Method for generating roadway feedback for a steer-by-wire steering system for a vehicle driver, and a steer-by-wire steering system

Abstract

The invention relates to a method for generating roadway feedback of roadway excitations of a steer-by-wire steering system for a vehicle driver, wherein a lateral acceleration and / or a rolling movement of the vehicle is calculated, and wherein the calculated lateral acceleration and / or rolling movement is compared with measured sensor signals via a lateral acceleration and / or a rolling movement of the vehicle and a difference is calculated from these, wherein, if the calculated difference exceeds a threshold value, a haptic roadway feedback is generated at a steering controller actuator of the steer-by-wire steering system.

Description

[0001]Description Method for generating road surface feedback from a steer-by-wire steering system for a vehicle driver and steer-by-wire steering system The invention relates to a method for generating road surface feedback from 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 10. With regard to the prior art, reference is made, for example, to DE 10 2014 211 815 A1. So-called steer-by-wire steering systems for vehicles are already known in various forms from the prior art. Such a system differs from conventional steering systems in that the steering of the wheels is completely decoupled from the mechanical steering movement of the driver and only takes place via a purely electronic transmission. The conventional mechanical transmission devices are omitted; instead, the driver generates the road surface feedback through his steering movement on the so-called steering handle orat the steering wheel, which is fed to an electronic control unit. This control module evaluates the data and converts it into corresponding steering commands. This controls the steering gear, which executes the desired steering movement. In order to give the driver an appropriate steering feel in a steer-by-wire steering system, as is usual with conventional steering systems, a steering wheel actuator or an actuation force simulator or a steering wheel motor or a feedback actuator is usually arranged on the steering wheel module. Based on the available sensor data, the control electronics calculates a control value for the feedback actuator, which then maps a steering wheel resistance to the steering wheel. Ideally, this should reflect the adhesion between the tires and the road at an appropriate force level. Such a steer-by-wire steering system is described in DE 10 2014 211 815 A1.The object of the invention is to provide a method for operating a steer-by-wire steering system that provides authentic road feedback to the vehicle driver. This object is achieved by a method having the features of claim 1 and by a steer-by-wire steering system having the features of the independent claim 8. Advantageous embodiments and further developments are the subject of the dependent claims. A method for generating road feedback from a road excitation of a steer-by-wire steering system for a vehicle driver is proposed. A lateral acceleration and / or a roll motion of the vehicle is calculated. The calculation of this lateral acceleration or roll motion is preferably carried out using a model-related calculation method, for example, using a so-called single-track model or roll model.It is further provided that the calculated lateral acceleration and / or roll motion is compared with measured sensor signals regarding a lateral acceleration and / or roll motion (also referred to as measured lateral acceleration or roll motion) of the vehicle, and a difference is calculated between these. In other words, the calculated lateral acceleration or roll motion is compared with a measured lateral acceleration or roll motion, and the difference is calculated from these. If the determined difference exceeds a threshold value or a predetermined threshold, haptic road feedback is generated at a steering handle actuator (preferably a steering wheel actuator) of the steer-by-wire steering system.Preferably, when the threshold value is exceeded, a steering handle or steering wheel torque is transmitted to the steering handle actuator or the steering wheel actuator, depending on the rack force applied to the steering system's rack, thus providing the driver with haptic feedback on a steering handle of the vehicle. The calculated lateral acceleration and the calculated roll of the vehicle, in addition to the applied rack force, are then indicators of the presence of road surface excitation. Exceeding the threshold value of the difference between the calculated and measured signals indicates that a lateral acceleration or roll of the vehicle is exceeding or deviating from a steering movement. This indicates that the lateral acceleration or roll of the vehicle is due to road surface excitation.Exceeding the threshold value therefore indicates that the vehicle is experiencing lateral acceleration or roll that is independent of the vehicle's steering movement but is caused by road conditions. This should be reported to the driver via haptic feedback, preferably at the steering handle. This advantageously demonstrates a detection, analysis, and implementation methodology that provides reliable, authentic, haptic feedback to a vehicle occupant in response to road surface excitation. Furthermore, it is preferably provided that the vehicle's roll motion is calculated in the form of a roll velocity.The roll movement, in particular the roll velocity, is preferably calculated using a calculation model, for example a roll model, and then compared with a roll movement signal, in particular a roll velocity signal, measured at the center of gravity of the vehicle, from a sensor in the vehicle. To calculate the roll velocity, for example, an angle can be used that results from the difference between a left and right height position on an axle, in particular the front axle, of the vehicle. The roll velocity can then be calculated from the derivative of this angle. When calculating the lateral acceleration of the vehicle, a single-track model, for example, can be used. The lateral acceleration is calculated as a function of the current rack force applied to a rack of the steering system.This calculated lateral acceleration is then compared with the lateral acceleration of the vehicle using measured sensor signals. Furthermore, a steer-by-wire steering system (steering system for short) according to the independent claim 7 is proposed. The steering system comprises at least one computing unit for calculating a lateral acceleration and / or a roll motion of the vehicle. For example, the ride height sensors on a right and a left wheel or wheel suspension can be used to calculate the lateral acceleration. From their ride height difference, a roll motion can be calculated by deriving the resulting angle. Furthermore, the steering system comprises at least one sensor unit for measuring at least one lateral acceleration and / or roll motion of the vehicle. A sensor in the vehicle's center of gravity can be used to measure the roll velocity, for example.The steering system further comprises at least one evaluation unit for comparing the calculated and measured lateral acceleration and / or roll motion of the vehicle. Furthermore, the steering system comprises a steering handle actuator that can be controlled by a control unit and is configured to generate synthetic, haptic road feedback to a driver in response to the comparison. These and other features emerge not only from the claims and the description, but also from the drawings. The individual features can be implemented individually or in combination in an embodiment of the invention, and can represent advantageous and individually protectable designs, for which protection is claimed here. The invention is explained in more detail below using an exemplary embodiment. All of the features described in more detail can be essential to the invention.Figure 1 explains the calculation of the roll velocity using an exemplary embodiment. Figures 2 and 3 each show an example of a calculated and a measured roll velocity, wherein in the curve in Figure 1 the roll is caused by a steering movement, while in the curve in Figure 2 the roll is caused by an uneven road surface. Figure 1 shows a schematic illustration of a vehicle in a frontal view, which vehicle experiences a roll movement W about its longitudinal axis due to a spring movement of the vehicle suspension F. Height sensors are arranged on the respective vehicle suspension F on the two wheels R of the front axle of the vehicle, with which the exact height here, he. of the wheel suspension or the wheel house at a respective wheel can be measured. It is now intended to calculate the roll velocity 62 using the roll model shown in Figure 1.The roll velocity 61 measured at the center of gravity SP is then to be compared with the calculated one. If the difference between these two values ​​exceeds a certain predetermined threshold, it can be assumed that the rolling movement of the vehicle was caused by an uneven road surface. The driver is then given road surface feedback in the form of a steering handle torque on the steering handle, depending on the rack force Fz applied to the vehicle's steering rack at that time. In this specific case, the roll velocity 82 is calculated by deriving the difference between the two heights, h.e. from the ride height sensors on the front axle, and the resulting angle 82. Figures 2 and 3 show the measured roll velocity 81 and the calculated roll velocity 82 over time t, as well as the rack force Fz over time t.Figure 2 shows the roll behavior during a steering intervention, while Figure 3 shows the roll behavior triggered by a road bump. As can be seen in Figures 2 and 3, the rack force Fz acts or arises earliest in time. With every roll movement (regardless of whether it is caused by a steering intervention or a road bump), a rack force Fz arises. However, if the rack force Fz is caused by a steering intervention, this is not reported to the driver in the form of a steering torque. If, on the other hand, the rack force Fz is caused by a road bump, the driver is provided with haptic feedback in the form of a steering torque. The distance to the respective roll velocities 82 and 81 is shown only as an example and schematically in the figures and may differ from these.As can be seen in Figure 2, the signal curve and thus the difference between the measured and calculated roll speeds Ayı as well as the time difference Atı are small when the vehicle rolls due to a steering movement. For example, when driving through a rut (i.e. a road surface excitation), the wheel contact point on the vehicle shifts, causing the vehicle to compress or extend. This reaction can be detected early on in the ride height sensor, which, as can be seen in Figure 3, results in a larger time difference At2 and a larger difference Ay2 compared to the measured roll speed 81 at the vehicle's center of gravity SP (cf. Ayı and At2 from Figure 2). During normal steering, a harmonious roll behavior can therefore be seen as shown in Figure 2, i.e. the wheel spring travel (e.g. measured by the ride height sensors) and the measured roll behavior in the SP are very close together in time.If a rack movement is caused by road irregularities, the calculated roll velocity 62 is significantly offset in time from the actually measured roll velocity 61. Therefore, if a certain time difference Δt2 or roll difference Δy is exceeded, this is an indication that a road excitation is responsible for the vehicle roll. Depending on the current rack force Δfz, this is reported haptically to the driver in the form of a steering torque. This advantageously provides authentic feedback about the road conditions.

Claims

Patent Claims 1. A method for generating road feedback from a road excitation of a steer-by-wire steering system for a vehicle driver, wherein - a lateral acceleration and / or a roll motion of the vehicle is calculated - and wherein the calculated lateral acceleration and / or roll motion is compared with measured sensor signals concerning a lateral acceleration and / or a roll motion of the vehicle, and a difference (Ayz) is calculated therefrom, - wherein, if the calculated difference (Ay2) exceeds a threshold value, haptic road feedback is generated at a steering handle actuator of the steer-by-wire steering system.

2. The method according to claim 1, wherein the roll motion is calculated and measured in the form of the roll velocity (61, 92). 3.Method according to claim 1 or 2, wherein the roll movement of the vehicle is calculated by a calculation model and compared with a roll movement signal of a sensor in the vehicle, measured at the center of gravity (SP) of the vehicle.

4. Method according to claim 2 and 3, wherein the calculated roll speed (θ) is calculated from the derivative of an angle (θ1, 82) which results from the difference between a left-hand ride height sensor and a right-hand ride height sensor on an axle.

9. Method according to one of the preceding claims, wherein the lateral acceleration of the vehicle is calculated via a single-track model as a function of a current rack force (Fz) applied to a rack of the steering system, and wherein the calculated lateral acceleration is calculated by means of |. measured sensor signals are compared with the lateral acceleration of the vehicle.

6. Method according to one of the preceding claims, wherein, when the threshold value is exceeded, a torque of a steering handle of the steer-by-wire steering system is switched to the steering handle actuator as a function of a currently applied rack force (Fz).

7. Steer-by-wire steering system of a vehicle for carrying out the method according to one of claims 1 to 6, comprising - at least one computing unit for calculating a lateral acceleration and / or a roll movement of the vehicle - and at least one sensor unit for measuring at least one lateral acceleration and / or roll movement of the vehicle - and at least one evaluation unit for comparing the calculated and the measured lateral acceleration and / or roll movement of the vehicle.- and a steering handle actuator controllable by a control unit which is configured to generate synthetic, haptic road feedback to a vehicle driver in response to the comparison.

Images