CVT Efficiency Optimization Based On Slip Tendency Observation

In recent years,with the national energy-saving and emission reduction regulations increasingly stringent and the demand for small-displacement vehicles increasing,CVT with the structural characteristics of the continuous adjustable speed ratio,real-time maintaining the engine near optimal economy or the optimal power curve and silky gear change and other significant advantages,meets the needs of consumers and extensively favored by many countries in the world.Theoretically speaking,the vehicles with CVT should have a significant advantage in the aspects of fuel economy,power and emissions,but the market feedback shows that the energy-saving advantages of CVT did not play out.The main reasons are the following two aspects: CVT did not match the engine to reach the optimal CVT and its transmission efficiency is not very high.The friction loss and the power loss of the hydraulic system are the key factors which affect the efficiency of the CVT transmission mechanism,and the reasonable choice of clamping force can not only realize the reliable transmission of torque,but also improve the efficiency of CVT transmission.In order to ensure the reliability of the CVT transmission torque in the extreme working conditions,the clamping force of the driven cone wheel is multiplied by a certain safety factor in the present clamping force control strategy by the major automobile manufacturers.The safety factor method not only increases the additional friction loss,but also requires that the hydraulic system must provide greater pressure and thus cause a large overflow loss.In this paper,an optimal control strategy of clamping force based on the feed forward controller and the feedback controller judged by slip tendency is proposed to improve the transmission efficiency of CVT.The research contents are focused on the following four aspects in view of the proposed optimal control strategy of clamping force:1.The author reads a lot of references in English and Chinese,understands the CVT structure,transmission principle and hydraulic control principle,does a comparative analysis of single and double pressure hydraulic pressure control loop system.It is confirmed that the CVT main energy consumptions are friction loss which mainly comes from variable speed gear and spill loss comes from hydraulic actuator system.2.The driving mode is established by quantifying the vehicle driving relevant parameters and it can distinguish the extremely working conditions such as rapid acceleration,rapid deceleration,up and down steep slope.It will exit slip trend monitoring model directly and uses the larger safety parameters under some extremely working conditions.Under different conditions the author makes a difference of the change rate of the target speed and the actual ratio,according to software simulation and experience to determine the threshold of the slip.The difference and threshold were compared according to the results determine whether there is a sliding trend,and with this trend to adjust the clamping force on the driven wheel.3.The comprehensive control strategy of clamping force optimization contains working condition recognition and slip trend judgment.Firstly,determine whether the current working condition can optimize the clamping force or not,if it can,the clamping force is calculated based on the target oil pressure and take it as a small safety factor.Take this clamping force as the active control signal,at the same time,give the feedback control signal according to the output results of sliding tendency observer.4.The optimal comprehensive control strategy of clamping force is proposed based on the working condition recognition feed forward controller and the sliding trend judgment feedback controller,and the Simulink-AMESim simulation model of vehicle with CVT is established.To verify the reliability of clamping force optimization control strategy in specific conditions,the author does comparative analysis of the new-type clamping force optimization control strategy and traditional clamping force control method in a typical simulation model.The simulation results show that the new-type clamping force optimization control strategy in torque transmission stability and efficiency of CVT both improve by comparing the two factors of the slip ratio and clamping force,and the new-type clamping force optimization control strategy of reliability and oil-saving characteristics are proved.