Modeling And Reduction Of Hydraulic Control System For Automatic Transmission

The accurate control and multi shift position are the development trend of automotive automatic transmission which proposes challenges to transmission actuator system design and controller development. As the clutch actuator, the hydraulic control system is essential component which realizes the shift process. Thus, design and control of hydraulic system is one of the key points in automatic transmission technology. The model based design and optimization, which requires an accurate and fast model, has been the main R&D method in automotive electronics field. In this paper, the hydraulic control system of a 4-speed AT is analyzed and modeled. The model is validated by experiments results.Firstly, the bond graph modeling theory is introduced. This theory is suitable to deal with multi-domain energetic system due to its concept of energy. The content of this paper about modeling is presented in the sequence: system division, bond graph analysis and mathematical description.Secondly, the hydraulic control system for AT is studied. For convenience, the whole system is divided into two subsystems: clutch pressure control subsystem and system pressure regulation subsystem. The former subsystem control the pressure imposed on clutch and accumulator. The solenoid valve is commanded by controller and actuates the pressure control valve. The solenoid valve model is validated by test bench experiment while this subsystem is validated by real vehicle experiment. The function of the other subsystem is regulating the output pressure of the pump. This subsystem model is validated by the reference design parameters in the spec. The model validation indicates that the model built in this paper is accurate. The calculation of the model is time consuming as that its complexity as well as 1μs simulation step size. The step size cannot be increased due to the simulation error of the pressure-flowrate function in the model. The energy based model reduction algorithm is applied to solve this problem. The original algorithm is modified to reduce the solenoid valve which features multi-domain dynamics coupling. By modifying the evaluation index, the high energy flow elements in hydraulic domain are sorted to unimportant and deleted. The reduced model can be run in step size of 10-4s. The error caused by model reduction is acceptable and the calculation time is saved significantly.