Patent ID: 7037235

Claim:
A speed change ratio control unit for a continuously variable transmission which converts input rotation into output rotation in continuously changing speed manner through controlling a step motor that is a driving actuator for a speed change control valve, said speed change ratio control unit comprising: a computing device for generating a command signal to control said step motor; storage for storing a step position ASTP of said step motor corresponding to said command signal; an input rotation detection means for detecting said input rotation; an output rotation detection means for detecting said output rotation; an actual speed change ratio calculation means that calculates actual speed change ratio from said input rotation detected and said output rotation detected; a step-out determination means which compares said step position ASTP of said step motor stored by said storage and a step position BSTP of said step motor corresponding to said calculated actual speed change ratio at every predetermined operation cycle, and if ASTP≠BSTP is satisfied determines that a step-out has occurred on said step motor in which a synchronization between said command signal and said calculated actual speed change ratio is lost; a step-out correction means that when the step-out is determined by said step-out determination means corrects said ASTP so as to reduce a difference between said ASTP and BSTP; and a drive means for driving said step motor using said corrected ASTP.