| Vehicle ESP hydraulic system is composed of several components, which operating performance and control quality not only related with sensor and the control logic of control unit, but also closely related with its hydraulic system's dynamic characteristic. Hydraulic elements working collaboratively under the control of ECU, To realize initiative intervention to the running status of vehicles, exert the hydraulic pressure braking force to the corresponding wheel according to vehicles' different transport condition. The hydraulic system is an electron stable procedure of vehicles, and it is an implementing agency that could completes the dynamic response with high-speed in a short time. In order to guarantee the ESP operational reliability and the control precision, it is essential to study hydraulic system dynamic characteristic.This paper takes the ESP as the study object, and has analyzed its structure and the principle of work. Vehicle ESP system mainly includes three parts which are the sensor, the electrically controlled unit and the implementing agency. Electronic control unit analyzed the vehicles running status signal which transported by sensors, if detected that vehicle in unstable operation or in unstable running trend, the electronic control unit will send corresponding instruction to the implementing agency, and then the implementing agency will action according the instruction, So that the vehicle can running stably within the physical limits.Used the AMESim software to establish the ESP model which include brake booster, brake master cylinder, pre-press unit, hydraulic control, brake wheel cylinders etc, and simulation results show the operation of each model is correct; Meanwhile, establish the mathematical model to main modules of ESP hydraulic system (which including the return to liquid piston pump, low pressure accumulator spring, throttle control, two two-way solenoid valve) according to the theory of fluid dynamics, which provides theoretical support to the hydraulic unit stability program design and dynamic analysis.Used the AMESim software to simulate vehicle braking passive electronic stability program, all semi-active braking and active brake booster under the three operating states, the process of packing and pressure of work, and this further validate the correct of the hydraulic automotive electronic stability program system model is.According to the dynamic design theory, development dynamic characteristics evaluation of vehicle ESP which called hydraulic systems. The dynamic characteristics of the hydraulic system include two aspects:a:the flow pulsation of Vehicle ESP hydraulic system, the instantaneous peak pressure and pressure fluctuations, which means System's stability; b:response speed of the brake wheel cylinder pressure. And carry on the batch run simulation analysis to the Key factors (including pressure medium, precompression unit, returns to the fluid ram pump, to enter the fluid valve, platoon fluid valve, brake wheel cylinder and low pressure accumulator) which affect ESP hydraulic system dynamic characteristic, then get response curse of the pressure to responsed brake wheel cylinder and the flow of brake wheel cylinder. We get conclusion through analyzing various simulation results, which the precompression unit, returns to the fluid ram pump, to enter the fluid valve, the platoon fluid valve, the brake wheel cylinder and the low pressure accumulator has the important influence to the hydraulic system dynamic characteristic, and then it is request match reasonablely to the above components' key parameter of characteristics when design the Vehicle ESP.
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