Study On The Control Strategy Of CVT By CAN Bus

Continuously Variable Transmission (CVT) has continuous transmission ratio, It makes CVT has better cooperation ability with engine which greatly improves the efficiency and power of vehicles, so CVT has been widely used. Nowdays, as the most ideal bus, CAN BUS could connect control units, realize multifarious data transmission, greatly reduce the cost and weight of the vehicles, so it has been widely used in the vehicle industry. It has great correction ability and anti-jamming ability. it is more easier to realizing remote signal transmission, and support for the receiving and checking, which make CAN BUS be one of the most promising BUSes.As a transmission system, comprised of a CVT and an engine, the information transmission between engine control unit ECU and transmission control unit TCU is inevitable. Because the advantages of CAN BUS, For CAN BUS has a lot of advantages, it's an inevitable trend to use CAN bus in a combined control system of engine and CVT.The CVT ratio control system has hundreds-millisecond lag. An integrated engine-CVT control algorithm was proposed to compensate for the response lags of the speed ratio, so as to optimize the dynamics of the transmission system. According to the concept that the power equals to the product of the torque and the rotate speed, the torque can be calculated before the engine's rotate engine speed changes to meet the target power. Using the datum of the experiments, a function which expresses the relationship between the engine's output torque, the throttle percentage and the engine speed is established. Then the curves can be made, using the engine's torque and the engine rotate speed as inputs and the throttle percentage as output. Thus the throttle percentages can be calculated, according to the engine's torque and the engine speed, in order to realize the combination control on the engine.The speed ratio control part of the CVT adopts a fuzzy-PID controller. There are three parameters of the PID controller adjusted by the Fuzzy logic controller to get a better track of the speed ratio. Select three parameters to transform the information of the CVT-Engine's combination control, draft the corresponding CAN agreement, and compile the mex files, in order that the CAN-USB II's information can be read successfully by Matlab-Simulink.Based on the above work, the semi-entity simulation model was established ,using Matlab–Simulink. According to the vehicle simulation model, the simulation results were analyzed at different driving conditions, such as Hill-start, ramp acceleration, and driving cycles. As the engine model was running, the torque of the engine was worked out on unsteady conditions, and the target ratio of the best fuel economy and power performance can be worked out. According to the mathematical formula, a mathematical simulation model for CVT was built , making the model simulation process carried out more accurately. Using the parameters from the models of the engine and the CVT, the ratio of its target was calculated out to realize the optimal ratio follow using Fuzzy-PID control. The throttle control module was built up, in order that the throttle percentages could be calculated out according to the engine speed and torque. The vehicle model was simulated at three driving conditions, and by analyzing the simulation results, the real-time and the excellence were proved.