Research On The Slip Ratio Control For V-belt CVT

V–belt continuously variable transmission (CVT) is an ideal transmission forvehicle, which can continuously adjust the ratio to adapt to the ever-changing vehicleloads. It can realize the optimum matching between the engine and vehicle, so it canimprove the vehicle’s fuel economy and dynamic performance, and lower air pollution.Recently, with the fast development of new energy vehicle, especially hybrid electricvehicle, the advantages of V-belt CVT have been fully reflected so that the CVT is thebest choice for hybrid transmission system. On account of the traditional force controlstrategy supplying the clamping force largely beyond the required level even undernormal conditions, the thesis put forward a new method that is the clamping forcecontrol in CVT based on the slip ratio, which can decrease the clamping forceeffectively and improve transmission efficiency of CVT.Firstly, the impact of transmission efficiency of V-belt CVT is analyzed, whichconsists of three main factors: torque losses caused by slip between metal belt andpulley belt, torque losses caused by internal friction of metal belt, and torque lossescaused by oil pump. Point to the conditions above, the methods of decreasing torquelosses are put forward, which pave the way for proposing slip ratio theory.Secondly, the slip ratio among driving wheel, driven wheel and metal pulley, andthe relations between slip ratio and friction coefficients are discussed. The researchshows that friction coefficients are only related to speed ratio and slip ratio. The newslip ratio theory and standard slip ratio are put forward. By comparing them, it showsthat the new slip ratio theory can reflect slip characteristics of CVT better.Thirdly, load distribution and frictional characteristic of metal belt and beltpulley under pulley deformation are studied, which aims to analyze the steady-statecharacteristic of V-belt CVT. Based on the force bearing analysis between metal beltand belt pulley, the mathematical model and corresponding computation model ofload distribution and frictional characteristic are established. The results show thatthe corresponding computation model can be further used in strength analysis ofV-belt CVT and evaluation of transmission efficiency.Finally, a clamping force control model based on slip ratio is established byMatlab/Simulink, whose rationalities are tested and verified by experimental data. Indifferent throttle position, the compared simulation results under two control strategies show that the clamping force control strategy based on slip ratio canincrease friction coefficients between metal belt and belt pulley, decrease clampingforce of driving wheel and driven wheel, and improve transmission efficiency ofCVT.