WO2024094369A1

WO2024094369A1 - Method for operating a steering assembly for a motor vehicle, and steering assembly

Info

Publication number: WO2024094369A1
Application number: PCT/EP2023/076425
Authority: WO
Inventors: Christian Brenndoerfer; Luc Diebold; Ralph Michalski; Magnus Rau; Bjoern Spangemacher; Wolfgang Stoeckle
Original assignee: Mercedes-Benz Group AG
Priority date: 2022-10-31
Filing date: 2023-09-25
Publication date: 2024-05-10
Also published as: DE102022004044A1

Abstract

The invention relates to a method for operating a steering assembly (10) for a motor vehicle, which steering assembly has a steering control element (14) rotatable about an axis of rotation (12) and an electric machine (24), wherein: for the purpose of cornering and/or changing the direction of the motor vehicle, the rotation of the steering control element (14) about the axis of rotation (12) is accompanied by the swiveling, caused by the electric machine (24), of a vehicle wheel (16) of the motor vehicle about a wheel swivel axis (20) of the vehicle wheel (16), and a variable (36) characterizing a thermal load on the steering assembly (10) is determined by means of an electronic computing device (26); and, in a protective operating mode (38) of the steering assembly (10), a torque (42) to be applied by a driver of the motor vehicle for rotating the steering control element (14) about the axis of rotation (12) is adjusted on the basis of the determined variable (36), and/or a ratio (44) of an angle of rotation of the steering control element (14) and a swivel angle of the vehicle wheel (16), caused by the electric machine (24) according to the angle of rotation, is adjusted.

Description

Method for operating a steering system for a motor vehicle and steering

The invention relates to a method for operating a steering system for a motor vehicle according to the preamble of patent claim 1. Furthermore, the invention relates to a steering system for a motor vehicle.

DE 102020210 048 A1 discloses a method for protecting the components of a steer-by-wire steering system, wherein the steer-by-wire steering system has a spindle drive with self-locking, wherein the spindle is linearly displaced by means of a rotary drive of a stationary spindle nut. In this case, it is provided that in order to estimate a maximum thermal load as a function of the vehicle speed, the linear displacement of the spindle relative to the spindle nut is continuously summed up over time as a temperature integral until a first threshold value is reached.

The object of the present invention is to provide a method for operating a steering system for a motor vehicle and a steering system for a motor vehicle, so that a temperature of the steering system can be kept particularly low.

This object is achieved according to the invention by a method for operating a steering system for a motor vehicle with the features of patent claim 1 and by a steering system for a motor vehicle with the features of patent claim 10. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

A first aspect of the invention relates to a method for operating a steering system for a motor vehicle. The motor vehicle is designed, for example, as a motor vehicle, in particular as a passenger car, commercial vehicle or truck. Preferably, the motor vehicle, particularly in its fully manufactured state, has the steering.

The steering has a steering handle that can be rotated about an axis of rotation, in particular manually and/or automatically. The fact that the steering handle can be rotated manually about the axis of rotation can be understood in particular to mean that the steering handle can be rotated about the axis of rotation by a person or a vehicle occupant, for example a driver of the motor vehicle. For example, the person, in particular by means of his hand, can apply a torque to the steering handle to rotate the steering handle about the axis of rotation. The person preferably touches the steering handle directly. The steering handle is preferably designed as a steering wheel.

The steering has at least one electric machine, wherein in order to bring about cornering and/or changes of direction of the motor vehicle, when the steering handle is turned, in particular manually, about the axis of rotation, at least one vehicle wheel of the motor vehicle is pivoted about a wheel pivot axis of the vehicle wheel, in particular exclusively by means of the electric machine. In other words, the steering handle and the electric machine are coupled to one another in such a way that when the steering handle is turned, in particular manually, about the axis of rotation, a torque for pivoting the at least one vehicle wheel about the wheel pivot axis is provided by means of the electric machine, in particular via an output shaft of the electric machine. This means that when the steering handle is turned about the axis of rotation by means of the electric machine, the vehicle wheel of the motor vehicle is pivoted about the wheel pivot axis.

The vehicle wheel can be rotated about a wheel rotation axis of the vehicle wheel. The vehicle wheel can be understood in particular as a ground contact element of the motor vehicle. For example, the vehicle wheel rolls on a surface, such as a roadway, while the motor vehicle is traveling. As a result, the vehicle wheel preferably touches the surface directly. The vehicle wheel is, for example, part of the steering. Alternatively, the vehicle wheel is designed separately from the steering.

For example, the wheel pivot axis runs diagonally or perpendicular to the wheel rotation axis.

For example, the wheel pivot axis runs at least substantially in Vehicle vertical direction. The rotation axis of the steering handle preferably runs obliquely or perpendicular to the wheel rotation axis and/or the wheel swivel axis.

The steering is preferably designed as a steer-by-wire steering system. This means that the steering preferably has no mechanical connection between the steering handle and the vehicle wheel, in particular for pivoting the vehicle wheel. This means that the steering is free of the, in particular direct, mechanical connection between the steering handle and the vehicle wheel. The torque for pivoting the vehicle wheel is thus, for example, a torque provided or caused exclusively by the electric machine.

At least one variable characterizing a thermal load on the steering, in particular on at least one device of the steering, is determined, in particular calculated, by means of at least one electronic computing device. In other words, at least one variable characterizing a thermal load on the steering is determined or calculated by means of the electronic computing device.

The quantity characterizing the thermal load on the steering can be understood in particular as at least one piece of information characterizing the thermal load on the steering. The thermal load is, for example, a temperature. The electronic computing device is preferably part of the motor vehicle, in particular the steering.

For example, the variable characterizing the thermal load has a first value when the steering, in particular the device, is or will be loaded with a first thermal load and the variable characterizing the thermal load of the steering, in particular the device, has, for example, a second value that is different from the first value when the steering, in particular the device, is or will be loaded with a second thermal load that is different from the first thermal load.

The device is, for example, a component or a structural element of the steering. The device is, for example, a transmission, particularly referred to as a steering gear, and/or the electric machine. This means that the A quantity characterizing the thermal load on the steering is, for example, a quantity characterizing the thermal load on the electrical machine. Thus, at least one quantity characterizing the thermal load on the electrical machine is determined by means of the electronic computing device.

In order to be able to keep the temperature of the steering, in particular of the device, particularly low, it is provided according to the invention that in a protective operating state of the steering, which differs in particular from a normal operating state of the steering, a torque to be applied by the driver of the motor vehicle to rotate the steering handle about the axis of rotation, in particular between two different rotational positions, is set, in particular in a targeted manner, depending on the variable determined, in particular by means of the electronic computing device, for example by means of at least one actuator. In other words, in the operating state, a stiffness or a smoothness of movement, in particular for rotating the steering handle about the axis of rotation, of the steering handle is set, in particular in a targeted manner, depending on the variable determined, for example by means of the actuator. This means, for example, that in the protective operating state, for example by means of the actuator, a resistance torque is set, in particular in a targeted manner, depending on the variable determined, which counteracts the torque to be applied or applied by the driver to rotate the steering handle about the axis of rotation, in particular between the two rotational positions.

In order to be able to keep the temperature of the steering, in particular of the device, particularly low, it is alternatively or additionally provided that a ratio, in particular a transmission ratio, for example by means of the electric machine or the electronic computing device, is set, in particular in a targeted manner, from a rotation angle between two, in particular different, rotation positions of the steering handle and a swivel angle caused by the electric machine as a function of the rotation angle between two, in particular different, swivel positions of the vehicle wheel. In other words, it is provided that the swivel angle of the vehicle wheel, in particular between the two swivel positions, is set, in particular in a targeted manner, by means of the electric machine as a function of the rotation angle of the steering handle, in particular between the two rotation positions, and as a function of the size determined by means of the electronic computing device. The ratio or transmission ratio can in particular be a steering ratio, in particular between the steering handle and the vehicle wheel. This means that the steering ratio is adjusted by means of the electric machine depending on the value determined by the electronic computing device. The steering ratio can in particular be referred to as the steering ratio.

For example, the actuator is designed as a second electrical machine that is separate from the electrical machine. For example, the steering handle can be rotated around the axis of rotation by means of the actuator, in particular automatically. For example, the resistance torque is determined, in particular calculated, by means of the electronic computing device depending on the value determined by means of the electronic computing device. For example, the resistance torque determined by means of the electronic computing device is set, in particular in a targeted manner, by means of the actuator. The resistance torque determined by means of the electronic computing device is thus transmitted to the actuator for adjustment.

For example, the swivel angle is determined, in particular calculated, by means of the electronic computing device depending on the angle of rotation of the steering handle and depending on the size determined by means of the electronic computing device. For example, the swivel angle determined by means of the electronic computing device is set, in particular in a targeted manner, by means of the electric machine. The swivel angle determined by means of the electronic computing device is thus transmitted to the electronic computing device, for example for adjustment.

For example, in the protective operating state of the steering, in particular depending on the determined variable, a first torque value of the torque to be applied by the driver to rotate the steering handle about the axis of rotation or the resistance torque is set by means of the actuator. For example, in the normal operating state, in particular independently of the variable determined by means of the electronic computing device, a second torque value, different from the first torque value, of the torque to be applied by the driver to rotate the steering handle about the axis of rotation or the resistance torque is set by means of the actuator.

For example, in the protective operating state, in particular depending on the determined size, a first value of the ratio or the For example, in the normal operating state, in particular independently of the value determined by means of the electronic computing device, a second value of the ratio or the transmission ratio is set which is different from the first value of the ratio.

For example, in the protective operating state, in particular depending on the value determined by the electronic computing device, when the steering handle is pivoted by the angle of rotation, a first angle value of the pivot angle of the vehicle wheel is set by the electronic computing device. For example, in the normal operating state, in particular independently of the value determined by the electronic computing device, when the steering handle is pivoted by the angle of rotation, a second angle value of the pivot angle of the vehicle wheel, which is different from the first angle value, is set by the electric machine.

The invention is based in particular on the following findings and considerations: In principle, it is conceivable to protect the steering, in particular the device, from overheating. In a conventional mechanical or electromechanical steering system (EPS), a protective function to protect the steering, in particular the device, from overheating can be carried out automatically by a particularly increased effort when steering with the steering handle if the device goes into temperature derating. With steer-by-wire steering, this may not be possible, in particular due to independent actuators in the form of a feedback actuator and the steering gear. The feedback actuator can in particular be referred to as a steering wheel unit (SWU). The steering gear can in particular be referred to as a steering rack unit (SRU). For example, the feedback actuator has the second electric machine. For example, the steering gear has the electric machine or the electric machine is provided to drive the steering gear.

By means of the method according to the invention, a particularly anticipatory temperature protection function can be implemented, in particular in the protective operating state, which can be understood in particular as a component protection function. By means of the temperature protection function, for example in the case of excessive steering, in particular when the motor vehicle is stationary or parked, the device can be protected, in particular in a particularly safe manner, from overheating. The protection can be achieved in particular by anticipating or Pre-control can take place. This means that, for example, an impending overheating can be predicted by means of the electronic computing device before the overheating actually occurs, whereby measures can be initiated to prevent the overheating, for example in the form of stiff steering and/or the steering gear ratio. In other words, the method according to the invention can be used to prevent overheating and thus degradation of the steering, in particular of a steer-by-wire system, due to excessive or particularly pronounced steering movements by the driver, in particular when stationary, by means of a temperature protection function, in particular a predictive one. The device can be protected particularly early on by means of the pre-control and associated measures, whereby the availability of the steering, in particular of the device, is not restricted, for example. Without this pre-control or predictive action, measures could only be taken subsequently, in particular by means of the electronic computing device, and thus in particular after the overheating or when the overheating occurs, for example via a measured temperature increase. This could, for example, require deactivation or degradation of the steering. This can be prevented by means of the method according to the invention.

Overall, it can be seen that the method according to the invention can be used to particularly increase safety against overheating of the steering, in particular the device. This can particularly increase the availability of the steering. The electronic computing device can be used to detect a situation, in particular a current situation, in particular a thermal situation, of the steering depending on the variable characterizing the thermal load on the steering, and depending on the detected situation, the measures, in particular adjusting the stiffness and/or adjusting the gear ratio, can be implemented in order to be able to keep the temperature of the steering, in particular the device, particularly low.

In a further embodiment, it is provided that in the protective operating state, the torque to be applied by the driver of the motor vehicle to rotate the steering handle about the axis of rotation is greater than in the normal operating state of the steering. In other words, a torque increase is carried out by means of the actuator or the electronic computing device in the protective operating state, in particular compared to the normal operating state, in order to make the steering or the steering handle more difficult or particularly difficult to move. Thus, the first torque value of the torque in the Protective operating state preferably greater than the second torque value of the torque in the normal operating state. The stiffer steering can cause the driver to steer less or very little. Thus, for example, during a degradation of the steering, the torque increase, particularly in the steering wheel unit, can be carried out in order to make steering, particularly when stationary, particularly stiff for the driver, and in particular to particularly reduce the steering speed. This allows the temperature of the steering, particularly of the device, to be kept particularly low. This allows the steering to be particularly reliably protected against overheating. The steering speed can be understood in particular as a rotational speed when turning the steering handle about the axis of rotation.

In a further embodiment, it is provided that in the protective operating state, when the steering handle is rotated about the axis of rotation between the two rotation positions, the pivoting of the vehicle wheel about the wheel pivot axis by means of the electric machine is accompanied by a smaller pivot angle than in the normal operating state of the steering. In other words, the gear ratio in the protective operating state, in particular in relation to the normal operating state, is adjusted in the indirect direction. This means that in the protective operating state a more indirect gear ratio is present or set than in the normal operating state. In other words, the ratio of the angle of rotation and the pivot angle is set larger in the protective operating state than in the normal operating state. Thus, the first value of the ratio is, for example, larger than the second value of the ratio. The more indirect gear ratio can result in a smaller or particularly small pivot angle, whereby movements of the steering gear or in the steering gear can be kept particularly small. This means that, for example, during degradation, the steering ratio is adjusted in the indirect direction so that less or very little swivel angle, which can be referred to in particular as the wheel angle, is set or adjusted with the same angle of rotation of the steering handle. This means that the temperature of the steering can be kept particularly low. In particular, safety against overheating of the steering can be particularly increased. The angle of rotation of the steering handle can be referred to in particular as the steering wheel angle.

In a further embodiment, it is provided that the steering is operated in the protective operating state when the electronic The value determined by the computing device and characterizing the thermal load on the steering deviates from a, in particular, predetermined, threshold value by more than a predetermined amount. In other words, the steering is operated in the protective operating state if the value detected by the electronic computing device is greater or smaller than the threshold value, i.e., for example, exceeds or falls below the threshold value. This allows the temperature of the steering to be kept particularly low. In particular, a particularly strong rise in temperature of the steering, in particular of the device, can be particularly reliably avoided at an early stage. The predetermined value can be understood to mean any value, for example. For example, the predetermined value is zero or greater than zero.

Preferably, it is provided that the steering is operated in the normal operating state if the deviation of the variable determined by means of the electronic computing device from the threshold value by more than the predetermined amount is avoided.

In a further embodiment, it is provided that if the variable characterizing the thermal load on the steering determined by means of the electronic computing device deviates by more than a predetermined amount from a second threshold value, in particular a predetermined one, which is different from the threshold value, the steering is operated in a second protective operating state, in particular different from the protective operating state. In other words, the steering is operated in the second protective operating state if the variable determined by means of the electronic computing device is greater or smaller than the second threshold value, that is to say, for example, exceeds or falls below the second threshold value. In the second protective operating state, a maximum swivel angle by which the vehicle wheel can be swiveled about the wheel swivel axis, in particular from its zero position or its starting position, is smaller in the second protective operating state than in the protective operating state, and in particular than in the normal operating state. In other words, in the second protective operating state, the vehicle wheel can be pivoted less around the wheel pivot axis, in particular from the zero position or the starting position, than in the protective operating state and/or the normal operating state. This means that in the second protective operating state, for example, an angle limitation is set or brought about with regard to the pivoting of the vehicle wheel. As a result, the movement of the steering gear or the movement in the steering gear can be kept particularly small, which, for example, makes it particularly little heat can be generated. This means that the temperature of the steering can be kept particularly low. In particular, in the second protective operating state, the maximum steering wheel angle and thus the swivel angle of the vehicle wheel, referred to in particular as the wheel angle, can be limited, particularly when stationary. The protective operating state can be referred to as the first protective operating state, in particular to distinguish it from the second protective operating state.

In a further embodiment, it is provided that the variable characterizing the thermal load on the steering is determined, in particular calculated, by means of the electronic computing device as a function of a, in particular current, driving speed of the motor vehicle. In other words, the driving speed of the motor vehicle is used as an input variable for determining the variable characterizing the thermal load on the steering by means of the electronic computing device. This allows the thermal load on the steering to be predicted particularly precisely, in particular because the driving speed can have a particularly large influence on the temperature of the steering, in particular the device.

In a further embodiment, it is provided that the variable characterizing the thermal load on the steering is determined by means of the electronic computing device as a function of the, in particular current, angle of rotation of the steering handle and/or the, in particular current, speed of rotation of the steering handle about the axis of rotation. In other words, the angle of rotation and/or the speed of rotation of the steering handle are used as, in particular respective, input variables for determining the variable characterizing the thermal load on the steering by means of the electronic computing device. This makes it possible to predict the thermal load, in particular overheating, of the steering, in particular of the device, particularly precisely. This can be brought about in particular by the fact that the angle of rotation and/or the speed of rotation can have a particularly large influence on the temperature of the steering, in particular of the device.

In particular, it can be seen that in the protective operating state, a pre-control can be effected depending on the angle of rotation, referred to in particular as the steering wheel angle, and/or the speed of rotation, referred to in particular as the steering wheel angular velocity, and/or the driving speed, so that in particular, particularly at an early stage, a particularly strong increase in temperature of the steering, in particular the device, can be particularly safely avoided.

In a further embodiment, it is provided that the vehicle wheel can be pivoted about the wheel pivot axis by means of the electric machine via the at least one steering gear, which has at least one wheel and at least one rack that is coupled to the wheel in a translational manner relative to the wheel, in particular directly. In other words, the steering gear can be driven by means of the electric machine in order to pivot the vehicle wheel about the wheel pivot axis via the steering gear. The wheel of the steering gear can be driven by means of the electric machine, in particular by means of the output shaft of the electric machine, and the rack can be driven by the wheel, whereby the rack can be moved or translated relative to the wheel, for example in the transverse direction of the vehicle, in particular in order to pivot the vehicle wheel about the pivot axis. The wheel is designed, for example, as a gear or as a spur gear. The wheel can be rotated about a wheel rotation axis of the wheel relative to the rack.

Preferably, it is provided that the variable characterizing the thermal load on the steering is determined, in particular calculated, by means of the electronic computing device as a function of a, in particular current, axial position of the rack, in particular in the motor vehicle or relative to the wheel. In other words, the axial position of the rack, which can in particular be referred to as the rack position, is used as an input variable for calculating the variable characterizing the thermal load on the steering by means of the electronic computing device. This allows the thermal load on the steering to be predicted particularly precisely. This can be achieved in particular by the rack position characterizing an extent of steering movements caused by the steering gear or an extent with regard to the pivoting of the vehicle wheel.

The axial position of the rack can be understood in particular as a position or a deflection of the rack during the translational movement of the rack relative to the wheel, in particular with respect to a zero position or an initial position of the rack. In a further embodiment, it is provided that the steering system changes from the normal operating state to the first protective operating state and/or the second protective operating state depending on a current operating parameter of the electrical machine. In other words, the quantity characterizing the thermal load on the steering system is determined, in particular calculated, by means of the electronic computing device depending on the current operating parameter of the electrical machine. This allows the protective operating state and thus the component protection function to be started depending on a current state of the electrical machine. This allows the temperature of the steering system to be kept particularly low.

The operating parameter of the electrical machine can be understood in particular as information characterizing a current state of the electrical machine. For example, the operating parameter is a temperature of the electrical machine, in particular referred to as motor temperature. For example, the operating parameter is a torque of the electrical machine, in particular referred to as motor torque. The torque can be understood in particular as the torque currently provided by the electrical machine, for example via its output shaft, for pivoting the vehicle wheel. For example, the operating parameter of the electrical machine is a state of a protective function of the electrical machine. This can be referred to in particular as status derating. This can thus make it possible, for example, to start the protective operating state of the steering via an internal degradation state of the electrical machine.

A second aspect of the invention relates to a steering system for a motor vehicle, which is designed to carry out a method according to the first aspect of the invention. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention and vice versa.

Also disclosed is a motor vehicle having a steering system designed to carry out a method according to the first aspect of the invention. This means that the motor vehicle can have the steering system according to the second aspect of the invention. Further advantages, features and details of the invention emerge from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and/or shown alone in the figures can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the invention.

Showing:

Fig. 1 is a schematic partial sectional view of a steering system according to the invention, by means of which a method according to the invention can be carried out; and

Fig. 2 is a schematic process diagram of a process according to the invention; and

Fig. 3 is a schematic representation of a method according to the invention according to a further embodiment.

Fig. 1 shows a steering system 10 for a motor vehicle in a schematic partial sectional view. The steering system 10 is designed to carry out a method which is illustrated by way of example in Fig. 2 in a schematic method diagram.

The steering system 10 has a steering handle 14 that can be rotated about a rotation axis 12, in particular relative to a body of the motor vehicle. The steering system 10 is provided for causing the motor vehicle to turn and/or change direction. At least one vehicle wheel 16, 18 can be pivoted about a wheel pivot axis 20, 22 of the vehicle wheel 16, 18 to cause the motor vehicle to turn and/or change direction, in particular relative to the body of the motor vehicle. In Fig. 1, two vehicle wheels 16, 18 that can be pivoted about a respective wheel pivot axis 20, 22 are shown. The vehicle wheel 16 can be referred to in particular as the first vehicle wheel 16 and can be pivoted about the wheel pivot axis 20, which can be referred to in particular as the first wheel pivot axis 20, for example relative to the body of the motor vehicle. The vehicle wheel 18 can in particular referred to as the second vehicle wheel 18 and is pivotable about the wheel pivot axis 22, which can in particular be referred to as the second wheel pivot axis 22, for example relative to the body of the motor vehicle.

The steering system 10 is preferably designed as a steer-by-wire steering system. The steering system 10 has at least one electric machine 24, wherein in order to bring about cornering and/or changes of direction of the motor vehicle when the steering handle 14 is turned, in particular manually, about the axis of rotation 12, the respective vehicle wheel 16, 18 is pivoted about the respective wheel pivot axis 20, 22, in particular exclusively by means of the electric machine 24. The steering handle 14 is thus coupled or can be coupled, for example via the electric machine 24, to the respective vehicle wheel 16, 18, in particular for pivoting the respective vehicle wheel 16, 18. For example, the steering system 10 has at least one sensor element 28, by means of which the rotation of the steering handle 14 about the axis of rotation 12, in particular a rotational position of the steering handle 14, can be detected or is detected. For example, the sensor element 28 is or can be coupled to the electric machine 24 via an electronic computing device 26 of the steering system 10. As a result, the respective vehicle wheel 16, 18 can be pivoted about the respective wheel pivot axis 20, 22 by means of the electric machine 24 depending on the rotation of the steering handle 14 detected by means of the sensor element 28, in particular depending on the detected rotational position.

For example, the steering system 10 has a drive unit 30. The drive unit 30 preferably has the electric machine 24. For example, the drive unit 30 has at least one steering gear 32, via which the respective vehicle wheel 16, 18 can be or is pivoted about the respective wheel rotation axis 16, 18 by means of the electric machine 24. The drive unit 30 can in particular be referred to as a steering rack unit (SRU).

For example, the steering 10 has a control unit 34, which is preferably designed separately from the drive unit 30. The control unit 34 can in particular be referred to as a feedback actuator or feedback actuator system or steering wheel unit (SWU). For example, the sensor element 28 is part of the control unit 34. For example, the drive unit 30 and the control unit 34 are or can be coupled to one another via the electronic computing device 26. For example, the electronic computing device 26 is part of the control unit 34. In the method, it is provided that at least one variable 36 characterizing a thermal load on the steering system 10, in particular on the drive unit 30, is determined, in particular calculated, by means of the electronic computing device 26. The variable 36 is, for example, a temperature of the steering system 10, in particular on the drive unit 30, for example on the electric machine 24.

In order to be able to keep a temperature of the steering 10, in particular of the drive unit 30, particularly low, it is provided that in a protective operating state 38 of the steering 10, which is different in particular from a normal operating state, a torque 42 to be applied by a driver of the motor vehicle to rotate the steering handle 14 about the axis of rotation 12 is set, in particular in a targeted manner, depending on the variable 36 determined by means of the electronic computing device 26, in particular by means of a second electric machine 40. In other words, in the protective operating state, in particular by means of the second electric machine 40, a torque increase 50 is brought about depending on the determined variable 36 in order to make the steering handle 14 stiff, in particular stiffer than in the normal operating state, as a result of which the driver steers less or particularly little, for example. Alternatively or additionally, it is provided that in the protective operating state 38, depending on the determined variable 36, a ratio 44, in particular referred to as a steering ratio, is set from a rotation angle 72 between two rotational positions of the steering handle 14 and a swivel angle caused by the electric machine 24 as a function of the rotation angle 72 between two swivel positions of the respective vehicle wheel 16, 18, in particular in a targeted manner, for example by means of the electric machine 24 or the electronic computing device 26. In other words, in the protective operating state 38, the steering ratio is set particularly indirectly, in particular more indirectly than in the normal operating state, so that, for example, less or particularly little target angle arrives at the drive unit 30. This can be understood in particular to mean that a target angle specified by the driver of the motor vehicle by manually turning the steering handle 14 about the axis of rotation 12 leads to a smaller swiveling of the respective vehicle wheel 16, 18 in the protective operating state 38 than in the normal operating state.

This is illustrated in Fig. 3 in a schematic representation of the method. The protective operating state 38 can be used to Temperature protection function 46 can be activated to protect the steering 10, in particular to protect the drive unit 30. The electronic computing device 26 can be used to detect a situation 48, in particular with regard to the thermal load on the steering 10, in particular by determining the value 36. Depending on the detected situation, the torque increase 50 can be carried out in the protective operating state 38. In this case, for example, a steering torque controller 52 can be controlled or adjusted. Alternatively or additionally, depending on the detected situation, the ratio 44, referred to in particular as the steering ratio, can be adjusted, in particular made more indirect. In particular, a target value 54 of the respective swivel angle can be set or specified by means of the electronic computing device 26 as a function of the determined variable 36 and as a function of the angle of rotation 72 or the rotational position of the steering handle 14, wherein the set or specified target value 54 can be set as the swivel angle, in particular actually, by means of the electric machine 24 for swiveling the respective vehicle wheel 16, 18. The target value 54 can in particular be referred to as a wheel angle target value.

The second electrical machine 40 is preferably designed separately from the electrical machine 24, which can in particular be referred to as the first electrical machine. The second electrical machine 40 is preferably part of the control unit 34. The temperature protection function 46 is implemented, for example, in the control unit 34.

For example, it is provided that the steering 10 changes from the normal operating state to the protective operating state 38 depending on a, in particular current, driving speed 56 of the motor vehicle, in particular when stationary or at a particularly low driving speed, for example less than two kilometers per hour. The protective operating state 38 or the temperature protection function 46 is thus active, for example, in particular exclusively, when the motor vehicle is stationary or at particularly low driving speeds 56. The position of the motor vehicle can be understood in particular to mean that the motor vehicle is stationary, i.e. not moving. For example, the steering 10 is in the protective operating state when the, in particular current, driving speed 56 of the motor vehicle is greater than a, in particular predetermined, reference value. For example, the steering 10 is in the normal operating state when the, in particular current, driving speed 56 of the motor vehicle is less than the reference value. For example, the, in particular current driving speed 56 of the motor vehicle is detected by means of a sensor element, whereby the driving speed 56 can be understood in particular as a driving speed 56 detected, for example, by means of the sensor element.

Overall, it can be seen that the situation detection 48 can therefore be a situation detection 48 with regard to excessive steering when stationary or at a particularly low driving speed 56.

In a further embodiment, it is provided that in the protective operating state 38 the torque 42 to be applied by the driver of the motor vehicle to rotate the steering handle 14 about the axis of rotation 12 is greater than in the normal operating state of the steering 10. It is preferably provided that in the protective operating state 38 when the steering handle 14 is rotated about the axis of rotation 12 between two rotation positions, the pivoting of the respective vehicle wheel 16, 18 about the respective wheel pivot axis 20, 22 caused by the electric machine 24 is accompanied by a smaller pivot angle than in the normal operating state of the steering 10.

In a further embodiment, it is provided that the steering system 10 is operated in the protective operating state 38 if the determined variable 36 characterizing the thermal load on the steering system 10 deviates from a threshold value 60 by more than a predetermined amount 58. The predetermined amount 58 can be any value, which can be zero or greater than zero, for example. For example, a comparison 62 is carried out between the determined variable 36 and the threshold value 60 by means of the electronic computing device 26. For example, the steering system 10 is operated in the protective operating state 38 if the determined variable 36 is greater than the threshold value 60. For example, the steering system 10 is operated in the normal operating state if the determined variable 36 is smaller than the threshold value 60.

In a further embodiment, it is provided that if the determined variable 36 characterizing the thermal load of the steering 10 deviates by more than a predetermined amount 64 from a second threshold value 66 different from the threshold value 60, the steering 10 is operated in a second protective operating state 68, which is different from the protective operating state 38, in particular, in which a maximum swivel angle 70 by which the respective vehicle wheel 16, 18 can be swiveled about the respective wheel swivel axis 20, 22 is smaller than in the protective operating state 38. In other words, in the second protective operating state 68 causes a limitation, in particular referred to as angle limitation, of the maximum swivel angle 70, in particular when stationary.

The predetermined measure 64 can be any value, which can be zero or greater than zero, for example. The predetermined measure 64 can be the same as or different from the predetermined measure 58. For example, a comparison 71 is carried out between the determined value 36 and the second threshold value 66 by means of the electronic computing device 26. The second threshold value 66 is, for example, greater than the first threshold value 60. For example, the steering system 10 is operated in the second protective operating state 68 if the determined value 36 is greater than the second threshold value 66. For example, the steering system 10 is operated in the protective operating state 38 if the determined value 36 is greater than the first threshold value 60 and less than the second threshold value 66.

In a further embodiment, it is provided that the variable 36 characterizing the thermal load of the steering 10 is determined by means of the electronic computing device as a function of the driving speed 56 of the motor vehicle.

In a further embodiment, it is provided that the variable 36 characterizing the thermal load of the steering 10 is determined by means of the electronic computing device 26 as a function of the angle of rotation 72 of the steering handle 14 and/or of a rotational speed 74 of the steering handle 14 about the axis of rotation 12.

For example, the steering gear 32 has at least one wheel 76 and at least one rack 78 coupled to the wheel so as to be movable in translation relative to the wheel 76. The respective vehicle wheel 16, 18 can be pivoted about the respective wheel pivot axis 20, 22 via the steering gear 32 by means of the electric machine 24.

Preferably, it is provided that the variable 36 characterizing the thermal load on the steering 10 is determined by means of the electronic computing device 26 as a function of an axial position 80 of the rack 78. An axial direction of the rack 78 runs, for example, at least substantially in the transverse direction of the motor vehicle.

For example, the quantity 36 is determined, in particular calculated, by means of an integral, in particular an integral characterizing a steering movement of the steering 10. Thus, the situation recognition 48 or a recognition of a Degradation of the steering 10 can take place via an integral of a steering wheel movement, for example with weighting over the driving speed 56. This integral includes, for example, the driving speed 56 and/or the angle of rotation 72 and/or the speed of rotation 74 and/or the axial position 80 of the rack 78. For example, a decay behavior can be taken into account by means of the electronic computing device, which characterizes, for example, a cooling of the steering 10, in particular of the drive unit 30. For example, when steering particularly quickly when stationary with a particularly large amplitude, the degradation or transition to the protective operating state 38 takes place after several, for example after ten, complete steering angles. This can be referred to in particular as 10 x Lock2Lock. The weighting of the quantity 36, in particular of the integral, over the driving speed 56 can, for example, take place in stages. These stages can be, for example, zero kilometers per hour, 0.5 kilometers per hour and/or two kilometers per hour. For example, the quantity 36 can be determined, in particular calculated, as a function of a temperature model by means of the electronic computing device 26.

In a further embodiment, it is provided that the steering 10 changes from the normal operating state to the protective operating state 38 and/or to the second protective operating state 68 depending on at least one operating parameter 82 of the electric machine 24. The operating parameter 82 is, for example, a temperature 82a of the electric machine 24 and/or a torque 82b of the electric machine 24 and/or a protective state 82c of the electric machine 24. The protective state 82c can in particular be referred to as a protective status or as a status derating. As a result, the temperature protection function 46 can be activated by a, in particular general, protective function 84 of the electric machine 24 or the drive unit 30. The protective function can in particular be understood as a derating of the electric machine 24 or the drive unit 30.

Claims

Patent claims Method for operating a steering system (10) for a motor vehicle, which has a steering handle (14) that can be rotated about an axis of rotation (12) and at least one electric machine (24), wherein in order to effect cornering and/or changes of direction of the motor vehicle when the steering handle (14) is rotated about the axis of rotation (12), at least one vehicle wheel (16) of the motor vehicle is pivoted about a wheel pivot axis (20) of the vehicle wheel (16) by means of the electric machine (24), and at least one variable (36) characterizing a thermal load on the steering system (10) is determined by means of an electronic computing device (26), characterized in that in a protective operating state (38) of the steering system (10), depending on the determined variable (36)

• a torque (42) to be applied by a driver of the motor vehicle to rotate the steering handle (14) about the axis of rotation (12) is set and/or

• a ratio (44) is set between a rotation angle (72) between two rotation positions of the steering handle (14) and a swivel angle between two swivel positions of the vehicle wheel (16) caused by the electric machine (24) as a function of the rotation angle (72). Method according to claim 1, characterized in that in the protective operating state (38) the torque (42) to be applied by the driver of the motor vehicle to rotate the steering handle (14) about the rotation axis (12) is greater than in a normal operating state of the steering (10). Method according to claim 1 or 2, characterized in that in the protective operating state (38) when the steering handle (14) is rotated about the axis of rotation (12) between two rotational positions, the vehicle wheel (16) is pivoted about the wheel pivot axis (20) by a smaller pivot angle (70) by means of the electric machine (24) than in a normal operating state of the steering (10). Method according to one of the preceding claims, characterized in that the steering (10) is operated in the protective operating state (38) when the determined variable (36) characterizing the thermal load on the steering (10) deviates from a threshold value (60) by more than a predetermined amount (58). Method according to claim 4, characterized in that if the determined variable (36) characterizing the thermal load on the steering (10) deviates by more than a predetermined amount (64) from a second threshold value (66) that is different from the threshold value (60), the steering (10) is operated in a second protective operating state (68) in which a maximum swivel angle (70) by which the vehicle wheel (16) can be swiveled about the wheel swivel axis (20) is smaller than in the protective operating state (38). Method according to one of the preceding claims, characterized in that the variable (36) characterizing the thermal load on the steering (10) is determined by means of the electronic computing device (26) as a function of a driving speed (56) of the motor vehicle. Method according to one of the preceding claims, characterized in that the variable (36) characterizing the thermal load on the steering (10) is determined by means of the electronic computing device (26) as a function of the driving speed (56) of the motor vehicle. The angle of rotation (72) of the steering handle (14) and/or the speed of rotation (74) of the steering handle (14) about the axis of rotation (12) is determined. Method according to one of the preceding claims, characterized in that the vehicle wheel (16) can be pivoted about the wheel pivot axis (20) by means of the electric machine (24) via at least one steering gear (32) which has at least one wheel (76) and at least one rack (78) which is coupled to the wheel so as to be movable in translation relative to the wheel (76), the variable (36) characterizing the thermal load on the steering (10) being determined by means of the electronic computing device (26) as a function of an axial position (80) of the rack (78). Method according to one of the preceding claims, characterized in that the steering (10) changes from a normal operating state to the protective operating state (38) as a function of an operating parameter (82) of the electric machine (24). Steering system (10) for a motor vehicle, which is designed to carry out a method according to one of the preceding claims.