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DE-102024210873-A1 - Method for determining a friction parameter that characterizes existing friction within a steering system, a steering system and a steering system encompassing the vehicle

DE102024210873A1DE 102024210873 A1DE102024210873 A1DE 102024210873A1DE-102024210873-A1

Abstract

Steering system, a vehicle comprising the steering system, and a method (100) for determining a friction parameter (18) that characterizes existing friction within a steering system, comprising: acquiring (102) a first value (26) of a parameter of the steering system (300), wherein the parameter, for example a steering torque, influences an actuated variable of the steering system that characterizes a steering angle of the steering system, wherein the first value (26) of the parameter is acquired (102) before a change (30) in the direction of variation of the actuated variable (20); detecting (104) the change (30) in the direction of variation of the actuated variable; acquiring (106) a second value (28) of the parameter, in particular one that is present, when the change (30) in the direction of variation of the actuated variable is detected (104); Determine (108) a hysteresis value (14) that characterizes any existing hysteresis of the steering system (300), depending on the first value (26) and the second value (28), in particular by subtracting the second value (28) from the first value (26); determine (110) an estimate (16) of the existing hysteresis depending on a nominal friction within the steering system (300) determined by a friction model encompassed by the steering system; determine (112) the friction parameter (18) depending on the hysteresis value (14) and the estimate (16), for example by subtracting the estimate (16) from the hysteresis value (14).

Inventors

  • Stefan Gruener
  • Holger Schmitt
  • Alexander Cziriak
  • Florian Waldenmaier

Assignees

  • Robert Bosch Gesellschaft mit beschränkter Haftung

Dates

Publication Date
20260513
Application Date
20241113

Claims (9)

  1. A method (100) for determining a friction parameter (18) that characterizes existing friction within a steering system (300), comprising: - Acquiring (102) a first value (26) of a parameter (22) of the steering system (300), wherein the parameter (22), for example, a steering torque, influences a control variable (20) of the steering system (300) that characterizes a steering angle of the steering system (300), wherein the first value (26) of the parameter (22) is acquired (102) before a change (30) in the direction of variation of the control variable (20); - Detecting (104) the change (30) in the direction of variation of the control variable (20); - Acquiring (106) a second value (28), in particular one already present, of the parameter (22) when the change (30) in the direction of variation of the control variable (20) is detected (104); - Determine (108) a hysteresis value (14) that characterizes the existing hysteresis of the steering system (300), depending on the first value (26) and the second value (28), in particular by subtracting the second value (28) from the first value (26); Determine (110) an estimated value (16) of the existing hysteresis depending on a nominal friction within the steering system (300), which is determined by a friction model encompassing the steering system (300); Determine (112) the friction parameter (18) depending on the hysteresis value (14) and the estimated value (16), for example by subtracting the estimated value (16) from the hysteresis value (14).
  2. The procedure (100) according to Claim 1 , encompassing: - Adapting (114) at least one parameter of the friction model depending on the determined friction characteristic (18), for example by means of a Kalman filter.
  3. The method (100) according to one of the preceding claims, wherein the estimated value (16) of the present hysteresis is determined depending on nominal frictions which are determined by the friction model depending on the first value (26) and second value (28).
  4. The method (100) according to one of the preceding claims, wherein the steering system (300) comprises a steering actuator (302) and a determined input variable (305) of a steering controller (306) controlling the steering actuator (302) is adapted depending on the determined friction characteristic (18), in particular to eliminate a variation of friction within the steering system (300) characterized by the friction characteristic (18).
  5. The method (100) according to one of the preceding claims, wherein, depending on the determined friction characteristic (18), a restoring behavior caused by an external force acting on the steering system (300) is adapted by means of an active return generated by a steering actuator (302).
  6. The procedure (100) according to Claim 5 , wherein to adapt the return behavior a drive torque of the steering actuator (302) is scaled, wherein the drive torque is increased in particular with increasing friction within the steering system (300) as characterized by the friction parameter (18) and is decreased with decreasing friction within the steering system (300).
  7. The method (100) according to one of the preceding claims, wherein, depending on the friction characteristic (18) and, for example, depending on a state of motion of a vehicle (400) comprising the steering system (300), a damping behavior is adapted for a hand input of a user of the steering system (300).
  8. Steering system (300), in particular an electronic power steering system, comprising a steering actuator (302), a steering controller (306) and a computing unit (200), wherein the computing unit (200) is configured to comprise a method (100) according to the Claims 1 until 7 to execute.
  9. Vehicle (400) comprising a steering system (300) according to Claim 8 .

Description

State of the art The present invention relates to a method for determining a friction parameter that characterizes existing friction within a steering system, a steering system and a vehicle comprising the steering system. Parameters of a steering software that represent the steering feel for a user of a steering system are applied under different operating conditions, particularly temperatures. The prevailing temperature has a significant influence on the friction within the steering system and thus also on the steering feel. This application shows that under normal conditions, especially at normal temperatures, for example, in the range of 5 to 40°C, a desired steering feel can be achieved. At lower temperatures, for example, below -5°C or below -10°C, particularly during a cold start when a vehicle with a steering system has been standing outside overnight in low temperatures, the steering feel achieved by the aforementioned application no longer meets the desired requirements. Therefore, a compromise is made in the steering feel application, with the aim of achieving an acceptable steering feel at low temperatures by minimizing the reduction in steering feel at normal temperatures. Therefore, a steering system is desirable that provides a consistent steering feel for the user, regardless of operating conditions. Disclosure of the invention This is achieved by a method, a steering system and a vehicle comprising the steering system according to the independent claims. The method for determining a friction parameter that characterizes existing friction within a steering system comprises: acquiring a first value of a parameter of the steering system, wherein the parameter, for example a steering torque, influences a control variable of the steering system that characterizes a steering angle of the steering system, wherein the first value of the parameter is acquired before a change in the direction of variation of the control variable; detecting the change in the direction of variation of the control variable; acquiring a second value of the parameter, in particular one that is present, when the change in the direction of variation of the control variable is detected; determining a hysteresis value that characterizes existing hysteresis of the steering system, depending on the first value and the second value, in particular by subtracting the second value from the first value; determining an estimate of the existing hysteresis depending on a nominal friction within the steering system, which is determined by a friction model encompassed by the steering system; Determine the friction parameter as a function of the hysteresis value and the estimated value, for example, by subtracting the estimated value from the hysteresis value. Friction within the steering system is primarily influenced by the friction of a steering actuator, such as a rack and pinion actuator. Further influences on friction within the steering system can be caused, for example, by axle kinematics coupled to the steering system. In this context, the steering torque comprises a manual torque applied by a user of the steering system and an output torque applied by an actuator, such as a servo drive of the steering actuator, which is used to drive the steering system. The manipulated variable of the steering system influences the trajectory of a vehicle encompassing the steering system. The manipulated variable can be, for example, a steering angle to be set, a position of a rack and pinion, or a rotor position of the steering actuator of the steering system. The phrase "before a change in the direction of variation" refers specifically to a point in time, particularly the last point in time before the manipulated variable becomes static. This is the case, for example, when, mathematically speaking, the gradient of the manipulated variable takes on the value zero. If this gradient changes its sign, for instance, this indicates a change in the direction of variation of the manipulated variable. For example, in a hypothetical time series of the manipulated variable, the point before a change in the direction of variation occurs is the time before the first time derivative of the series takes on the value zero, meaning the manipulated variable exhibits a slope over time. The change in the direction of variation is detected, for example, when the gradient of the manipulated variable, or of a quantity that is operatively related to the manipulated variable, particularly a correlated quantity, changes its sign. This operative quantity could be, for example, a rotor position or rotor angle of the steering actuator, or a position of the rack. A change in the direction of variation of the manipulated variable is understood, in particular, as a deflection followed by a subsequent steering input of the steering system, i.e., a change in the steering direction. Hysteresis describes, for example, a deviation between the required steering torque when defle