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DE-102024133193-A1 - Method for operating a steer-by-wire steering system for a motor vehicle and steer-by-wire steering system

DE102024133193A1DE 102024133193 A1DE102024133193 A1DE 102024133193A1DE-102024133193-A1

Abstract

The disclosure generally relates to a method for operating a steer-by-wire steering system (12) for a motor vehicle (10) and a steer-by-wire steering system (12). The steer-by-wire steering system (12) comprises at least one road wheel actuator (16) and a control device (14) coupled to at least one road wheel actuator (16). A steering input is received by the control device (14). A regular angle input for a road wheel angle of steerable vehicle wheels (20) of the motor vehicle (10) coupled to the road wheel actuator (16) is determined by the control device (14) based on the steering input. An adapted angle input profile for the road wheel angle is determined by the control device (14) by superimposing the regular angle input with a superimposed angle profile. A control signal based on the adapted angle input profile is transmitted by the control device (14) to the road wheel actuator (16). The control signal is such that the road wheel actuator (16) adjusts the road wheel angle of the steerable vehicle wheels (20) based on the adapted angle profile. At least one operating parameter influenced by the road wheel actuator (16) is detected by at least one sensor (26) of the steer-by-wire steering system (12) during the adjustment of the road wheel angle of the steerable vehicle wheels (20). An updated friction value of the road wheel actuator (16) is estimated by the control device (14) based on the detected operating parameter. The current friction value of the road wheel actuator (16) is adjusted by the control device (14) based on the estimated updated friction value.

Inventors

  • Oliver Nehls
  • Sergio Codonesu
  • Alexander Ein Waldt
  • Hannah Denomme

Assignees

  • FORD GLOBAL TECHNOLOGIES, LLC

Dates

Publication Date
20260513
Application Date
20241113

Claims (16)

  1. A method for operating a steer-by-wire steering system (12) for a motor vehicle (10), wherein the steer-by-wire steering system (12) comprises at least one road wheel actuator (16) and a control device (14) coupled to at least the road wheel actuator (16), the method comprising at least the following steps: - Receiving a steering input by the control device (14), - Determining a regular angle input for a road wheel angle of steerable vehicle wheels (20) of the motor vehicle (10) coupled to the road wheel actuator (16) by the control device (14) based on the steering input, - Determining an adapted angle input profile for the road wheel angle by the control device (14) by superimposing the regular angle input with a superimposed angle profile, - Transmitting a control signal based on the adapted angle input profile to the road wheel actuator (16) by the control device (14), wherein the control signal such that the road wheel actuator (16) tracks the road wheel angle of the steerable vehicle wheels based on the adapted angle specification profile, - Detect at least one operating parameter influenced by the road wheel actuator (16) using at least one sensor (26) of the steer-by-wire steering system (12) during the tracking of the road wheel angle of the steerable vehicle wheels (20), - Estimate an updated friction value of the road wheel actuator (16) by the control device (14) based on the detected operating parameter, and - Adjust a current friction value of the road wheel actuator (16) based on the estimated updated friction value by the control device (14).
  2. Procedure according to Claim 1 , characterized in that the adapted angle specification is determined by the control device (14) only if the control device (14) has determined at least one fulfilled trigger condition.
  3. Procedure according to Claim 2 , characterized in that the triggering condition comprises at least one of: - a predetermined time interval, - a predetermined driving distance covered by the motor vehicle (10), - a predetermined number of ignition cycles and/or charging cycles of the motor vehicle, - a predetermined maintenance interval, - an actuator temperature of the road wheel actuator (16) and/or an ambient temperature that is below or above a respective temperature threshold and/or within a predetermined respective temperature interval, - a vehicle speed that is within a speed interval, - a regular angle specification that is within an angle interval and/or an angular velocity interval, and - a predetermined surface type.
  4. Method according to one of the preceding claims, characterized in that the superposition angle profile comprises a profile of a varying superposition angle.
  5. Procedure according to Claim 4 , characterized in that the course of the varying superposition angle comprises a sinusoidal course, a rectangular course, a triangular course, a sawtooth course, a random course, and wherein a frequency of the varying superposition angle course is constant or varies.
  6. Method according to one of the preceding claims, characterized in that the superposition angle profile has a duration that is shorter than a predetermined time threshold.
  7. Method according to one of the preceding claims, characterized in that the control device (14) takes into account the respective current friction value when adjusting the road wheels (20) based on the control signal transmitted to the road wheel actuator (16).
  8. A method according to one of the preceding claims, characterized in that the detected operating parameter, at least one of which is influenced by the road wheel actuator (16), comprises at least one of: - the superimposed angle profile, - the regular angle input based on the steering input, - a wheel angle of at least one steerable vehicle wheel (20) of the motor vehicle detected by means of at least one wheel angle sensor, - a motor torque and/or a motor current of the road wheel actuator (16), - an electrical power input or mechanical power output by the road wheel actuator (16), - a required amount of electrical energy of the road wheel actuator (16), - an expected value of the electrical power required by the road wheel actuator (16) based on the adapted angle input profile, - an expected value of the power input based on the adapted angle input profile with respect to the superposition angle profile recorded by the road wheel actuator (16).
  9. A method according to one of the preceding claims, characterized in that the control device (14), when estimating the updated friction value, takes into account at least one of the following: - a transfer function of a controlled system of the steer-by-wire steering system (12) and/or the motor vehicle (10), - a Kalman filter and/or an estimation algorithm, - changes in an amplitude response and/or a frequency response of the angular profile of the steerable vehicle wheels (20) determined from the operating parameter, in particular a phase shift in the frequency response of the transfer function, - a change in a cutoff frequency, - a time delay and/or an overshoot and/or a static offset between a detected wheel angle of the steerable vehicle wheels (20) and a nominal wheel angle of the steerable vehicle wheels (20), wherein the nominal wheel angle of the steerable vehicle wheels (20) is based on an ideal transfer function of the control signal, - a change in an electrical power consumption of the road wheel actuator (16) depending on successive superposition angle profiles or depending on a nominal profile, and - a change in a breakaway torque, wherein the breakaway torque is determined based on a requirement for a quantity of electrical energy.
  10. Method according to one of the preceding claims, characterized in that the control device (14) refrains from estimating an updated friction value if, based on at least one environmental sensor (24) and/or sensor (26), an external disturbance acting on the motor vehicle (10) is detected, the disturbance amplitude of which is greater than a predetermined amplitude threshold.
  11. Method according to one of the preceding claims, characterized in that the control device (14) adjusts the current friction value only if a difference between the estimated updated friction value and the current friction value is less than a difference threshold value.
  12. Method according to one of the preceding claims, characterized in that the control device (14) takes into account at least one of the following when adjusting the current friction value: - a filtering of the estimated updated friction value, - a moving average or a weighted average of the friction value, and - a gradient limitation of the change in the friction value.
  13. Method according to one of the preceding claims, characterized in that the control device (14) selects the superposition angle profile at least such that: - the superposition angle profile causes only a negligible change in the rack force caused by the road wheel actuator (16), and/or - an amplitude of the superposition angle profile is smaller than an amplitude threshold value, and/or - a frequency of the superposition angle profile is smaller than a frequency threshold value.
  14. Method according to one of the preceding claims, characterized in that the control device (14) additionally estimates the rack force caused by the road wheel actuator (16) at least on the basis of the steering input and the superposition angle profile.
  15. Procedure according to Claim 14 , characterized in that the control device (14) takes into account a filtering for a period of time corresponding to the actuating signal transmitted to the road wheel actuator (16) when estimating the rack force.
  16. A steer-by-wire steering system (12) for a motor vehicle (10), wherein the steer-by-wire steering system (12) comprises at least one road wheel actuator (16), a sensor (26), and a control device (14) coupled to the road wheel actuator (16) and the sensor (26), wherein the control device (14) is configured to: - receive a steering input, - determine a regular angle input for a road wheel angle of steerable vehicle wheels (20) of the motor vehicle (10) coupled to the road wheel actuator (16) based on the steering input, - determine an adapted angle input profile for the road wheel angle by superimposing the regular angle input with a superimposed angle profile, - transmit a control signal based on the adapted angle input profile to the road wheel actuator (16), wherein the control signal is such that the road wheel actuator (16) adjusts the road wheel angle of the steerable vehicle wheels. (20) follows the adapted angle specification profile, wherein the sensor (26) is configured to detect at least one operating parameter influenced by the road wheel actuator (16) during the following of the road wheel angle of the steerable to detect vehicle wheels (20) and transmit them to the control device (14), the control device (14) being further configured to: - estimate an updated friction value of the road wheel actuator (16) based on the detected operating parameter, and - adjust a current friction value based on the estimated updated friction value.

Description

The disclosure generally relates to a method for operating a steer-by-wire steering system for a motor vehicle and a steer-by-wire steering system. Steer-by-wire steering systems (hereinafter referred to as SBW steering systems) are a new automotive steering technology that represents an evolution of electric power steering (also called EPAS steering systems), in which a mechanical linkage transmits the driver's steering inputs directly to the wheels. SBW steering systems eliminate this mechanical linkage. Two actuator subsystems work together to steer the vehicle: a feedback steering actuator (FBA), which generates feedback torque at the steering wheel for the driver, and a road wheel actuator (RWA), which controls at least one, but typically several, steerable vehicle wheels into the desired position. In rack-and-pinion EPAS steering systems, the accumulation of water from the environment within the housing, particularly through the tie rods, can lead to increased friction over time due to corrosion. The electric motor and the driver can overcome this friction for a while to continue providing assistance and allow the rack to move and steer the vehicle. Eventually, the internal corrosion and friction become so severe that a blockage can occur, resulting in a loss of steering. In self-balancing (SBW) steering systems, increased friction within the road wheel actuator leads to a deterioration in the actuator's ability to track the road angle in relation to the driver's steering input. This can progress to wheel lockup. Because the road wheel actuator is mechanically decoupled from the steering wheel, the increased friction may go unnoticed by the driver. Furthermore, this decoupling prevents the driver from applying any mechanical assistance to compensate for or overcome the friction. The deteriorated tracking is accompanied by the fact that the angle controller, in the form of the road wheel actuator, requires a higher torque for tracking. Furthermore, the time lag in adjusting the angle of the steerable road wheels compared to the actual steering input increases. Additionally, the increased friction leads to a reduction in tracking precision, i.e., a greater difference between the target angle of the steerable vehicle wheels and the actual angle. Moreover, the frequency response of the angle control of the steerable vehicle wheels deteriorates. A further challenge arises from the fact that the required angle tracking performance and the engine torque demanded by the road wheel actuator to follow the angle request as desired (despite friction variations/increases) are also strongly influenced by the road surface, tire condition, and the vehicle's suspension condition. This means that different road surfaces, such as ice, asphalt, gravel, bumps, or camber, differing tire conditions, such as varying air pressure, winter tires, or summer tires, and the condition of the suspension—that is, how "good" (as intended) it still is, for example, altered stiffness in the ball joints or bearings due to aging processes—have a non-negligible, significant impact on angle tracking performance and the required engine torque. Therefore, a variation in friction, especially an increase, cannot be readily distinguished from variations in one or more of these exemplary variables. This results in a relatively poor signal-to-noise ratio relating to friction due to other influencing factors, making reliable identification of the friction-induced component not yet possible. US 2024/067264 A1 This document discloses a steering control device and a method that can be used to compensate for the effects of increased friction levels in a road wheel actuator at low temperatures. If a friction level is determined at a low temperature during driving according to a preset compensation condition, this information is used to compensate for variations in the rack force with respect to the friction level. However, this only takes into account variations caused by discrete changes in the friction properties. As a result, the steering behavior of the steering system is only adjusted at specific points. A consistently smooth steering feel for the vehicle's lateral control is thus prevented, limiting the application range of the method and driver comfort. There is therefore a need to eliminate or at least reduce the disadvantages of known methods for operating self-steering systems and self-steering systems for motor vehicles. In particular, there is a need to improve the ability of the vehicle to laterally control the vehicle. to be able to continuously adapt to varying friction properties, so that a desired steering feel is permanently ensured and the comfort for the driver remains constant. The problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are specified in the dependent patent claims and the subsequent description, each of which, individually or in (sub-)combination, can represent aspects of t