Analysis And Parameter Optimization Of Traction Drive CVT

Automobile drive system is a subsystem of chassis. As the most important part of drive system, transmission has an important influence on the power, economy and comfort of vehicle. Continuously variable transmission(CVT) can realize continuous change of transmission ratio, and has better power and economy, so it becomes ideal drive system. The commonly-used CVTs are belt type among a variety of CVTs, but theirs bearing capacity is limited. With the development of materials, transmission oil, control and manufacturing technology, traction drive CVT has been developed, which has higher bearing capacity, higher efficiency and better stability. This transmission can be used in the larger displacement vehicle power drive system.Loading mechanism, transmission mechanism and regulating mechanism, as the main components of traction drive CVT, and theirs working principle were firstly described, the calculation formula of transmission ratio was analyzed. At the same time, the geometrical parametric equations of conical disk and power roller were established by using coordinate system.Then, the stress of traction drive CVT and the contact pressure between power roller and conical disks were analyzed in detail. Using the Hertz contact theory as a guide, the calculation formula of contact stress was given, and the curves under different parameters that the contact stresses changed with the rolling angle of roller were obtained. In view of the limitation of Hertz contact theory, the conical disks and power roller are revolving body, so the 3D solid model of transmission mechanism can be obtained by rotation and other modeling characteristics of UG. Then the solid model was imported into the finite element analysis software ANSYS, and the contact stresses were analyzed after loading and solving.The contact stresses between power roller and conical disks can seriously affect the fatigue life of contact elements, and traction efficiency is an important index to measure performance. Considering influence factors of contact stress, the multi-objective optimization was proposed, which was based on the objects of contact stress and average traction efficiency, and the constraint conditions of the film thickness ratio, contact strength, efficiency and geometric noninterference, then the mathematical model of structural parameters optimization was established. MATLAB/GADS genetic algorithm toolbox was used to solve the optimization model.A part of parameters of traction drive CVT can only be obtained by multi-objective optimization. At last, with the method of orthogonal experiment design, combined with the parameter equation studied, the influence of four factors on contact stresses was analyzed, including the height of power roller, the height of power surface, the radius of conical disk end face and the axial distance. The best combination was obtained after analyzing simulation results with range analysis and horizontal trend analysis. The data after optimization were compared with the ones before optimization, the results were reasonable.From power transmission capability analysis of traction drive CVT and the optimization of its related parameters, not only we can obtain a complete set of design theory, but also there is a certain application value to power transmission system development of the larger displacement vehicles.