Redundant steer-by-wire system fault-tolerant control method based on dynamic torque distribution

Abstract

The invention is applicable to the technical field of automobile steer-by-wire, and provides a fault-tolerant control method for a redundant steer-by-wire system based on dynamic torque distribution, which comprises the following steps: judging whether the steer-by-wire system has a fault according to vehicle state information, and if the current steering motor has a fault, entering a dual-motor fault-tolerant switching state; performing coordination control on the double motors according to a real-time fault diagnosis result, and determining expected torque and expected torque switching time of the current double motors; according to the expected torque and the expected switching time of the current double motors, the torque is smoothed by using a quintic S curve, and a torque switching curve of the double motors is obtained; and after the dual-motor torque switching curve is determined, a redundant motor torque curve is obtained through torque relation calculation, so that torque switching can be completed when the steering system breaks down. According to the method, torque switching can be rapidly and stably completed when the steer-by-wire system breaks down, and therefore the fault tolerance performance and driving safety of the steer-by-wire system are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of automobile wire-controlled steering, and in particular relates to a fault-tolerant control method of a redundant wire-controlled steering system based on dynamic torque distribution. Background Art

[0002] With the rapid development of intelligent automobile technology, the wire-controlled steering system has gradually become an important development direction for future vehicle steering systems due to its high precision, lightweight and integration advantages with the autonomous driving system. However, the steering system may fail to work due to hardware failure or software anomaly during operation, which seriously threatens driving safety. In order to improve the reliability and fault tolerance of the system, redundant design has become a key solution. The dual-motor redundant architecture realizes fault-tolerant control after failure through the torque switching mechanism, which is the key to ensuring the safety of the wire-controlled steering system.

[0003] Invention patent CN118062101A provides a wire-controlled redundant coordinated control system, method, device, equipment and medium. The invention sets a dual-input execution device and performs execution control according to the first control information output by the first control system and the second control information output by the second control system. When the first control system or the second control system fails or partially fails, the working state of the control system can be adjusted to keep the execution control result of the dual-input execution device unchanged, thereby improving the stability of the wire-controlled redundant coordinated control system. However, the method does not explain in detail how to switch the torque of the dual steering motors when the steering motor fails to ensure the functional safety of the steering system.

[0004] Invention patent CN119262059A provides an integrated system of redundant wire-controlled steering and auxiliary drive for vehicles and its control method. The invention integrates wire-controlled steering and drive systems, and uses the coupling mode switching of auxiliary motors and electromagnetic clutches to solve the safety problem of traditional wire-controlled steering systems when the wire-controlled steering motor fails. It can achieve safer and more efficient vehicle steering and driving, and improve the energy efficiency of vehicles under different working conditions. However, this method does not take into account the torque switching control of the redundant steering motor. The torque switching of the dual steering motors should be controlled and smoothed to improve the sense of frustration caused by the sudden change of the steering torque. Summary of the invention

[0005] The purpose of the embodiments of the present invention is to provide a fault-tolerant control method for a redundant steer-by-wire system based on dynamic torque distribution, aiming to solve the problems raised in the above-mentioned background technology.

[0006] The embodiment of the present invention is implemented as follows: a fault-tolerant control method for a redundant wire-controlled steering system based on dynamic torque distribution comprises the following steps: Step 1: Determine whether the steer-by-wire system is faulty based on the vehicle status information. If the current steering motor is faulty, enter the dual-motor fault-tolerant switching state; Step 2: Coordinate the control of the dual motors according to the real-time fault diagnosis results to determine the current expected torque of the dual motors and the expected torque switching time; Step 3: According to the current expected torque and expected switching time of the dual motors, the torque is smoothed using a quintic S curve to obtain a dual motor torque switching curve; Step 4: After determining the dual-motor torque switching curve, the redundant motor torque curve is obtained through torque relationship calculation, so that the steering system can complete the torque switching when a fault occurs and ensure that the torque switching is fast and smooth.

[0007] According to a further technical solution, step 1 comprises the following specific steps: Based on real-time monitoring of the motor status, the following two typical faults can be identified: First, the motor fails completely: Step 1.1: When the motor speed is detected And the duration exceeds the threshold, the corresponding fault is motor stall; Step 1.2: When the motor current is detected , the corresponding fault is power outage; Step 1.3: When it is detected that the duty cycle D of the motor PWM signal deviates from the command value by more than 10% and continues to exceed the limit, the corresponding fault is a drive circuit fault; Second, the motor performance decreases: Step 1.4: When it is detected that the motor output torque T is less than the expected torque, the corresponding fault is insufficient motor torque output; Step 1.5: When it is detected that the motor power factor is less than the threshold, the corresponding fault is reduced motor efficiency; If the current steering motor fails, the dual motor fault tolerance switching state is entered.

[0008] According to a further technical solution, in step 2, the method for determining the torque switching time is as follows: Step 2.1: For severe faults (complete motor failure), the initial steering torque before the fault of the faulty motor drops to 0, at which point the torque of the redundant steering motor needs to be quickly increased to , in order to restore the steering torque as quickly as possible. The first-order inertia link is used to smooth the process and improve the frustration caused by the sudden change of steering torque; Step 2.2: For minor faults (motor performance degradation), the steering motor torque switching time can be appropriately extended , the initial steering torque of the faulty motor before the fault Gradually reduce to 0, and at the same time gradually increase the torque of the redundant steering motor to , in order to optimize the smoothness of the switching process.

[0009] Steering motor torque switching time The following dynamic adjustment model is adopted: ; in, is the basic switching time, calibrated according to experiments; is the degree of failure, ranging from 0 to 1, 0 is normal, and 1 is complete failure; is the vehicle speed, is the reference speed; is the vehicle mass, is the reference quality; is the weight coefficient, which is optimized through actual vehicle testing.

[0010] A further technical solution is that in step 3, the general form of the quintic S curve is as follows: ; in, Over time t Function of change; and is the coefficient of the quintic S-curve.

[0011] The first derivative form of is: ; The second derivative form of is: ; The constraints satisfied by the equation are as follows: ; in, t 0 is the initial time of torque switching, unit: s; t 1 It is the end time of torque switching, unit: s.

[0012] The matrix expression of the quintic S-curve is as follows: ; ; in, T is the coefficient matrix, A is the coefficient of the quintic S-curve, B is a constraint condition; By solving the linear equations, the coefficients of the quintic S-curve can be obtained as follows: ; Therefore, the switching torque of the faulty motor is: ; in, It is the switching torque of the faulty motor, unit: N·m.

[0013] According to a further technical solution, in step 4, the redundant steering motor torque formula is as follows: ; in, is the initial steering torque before the fault, unit: N·m; is the redundant steering motor torque, unit: N·m.

[0014] An embodiment of the present invention provides a fault-tolerant control method for a redundant steer-by-wire system based on dynamic torque distribution, and its beneficial effects are as follows: (1) Through the redundant torque distribution strategy, when the steer-by-wire system fails, the dual-motor torque can be redistributed according to the fault-tolerant switching strategy, so that the steering system can achieve complete steering function when a fault occurs.

[0015] (2) The dual motor torque is switched based on dynamic torque distribution to ensure that the torque switching can be completed quickly and smoothly when a fault occurs in the steer-by-wire system, thereby improving the fault tolerance and driving safety of the steer-by-wire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A fault-tolerant control functional architecture diagram of a fault-tolerant control method for a redundant steer-by-wire system based on dynamic torque distribution provided by an embodiment of the present invention; Figure 2 A flow chart of a dual-motor fault-tolerant switching strategy in a redundant steer-by-wire system fault-tolerant control method based on dynamic torque distribution provided by an embodiment of the present invention; Figure 3 A schematic diagram of a switching torque change curve in a fault-tolerant control method for a redundant steer-by-wire system based on dynamic torque distribution provided in an embodiment of the present invention; wherein (a) is a torque change curve for rapid switching, and (b) is a torque change curve for smooth switching. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0019] like Figure 1 and Figure 2 As shown, a fault-tolerant control method for a redundant wire-controlled steering system based on dynamic torque distribution is provided in one embodiment of the present invention, comprising the following steps: Step 1: Determine whether the steer-by-wire system is faulty based on the vehicle status information. If the current steering motor is faulty, enter the dual-motor fault-tolerant switching state; Step 2: Coordinate the control of the dual motors according to the real-time fault diagnosis results to determine the current expected torque of the dual motors and the expected torque switching time; Step 3: According to the current expected torque and expected switching time of the dual motors, the torque is smoothed using a quintic S curve to obtain a dual motor torque switching curve; Step 4: After determining the dual-motor torque switching curve, the redundant motor torque curve is obtained through torque relationship calculation, so that the steering system can complete the torque switching when a fault occurs and ensure that the torque switching is fast and smooth.

[0020] As a preferred embodiment of the present invention, step 1 includes the following specific steps: Based on real-time monitoring of the motor status, the following two typical faults can be identified: First, the motor fails completely: Step 1.1: When the motor speed is detected And the duration exceeds the threshold, the corresponding fault is motor stall; Step 1.2: When the motor current is detected , the corresponding fault is power outage; Step 1.3: When it is detected that the duty cycle D of the motor PWM signal deviates from the command value by more than 10% and continues to exceed the limit, the corresponding fault is a drive circuit fault; Second, the motor performance decreases: Step 1.4: When it is detected that the motor output torque T is less than the expected torque, the corresponding fault is insufficient motor torque output; Step 1.5: When it is detected that the motor power factor is less than the threshold, the corresponding fault is reduced motor efficiency; If the current steering motor fails, the dual motor fault tolerance switching state is entered.

[0021] As a preferred embodiment of the present invention, in step 2, the method for determining the torque switching time is as follows: Step 2.1: For severe faults (complete motor failure), the initial steering torque before the fault of the faulty motor (Unit: N·m) drops to 0. At this time, the torque of the redundant steering motor needs to be quickly increased to , in order to restore the steering torque as quickly as possible. The first-order inertia link is used to smooth the process and improve the frustration caused by the sudden change of steering torque; Step 2.2: For minor faults (motor performance degradation), the steering motor torque switching time can be appropriately extended , the initial steering torque of the faulty motor before the fault Gradually reduce to 0, and at the same time gradually increase the torque of the redundant steering motor to , in order to optimize the smoothness of the switching process.

[0022] For the steering motor torque switching time Specifically, the switching time is determined according to the fault severity, the vehicle's real-time status, and the vehicle's dynamic system characteristics. Its core purpose is to strike a balance between quickly restoring safety redundancy and avoiding torque mutation shocks. Steering motor torque switching time The following dynamic adjustment model is adopted: ; in, is the basic switching time, calibrated according to experiments; is the degree of failure (0~1, 0 is normal, 1 is complete failure); is the vehicle speed, is the reference speed; is the vehicle mass, is the reference quality; is the weight coefficient, which is optimized through actual vehicle testing.

[0023] In the embodiment of the present invention, the switching torque variation curve is as follows: Figure 3 As shown, Figure 3 (a) is the torque change curve of fast switching. Figure 3 (b) is the torque change curve of smooth switching.

[0024] As a preferred embodiment of the present invention, in step 3, the general form of the quintic S-curve is as follows: ; in, is a function that changes with time t; and is the coefficient of the quintic S-curve.

[0025] The first derivative form of is: ; The second derivative form of is: ; The constraints satisfied by the equation are as follows: ; in, t 0 is the initial time of torque switching, unit: s; t 1 It is the end time of torque switching, unit: s.

[0026] The matrix expression of the quintic S-curve is as follows: ; ; in, T is the coefficient matrix, A is the coefficient of the quintic S-curve, B is a constraint condition; By solving the linear equations, the coefficients of the quintic S-curve can be obtained as follows: ; Therefore, the switching torque of the faulty motor is: ; in, It is the switching torque of the faulty motor, unit: N·m.

[0027] As a preferred embodiment of the present invention, in step 4, the redundant steering motor torque formula is as follows: ; in, is the initial steering torque before the fault, unit: N·m; is the redundant steering motor torque, unit: N·m.

[0028] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A fault-tolerant control method for a redundant wire-controlled steering system based on dynamic torque distribution, characterized in that: The following steps are involved: Step 1: Determine whether the steer-by-wire system has a fault based on the vehicle status information. If the current steering motor has a fault, enter the dual-motor fault-tolerant switching state; Step 2: Coordinate the control of the dual motors according to the real-time fault diagnosis results to determine the current expected torque of the dual motors and the expected torque switching time; Step 3: According to the current expected torque and expected switching time of the dual motors, the torque is smoothed using a quintic S curve to obtain a dual motor torque switching curve; Step 4: After determining the dual motor torque switching curve, the redundant motor torque curve is obtained through torque relationship calculation, so that the steering system can complete torque switching when a fault occurs.

2. The fault-tolerant control method of redundant steer-by-wire system based on dynamic torque distribution according to claim 1, characterized in that: The step 1 comprises the following specific steps: Based on real-time monitoring of the motor status, the following two typical faults can be identified: First, the motor fails completely: Step 1.1: When the motor speed is detected And the duration exceeds the threshold, the corresponding fault is motor stall; Step 1.2: When the motor current is detected , the corresponding fault is power outage; Step 1.3: When it is detected that the motor PWM signal duty cycle D deviates from the command value by more than 10% and continues to exceed the limit, the corresponding fault is a drive circuit fault; Second, the motor performance decreases: Step 1.4: When it is detected that the motor output torque T is less than the expected torque, the corresponding fault is insufficient motor torque output; Step 1.5: When it is detected that the motor power factor is less than the threshold, the corresponding fault is reduced motor efficiency; If the current steering motor fails, the dual motor fault tolerance switching state is entered.

3. The fault-tolerant control method of redundant steer-by-wire system based on dynamic torque distribution according to claim 2, characterized in that: In step 2, the method for determining the torque switching time is as follows: Step 2.1: For a complete motor failure, the initial steering torque of the faulty motor before the failure drops to 0, at which point the torque of the redundant steering motor needs to be quickly increased to , the first-order inertia link is used to smooth the process; Step 2.2: For motor performance degradation faults, extend the steering motor torque switching time , the initial steering torque of the faulty motor before the fault Gradually reduce to 0, and at the same time gradually increase the torque of the redundant steering motor to ; Steering motor torque switching time The following dynamic adjustment model is adopted: ； in, is the basic switching time, calibrated according to experiments; is the degree of failure, ranging from 0 to 1, 0 is normal, and 1 is complete failure; is the vehicle speed, is the reference speed; is the vehicle mass, is the reference quality; is the weight coefficient, which is optimized through actual vehicle testing.

4. The fault-tolerant control method of redundant steer-by-wire system based on dynamic torque distribution according to claim 3, characterized in that: In step 3, the general form of the quintic S-curve is as follows: ； in, is a function that changes with time t; ,and is the coefficient of the quintic S curve; The first derivative form of is: ； The second derivative form of is: ； The constraints satisfied by the equation are as follows: ； in, t 0 is the initial time of torque switching, unit: s; t 1 is the end time of torque switching, unit: s; The matrix expression of the quintic S-curve is as follows: ； ； in, T is the coefficient matrix, A is the coefficient of the quintic S-curve, B is a constraint condition; By solving the linear equations, the coefficients of the quintic S-curve are as follows: ； Therefore, the switching torque of the faulty motor is: ； in, It is the switching torque of the faulty motor, unit: N·m.

5. The fault-tolerant control method of redundant steer-by-wire system based on dynamic torque distribution according to claim 4, characterized in that: In step 4, the redundant steering motor torque formula is as follows: ； in, is the initial steering torque before the fault, unit: N·m; is the redundant steering motor torque, unit: N·m.

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