The Research Of The Electro-hydraulic Controlling System Of CVT

From the appearance of the automobile,People have made great efforts to improve the performance of automotive transmission.The continuously variable transmission (CVT) can change speed ratio automatically and continuously,satisfy the driver's every driving purpose,propitious to achieve the optimal matching and control of power train,and it is regarded as the ideal automobile transmission with the advantages of easy operation,comfortable and smooth driving,excellent performance.Metal V-belt type CVT has such merits as bigger power transferring capacity,transmission efficiency and longer life,so it has been the most widely used.Early CVT was always controlled by the mechanical-hydraulic servo technology,its response is quick and its precision high,but its controlling module complicated and power loss big.Besides,it is sensible of oil pollution,and needs developing for a certain type as it can't be applied to other CVT,the development of such controlling module is so expensive that it hasn't been widely used.It is inevitable for CVT to adopt digital controlling technology with the development of the computer.Digital controlling technology combines both the superiority of big hydraulic power-weight ratio and flexible electronic-computer controlling,so it develops quickly in all industry fields.Digital controlling technology can meet the requirement of dynamic and static performance of CVT ,and has such merits as low cost,strong anti-pollution ability,handling performance,easy automobile,simple structure and low energy consumption.On the whole,it is beneficial to research and develop the digital electro-hydraulic controlling module to improve the performance of CVT and reduce its cost for economical and social benefit.Based on the demands above and aiming at electro-hydraulic controlling system of metal belt CVT,this paper is to research the controlling theory and digital proportional controlling technology on CVT.This paper has five chaprers,and the main contents are following:(1) Based on lots of professional documents, the dissertation reviews the development process and the technique of CVT briefly. Through the comparison with other transmission, showing that the metal pushing V-Belt type CVT can meet the currently demand of drivability, economics and emission etc, and stating that the CVT is the ideal transmission which will be the developing tendency for the transmission of passenger car. In the paper the background and the necessityof this theme in science and practice are given.(2) The structure and principle of operation of CVT were introduced.The key sections of the transmission are introduced.The main research issue is the control method that include three point:the clamp force control,the ratio control and the clutch control.Only when the three aspects are all in optimum state the vehicle function quota can elaborate completely.(3) The advanced digital proportional electro-hydraulic controlling technology was applied on CVT to improve the controlling system of CVT.The structure and principle of high-speed on-off valve were introduced.(4) The digital valve were designed,and the math model of the digital valve built and analyzed through computer simulation with Matlab.The analysis shows that the digital valve has fine performance on dynamic and static state,and as the result,it can meet the requirement of electro-hydraulic controlling system of CVT.(5) Design of experiment was applied on the application parameters of the digital valve owing to the fluctuation of hydraulic pressure. In the end, we did bench test under the test condition we have to demonstrate the control-theory right or not. The test included constant speed ratio follow and step speed ratio follow , from the test resule we can see this control system effect all right and possess definite feasibility,but owing to limitation of test condition, we can't proceed the next bench test and auto-test.The result shows that the digital valve can meet the requirement of ratio controlling of CVT.The mostly innovation of the paper is to develop a step motor controlled digital valve suitable for electro-hydraulic controlling system of CVT and apply digital proportional controlling technology to CVT.The test result shows that the digital valve has high controlling accuracy and reliability,and that digital proportional controlling technology can reduce the cost of electro-hydraulic controlling system.At the same time,it can improve the quality and the competitiveness of CVT,so the digital proportional controlling technology has a bright future.