A Fault Tolerant Control Method for a Redundant By-Wire Steering System Based on Dynamic Torque Distribution

Abstract

The present invention is applicable to the technical field of steer-by-wire systems for automobiles, and provides a fault-tolerant control method for a redundant steer-by-wire system based on dynamic torque distribution. It determines whether there is a fault in the steer-by-wire system according to vehicle state information. If the current steering motor fails, it enters the fault-tolerant switching state of dual motors. Coordinate the control of the dual motors according to the real-time fault diagnosis results, determine the expected torques of the current dual motors and the expected torque switching time. According to the expected torques and the expected switching time of the current dual motors, use the fifth-order S-curve to smooth the torque and obtain the torque switching curve of the dual motors. After determining the torque switching curve of the dual motors, calculate the redundant motor torque curve through the torque relationship, so that the steering system can complete the torque switching when a fault occurs. This method can quickly and smoothly complete the torque switching when the steer-by-wire system fails, thereby improving the fault-tolerant performance and driving safety of the steer-by-wire system.

Description

Technical Field

[0001] The present invention belongs to the technical field of steer-by-wire systems for vehicles, and particularly relates to a fault-tolerant control method for a redundant steer-by-wire system based on dynamic torque distribution. Background Technique

[0002] With the rapid development of automotive intelligent technologies, steer-by-wire systems have gradually become an important development direction for future vehicle steering systems due to their advantages of high precision, lightweight, and integration with autonomous driving systems. However, during operation, steer-by-wire systems may experience steering failures due to hardware faults or software anomalies, seriously threatening driving safety. To improve the reliability and fault tolerance of the system, redundant design has become a key solution. Among them, the dual-motor redundant architecture realizes fault-tolerant control after a fault through a torque switching mechanism, which is crucial for ensuring the safety of steer-by-wire systems.

[0003] The invention patent CN118062101A provides a redundant coordinated control system, method, device, equipment, and medium for steer-by-wire. By setting a dual-input execution device and performing execution control based on the first control information output by the first control system and the second control information output by the second control system, it is realized that 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, improving the stability of the redundant coordinated control system for steer-by-wire. However, this method does not elaborate on how to perform torque switching between the two steering motors to ensure the functional safety of the steering system when a steering motor fails.

[0004] The invention patent CN119262059A provides an integrated system for redundant steer-by-wire and auxiliary drive of a vehicle and its control method. This invention integrates the steer-by-wire and drive systems and uses the coupling mode switching between the auxiliary motor and the electromagnetic clutch to solve the safety problem of traditional steer-by-wire systems when the steer-by-wire motor fails, enabling safer and more efficient vehicle steering and driving, and at the same time improving the energy utilization efficiency of the vehicle under different working conditions. However, this method does not consider the torque switching control of the redundant steering motors. When switching the torques of the two steering motors, it should be controlled and smoothly processed to improve the jerks caused by sudden changes in 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 background technique.

[0006] The embodiments of the present invention are implemented as follows. A fault-tolerant control method for a redundant steer-by-wire system based on dynamic torque distribution includes the following steps:

[0007] Step 1: Determine whether there is a fault in the steer-by-wire system according to the vehicle status information. If the current steering motor fails, enter the dual-motor fault tolerance switching state;

[0008] Step 2: Coordinate and control the dual motors according to the real-time fault diagnosis result, and determine the expected torque of the current dual motors and the expected torque switching time;

[0009] Step 3: Smooth the torque using a fifth-order S-curve according to the expected torque and expected switching time of the current dual motors, and obtain the dual-motor torque switching curve;

[0010] Step 4: After determining the dual-motor torque switching curve, calculate the redundant motor torque curve through the torque relationship, so that the steering system can complete the torque switching when a fault occurs and ensure the rapidity and smoothness of the torque switching.

[0011] Further technical solution, Step 1 includes the following specific steps:

[0012] Judge the following two types of typical faults according to the real-time monitored motor status:

[0013] First, the motor fails completely:

[0014] Step 1.1: When the motor speed is detected and the duration exceeds the threshold, the corresponding fault is that the motor stops rotating;

[0015] Step 1.2: When the motor current is detected , the corresponding fault is power interruption;

[0016] Step 1.3: When the deviation between the duty cycle D of the motor PWM signal and the command value is >10% and the overlimit persists, the corresponding fault is a drive circuit fault;

[0017] Second, the motor performance degrades:

[0018] 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;

[0019] Step 1.5: When it is detected that the motor power factor is less than the threshold, the corresponding fault is a reduction in motor efficiency;

[0020] If the current steering motor fails, enter the dual-motor fault tolerance switching state.

[0021] Further technical solution, in Step 2, the method for determining the torque switching time is as follows:

[0022] Step 2.1: For a severe fault (the motor fails completely), the initial steering torque of the faulty motor before the fault Drop to 0. At this time, the torque of the redundant steering motor needs to be quickly increased to , so as to restore the steering torque as soon as possible. A first-order inertia link is used to smooth this process and improve the jerks caused by sudden changes in the steering torque;

[0023] Step 2.2: For minor faults (motor performance degradation), the steering motor torque switching time can be appropriately extended , gradually reduce the initial steering torque before the fault of the faulty motor to 0, and at the same time gradually increase the torque of the redundant steering motor to to optimize the smoothness of the switching process.

[0024] Steering motor torque switching time Adopt the following dynamic adjustment model:

[0025] ;

[0026] Among them, is the basic switching time, calibrated according to experiments; is the degree of fault, and its range is 0 to 1, 0 means normal, and 1 means complete fault; is the vehicle speed, is the reference vehicle speed; is the vehicle mass, is the reference mass; is the weight coefficient, optimized through on-road vehicle tests.

[0027] For a further technical solution, in the said Step 3, the general form of the five S-curves is as follows:

[0028] ;

[0029] Among them, is a function that changes with time t ; and are the coefficients of the five S-curve.

[0030] The first derivative form of

[0031] ;

[0032] The second derivative form of

[0033] ;

[0034] The constraint conditions satisfied by the equation are as follows:

[0035] ;

[0036] Among them, t 0 is the initial time of torque switching, unit: s; t 1 is the end time of torque switching, unit: s.

[0037] The matrix expression of the quintic S-curve is as follows:

[0038] ;

[0039] ;

[0040] Among them, T is the coefficient matrix, A is the coefficient of the quintic S-curve, B is the constraint condition;

[0041] By solving the linear equations, the coefficients of the quintic S-curve can be obtained as follows:

[0042] ;

[0043] Therefore, the torque of the faulty motor during switching is:

[0044] ;

[0045] Among them, is the torque of the faulty motor during switching, unit: N·m.

[0046] Furthermore, in the said step 4, the torque formula of the redundant steering motor is as follows:

[0047] ;

[0048] Among them, is the initial steering torque before the fault, unit: N·m; is the torque of the redundant steering motor, unit: N·m.

[0049] A fault-tolerant control method for a redundant by-wire steering system based on dynamic torque distribution provided by an embodiment of the present invention has the following beneficial effects:

[0050] (1) Through the redundant torque distribution strategy, when a fault occurs in the by-wire steering system, the torques of the dual motors can be redistributed according to the fault-tolerant switching strategy, so that the steering system can achieve the complete steering function when a fault occurs.

[0051] (2) Based on dynamic torque distribution, the torque switching control of the dual motors is carried out to ensure that the torque switching can be completed quickly and smoothly when a fault occurs in the by-wire steering system, thereby improving the fault-tolerant performance and driving safety of the by-wire steering system. Description of the Drawings

[0052] Figure 1 This is the fault tolerance control function architecture diagram of a fault tolerance control method for a redundant by - wire steering system based on dynamic torque distribution provided by an embodiment of the present invention;

[0053] Figure 2 This is the flow chart of the dual - motor fault tolerance switching strategy in a fault tolerance control method for a redundant by - wire steering system based on dynamic torque distribution provided by an embodiment of the present invention;

[0054] Figure 3 This is a schematic diagram of the switching torque change curve in a fault tolerance control method for a redundant by - wire steering system based on dynamic torque distribution provided by an embodiment of the present invention; among them, (a) is the torque change curve of rapid switching, and (b) is the torque change curve of smooth switching. Detailed implementation manners

[0055] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to 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 used to limit the present invention.

[0056] The following describes the specific implementation of the present invention in detail with reference to specific embodiments.

[0057] As shown in Figure 1 and Figure 2 A fault tolerance control method for a redundant by - wire steering system based on dynamic torque distribution provided by an embodiment of the present invention includes the following steps:

[0058] Step 1: Determine whether the by - wire steering system has a fault according to the vehicle state information. If the current steering motor fails, enter the dual - motor fault tolerance switching state;

[0059] Step 2: Coordinate and control the dual motors according to the real - time fault diagnosis result, and determine the expected torque of the current dual motors and the expected torque switching time;

[0060] Step 3: Smooth the torque using a fifth - order S - curve according to the expected torque of the current dual motors and the expected switching time, and obtain the dual - motor torque switching curve;

[0061] Step 4: After determining the dual - motor torque switching curve, calculate the redundant motor torque curve through the torque relationship, so that the steering system can complete the torque switching when a fault occurs and ensure the rapidity and smoothness of the torque switching.

[0062] As a preferred embodiment of the present invention, the specific steps of the said Step 1 include the following:

[0063] Judge the following two types of typical faults according to the real - time monitored motor state:

[0064] First, the motor completely fails:

[0065] Step 1.1: When the motor speed is detected and the duration exceeds the threshold, the corresponding fault is that the motor stops rotating;

[0066] Step 1.2: When the motor current is detected , the corresponding fault is power interruption;

[0067] Step 1.3: When the deviation between the duty cycle D of the motor PWM signal and the command value is > 10% and the overlimit continues, the corresponding fault is a drive circuit fault;

[0068] Second, the motor performance degrades:

[0069] Step 1.4: When the detected motor output torque T is less than the expected torque, the corresponding fault is insufficient motor torque output;

[0070] Step 1.5: When the detected power factor of the motor is less than the threshold, the corresponding fault is reduced motor efficiency;

[0071] If a fault occurs in the current steering motor, enter the dual-motor fault tolerance switching state.

[0072] As a preferred embodiment of the present invention, in the said Step 2, the method for determining the torque switching time is as follows:

[0073] Step 2.1: For a severe fault (the motor completely fails), the initial steering torque (unit: N·m) of the faulty motor before the fault drops to 0. At this time, it is necessary to quickly increase the torque of the redundant steering motor to to quickly restore the steering torque. A first-order inertia link is used to smooth this process and improve the jerks caused by the sudden change of the steering torque;

[0074] Step 2.2: For a minor fault (the motor performance degrades), the switching time of the steering motor torque can be appropriately extended , gradually reduce the initial steering torque of the faulty motor before the fault to 0, and at the same time gradually increase the torque of the redundant steering motor to to optimize the smoothness of the switching process.

[0075] Regarding the switching time of the steering motor torque, specifically, the switching time is determined according to the fault degree, the real-time state of the vehicle, and the characteristics of the vehicle dynamic system. Its core purpose is to achieve a balance between quickly restoring safety redundancy and avoiding the impact of sudden torque changes. The switching time of the steering motor torque adopts the following dynamic adjustment model:

[0076] ;

[0077] Among them, is the basic switching time, calibrated according to experiments; is the degree of failure (0 - 1, 0 for normal, 1 for complete failure); is the vehicle speed, is the reference vehicle speed; is the vehicle mass, is the reference mass; is the weight coefficient, optimized through on - vehicle tests.

[0078] In the embodiment of the present invention, the switching torque change curve is as shown in Figure 3 wherein, Figure 3 (a) is the torque change curve for rapid switching, Figure 3 (b) is the torque change curve for smooth switching.

[0079] As a preferred embodiment of the present invention, in the said step 3, the general form of the five - time S - curve is as follows:

[0080] ;

[0081] wherein, is a function that changes with time t; and are the coefficients of the five - time S - curve.

[0082] The first - derivative form of

[0083] ;

[0084] The second - derivative form of

[0085] ;

[0086] The constraint conditions satisfied by the equation are as follows:

[0087] ;

[0088] wherein, t 0 is the initial torque - switching time, unit: s; t 1 is the end torque - switching time, unit: s.

[0089] The matrix expression of the five - time S - curve is as follows:

[0090] ;

[0091] ;

[0092] Among them, T is the coefficient matrix, A is the coefficient of the fifth-order S-curve, B is the constraint condition;

[0093] By solving the linear equations, the coefficients of the fifth-order S-curve can be obtained as follows:

[0094] ;

[0095] Therefore, the switching torque of the faulty motor is:

[0096] ;

[0097] Among them, is the switching torque of the faulty motor, unit: N·m.

[0098] As a preferred embodiment of the present invention, in the step 4, the redundant steering motor torque formula is as follows:

[0099] ;

[0100] Among them, is the initial steering torque before the fault, unit: N·m; is the redundant steering motor torque, unit: N·m.

[0101] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall 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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