Method for operating a steer-by-wire steering system and steer-by-wire steering system

Abstract

The invention relates to a method for operating a steer-by-wire steering system (1), wherein the steer-by-wire steering system (1) has a first control path (3) and a second control path (4), wherein the first control path (3) has a first position controller (5), a first power electronics unit (6) and a first electric motor (7), and the second control path (4) has a second position controller (8), a second power electronics unit (9) and a second electric motor (10), wherein a first target position (SP1) is specified to the first position controller (3) and a second target position (SP2) is specified to the second position controller (8), wherein at least situationally the two control paths (3, 4) operate in a master-master mode, wherein the two position controllers (5, 8) have at least an integral component, and wherein the two electric motors (7, 10) move a wheel positioning unit.wherein in the area of ​​a neutral position of the wheel positioning unit, a periodic signal (S1, S2) with alternating signs is added to the first target position (SP1) and the second target position (SP2) in master-master operation, as well as a steer-by-wire steering system (1).

Description

[0001] The invention relates to a method for operating a steer-by-wire steering system according to the preamble of claim 1 and a steer-by-wire steering system according to the preamble of claim 6.

[0002] From DE 10 2018 108 597 A1, a redundant control unit for an electromechanical steering system of a motor vehicle is known, which can also be configured as a steer-by-wire steering system. The control unit has a primary control path and a secondary control path, wherein the primary control path comprises a primary processing unit, a primary driver stage, and a primary power module. The secondary control path comprises a secondary processing unit, a secondary driver stage, and a secondary power module, wherein the power modules are designed to control two physically separate electric motors or a single electric motor with two winding sets. The electric motors, or the electric motor, exert a torque on a shaft. Communication between the two control paths takes place via a signal line directly between the processing units.

[0003] From generic German patent DE 10 2020 207 196 A1, a method for operating a steering system with an electromechanical steering intervention system, which can also be configured as a steer-by-wire steering system, is known. The steering intervention system has several redundant control paths, each control path comprising a control unit, a power unit, and a winding circuit of an actuator motor. Each control unit includes a manifold control unit to provide a manipulated variable depending on input variables. The manipulated variables of all manifold control units are averaged, and each setpoint variable is provided by each control unit depending on the averaged manipulated variable. This prevents windup that can occur in master-master control systems with an integrator component.Otherwise, even minor control deviations can cause the manipulated variables to accumulate with opposite signs on both control paths, leading to differently directed actuating torques or forces. It is further proposed that the integrator component be controlled based on events to implement anti-windup. This can be achieved, among other things, by setting the integration to a suitable value and temporarily suspending it.

[0004] One problem is that this method requires communication between the control paths to still be possible. Another problem is that controlling the system interferes with the control algorithm.

[0005] The invention addresses the technical problem of providing a robust method for operating a steer-by-wire steering system while preventing windup. A further technical problem is the creation of a suitable steer-by-wire steering system.

[0006] The problem is solved by the features of claim 1 and the features of claim 6.

[0007] A method for operating a steer-by-wire steering system is described. The steer-by-wire steering system has a first control path and a second control path. The first control path includes a first position controller, a first power electronics unit, and a first electric motor. The second control path includes a second position controller, a second power electronics unit, and a second electric motor. The first and second electric motors can be separate individual motors or independent stator windings on a common core, which then preferably operate on a common rotor. A first target position is specified for the first position controller, and a second target position is specified for the second position controller. The target positions depend, for example, on a driver steering input at a steering handle and / or specifications from a driver assistance system.At least situationally, the two control paths operate in a master-master configuration; that is, either they always operate in a master-master configuration, or they normally operate in a master-slave configuration and switch to master-master operation depending on an event (e.g., loss of communication between the control paths) or condition. Both position controllers have an integral component. The two electric motors move a wheel positioner (e.g., a pushrod or rack). For example, the common rotor or the two rotors are connected to the wheel positioner (e.g., a pushrod or rack) via a gearbox. The wheel positioning unit is, for example, a pushrod or rack.

[0008] In the neutral position (zero position) of the wheel positioner (e.g., pushrod or rack), a periodic signal with alternating signs is added to both the first and second target positions in master-master operation. This prevents the control deviations from always having opposite signs, thus avoiding windup. The range around the neutral position is, for example, ±0.05 mm in a rack position. The advantage is that the actual control algorithm of the position controller does not need to be modified, which allows for simple verification of a robust and stable position controller for the steering gear of the steer-by-wire steering system. Furthermore, a functional data connection between the two position controllers is not required.

[0009] In one embodiment, the periodic signal is a sine wave, so that there are no jumps in the rack movement. Preferably, the two periodic signals are equal in amplitude and frequency.

[0010] In another embodiment, the periodic signal for the first target position and the periodic signal for the second target position are generated independently of each other, so that full redundancy is provided.

[0011] In another embodiment, the first and second position controllers communicate via at least one data connection, with periodic signals being generated only if the data connection fails. With a functioning data connection, the two position controllers can prevent a windup through other coordinated measures. The data connection can be, for example, an SPI connection and / or a bus connection (e.g., CAN). However, the data communication between the two position controllers is not safety-critical, so it does not necessarily need to be redundant.

[0012] In another embodiment, the periodic signals generate a rod stroke (pushrod or rack) of less than 0.1–0.2 mm, so that these vibrators around the neutral position are sufficiently large to prevent windup and sufficiently small to avoid unwanted steering movements. The signal frequency is, for example, between 10 and 50 Hz.

[0013] Alternatively, the rod stroke can be made larger so that the driver receives acoustic and haptic feedback about the system's problems due to the stronger vibration, which can support a visual warning indicator.

[0014] The steer-by-wire steering system has a first control path and a second control path. The first control path includes a first position controller, a first power electronics unit, and a first electric motor, while the second control path includes a second position controller, a second power electronics unit, and a second electric motor. Both position controllers have an integral component. The first position controller is configured to control to a first target position, and the second position controller is configured to control to a second target position. The steer-by-wire steering system is designed such that, at least situationally, the two control paths operate in master-master mode. The two electric motors are coupled to a wheel positioning unit.The steer-by-wire steering system is designed such that, in the neutral position of the wheel positioning unit, a periodic signal with alternating signs is added to the first and second target positions in master-master operation. For further details, please refer to the preceding explanations.

[0015] The invention is explained in more detail below with reference to a preferred embodiment. The single figure schematically shows a block diagram of a part of a steer-by-wire steering system.

[0016] In the Fig.Figure 1 schematically shows a block diagram of a part of a steer-by-wire steering system 1, omitting, for clarity, the representation of a steering column module with steering handle, angle and / or torque sensors, and force feedback actuator. A steering gear module 2 of the steer-by-wire steering system 1 has a first control path 3 and a second control path 4. The first control path 3 has a first position controller 5, a first power electronics unit 6, and a first electric motor 7. The second control path 4 has a second position controller 8, a second power electronics unit 9, and a second electric motor 10. The first electric motor 7 and the second electric motor 10 are formed by independent stator windings on a common core, with both stator halves acting on a common rotor 11, which is coupled to a rack 12 as a wheel positioning unit (e.g.,(via a worm gear or ball screw drive). The rotational movement of the rotor 11 is translated into a translational movement of the rack 12. The first control path 3 is connected to a first power supply U1, and the second control path 4 is connected to a second power supply U2; these are independent of each other. The first position controller 5 receives a first target position SP1 for the rack 12, and the second position controller 8 receives a second target position SP2 for the rack 12. The two target positions SP1 and SP2 are determined independently and ideally are identical. Each target position SP1 or SP2 is composed of a sum of partial target positions. One partial target position SPLS1 or SPLS2 originates from the steering column module and relates to settings set by the driver via a steering handle.A second partial target position FA1, FA2 is provided by at least one driver assistance system (e.g., Lane Keeping Assist). A further partial target position S1, S2 is provided by a unit 13 or 14, respectively, which generates a periodic signal S1, S2 with alternating polarity, wherein the signals S1, S2 are preferably sinusoidal. The first position controller 5 and the second position controller 8 are connected to each other via at least one data connection 15. This data connection 15 does not necessarily have to be located between the position controllers 5, 8, but can also be located elsewhere to connect the first control path 3 and the second control path 4. The first position controller 5 receives a first actual rack position ZP1, and the second position controller 8 receives a second actual position ZP2 as feedback.

[0017] The two control paths 3 and 4 can operate permanently in master-master mode or only situationally. In master-slave mode, the first position controller 5 can be configured to calculate the control signals for the first power electronics unit 6 and the second power electronics unit 9, as shown by the dashed line. In case of a fault, for example, due to a fault in the data connection 15, the system switches to master-master mode situationally, so that both control paths 3 and 4 operate independently of each other. The two position controllers 5 and 8 each have an integral component.

[0018] In master-master operation, where both control paths 3 and 4 operate completely independently, a windup can occur if the two electric motors 7 and 10 operate against each other due to differing signs of a control deviation. The two units 13 and 14 serve to prevent this windup. If the two position controllers 5 and 8 detect that the rack 12 is in a neutral position or zero position in master-master operation, they control the two units 13 and 14 with a control signal N. This causes each unit to generate a periodic signal S1 and S2 with alternating signs, which is then summed at the respective target position SP1 and SP2. The amplitude is sufficiently large to temporarily shift the control deviation for both position controllers 5 and 8 in a direction with the same sign, thus preventing a windup.Alternatively, the actual rack positions ZP1 and ZP2 can be directly fed to units 13 and 14, so that these can independently trigger the periodic signal. This eliminates the signal path from position controllers 5 and 8 to units 13 and 14, simplifying the verification of a robust and stable position controller. Reference symbol list 1 Steer-by-wire steering system 2 Steering gear module 3 first control path 4 second control path 5 first position controller 6 first power electronics 7 first electric motor 8 second position controller 9 second power electronics 10 second electric motor 11 Rotor 12 Rack and pinion 13 Unit 14 units 15 Data connection ZP1 first actual rack position ZP2 second actual rack position U1 first power supply U2 second power supply S1 periodic signal S2 periodic signal N control signal SP1 first target position SP2 second target position FA1 second partial target position FA2 second partial target position SPLS1 Partial Target Position SPLS2 Partial Target Position

Claims

[1] Method for operating a steer-by-wire steering system (1), wherein the steer-by-wire steering system (1) has a first control path (3) and a second control path (4), wherein the first control path (3) has a first position controller (5), a first power electronics unit (6) and a first electric motor (7) and the second control path (4) has a second position controller (8), a second power electronics unit (9) and a second electric motor (10), wherein a first target position (SP1) is specified to the first position controller (5) and a second target position (SP2) is specified to the second position controller (8), wherein at least situationally the two control paths (3, 4) operate in a master-master mode, wherein the two position controllers (5, 8) have at least an integral component, and wherein the two electric motors (7, 10) move a wheel positioning unit. characterized by, that in the area of ​​a neutral position of the wheel positioning unit, a periodic signal (S1, S2) with alternating signs is added to the first target position (SP1) and the second target position (SP2) in master-master operation. [2] Method according to claim 1, characterized by that the periodic signal (S1, S2) is a sine signal. [3] Method according to claim 1 or 2, characterized by , that the periodic signal (S1) for the first target position (SP1) and the periodic signal (S2) for the second target position (SP2) are generated independently of each other. [4] Method according to any of the preceding claims, characterized by , that the first position controller (5) and the second position controller (8) communicate via at least one data connection (15), whereby the periodic signals (S1, S2) are generated only when the data connection (15) fails. [5] Method according to any of the preceding claims, characterized by, that the periodic signals (S1, S2) generate a pushrod stroke of less than 0.1 - 0.2 mm. [6] Steer-by-wire steering system (1) comprising a first control path (3) and a second control path (4), wherein the first control path (3) comprises a first position controller (5), a first power electronics unit (6) and a first electric motor (7), and the second control path (4) comprises a second position controller (8), a second power electronics unit (9) and a second electric motor (10), wherein the two position controllers (5, 8) each have an integral component, wherein the first position controller (5) is configured to control to a first target position (SP1), and the second position controller (8) is configured to control to a second target position (SP2), wherein the steer-by-wire steering system (1) is configured such that, at least situationally, the two control paths (3, 4) operate in master-master mode, wherein the two electric motors (7, 10) are connected to a Wheel positioning unit are coupled, characterized by, that the steer-by-wire steering system (1) is designed such that in the area of ​​a neutral position of the wheel positioning unit, a periodic signal (S1, S2) with alternating signs is added to the first target position (SP1) and the second target position (SP2) in master-master operation. [7] Steer-by-wire steering system (1) according to claim 6, characterized by , that the steer-by-wire steering system (1) is designed such that the periodic signal (S1, S2) is a sine signal. [8] Steer-by-wire steering system (1) according to claim 6 or 7, characterized by , that the steer-by-wire steering system (1) is designed such that the periodic signal (S1) for the first target position (SP1) and the periodic signal (S2) for the second target position (SP2) are generated independently of each other. [9] Steer-by-wire steering system (1) according to any one of claims 6 to 8, characterized by, that the first position controller (5) and the second position controller (8) are connected to each other via at least one data connection (15), wherein the steer-by-wire steering system (1) is designed such that the periodic signals (S1, S2) are generated only when the data connection (15) fails. [10] Steer-by-wire steering system (1) according to any one of claims 6 to 9, characterized by , that the periodic signals (S1, S2) are designed to generate a pushrod stroke of less than 0.1 - 0.2 mm.

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