Control system for continuously variable transmission

A control system for a continuously variable transmission having primary and secondary pulleys, each having a fixed sheave and a movable sheave, and a belt intercoupling the pulleys, which control system comprises

• a supply line, means for establishing fluid flow in the supply line, and a secondary sheave control valve coupled to the supply line for regulating the line pressure supplied to the secondary pulley movable sheave,
• a throttle valve connected to develop a throttle pressure signal as a function of throttle opening, which throttle pressure signal is utilized to regulate the secondary sheave control valve in a sense to increase said line pressure as the throttle opening indicates an increased torque demand and to decrease said line pressure as the throttle opening indicates a reduced torque demand, thus providing a throttle-sensitive regulation of the fluid pressure in the supply line to the secondary pulley movable sheave, and a throttle boost valve, connected to the supply line as a pressure source, and coupled between the throttle valve and the secondary sheave control valve, which throttle boost valve utilizes the throttle pressure signal to provide the secondary sheave control valve with a boosted throttle pressure lower than the line pressure and varying as a function of the throttle pressure.

A control system for a continuously variable transmission having primary and secondary pulleys, each having a fixed sheave and a movable sheave, and a belt intercoupling the pulleys, which control system comprises

• a supply line, means for establishing fluid flow in the supply line, a secondary sheave control valve coupled to the supply line for regulating the line pressure supplied to the secondary pulley movable sheave, and a sheave follower for providing an indication of the position of one of said movable sheaves,
• characterized in that a ratio valve is provided to develop a ratio pressure signal as a function of the transmission ratio, the ratio valve including means for applying a combination of hydraulic and spring forces to produce a resultant force to urge the sheave follower against said one movable sheave, which resultant force is substantially constant throughout the stroke of the ratio valve, to develop a ratio pressure signal which is applied to the secondary sheave control valve in a sense to decrease said line pressure as the ratio pressure signal indicates a change in the transmission ratio in the direction from underdrive to overdrive.

A control system for a continuously variable transmission having primary and secondary pulleys, each pulley having a fixed sheave and a movable sheave, and a belt intercoupling the pulleys, which control system comprises

• a supply line, means for establishing fluid flow in the supply line, a primary sheave control valve, coupled between the supply line and the primary pulley movable sheave, for regulating the position of the primary pulley movable sheave and thus controlling the drive ratio between the pulleys, and a shift signal valve connected to provide a shift signal pressure related to a desired engine speed,
• characterized in that a timing valve has an inlet coupled to the shift signal valve and an outlet, an accumulator coupled to one end of the primary sheave control valve, a channel communicating between the timing valve outlet and the common connection between the accumulator valve and the primary sheave control valve, and means defining an orifice positioned between said channel and the timing valve outlet, such that the rate of downshifting of the transmission is controlled as the timing valve and accumulator valve cooperate to provide a slow, controlled buildup of pressure on the primary sheave control valve to produce a corresponding slow exhaust of the primary sheave chamber.