Study On The Clamping Force Control Of Metal V-Belt Type CVT

As the non-renewable resources is reducing day by day and the people's awareness of environmental protection is increasing gradually, the energy conservation and emission reduction are becoming an important subject in study of the car industry. The maximum improvement of energy utilization ratio is essential for the car consuming traditional energy. The cars with Metal V-Belt Type CVT, an ideal speed change device, do better than those with MT or AT in the performance of power, economic and exhaust of emission. Using the electro-hydraulic control system, CVT regulate speed ratio based on the requirement at any run-time, making the engine run in best operating area and improving oil consumption and reduce hazardous substances emissions.But, the ability to save fuel of the present vehicles which are equipped with CVT has not been very well. The main reason is that the drive efficiency for CVT is low. The clamping force control is the determining factor on the drive efficiency of CVT. While the clamping force being too big, the load of the metal belt will be big, and the interaction force of internal components is becoming bigger. It would not only raise unnecessary friction losses, but also reduce the life of the metal belt. The clamping force is provided by hydraulic control system. For single loop control mode,'excessive clamping force needs large system pressure which is provided by hydraulic control system. It would directly lead to the increasing in energy consumption of the engine, and reduce the fuel economy. While the clamping force being too small, slip will appear between belt and pulleys. When the slip level comes to certain degree, the engine output torque would not be transmitted reliably, and the interface of the metal belt and the pulleys would have serious wear. Therefore, only the target clamping force is made reasonably base on driving demand, and the control system make the clamping force being the best condition, the drive efficiency for CVT would be improved. The previous conventional control tactics of clamping force is to estimate destination clamping force according to engine torque and destination speed ratio, and there is a multiply safety factor to the destination clamping force to prevent slip between belt and the pulley caused by load torque peak. In the conventional control tactics, the principle of clamping force determining is the prevention of slip. But recent study shows that, the slip between belt and pulley cased by reducing clamping force did not reduce the ability to transmit torque of CVT,it improve the transmit efficiency and reduce the pump power consumption of the engine, because the clamping force reduction leads to the reduction of system pressure.Basing on the Predecessor's achievement, my researches which are focused on the control of the clamping force are as follows.1. Basing on the reading of a number of literatures from both domestic and abroad, the development of CVT is introduced, a comparison of common AT was carried on, and at the same time, the advantages of the CVT and its key technologies are analyzed.2. The structures and the principles of the CVT were analyzed, and the losses of transmission and hydraulic system were analyzed, and a mathematical model of the torque losses both integral and partial was built.3. In order to transmit torque reliably, the methods to ensure the clamping force of the CVT were analyzed. Then according to the previous model of the torque losses, the losses of the torque at different input rotate speed or output torque under the same clamping force level are simulated with the Matlab software, which helped to analyze the influences of friction and security coefficient on the torque losses. Basing on the researches on the slip between the belt and the pulley, the common control methods of clamping force and the method by slip controlling are compared.4. The mathematic model of unstable output torque of the engine is built using Matlab, and the model of the control valve of clamping force is built using AMESim, based on both of which, an expert PID controller was designed to control the clamping force. Basing on the controlling of the clamping force, a union simulation model of vehicle is built using AMESim_Simulink, and then some specific working conditions are simulated. It turns out that, with the help of the PID expert controller, the oil pressure of hydro-cylinder of the driven wheel always follows the target pressure, and the results are satisfactory.5. The standardizations of the clamping force control valve and the ratio control valve are carried on in the CVT test rig, and the fitting results are obtained. Then the measurement method of slip is ensured and the experiments on the slip control with PID controller is carried on, basing on that, the expert PID controller to control the slip under the condition of a quick change of the loaded torque is also carried on. It turns out that the new-designed expert PID controller was available on the control of slip.