Steering system and method for operating a steering system

Abstract

The invention relates to a steering system (1) for a motor vehicle, comprising a steering handle (2), at least one sensor mechanism (3) for detecting a steering wheel angle (φ) at the steering handle (2), at least one controller (4) for determining a theoretical steering angle (φT) from the steering wheel angle (φ), at least one servo motor (5), wherein the servo motor (5) is connected to a rack (12), and at least one sensor mechanism for detecting or determining an actual steering angle (φA), wherein the controller (4) is configured such that the servo motor (5) is actuated in order to adjust the theoretical steering angle by means of at least one characteristic line and such that a deviation between the theoretical steering angle and the actual steering angle is determined, wherein the steering handle (2) and the rack (12) are mechanically decoupled, wherein the controller (4) is further configured such that a control instruction (S) for a one-sided brake intervention is generated, which counteracts the deviation, if the deviation is greater than a threshold value, and a method for operating such a steering system (1).

Description

Technical Field

[0001] The present invention relates to a steering system for a motor vehicle and a method for operating such a steering system. Background Technology

[0002] A method for controlling a steering system for a motor vehicle is known from DE 10 2019 202 003 A1. The motor vehicle has electronic control equipment for manipulating a steering adjuster acting on the steering wheels by means of an adjustment signal to pivot the steering wheels according to a selectable associated function based on the handle position applied at the steering handle. The handle position and steering speed of the steering handle are detected. Furthermore, the wheel positions of the steering wheels are detected, and a position deviation is determined taking into account the associated function. If a preset minimum driving speed and / or a preset minimum steering speed are exceeded, the wheel positions are adapted by applying a correction signal to the adjustment signal for the steering adjuster, the correction signal reducing the position deviation using a preset correction function. The steering system can hereby be configured, in particular, as a steer-by-wire system.

[0003] A method for adjusting the rack position in a steer-by-wire system is known from DE 10 2017 115 850 A1. This method includes a module for adjusting the rack position. In a feedback structure, this module determines a position error based on the difference between theoretical and estimated values ​​of the rack position and rack speed, thereby determining adjustment parameters for controlling the rack. In a feedforward structure, interference parameter compensation for the adjustment parameters is performed through rack force estimation.

[0004] A steer-by-wire system is known from DE 10 2018 122 987 A1, comprising a steering wheel adjustment element that provides a travel position for a road wheel adjustment element of the vehicle, the vehicle moving its rack to a rack position based on the travel position of the steering wheel adjustment element. The steering system also includes a controller for generating a steering wheel torque command, wherein the steering wheel adjustment element generates a feedback torque based on the steering wheel torque command. The controller calculates a hysteresis error (Schleppfehler) based on the difference between the commanded position and the rack position. Furthermore, a compensation motor torque value is determined based on the hysteresis error to modify the steering wheel torque command when using the compensation motor torque value, wherein the steering wheel adjustment element generates a torque quantity that is essentially a sum of the feedback torque and the compensation motor torque.

[0005] A motor-driven steerable road vehicle is known from DE 10 2004 034 126 A1, comprising: a steer-by-wire system having a manually operable steering element, a sensor for detecting the steering position of the steering element, and a steer-by-wire element that interacts with the steerable wheels of the vehicle; and an electronic stability program for the vehicle, which can be effectively connected to the vehicle's brakes and has a yaw rate sensor. In the event of an inconsistency between the steering element sensor and the yaw rate sensor, a fallback layer of the steer-by-wire system is activated, which uses the function of the electronic stability program to generate steering motion of the vehicle based on the steering position of the steering element and brakes the vehicle to a stop. Summary of the Invention

[0006] The present invention is based on the following technical problem: to further improve a steering system in which there is no mechanical coupling between the steering handle and the rack, and to provide a corresponding method for operating such a steering system.

[0007] This technical problem is solved by the steering system and method according to the invention.

[0008] A steering system for a motor vehicle includes: a steering handle; a steering wheel angle at the steering handle; at least one controller for determining a theoretical steering angle based on the steering wheel angle; at least one servo motor connected to a rack; and at least one sensing mechanism for detecting or determining the actual steering angle. The controller is configured such that it actuates the servo motor to adjust the theoretical steering angle using at least one feature line and determines the offset between the theoretical and actual steering angles, wherein the steering handle and rack are mechanically disengaged. The controller is further configured such that when the offset exceeds a threshold, a control command for unilateral braking intervention is generated, which counteracts the offset. This increases the usability of the steering system. The invention is based on the knowledge that, under power limitations (attenuation systems) of the servo motor, in certain situations, the actual steering angle cannot follow the theoretical steering angle so quickly, resulting in a larger offset. In particular, a larger offset is generated with faster steering movements. According to the invention, the motor vehicle is now stopped in a controlled manner, but a steering movement that counteracts the offset is generated through unilateral braking intervention. It can also be configured such that a second threshold for the offset exists, which is greater than the first threshold, wherein the motor vehicle stops in a controlled manner when the second threshold is exceeded.

[0009] In another embodiment, the controller is further configured such that a steering wheel angular velocity is determined, wherein a threshold for offset is determined based on the steering wheel angular velocity. It can be configured to lower the threshold at higher steering wheel angular velocities, thereby enabling faster unilateral braking intervention for assistance. Conversely, the threshold can also be increased if the steering wheel angular velocity increases.

[0010] In another embodiment, the controller is configured such that the offset is determined using data from a rotor position sensor and / or a yaw sensor and / or a rack position sensor of the servo motor's rotor. The controller here knows the theoretical steering angle and can determine relevant theoretical data for the rotor position and / or yaw and / or rack position, respectively. The deviation between the theoretical and actual steering angles can be determined by comparing these values ​​with actual values. Preferably, this determination is performed using data from the rotor position sensor.

[0011] In another embodiment, the servo motor consists of two half-motors that share a common rotor. Here, the half-motors and their respective associated power electronics are preferably supplied with independent voltage sources.

[0012] In another embodiment, the controller is configured such that a warning message is generated when a control command for unilateral braking intervention is generated.

[0013] The steering system can preferably be configured as a steer-by-wire system or as a steering system with a superimposed transmission device.

[0014] For a complete explanation of the methodology, please refer to the preceding text. Attached Figure Description

[0015] The invention will now be explained in more detail with the aid of preferred embodiments. The only accompanying drawing shows a schematic block diagram of the steer-by-wire system. Detailed Implementation

[0016] Figure 1 A block diagram schematically illustrates a steering system 1 for a motor vehicle in the form of a steer-by-wire system. The steering system 1 has a steering handle 2 in the form of a steering wheel, which is associated with a mechanism for detecting the steering wheel angle. The sensing mechanism 3 is connected to the controller 4 in terms of data technology. The controller 4 controls the servo motor 5. The servo motor 5 has two half-motors 6 and 7, each associated with its own power electronics 8 and 9. The two half-motors 6 and 7 are symmetrically constructed. The two half-motors 6 and 7 have a common rotor 10, which is associated with a rotor position sensor 11. The rotor 10 is connected to a rack 12 via a transmission device (not shown). The controller 4 determines the steering wheel angle by means of at least one feature line. The theoretical steering angle at the vehicle wheel (not shown) is determined. Here, the rack position is associated with the theoretical steering angle. The rack position can be converted into the rotor position of the servo motor 5 via a known gear ratio. Data from the rotor position sensor 11 is reported back to the controller 4, allowing the controller 4 to determine the offset between the theoretical and actual steering angles. It is also shown that the first half-motor 6 and its power electronics 8 are supplied by a first voltage supply device U1, while the second half-motor 7 and its power electronics 9 are supplied by a second voltage supply device U2. If the voltage supply devices U1, U2, or the half-motors 6, 7, or the power electronics 8, 9 fail, only half the torque is available at the rotor 10. This causes the actual steering angle to no longer follow the theoretical steering angle as quickly. This, in turn, leads to a larger deviation between the theoretical and actual steering angles in certain steering situations. If the deviation exceeds a first threshold, the controller 4 generates a control command S for unilateral braking intervention, which counteracts the deviation. The braking command is then implemented by the brake controller 13. Furthermore, the controller 4 generates a warning message for the driver, informing them of the limited working capacity and that they should seek a shop if necessary. The threshold for offset can be parameterized, and in particular adapted to the steering wheel angular velocity. If the offset exceeds another threshold despite unilateral braking intervention, the vehicle can be brought to a controlled stop.

[0017] List of reference numerals 1. Steering System 2. Steering handle 3. Sensing Mechanism 4 Controller 5 servo motors 6.7 half motors 8,9 Power Electronic Devices 10 motors 11 Motor position sensor 12 racks 13. Brake controller.

Claims

1. A steering system (1) for a motor vehicle, comprising: Steering handle (2); Used to detect the steering wheel angle at the steering handle (2) At least one sensing mechanism (3) for, based on the steering wheel angle ( The system comprises: at least one controller (4) for determining a theoretical steering angle; at least one servo motor (5) connected to a rack (12); and at least one sensing mechanism for detecting or determining an actual steering angle, wherein the controller (4) is configured to manipulate the servo motor (5) to adjust the theoretical steering angle by means of at least one feature line and to determine the offset between the theoretical steering angle and the actual steering angle, wherein the steering handle (2) and the rack (12) are mechanically disengaged, and wherein the controller (4) is further configured to generate a control command (S) for unilateral braking intervention when the offset is greater than a threshold, the control command offsetting the offset. Its features are, The controller (4) is further configured such that the steering wheel angular velocity is determined, wherein a threshold for the offset is determined based on the steering wheel angular velocity.

2. The steering system according to claim 1, characterized in that, The controller (4) is configured such that the offset is determined by means of data from the rotor position sensor (11) of the rotor (10) of the servo motor (5) and / or data from the yaw sensor and / or data from the rack position sensor.

3. The steering system according to any one of the preceding claims, characterized in that, The servo motor (5) is formed by two half-motors (6,7) having a common rotor (10).

4. The steering system according to any one of the preceding claims, characterized in that, The controller (4) is configured such that a warning message is generated when a control command (S) for unilateral braking intervention is generated.

5. A method for operating a steering system (1), wherein, The steering system (1) includes: a steering handle (2); and a system for detecting the steering wheel angle at the steering handle (2). The steering wheel includes at least one sensing mechanism (3); at least one controller (4) for determining a theoretical steering angle based on the steering wheel angle; at least one servo motor (5), wherein the servo motor (5) is connected to a rack (12); and at least one sensing mechanism for detecting or determining an actual steering angle, wherein the controller (4) manipulates the servo motor (5) to adjust the theoretical steering angle and determines the offset between the theoretical steering angle and the actual steering angle, wherein the steering handle (2) and the rack (12) are mechanically disengaged, and wherein the controller (4) generates a control command (S) for unilateral braking intervention when the offset is greater than a threshold, the control command counteracting the offset. Its features are, The controller (4) determines the steering wheel angular velocity, wherein a threshold for the offset is determined based on the steering wheel angular velocity.

6. The method according to claim 5, characterized in that, The controller (4) determines the offset using data from the rotor position sensor (11) of the rotor (10) of the servo motor (5) and / or data from the yaw sensor and / or data from the rack position sensor.

7. The method according to claim 5 or 6, characterized in that, The servo motor (5) is formed by two half-motors (6,7), which drive a common rotor (10).

8. The method according to any one of claims 5 to 7, characterized in that, The controller (4) generates a warning message when it generates a control command (S) for unilateral braking intervention.

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