Research Of Control Valve And Drive Strategy For Electrohydraulic Proportional Shift Control System Of High Power AT

Automatic Transmission is widely used in various types of vehicles,because it reduces the labor intensity of the driver by realizing gear shifting via a very simple operation.Due to the adaptive performance of the torque converter,the hydraulic mechanical automatic transmission enables the vehicle to present excellent properties in power and adaptability when working in off-road condition especially.As a key part of the hydraulic mechanical automatic transmission,the electro-hydraulic proportional shift system impacts the shifting quality of the automatic transmission dramatically,according to its static and dynamic properties;while the shifting quality is a critical index to evaluate the performance of the automatic transmission in regard to comfort,reliability and operating life.Nowadays,the development of automatic transmission requires high shifting quality,which leads to higher requirements for precision and high-frequency response of the electro-hydraulic proportional control in the aspects of both elements and technologies.Thus,this thesis,based on the superior research topic about the design and research of high power automatic transmission,carried out deep analysis,designed modification and simulated the high speed electro-hydraulic proportional valve shift system,and finally proved that the performance of proposed system satisfies the functional and operational requirements of the automatic transmission.Firstly,for the electro-hydraulic proportional valve,which is the key component of the electro-hydraulic shift control system,the corresponding working principle is analyzed and studied theoretically.Its static characteristic is tested experimentally,from which the current--pressure characteristics is obtained,as well as the hysteresis curve.Meanwhile,the electrical parameters and electrohydraulic characteristics of the proportional valve are also obtained and studied.The aforementioned work provides strong fundamentals for the research on improving the control accuracy of the shift control system.Secondly,the design task and detailed technical requirements of the electro-hydraulic proportional shifting system are figured out by analyzing the working process of the shifting system.The structure of the secondary main valve is designed according to the requirements;the affecting factors over the accuracy of the main valve are also obtained by mathematical modeling and force analyzing.Optimization of the main valve is proposed to improve its accuracy and stability.Corresponding numerical modeling and simulation are also conducted based on AMESim,and the simulation results verify the conclusions that are proposed through previous mathematical analysis.What follows is the constant-current control of the electro-hydraulic proportional valve using high-frequency PWM,which is in response to the shortcoming that exists in the conventional solenoid valve drive,such as of high ripple current and difficult to adjust.Special drive IC is applied to drive the electro-hydraulic proportional valve using a high frequency carrier dither signal which owns small driving ripple.The usage of variable dither signal promotes the static characteristics of the electro-hydraulic proportional valve,thus improving the control accuracy of the system.Finally,experimental platform is built up and experiments are carried out to test the performance of the designed electro-hydraulic proportional valve and electro-hydraulic proportional shift system.Hysteresis characteristic tests of the electro hydraulic proportional valve are carried out with and without dither signal,respectively.The effectiveness of the proposal to improve accuracy of the electro-hydraulic slide control system is discussed according to the experimental results.The shift quality is verified to be improved greatly by adding the dither signal into the control system of a real vehicle.The work presented in this thesis is of great value and significance in both technical and engineering application for the optimization of electro-hydraulic proportional shifting system and for the improvement of the shift quality of automatic transmissions.