Continuously variable transmission with control of switching between a high mode and a low mode

A continuously variable transmission system for speed change of rotation received from an engine output shaft and for transmitting that rotation, at the changed speed to vehicle wheels, said system comprising:

• an input shaft for receiving engine torque from the engine output shaft;
• an output shaft for outputting torque to the vehicle wheels;
• a belt type continuously variable transmission unit having a first pulley for receiving engine torque from said input shaft, a second pulley, a belt trained around both of said first and second pulleys and axial force actuating means for changing the pulley ratio of said first and second pulleys by applying axial forces to said first and second pulleys;
• a planetary gear unit having a first rotary element rotatable with said input shaft, a second rotary element rotatable with said second pulley and a third rotary element rotatable with said output shaft;
• a first clutch, interposed between said input shaft and said first rotary element, for engaging and disengaging power transmission therebetween;
• a second clutch, interposed between any two of said first, second, and third rotary elements of said planetary gear unit, for engaging and disengaging power transmission therebetween;
• low-high shifting means for shifting between a low mode for providing a comparatively high torque ratio by engaging said first clutch and a high mode for providing a comparatively low torque ratio by engaging said second clutch, wherein direction of torque transmission between said first pulley and said second pulley of said belt type continuously variable transmission unit is changed by switching between said low mode and said high mode;
• control means for controlling said axial force actuating means so that axial forces acting on said first and second pulleys produce a difference corresponding to the pulley ratio of said first and second pulleys;
• and
• switching means for changing the relative relationship in magnitude between the axial forces which act on said first and second pulleys, responsive to switching between said low mode and said high mode by said low-high shifting means, so that said relative relationship in magnitude is reversed.