Traction Drive Continuously Variable Transmission Mechanics Research

As the transmission ratio of continuously variable transmission (CVT) for the vehicle can be adjusted, the engine can reasonably match with the variation of exterior load. It is useful to improve the dynamics and economic and reduce the exhausting emission of the vehicle. There mainly exist two types of CVT in the vehicle: metal V-belt and traction drive. The traction drive CVT is characterized with high capacity of power transmission and low noise. Thus, it can be applied in middle/large displacement vehicle. Except that Nissan Motor assembled this drive on the vehicle in 1999, others vehicle-manufacturing companies don't succeed in developing this powertrain. At the same time, it is lack of deep research on this drive. This thesis is oriented at modeling the shift, elastic contact analysis and the capacity of power transmission.The ratio adjusting process of Toroidal traction drive CVT is realized by offsetting the power rollers by hydraulic cylinder and utilizing the sideslip force to tilt the axis of rollers and thus changing the contact radius between input/output disc and rollers. Using the geometric theory and dynamics, this adjusting process is modeled, and the relationship between the distance of hydraulic cylinder and the ratio of the variator is determined.The contact stress and deformation between rollers and input/output disc have an important effect on the fatigue life of contact components and the formation of minimum film. The elastic contact algorithm is applied to calculate the contact stress and deformation in order to minimize the error of Hertizan formulas. The film between the rotating contact bodies not only separates them to avoid direct contact, but also is considered as the media of power transmission. So, The film thickness must be greater than the given values so that the traction oil can transmit the power. Based on the Dawson formula, the factors of film thickness include the normal force, enter velocity, the properties of traction oil, the increase of the temperature, relative curvature and so on.The capacity of power transmission is an important parameter for designing the traction drive CVT. In order to obtain reliable capacity of power transmission three constraint conditions are considered: the fatigue life of contact components, the minimum film thickness, and the increase of temperature in contact zones. The multiple-parameter optimization is used to get the capacity of power transmission.