Electromechanical steering system and method for operating electromechanical steering system

Abstract

The invention relates to a method for operating an electromechanical steering system (1) in a motor vehicle, in which the steering system (1) comprises at least one actuator (2, 3) having at least one electric motor (21, 31), in which the at least one electric motor (21, 31) is connected to an electrical on-board power supply system of the motor vehicle via a DC bus (40), and in which the at least one electric motor (21, 31) is connected to the at least one actuator (2, 3) via a DC bus (40). 31) is operated in a motor mode or a generator mode depending on the driving situation. At least one control unit (22, 32) of the steering system (1) monitors an actual voltage level of the DC bus (40) with respect to exceeding a target voltage level predetermined value of the DC bus (40), the actual voltage level being reduced by converting electrical energy in at least one of the electric motors (21, 31) in the event that a first predetermined value is detected. The invention also relates to an electromechanical steering system (1) designed to operate according to such a method.

Description

Technical Field

[0001] This invention relates to a method for operating an electromechanical steering system in a motor vehicle, wherein the steering system includes at least one actuator having at least one electric motor, wherein the at least one electric motor is connected to the vehicle's electrical on-board power supply system via a DC bus (also referred to as a DC voltage bus), and wherein the at least one electric motor operates in motor mode or generator mode depending on driving conditions. The invention also relates to an electromechanical steering system including at least one actuator having at least one electric motor and at least one control unit, wherein the at least one electric motor operates in motor mode or generator mode depending on driving conditions. In particular, the steering system includes a steering actuator or a steering actuator and a feedback actuator as actuators. Specifically, the invention relates to electromechanical steering systems and methods for operating electromechanical steering systems with reduced energy feedback. Background Technology

[0002] In the prior art, for example, from EP 4273025 A1, there are methods for steer-by-wire systems that are electromechanical steering systems, as well as steer-by-wire systems having a feedback actuator as a first actuator and a steering actuator as a second actuator.

[0003] In motor vehicles, especially electric vehicles, the DC bus plays a crucial role in the distribution and management of electrical energy. The DC bus is an electrical line that supplies direct current (DC) from the vehicle battery to various power-consuming devices within the vehicle, particularly to the actuators of the steering system, and more specifically, to the steering actuators and / or feedback actuators. Depending on the power requirements of the respective power-consuming devices connected to the DC bus, the DC bus may also include DC / DC converters to provide different voltage levels. For the power-consuming devices connected to the DC bus to operate correctly, the supplied voltage must remain substantially constant.

[0004] Specifically, if the motor connected to the DC bus operates in generator mode, there is a problem of current generation. This is because the DC voltage source providing the operating voltage to the DC bus and / or the connection to the DC voltage source, especially the DC / DC converter, is unsuitable, or in newer vehicles that include not only a conventional starter battery (automotive battery), it is no longer suitable to receive such current due to cost reasons, etc. In particular, the motor of the steering system, and more specifically the motor of the feedback actuator of the steering system, also operates in generator mode in the normal steering system mode. Therefore, the current generated in this case may potentially cause damage to electronic components. Therefore, conventional vehicle batteries, especially those used in motor vehicles that only include an internal combustion engine, are generally suitable to receive such current. However, newer designs of onboard power supply systems with higher onboard power supply system voltages, and those in hybrid or electric vehicles utilizing the DC bus and providing operating voltage via the drive battery, are generally not designed to receive or feedback the generated current. This problem is also addressed in DE 102021205851A1, which proposes that if feedback would cause overvoltage in the onboard power supply system, unnecessary power-consuming devices should be switched on.

[0005] Against this backdrop, the object of the present invention is to provide an improved method for operating an electromechanical steering system and an improved electromechanical steering system. In particular, the object is to prevent damage caused by the generated current in the generator mode of the motor of the steering system's actuator.

[0006] In this context, the object of the present invention is to provide an improved method for operating an electromechanical steering system and an improved electromechanical steering system. In particular, the object is to prevent current that could cause a critical overvoltage from flowing back to the DC bus supplying energy to the actuators of the steering system. Summary of the Invention

[0007] To achieve this objective, a method for operating an electromechanical steering system and an electromechanical steering system are provided according to exemplary embodiments. Other advantageous modifications of the invention are described in the specification and preferred embodiments and are illustrated in the accompanying drawings.

[0008] The proposed solution provides a method for operating an electromechanical steering system, particularly a steer-by-wire type steering system, in a motor vehicle. This steering system includes at least one actuator with at least one electric motor, which is connected via a DC bus to the vehicle's onboard electrical power supply system. Depending on driving conditions, the at least one electric motor operates in either motor mode or generator mode. It is also specified that at least one control unit of the steering system monitors the actual voltage level of the DC bus for any deviation from a predetermined target voltage level. If a deviation from the target voltage level is detected, the actual voltage level is reduced by converting electrical energy in the at least one electric motor. Therefore, the current generated by the actuator connected to the DC bus can advantageously be converted into energy in the at least one electric motor of the steering system. Specifically, the phase resistance of the at least one electric motor of the steering system is used to compensate for the regenerative DC current in the DC bus.

[0009] At least one motor is specifically designed as a three-phase motor, and more particularly as a permanent magnet synchronous motor. By directly converting the current in the motor of the steering system, damage caused by the current fed to the DC bus is advantageously largely avoided. This conversion is advantageously kept largely imperceptible to the vehicle user and, more advantageously, has no negative impact on the steering behavior of the motor vehicle and no negative impact on the steering feel of the vehicle user. The voltage level on the DC bus can be, in particular, 12V or 48V (V: volts). Other voltage levels, especially even greater than 48V, can also be provided.

[0010] Specifically, the steering system is specified to include a steering actuator with an electric motor as the actuator. The steering actuator is advantageously designed to convert detected steering commands into wheel steering angles of the steering wheels. Additionally, particularly in the case of a steer-by-wire steering system, the steering system may be specified to include a feedback actuator with an electric motor as an additional actuator, wherein the feedback actuator is specifically designed to act on the steering handle via the steering shaft. The electric motors of the steering actuator and / or the feedback actuator may each have redundant designs. Specifically, in the normal mode of the steering system, the operation of these electric motors, particularly the electric motor of the feedback actuator, results in the generation of current, which may lead to the above-described deviation from the predetermined target voltage level of the DC bus. However, this current is advantageously "consumed" directly by at least one electric motor of the steering system, i.e., energy conversion. However, advantageously, the generated current can be energy converted in at least one electric motor of the steering system, and particularly also through an additional actuator connected to the DC bus, which is not specifically part of the steering system.

[0011] According to an advantageous improvement of the method, for different actual voltage levels exceeding the target voltage level, different actuations of at least one motor associated with the corresponding actual voltage level are advantageously performed. Specifically, different measures are defined for the manner in which electrical energy is converted in the at least one motor. Therefore, it is specifically stipulated that the steering system includes multiple motors, wherein a particular motor of the steering system is advantageously actuated according to the degree of deviation between the actual voltage level and the target voltage level for energy conversion of the generated current, particularly ensuring that the target voltage level is kept as constant as possible, and that the steering behavior and steering feel perceived by the vehicle user are not adversely affected.

[0012] Another advantageous embodiment specifies that, upon detecting an excess of a target voltage level by a second predetermined value, wherein the second predetermined value is lower than a first predetermined value, a DC bus control unit associated with the DC bus controls a reduction in the actual voltage level. This advantageously utilizes the fact that DC buses are typically designed to absorb excesses of the target voltage level to a very small extent, particularly when the resulting current is less than 10 A (A: ampere). Advantageously, in cases of a small excess of the target voltage level, actuation of at least one motor of the steering system for the energy conversion of these currents can be suppressed.

[0013] More advantageously, the DC bus has a redundant design and includes a DC A side and a DC B side, wherein the DC B side takes over the voltage supply in the event of a failure on the DC A side. The tolerance for the deviation between the actual voltage level and the target voltage level is lower for the DC A side than for the DC B side. Furthermore, the deviations between the actual voltage level and the target voltage level for both the DC A and DC B sides are defined by different predetermined values ​​used to trigger energy conversion in at least one motor. Specifically, the DC A side, particularly the control unit assigned to the DC A side, controls the reduction of the actual voltage level based on the generated current, particularly the current generated by the motor of the feedback actuator, and more particularly, the generated current with a maximum value of up to 10A. Therefore, it is advantageous to distinguish between a normal mode and a special mode, wherein in the normal mode, the supply voltage is provided via the DC A side, and wherein in the normal mode, damage to power-consuming devices connected to the DC bus should be avoided, and wherein in the special mode, at least one basic function of the vehicle remains prioritized.

[0014] According to another particularly advantageous embodiment, the steering system includes a plurality of actuators, each of which is assigned a corresponding control unit. Each of these control units advantageously monitors the actual voltage level of the DC bus with respect to a predetermined value exceeding a target voltage level. Specifically, for each control unit, different deviations between the specified actual voltage level and the target voltage level trigger an actuation to reduce the actual voltage level, particularly to bring the actual voltage level closer to the target voltage level. Advantageously, the actual voltage level is recorded in real time. More advantageously, the detection of the actual voltage level between control units is synchronized, with the DC bus advantageously serving as an indirect communication channel. Specifically, the applied DC voltage itself is used as a "communication channel" because it is measured in real time by all relevant control units (ECUs: Electronic Control Units) on the DC bus. Therefore, advantageously, direct private CAN communication (CAN: Computer Local Area Network) is not required to enable interaction between control units. Thus, each control unit of the actuator unit advantageously monitors only precisely the exceedance of the actual voltage value specifically specified for the corresponding control unit, and triggers a control command specified for the corresponding control unit in the event of an exceedance. This method is advantageously error-resistant and very robust in this manner.

[0015] At least one motor of the steering system is preferably controlled by a control unit, specifically by a control unit using vector control, wherein a first controller of the control unit, particularly a PI controller, influences the d-vector of the rotor-related d / q system for the at least one motor, having an associated current I_d, and the q-vector of the associated current I_q. The d-vector of the rotor-related d / q system, and thus the current I_d of the first motor, is advantageously adjusted for the energy conversion of the resulting current applied to the DC bus.

[0016] For such vector control, in particular, the mathematical transformation from a stator-dependent three-phase system to a rotor-dependent d / q system is performed in a known manner by means of the Clarke transform and subsequently the Park transform, where the d-vectors and q-vectors are orthogonally aligned relative to each other. Following the conventions in vector control, the q-vector is used to set the torque to be supplied, while the d-vector affects the flux density.

[0017] Therefore, the d-vector of the rotor-related d / q system of the electric motor for the steering system is adjusted, particularly increased, for energy conversion and to reduce the actual voltage level exceeding the target voltage level. Advantageously, the d-vector is adjusted in such a way that the actual voltage level is reduced back to the target voltage level, and in particular, that the resulting current applied to the DC bus is completely or at least almost completely converted in the electric motor of the steering system. Specifically, the d-vector and thus the I_d current are adjusted by means of a controller for vector control. The q-vector and thus the I_q current advantageously remain unaffected, so that during the operation of the steering system, no torque perceptible to the vehicle user is generated due to the conversion of the resulting current applied to the DC bus.

[0018] As at least one actuator having at least one electric motor, the steering system preferably includes a feedback actuator acting on the steering handle via a steering shaft and having a first electric motor, and a steering actuator acting on the steering wheels of the motor vehicle via a steering mechanism and having a second electric motor. Specifically, the second electric motor of the steering actuator is actuated to convert the generated energy, which would increase the actual voltage level above a target voltage level. Therefore, if an excess of at least a first predetermined value is detected, the actual voltage level is advantageously reduced by converting electrical energy in the second electric motor. In particular, this embodiment utilizes the fact that during operation of the motor vehicle, the electric motor of the steering actuator mainly operates in motor mode and almost never in generator mode, while the electric motor of the feedback actuator typically operates in generator mode. Avoiding the conversion of electrical energy in the first electric motor of the feedback actuator also advantageously keeps the pulsation in the first electric motor low, resulting in advantageously avoiding or at least minimizing adverse effects on the driver's steering feel.

[0019] Advantageously, the second motor of the steering actuator has a redundant design and has an independently actuable A side and an independently actuable B side, wherein, upon detection of an excess of at least a first predetermined value, the actual voltage level is reduced by converting electrical energy on the A side of the second motor. According to an advantageous improvement, upon detection of an excess of at least a third predetermined value, wherein the third predetermined value is greater than the first predetermined value, the actual voltage level is reduced or further reduced by converting electrical energy on the B side of the second motor. Such a cascaded chain of measures is advantageously defined to return the actual voltage level, which significantly exceeds the target voltage level, to the target voltage level. In particular, it is specified that the A side and the B side can be considered as two completely separate systems, wherein the A side is supplied with voltage via DC A side, and the B side is supplied with voltage via DC B side.

[0020] As another advantageous improvement, it is specified that if an excess of at least a second predetermined value is detected, where the second predetermined value is greater than the first predetermined value, the actual voltage level is reduced by additionally converting electrical energy in the first motor, i.e., the motor of the feedback actuator. Through these additional measures, particularly the different actuation of the A and B sides of the steering actuator motor and / or the actuation of the first motor of the feedback actuator, the limiting of the damping torque provided by the steering actuator motor can be advantageously prevented. Specifically, it is therefore specified that when the actual voltage level exceeds the target voltage level, the A side of the steering actuator motor is actuated first, then the motor of the feedback actuator is actuated, followed by the B side of the steering actuator motor for the conversion of excess electrical energy.

[0021] To address the aforementioned problem, an electromechanical steering system, particularly a steer-by-wire type steering system, is proposed. This system includes at least one actuator having at least one electric motor and at least one control unit, wherein the at least one electric motor can operate in either electric motor mode or generator mode depending on driving conditions. This steering system is designed to operate based on a method devised according to the invention. The features and advantages described in conjunction with the described method also apply accordingly to the proposed steering system.

[0022] An advantageous embodiment of this steering system specifies that it includes a feedback actuator acting as a first actuator via a steering shaft on a steering handle, and a steering actuator acting as a second actuator via a steering mechanism on the steering wheels of the motor vehicle. In this case, the first electric motor is the electric motor of the feedback actuator, a first control unit is assigned to the first electric motor, and the second electric motor is the electric motor of the steering actuator, a second control unit is assigned to the second electric motor, wherein the first and second control units can in particular be control units included in the power units of the respective electric motors. Specifically, this embodiment of the steering system utilizes the fact that during operation of the motor vehicle, the electric motor of the steering actuator operates primarily in electric motor mode and almost never in generator mode, while the electric motor of the feedback actuator typically operates in generator mode. Advantageously, when operating the steering system in the motor vehicle, the driver will not feel any additional pulsations in the first electric motor and therefore not in the feedback actuator. This means that the steering feel will advantageously remain unchanged.

[0023] Specifically, the first and second motors are each designed as three-phase motors, and more specifically, as permanent magnet synchronous motors. The first and second control units are advantageously directly assigned to their respective motors. However, the first and second control units can, in particular, be comprised of a higher-level control unit. The first and second motors are advantageously controlled by means of vector control, wherein each motor is advantageously assigned a corresponding controller, particularly a PI controller.

[0024] The PI controller advantageously has a reference input that, when the first motor operates in generator mode, depends on the rotational speed of the corresponding motor. Advantageously, the current actually supplied in the DC bus for supplying energy to the motor in the steering system is calculated based on the dq voltage output of the PI controller and information related to the dq current. The PI controller is advantageously designed to adjust the Id current required to reduce the current regenerated by the motor in the DC bus in generator mode. This Id current is advantageously added to the Id reference output of the second control system for the second motor. The second motor then operates at a sum of Id_ref, and thus the current generated in generator mode is converted into energy, advantageously with almost no impact on the torque supplied by the motor. Attached Figure Description

[0025] Other advantageous details, features, and design details of the invention will be described in more detail with reference to the exemplary embodiments shown in the accompanying drawings, in which:

[0026] Figure 1 A simplified perspective view of an exemplary embodiment of an electromechanical steering system designed according to the present invention is shown; and

[0027] Figure 2 A simplified block diagram is shown to illustrate an exemplary embodiment of a method for operating an electromechanical steering system designed according to the present invention.

[0028] In the various figures, the same parts usually have the same reference numerals, and therefore in some cases each part is described in conjunction with only one figure in the figures. Detailed Implementation

[0029] Figure 1An exemplary embodiment of an electromechanical steering system 1 designed according to the present invention is depicted in a simplified manner, and in this exemplary embodiment, the electromechanical steering system 1 is designed as a steer-by-wire type steering system. In this exemplary embodiment, the steering system 1 includes a first actuator 2 having a first electric motor 21 and a first control unit 22. The steering system 1 also includes a second actuator 3 having a second electric motor 31 and a second control unit 32. The first actuator 2 is a feedback actuator that acts via the steering shaft 4 of the steering system 1 on a steering handle 5 that is rotatably fixed to the steering shaft 4, and the first electric motor 21 is correspondingly a feedback actuator motor. The second actuator 3 of the steering system 1 is a steering actuator that acts via a steering device 6 on the steering wheels 8 of a motor vehicle, and the second electric motor 31 is correspondingly a steering actuator motor. Both motors 21 and 31 are three-phase motors, particularly permanent magnet synchronous motors.

[0030] The first electric motor 21 operates in motor mode depending on driving conditions, specifically to generate an active counteracting action against the steering input applied by the driver to the steering handle 5, or in generator mode, particularly when the steering motion applied by the driver is subject to a certain steering resistance. The first actuator 2, having the first electric motor 21, is therefore specifically designed to apply torque or steering resistance torque to the steering shaft 4, specifically for transmitting steering feel perceptible to the driver of the motor vehicle.

[0031] The second electric motor 31 can, in principle, operate in both electric motor mode and generator mode. The generator mode of the second electric motor 31 occurs relatively less frequently, for example, when different wheel steering angles are applied externally to the steering wheel 8 due to an obstacle. In this case, especially when a steering command is detected, particularly when the steering movement applied by the driver via the steering handle 5 must be converted into the corresponding wheel steering angle of the steering wheel 8, the electric motor mode of the second electric motor 31 is required. To convert the steering command into the wheel steering angle of the steering wheel 8, the second actuator 3 acts on the steering wheel 8 via the steering mechanism 6.

[0032] Specifically, in this exemplary embodiment, a second motor 31, which specifies a second actuator 3, acts on a main shaft drive mechanism 62 via a drive belt 63. The main shaft drive mechanism is operatively connected to a connecting rod 61 formed as a rack. Proper actuation of the second motor 31 drives the main shaft drive mechanism 62 to convert steering commands into steering motion of the steering wheels 8. In this case, the second actuator acts on the connecting rod 61 via the main shaft drive mechanism 62 driven by the second motor 31, and thus triggers steering motion of the steering wheels 8 of the motor vehicle, wherein, in this exemplary embodiment, the steering wheels 8 are connected to the connecting rod 61 in a known manner via tie rods 9. Each tie rod 9 is itself connected to a steering wheel 8 in a known manner via a steering knuckle.

[0033] The first electric motor 21 and the second electric motor 31 of the steering system 1 are connected to the vehicle's electrical on-board power supply system via a DC bus 40, wherein other power-consuming devices (in Figure 1 (Not explicitly shown) Specifically, the DC / DC converter 50 is also connected to the DC bus 40 via the DC bus 40. Here, the energy required for the motor mode of motors 21 and 31 is provided via the DC bus 40.

[0034] The first motor 21 and the second motor 31 are actuated by control units 22 and 32, respectively, assigned to motors 21 and 31, based on vector control. For this purpose, the stator-dependent three-phase system is transformed into a rotor-dependent d / q system in a known manner, which is performed using the Clarke transformation and subsequently the Park transformation. The resulting d and q vectors for controlling the respective motors 21 and 31 are then adjusted accordingly by means of PI controllers included in the respective control units 22 and 32 to implement control commands. Typically, the torque provided by the respective motors 21 and 32 is controlled by adjusting the q value, while the d value affects the magnetic flux density.

[0035] The first electric motor 21 and the second electric motor 31 operate in either motor mode or generator mode depending on driving conditions, with the generator mode of the second electric motor 31 rarely occurring. During operation of the motor vehicle, the first control unit 22 and the second control unit 32 of the steering system 1 monitor whether the actual voltage level of the DC bus 40 exceeds a predetermined target voltage level of the DC bus 40. In this exemplary embodiment, in order to reduce the actual voltage level to the target voltage level, it is further specified that when the second control unit 32 identifies that the actual voltage level of the DC bus 40 has exceeded the first predetermined target voltage level of the DC bus 40, electrical energy will be converted in the second electric motor 31.

[0036] Specifically, an overshoot of such a target voltage level in the DC bus 40 may occur when the first motor 21 is operating in generator mode. Then, the second control unit 32 controls the second motor 31 in such a way, by means of a PI controller included in the second control unit 32, that the second motor 31 converts the current generated by the first motor 21 in generator mode into energy.

[0037] If the first motor 21 is now operating in generator mode, causing the actual voltage level to exceed a first predetermined value of the target voltage level, the PI controller of the second control unit 32 actuates the second motor 31 in such a way that the I_d current specified for the second motor 31 as part of vector control is adjusted, specifically increased, by appropriately adjusting the d vector. Thus, the second motor 31 converts the current generated by the first motor 21 in generator mode, which has led to an undesirable increase in the actual voltage level. As a result of adjusting only the d vector and not the q vector, the adjusted current I_d advantageously does not affect the behavior of the steering system 1 as perceived by the vehicle user during steering. Therefore, the current generated by the first motor 21 is advantageously "consumed" in the second motor 31, and therefore advantageously does not burden the DC bus 40 and further to other electronic components connected to the DC bus 40. In particular, different values ​​are specified, wherein the actual voltage level is monitored to at least exceed the target voltage level.

[0038] refer to Figure 2 The block diagram shown illustrates in more detail the electromechanical steering system used to operate motor vehicles, particularly... Figure 1 An advantageous embodiment of the method of the steer-by-wire type steering system 1 shown.

[0039] Again, the steering system 1 is a steer-by-wire type steering system, comprising a feedback actuator 2 that acts on the steering handle via the steering shaft and has a first electric motor 21, and a steering actuator 3 that acts on the steering wheels of the vehicle via the steering mechanism and has a second electric motor 31. The second electric motor 31 of the steering actuator is redundantly designed, having an independently actuable A side and an independently actuable B side. The A side and B side can be configured as independent motors, such that the second electric motor 31 effectively comprises two motors (A side and B side), or it can be configured as independently actuable winding groups (A side and B side) of the second electric motor 31. The first electric motor 21 and the second electric motor 31 are each assigned a control unit 22, 32. Here, the respective electric motors 21, 31, and especially the A side and B side of the respective electric motors 21, 31, are controlled by the assigned control units 22, 32 according to field-oriented control, i.e., vector control.

[0040] Furthermore, in this exemplary embodiment, the DC bus 40 is also specified to have a redundant design and has a DC A side and a DC B side, wherein the DC B side takes over the voltage supply in the event of a failure of the DC A side. The tolerance for the deviation between the actual voltage level and the target voltage level is defined as follows: the tolerance for the DC A side is smaller than the tolerance for the DC B side. For this reason, different predetermined values ​​are stored for the deviation between the actual voltage level and the target voltage level on both the DC A and DC B sides to trigger actions that trigger feedback when the actual voltage level exceeds the target voltage level. The triggering of actions when the actual voltage level of the DC bus 40 exceeds the target voltage level of the DC bus 40 is described below using the DC A side as an example.

[0041] In this exemplary embodiment, the slight overshoot of the target voltage level, specifically caused by the current of up to 10A generated by the first motor 21 in generator mode, is reduced by the DC bus control unit 45, which is responsible for the energy management of the DC bus, and thus reduces the actual voltage level to bring it closer to the target voltage level.

[0042] Additionally, the second control unit 32 of the steering system monitors the current actual voltage level of the DC bus 40 regarding a first predetermined value exceeding the target voltage level of the DC bus 40. If the first predetermined value is detected, the second control unit 32 actuates side A of the second motor 31 to convert electrical energy on side A of the second motor 31, thereby reducing the actual voltage level back to the target voltage level in the DC bus 40. The first predetermined value can be, in particular, between 0.1V and 10V (V: volts), depending specifically on the voltage level applied to the DC bus 40. If the target voltage level on the DC bus 40 is, for example, 12V, then the first predetermined value can be, in particular, 2V, such that side A of the second motor 31 is actuated accordingly at an actual voltage level of 14V.

[0043] In order to convert the energy of the current that increases the actual voltage level, the d-vector of the rotor-related d / q system on the A side of the second motor 31, and therefore the current I_d on the A side of the motor 31, is adjusted to reduce the actual voltage level back to the target voltage level. Specifically, for this purpose, in addition to the actual voltage based on the actual voltage level of the DC bus 40, it can be specified that when it is identified that the actual voltage level has exceeded a first predetermined value of the target voltage level, a target voltage based on the target voltage level of the DC bus 40 is applied to the input of the PI controller of the second control unit 32. Taking into account the actual voltage and target voltage applied to the PI controller, the voltages U_d and U_q currently applied to the dq voltage output of the PID controller, and the currents I_d and I_q fed back as part of vector control, it is advantageous to determine that the current I_d needs to be adjusted, and a correspondingly adjusted current I_d is provided. This is necessary, on the one hand, so that the A side of the second motor 31 can be operated according to the detected steering command, and on the other hand, the excess electrical energy on the A side of the second motor 31 is converted to reduce the actual voltage level to the target voltage level.

[0044] Furthermore, the first control unit 21 monitors the actual voltage on the DC bus 40 to ensure it exceeds a second predetermined value relative to the target voltage. In this case, the second predetermined value is greater than the first predetermined value and can be specifically set to be between 1V and 18V, tailored to the specific system. This monitoring is performed independently of the monitoring by the second control unit 32. Since the first predetermined value is also exceeded when the actual voltage exceeds the second value specified for the target voltage level or is greater, the second motor 31 is actuated on side A by the second control unit 32, as described above. However, the first motor 21 is now actuated by the first control unit in a similar manner to assist in reducing the actual voltage level.

[0045] For example, the nominal voltage level can be specified as 13.8V. In this example, the first predetermined value is 0.2V, and the second predetermined value is 2.2V. If the actual voltage level is therefore 14V or higher, the A side of the second motor 31 is actuated to convert electrical energy and reduce the actual voltage level to the target voltage level. If the actual voltage level is 16V or higher, it is advantageous to further actuate the first motor 21 to convert the energy generated by the current that increases the actual voltage level, specifically until the actual voltage level drops below 16V again. If the actual voltage level drops further below 14V, the actuation of the A side of the second motor 31 for "consuming" excess energy also advantageously ends.

[0046] Alternatively, it may be specified that the second control unit 32, assigned to the B side of the second motor 31 on the DC bus 40, monitors the actual voltage exceeding a third predetermined value of the target voltage, wherein this third predetermined value is greater than a second predetermined value. This third predetermined value can be specifically set to have a value between 10V and 20V. This monitoring is performed independently of the monitoring of the first predetermined value by the second control unit 32 assigned to the A side of the second motor 31, and independently of the monitoring of the second predetermined value by the first control unit 22 assigned to the first motor 21. At an actual voltage level exceeding the target voltage level by at least the set third value, the A side of the second motor 31, the first motor 21, and the B side of the second motor thus operate with an adjusted value of current I_d to reduce the actual voltage level and return it to the target voltage level. Therefore, for different actual voltage levels exceeding the target voltage level, different actuations of the motors 21 and 31 are performed corresponding to the respective actual voltage levels. The actual voltage level is detected in real time by the control units 22 and 32, wherein this detection is synchronized between the control units 22 and 32.

[0047] The exemplary embodiments shown in and described in conjunction with the accompanying drawings are used to illustrate the invention and are not intended to limit the invention.

[0048] List of reference numerals

[0049] 1. Steering System

[0050] 2 First actuator

[0051] 21 First Electric Motor

[0052] 22 First Control Unit

[0053] 3 Second Actuator

[0054] 31 Second Electric Motor

[0055] 32 Second Control Unit

[0056] 4. Steering shaft

[0057] 5. Steering handle

[0058] 6. Steering mechanism

[0059] 61 Connecting rod (rack)

[0060] 62 Spindle drive mechanism

[0061] 63. Transmission belt

[0062] 8 Steering wheels

[0063] 9. Tie rod

[0064] 10 signal lines

[0065] 40DC bus

[0066] 45DC bus control unit

[0067] 50DC / DC converter

Claims

1. A method for operating an electromechanical steering system (1) in a motor vehicle, wherein, The electromechanical steering system (1) includes at least one actuator (2, 3) having at least one electric motor (21, 31), wherein the at least one electric motor (21, 31) is connected to the vehicle's electrical on-board power supply system via a DC bus (40), and wherein the at least one electric motor (21, 31) operates in motor mode or generator mode depending on driving conditions. The system is characterized in that at least one control unit (22, 32) of the electromechanical steering system (1) monitors the actual voltage level of the DC bus (40) with respect to a predetermined value exceeding a target voltage level, wherein, upon detecting an exceedance of the first predetermined value, the actual voltage level is reduced by converting electrical energy in at least one of the at least one electric motor (21, 31).

2. The method according to claim 1, characterized in that, For different actual voltage levels exceeding the target voltage level, perform different actuations of the at least one motor (21, 31) associated with the corresponding actual voltage level.

3. The method according to claim 1 or 2, characterized in that, If a second predetermined value is detected that the target voltage level exceeds the target voltage level, the DC bus control unit (45) associated with the DC bus (40) controls the reduction of the actual voltage level, wherein the second predetermined value is lower than the first predetermined value.

4. The method according to any one of the preceding claims, characterized in that, The DC bus (40) has a redundant design and has a DC A side and a DC B side, wherein, in the event of a failure on the DC A side, the DC B side takes over the voltage supply, wherein the tolerance of the deviation between the actual voltage level and the target voltage level on the DC A side is lower than the tolerance of the DC B side, and wherein, for the deviation between the actual voltage level and the target voltage level on the DC A side and the DC B side, different predetermined values ​​are defined for triggering the conversion of electrical energy in the at least one motor (21, 31).

5. The method according to any one of the preceding claims, characterized in that, The electromechanical steering system (1) includes a plurality of actuators (2, 3), wherein each actuator (2, 3) is assigned a corresponding control unit (22, 32), wherein each of the control units (22, 32) monitors the actual voltage level of the DC bus (40) with respect to a predetermined value exceeding the target voltage level of the DC bus (40), wherein for each of the control units (22, 32) a different deviation between the actual voltage level and the target voltage level is specified, the different deviation triggering an actuation to reduce the actual voltage level.

6. The method according to any one of the preceding claims, characterized in that, The at least one motor (21, 31) is controlled by a control unit (22, 32) by means of vector control, wherein the d vector of the rotor-related d / q system of the at least one motor (21, 31) having an associated current I_d and the q vector having an associated current I_q are influenced by a first controller in the control unit (22, 32), wherein the d vector of the rotor-related d / q system of the at least one motor (21, 31) is adjusted for the conversion of electrical energy.

7. The method according to any one of the preceding claims, characterized in that, As at least one actuator (2, 3) having at least one electric motor (21, 31), the electromechanical steering system (1) includes a feedback actuator (2) and a steering actuator (3), the feedback actuator acting on the steering handle (5) via a steering shaft (4) and having a first electric motor (21), and the steering actuator acting on the steering wheel (8) of the motor vehicle via a steering device (6) and having a second electric motor (31).

8. The method according to claim 7, characterized in that, If an actual voltage level is detected to exceed at least the first predetermined value, the actual voltage level is reduced by converting electrical energy in the second motor (31).

9. The method according to claim 7 or 8, characterized in that, The second motor (31) of the steering actuator (3) has a redundant design and has an A side that can be actuated independently and a B side that can be actuated independently, wherein, in the event that an excess of at least the first predetermined value is detected, the actual voltage level is reduced by converting electrical energy on the A side of the second motor (31).

10. The method according to claim 9, characterized in that, If a value exceeding at least a third predetermined value is detected, the actual voltage level is reduced by converting electrical energy on the B side of the second motor (31), wherein the third predetermined value is greater than the first predetermined value.

11. The method according to any one of claims 7 to 10, characterized in that, If an actual voltage level is detected to exceed at least a second predetermined value, the actual voltage level is reduced by further converting electrical energy in the first motor (21), wherein the second predetermined value is greater than the first predetermined value.

12. An electromechanical steering system (1), the electromechanical steering system comprising at least one actuator (2, 3), the at least one actuator having at least one electric motor (21, 31) and at least one control unit (22, 32), wherein, The at least one electric motor (21, 31) is capable of operating in motor mode or generator mode depending on driving conditions, characterized in that the electromechanical steering system (1) is designed to operate according to the method of any one of claims 1 to 11.

13. The electromechanical steering system (1) according to claim 12, characterized in that, The electromechanical steering system (1) is a steer-by-wire type steering system.

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