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EP-4669560-B1 - METHOD FOR CONTROLLING AN ELECTROMECHANICAL STEERING SYSTEM IN A SEMI-AUTONOMOUS DRIVING MODE OF THE STEERING SYSTEM WITH A POSITION CONTROL USING A BOOST CONTROL

EP4669560B1EP 4669560 B1EP4669560 B1EP 4669560B1EP-4669560-B1

Inventors

  • FAZEKAS, CSABA
  • MULLER, MARK

Dates

Publication Date
20260513
Application Date
20240220

Claims (12)

  1. Method for controlling an electromechanical steering system (1) during a semi-autonomous or semi-automatic steering operation, comprising the following step: - Determining a required motor torque (MotReqTrq) for driving an electric motor (9) of a servo unit (10) of the electromechanical steering system (1), wherein a boost control (14) is performed which determines the required motor torque (MotReqTrq) as a function of a hand torque (TsuTrq) applied to the steering wheel and the vehicle speed (VhlSpd) as well as a steering column offset torque (TsuTrq_offset), wherein the steering column offset torque (TsuTrq_offset) represents a position control of the electric motor (9), a steering pinion, or a rack.
  2. The method according to claim 1, characterized in that the method comprises an LQ controller (17) that is connected upstream of the boost controll (14) and that determines the steering column offset torque (TsuTrq_offset) based on either a reference position of the electric motor and a measured position of the electric motor or a reference pinion position of a steering pinion of the steering system (RefPinAngRad) and a measured position of the steering pinion (PinAngRad), or a reference rack position and a measured rack position.
  3. The method according to claim 1 or 2, characterized in that the method comprises a steering model (15) for the boost control (14), which comprises the boost control (14) and a downstream steering model (16), wherein a gain curve of the boost control (14) has different operating points and is linearized at these operating points, and a steering model is available for each of these operating points.
  4. The method according to claim 2 and claim 3, characterized in that the downstream steering model (16) transmits the measured position of the electric motor or the measured pinion position of a steering pinion (PinAngRad) of the steering system to the input of the LQ controller (17).
  5. The method according to any of the preceding claims, insofar as it depends on claim 2,, characterized in that the method comprises a state estimator (18) that determines states of the steering system and transmits these to the LQ controller (17).
  6. The method according to claim 5, characterized in that the state estimator (18) comprises a Kalman filter.
  7. The method according to any of the preceding claims, as referred to in claim 2, characterized in that the LQ controller (17) defines a loss function that includes the square of the tracking error, the square of the integral of the tracking error, and the square of the steering column offset torque (TsuTrq_offset).
  8. The method according to claim 7, characterized in that the method comprises an integration unit (20) and a damping unit (22), wherein the integration unit (20) provides the integral of the tracking error and transmits it to the LQ controller (17), and the damping unit (22) determines a damping torque that depends on the vehicle speed (VhlSpd), other measured values, and a gain derived from the boost control (14).
  9. The method according to claim 8, characterized in that the damping torque is provided to reduce the influence of the integral of the tracking error in determining the steering column offset torque (TsuTrq_offset) in the LQ controller (17).
  10. The method according to any of the preceding claims, characterized in that the method comprises a steering algorithm (23) that determines a required motor torque (MotReqTrq_SA) using a reference motor torque and further measured values (25), which is added to the required motor torque (MotReqTrq_boost) determined by the boost control (14).
  11. The method according to claim 10, characterized in that the value resulting from the addition is limited to a predetermined range by a motor torque limiter (24), and the resulting value (MotReqTrq_Lim) is fed into the steering model (16).
  12. Electromechanical steering system (1) for a motor vehicle, comprising - a pinion (5) connected to a lower steering shaft (4), which meshes with a rack (6) mounted in a housing so as to be slidable along a longitudinal axis for steering wheels (8), - at least one electric motor (9) for steering assistance, and - an electronic control unit (12) for calculating the steering assistance, which is configured to perform the method according to one of the preceding claims.

Description

The present invention relates to a method for controlling an electromechanical steering system in semi-autonomous or semi-automatic driving mode of the steering system and to an electromechanical steering system of a motor vehicle. Driver assistance systems are used in motor vehicles to support the driver in performing various driving maneuvers. Semi-autonomous or semi-automatic driver assistance systems are known in the prior art. These systems can control the vehicle's movement, but the driver can intervene and take over control. The driver assistance system includes a position controller to determine the additional steering torque. A torque controller, on the other hand, is responsible for the driver's steering input. If the driver intervenes with the driver assistance system active, both controllers are used in combination to calculate a control signal for the electric motor. It is possible that the two controllers may interfere with each other, resulting in undesirable oscillations that negatively affect the steering feel. From the patent specification EP 284 2833 B1 A position controller is implemented in the form of a PID controller, whose output is a requested motor torque. This requested motor torque is added to a required motor torque determined by a boost controller to determine a manipulated variable for the electric motor. The purpose of the present application is to specify a method for controlling an electromechanical steering system in semi-autonomous or semi-automatic driving mode of the steering system, which features an improved determination of the required engine torque. The problem is solved by a method having the features of claim 1 and an electromechanical steering system having the features of claim 12. Accordingly, a method for controlling an electromechanical steering system during semi-autonomous or semi-automatic steering is provided, comprising the following step: Determining a required motor torque for controlling an electric motor of a servo unit of the electromechanical steering system, wherein a boost control (also known as amplification control) is performed, which determines the required motor torque depending on a hand torque applied to the steering wheel and the vehicle speed as well as a steering column offset torque, and wherein the steering column offset torque includes a position control of the electric motor, a steering pinion or a rack. By performing the combination of position control and torque control at the input of the boost control, the occurrence of stability problems can be prevented. Preferably, the method comprises an LQ controller that is upstream of the boost control and that determines the steering column offset torque based on either a reference position of the electric motor and a measured position of the electric motor, or a reference pinion position of a steering pinion of the steering system and a measured position of the steering pinion, or the reference rack position and the measured rack position. Furthermore, it is advantageous if the method comprises a steering model for the boost control, which includes the boost control and a downstream steering model, wherein a gain curve of the boost control has various operating points and is linearized at these operating points, and a steering model is provided for each of these operating points. It is preferably provided that the downstream steering model passes the measured position of the electric motor or the measured pinion position of a steering pinion of the steering system to the input of the LQ controller. Preferably, the method includes a state estimator that determines the states of the steering system (preferably including load and driver torques) and passes these to the LQ controller. The state estimator may include a Kalman filter. In one embodiment, the LQ controller defines a loss function that includes the square of the following error (difference between the reference motor position or reference pinion position or reference rack position and the measured motor position or measured pinion position or measured rack position), the square of the integral of the following error, and the square of the steering column offset torque. Furthermore, the method may include an integration unit and a damping unit, wherein the integration unit provides the integral of the following error and transmits it to the LQ controller, and the damping unit determines a damping torque that depends on the vehicle speed, other measured values, and preferably a boost gain derived from the boost control, wherein the boost gain is the tangent to the gain curve at a fixed (TSU) torque. The damping moment is preferably intended to reduce the influence of the integral of the following error when determining the steering column offset torque in the LQ controller. Furthermore, the method can include a steering algorithm that uses a reference engine torque and other measured values to determine a required engine torque,