Steer-by-wire steering system, steering input unit, steering actuator, and method for operating a steer-by-wire steering system

Abstract

The invention relates to a steer-by-wire steering system (1) for steering an axle (15), comprising: - a steering input unit (2); - a steering actuator (9); and - a steering input element (5), the steering input unit (2) having a feedback unit (3), which is coupled to the steering input element (5), and being designed to generate feedback, which can be haptically experienced by a driver on the steering input element (5), on the basis of a steering input variable (7) on the steering input element (5) by means of the feedback unit (3). The invention also relates to a steering input unit (2), to a steering actuator (9), and to a method for operating a steer-by-wire steering system (1).

Description

[0001] Steer-by-wire steering system, steering hub unit, steering actuator and a method for operating a steer-by-wire steering system

[0002] The present invention relates to a steer-by-wire steering system, a steering input unit, a steering actuator and a method for operating a steer-by-wire steering system.

[0003] State of the art

[0004] Nowadays, both mechanical steering systems and steer-by-wire systems are common. These systems can be divided into two subsystems. One subsystem is the steering input unit, which can be coupled to a steering input element, such as a steering wheel; this subsystem is also known as the "Hand Wheel Actuator" (HWA) system. The other subsystem is the steering actuator for steering the wheels, also known as the "Road Wheel."

[0005] The system is referred to as the "Actuator" (RWA) system. In mechanical steering systems, these two subsystems are mechanically connected via a mechanical linkage, such as the steering column and, if applicable, a steering gear. Thus, the two subsystems in mechanical steering systems are directly, i.e., physically, connected. With these mechanical steering systems, a user or operator always experiences noticeable haptic feedback, so-called force feedback, when operating the steering input element, in the form of perceptible resistance at the steering input element, especially when cornering, hitting curbs, etc. This feedback is generally caused by the forces acting on the wheel, which are then transmitted directly to the steering input element via the mechanical linkage.

[0006] In steer-by-wire steering systems, the mechanical linkage between the two subsystems via the steering column is omitted. Instead, the steering of the wheels, corresponding to a movement of the steering input, is controlled by the transmission of corresponding signals between the two subsystems, HWA (head-wheel steering) and RWA (tail-wheel steering). In other words, with steer-by-wire steering systems, steering of the wheels is achieved by transmitting a signal from the HWA to the RWA, where these signals are converted into an axle steering input. Direct feedback to the operator is not provided due to the absence of a mechanical linkage.

[0007] There is therefore a need for steer-by-wire steering systems that can adjust the steering feel for the operator. The object of the present invention is therefore to create a steer-by-wire steering system that can generate haptic feedback for the operator.

[0008] Disclosure of the invention

[0009] These and other problems, which will be mentioned in the following description or which can be recognized by a person skilled in the art, are solved by the subject matter of the independent claims. Advantageous embodiments and further developments can be found in the dependent claims, the following description, and the drawings.

[0010] The steer-by-wire steering system according to the invention for steering an axle comprises a steering input unit, a steering actuator, and a steering input element. The steering input unit includes a feedback unit and is coupled to the steering input element, wherein the steering input unit is configured to generate haptically perceptible feedback at the steering input element for the driver based on a steering input parameter at the steering input element via the feedback unit.

[0011] The feedback unit can include a motor, such as an electric motor, and / or a brake, such as a friction brake, in particular a magnetorheological brake, which makes it possible to imprint the haptically perceptible feedback onto the steering input element, e.g. via a mechanical coupling of motor and / or brake.

[0012] The steering input element is a manually operated steering input element, which can be designed as a steering wheel or joystick. An operator, such as a driver, can use it to generate a steering input variable, which then serves as the basis for generating haptic feedback. This steering input variable can be defined as an angle, such as the steering wheel angle or the swivel angle of a joystick.

[0013] To couple the steering input element with the steering input unit, the steering input unit can have a mechanical interface, such as a shaft or shaft section, to which the steering input element can be coupled. In particular, it can be provided that a steering input element designed as a steering wheel or joystick can be, or is, coupled to the mechanical interface in a rotationally fixed manner, so that a rotary or pivoting movement can be transmitted by an operator to the steering input unit via the steering element and / or that haptic feedback, e.g., in the form of a feedback torque, can be transmitted to the operator.

[0014] The haptic feedback can be perceived in particular as a counter-moment or counter-force at the steering input element, against which the operator must apply a steering input moment or steering input force.

[0015] The steer-by-wire steering system, preferably the steering input unit, can be configured to generate haptic feedback linearly or non-linearly in relation to the detected steering input. A combination of linear and non-linear generation of haptic feedback is also possible. In particular, it can be provided that the mechanical limits of the steer-by-wire steering system are taken into account in the haptic feedback. For example, a sudden increase in counter-torque at the maximum possible steering input may be possible. That is, at a steering input where the wheels have reached full steering lock and cannot be turned any further.

[0016] To control the feedback unit, a target feedback parameter, such as a target feedback torque or a target feedback force, can be generated based on the steering input parameter, which is then produced by the feedback unit. Alternatively, such a target parameter can also be an electrical parameter. For example, it could be a target current and / or a target voltage with which the feedback unit, in particular the motor and / or the brake, is operated.

[0017] A method for operating such a steer-by-wire steering system can therefore include a step in which the steering input is detected. Furthermore, such a method can include a step in which haptic feedback is generated based on the detected steering input.

[0018] The control of the feedback unit for generating the haptically perceptible feedback and / or for generating the target feedback value can be carried out via a control unit of the steer-by-wire steering system and in particular the steering input unit, which may be designed to execute the procedure step(s) described above.

[0019] If the control unit is designed as the control unit of the steering input unit, the steering input unit can be modular. In addition to the control unit and the feedback unit, it can then include a steering input detection device, such as a sensor (e.g., an angle sensor), with which the steering input can be detected. With the steer-by-wire steering system, the steering input unit, and the method described above, it is possible to generate haptic feedback to the operator via the steering input element.

[0020] The control unit can be designed as a freely programmable control unit that allows the haptically perceptible feedback to be generated depending on the steering input size, whereby the generation can be implemented arbitrarily, i.e. according to a function that can be specified by a developer or by the user.

[0021] According to one embodiment, the steering input unit is designed to generate haptically perceptible feedback based on a steering input deviation, where the steering input deviation describes a deviation of an actual steering input from a target steering input. The actual steering input can be the steering angle of a wheel or the average steering angle of the wheels of a steered axle. This describes the steering angle of a wheel or the average steering angle of the wheels of a steered axle relative to a steering angle for straight-ahead driving. Alternatively or additionally, the steering input deviation can be understood as the difference in the angles of a virtual torsion bar, which is stored as a model in the steer-by-wire steering system, particularly in the steering input unit and / or in the steering actuator. The torsion bar can represent an imaginary mechanical connection between the steering input unit and / or the steering actuator.The steering element and the steered wheels can be represented by the steer-by-wire steering system disclosed here. The target steering input can be understood as the angle describing the rotation angle of one end of the torsion bar. This can be, in particular, the end facing the steering input unit. The actual steering input can be understood as the angle describing the rotation angle of the other end of the torsion bar. This can be, in particular, the end facing the steering actuator. A corresponding steering input deviation, delta_phi, can then be expressed as the following difference: delta_phi = target steering input phi_RWA_target - actual steering input phi_RWA_ist.

[0022] The target steering input can be determined as a function of the steering input input generated by the operator via steering input at the steering input element. In particular, it can be provided that a conversion of the steering input input into the target steering input takes place. This conversion can correspond to a steering ratio between the steering input element and the steered wheel(s) and / or the corresponding end of the virtual torsion bar. The conversion can be performed, in particular, by multiplying the steering input input by a fixed parameter, a speed-based parameter, and / or a parameter dependent on the steering input input. A fixed parameter represents a simple and cost-effective parameterization method and can be interpreted as a fixed ratio.Speed-based multiplication can be implemented, in particular, by a characteristic curve or map where the vehicle speed is used as an input and a corresponding parameter is output. This allows for speed-dependent steering, specifically a higher steering ratio at low speeds, e.g., between 0 and 10 km / h, as when maneuvering, and a lower steering ratio at high speeds, e.g., above 100 km / h, as on the motorway. Steering input-dependent multiplication can also be implemented, in particular, by a characteristic curve or map where the steering input is used as an input and a corresponding parameter is output. This allows, for example, a non-linear steering ratio to be implemented.

[0023] The actual steering input can be detected by a suitable steering detection device, such as a sensor, for example, an angle sensor. The detected value can be converted into the actual steering input, for example, into a rotation angle of the corresponding end of the virtual torsion bar, or the detected value can be used directly as the actual steering input.

[0024] The steering input deviation can be determined using the control unit of the steer-by-wire steering system, in particular the control unit of the steering input unit or a steering control unit of the steering actuator. These are programmable or parameterizable units, so that the calculation of the steering input deviation, especially the calculation of the target steering input and thus the behavior of the steer-by-wire steering system in response to steering inputs from an operator, can be adjusted accordingly during parameterization or, more generally, during the system design.

[0025] To control the feedback unit and thus generate haptic feedback, the target feedback value can be generated as a function of the target steering input. In this way, haptic feedback via the steering element can be provided to the user, which, by considering the actual steering input in the steering input deviation, can reflect the current steering state of the wheels.

[0026] The procedure for operating such a steer-by-wire steering system can therefore include a step in which the target steering input is determined, e.g., as described above. Alternatively or additionally, the procedure can include a step in which the actual steering input is determined, e.g., as described above. Alternatively or additionally, the procedure can include a step in which the steering input deviation is determined, e.g., as described above.

[0027] According to one embodiment, the steering input unit is configured to generate haptic feedback based on a first model of a steering system with a virtual mechanical linkage to the axle. As described above, steering systems are known in which a mechanical linkage from the steering input unit to the axle or to the steered wheels of the axle is present. A steer-by-wire steering system according to the invention does not have this mechanical linkage. Instead, it can be configured such that the haptic feedback corresponds to, or at least closely approximates, that which an operator would experience with a system with a mechanical linkage.

[0028] To control the feedback unit, it can therefore be provided that a target feedback quantity, such as a target feedback torque or a target feedback force, is generated based on the steering input quantity and the actual steering quantity or the steering quantity deviation, so that a rotation on a virtual mechanical drive is simulated and the associated twisting of the virtual mechanical drive due to elasticities on the transmission path between input element and axle or wheels is represented by the haptically perceptible feedback.

[0029] Such a model can, for example, be implemented as a linear model where the target feedback parameter is calculated as the product of the steering input deviation delta_phi and a spring stiffness c1, thus representing the elasticity of a virtual mechanical linkage. The target feedback parameter, e.g., a target feedback torque applied to the steering element by the feedback unit, is then calculated as:

[0030] Target feedback size = c1 * steering size deviation delta_phi. In particular, the parameter c1 can characterize the torsional stiffness of a virtual torsion bar, as described above, of the virtual drive. The parameter value can be adapted to existing EPS steering systems to imitate their steering characteristics. However, it can also be freely parameterized, thus making it possible to simulate various steering system characteristics. Advantageously, different values ​​for c1 can be defined and used for each driving mode within the framework of the procedure.

[0031] According to one embodiment, damping of the virtual mechanical drive can also be modeled by multiplying a rate of change of the steering size deviation delta_phi with a damping coefficient d1.

[0032] Target feedback size = c1 * steering parameter deviation delta_phi + + d1 * steering parameter deviation change rate delta_phi_point

[0033] This allows for a more accurate modeling of the virtual mechanical drive, compared to modeling solely via the spring stiffness c1.

[0034] Both model approaches clearly demonstrate that modeling the virtual mechanical drive can be achieved simply and with minimal effort by using one parameter (spring stiffness c1) or two parameters (spring stiffness c1 and damping d1).

[0035] The determination of the target feedback size can be carried out using the control unit of the steer-by-wire steering system, in particular with the control unit of the steering input unit.

[0036] The procedure for operating such a steer-by-wire steering system may therefore include a step in which the target feedback value is generated based on the modeling described above.

[0037] In particular, the procedure can include a step in which the target steering parameter phi_RWA_target is determined, for example, as described above. Alternatively or additionally, the procedure can include a step in which the actual steering parameter phi_RWA_ist is determined, for example, as described above. Alternatively or additionally, the procedure can include a step in which the steering parameter deviation delta_phi is determined, for example, as described above. In particular, the procedure can include a step for generating the target feedback parameter.

[0038] According to one embodiment, the steering actuator has a drive unit, e.g., an electric motor, and is configured to generate an axle steering input to steer the axle or the axle's wheels. The axle steering input can be generated, in particular, by the steering actuator's drive unit. The axle steering input can be a force or a torque that can be applied by the steering actuator to the axle or a corresponding pivot point of the axle to steer the axle or the axle's wheels. The axle steering input can, in particular, be an axle steering torque or an axle steering force that is applied depending on the geometry or kinematics of the axle. This enables steering of the wheels or the axle.

[0039] The steering actuator can include a gearbox located between the drive unit and the axle. This gearbox converts a quantity generated by the drive unit, such as a torque or force, into the axle steering input through a transmission mechanism. This allows the drive unit to be smaller. Alternatively, the gearbox can be omitted, resulting in a less complex steering actuator.

[0040] According to one embodiment, the steering actuator is configured to generate the axle steering input based on the steering input deviation, as described above. This allows for consideration of the steering input value generated by the operator via steering input at the steering input element. Furthermore, this allows for consideration of the actual steering input value. Thus, for the steer-by-wire system, this provides a control and steering option for the axle or the axle's wheels without a mechanical drive.

[0041] To control the drive unit, a target drive variable, such as a target drive torque or a target drive force, can be generated, at least partially, based on the steering input deviation, which is then produced by the drive unit. Alternatively, such a target variable can also be an electrical variable. For example, it could be a target current and / or a target voltage with which the drive unit is operated. The drive unit can be controlled by the steering control unit of the steering actuator by supplying the drive unit with a steering input variable that contains or is based on the target drive variable. In particular, the steering control unit can be connected to a steering input sensor, such as a sensor, to detect the actual steering input, for example, by detecting a steering angle as described above.In this way, the actual steering input can be provided to the steer-by-wire steering system for calculating the steering input deviation.

[0042] The procedure for operating such a steer-by-wire steering system may include a step in which the axle steering input is generated based on the steering size deviation, as described above.

[0043] According to one embodiment, the steering actuator is designed to generate the axle steering input at least partially on the basis of a second model of a steering system with a virtual mechanical connection to the axle.

[0044] A virtual through-drive can be provided or modeled as an alternative or additional to the virtual mechanical through-drive at the steering input unit on the wheel or axle side of the steer-by-wire steering system.

[0045] To control the drive unit, it can therefore be provided that a target drive parameter is generated for the drive unit of the steering actuator, whereby this is generated on the basis of the steering parameter deviation, so that a rotation on a virtual mechanical drive and an associated twisting of the mechanical drive due to elasticities on the transmission path between input element and axle or wheels is virtually represented by the haptically perceptible feedback.

[0046] Such a model can, for example, be implemented as a linear model in which the target drive parameter is multiplied by the product of the steering deviation delta_phi and a spring stiffness c2, thereby representing the elasticity of a virtual mechanical drive. The target drive parameter, e.g., a target drive torque applied to the axle or wheels by the drive unit, is then calculated as:

[0047] Target drive size = c2 * steering size deviation delta_phi According to one embodiment, damping of the virtual mechanical drive can also be modeled by multiplying a rate of change of the steering size deviation delta_phi with a damping coefficient d2.

[0048] Target drive parameter = c2 * steering parameter deviation delta_phi + + d2 * steering parameter deviation change rate delta_phi_point

[0049] This allows for a more accurate modeling of the virtual mechanical drive, compared to modeling solely via the spring stiffness c2.

[0050] Both model approaches clearly demonstrate that modeling the virtual mechanical drive can be achieved simply and with minimal effort by using one parameter (spring stiffness c2) or two parameters (spring stiffness c2 and damping d2).

[0051] The determination of the target drive size can be carried out using the control unit of the steer-by-wire steering system, in particular with the steering control unit of the steering actuator.

[0052] The procedure for operating such a steer-by-wire steering system may therefore include a step in which the target drive parameter is generated based on the modeling described above.

[0053] According to one embodiment, the first model and the second model have different parameter settings. This means that with these parameter settings, particularly with different spring stiffnesses c1, c2 or different spring stiffnesses c1, c2 and damping values ​​d1, d2, it is possible to achieve a steering feel at the steering element that the operator is familiar with, or that can be optimized for them or at least adjusted according to their preferences. Simultaneously, the parameter settings for the virtual mechanical drive on the axle or wheel side can be set independently. For example, the steer-by-wire steering system, or the second model, can be set to be as stiff or direct as possible to improve driving safety.The response to steering inputs can be increased, while on the steering input unit side a softer, more compliant first model of a virtual mechanical transmission can be parameterized to improve ride comfort. If such modeling is done via the spring stiffnesses and, if applicable, damping values ​​mentioned above, then the following can apply: C1 < C2 or d < c2 and d1 < d2.

[0054] This makes it possible to achieve individually adjustable system behavior at both ends (steering element or axle or wheels) of the steer-by-wire steering system.

[0055] According to one embodiment, the first and second models can also be parameterized identically. In particular, it can be provided that the spring stiffnesses c1, c2 and / or the damping values ​​d1, d2 are the same. This allows a virtual mechanical linkage to be simulated, which has the same mechanical properties on both the steering input unit and the steering actuator side, in particular as an actually used torsion bar.

[0056] In general, a virtual through-drive can be simulated via parameterization, whereby in particular mechanical properties of the through-drive, e.g. caused by the geometry or material properties of the through-drive, can be set via parameterization.

[0057] According to one embodiment, the steering actuator is configured to generate the axle steering input at least partially based on a support input and / or a steering input. That is, alternatively or additionally to the above-described generation of the axle steering input based on the steering parameter deviation, the steering actuator may have supplementary or alternative means of generating the axle steering input.

[0058] This can be achieved based on a support parameter. For this purpose, the steering actuator, in particular the steering control unit, can be configured to generate a target support input that depends on the actual state of the steered axle or wheels and / or the steering input deviation. Specifically, this target support input can be determined based on a function, characteristic curve, or map that processes a parameter describing the actual state of the steered axle or wheels, for example, by means of the steering input deviation. Therefore, a corrective or supplementary target support input can be generated as a support parameter, which can be supplied to the drive unit in addition to the target input described above.

[0059] Advantageously, several characteristic maps are used, which can be switched between depending on the driving mode. This makes it possible to define a support level, such as a support torque, across a wide range, thus allowing the operator to freely determine the required effort over a broad range. Furthermore, suitable reductions or increases in the support level can be defined in the support level functions depending on the steering input deviation, particularly as support curves, preferably as non-linear support curves. In this way, the behavior of the steer-by-wire steering system can be adjusted relatively freely.

[0060] Alternatively or additionally, this can be done based on a steering input. This can, in particular, provide a target steering input value, which is generated, for example, by a driver assistance system such as a lane keeping assist system or an autonomous or at least semi-autonomous assistance system.

[0061] The target drive parameter, the support target drive parameter, and / or the steering parameter target drive parameter generated above can be sent by the steering control unit to the drive unit as steering control parameters for control purposes. Alternatively, the target drive parameter, the support target drive parameter, and / or the steering parameter target drive parameter can first be added together to form a single steering control parameter.

[0062] The method for operating such a steer-by-wire steering system can therefore include a step in which the target assist drive value and / or the target steering drive value are generated as described above. Furthermore, the method can include a step in which the target drive value, the target assist drive value, and / or the target steering drive value are sent to the drive unit to control it. Alternatively, the target drive value, the target assist drive value, and / or the target steering drive value can be added together beforehand.

[0063] The target drive size, the support target drive size and / or the steering size target drive size can be corrected by correction functions, such as a size and / or gradient limit, in order to implement component protection, for example.

[0064] This is especially important to protect the drive unit. Alternatively or additionally, the steering control variable can also be corrected using a correction function such as a size and / or gradient limit.

[0065] According to one embodiment, the steer-by-wire system is configured to change its system behavior depending on a mode, such as an operating or driving mode. For example, an operator can set a driving mode via an interface to the system, so that the parameterization of the virtual torsion bar model, in particular the first model and / or the second model, is changed by switching to other predetermined parameters stored in the respective control units, such as spring stiffnesses c1, c2 and / or damping d1, d2. Other parameters and characteristic maps described above, which will not be listed in detail here, can also be changed in this way depending on a driving mode.To configure the virtual torsion bar model, it may be possible for the user to set parameters such as spring stiffnesses c1, c2 and / or damping d1, d2 in such a way that they cannot switch between previously saved values ​​when changing modes. Instead, the parameters may be freely selectable, for example, by entering numerical values ​​and / or using a slider, perhaps on a screen. This can be done during development and system tuning or calibration, for example, by an application engineer as the user. It may also be intended for end users. Furthermore, the setting options may be limited to prevent safety-critical parameter ranges, such as excessively soft spring stiffnesses c2.

[0066] According to one embodiment, the steer-by-wire steering system is configured to enter a state in which no axle steering input is generated by the steering actuator, regardless of any driver steering input at the steering input element. In this state, which is preferably activatable when stationary or during autonomous driving, the operator's steering input has no effect on the axle or wheels of the vehicle. Instead, the steering element can be used as an input device for other purposes. For example, an interactive entertainment program, such as a video game or fitness application, can be displayed on a screen in the vehicle. The steering element can then be used to input input, enabling interaction with the entertainment program. In particular, a screen in the vehicle or a mobile device that can be connected to the vehicle can be used as the display element.This feature allows the steering to be used for other purposes when operator input is not required for the driving task, for example, when stationary or during autonomous driving. In this way, it is possible to bridge or make waiting or travel time in the vehicle more enjoyable.

[0067] According to one embodiment, the steer-by-wire steering system comprises a vehicle axle with at least one steered wheel, wherein the axle or the at least one steered wheel of the axle can be steered by the steering actuator of the steer-by-wire steering system.

[0068] According to a further aspect of the invention, a steering input unit as described above is provided. The steering input unit is specifically designed to be integrated into a steer-by-wire steering system as described above. Therefore, reference is made to the above explanations.

[0069] According to a further aspect of the invention, a steering actuator as described above is provided. The steering actuator is specifically designed to be used in a steer-by-wire steering system as described above. Therefore, reference is made to the above explanations.

[0070] According to a further aspect of the invention, a method for operating a steer-by-wire steering system as described above is provided. It is clear to a person skilled in the art that features and characteristics described above in connection with the steer-by-wire steering system, the steering input unit, and the steering actuator are to be understood analogously or directly, at least as further developments of the method disclosed herein.

[0071] Detailed description based on drawing

[0072] Further measures improving the invention are described in more detail below, together with a description of an embodiment of the invention with reference to the figures. The figures show:

[0073] Fig. 1 shows a schematic representation of a steer-by-wire system according to an embodiment of the invention,

[0074] Fig. 2 shows a simplified signal flow diagram for generating a target feedback value for a feedback unit, and

[0075] Fig. 3 shows a simplified signal flow diagram for generating a steering control signal for a drive unit. The figures are purely schematic and serve only to illustrate the invention. The same elements are labelled with the same reference numerals.

[0076] Fig. 1 shows a schematic and exemplary representation of a steer-by-wire system according to an embodiment of the invention.

[0077] Shown is a steer-by-wire steering system 1 with a steering input unit 2 and a steering actuator 9 and a steering input element 5.

[0078] The steering input unit 2 includes a feedback unit 3, a steering input detection device 4 and a control unit 6.

[0079] The steering input detection device 4, e.g., an angle sensor, is configured to detect steering input via the steering element 5, e.g., a steering wheel, and send it as steering input variable 7 to the control unit 6. The control unit 6 is configured to process the steering input variable 7 and, based on this variable, to control the feedback unit 3 by sending a target feedback variable 8 to the feedback unit 3. By appropriately controlling the feedback unit 3, a haptic feedback is perceived by the operator at the steering element 5, as the feedback unit 3 can, for example, apply a corresponding feedback torque.

[0080] The steering actuator 9 comprises a drive unit 10, a steering detection device 11 and a steering control unit 12.

[0081] The steering sensing device 11, e.g., an angle sensor, is configured to detect an actual steering parameter 13, e.g., a steering angle, of an axle 15 with steered wheels 17. This can be done, e.g., directly or via kinematic relationships, such as the displacement of the tie rod 16 shown. The steering control unit 12 is configured to actuate the drive unit 10 based on the steering input parameter 7 and the actual steering parameter 13, e.g., based on the steering parameter deviation, as described above, by sending a steering control parameter 14 to actuate the drive unit 10. By appropriately controlling the drive unit 10, steering of the axle 15 is possible, since the drive unit 10 can apply a corresponding steering torque to the axle 15. A connection 38 exists between the control unit 6 and the steering control unit 12, e.g.,a data connection via which calculation and / or control variables, such as the steering variable deviation, the steering input variable 7 and / or the actual steering variable 13 and / or the steering control variable 14, can be exchanged between the control units 6, 12.

[0082] Fig. 2 shows a simplified signal flow diagram for generating a target feedback variable for a feedback unit. Fig. 3 shows a simplified signal flow diagram for generating a steering control variable for a drive unit. Both drawings are explained together below.

[0083] The control unit 6 of the steering input unit 2 can, for example, be designed to operate according to this signal flow diagram.

[0084] On the right is the output target feedback parameter 8 for controlling the feedback unit 3, as shown in Fig. 1. On the left is the input of the steering input parameter 7. This is fed to an input parameter limiter 18. The input parameter limiter 18 generates a limit feedback parameter 8", which takes into account the steering stops of the wheels 17. That is, if the steering input parameter 7 is at a value corresponding to a maximum steering angle of the wheels 17, the limit feedback parameter 8" is abruptly increased by the input parameter limiter 18, which is otherwise zero.

[0085] In the lower left, the steering input deviation 20, i.e., a deviation between the target steering input 19 and the actual steering input 13, is fed into a first model 36. This first model corresponds to the modeling of a virtual mechanical connection between a steering input element 5 and the axis 15. In this specific case, a spring stiffness is defined here, which is combined with the steering input deviation 20 to create a model feedback control variable 8'. The model 36 depends on a mode 24, e.g., a driving or operating mode, of the steering system 1. This means that the calculation of the model feedback control variable 8' can vary depending on the mode 24, for example, because different parameters are defined in the model 36 depending on the mode 24.

[0086] The model feedback control variable 8' and the limiting feedback variable 8" are then added to form a raw target feedback variable 8'". This takes into account both the steering stops and the model of the virtual mechanical drive. The raw target feedback variable 8'" is then passed on by a switch 32 and, via a gradient limit 27 for component protection, which is dependent on the temperature 25 of the feedback unit 3, e.g., the temperature of the coil winding, is passed to a limiter 30, which may further limit the variable to prevent excessively high or potentially dangerous feedback at the steering element 5.

[0087] After the limiter 30, the target feedback value 8 is output, which is then used to control the feedback unit 3.

[0088] The entire signal flow plan can be implemented, for example, using software on the control unit 6.

[0089] Fig. 3 shows the signal flow diagram as it can be implemented, for example, on the steering control unit 12.

[0090] The output of the steering control variable 14 for controlling the drive unit 10 is shown on the right. The upper left shows how the steering input variable 7 and, optionally, a vehicle speed 34 are passed to a target steering variable generator 33. The target steering variable generator 33 calculates the target steering variable 19 from this, and, if the speed 34 is passed, depending on the speed 34.

[0091] The steering sensor 11, which outputs the actual steering parameter 13, is shown in the lower left.

[0092] The actual steering parameter 13 is then subtracted from the target steering parameter 19, resulting in the steering parameter deviation 20 mentioned above. As shown in Fig. 1, there is a connection 38 between the control unit 6 and the steering control unit 12, through which parameters such as the steering parameter deviation 20 and / or the actual steering parameter 13 and / or the steering input parameter 7 can be exchanged. The connection 38 can be a data connection, in particular a CAN connection.

[0093] Furthermore, a second model 37 is shown, which models a virtual mechanical transmission from the steering element 5 to the axle 15. Model 37 contains model parameters 35, which are multiplied by the steering deviation 20. These parameters can be a spring stiffness and a damping, which are included as vectors in the model parameters 35 and are calculated accordingly with the steering deviation 20 and the steering deviation change rate 20', which is a time derivative of the steering deviation 20. Thus, model 37 outputs a stiffness component 21 and a damping component 22, which are added together as components of a target drive parameter 41, a support target drive parameter 23, and a steering target drive parameter 29. This sum is then fed to a gradient limiter 28 for component protection, which is designed depending on the temperature 26 of the drive unit 10, e.g., the temperature of the coil winding of the drive unit 10.

[0094] This results in the steering control variable 14, which is supplied to the drive unit 10 to steer the axle 15 or the wheels 17.

[0095] The target support drive parameter 23 is calculated here by a support generator 39 and is dependent on the steering parameter deviation 20, which serves as the input parameter to the support generator 39, and also depends on a mode 24, e.g., a driving mode. This allows the steering control parameter 14 to be increased in addition to the component resulting from the steering input parameter 7, thus creating a servo effect in the steering.

[0096] The steering input variable 29 is calculated here by a steering input variable generator 40 and can be generated, for example, independently of the steering input variable 7 and the steering input deviation 20, and can also be applied to the steering control variable 14. This is, for example, a component of a driver assistance system that supports the driver or controls the vehicle autonomously.

[0097] Figure 2 also shows a feedback control source 31 connected to the switch 32. When the switch 32 is in the position shown, the feedback control source 31 does not influence the target feedback value 8. However, when the switch 32 is toggled, for example, when stationary or in autonomous driving mode, it can be seen that the left branch in Figure 2 no longer has any effect on the target feedback value 8. Instead, only the feedback control source 31 is now active. In this mode, the steering element can be used as an input device for other purposes, as described above. For example, an interactive entertainment program, such as a video game or a fitness application, could be offered on a display element in the vehicle. The steering element can then be used to input the corresponding input, enabling interaction with the entertainment program.In particular, it may be possible to use a screen in the vehicle or a mobile device that can be paired with the vehicle as a display element. This allows the steering to be used for other purposes when operator input is not required for the driving task, for example, when stationary or during autonomous driving. In this way, waiting or driving time in the vehicle can be bridged or made more engaging. The feedback control source 31 can be linked to the corresponding application, with the application sending the relevant control variables to the feedback control source 31.

[0098] Finally, some advantages of the previously presented embodiments of the invention will be explained.

[0099] By specifying a driving or operating mode, different steering system characteristics can be set. This makes it possible to change the steering system characteristics depending on the situation and / or to set personalized steering system settings for different drivers or driver groups.

[0100] The ability to specify steering input allows driver assistance systems and autonomous driving systems to be used with the steer-by-wire steering system.

[0101] The option to specify support levels allows for the configuration of additional, freely definable target support drive parameters, such as steering assist torque. This enables the steering force requirement for the steering system to be freely adjusted across a wide range, e.g., for different vehicle classes, for drivers with special needs (e.g., disabled persons), etc.

[0102] By positioning the variable steering ratio characteristics in the steering actuator, particularly in the steering control unit, the steering input unit can be simple in design and construction. This results in space savings in the interior and / or cost advantages.

[0103] By transmitting the steering input deviation delta_phi, instead of a hand torque, via the connection, in particular via the data connection, between the steering input unit and the steering actuator or between the control unit of the steering input unit and the steering control unit, it is possible to implement different torque feedbacks to the driver in the hand actuator in the steering input unit via a parameterizable parameter c1, which may be switchable via operating or driving modes, or via the parameters c1 , d1.

[0104] Using the steering input deviation delta_phi to describe the driving state, and especially as a parameter for controlling the steering input unit and steering actuator, offers advantages. This parameter is a purely geometric quantity that describes a deviation of the actual state from a target state in the steering system. Exchanging this parameter between the steering input unit and steering actuator, or between the steering input unit's control unit and the steering control unit, allows for haptic feedback to be set at the steering element by the steering input unit, without other influences that might be disruptive to the driver, such as those from the assistance setting or the steering input setting, affecting the haptic feedback. Thus, driver irritation from such influences is eliminated. The assistance setting and / or the steering input setting then act exclusively at the axle or wheel side.

[0105] Using the steering input deviation delta_phi to describe the driving condition has the particular advantage that a quick calculation of the steering input and / or target feedback is possible without needing the steering input and / or target feedback to calculate the other input, which ultimately leads to an efficient and fast calculation of the required inputs.

[0106] The control unit for the steering input unit and the steering control unit can also be combined into a single control unit. This can offer space-saving advantages, for example, if the steering input unit and / or the steering actuator do not require their own separate control unit and can therefore be built smaller.

[0107] Reference symbol list

[0108] 1 Steer-by-wire steering system

[0109] 2 Steering input unit

[0110] 3 Feedback Unit

[0111] 4 Steering input acquisition devices

[0112] 5 Steering input element

[0113] 6 Control unit

[0114] 7 Steering input size

[0115] 8 Target feedback size

[0116] 8' Model feedback control size

[0117] 8" Limit feedback size

[0118] 8'“ Raw target feedback size

[0119] 9 steering adjusters

[0120] 10 Drive unit

[0121] 11 Steering detection devices

[0122] 12 Steering control unit

[0123] 13 Actual steering size

[0124] 14 Steering control parameter

[0125] 15 vehicle axle

[0126] 16 tie rod

[0127] 17-inch wheel

[0128] 18 Input size limit

[0129] 19 Target steering size

[0130] 20 steering size deviation

[0131] 20' Steering size deviation change rate

[0132] 21 Stiffness component

[0133] 22 Damping component

[0134] 23 Support target drive size

[0135] 24 mode

[0136] 25 Temperature

[0137] 26 Temperature

[0138] 27 Gradient Limitation

[0139] 28 Gradient Limitation

[0140] 29 Steering size target drive size

[0141] 30 limiters

[0142] 31 Feedback control variable source 32 Switches

[0143] 33 Target Steering Parameter Generator

[0144] 34 Speed

[0145] 35 Model parameters 36 First model

[0146] 37 second model

[0147] 38 connection

[0148] 39 Support Generator

[0149] 40 Steering parameter setpoint generator 41 Setpoint drive parameter

Claims

Claims 1. Steer-by-wire steering system (1) for steering an axle (15), comprising: - a steering input unit (2); - a steering divider (9), - a steering input element (5) wherein the steering input unit (2) has a feedback unit (3) coupled to the steering input element (5), and the steering input unit (2) is configured to generate feedback on the steering input element (5) that can be felt haptically by a driver on the basis of a steering input parameter (7) at the steering input element (5) by means of the feedback unit (3).

2. Steer-by-wire steering system (1) according to claim 1, wherein the steering input unit (2) is configured to generate haptically perceptible feedback based on a steering input deviation (20), wherein the steering input deviation (20) describes a deviation of an actual steering input (13) from a target steering input (19).

3. Steer-by-wire steering system (1) according to one of the preceding claims wherein the steering input unit (2) is configured to generate the haptically perceptible feedback based on a first model of a steering system with virtual mechanical transmission to the axle (15).

4. Steer-by-wire steering system (1) according to one of the preceding claims, wherein the steering actuator (9) has a drive unit (10) and the The steering actuator (9) is designed to generate an axle steering input in order to steer the axle (15).

5. Steer-by-wire steering system (1) according to claim 4, wherein the steering actuator (9) is configured to generate the axle steering input at least partially on the basis of a second model of a steering system with virtual mechanical transmission to the axle (15).

6. Steer-by-wire steering system (1) according to one of the preceding claims with claims 3 and 5, wherein the first model and the second model have different parameterizations.

7. Steer-by-wire steering system (1) according to one of claims 3 to 5, wherein the steering divider (9) is configured to generate the axle steering input at least partially on the basis of a support input and / or a steering input.

8. Steer-by-wire steering system (1) according to one of the preceding claims, wherein the steer-by-wire steering system (1) is configured to be brought into a state in which, irrespective of a driver steering input at the steering input element (5), no axle steering input is generated by the steering actuator (9).

9. Steering input unit (2) according to one of claims 1 to 8 or steering actuator (9) according to one of claims 1 to 8.

10. Method for operating a steer-by-wire steering system (1) according to any one of claims 1 to 8.

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