| After the development of more than one hundred years, automobile has become an indispensable part of our daily life. As the automobile technology continues to mature, people put forward more and more requirements on the performance of the automobile. As a part of the automatic transmission family, the continuous and adjustable ratio of CVT (Continuously Variable Transmission) improves the comfort of vehicle, avoiding the impact during shifting process. What is more, through adjusting the ratio Continuously, CVT could make the engine work in its best area. According to his own needs, the driver could make the vehicle run in the best performance on the dynamic or the economy, in what the CVT shows its tremendous potential development.Though the vehicle armed with CVT makes a good performance of fuel economy, people expect much more. The reason is low efficiency in transmission though makes the engine work in its best area. Except for energy loss caused by mechanical transmission, the ratio change mechanism needs a very high pressure to transfer the torque. However, the clutch control system and the cooling and lubrication system need more flow rate from the oil pump. As a result, most of the oil is released though pressure relief valve in practice. As much of the energy is wasted, the temperature of hydraulic control module rises, with the reliability reduced. Because of the unreasonable control made by hydraulic control system on the clamping force, in addition, the friction between the V-belt and pulley leads quite much power loss. So, getting a high match degree and raising the transmission efficiency is of very importance of realism and innovation to reduce the fuel consumption and its applications through improving hydraulic control system.For the hydraulic control system of CVT, The studying contents in the paper is expatiated in several ways as below.1) By reading a large number of references, the major reasons for the power loss are pointed out based on the analysis of working principles of CVT hydraulic control system, with the possible route of reducing the loss is put forward.2) According to different levels of pressure, the hydraulic control system is divided into two parts. They are main circuit used to control the ratio change mechanism and auxiliary circuit used for the clutch control system and the cooling and lubrication system. Concept of Double-Circuit hydraulic system is proposed in order to reduce the loss of the hydraulic control system. The corresponding flow rates are supplied by different pump after separation of the two parts.3) Through the analysis of requirements for the hydraulic control system under the limit condition of the performance, the parameters of the main components of Double-Circuit hydraulic system are calculated, providing a fundamental basis for the simulation.4) Good advantage of the two software-Simulink and AMESim is taken. PID controller of the clamping force and ratio is designed by Simulink while the power transmission model of the vehicle and hydraulic control system is established. After the joint simulation in several limit conditions, the accuracy of the model and the parameters is validated, laying a foundation of efficiency analysis of hydraulic system.5) Compared with the original system, the changes of flow rate, pressure and power are analyzed, summarizing the reason of power loss. The result shows that the system gets a better matching level with a lower power loss. |
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