Speed change ratio control unit for continuously variable transmission

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 as a driving actuator for a speed change control valve is characterized in comprising:

• 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 a step position (ASTP) of said step motor stored by said speed change ratio control unit 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;
• a step-out correction means that when a 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 said driving step motor using said corrected ASTP.