Research On Steering Stability Control Algorithm For Light Vehicle And Hardware In-the-loop Test Platform

Vehicle electronic stability program (ESP) is an active safety technology of vehicle. It can improve the controllability and stability of vehicle by restraining the overturning and underturning of vehicle。This paper gives the research of ESP based on projects"Research and Development of Vehicle Stability Control System on low-adhesion road"and"Research of control strategy for Vehicle Stability Control System on low-adhesion road".Firstly, three methods of brake pressure estimation are proposed based on the test of hydraulic control unit. Secondly, the the research of vehicle longititude speed estimation, slip angle rate estimation, road adhesion coefficient estimation were carried out based on the primary structure of ESP control algorithm , and the ESP control algorithm was proposed. The target yaw moment control algorithm was proposed based on integrate control of distribution coefficient yaw rate control by PI and slip angle rate control by PI. The target yaw torque distribution algorithm and the brake torque control algorithm on the base of brake pressure estimation were proposed. The ESP out-line simulation platform was built on Matlab/Simulink environment, and some out-line simulations on different situations were proceeded. Finally, the structure of ESP hardware-in-the-loop test platform was proposed, and ESP hardware-in-the-loop test platform was built based on Matlab/xPC Target platform. Some different situation hardware-in-the-loop tests were carried out on the ESP hardware-in-the-loop test platform.1. Vehicle Dynamics ModelAccording to the needs of ESP strategy research, the 15DOF of nonlinear vehicle dynamics model was established. The vehicle model, including driver model, engine model, powertrain model, tire model, wheel dynamics model, suspension model, brake system model, vehicle body model and other assistant modules, was provided. The Preview Optimal Artificial Neural Network (POANN) Driver Model and UA tire model are used in the paper. Using these models, conditions such as acceleration with straight line and steering, the double change steering could be simulated. The program foundations for ESP off-line simulation platform and hardware-in-loop platform were made.2. Test of ESP Hydraulic Control Unit and Brake Pressure EstimationThe hydraulic control unit (HCU) is the primary actuator, including 12 electromagnetic valves and two pumps. The hydraulic characteristic of HCU was analyzed by the test of brake pressure response for pump,increasing pressure valve and decreasing pressure. Three methods of brake pressure estimation were proposed on the basis of test of HCU. The open-loop and close-loop tests for pressure estimation methods were carried out. The results showed that: the brake pressure estimation could estimate the pressure of Wheel Cylinder.3. Study of ESP Control AlgorithmWith request of the project, the study ESP control algorithm has been accomplished:①Hierarchical structure of ESP control algorithm and modular functions of the algorithm program are proposed;②When the car is steering,method of estimation of vehicle velocity is mentioned;③slip angle estimation algorithm and road adhesion coefficient estimation algorithm are proposed;④based on the yaw rate PI control and side angle PI control,the yaw torque control algorithm has been confirmed, and by introducing partition coefficientα, switching between the two controller is implemented;⑤distribution strategy of target yaw torque is proposed;⑥Based on the dual-PI controller,brake pressure control algorithm is proposed4.ESP Off-line Simulation Platform and Simulationvehicle dynamics simulation model and ESP control algorithm model were bulit with Matlab/Simulink based on vehicle dynamics model and ESP control algorithm prototype; the GUI interface of the ESP off-line simulation platform was built by used of the Matlab/GUIDE toolbox; 3-D virtual scene was designed by used of Matlab virtual tool. The offline simulations of ISO3888-2 double line turning, double line turning on low adhesion road, step turning on alterable adhesion road, sine wave turning and square wave steering, etc. were carried out on the platform.The simulation results showed:①the offline simulation platform was qualified to the development of ESP algorithm;②the vehicle yaw rate variety was controlled effectively by ESP control algorithm, and the slip angle of center of mass was restricted, so the lateral stability of vehicle was improved effectively.The building of offline simulation platform and the offline simulations established theory foundation for the design and development of HIL test platform and HIL test.5. The research of ESP HIL test platform development and HIL testAccording to the scheme of ESP HIL test platform, the ESP HIL test platform was built based on Matlab/xPC platform. The platform consisted of test bench, sensors, acuators, real-time platform, signal collecting system and software system. And the controller of electronic throttle, the drive circuit of solenoid valve and pump, the wheel velocity pulse generating model were designed. Some ESP HIL tests on all kinds of conditions were proceeded on the platform based on control algorithm prototype. The test simulations showed:①The ESP control algorithm could restrain the overturning or underturning of vehicle effectively through brake torque regulation, thus the lateral stability of automotive was improved. The ESP control algorithm was provided with better robust and better adaptation.②The ESP HIL test proved that the HIL platform was qualified to the test.Through the research of the control algorithm of vehicle steering stability and ESP HIL test platform, we could achieve the following conclusion:1. Using the modern development method of "V" cycle could accelerate the development of ESP system, the smooth transition of "system modeling—offline simulation—rapid prototype—HIL test" could be achieved on the Matlab environment. There was some important significance to the development of ESP control system based on the platforms of offline simulation and HIL test with Matlab.2. The brake pressure subtle regulation was the key technology of ESP control system; brake pressure estimation was achieved by building the lookup table of the brake pressure and the PWM Duty cycle. Trough the controlling of increaching valve by PWM control, the brake pressure subtle regulation could be achieved.3. The coupling of yaw rate and slip angle could be resolved by the yaw torque control algorithm based on the distribution coefficient "α". ESP controlled the vehicle by yaw rate PD controller when the slip angle was small and by slip angle PI controller when the slip angle was large.