Method for generating roadway feedback for a vehicle driver from low-frequency roadway excitations of a steer-by-wire steering system, and a steer-by-wire steering system

Abstract

The invention relates to a method for generating roadway feedback for a vehicle driver from low-frequency roadway excitations of a steer-by-wire steering system, wherein, on the basis of a rack force generated by a low-frequency roadway excitation, a change in the position of the rack takes place, and wherein haptic roadway feedback to a steering wheel actuator of the steer-by-wire steering system is generated depending on the change in the position of the rack.

Description

[0001] Method for generating road feedback from low-frequency road excitations of a steer-by-wire steering system for a vehicle driver and a steer-by-wire steering system

[0002] The invention relates to a method for generating road surface feedback from low-frequency road surface excitations of a steer-by-wire steering system for a vehicle driver according to claim 1 and to a steer-by-wire steering system according to claim 8. For the prior art, reference is made, for example, to DE 10 2014 211 815 A1.

[0003] So-called steer-by-wire steering systems for vehicles are already known in various forms from the state of the art. This differs from conventional steering systems in that the steering of the wheels is completely decoupled from the driver's mechanical steering movement or takes place solely through a purely electronic transmission. The conventional mechanical transmission devices are eliminated; instead, the driver generates data through their steering movement on the so-called steering handle or steering wheel, which is fed into an electronic control unit. This control module evaluates the data and converts it into corresponding steering commands. This then controls the steering gear, which executes the desired steering movement.

[0004] To provide the driver with the appropriate steering feel in a steer-by-wire steering system, as is customary with conventional steering systems, a steering wheel actuator, an actuation force simulator, a steering wheel motor, or a feedback actuator is typically installed on the steering wheel module. Based on the available sensor data, control electronics calculate a control value for the feedback actuator, which then maps steering wheel resistance to the steering wheel. Ideally, this should reflect the adhesion between the tires and the road surface at an appropriate force level.

[0005] Such a steer-by-wire steering system is described in DE 10 2014 211 815 A1. However, due to inaccuracies in rack force estimation and other interference, steering wheel inputs can occur that are inappropriate to the driving situation and irritate the driver. Steering wheel feedback in current systems cannot always be reproduced authentically.

[0006] It is therefore an object of the invention to provide a method for generating road feedback from low-frequency road excitations of a steer-by-wire steering system for a vehicle driver, which method reproduces road feedback that is as authentic as possible.

[0007] The solution to the problem arises from a method having the features of claim 1 and from a steer-by-wire steering system having the features of claim 7. Advantageous embodiments and further developments are the subject of the subclaims.

[0008] A method for generating road feedback from low-frequency road excitations of a steer-by-wire steering system for a vehicle driver is proposed.

[0009] Such road feedback, in this case haptic, is provided by a steering wheel actuator of the steer-by-wire steering system.

[0010] Such a steering wheel actuator, also referred to as a feedback actuator, represents an actuator arranged particularly on a steering handle for initiating a steering maneuver by a driver of a vehicle. This actuator generates, for example, the restoring force or torque for the steering handle or steering wheel in order to provide a haptic response familiar from conventional steering systems. Such a steering wheel actuator generates feedback, which is transmitted to the driver or steering handle based on wheel-road forces. This feedback is referred to as road feedback in the further course of the application.

[0011] In a steer-by-wire steering system, the steering handle or steering mechanism, which a driver operates to achieve wheel steering, is completely mechanically decoupled from the steered wheels. However, to still inform the driver about the current wheel-road forces or road feedback, as they are accustomed to, these are synthetically generated or simulated by the actuation simulator, for example, in the form of torques on the steering handle. The idea is that a rack position change occurs based on a rack force generated by a low-frequency road excitation.

[0012] Such low-frequency road surface excitation can be detected, for example. This detection can be achieved using suitable sensors or measurements, calculation or simulation methods, or similar. In particular, such detection is carried out using a so-called rack force estimator. Alternatively, such road surface excitation can also be detected using other suitable sensors or calculations or similar methods.

[0013] The rack force estimator estimates the current rack force based on measured currents in the steering gear's servo motor and other physical variables. It can determine whether road surface excitations in a conventional steering system would result in rack movement—and the associated steering wheel movement.

[0014] Based on the rack force estimate, a rack position change is then preferably performed. This rack position change is carried out, for example, via a suitable rack position controller.

[0015] Depending on the change in the rack position, a haptic road feedback as explained above is then generated, e.g. in the form of a torque on the steering wheel actuator of the steer-by-wire steering system.

[0016] In particular, low-frequency road excitations are fed back to the steering handle. For the purposes of this invention, low-frequency includes excitations or vibrations in the range between approximately 0.2 Hz and 3 Hz. Especially with low-frequency excitations, it is often difficult to provide the driver with suitable, haptic road feedback that is perceived as authentic and non-disturbing. Alternatively or in addition to the rack force estimator, the rack position change can be achieved by a rack position controller, whose controller stiffness is selected such that a slight change in the position of the rack is permitted, depending on the current rack force.

[0017] Depending on the rack force encountered, the position controller adjusts (within a defined stiffness) and allows a certain deviation in the rack position. If a rack force is generated by a low-frequency road excitation, the stiffness of the rack position controller allows a certain change in the position of the rack, causing it to shift or move. In direct response to this rack movement, which is detected by a suitable sensor (e.g., a rack position sensor), corresponding feedback of this rack movement is sent to the steering handle.

[0018] After the load has been removed, this rack movement is then preferably corrected back to its original position - at the same time, the steering wheel angle on the steering handle is also set back to its original position.

[0019] The proposed method of reporting the rack position change to a vehicle driver enables authentic road feedback from low-frequency road excitations.

[0020] Particularly preferably, the rack position change takes place as a function of driving dynamics variables, such as the current vehicle speed, the lateral acceleration, the roll angle, a steering wheel angle or a steering wheel speed and / or as a function of the current excitation spectrum of the road surface (the amplitude and the frequency) and / or as a function of physical influencing variables (for example motor currents or steering gear properties).

[0021] In this case, it is particularly preferred that the rack movement follows one or more stored characteristic curves. In an advantageous embodiment of the invention, the path of the rack position change includes a limit value beyond which no further position change occurs. This limit value cannot be exceeded. The limit value can also be adjusted depending on the current driving dynamics state (e.g., speed, lateral acceleration, steering wheel angle, steering wheel speed, etc.) and the excitation spectrum of the road surface (amplitude and frequency).

[0022] Particularly preferably, the limit value is approximately 1 mm, depending on the steering ratio.

[0023] A steer-by-wire steering system of a vehicle for carrying out the method according to one of claims 1 to 7 is also proposed.

[0024] The steering system comprises a rack controllable by a control unit. A change in the rack position can be detected by a suitable sensor (e.g., a rack position sensor) and transmitted to the steering handle in the form of haptic feedback.

[0025] The steering system may comprise at least one detection unit for detecting the low-frequency excitations. Such a detection unit may, for example, be one or more sensor units and / or a control unit for estimating, calculating, or simulating the excitation. In particular, the detection unit is a rack force estimator as described above.

[0026] Furthermore, the steering system comprises a steering wheel actuator which can be controlled by a control unit and which is configured to generate synthetic, haptic road feedback to a vehicle driver as a function of the detected change in the rack position.

[0027] Furthermore, the steering system can include a rack position controller for adjusting the rack, the stiffness of which is selected such that a position deviation of the rack is permitted depending on the current rack force. The advantage of the invention is that road information relevant to driving dynamics (limit range, road surface irregularities, etc.) can be provided to the driver as with a conventional steering system.

[0028] In the following, the invention is further explained using an exemplary embodiment, wherein the attached Figure 1 shows an exemplary characteristic curve for the position change of the rack as a function of the current rack force F. All features described in more detail can be essential to the invention.

[0029] A rack position change characteristic curve is shown, where the rack travel x in mm depends on the force F acting on the rack (which in turn is generated by the road surface excitations). The higher the rack force F, the greater the rack position change. In this specific case, a limit value for the rack travel x of 1 mm is set. However, this limit value can be changed depending on the current driving situation and the current driving dynamics, as well as the excitation spectrum of the road surface.

Claims

Patent claims 1. A method for generating road feedback from low-frequency road excitations of a steer-by-wire steering system for a vehicle driver, wherein - a rack position change occurs based on a rack force (F) generated by a low-frequency road excitation and - whereby a haptic road feedback is generated at a steering wheel actuator of the steer-by-wire steering system depending on the change in the rack position.

2. The method according to claim 1, wherein the low-frequency road excitation is detected by a rack force estimator.

3. The method of claim 1 or 2, wherein the rack position change is initiated by the rack force estimator.

4. Method according to claim 1, wherein the change in the rack position is carried out by a rack position controller, the controller stiffness of which is selected such that a change in the position of the rack is permitted depending on the rack force (F).

5. Method according to one of the preceding claims, wherein the rack position change occurs as a function of driving dynamics variables and / or physical influencing variables of the vehicle and / or the current excitation spectrum of the road surface.

6. Method according to one of the preceding claims, wherein the path (x) of the rack position change comprises a limit value beyond which no further rack position change occurs.

7. The method according to claim 6, wherein the limit value is set so as to be variable as a function of driving dynamics variables and / or physical influencing variables and / or the current excitation spectrum of the road surface.

8. Steer-by-wire steering system of a vehicle for carrying out the method according to one of claims 1 to 7, comprising a rack controllable by a control unit, a rack position sensor for detecting a change in the rack position, and a steering wheel actuator controllable by a control unit which is configured to generate synthetic, haptic road feedback to a vehicle driver as a function of the detected change in the rack position.

9. Steer-by-wire steering system according to claim 8, comprising a Rack force estimator for detecting a low-frequency Road excitation and initiation of the rack position change.

10. Steer-by-wire steering system according to claim 8, comprising a Rack position controller for adjusting the rack, the stiffness of which is selected such that a position deviation of the rack is permitted depending on the rack force.

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