Research On Coordinated Control Of ESP And EPS In Typical Working Conditions

With the increasing development of automobile electronic technology, more and more control systems are assembled on the vehicle chassis. Study of integrated control among each system has become a hot topic in the field of chassis control technology. The Electronic Stability Program (ESP, Electronic Stability Program) and Electric Power Steering System (EPS, Electronic Power Steering) are closely related to operation stability of vehicles. Thus, research on integrated control of both systems has better practicability and popularization. For three kinds of typical working conditions of ESP including emergency obstacle avoidance, braking on split cohesion coefficient road and steering in low tire-road friction, the coupling relationships between these conditions and EPS were analyzed. The method of hierarchical coordinated control structure was used for research on coordinated control of ESP and EPS under these working conditions.In this paper, there are three layers in the designed coordinated control structure of ESP and EPS. The upper is coordinated control layer, which is used for working condition identification parameter estimation and judgement on motion state of vehicles. Then the reasonable control strategy can be selected and the coordinated control command can be output based on working condition and motion state of vehicles. The middle is control sublayer of ESP and EPS system. In this layer local optimal algorithm is performed according to the coordinated control command and instruction of controllers will be output. The lower is subsystem actuator, to the corresponding control of vehicle according to the controller instructions.According to the research necessity, the complete vehicle model with seven degrees of freedom, the reference vehicle model with two degrees of freedom, ESP hydraulic execution control system model and EPS system model were established, which are used to estimate the vehicle state and convenient to build simulation model. Furthermore, vehicle state variable including centroid side-slip angle and longitudinal speed are estimated which are necessary to the coordination control layer.On the basis of the built models and estimated parameters, in conditions of emergency obstacle avoidance, braking in split cohesion coefficient road and steering in low tire-road friction, the driving state of vehicle and work characteristics of ESP and EPS were analyzed. Besides, under the corresponding conditions, coordinated control strategies of ESP and EPS and operating mode recognition were designed.Finally, simulation models were built up in Simulink, coordinated control strategies in two conditions of braking in split cohesion coefficient road condition steering in low tire-road friction condition were co-simulated with Carsim. Based on the designed and developed ESP controller, the test bed of ESP was established. Combining with the existing EPS test bed in the laboratory, hardware-in-loop experiment of coordinated control strategy emergency obstacle avoidance condition is conducted. Simulation and experimental results show that, in view of the designed coordinated control strategies in different working conditions, the operation stability of vehicle has improved to some extent.