Design And Research On A Novel Continuously Variable Transmission

Transmission system is an important part of the vehicle, while continuously variable transmission (CVT) can make full use of engine performance and improve fuel economy and emission, In the premise of using the stepless speed characteristic of CVT, power split continuously variable transmission system (PSCVT) in this thesis improved the transmission efficiency of the whole transmission system by making the output power of engine split and converged with the planetary gear train and fixed axis gear train.Based on the mechanism of PSCVT system, the theoretical analyses of kinematics of continuously variable unit and planetary gear are made. According to the different combinations of continuously variable unit, planetary gear and fixed axis gear, PSCVT system is divided into two different forms of power flow, then its power flow and transmission efficiency are analyzed; A optimization scheme of PSCVT is proposed in this thesis, the relationship between the speed ratio of continuously variable unit and the speed ratio of PSCVT system is obtained and the transmission system performance is analyzed. Analysis shows that this scheme can make the transmission system capacity at high levels in the whole range of speed ratio.As the core components of PSCVT, continuously variable unit has important influence on the performance of whole transmission system. Based on the phenomenon of axial offset of the metal belt in the process of transmission, analyzed the causes and calculated the relationship between the offset and the ratio of continuously variable unit through theory. Based on the analysis of existing method of eliminating and reducing the axial offset, it is proposed to replace the original structure by the combination of asymmetric metal belt and straight-line generator cone. This form can ensure that there is not phenomenon of axial offset of the metal belt in the whole process of transmission, and can improve the transmission capacity of the continuously variable unit.The control of continuously variable unit is the most important element of the control of PSCVT. Based on the study of the existing control method, a pure electric control system using a stepping motor as the source of the control is proposed. Analyzed its structure and control principle, and obtained the relationship between the axial movement and the ratio of continuously variable unit, then the relationship between the axial movement and the ratio of PSCVT. Based on the conclusions above, PID control method for speed ratio of PSCVT system is used, and it is simulated with the Matlab/Simulink.