Method for controlling a steering system, control unit, steering system and motor vehicle

Abstract

The underlying invention relates, in particular, to a method for controlling an electrically assisted steering system (1) of a motor vehicle, wherein the steering system (1) comprises at least two steered wheels (5) and at least one electric motor (7) at least for assisting a steering action of at least one of the steered wheels (5), wherein the electric motor (7) is connected for its energy supply via at least two, in particular three, line phases to an energy source, wherein the method comprises the following steps carried out by a control unit (3): - determining whether there is an existing or imminent occurrence of a generator mode of the electric motor (7), in which the electric motor (7) operates as a generator; and - if an existing or an imminent occurrence of a generator mode is determined, short-circuiting of at least two of the line phases of the electric motor (7).

Description

[0001] Method for controlling a steering system, control unit, steering system and motor vehicle

[0002] The underlying invention relates to a method for controlling a steering system, a control unit, a steering system and a motor vehicle.

[0003] Motor vehicles, such as electric cars, can incorporate so-called electrically operated or electrically assisted steering systems. In these systems, a steering movement is assisted or performed by an electric motor. There is also a trend toward using so-called steer-by-wire systems, in which the steering system is controlled entirely electronically and via electric motors assigned to the wheels to be steered.

[0004] DE 10 2016 209 834 A1 describes a steering system with an electric motor controlled by a control unit via an inverter. It is disclosed that the internal resistance of a battery is detected to operate the electric motor. If an increase in internal resistance is detected and the electric motor is operating as a generator, the electric motor is controlled to apply a motor damping force to prevent overvoltages caused by generator operation.

[0005] In addition, US 8,571,757 B2 discloses an electromechanical steering system with an electric motor, wherein a short-circuiting of the phases of the electric motor is provided as a protective measure, in particular to prevent rotation of the motor when a fault is detected and / or in the event of an interruption of the power supply.

[0006] It is an object of the underlying invention to provide a novel and improved method for controlling a steering system in which a steering movement or action is at least assisted by one or more electric motors. Furthermore, a corresponding control unit, a steering system, and a motor vehicle are to be provided. This object is achieved by the independent claims. Further embodiments emerge from the dependent claims and the following description.

[0007] The invention is based on the finding that in an electrically assisted or electric steering system with a steering actuator having an electric motor for assisting or executing a steering movement of a motor vehicle, high voltage peaks can occur in the power or on-board electrical system of the motor vehicle during damping or generator operation (or generator mode), in which the electric motor operates as a generator. Such voltage peaks can ideally be compensated or absorbed, for example, by one or more power consumers, e.g., a storage battery. However, such voltage peaks cannot be compensated by power consumers in all operating situations.If, for example, the charge level of a battery used as a consumer is comparatively high, it may happen that feedback current from the electric motor operating in generator mode cannot be compensated and unwanted voltage peaks occur for the power or on-board network.

[0008] The underlying invention is particularly applicable to electrically assisted steering systems, but is not limited to such.

[0009] An electrically assisted steering system of a motor vehicle with at least two steered wheels can, for example, comprise at least one or more electric motors, in particular servo drives, for controlling the steering angle of the wheels. Permanent magnet synchronous motors (PMSM), for example, can be used as steering actuators, with associated electric motors being controllable using pulse width modulation (PWM).

[0010] During dynamic steering maneuvers, such steering systems may encounter situations in which external kinetic energy is introduced, for example, caused by the vehicle's driving motion and inertia. This causes the steering actuator's electric motor(s) to operate in generator mode, thus damping the introduced energy. In generator mode, the steering actuator's electric motor feeds power back into the vehicle's electrical system or on-board power supply. The feedback current increases the voltage in the vehicle's electrical system or on-board power supply.

[0011] If there is no electrical consumer in the vehicle's power or on-board network that can consume the feedback current generated by the steering actuator quickly enough, the voltage may rise to a critical level, which may cause a common-mode fault, e.g. an overvoltage, for all actuators connected to the power or on-board network.

[0012] The underlying invention is based on this finding and provides a solution with which such voltage peaks can be comparatively reliably avoided in an electric steering system, preferably in an electrically assisted steering system.

[0013] According to one embodiment of the invention, a method for controlling an electric, in particular an electrically assisted, steering system of a motor vehicle is provided. The steering system may comprise at least two steered wheels, ie, two or more steered wheels, wherein the steered wheels and the steering system may be provided or used, for example, as a steered front axle of a motor vehicle, such as an electric car.

[0014] The steering system comprises at least one electric motor, e.g., a PMSM, designed to at least assist a steering action of at least one of the steered wheels. The expression "at least assist a steering action" is intended to mean that the operation of the electric motor assists at least one steering action, which includes, but is not limited to, both fully electric steering and motor-assisted steering.

[0015] To supply power to the electric motor of the steering system, it is connected to an energy source, in particular a power supply unit, via at least two, in particular three, line phases. The power supply unit can, for example, comprise an inverter.

[0016] The method comprises the following steps, carried out by a control unit: - Determining whether there is an existing or imminent occurrence of generator operation of the electric motor, in which the electric motor operates as a generator, and

[0017] - if an existing or imminent occurrence of generator operation is detected, short-circuit at least two of the line phases, preferably all line phases, of the electric motor.

[0018] In the usual sense of electrical engineering, a line phase is understood to be a connection or connecting conductor designed to supply current and energy to a consumer.

[0019] By short-circuiting the electric motor's line phases, feedback current can be reliably prevented from being fed back into the power or vehicle electrical system, thus avoiding associated voltage spikes. Short-circuiting can also generate a braking or damping torque, which can be used to dampen torques acting on the steering system, for example, during dynamic steering maneuvers.

[0020] Determining whether generator operation is occurring or whether generator operation is about to occur is also referred to herein as determining generator operation.

[0021] In embodiments, determining generator operation may be based on one or more operating parameters of the steering system and / or the motor vehicle. For example, the control unit may have access to, determine, or ascertain operating conditions of the steering system and / or the motor vehicle and use these operating conditions to determine whether the electric motor is in generator operation (or mode) or whether generator operation is imminent or likely.

[0022] According to embodiments, the control unit can analyze or monitor one or more operating parameters and determine the probability of generator operation occurring or of impending generator operation. For example, the occurrence of generator operation can be determined at least partially based on one or more comparison values ​​characteristic of generator operation, which can be stored, for example, in a database or a memory connected to the control unit.

[0023] According to embodiments, the control unit can determine the occurrence of generator operation at least partially based on a model, for example, a trained model that can be part of an artificial intelligence system implemented in the control unit. The model can be trained based on a variety of operating conditions of the steering system and / or motor vehicle used.

[0024] In some embodiments, generator operation can be determined based on a current measured in at least one of the line phases. For example, a current flowing back from the electric motor indicates generator operation. Impending generator operation can be determined, for example, based on the current consumption of the electric motor, in particular a current profile, a change in the current profile, and / or a rate of change of the current profile, and / or using other parameters. If, for example, the current consumption of the electric motor decreases according to a predetermined current curve that is characteristic of the occurrence of generator operation, it is possible to determine the occurrence of impending generator operation.

[0025] In some embodiments, the short-circuiting of the line phases can be carried out depending on the respective possible current consumption capacity of consumers in the power supply or on-board network of the motor vehicle. If, for example, electrical consumers are active or present in the power supply or on-board network that can absorb the feedback current generated by generator operation, so that undesirable voltage peaks do not occur, short-circuiting of the line phases is not absolutely necessary. Accordingly, the control unit can be configured to determine the respective possible current consumption capacity of consumers in the power supply or on-board network of the motor vehicle. If the control unit determines that the current consumption capacity of the consumers is sufficient to absorb the feedback current generated by generator operation, the control unit can refrain from short-circuiting the line phases. Possible consumers include, for example:one or more accumulators, a ventilation and / or air conditioning system of the motor vehicle, etc.

[0026] If the vehicle's on-board or power system does not have a rechargeable battery or other electrical consumer with which feedback current can be absorbed relatively quickly to avoid voltage peaks, the line phases are short-circuited when generator operation is detected. This is particularly advantageous in an electric drive in which the current to operate the electric motor(s) is supplied by an inverter from a high-voltage network (e.g. rechargeable battery), and the inverter is not able to process feedback current. By short-circuiting the line phases with one another, the electric motor in generator mode generates a braking or damping torque without current flowing back into the power system or on-board network, thus avoiding voltage peaks in the power system or on-board network.

[0027] If the measurement or monitoring of the current assigned to the electric motor indicates, for example, a current feed-back, particularly an impending current feed-back, the control unit can short-circuit the line phases. This short-circuiting can occur, in particular, if the current fed back during generator operation cannot be absorbed by consumers in the vehicle's on-board or electrical system.

[0028] The proposed method can advantageously prevent the occurrence of voltage peaks in the power or on-board network of the motor vehicle.

[0029] In embodiments, the control unit can be coupled to a switching unit for control purposes, wherein the switching unit is connected to the two or more line phases, and wherein the control unit is configured to control the switching unit to short-circuit the at least two line phases.

[0030] In embodiments, it can be provided that the control unit determines whether generator operation has ended or is about to end. In response to determining an end or an imminent end of generator operation, the control unit can remove an existing short circuit in the at least two line phases. The determination that generator operation no longer prevails or is about to end can be based on operating parameters monitored by the control unit, such as current consumption, etc. Analogous to determining existing or imminent generator operation, the control unit can compare monitored parameters, such as the current or current consumption of the electric motor, with stored parameters or parameter values ​​and, on the basis of the comparison, determine that generator operation no longer prevails or will soon end.Furthermore, a corresponding determination can be made based on a trained model, e.g., an artificial intelligence system implemented in the control unit. The model can be trained based on a variety of operating states of a corresponding steering system and / or motor vehicle.

[0031] In embodiments, the control unit can determine a probability of impending generator operation of the electric motor, e.g., based on a model, in particular a trained model. If the probability exceeds a predetermined threshold, the control unit can short-circuit the at least two line phases.

[0032] In some embodiments, the control unit can be configured to continuously monitor whether generator operation is present, imminent, or about to end. Such continuous monitoring is advantageous, on the one hand, with regard to preventing energy feedback and voltage spikes during generator operation, and, on the other hand, enables appropriate steering support.

[0033] According to embodiments, a control unit is provided. The control unit comprises a control circuit, such as a processor, which contains operating instructions which, when executed by the control circuit, cause the control unit to execute a method according to one of the method-related embodiments described herein. In embodiments, the control unit may comprise a non-volatile memory in which computer-executable instructions are stored which, when executed by the control unit, in particular the control circuit, in particular a processor, cause the control unit to execute a method according to one of the method-related embodiments described herein. The control unit may, as described herein, be connectable or connected to a steering system for control purposes and be functionally implemented to control steering processes of the steering system.

[0034] In embodiments, a non-volatile memory may be provided in which instructions are stored which, when executed by a processor, cause the processor to carry out a method according to one of the method-related embodiments described herein.

[0035] In embodiments, a steering system for a motor vehicle is provided. The steering system comprises at least two steered wheels, e.g., a steered front axle of a motor vehicle, such as an electric car. The steering system further comprises at least one electric motor for executing, preferably for assisting, a steering movement or steering action of at least one of the steered wheels. The electric motor is configured such that it is connectable or is connected via at least two line phases, preferably three line phases, to a power supply source, e.g., to an inverter fed by a storage battery, in order to supply the electric motor with electrical energy. The steering system further comprises a control unit according to one of the embodiments described here. For advantages and advantageous effects, reference is made to the above explanations.

[0036] In some embodiments, a motor vehicle is provided that includes a steering system according to one of the embodiments described here. The motor vehicle may be an electric vehicle, in particular an electric car.

[0037] Exemplary embodiments and embodiments of the invention will now be described in conjunction with the attached figures. They show:

[0038] FIG. 1 shows an example of a steering system for a motor vehicle;

[0039] FIG. 2 shows a schematic representation of the steering system; and FIG. 3 shows a method sequence for steering control;

[0040] FIG. 4 schematically shows components of an electronic control unit for steering control.

[0041] FIG. 1 shows an example of a steering system 1 for a motor vehicle, in particular an electric car. The steering system 1 is an electrically assisted steering system in which a steering movement is executed or at least assisted by an electric motor.

[0042] The steering system 1 comprises a steering wheel 2 and a steering control or control unit 3 connected thereto. The steering system 1 further comprises a steering axle 4 with two steered wheels 5 (only one wheel is shown in FIG. 1).

[0043] To provide steering assistance, the steering system 1 comprises a steering actuator 6 with one or more servo drives 7 or electric motors 7 or actuators 7 for controlling a steering angle 8 or steering angle (FIG. 2) of the wheels 5 via a steering movement 9 (FIG. 2) of the steering actuator 6. In the following, the term "actuator" is used in particular to represent actuators 7 or electric motors 7 or servo drives. The actuators 7 can, for example, comprise permanent magnet synchronous motors (PMSM), or the electric motors can be permanent magnet synchronous motors (PMSM).

[0044] The control unit 3 is connected to the actuator(s) 7 via a control line 10. The control unit 3 and the actuator(s) 7 are connected or connectable to a power source (not shown) for supplying electrical energy via one or more supply lines (not explicitly shown), wherein each actuator 7 is connected or connectable to the power source via at least two line phases, in particular three line phases.

[0045] The control unit 3 is configured to execute a steering control according to FIG. 3. Specifically, the control unit 3 is configured to execute the following steps (FIG. 3): Determining 101 whether there is an existing or imminent occurrence of a generator operation of the actuator 7, in which the actuator 7 operates as a generator; and

[0046] - if an existing or impending occurrence of generator operation is detected, short-circuiting 102 of at least two of the line phases of the actuator 7.

[0047] By short-circuiting the line phases, voltage spikes caused by power feedback in the vehicle's electrical system or on-board network can be prevented during damping or generator operation. Furthermore, short-circuiting the line phases can create a damping effect, which can counteract torques generated during dynamic steering processes.

[0048] FIG. 4 shows a schematic circuit diagram of a control unit for steering control, in particular for controlling the actuator(s) 7.

[0049] As shown in FIG. 4, the actuator 7 is supplied with electrical energy via three line phases Iu, Iv, and Iw. A switching unit 11 with three switches 12 is arranged upstream in the power supply. The switching unit 11 is connected to an inverter 13, which is connected to the line phases for supplying energy to the actuator 7. The inverter 13 typically has several MOSFETs 14.

[0050] The control device according to FIG. 4 further comprises a control unit 15 for controlling the inverter 13. The control unit 15 is connected to the switching unit 11 via a first line 16 and to a current sensor unit 18 via a second line 17.

[0051] The current sensor unit 18 comprises a current sensor 19 configured to measure the current drawn by the electric motor 7. Outputs of the current sensor 19 are connected to a signal amplifier 20, which is connected to the control unit 15 via an A / D converter 21 and the second line 17. If the control unit 15 detects the presence of generator operation or an imminent occurrence of generator operation, the control unit controls the switching unit 11 or the switches 12 to short-circuit the line phases.

[0052] If the control unit 15 determines that generator operation is not present or no longer present or will no longer occur in an upcoming operating state, the control unit 15 controls the switching unit 11 or the switches 12 in order to remove the short circuit of the line phases or to open the switches 12.

[0053] To decide whether generator operation is present or not, or whether generator operation is likely imminent or no longer exists, the control unit 15 can use, among other things, a signal from the current sensor unit 18 or the current sensor 19. For example, the control unit 15 can monitor the signal from the current sensor unit 18 and, if a current waveform characteristic of generator operation occurs, short-circuit the line phases. Conversely, the control unit 15 can remove the short circuit if the current waveform or the current consumption of the electric motor 7 is not or no longer characteristic of generator operation.

[0054] A characteristic of generator operation, for example, is a negative current consumption of the electric motor 7, i.e. a feedback of current. Since feedback is already taking place at the time a negative current consumption is detected and this can lead to voltage peaks, the control unit can use not only the instantaneous current value as such, but also, for example, the course of the current consumption, the change in the current consumption and / or the rate of change of the current consumption and compare this with predetermined curves or limit values, for example. If, for example, the course of the current consumption etc. follows a curve that is characteristic of generator operation or impending generator operation, the control unit 15 can short-circuit the line phases and thus prevent feedback of current and the associated voltage peaks in the power supply or on-board network.the current consumption of the actuator 7 as an operating parameter, the control unit 15 can further use one or more additional or alternatively one or more other operating parameters of the motor vehicle or the steering system 1.

[0055] The determination that generator operation is present or imminent can be made, for example, by comparing the operating parameter(s) with respective predefined limit values. The limit values ​​can be stored, for example, in a database, e.g., in a look-up table or the like. In embodiments, an artificial intelligence system can be installed on the control unit, which is trained to determine the presence or imminent presence of generator operation from operating data. Similarly, based on the operating parameter(s), it can be determined that generator operation is no longer present or that a detected generator operation will shortly end.

[0056] List of reference symbols

[0057] 1 steering system

[0058] 2 steering wheel

[0059] 3 Control unit

[0060] 4 steering axle

[0061] 5 wheel

[0062] 6 Steering actuator

[0063] 7 Servo drive

[0064] 8 steering angles

[0065] 9 Steering movement

[0066] 10 Control line

[0067] 11 Switching unit

[0068] 12 switches

[0069] 13 inverters

[0070] 14 MOSFET

[0071] 15 Control unit

[0072] 16 first line

[0073] 17 second line

[0074] 18 Current sensor unit

[0075] 19 Current sensor

[0076] 20 signal amplifiers

[0077] 21 A / D converters

Claims

Claims 1. A method for controlling an electric, in particular an electrically assisted, steering system (1) of a motor vehicle, wherein the steering system (1) comprises at least two steered wheels (5) and at least one electric motor (7) at least for assisting a steering action of at least one of the steered wheels (5), wherein the electric motor (7) is connected to an energy source via at least two, in particular three, line phases for its energy supply, wherein the method comprises the following steps carried out by a control unit (3): - determining (101) whether there is an existing or imminent occurrence of a generator operation of the electric motor (7), in which the electric motor (7) operates as a generator; and - if an existing or imminent occurrence of generator operation is detected, short-circuiting (102) at least two of the line phases of the electric motor (7).

2. The method according to claim 1, wherein the determination of generator operation is based on one or more operating parameters of the steering system (1) and / or the motor vehicle.

3. Method according to one of the preceding claims, wherein the determination of generator operation is carried out on the basis of a current measured in at least one of the line phases.

4. Method according to one of the preceding claims, wherein the control unit (3) is control-technically coupled to a switching unit (11) which is connected to the two or more line phases, and wherein the control unit (3) is configured to control the switching unit (11) to short-circuit the at least two line phases.

5. Method according to one of the preceding claims, wherein the control unit (3) determines whether there is an end or an imminent end of generator operation, and in response to a determination of an end or an imminent end of generator operation, removes an existing short circuit of the at least two line phases.

6. Method according to one of the preceding claims, wherein the control unit (3) continuously determines whether generator operation is present, imminent or is about to end.

7. Control unit (3) with a control circuit containing operating instructions which, when executed by the control circuit, cause the control unit (3) to carry out a method according to one of claims 1 to 6.

8. Steering system (1) for a motor vehicle, wherein the motor vehicle has at least two steered wheels (5) and at least one electric motor (7) for carrying out, in particular assisting, a steering movement of at least one of the steered wheels (5), wherein the electric motor (7) has at least two line phases for connection to an electrical energy source to supply it with electrical energy, and wherein the steering system further comprises a control unit (3) according to claim 7.

9. Motor vehicle comprising a steering system (1) according to claim 8.

10. Motor vehicle according to claim 9, wherein the motor vehicle is an electric vehicle, in particular an electric car.

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