Method for generating roadway feedback for a vehicle driver from low-frequency roadway excitations of 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 a low-frequency roadway excitation is detected, haptic roadway feedback is generated on a steering wheel actuator of the steer-by-wire steering system using the detected roadway excitation, and the generated roadway excitation is generated on the steering wheel actuator on the basis of the frequency of the low-frequency roadway excitation.

Description

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

[0002] The invention relates to a method for generating road feedback from low-frequency road excitations of a steer-by-wire steering system for a vehicle driver according to the preamble of claims 1 and 10. 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 shown in DE 10 2014 211 815 A1.

[0006] It is particularly difficult to display road surface excitations caused by low-frequency vibrations (referred to as low-frequency road excitations) as road feedback on the steering wheel actuator. Furthermore, the greatest energy is fed into the steering gear in the low-frequency road excitation range.

[0007] 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.

[0008] 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 9. Advantageous embodiments and further developments are the subject of the subclaims.

[0009] A method for generating road feedback from low-frequency road excitations of a steer-by-wire steering system for a vehicle driver is proposed.

[0010] Such road feedback, in this case haptic, is provided by a steering wheel actuator of the steer-by-wire steering system.

[0011] 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.

[0012] 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 intention is to detect low-frequency road excitation. Such detection can be achieved, for example, using suitable sensors or measurements, calculation or simulation methods, or similar. In particular, such detection is performed by a so-called rack force estimator.By estimating the current rack force based on measured currents in the steering gear's servo motor and other physical variables, it is possible to determine whether road surface excitations in a conventional steering system would lead to rack movement—and the associated steering wheel movement. The associated steering wheel movement (i.e., haptic feedback) can then be implemented by the steering wheel actuator on the steering wheel based on the rack force estimate.

[0013] This involves detecting low-frequency road surface excitation. For the purposes of this invention, low-frequency refers to excitations or vibrations in the range between approximately 0.5 Hz and 3 Hz. Especially with low-frequency excitations, it is often difficult to provide the driver with suitable, haptic road surface feedback that is perceived as authentic and non-disturbing.

[0014] It is also planned that the road surface feedback generated at the steering wheel actuator is dependent on the frequency of the low-frequency road surface excitation at the steering wheel actuator. This means that, depending on the detected frequency of the road surface excitation, different levels of feedback are generated at the steering wheel actuator. The lower the frequency, for example, the more precisely or realistically the excitations can be implemented as feedback on the steering wheel actuator.

[0015] In this case, it is particularly preferred that at least two frequency ranges are provided or defined in which a specific road feedback is generated at the steering wheel actuator with different levels of accuracy or precision. In this way, feedback at the steering wheel actuator from a detected excitation which lies in a frequency range between 0.5 - 1.5 Hz can be implemented more precisely or authentically than feedback from an excitation which is in a higher frequency range, for example 1.5 - 3 Hz. This is because excitations in the higher frequency range have greater interference and, if implemented precisely or authentically, can be perceived as annoying by a driver since, for example, the steering wheel then performs constant movements.

[0016] Particularly preferably, three frequency ranges are provided, wherein a first frequency range includes frequencies in the order of 0.5 to 1 Hz, a second frequency range 1 - 2 Hz and a third frequency range 2 - 3 Hz.

[0017] It is preferably provided that each frequency range is assigned a filter or smoothing function that eliminates respective interference and inaccuracies in the excitation, so that no disruptive feedback is displayed or transmitted to the driver. Such a filter, conceivable for example as a low-pass filter or similar, smooths the respective frequency curve of the excitation in the frequency range before the excitation is transmitted to the steering wheel actuator. The driver is thus provided with authentic feedback, free from interference. The interference in the respective frequency ranges is absorbed by the respective filters, so that appropriate feedback is provided to the driver for each frequency range.

[0018] In a very low-frequency range, for example, from 0.5 to 1 Hz, a suitable filter is required that filters out only a small amount of noise, as the interference is less significant. In a slightly higher range, for example, from 2 to 3 Hz, without a suitable filter or with a lower filter, too much noise might be transmitted to the steering wheel, which in turn can be perceived as annoying for the driver.

[0019] Thus, the frequency dependency allows low-frequency excitations to be fed back to the driver. A filter for the respective frequency ranges also ensures that authentic feedback is provided to the driver, free from interference.

[0020] Alternatively or additionally, it is possible to define a threshold value for the amplitudes of the road surface excitation, which must first be exceeded before any road surface feedback is generated at the steering wheel actuator. This also ensures that excitations with very low amplitudes, which in turn are associated with high levels of interference, are not fed back at all. It is then possible for this threshold value to be frequency-dependent, so that, for example, the threshold value is set lower at a low frequency (e.g., 0.5 Hz) than at a higher frequency (e.g., 2.5 Hz).

[0021] When selecting the filters, threshold values ​​and frequency ranges and the associated respective feedback on the steering wheel actuator, the aim is always to achieve maximum disturbance elimination with maximum authenticity of the simulation or feedback of the road excitations.

[0022] It is also preferred that the respective frequency ranges, filters, or threshold values ​​be adjusted depending on specific vehicle data or vehicle genes. For example, the ranges, values, or filters can differ for comfortable vehicles, sporty vehicles, long and short vehicles, and for vehicles with different roll behavior, axle kinematics, tires, or steering ratios.

[0023] A steer-by-wire steering system of a vehicle for carrying out the method according to one of claims 1 to 8 is also proposed.

[0024] The steering system comprises at least one detection unit for detecting the low-frequency excitations. Such a unit can be, for example, 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.

[0025] Furthermore, the steering system comprises a steering wheel actuator which can be controlled by a control unit and is configured to generate synthetic, haptic road feedback to a vehicle driver.

Claims

Patent claims 1. Method for generating road feedback from low-frequency road excitations of a steer-by-wire steering system for a vehicle driver, - where a low-frequency road excitation is detected and - wherein, based on the detected road excitation, a haptic road feedback is generated at a steering wheel actuator of the steer-by-wire steering system, characterized in that the generated road feedback is generated at the steering wheel actuator depending on the frequency of the low-frequency road excitation.

2. The method according to claim 1, wherein at least two frequency ranges are defined in which a specific road feedback is generated at the steering wheel actuator.

3. Method according to claim 2, wherein each frequency range is assigned a filter and / or a smoothing function.

4. The method according to claim 1, wherein a threshold value is defined for the amplitudes of the road excitation, above which, if exceeded, a road feedback signal is generated at the steering wheel actuator.

5. The method according to claim 4, wherein the threshold value is frequency dependent.

6. The method according to claim 5, wherein the threshold value is divided into frequency ranges and a filter is assigned to each frequency range.

7. Method according to one of the preceding claims 2 to 6, wherein a first frequency range is 0.5 to 1 Hz, a second frequency range is 1-2 Hz and a third frequency range is 2-3 Hz.

8. Method according to one of the preceding claims, wherein the frequency ranges are set depending on specific vehicle data.

9. Steer-by-wire steering system of a vehicle for carrying out the method according to one of claims 1 to 8, comprising at least one detection unit which detects the low-frequency road excitation, and a steering wheel actuator which can be controlled by a control unit and is configured to generate synthetic, haptic road feedback to a vehicle driver.

10. The steer-by-wire steering system of claim 9, wherein the sensing unit is a rack force estimator.

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