Study On The Electro-Hydraulic Control System For CVT Based On Digital Control Technology

The Metal V-belt CVT is a type of ideal transmission for passenger cars for itsspecialty, which is developing rapidly for its specialty. There will be also a greatdeveloping potentiality and extensive market in China. Affecting the quality oftransmission and the car performances such as fuel economy, dynamic performanceand emission directly, its electro-hydraulic control system is the key in CVT. Theelectro-hydraulic control system is a complicated system because it integratestransmission mechanism of CVT, electronic control technology and hydraulictransmission technology. Now the research in this field in china is in the startingperiod. There are many obstacles in both transmission theory and actual controlsystem design. Grasping these theories and critical technologies is helpful toimprove our independent auto-developing ability and to compete with foreign autoenterprises. So this paper makes some study on the electro-hydraulic controlsystem for CVT based on digital control technology and its main components. Themain work has been completed as follows: 1, According on many domestic and overseas references, the typical structureand work mechanism of CVT are elaborated. The transmission mechanism ofMetal V-belt correlating closely with clamping control and ratio control isemphases. Ratio control principles are analyzed aimed at more accurate in ratiocontrol. This work starts from matching between engine and CVT. The maincontrol strategies of electro-hydraulic control system of CVT are confirmed basedon above research. 85吉 林 大 学 硕 士 学 位 论 文 2, Finished the study on the original mechan-hydraulic control system in P811CVT, a electro-hydraulic control system based on digital control is designed.Instead of the conventional solenoid valve, the new control system use aproportional valve with digital control as clamping force control valve and use highspeed on-off valves as ratio control valve and clutch control valve. Digital controlis achieved in control system of CVT. 3, A proportional valve with digital control based on stepper motor is designedindependently. The parameters of the valve are validated by simulation analysisbased on mathematical models and specialty experimentation. The results showthat the digital valve has great improvement in response to steady state anddynamic state compared with conventional proportion solenoid valve. It can satisfythe actual requirements for its good precision in opening control. 4, A model of high speed on-off valve is built on the base of mathematicalanalysis of the valve. And pulse-width modulation control technology based onduty cycle is researched. Relations between exported pressure and duty circle underdifferent frequency are concluded. Furthermore, a special current controltechnology of HSV is created for saving energy. And based on the technology acontrol electro-circuit is designed. During the test of the integratedelectro-hydraulic control unit on a test rig, the HSV shows good response todynamic state and convenient control specialty, which match the requirement ofutility. The main contribution of the research is that a proportional valve with digitalcontrol for CVT is designed to utilize digital control technology in theelectro-hydraulic control system of CVT. The test data show that the utility ofdigital opponents brings great improvement in control precision and reliability forthe control system. It's also helpful to reduce design cost of the system. So theelectro-hydraulic system using digital control technology can satisfy the demandsof cars with CVT.