Continuously variable transmission

In a vehicle drivetrain including an engine and a continuously variable transmission having first and second sheave assemblies with relatively movable sheaves and a chain which transfers power between the assemblies, a flow control valve means for controlling flow of fluid between said sheave assemblies, a control system for controlling said flow control valve means to effect said flow of control fluid, the flow of control fluid being utilized by a drive mechanism of one of the sheave assemblies to provide a pressure on a sheave of said one sheave assembly, the control system comprising:

• means for generating a speed signal based on the speed of the vehicle;
• means for generating a chain ratio signal based on a variable chain ratio of the chain;
• an electric actuator coupled to the flow control valve for driving the flow control valve as a function of a control signal;
• control means for generating said control signal as a function of said speed signal and said chain ratio signal to control said actuator to prevent slippage of the chain during drive-away of the vehicle and to allow substantially total control of the chain ratio, said flow control valve having a first position that effects flow of control fluid to said one sheave assembly, a second position that effects flow of control fluid from said one sheave assembly and a third position intermediate said first and second positions whereby transfer of control fluid between said sheave assemblies is blocked, thereby effecting a null condition in which changes in said chain ratio are prevented thereby providing decreased sensitivity of said flow control valve means.