Study Of Clamping Force Control Strategy For CVT

Steel V-belt continuously variable transmission(CVT) is one of developing focus on the transmission of vehicle at present.Cars with CVT have good performance in riding comfort.But it is worse than manual transmission in transmitting efficiency and torque because of its drawback in mechanical structure.All above cause CVT's developing chock point.Researches are provided by the project of Jiangsu tackle key problem of science and technology in CVT.Based on the original hardware condition, and study on characteristic of power transmitting and carrying load,the clamping force control strategy has been designed creatively,which improved transmitting efficiency and reacting speed of control system.This paper involves the following content:(1) The developing status of CVT nowadays through world is concluded.The structure and principle of speed change of Steel V-belt CVT are introduced,also its study and developing process.Throughout analyzing on study status of clamping force control strategy,the significance and the necessity of this theme are figured out.(2) Firstly,engine working properties are analyzed,and based on this,the best matching lines with CVT are studied.Mathematical models of engine,hydraulic system and vehicle are set up according to above studies.(3) Secondly,pressures between steel belt and pushing pulleys are studied within two ways:due to the transmitting type is frictional,the analysis of driving ability of power and determining axial force of pulley are very important;there is not only tensile force on steel ring,but also compression between blocks during power transmitting,which make differences of study methods between common belt transmission and CVT.Based on this,mathematical models of CVT are set up and theory basis is provided for the next control strategy emulation.(4) In order to make sure reacting fast and steady,precise control of target clamping force,and eliminate the effect of the proportion overfall valve saturation characteristic,a fuzzy-PID complex controller is designed based on study of fuzzy control and PID control theory and analysis of extreme acceleration characteristics. Then,this controller is verified under extreme acceleration driving contion.(5) RCP models of damping force control strategy are built.Hardware in loop emulation test rig based on dSPACE/Simulator is put up.The control strategy of clamping force designed in paper is proved as reaction speed quite fast and little steady state error.Finally,CVT controller has its road tests and results show the performances of economical and powerful are perfect,meanwhile remain good driving comfort.