CN-121990039-A - Vehicle rear wheel active steering control system and method based on single motor driving and differential braking

CN121990039ACN 121990039 ACN121990039 ACN 121990039ACN-121990039-A

Abstract

The invention belongs to the technical field of vehicle dynamics control and drive-by-wire chassis, and particularly relates to a vehicle rear wheel active steering control system and method based on single motor driving and differential braking. The control system comprises a sensing module, a control unit and an executing mechanism, wherein the sensing module and the executing mechanism are connected with the control unit through electric signals, the sensing module comprises a steering wheel angle sensor and a vehicle state sensor, the control unit comprises a vehicle dynamics controller, the vehicle dynamics controller comprises a vehicle motion controller and a coordination distributor, and the executing mechanism comprises a rear axle driving motor and a controller thereof. According to the technical scheme, motor driving and braking are overlapped into a unified rear wheel steering force generating unit, a layered coordination control strategy is formed, a whole set of mechanical actuating mechanism required by rear wheel steering is omitted, and only the existing driving motor and braking system of the vehicle are utilized. Through the control strategy, multiple modes of the rear wheel steering angle changing along with the speed of the vehicle are easily realized, and the mode switching is seamless and smooth.

Inventors

CHI YUHUA
ZHANG HAO
ZHAO XUEMING
LI HAILIANG
YANG DONG
WANG JIAJUN
YU CHUNFENG
WANG SHUAI

Assignees

安徽江淮汽车集团股份有限公司

Dates

Publication Date: 20260508
Application Date: 20260402

Claims (10)

1. The vehicle rear wheel active steering control system based on single motor driving and differential braking is characterized by comprising a sensing module, a control unit and an executing mechanism, wherein the sensing module and the executing mechanism are electrically connected with the control unit; The sensing module comprises a steering wheel angle sensor and a vehicle state sensor, the control unit comprises a vehicle dynamics controller which is used as an operation carrier of an upper layer decision and middle layer coordination algorithm, the vehicle dynamics controller comprises a vehicle motion controller and a coordination distributor, and the execution mechanism comprises a rear axle driving motor and a controller thereof.
2. The vehicle rear wheel active steering control system based on single motor drive and differential braking according to claim 1, wherein the vehicle state sensor includes at least a vehicle speed sensor, a yaw rate sensor, and an acceleration sensor.
3. A method for actively steering a rear wheel of a vehicle based on single motor driving and differential braking is characterized in that the motor driving and the braking are overlapped into a unified rear wheel steering force generating unit to form a layered coordination control strategy, and the method comprises the following steps: S1, upper layer decision, wherein a vehicle upper layer motion controller calculates a target additional yaw moment M des required for optimizing steering response based on a vehicle model according to steering input of a driver, vehicle speed and vehicle body state; S2, middle-layer coordination distribution, taking M des as input, and simultaneously solving an optimal motor total torque instruction T motor and a single-side rear wheel additional braking instruction F brake in a unified optimization framework; S3, executing the bottom layer, wherein the driving motor controller executes a total torque command comprising driving or regenerative braking, and simultaneously, the electronic stabilizing system applies accurate additional braking force to the rear wheel at the designated side.
4. The method for actively steering the rear wheels of the vehicle based on single motor driving and differential braking according to claim 3, wherein the specific flow comprises the following steps: S100, signal acquisition and processing; S200, calculating a target yaw moment by the vehicle upper layer motion controller; S300, performing joint optimization by a middle layer coordination distributor; S400, executing and coordinating the bottom instruction.
5. The method according to claim 4, wherein the step S100 of signal acquisition and processing includes at least acquiring steering wheel angle δ sw , vehicle speed V x , yaw rate γ and lateral acceleration a γ .
6. The method for active steering control of rear wheels of a vehicle based on single motor driving and differential braking according to claim 4, wherein in step S200, the upper vehicle motion controller calculates the target yaw moment by: S210, calculating an ideal yaw rate gamma des , wherein the calculation formula is as follows: γ des = (V x / L) / (1 + K × V x ^2)×δ f ; The method comprises the steps of determining a vehicle steering gradient, wherein L is a vehicle wheelbase, K is a vehicle understeer gradient, and can be determined according to parameters such as a vehicle mass center position, tire cornering stiffness and the like, and performing amplitude limiting treatment on gamma des based on road surface adhesion coefficients, namely |gamma des | ≤ μ×g / V x , wherein mu is an estimated road surface adhesion coefficient, and g is gravity acceleration; S220, calculating tracking error, obtaining the yaw rate gamma actual actually measured by the vehicle-mounted sensor, and calculating error e γ and error derivative e γdot between the yaw rate gamma actual and an ideal value gamma des : e γ = γ des - γ actual ; e γdot = d(e γ ) / dt; S230, calculating a target yaw moment by adopting a sliding mode variable structure control algorithm.
7. The method for actively steering control of rear wheels of a vehicle based on single motor driving and differential braking according to claim 6, wherein in step S230, the specific step of calculating the target yaw moment by using a sliding mode variable structure control algorithm is as follows: s231, defining a sliding mode surface S: s=e γdot + λ×e γ , where λ is a positive constant, determining the error convergence rate; S232, designing an approach law, wherein in order to weaken buffeting, an exponential approach law is adopted: s_dot = -ε×sat(s/Φ)-k×s, Epsilon and k are control gains, sat () is a saturation function, and phi is the boundary layer thickness; S233, deducing control output, namely according to a vehicle yaw motion dynamics equation I z × γ dot = M z , wherein I z is rotational inertia of the vehicle around a Z axis, gamma dot is yaw angular acceleration and M z is external yaw moment, combining sliding mode surface differentiation and dynamics equation, and solving a required target additional yaw moment M des : M des = I z ×(γ desdot +λ×e γdot -(-ε×sat(s/Φ)-k×s)); Wherein gamma desdot is the derivative of the ideal yaw acceleration, and the final output M des is limited according to the actuator capacity.
8. The method for active steering control of rear wheels of a vehicle based on single motor driving and differential braking according to claim 4, wherein in step S300, the middle layer coordination distributor performs joint optimization by specifically adopting the following steps: S310, defining an optimization variable, wherein the definition is as follows: X = [T motor , F regen , F friction , side]^T, T motor is a total output torque instruction of the motor, the driving is positive, the regenerative braking is negative, and the unit Nm is shown; f regen is the desired braking force allocated to the regenerative braking system in N, which force is equivalently generated by the motor negative torque at the wheels; F friction is the desired additional braking force allocated to the friction braking system in N; Side is a brake intervention Side selection variable, side= +1 represents intervention of the right rear wheel to generate a left turning moment, side= -1 represents intervention of the left rear wheel to generate a right turning moment, |side|=1; s320, constructing an objective function J to minimize the following cost: J=w1×(T motor -T driver )^2 + w2×F friction ^2 + w3×(P regen -P opt )^2 + w4×(ΔF y )^2, Wherein, w1, w2, w3 and w4 are weight coefficients and are self-adaptively adjusted according to working conditions; T driver is the driving torque requested by a driver through an accelerator pedal, P regen = F regen ×V x is the regenerative braking power, P opt is the optimal feedback power point under the current battery and motor working conditions, the optimal feedback power point is obtained based on battery SOC and temperature table lookup, and delta F y is the left and right rear wheel lateral force change estimated value caused by intervention braking; S330, setting constraint conditions, including: 1) Yaw moment equation constraint; 2) An actuator physical boundary constraint; s340, in each control period, solving the quadratic programming problem with the constraint on line by utilizing a sequence quadratic programming real-time optimization algorithm to obtain an optimal solution.
9. The method of active steering control of rear wheels of a vehicle with single motor drive and differential braking as set forth in claim 8, wherein the actuator physical boundary constraints include a motor torque limit, a regenerative braking force limit, a friction braking force limit, and a tire adhesion ellipse constraint in step S330.
10. The method of claim 4, wherein in step S400, the bottom level command execution and coordination is specifically: 1) Transmitting a torque command to a motor controller; 2) A pressure command is sent to the braking system.

Description

Vehicle rear wheel active steering control system and method based on single motor driving and differential braking Technical Field The invention belongs to the technical field of vehicle dynamics control and drive-by-wire chassis, and particularly relates to a vehicle rear wheel active steering control system and method based on single motor driving and differential braking. Background The active steering technology for rear wheels for improving the maneuverability and stability of the vehicle mainly relies on adding additional mechanical steering mechanisms (such as steering tie rods, executing motors and the like), which is high in cost and complex in arrangement. For the increasingly popular rear-drive electric vehicles, particularly for economic vehicle types adopting a single-motor rear-drive architecture, a driving system of the rear-drive electric vehicle does not have the capability of actively distributing left and right wheel torques. Although the electronic stability program (ESC) in the prior art can generate yaw moment to assist stability through differential braking, the prior art has the obvious defect that the continuous friction braking can cause energy waste, component overheating and unnecessary vehicle speed reduction, and the driving experience and energy efficiency are seriously affected. The traditional technology regards driving and braking as independent systems, and the steering control of the single-motor rear-drive vehicle cannot be systematically optimized from the whole vehicle energy management perspective. Disclosure of Invention The invention aims to provide a vehicle rear wheel active steering control system and method based on single motor driving and differential braking, which can fully utilize the existing single driving motor and electronic stabilizing system on the premise of not increasing hardware cost, namely not changing the driving structure of the original single motor and differential mechanism, and realize a complete solution of an active rear wheel steering effect with high efficiency, smoothness and low energy consumption through an innovative cooperative control strategy. In order to achieve the above purpose, the application is realized by the following technical scheme: the vehicle rear wheel active steering control system based on single motor driving and differential braking comprises a sensing module, a control unit and an executing mechanism, wherein the sensing module and the executing mechanism are electrically connected with the control unit; The sensing module comprises a steering wheel angle sensor and a vehicle state sensor, the control unit comprises a vehicle dynamics controller which is used as an operation carrier of an upper layer decision and middle layer coordination algorithm, the vehicle dynamics controller comprises a vehicle motion controller and a coordination distributor, and the execution mechanism comprises a rear axle driving motor and a controller thereof. Further, the vehicle state sensor at least includes a vehicle speed sensor, a yaw rate sensor, and an acceleration sensor. A vehicle rear wheel active steering control method based on single motor driving and differential braking is characterized in that motor driving and braking are overlapped into a unified rear wheel steering force generating unit to form a layered coordination control strategy, and the method comprises the following steps: S1, upper layer decision, wherein a vehicle upper layer motion controller calculates a target additional yaw moment M des required for optimizing steering response based on a vehicle model according to steering input of a driver, vehicle speed and vehicle body state; S2, middle-layer coordination distribution, taking M des as input, and simultaneously solving an optimal motor total torque instruction T motor and a single-side rear wheel additional braking instruction F brake in a unified optimization framework; S3, executing the bottom layer, wherein the driving motor controller executes a total torque command comprising driving or regenerative braking, and simultaneously, the electronic stabilizing system applies accurate additional braking force to the rear wheel at the designated side. Further, the specific flow adopts the following steps: S100, signal acquisition and processing; S200, calculating a target yaw moment by the vehicle upper layer motion controller; S300, performing joint optimization by a middle layer coordination distributor; S400, executing and coordinating the bottom instruction. Further, in step S100, the signal acquisition and processing specifically includes at least acquiring signals of steering wheel angle δ sw, vehicle speed V x, yaw rate γ and lateral acceleration a γ. Further, in step S200, the specific step of calculating the target yaw moment by the upper vehicle motion controller is as follows: S210, calculating an ideal yaw rate gamma des, wherein the calculation formula is as follows: γdes = (Vx / L) / (