Research On Aability And Thermal Stability Of Vehicle Load Simulation Based On The Hydraulic Retarder

Vehicle road test is an important part of vehicle product development and quality assurance.Because of the lack of the effective testing methods,the car manufacturer often rely on lots of vehicle real roads test.In the process of finding the appropriate roads,a lot of manpower,physical and financial resources are consumed.It not only has a large test risk,but also it has long test cycle and poor repeatability.At present,the most effective method is the load-testing-vehicle technology,the car manufacturer use this technology in test ground instead of the vehicle real road test.The structure of the load-testing-vehicle is complex and the cost of design is expensive.The vehicle performance in the real environment cannot be completely obtained through the test ground.Therefore,a vehicle driving load simulation technology based on hydraulic retarder is proposed in this thesis.It has simple structure and the simulation load is controllable.The technology can use in the real environment to test vehicle performance.This thesis focuses on the simulation load values that can be provided by hydraulic retarders.In order to determine the feasibility of the hydraulic retarder as a driving load simulation device,this thesis analyzed the load simulation demand of the hydraulic retarder,then the best installation position of the hydraulic retarder in the vehicle is determined.The range of simulation load of the hydraulic retarder can provide are obtained based on the basis of the vehicle driving force-driving resistance balance.In order to get the torque characteristics of hydraulic retarder and its influencing factors,the hydraulic retarder test bench is built in this thesis.Then the relationship among the output torque of the hydraulic retarder and the input speed,the temperature of the transmission oil,the rate of liquid filling are revealed.And it is pointed out that the technology can provide the maximum 3500 Nm simulation load for vehicle road test.By adjusting the flow rate,it can provide at least 3000 Nm load between idle speed and maximum speed of the engine.In order to keep the temperature balance,this thesis designs a thermal cycle for the hydraulic retarder.After the structure analysis of mathematical modeling of the heat exchanger,the matching calculation with the radiator fan is carried out.The thermal model of the hydraulic retarder,the heat dissipation model and the heat balance equation are established,and the energy change during the load simulation of the hydraulic retarder is explored in this thesis.It is pointed out that during the process of load simulation,the heat of 75%~80% is dissipated by the thermal cycle system,and the heat of the remaining 20%~25% is transformed into the kinetic energy of transmission oil and the discharge of the hydraulic retarder shell.Based on the test bench,the dynamic of the load simulation of the hydraulic retarder is analyzed in this thesis.The response characteristics of the hydraulic retarder and its thermal cycle and the response characteristic of hydraulic retarder filling rate and the hysteresis characteristic of cooling system were tested.A control method to ensure the thermal stability of the simulated load is proposed.It is pointed out that the hydraulic retarder should adjust the cooling flow time before the lifting time is about 5 seconds.The driving load simulation technology designed in this thesis has the guiding theory and practical application value for the development of the hydraulic retarder and the vehicle real road test.