the control device includes a calculation unit, in particular the calculation unit already mentioned above, which is configured to monitor the operation of the primary driver unit in normal operating conditions and, if a fault and / or failure of the primary driver unit is detected, to deactivate the primary driver unit, in particular by switching it to a high-impedance or "high-Z" state, in particular by driving a control pin with a corresponding switching signal, and to activate the secondary driver unit, in particular by switching it to an active state, in particular by driving a further control pin with a corresponding switching signal. Thus, in the present invention, the calculation unit is configured as a switching and monitoring unit and is configured to monitor the operation of the primary driver unit in normal operating conditions. Furthermore, the calculation unit is configured to change the state of the primary driver unit and the secondary driver unit by driving the control pin and the further control pin. This makes it possible, inter alia, to minimize the computational costs and / or simplify the control algorithms.

[0011] The invention also relates to an actuator assembly comprising an electric motor, in particular an electric motor as already described above, and a control device as described above, wherein the control device and the electric motor are particularly preferably part of a steering system provided here for use in particular in a vehicle, preferably in a motor vehicle.

[0012] Furthermore, a method for operating an electric motor using the above-mentioned control device is proposed, in which the power electronics are controlled by a primary driver unit in a normal operating state and by a secondary driver unit connected in parallel to the primary driver unit in an error operating state in which a fault and / or failure of the primary driver unit occurs, the primary driver unit and the secondary driver unit each having an integrated tri-state function, the secondary driver unit being in a high-impedance state in the normal operating state. This allows the advantages already mentioned above to be achieved. In particular, efficiency, in particular power efficiency, control efficiency, energy efficiency, structural space efficiency, component efficiency, and / or cost efficiency, can be improved. Also, advantageously, availability of the control device can be increased. Furthermore, in particular, calculation costs can be minimized and / or the control algorithm can be simplified.

[0013] The control device, actuator assembly, steering system and method herein should not be limited to the applications and embodiments described above, and in particular, the control device, actuator assembly, steering system and method for fulfilling the functions described herein may have a different number of individual elements, components and units than those listed herein.

[0014] Further advantages can be gleaned from the following description of the drawings, in which an embodiment of the invention is shown. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view of a portion of an exemplary steering system including an actuator assembly including an electric motor and a controller. [Figure 2] FIG. 2 is a schematic diagram showing a control device and an electric motor. [Figure 3] 1 is an exemplary flow chart including main method steps of a method for operating an electric motor. DETAILED DESCRIPTION OF THE INVENTION

[0016] Description of the Examples The following examples relate exemplarily to steering systems, but in principle the invention is not limited to use in steering systems, but can also be used in other areas of the vehicle, such as wiper systems, power window systems and / or drive systems, and / or in other electronic systems, such as in the area of household appliances and / or machine tools.

[0017] FIG. 1 exemplarily shows at least a portion of a steering system 14 in a perspective view. In the present invention, this steering system 14 is configured as an electrically assisted steering system. The steering system 14 is exemplarily configured as a conventional steering system and includes an electrically assisted steering function in the form of power steering. Furthermore, the steering system 14 is provided for use in a vehicle (not shown), in particular an automobile. In an installed state, the steering system 14 is operatively connected to the vehicle wheels (not shown) of the vehicle and is provided for influencing the direction of travel of the vehicle. However, it is also conceivable to provide a steering system with an electrically superimposed steering section and / or an active steering section. The steering system can also essentially be configured as a steer-by-wire steering system.

[0018] The steering system 14 includes a steering gear 34, which is illustratively configured as a rack-and-pinion steering gear, and which is provided for converting the steering settings into steering movements of the vehicle wheels. For this purpose, the steering gear 34 includes at least one steering adjustment element 36, which in the present case is configured in particular as a rack.

[0019] Furthermore, the steering system 14 includes at least one actuator assembly 32. This actuator assembly 32 is configured as a steering actuator and is operatively connected to a steering adjustment element 36. The actuator assembly 32 is provided for providing a steering moment. In the present case, the actuator assembly 32 is provided for providing a steering moment in the form of an assist moment and / or a servo moment, and for introducing the steering moment into the steering gear 34, in particular for steering assistance. However, alternatively, the actuator assembly could also be part of an electric superimposed steering section and / or an active steering section, in particular for providing an additional steering angle and / or a variable transmission ratio. Furthermore, the actuator assembly could also be part of a steer-by-wire steering system. In this case, the actuator assembly can be provided in particular for use in a wheel steering angle adjuster, in particular for providing a steering moment for direct control of the vehicle's driving direction. The wheel steering angle adjuster here may in particular be associated with the rear and / or front axle of the vehicle. The actuator assembly can also be provided in this case for use in an operating unit of a steer-by-wire steering system and for providing a feedback moment and / or a reset moment to the steering operating element. Furthermore, the actuator assembly can also be used independently of the steering system, as mentioned at the beginning.

[0020] The actuator assembly 32 includes an electric motor 12, which is known per se. The electric motor 12 is particularly configured as a permanently excited synchronous motor. The electric motor 12 is further configured as a polyphase electric motor. In the present case, the electric motor 12 is exemplarily configured as a three-phase electric motor. The electric motor 12 is operatively connected to a steering gear 34, in particular to a steering adjusting element 36. The electric motor 12 is provided for generating a steering moment. In this case, the electric motor 12 is part of the electric-assisted steering function in the present case and is used in particular for generating electric steering assistance. However, the electric motor can also be configured as a six-phase electric motor or have any other suitable number of phases.

[0021] The actuator assembly 32 further includes a control device 10 (see also, in particular, FIG. 2 ), which in the present invention is configured as a control device, in particular as a steering control device, and is operatively connected to the electric motor 12 and is provided for controlling the operation of the electric motor 12.

[0022] For this purpose, the control device 10 includes a computing unit 30. This computing unit 30 includes at least one processor (not shown), for example in the form of a microprocessor. In the present case, the computing unit 30 includes, by way of example, two or more processors, whereby redundancy requirements can preferably be met. The computing unit 30 may also include at least one operating memory (not shown). Furthermore, the computing unit 30 includes at least one operating program stored in the operating memory, which has at least one calculation routine and at least one control routine.

[0023] The control device 10 further includes a power electronics 16, which is known per se. The power electronics 16 is operatively connected to the calculation unit 30 and is connected downstream of the calculation unit 30 in terms of control technology. The power electronics 16 is also operatively connected to the electric motor 12. In the present invention, the power electronics 16 is configured as an output stage, in particular as a B6 bridge circuit, and includes a plurality of identically configured inverters 38, one of which is assigned to each phase of the electric motor 12. For clarity, only one of the inverters 38 is labeled in FIG. 2 . Each of the inverters 38 includes two, in particular identically configured, power switches 40, 42, in particular a high-side power switch 40 and a low-side power switch 42. Each of the inverters 38 is intended to convert a pulsating rectified voltage of an energy source 44, for example in the form of a vehicle battery, into a phase current and supply it to the electric motor 12, in particular to exactly one phase of the electric motor 12.

[0024] Furthermore, the control device 10 includes a primary driver unit 18. The primary driver unit 18 is operatively connected to the computing unit 30 and is connected downstream of the computing unit 30 in terms of control technology. The primary driver unit 18 is also operatively connected to the power electronics 16. Thus, the primary driver unit 18 is arranged between the computing unit 30 and the power electronics 16 in terms of control technology. The primary driver unit 18 is configured as an integrated electronic circuit. The primary driver unit 18 is configured as a half-bridge driver and / or a gate driver. The primary driver unit 18 is provided to drive and control at least one of the plurality of power switches 40, 42, in particular to provide a control voltage and / or a control current for at least one of the power switches 40, 42. In the present invention, the primary driver unit 18 is exemplarily provided to drive and control all of the power switches 40, 42 of the power electronics 16. In the present invention, the primary driver unit 18 is provided to drive and control the power electronics 16, at least in normal operating conditions.

[0025] Since the steering system 14 is a critical safety vehicle component that directly affects the driver and / or vehicle operation, a corresponding safety concept is required in error operating conditions in which failure and / or breakdown of the primary driver unit 18 itself and / or peripheral assemblies that cooperate with the primary driver unit 18, such as the energy supply, occurs, and the resulting failure of the primary driver unit 18 occurs.

[0026] For this reason, the control device 10 further includes a secondary driver unit 20. This secondary driver unit 20 is configured separately from the primary driver unit 18. The secondary driver unit 20 is configured redundantly with respect to the primary driver unit 18. The secondary driver unit 20 is also configured identically to the primary driver unit 18. In principle, however, the primary and secondary driver units can also be configured differently from each other, especially if the secondary driver unit is only provided for emergency use. The secondary driver unit 20 is also connected in parallel to the primary driver unit 18. The secondary driver unit 20 is therefore operatively connected to the computing unit 30 and is connected downstream of the computing unit 30 in terms of control technology. The secondary driver unit 20 is also operatively connected to the power electronics 16. The secondary driver unit 20 is arranged between the computing unit 30 and the power electronics 16 in terms of control technology. The secondary driver unit 20 is configured as an integrated electronic circuit. The secondary driver unit 20 is configured as a half-bridge driver and / or a gate driver. The secondary driver unit 20 is provided to drive and control at least one of the plurality of power switches 40, 42, particularly the same power switch 40, 42 as the primary driver unit 18, and particularly to provide a control voltage and / or a control current for the at least one power switch 40, 42. In the present invention, the secondary driver unit 20 is exemplarily provided to drive and control all of the power switches 40, 42 of the power electronics 16.

[0027] The secondary driver unit 20 is provided to drive and control the power electronics 16 at least in an error operating state. In this case, the secondary driver unit 20 is in a purely passive and / or standby operating mode in normal operating states and is provided exclusively to drive and control the power electronics 16 in an error operating state. In the present invention, the secondary driver unit 20 is provided to replace the primary driver unit 18 in an error operating state and take over control of the power electronics 16 and therefore the operation of the electric motor 12. Furthermore, the secondary driver unit 20 is provided to drive and control the same power switches 40, 42 for driving the power electronics 16, using at least partly the same and / or equivalent, in particular existing, assemblies and connection lines.

[0028] Therefore, in the present invention, the primary driver unit 18 and the secondary driver unit 20 are connected in parallel and are provided to drive and control the same power electronics 16, where the primary driver unit 18 is active in normal operating conditions and the secondary driver unit 20 is active in error operating conditions, in which case it is necessary to prevent or at least reduce the current flow from the active driver unit to the passive driver unit by appropriate means.

[0029] For this purpose, the primary driver unit 18 and the secondary driver unit 20 each have an integrated tri-state function 22, 24, by means of which each output 46, 48 of each driver unit 18, 20, which is connected to the power electronics 16, can assume at least three different states, in particular an active state, an inactive state and a high-impedance state. For driving and controlling each tri-state function 22, 24, the primary driver unit 18 comprises a control pin 26 and the secondary driver unit 20 comprises a further control pin 28.

[0030] In a normal operating state, the primary driver unit 18 is in an active state, while the secondary driver unit 20 is in a high-impedance state, as shown by the closed and open switches, particularly in FIG. 2 . In contrast, in an error operating state, the primary driver unit 18 is replaced by the secondary driver unit 20. As a result, the primary driver unit 18 and the secondary driver unit 20 are driven and controlled such that, in the event of an error and / or fault, the primary driver unit 18 switches from an active state to a high-impedance state, and the secondary driver unit 20 switches from a high-impedance state to an active state. Thus, in this error operating state, the primary driver unit 18 is in a high-impedance state, and the secondary driver unit 20 is in an active state. This advantageously allows the outputs 46, 48 of these driver units 18, 20 to be interconnected, which simultaneously prevents the influence of mutual interference between the driver units 18, 20, for example, in the form of a short circuit or superposition.

[0031] For switching and / or swapping between the primary driver unit 18 and the secondary driver unit 20, a calculation unit 30 is used in the present invention, which is electrically connected to the control pin 26 and the further control pin 28. The calculation unit 30 is therefore configured as a switching unit. Furthermore, the calculation unit 30 is configured as a monitoring unit. In the present invention, the calculation unit 30 is provided to monitor the operation of the primary driver unit 18 in normal operating conditions and, if a fault and / or failure of the primary driver unit 18 is identified, to deactivate the primary driver unit 18 by driving the control pin 26 with a corresponding switching signal, in particular by switching it to a high-impedance state, and to activate the secondary driver unit 20 by driving the further control pin 28 with a corresponding switching signal, in particular by switching it to an active state. For this purpose, the primary driver unit 18 can, for example, include an integrated diagnostic routine or self-diagnostic function, which identifies a corresponding internal error of the primary driver unit 18 and notifies the calculation unit 30 in order to trigger a switchover to the secondary driver unit 20. However, alternatively, it is also possible to automatically switch over to the secondary driver unit 20 in the event of a corresponding internal error of the primary driver unit 18. Furthermore, the control device may also include a separate switching unit for switching and / or interchanging between the primary and secondary driver units and a monitoring unit configured separately from the switching unit for monitoring the operation of the primary driver unit in normal operating conditions.

[0032] Finally, FIG. 3 shows an exemplary flow chart including the main method steps of an exemplary method for operating electric motor 12 using controller 10.

[0033] Method step 50 corresponds to a normal operating state. In this case, the primary driver unit 18 is provided for driving and controlling the power electronics 16 and is therefore in an active state. In contrast, the secondary driver unit 20 is in a high-impedance state and is therefore in a passive and / or inactive state. The operation of the primary driver unit 18 in the normal operating state is also monitored, for example by means of the computing unit 30.

[0034] In method step 52, a fault and / or failure of the primary driver unit 18 is identified, for example by means of the calculation unit 30. As a result, the primary driver unit 18 is replaced by the secondary driver unit 20. For this purpose, the primary driver unit 18 is deactivated, for example by driving the control pin 26 by the calculation unit 30 with a corresponding switching signal, in particular by switching it to a high impedance state, and the secondary driver unit 20 is activated, for example by driving the further control pin 28 by the calculation unit 30 with a corresponding switching signal, in particular by switching it to an active state.

[0035] Method step 54 corresponds to an error operating state. In this case, the secondary driver unit 20 is provided for driving the power electronics 16 and is therefore active. In contrast, the primary driver unit 18 is in a high-impedance state and is therefore passive and / or inactive. In this case, a warning message can be generated, for example, using the computing unit 30 and displayed to the vehicle occupants using corresponding output means (not shown).

[0036] 3 merely exemplarily illustrates a method for operating the electric motor 12 using the control device 10. In particular, individual method steps can be varied or additional method steps can be added. For example, a separate monitoring unit can be used to identify faults and / or failures of the primary driver unit 18. Also, an additional switching unit can be used for switching and / or swapping between the primary driver unit 18 and the secondary driver unit 20.

Claims

1. A control device (10) for operating an electric motor (12), in particular an electric motor (12) of a steering system (14), comprising: Power Electronics (16) and a primary driver unit (18) provided for driving and controlling said power electronics (16) under normal operating conditions; a secondary driver unit (20) connected in parallel to the primary driver unit (18) and adapted to drive and control the power electronics (16) in at least one error operating state in which a fault and / or failure of the primary driver unit (18) occurs; Equipped with the primary driver unit (18) and the secondary driver unit (20) each have an integrated tri-state function (22, 24), the secondary driver unit (20) being in a high impedance state under normal operating conditions; By having the tri-state function parts (22, 24), the primary driver unit (18) and the secondary driver unit (20) can be in an active state, an inactive state, and a high-impedance state, respectively. A control device (10).

2. The primary driver unit (18) and the secondary driver unit (20) are each configured as an integrated electronic circuit. The control device (10) of claim 1.

3. The primary driver unit (18) has a control pin (26) for controlling the tri-state function (22) of the primary driver unit (18). The control device (10) of claim 1.

4. The secondary driver unit (20) has a further control pin (28) for controlling the tri-state function part (24) of the secondary driver unit (20). The control device (10) of claim 1.

5. The control device (10) includes a calculation unit (30) configured to monitor the operation of the primary driver unit (18) under the normal operating condition, and to cause the primary driver unit (18) to be in the inactive state and the secondary driver unit (20) to be in the active state if a fault and / or failure of the primary driver unit (18) is identified. The control device (10) of claim 1.

6. An actuator assembly (32) comprising an electric motor (12) and a control device (10) according to claim 1.

7. A steering system (14) comprising at least one actuator assembly (32) according to claim 6.

8. A method for operating an electric motor (12) using a control device (10), in particular according to claim 1, comprising: The power electronics (16) are driven and controlled by a primary driver unit (18) under normal operating conditions; In an error operating state where a fault and / or failure of the primary driver unit (18) occurs, the secondary driver unit (20) is driven and controlled in parallel with the primary driver unit (18); The method, wherein the primary driver unit (18) and the secondary driver unit (20) each have an integrated tri-state function (22, 24), and the secondary driver unit (20) is in the high impedance state under normal operating conditions.

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