Continuously variable transmission clutch control system including special start mode operation

A method for providing a clutch control signal in a continuously variable transmission system to a fluid-actuated clutch to transfer torque between an engine and a drive line mounted in a vehicle, said clutch having an associated supply line to supply fluid to apply the clutch and discharge fluid to release the clutch controlled by a clutch control valve assembly in said supply line including:

• developing a signal representative of the difference between clutch input speed and clutch output speed;
• integrating said difference signal to provide a first pressure signal;
• developing a signal representative of a selected maximum torque value based on a driver demand signal;
• modifying said maximum torque signal to provide a second pressure signal;
• and
• combining said first and second pressure signals for controlling said clutch control valve.

In a continuously variable transmission system having at least an associated clutch disengage engine speed, a lowest engine speed setpoint and a maximum engine speed and operable at least in a normal start mode for clutch control during transition from a first system state to a second system state and a special start mode for clutch control during transition from a first system state to a second system state, a method for controlling the system operation mode including:

• sensing vehicle speed during clutch disengagement,
• calculating an engine speed, which would correspond to said sensed vehicle speed if the clutch were locked up,
• comparing said calculated engine speed with the maximum engine speed and the engine speed for clutch disengagement to determine whether the calculated engine speed corresponding to said sensed vehicle speed is between those values;
• and
• triggering said system to operate in said special start mode when said sensed vehicle speed is not between said values.

A method for generating a clutch control signal to control torque transfer at a fluid-actuated clutch in a continuously variable transmission system, said clutch being responsive to pressure in a fluid supply line controlled by a clutch control valve, comprising:

• providing a signal representative of the absolute value of a difference between a sensed clutch input speed and a sensed clutch output speed;
• adding a selected value to said signal representative of said absolute value of said difference;
• and then
• integrating the resulting signal to provide a speed difference signal for controlling said clutch control valve.

In a continuously variable transmission system, a method for selecting one of more than one control modes for controlling torque transfer at a clutch comprising:

• detecting conditions indicative of engine speed, clutch position, driver demand and clutch speed that represent a desired transition from a first system operating mode to a second system operating mode, said transition from a first system operating mode to a second system operating mode being representative of the system desirably being operated in one of more than one start control modes;
• enabling said system for a first start control mode when said detected conditions do not indicate that clutch lockup would cause engine acceleration;
• and
• enabling said system for a second start control mode when said detected conditions indicate that clutch lockup would cause engine acceleration.