Steer-by-wire system and control method

Abstract

The application provides a kind of drive-by-wire steering system and control method, it is related to automobile steering technical field.The steering system includes steering wheel angle acquisition module, road feeling feedback execution module, main control unit, steering execution module, vehicle state acquisition module, tire state acquisition module and redundancy safety module.The main control unit fuses multimodule signal, and calculates target front wheel angle based on two-degree-of-freedom vehicle dynamics model and magic tire model, and controls steering execution module through PID closed loop;At the same time, the target road feeling torque is generated by combining Lugre friction model and multi-component composite model, and is output by permanent magnet synchronous motor controlled by optimized ADRC.The system uses speed adaptive variable transmission ratio, active return strategy and full-dimensional redundancy safety design, and automatically switches the road feeling calculation source when sensor fails.The collision safety and automatic driving adaptability are improved, high-precision steering, real adjustable road feeling and high-level safety guarantee are realized.

Description

Technical Field

[0001] This invention relates to the field of automotive steering, and in particular to a steer-by-wire system and control method. Background Technology

[0002] Traditional automotive steering systems mostly employ mechanical steering or electric power steering (EPS), with the steering wheel and steering wheels rigidly connected via mechanical structures such as steering column, universal joint, and rack and pinion. These systems suffer from problems such as insufficient steering control precision, distorted road feel simulation, lag in dynamic response, and imperfect redundancy strategies, making it difficult to simultaneously achieve high-precision steering, realistic road feel, all-condition stability, and a high level of safety.

[0003] Existing steer-by-wire technologies generally suffer from the following problems: insufficient steering control precision, distorted road feel simulation, lag in dynamic response, and imperfect redundancy strategies, making it difficult to simultaneously achieve high-precision steering, realistic road feel, stability under all operating conditions, and high-level safety.

[0004] Therefore, there is a need to provide a steer-by-wire system and control method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a steer-by-wire system and control method that achieves closed-loop control of steering commands and road feel feedback through electrical signals. While eliminating mechanical connections, it achieves high-precision steering, high-stability performance, high safety level, and software-definable intelligent steering through precise control algorithms, realistic road feel simulation, and full-dimensional redundant safety design, thus meeting the technical requirements of intelligent vehicles and advanced autonomous driving.

[0006] To achieve the above objectives, the present invention provides a steer-by-wire system, including a steering wheel angle acquisition module, a road feel feedback execution module, a main control unit, a steering execution module, a vehicle status acquisition module, a tire status acquisition module, and a redundant safety module; the main control unit is electrically connected to the steering wheel angle acquisition module, the road feel feedback execution module, the steering execution module, the vehicle status acquisition module, and the redundant safety module respectively; The main control unit calculates the target front wheel angle and target road feel torque based on the steering wheel angle signal output by the steering wheel angle acquisition module, the vehicle speed signal, yaw rate signal, lateral acceleration signal output by the vehicle status acquisition module, and the tire status parameters acquired by the tire status acquisition module. It then uses a two-degree-of-freedom vehicle dynamics model and a magic tire model to calculate the target front wheel angle and target road feel torque. Finally, it uses a dual closed-loop control algorithm to output steering control commands and road feel control commands. The steering execution module drives the vehicle to steer according to the output steering command, and the road feel feedback execution module uses a permanent magnet synchronous motor (PMSM) as the actuator according to the road feel control command, and realizes the torque output based on the active disturbance rejection controller (ADRC) optimized by the improved particle swarm optimization (PSO) algorithm.

[0007] Preferably, the redundant safety module includes dual power supplies, dual corner sensors, dual communication interfaces, dual drive circuits, and a fault detection unit. The fault detection unit monitors the sensor status in real time using the residual chi-square test method. In the event of a fault in any single channel, the other channel automatically switches the road feel torque calculation source or control channel within a preset time.

[0008] Preferably, the road feel feedback execution module is also equipped with an adjustable coefficient group, including the stationary resistance torque adjustment coefficient, the assist torque adjustment coefficient, the damping torque adjustment coefficient, and the friction torque adjustment coefficient, supporting multi-mode road feel switching.

[0009] Preferably, the steering wheel angle acquisition module includes a dual-redundant angle sensor and a dual-redundant torque sensor for real-time acquisition of the steering wheel angle θ. s Steering wheel torque signal: When the steering wheel angle approaches the maximum steering angle of the front wheel ±35°, the steering resistance torque is gradually increased to simulate mechanical limit characteristics.

[0010] Preferably, the tire condition acquisition module includes a tire vertical load sensor and a tire pressure sensor, which collect tire vertical load parameters and tire pressure parameters in real time. The tire vertical load parameters are combined with the lateral acceleration signal from the vehicle condition acquisition module to correct the tire lateral stiffness calculation results.

[0011] A control method for a steer-by-wire system includes the following steps: S1: Collect the steering wheel angle θ via the steering wheel angle acquisition module. s and steering wheel torque; vehicle longitudinal speed is collected through the vehicle status acquisition module. yaw rate Lateral acceleration and wheel speed signals; tire vertical load parameters and tire pressure parameters are acquired through the tire condition acquisition module; S2: A vehicle mass estimation algorithm based on the fusion of Recursive Least Squares (RLS) and K-Nearest Neighbors (KNN) dynamically corrects the vehicle mass parameters; the tire lateral force is estimated by a sliding mode observer, and the road adhesion coefficient and tire self-aligning torque are calculated by combining the magic tire formula and the tire vertical load parameters and tire pressure parameters output by the tire state acquisition module. Calculate the target front wheel steering angle using a two-degree-of-freedom vehicle dynamics model: ; In the formula, This refers to the vehicle's wheelbase. This is the distance from the front axle to the vehicle's center of gravity. This is the distance from the rear axle to the vehicle's center of gravity. For the front axle equivalent mass, For the equivalent mass of the rear axle, For the front tire lateral stiffness, For rear tire lateral stiffness, Based on the basic steering gear ratio coefficient, Steering wheel angle; The longitudinal speed of the vehicle; S3: Based on the deviation between the target front wheel angle obtained in S2 and the actual front wheel angle, the steering drive motor control quantity is obtained using PID closed-loop control: ; in ; , and These represent the proportional coefficient, integral coefficient, and derivative coefficient of PID control, respectively. This is the actual front wheel steering angle; S4: Based on the Lugre nonlinear dynamic friction model, the friction force of the steering system is compensated. Combined with the kingpin caster or camber return torque, inertial torque, and damping torque, the target road feel torque is calculated. ; In the formula, This is the normalizing torque coefficient. This is the road feel damping coefficient. The angular velocity of the steering wheel. The rack force is the equivalent feedback torque. Friction compensation torque calculated for the Lugre model. For inertial compensation torque; S5: The main control unit dynamically adjusts the basic steering ratio coefficient K based on the vehicle speed signal output by the vehicle status acquisition module: when the vehicle speed is lower than the minimum preset threshold, K is increased to improve steering ease; when the vehicle speed is higher than the maximum preset threshold, K is decreased to improve driving stability. Control quantity of steering drive motor The output is sent to the steering actuator module to transmit the target road feel torque. The output is sent to the road feel feedback execution module to achieve synchronous closed-loop control of steering angle and road feel torque; S6: Based on the steering wheel angle and torque signals output by the steering wheel angle acquisition module and the vehicle speed signal output by the vehicle status acquisition module, the system reduces the return-to-center residual angle at low speeds and suppresses overshoot at high speeds; it performs real-time system fault diagnosis and detects faults in the lateral acceleration sensor in the vehicle status acquisition module using the residual chi-square test method. In case of a fault, it automatically switches the source of road feel torque calculation to maintain steering function.

[0012] Preferably, the load of the steering drive motor is obtained by a Kalman observer to acquire the load torque of the steering drive motor in the steering execution module in real time, which serves as a backup source for calculating the road feel torque when the lateral acceleration sensor in the vehicle state acquisition module fails.

[0013] Preferably, the lowest preset threshold in S5 is set to 30 km / h, and the highest preset threshold is set to 85 km / h.

[0014] Therefore, the present invention employs the above-described steer-by-wire system and control method, and the technical effects are as follows: (1) This invention reduces the corner tracking error by fusing dynamic model with multi-source state estimation, and has a faster dynamic response. It can adapt to complex working conditions such as low-adhesion road surface and sudden speed change, and greatly improves handling stability.

[0015] (2) This invention restores road feel through Lugre friction compensation and multi-component composite model; in order to meet different driving preferences and scenario requirements, it is designed with multiple adjustable modes to enhance the diversity of driving experience.

[0016] (3) The present invention adopts the synergistic effect of full-dimensional hardware redundancy and software fault tolerance mechanism. In the event of a single point of failure, it can achieve millisecond-level switching without interruption of the steering function, meet the functional safety ASIL-D level requirements, and greatly reduce the risk of failure.

[0017] (4) The present invention combines adaptive transmission ratio and active return-to-center strategy to solve problems such as heavy driving at low speed, floating at high speed and poor return-to-center, covering all scenarios such as parking, urban roads and high-speed driving, and comprehensively improving the driving comfort and stability. Attached Figure Description

[0018] Figure 1 This is an architectural diagram of a steer-by-wire system according to the present invention; Figure 2 This is a flowchart of a control method for a steer-by-wire system according to the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] Example like Figure 1As shown, the present invention provides a steer-by-wire system, including a steering wheel angle acquisition module, a road feel feedback execution module, a main control unit, a steering execution module, a vehicle status acquisition module, a tire status acquisition module, and a redundant safety module; the main control unit is electrically connected to the steering wheel angle acquisition module, the road feel feedback execution module, the steering execution module, the vehicle status acquisition module, and the redundant safety module respectively; The main control unit calculates the target front wheel angle and target road feel torque based on the steering wheel angle signal output by the steering wheel angle acquisition module, the vehicle speed signal, yaw rate signal, lateral acceleration signal output by the vehicle status acquisition module, and the tire status parameters acquired by the tire status acquisition module. It then uses a two-degree-of-freedom vehicle dynamics model and a magic tire model to calculate the target front wheel angle and target road feel torque. Finally, it uses a dual closed-loop control algorithm to output steering control commands and road feel control commands. The steering execution module drives the vehicle to steer according to the output steering command, and the road feel feedback execution module uses a permanent magnet synchronous motor (PMSM) as the actuator according to the road feel control command, and realizes the torque output based on the active disturbance rejection controller (ADRC) optimized by the improved particle swarm optimization (PSO) algorithm.

[0022] The redundant safety module includes dual power supplies, dual corner sensors, dual communication interfaces, dual drive circuits, and a fault detection unit. The fault detection unit monitors the sensor status in real time using the residual chi-square test method. If any single channel fails, the other channel will automatically switch the road feel torque calculation source or control channel within a preset time.

[0023] The road feel feedback execution module is also equipped with an adjustable coefficient group, including the stationary resistance torque adjustment coefficient, the assist torque adjustment coefficient, the damping torque adjustment coefficient, and the friction torque adjustment coefficient, supporting multi-mode road feel switching.

[0024] The steering wheel angle acquisition module includes dual redundant angle sensors and dual redundant torque sensors for real-time acquisition of the steering wheel angle θ. s Steering wheel torque signal: When the steering wheel angle approaches the maximum steering angle of the front wheel ±35°, the steering resistance torque is gradually increased to simulate mechanical limit characteristics.

[0025] The tire condition acquisition module includes a tire vertical load sensor and a tire pressure sensor, which collect tire vertical load parameters and tire pressure parameters in real time. The tire vertical load parameters are combined with the lateral acceleration signal from the vehicle condition acquisition module to correct the tire lateral stiffness calculation results.

[0026] like Figure 2 As shown, a control method for a steer-by-wire system includes the following steps: S1: Collect the steering wheel angle θ via the steering wheel angle acquisition module. s and steering wheel torque; vehicle longitudinal speed is collected through the vehicle status acquisition module. yaw rate Lateral acceleration and wheel speed signals; tire vertical load parameters and tire pressure parameters are acquired through the tire condition acquisition module; S2: A vehicle mass estimation algorithm based on the fusion of Recursive Least Squares (RLS) and K-Nearest Neighbors (KNN) dynamically corrects the vehicle mass parameters; the tire lateral force is estimated by a sliding mode observer, and the road adhesion coefficient and tire self-aligning torque are calculated by combining the magic tire formula and the tire vertical load parameters and tire pressure parameters output by the tire state acquisition module. Calculate the target front wheel steering angle using a two-degree-of-freedom vehicle dynamics model: ; In the formula, This refers to the vehicle's wheelbase. This is the distance from the front axle to the vehicle's center of gravity. This is the distance from the rear axle to the vehicle's center of gravity. For the front axle equivalent mass, For the equivalent mass of the rear axle, For the front tire lateral stiffness, For rear tire lateral stiffness, Based on the basic steering gear ratio coefficient, Steering wheel angle; The longitudinal speed of the vehicle; S3: Based on the deviation between the target front wheel angle obtained in S2 and the actual front wheel angle, the steering drive motor control quantity is obtained using PID closed-loop control: ; in ; , and These represent the proportional coefficient, integral coefficient, and derivative coefficient of PID control, respectively. This is the actual front wheel steering angle; S4: Based on the Lugre nonlinear dynamic friction model, the friction force of the steering system is compensated. Combined with the kingpin caster or camber return torque, inertial torque, and damping torque, the target road feel torque is calculated. ; In the formula, This is the normalizing torque coefficient. This is the road feel damping coefficient. The angular velocity of the steering wheel. The rack force is the equivalent feedback torque. Friction compensation torque calculated for the Lugre model. For inertial compensation torque; S5: The main control unit dynamically adjusts the basic steering ratio coefficient K based on the vehicle speed signal output by the vehicle status acquisition module: when the vehicle speed is lower than the minimum preset threshold, K is increased to improve steering ease; when the vehicle speed is higher than the maximum preset threshold, K is decreased to improve driving stability; the minimum preset threshold is set to 30km / h, and the maximum preset threshold is set to 85km / h.

[0027] Control quantity of steering drive motor The output is sent to the steering actuator module to transmit the target road feel torque. The output is sent to the road feel feedback execution module to realize synchronous closed-loop control of steering angle and road feel torque; the load of the steering drive motor adopts a Kalman observer to obtain the load torque of the steering drive motor in the steering execution module in real time, which serves as a backup source for calculating road feel torque when the lateral acceleration sensor in the vehicle state acquisition module fails.

[0028] S6: Based on the steering wheel angle and torque signals output by the steering wheel angle acquisition module and the vehicle speed signal output by the vehicle status acquisition module, the system reduces the return-to-center residual angle at low speeds and suppresses overshoot at high speeds; it performs real-time system fault diagnosis and detects faults in the lateral acceleration sensor in the vehicle status acquisition module using the residual chi-square test method. In case of a fault, it automatically switches the source of road feel torque calculation to maintain steering function.

[0029] Example 1 State estimation and road feel simulation were performed. On a low-adhesion road surface with a vehicle speed of 30 km / h and an adhesion coefficient of 0.2, the vehicle weight was increased from 1413 kg to 1763 kg due to changes in the number of passengers. The proposed solution integrates RLS and KNN in its quality estimation algorithm, achieving an error ≤4.8%. The sliding mode observer estimates tire lateral force error ≤5.6%, and road feel torque output fluctuation ≤±0.05N. m, the driver's subjective evaluation of road feel accuracy is ≥92%.

[0030] Example 2 Fault tolerance verification was performed. At a vehicle speed of 60 km / h, when the lateral acceleration sensor experienced a gain failure, reducing the gain to 1.5 times, the fault was detected within 8 ms using the residual chi-square test method of this scheme. The system automatically switched to the road feel calculation source based on motor load estimation, and the steering torque fluctuation was ≤ ±0.1 N. m, the vehicle's driving stability did not change significantly, and there was no deviation or interruption of road feel.

[0031] Example 3 Active return-to-center and variable transmission ratio were verified. In low-speed parking scenarios at 10km / h and straight-line driving scenarios at 90km / h, after verification of this solution, the return-to-center residual angle at low speed was ≤1.5°, and the return-to-center overshoot at high speed was ≤3%. The low-speed steering transmission ratio was increased to 2-3 times that of the high-speed ratio, and the steering ease was improved by 40%. After the high-speed transmission ratio was reduced, the straight-line driving deviation was ≤±0.2m / 100m.

[0032] Therefore, this invention adopts the above-mentioned steer-by-wire system and control method, which integrates dynamic model and multi-source state estimation algorithm to accurately control steering; achieves realistic and personalized road feel through multi-component composite model and adjustable coefficient; optimizes full-speed handling by using vehicle speed adaptive variable transmission ratio and active return-to-center strategy; and constructs a full-dimensional safety system of hardware redundancy and software fault tolerance to meet ASIL-D level requirements, adapt to high-level autonomous driving, and balance accuracy, safety and experience.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A control method for a steer-by-wire system, the steer-by-wire system comprising a steering wheel angle acquisition module, a road feel feedback execution module, a main control unit, a steering execution module, a vehicle status acquisition module, a tire status acquisition module, and a redundant safety module; wherein the main control unit is electrically connected to the steering wheel angle acquisition module, the road feel feedback execution module, the steering execution module, the vehicle status acquisition module, and the redundant safety module respectively; The main control unit calculates the target front wheel angle and target road feel torque based on the steering wheel angle signal output by the steering wheel angle acquisition module, the vehicle speed signal, yaw rate signal, lateral acceleration signal output by the vehicle status acquisition module, and the tire status parameters acquired by the tire status acquisition module. It then uses a two-degree-of-freedom vehicle dynamics model and a magic tire model to calculate the target front wheel angle and target road feel torque. Finally, it uses a dual closed-loop control algorithm to output steering control commands and road feel control commands. The steering execution module drives the vehicle to steer according to the output steering command, and the road feel feedback execution module, based on the road feel control command, uses a permanent magnet synchronous motor (PMSM) as the actuator and an active disturbance rejection controller (ADRC) optimized by an improved particle swarm optimization (PSO) algorithm to achieve torque output; characterized by including the following steps: S1: Collect the steering wheel angle θ via the steering wheel angle acquisition module. s and steering wheel torque; vehicle longitudinal speed is collected through the vehicle status acquisition module. yaw rate Lateral acceleration and wheel speed signals; tire vertical load parameters and tire pressure parameters are acquired through the tire condition acquisition module; S2: A vehicle mass estimation algorithm based on the fusion of Recursive Least Squares (RLS) and K-Nearest Neighbors (KNN) dynamically corrects the vehicle mass parameters; the tire lateral force is estimated by a sliding mode observer, and the road adhesion coefficient and tire self-aligning torque are calculated by combining the magic tire formula and the tire vertical load parameters and tire pressure parameters output by the tire state acquisition module. Calculate the target front wheel steering angle using a two-degree-of-freedom vehicle dynamics model: ； In the formula, This refers to the vehicle's wheelbase. This is the distance from the front axle to the vehicle's center of gravity. This is the distance from the rear axle to the vehicle's center of gravity. For the front axle equivalent mass, For the equivalent mass of the rear axle, For the front tire lateral stiffness, For rear tire lateral stiffness, Based on the basic steering ratio coefficient, Steering wheel angle; The longitudinal speed of the vehicle; S3: Based on the deviation between the target front wheel angle obtained in S2 and the actual front wheel angle, the steering drive motor control quantity is obtained using PID closed-loop control: ； in ; , and These represent the proportional coefficient, integral coefficient, and derivative coefficient of PID control, respectively. This is the actual front wheel steering angle; S4: Based on the Lugre nonlinear dynamic friction model, the friction force of the steering system is compensated. Combined with the kingpin caster or camber return torque, inertial torque, and damping torque, the target road feel torque is calculated. ； In the formula, This is the normalizing torque coefficient. This is the road feel damping coefficient. The angular velocity of the steering wheel. The rack force is the equivalent feedback torque. Friction compensation torque calculated for the Lugre model. For inertial compensation torque; S5: The main control unit dynamically adjusts the basic steering ratio coefficient K based on the vehicle speed signal output by the vehicle status acquisition module: when the vehicle speed is lower than the minimum preset threshold, K is increased to improve steering ease; when the vehicle speed is higher than the maximum preset threshold, K is decreased to improve driving stability. Control quantity of steering drive motor The output is sent to the steering actuator module to transmit the target road feel torque. The output is sent to the road feel feedback execution module to achieve synchronous closed-loop control of steering angle and road feel torque; S6: Based on the steering wheel angle and torque signals output by the steering wheel angle acquisition module and the vehicle speed signal output by the vehicle status acquisition module, the system reduces the return-to-center residual angle at low speeds and suppresses overshoot at high speeds; it performs real-time system fault diagnosis and detects faults in the lateral acceleration sensor in the vehicle status acquisition module using the residual chi-square test method. In case of a fault, it automatically switches the source of road feel torque calculation to maintain steering function.

2. The control method for a steer-by-wire system according to claim 1, characterized in that, The load of the steering drive motor is obtained using a Kalman observer to acquire the load torque of the steering drive motor in the steering execution module in real time, serving as a backup source for calculating the road feel torque when the lateral acceleration sensor in the vehicle state acquisition module fails.

3. The control method for a steer-by-wire system according to claim 1, characterized in that, The minimum preset threshold in S5 is set to 30km / h, and the maximum preset threshold is set to 85km / h.

4. The control method for a steer-by-wire system according to claim 1, characterized in that, The redundant safety module in the steer-by-wire system includes dual power supplies, dual steering angle sensors, dual communication interfaces, dual drive circuits, and a fault detection unit. The fault detection unit monitors the sensor status in real time using the chi-square test of residuals. If any single path fails, the other path automatically switches the road feel torque calculation source or control channel within a preset time.

5. The control method for a steer-by-wire system according to claim 1, characterized in that, The road feel feedback execution module in the steer-by-wire system is also equipped with an adjustable coefficient group, including the stationary resistance torque adjustment coefficient, assist torque adjustment coefficient, damping torque adjustment coefficient, and friction torque adjustment coefficient, supporting multi-mode road feel switching.

6. The control method for a steer-by-wire system according to claim 1, characterized in that, The steering wheel angle acquisition module in the steer-by-wire system includes dual redundant angle sensors and dual redundant torque sensors for real-time acquisition of the steering wheel angle θ. s Steering wheel torque signal; When the steering wheel angle approaches ±35° of the maximum steering angle of the front wheels, the steering resistance torque is gradually increased to simulate mechanical limit characteristics.

7. The control method for a steer-by-wire system according to claim 1, characterized in that, The tire status acquisition module in the steer-by-wire system includes a tire vertical load sensor and a tire pressure sensor, which collect tire vertical load parameters and tire pressure parameters in real time. The tire vertical load parameters are combined with the lateral acceleration signal from the vehicle status acquisition module to correct the tire lateral stiffness calculation results.

Images