Steer-by-wire system based on combined controller architecture

Abstract

The invention provides a steer-by-wire system based on a combined controller architecture. The steer-by-wire system comprises a master controller, a slave controller, a fault-tolerant control switching logic module and a variable transmission ratio control module, the fault-tolerant control switching logic module is used for switching to a degradation mode when the master controller breaks down or a motor winding of the master controller breaks down, and triggering emergency braking of the vehicle when the master controller and the slave controller both break down; in a normal mode, the master controller and the slave controller respectively control steer-by-wire and road feeling simulation of a vehicle, and the variable transmission ratio control module performs segmentation according to the vehicle speed and adopts different transmission ratios to realize a-section transmission ratio adjustment; and in the degradation mode, the master controller stops working, the slave controller controls steer-by-wire and road feeling simulation of the vehicle, the variable transmission ratio control module performs segmentation according to the vehicle speed and adopts different algorithms to realize b-section transmission ratio adjustment, and b is smaller than a.

Description

Technical Field

[0001] The present invention relates to the field of vehicle control technology, and in particular to a steer-by-wire system based on a combined controller architecture. Background Art

[0002] With the advancement of intelligent and electrified vehicles, steer-by-wire (SBW) systems are gradually replacing traditional mechanical steering systems, becoming a key technology for improving vehicle handling flexibility and driving safety. Traditional mechanical steering systems have a fixed angular transmission ratio, resulting in a significant speed-dependent impact on steering sensitivity. This results in sluggish steering response at high speeds and excessively sensitive steering at low speeds, making it difficult to balance handling stability and driving experience across various operating conditions. Steer-by-wire systems replace mechanical connections with electrical signal transmission, enabling dynamic adjustment of the transmission ratio. However, further improvements are needed in reliability, fault tolerance, and transmission ratio optimization algorithms.

[0003] Currently, variable transmission ratio control is essentially based on a fixed vehicle model, with various speed ranges optimized through different algorithms. In terms of redundant control, the existing redundant controller architecture uses dual-controller backup and implements fault switching through a single communication link. However, in normal mode, a single controller usually assumes all control tasks, such as steering control or road feedback, while the other controller remains idle, resulting in increased costs and low resource utilization.

[0004] However, transmission ratio design based on a fixed model or a single optimization algorithm often has a single optimization goal (such as optimal steering sensitivity or maximum steering stability), which ignores the driver's complex needs such as feel, comfort, and feedback consistency. At the same time, for the transmission ratio design of the vehicle under different states, the dual controller can not only meet the redundant safety requirements of the vehicle in normal mode, but also normally execute separate steering control and road feel feedback. Summary of the Invention

[0005] The present invention proposes a steer-by-wire system based on a combined controller architecture to solve the existing variable transmission ratio control considering vehicle failure.

[0006] To address the above technical problems, the present invention provides a steer-by-wire system based on a combined controller architecture. This system significantly improves resource utilization, control accuracy, and driving safety through a combined redundant controller architecture and a segmented variable transmission ratio algorithm. The system is unique in that it includes a master controller and slave controllers that serve as backups for each other, a fault-tolerant control switching logic module, and a variable transmission ratio control module.

[0007] The fault-tolerant control switching logic module is used to switch from the normal mode to the degraded mode when one of the controllers fails or one of the controller motor windings fails, and trigger an emergency brake of the vehicle when both the master controller and the slave controller fail;

[0008] In the normal mode, the master controller and the slave controller respectively control the steer-by-wire and road feel simulation of the vehicle, and the variable transmission ratio control module realizes the a-segment transmission ratio adjustment in sections according to the vehicle speed; in the degraded mode, the controller without failure simultaneously controls the steer-by-wire and road feel simulation of the vehicle, and the variable transmission ratio control module will realize the b-segment transmission ratio adjustment in sections according to the vehicle speed, where b < a.

[0009] Preferably, several corner sensors and vehicle speed sensors are provided on both the master controller and the slave controller. When not all of the corner sensors and vehicle speed sensors of the master controller and the slave controller fail, the fault-tolerant control switching logic module does not switch to the degraded mode.

[0010] Preferably, the master controller and the slave controller are communicatively connected via two SPI buses.

[0011] Preferably, in the normal mode, the variable transmission ratio control module realizes 4-segment transmission ratio adjustment according to the first vehicle speed, the second vehicle speed, and the third vehicle speed;

[0012] When the vehicle speed is less than or equal to the first vehicle speed, a fixed minimum transmission ratio is adopted;

[0013] When the vehicle speed is greater than the first vehicle speed and less than or equal to the second vehicle speed, a transmission ratio based on a constant yaw rate gain and optimized by a genetic algorithm is adopted;

[0014] When the vehicle speed is greater than the second vehicle speed and less than the third vehicle speed, a fuzzy control algorithm optimizes the transmission ratio;

[0015] When the vehicle speed is greater than or equal to the third vehicle speed, a fixed maximum transmission ratio is adopted.

[0016] Preferably, the transmission ratio based on the yaw rate gain has the following expression:

[0017] ;

[0018] In the formula, is the longitudinal speed of the vehicle; is the wheelbase; is the vehicle mass; is the front wheelbase; is the rear wheelbase; is the front wheel cornering stiffness; is the rear wheel cornering stiffness; is the yaw rate gain.

[0019] Preferably, the yaw rate gain is optimized by a genetic algorithm with as the objective function:

[0020] ;

[0021] wherein, , , and are weighting coefficients, is the trajectory tracking error; is the driver's operation burden index; is the rollover risk evaluation index; is the sideslip risk index;

[0022] ;

[0023] wherein, represents the ideal driving path of the vehicle; represents the actual driving path of the vehicle; is the test time; is the threshold value of the trajectory error standard; is the threshold value of the centroid side slip angular velocity standard; and are weighting coefficients; represents the vehicle speed, represents the derivative of the yaw rate;

[0024]

[0025] wherein, is the steering wheel rotation angular velocity; is 's standard threshold value; is the steering wheel torque; is the steering wheel torque standard threshold value; and are weighting coefficients;

[0026] ;

[0027] wherein, is the lateral acceleration threshold value; is the roll angle threshold value; and are weighting coefficients; represents the lateral acceleration, represents the roll angle;

[0028] ;

[0029] In the formula, , where i = 1 and 2 respectively represent the lateral forces on the front and rear axles of the vehicle; , where i = 1 and 2 respectively represent the normal pressures on the front and rear axles of the vehicle; is the threshold value of the lateral adhesion coefficient of the vehicle on a normal road surface; represents the evaluation index of the sideslip risk of the two axles of the vehicle.

[0030] Preferably, the method for optimizing the transmission ratio by using the fuzzy control algorithm includes: defining the input universe of discourse as {the second vehicle speed, the third vehicle speed}, setting the fuzzy universe of discourse of the steering wheel angle as {-180°, 180°}, setting the fuzzy universe of discourse of the transmission ratio according to the second vehicle speed and the third vehicle speed, and finally optimizing the transmission ratio according to the vehicle speed.

[0031] Preferably, in the degradation mode, the variable transmission ratio control module realizes three-stage transmission ratio adjustment according to the first vehicle speed and the third vehicle speed;

[0032] When the vehicle speed is less than the first vehicle speed, a fixed minimum transmission ratio is adopted;

[0033] When the vehicle speed is greater than the first vehicle speed and less than the third vehicle speed, a transmission ratio control based on the vehicle speed is adopted;

[0034] When the vehicle speed is greater than the third vehicle speed, a fixed maximum transmission ratio is adopted.

[0035] Preferably, the expression of the transmission ratio control based on the vehicle speed is:

[0036] ;

[0037] In the formula, is the longitudinal speed of the vehicle; is the wheelbase; is the stability factor. The beneficial effects of the present invention at least include:

[0038] 1) Optimization of resource utilization rate and real-time performance: In the normal mode, the main controller and the slave controller independently process the steering control and road feel information respectively, avoiding the situation that the redundant controllers in the dual-redundancy architecture are often in the "cold standby" or "hot standby" state and do not actively participate in the control, resulting in low hardware utilization rate, and improving the computing resource utilization rate and system response speed;

[0039] 2) Enhanced handling stability across all vehicle speeds: Based on vehicle speed segmentation (low speed, medium speed, high speed, ultra-high speed), genetic algorithm optimization, fuzzy control, and fixed gear ratio strategies are employed to address the poor adaptability of traditional fixed models or single algorithms. This avoids triggering steering limits at low speeds, reduces steering response hysteresis at high speeds, and optimizes the gear ratio gain considering the real vehicle road feel, comprehensively optimizing the driving experience.

[0040] 3) Safety guarantee in degraded mode: The reduced-order gear ratio algorithm is enabled in the first-level degraded state, simplifying the control logic while retaining low-speed sensitivity and high-speed stability, taking into account both the controller load and vehicle safety, and avoiding secondary failures caused by excessive algorithm complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the system structure framework of an embodiment of the present invention.

[0042] Figure 2 This is a simulation diagram of the gear ratio design under normal conditions of an embodiment of the present invention.

[0043] Figure 3 This is a simulation diagram of the gear ratio design under fault conditions of an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The following clearly and completely describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0045] As Figure 1 shown, an embodiment of the present invention provides a steer-by-wire system based on a combined controller architecture, including a primary controller and a secondary controller that are backups of each other, a fault-tolerant control switching logic module, and a variable gear ratio control module.

[0046] The fault-tolerant control switching logic module is used to switch to the degraded mode when the primary controller fails or the motor winding of the primary controller fails, and trigger an emergency brake for the vehicle when both the primary controller and the secondary controller fail.

[0047] In the normal mode, the primary controller and the secondary controller respectively control the steer-by-wire and road feel simulation of the vehicle, and the variable gear ratio control module realizes the a-section gear ratio adjustment according to the vehicle speed in segments; in the degraded mode, the controller without a fault controls both the steer-by-wire and road feel simulation of the vehicle, and the variable gear ratio control module will realize the b-section gear ratio adjustment according to the vehicle speed in segments, where b < a.

[0048] In this embodiment, the overall controller architecture adopts redundancy and mutual backup. Two independent controllers back up each other. The host and slave controllers run their respective control programs. When one of the controllers fails, the normal controller executes all control tasks. This method can reduce the load of the two controllers under normal circumstances and is also conducive to the coordinated control between the controllers. The communication connection between the dual-redundancy integrated controllers is carried out through two SPI buses. The SPI0 and SPI1 of the master controller are respectively configured as the master mode and the slave mode, and correspondingly, the SPI0 and SPI1 of the slave controller are respectively configured as the slave mode and the master mode. In this way, the synchronous clocks of the two channels are provided by the host and the slave respectively, which can ensure that the controller can still operate normally when a single controller or a single communication link fails.

[0049] In this embodiment, the inspection of the controller includes:

[0050] 1) Self-check of the steering actuator and lock-step core;

[0051] 2) Detection of the received command signal and sensor signal of the control;

[0052] 3) Faults in the communication between the controller and other hardware, including CAN and SPI.

[0053] The input detection unit includes:

[0054] 1) Check of the input signal range;

[0055] 2) Detection of input signal timeout or jamming;

[0056] 3) Rationality verification of the input signal.

[0057] In this embodiment, the downgrade control is carried out through the fault-tolerant control switching logic module, and its control conditions include:

[0058] 1) One of the controllers fails;

[0059] 2) The motor winding of one of the controllers fails.

[0060] When any of the above conditions is satisfied, the fault-tolerant control switching logic module controls the downgrade and enters the downgrade mode. The slave controller completes all control operations, and at the same time, the system issues a warning to remind the driver not to operate the steering device violently.

[0061] In this embodiment, the controller can also be provided with several corner sensors and vehicle speed sensors. When the corner sensors and vehicle speed sensors of one of the controllers are not all faulty, the fault-tolerant control switching logic module does not switch to the downgrade mode. At this time, the system issues a warning and the controllers all perform normal control.

[0062] To prevent the algorithm load of the controller from being too heavy in the downgrade mode, in the normal mode, the variable transmission ratio control module adjusts the transmission ratio in section a according to the vehicle speed by adopting different transmission ratios; in the downgrade mode, the variable transmission ratio control module will adjust the transmission ratio in section b according to the vehicle speed by adopting different algorithms. In the embodiment of the present invention, b is set to be less than a to prevent the driving safety problem caused by the overloaded algorithm when controlled by a single controller.

[0063] In the normal mode, while taking into account the handling stability and steering characteristics, the variation law of the front wheel angle transmission ratio of the SBW system is designed to improve the steering response of the vehicle. In the mechanical steering system, the angle transmission ratio is often a fixed value. This will cause the steering sensitivity of the vehicle to be affected by the vehicle speed.

[0064] Therefore, in this embodiment, according to the vehicle speed, it is segmented, and for each segment, a different transmission ratio control scheme is adopted. Less than the first vehicle speed is used as the low-speed segment, between the first vehicle speed and the second vehicle speed is used as the medium-speed segment, between the second vehicle speed and the third vehicle speed is used as the high-speed segment, and greater than the third vehicle speed is used as the ultra-high-speed segment. In this embodiment, the first vehicle speed is set to 20 km / h, the second vehicle speed is 80 km, and the third vehicle speed is 120 km / h.

[0065] For the transmission ratio of the low-speed segment, considering that when the vehicle speed starts to change from 0, the value of the ideal transmission ratio i is too small and it is easy to reach the steering limit position, which does not conform to the actual driving situation. Therefore, the minimum value of the ideal transmission ratio is set to i min .

[0066] For the medium-speed segment, the steering transmission ratio design in this embodiment is considered based on the constant yaw rate gain and the constant lateral acceleration gain.

[0067] 1. Based on the constant lateral acceleration gain

[0068] ;

[0069] Among them, is the gain between the lateral acceleration and the steering wheel angle, is the vehicle lateral acceleration, with the unit of m / s 2 ; is the steering wheel angle, with the unit of rad.

[0070] Design the transmission ratio based on the constant lateral acceleration to ensure that remains unchanged. Let = , and the expression of the transmission ratio is obtained as follows:

[0071] ;

[0072] In the formula, is the longitudinal speed of the vehicle, with the unit of m / s; is the wheelbase, with the unit of m; is the stability factor, is the optimized lateral acceleration gain.

[0073] 2. Based on the constant yaw rate gain

[0074] According to the vehicle dynamics model, it can be known that:

[0075] ;

[0076] In the formula, is the gain relationship between the front wheel steering angle and the yaw rate; is the yaw rate, with the unit of rad / s; is the front wheel steering angle, with the unit of rad;

[0077] ;

[0078] In the formula, is the distance from the front axle to the center of mass, with the unit of m; is the distance from the rear axle to the center of mass, with the unit of m; is the front wheel cornering stiffness, with the unit of N / rad; is the rear wheel cornering stiffness, with the unit of N / rad.

[0079] The gain between the yaw rate and the steering wheel angle can be obtained is expressed as:

[0080] ;

[0081] is the steering system transmission ratio, dimensionless.

[0082] Design the transmission ratio based on the constant yaw rate gain to ensure remains unchanged. Let = to obtain the ideal transmission ratio The expression is as follows:

[0083] ;

[0084] In the formula, is the designed yaw rate gain.

[0085] Compared with the lateral angular velocity gain, selecting the yaw angular velocity gain to design the transmission ratio is closer to the driver's handling perception. The yaw angular velocity is the most direct manifestation of the vehicle's steering response, and the driver's feedback on the speed of vehicle turning through visual and physical perception. And selecting the yaw angular velocity gain to design the transmission ratio is applicable to a wider speed range. Therefore, the embodiment of the present invention selects to design the transmission ratio based on the yaw angular velocity gain.

[0086] The expected yaw angle generated by the transmission ratio designed based on the vehicle two-degree-of-freedom model is the ideal yaw angle, and there is still a gap with the actual vehicle yaw angle. The curve of the yaw angular velocity gain of the vehicle changing with speed is compensated by using a Class B vehicle in Carsim, so that the designed transmission ratio is more suitable for real vehicle applications. Finally, the transmission ratio designed based on the yaw angular velocity gain is:

[0087] ;

[0088] In the formula, is the front wheel axle distance; is the rear wheel axle distance.

[0089] At the same time, when selecting different yaw angular velocity gain values, there are significant differences in the values of the transmission ratio, especially in the high-speed range. In this embodiment, the genetic algorithm is used to optimize with the vehicle handling stability index as the objective function, and design the transmission ratio based on the optimized value.

[0090] Comprehensive evaluation index of handling stability:

[0091]

[0092] In the formula, , , and are weighting coefficients, and in this embodiment, they are uniformly taken as 0.25; is the trajectory tracking error; is the driver's operation burden index; is the rollover risk evaluation index; is the sideslip risk index;

[0093] Trajectory tracking error is a key index to evaluate the quality of the vehicle's trajectory tracking performance. It is mainly composed of the path error evaluation index and the direction error evaluation index , and the expression is as follows:

[0094] ;

[0095] Where, Represents the ideal driving path of the car; Represents the actual driving path of the car; is the test time; is the threshold value of the trajectory error standard, which is taken as 0.4; is the threshold value of the center of mass sideslip angular velocity standard, which is taken as 0.8; and is the weighting coefficient; is the sideslip angle of the center of mass; Indicates vehicle speed; represents the derivative of the yaw rate.

[0096] Driver operating burden index It is a key indicator for evaluating the difficulty of the driver to control the car. The larger the index is, the more difficult it is for the driver to control the car. Mainly based on busyness index and steering wheel heaviness index The specific expression is as follows:

[0097] ;

[0098] Where, is the steering wheel angular velocity; for The standard threshold value of is the steering wheel torque; is the standard threshold value of steering wheel torque; and is the weighting coefficient.

[0099] Rollover hazard assessment index Mainly consider the lateral acceleration of the car and roll angle Impact on handling stability, if or If it exceeds a certain value, the car will be in danger of rolling over, seriously affecting the driving safety of the car. The expression is as follows:

[0100] ;

[0101] Where, is the lateral acceleration threshold; is the roll angle threshold; and is the weighting coefficient; represents the lateral acceleration; Indicates the roll angle.

[0102] Planning Hazard Index It is a key index for evaluating whether a vehicle skids. It mainly determines whether a vehicle skids based on the relationship between the lateral force and the adhesion force acting on the vehicle. The specific expression is as follows:

[0103] ;

[0104] In the formula, , where i = 1 and 2 respectively represent the lateral forces acting on the front and rear axles of the vehicle; , where i = 1 and 2 respectively represent the normal pressures acting on the front and rear axles of the vehicle; is the threshold value of the lateral adhesion coefficient of the vehicle on a normal road surface; represents the skid hazard evaluation index of the two axles of the vehicle.

[0105] To minimize the value of , this is a weighted root mean square optimization problem with multi-extremum characteristics and is suitable for global search optimization using the Genetic Algorithm (GA). Therefore, in this embodiment, the genetic algorithm is used to optimize the comprehensive handling evaluation index to obtain the optimized yaw rate gain . In this embodiment, the crossover probability is set to 0.77, the mutation probability is set to 0.008, and the population size is set to 100 to optimize .

[0106] For the design of the transmission ratio in the high-speed section, in this embodiment, the fuzzy algorithm is used for optimization. A typical fuzzy controller structure includes the following four parts:

[0107] 1. Fuzzification

[0108] Convert the input precise quantity (such as speed, steering angle, etc.) into a fuzzy quantity, that is, map the input value into the corresponding membership function to obtain its membership degree in different fuzzy sets.

[0109] 2. Knowledge Base

[0110] It includes two sub-parts: the Database and the Rule Base;

[0111] Database, which defines the fuzzy sets, the shapes of the membership functions, such as triangular, trapezoidal, Gaussian, etc., and the fuzzy ranges of the input / output.

[0112] Rule Base, which consists of "if-then" type rules (IF-THEN) refined from expert experience or system modeling, such as: IF the vehicle speed is high AND the steering angle is small THEN the transmission ratio is large.

[0113] 3. Fuzzy Inference (Inference Engine)

[0114] Based on the fuzzy values of the input variables and the fuzzy rules matched in the rule base, fuzzy inference is performed to obtain the fuzzy output result.

[0115] 4. Defuzzification

[0116] The fuzzy inference result, usually the weighted result of multiple fuzzy sets, is converted into the output of a definite control quantity.

[0117] In this embodiment, the high-speed driving range of the vehicle is defined as 80 km / h to 120 km / h. That is, the input universe of discourse of the fuzzy controller is {80, 120}, and the corresponding fuzzy sets are {NB, NM, NS, ZO, PS, PM, PB}. The triangular membership function is adopted. The fuzzy universe of discourse of the steering wheel angle is set as {-180°, 180°}, and the corresponding fuzzy sets are also {NB, NM, NS, ZO, PS, PM, PB}, and the triangular membership function is still adopted. After data query, the transmission ratio in the high-speed range is designed to be 19 - 25, the fuzzy universe of discourse is {19, 25}, and the fuzzy sets are {NB, NM, NS, ZO, PS, PM, PB}. The triangular membership function is also selected. Finally, the transmission ratio optimized according to the vehicle speed is selected in the high-speed section .

[0118] For the transmission ratio in the ultra-high-speed section, when the vehicle is in the ultra-high-speed section, the steering response is too sluggish and it is difficult to respond in time. Therefore, when the speed is greater than the third vehicle speed, the maximum transmission ratio is set for control.

[0119] In summary, in the normal mode, the designed transmission ratio is as follows:

[0120] ;

[0121] In the downgraded mode, to ensure that the system can still maintain the operation of basic functions when resources are limited or partial failures occur, the variable transmission ratio system also enters the downgraded operation state. Specifically, the system will appropriately simplify the calculation accuracy of the transmission ratio and the control strategy to reduce the operation burden and response pressure of the controller. First, in terms of segmented design, the number of segments of the transmission ratio division in the downgraded mode is reduced compared to the normal mode, that is, a coarser-grained segmentation scheme is adopted, thereby effectively reducing the number of calculations required in each control cycle. Second, for the intermediate speed segment (i.e., the non-low-speed or high-speed range), instead of using complex multi-parameter optimization algorithms or high-order interpolation models to calculate the transmission ratio, a linear approximation method or piecewise constant function with simple structure and high calculation efficiency is selected to further reduce the calculation complexity. This simplification strategy greatly alleviates the real-time operation pressure of the controller while ensuring a certain control accuracy, thereby improving the stability and recoverability of the system in case of failures or emergencies.

[0122] ;

[0123] The reduced-order transmission ratio control can still maintain low-speed sensitivity and high-speed stability. The optimization process of the control algorithm is cancelled to ensure the basic steering function.

[0124] As Figure 2 and Figure 3 shown, they are respectively the transmission ratio design in the normal state and the transmission ratio design in the fault state of this embodiment. At low speeds, the ideal transmission ratio of the steer-by-wire system is less than that of the traditional mechanical steering system, increasing the steering sensitivity at low speeds. With the same input of the steering wheel angle, the front-wheel angle response of the former is greater than that of the latter, and the steady-state value of the yaw rate response increases. When performing large-angle steering operations, the rotation amplitude of the steering wheel by the driver is effectively reduced. At high speeds, the ideal transmission ratio of the steer-by-wire system is determined by the fuzzy control strategy, and its transmission ratio is greater than that of the traditional mechanical steering system. The steady-state values of the front-wheel angle and yaw rate responses decrease, and the fluctuation amplitude of the yaw rate during the transient process also significantly decreases, indicating that the steer-by-wire system reduces the steering sensitivity of the vehicle at high speeds; in case of failures, although some functions are limited, the core feature of variable transmission ratio is still retained as much as possible to maintain the system's adaptability to different working conditions. By reducing the segmentation accuracy of the transmission ratio calculation, simplifying the calculation logic of the intermediate speed section, and adopting a more efficient approximation algorithm, not only the system's dependence on computing resources is effectively reduced, but also the real-time response ability of the system in abnormal states is improved. This design strategy takes into account the feasibility and robustness of engineering implementation while ensuring the availability of the basic functions of the system, reflecting the balanced consideration of function retention and complexity control in the downgraded control strategy.

[0125] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. Only the preferred embodiments of the present invention are expressed. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention. As long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0126] It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A steer-by-wire system based on a combined controller architecture, characterized in that: It includes a master controller and a slave controller that are backups of each other, a fault-tolerant control switching logic module, and a variable transmission ratio control module; The fault-tolerant control switching logic module is used to switch from the normal mode to the degraded mode when one of the controllers fails or one of the controller motor windings fails, and trigger an emergency brake for the vehicle when both the master controller and the slave controller fail; In the normal mode, the master controller and the slave controller respectively control the steer-by-wire and road feel simulation of the vehicle, and the variable transmission ratio control module realizes the a-segment transmission ratio adjustment in sections according to the vehicle speed; in the degraded mode, the controller without a fault controls the steer-by-wire and road feel simulation of the vehicle simultaneously, and the variable transmission ratio control module will realize the b-segment transmission ratio adjustment in sections according to the vehicle speed, where b < a.

2. The steer-by-wire system based on a combined controller architecture according to claim 1, wherein: Both the master controller and the slave controller are provided with a plurality of corner sensors and vehicle speed sensors. When not all of the corner sensors and vehicle speed sensors of the master controller and the slave controller fail, the fault-tolerant control switching logic module does not switch to the degraded mode.

3. The steer-by-wire system based on a combined controller architecture according to claim 1, characterized in that: The master controller and the slave controller are communicatively connected through two SPI buses.

4. The steer-by-wire system based on a combined controller architecture according to claim 1, wherein: In the normal mode, the variable transmission ratio control module realizes 4-segment transmission ratio adjustment according to the first vehicle speed, the second vehicle speed, and the third vehicle speed; When the vehicle speed is less than or equal to the first vehicle speed, a fixed minimum transmission ratio is adopted; When the vehicle speed is greater than the first vehicle speed and less than or equal to the second vehicle speed, a transmission ratio based on a constant yaw rate gain and optimized by a genetic algorithm is adopted; When the vehicle speed is greater than the second vehicle speed and less than the third vehicle speed, a fuzzy control algorithm is used to optimize the transmission ratio; When the vehicle speed is greater than or equal to the third vehicle speed, a fixed maximum transmission ratio is adopted.

5. The steer-by-wire system based on a combined controller architecture according to claim 4, wherein: The transmission ratio based on the yaw rate gain has the following expression: ； wherein, is the longitudinal speed of the vehicle; is the wheelbase; is the mass of the vehicle; is the front wheelbase; is the rear wheelbase; is the cornering stiffness of the front wheels; is the cornering stiffness of the rear wheels; is the yaw rate gain.

6. The steer-by-wire system based on a combined controller architecture according to claim 5, characterized in that: The yaw rate gain is optimized by using the genetic algorithm with as the objective function: ； In the formula, , , and are weighting coefficients, is the trajectory tracking error; is the driver's operation burden index; is the rollover risk assessment index; is the sideslip risk index; ； In the formula, represents the ideal driving path of the vehicle; represents the actual driving path of the vehicle; is the test time; is the threshold value of the trajectory error standard; is the threshold value of the yaw rate standard; and are the weighting coefficients; represents the vehicle speed, represents the derivative of the yaw rate; ； Wherein, is the angular velocity of the steering wheel rotation; is the standard threshold value of; is the steering wheel torque; is the standard threshold value of the steering wheel torque; and are the weighting factors; ； Wherein, is the lateral acceleration threshold value; is the roll angle threshold value; and are the weighting coefficients; represents the lateral acceleration, represents the roll angle; ； In the formula, , where \(i = 1\) and \(2\) respectively represent the lateral forces on the front and rear axles of the vehicle; , where \(i = 1\) and \(2\) respectively represent the vertical forces on the front and rear axles of the vehicle; is the threshold value of the lateral adhesion coefficient of the vehicle on a normal road surface; represents the evaluation index of the sideslip risk of the two axles of the vehicle.

7. The steer-by-wire system based on a combined controller architecture according to claim 6, characterized in that: The method for optimizing the transmission ratio using the fuzzy control algorithm includes: defining the input domain as {the second vehicle speed, the third vehicle speed}, setting the fuzzy domain of the steering wheel angle as {-180°, 180°}, setting the fuzzy domain of the transmission ratio according to the second vehicle speed and the third vehicle speed, and finally optimizing the transmission ratio according to the vehicle speed.

8. The steer-by-wire system based on a combined controller architecture according to claim 4, wherein: In the degraded mode, the variable transmission ratio control module realizes 3-segment transmission ratio adjustment according to the first vehicle speed and the third vehicle speed; When the vehicle speed is less than the first vehicle speed, a fixed minimum transmission ratio is adopted; When the vehicle speed is greater than the first vehicle speed and less than the third vehicle speed, a transmission ratio control based on the vehicle speed is adopted; When the vehicle speed is greater than the third vehicle speed, a fixed maximum transmission ratio is adopted.

9. The steer-by-wire system based on a combined controller architecture according to claim 8, characterized in that: The expression of the transmission ratio control based on the vehicle speed is: ； In the formula, is the longitudinal speed of the vehicle; is the wheelbase; is the stability factor.

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