Variator-Assisted Transmission and Launch Control Methods for Such a Transmission

A launch control method for a variator-assisted transmission comprising a hydro-mechanical variator, a summing transmission connected to an output side of the variator, and low and high speed clutches for selectively connecting the summing transmission to an output member, the method comprising the steps of:

• determining whether a launch has been requested;
• adjusting a variable displacement pump of the variator to a predetermined fixed displacement;
• commencing engagement of the low and high speed clutches;
• determining whether a predetermined degree of slip exists between input and output elements of the low speed clutch;
• holding both clutches at their present state of engagement when the predetermined degree of slip has been established;
• placing the variator into a torque control mode;
• determining when there is zero slip between the input and output elements of either the low or high speed clutch;
• instructing full engagement of whichever of the clutches has been determined to have zero slip;
• and
• holding the pump of the variator at its current displacement until a predetermined time period has elapsed.

A continuously variable transmission, comprising:

• an input shaft connectable to an engine;
• an output shaft connectable to a load;
• a hydro-mechanical variator having an input side connecting the input shaft to a variable displacement pump, and an output side;
• a summing transmission connected to input shaft and the output side of the variator;
• a first clutch which selectively connects a first output element of the summing transmission to the output shaft;
• a plurality of sensors monitoring the rotational speed of the first output element and the output shaft;
• and
• a controller which controls the displacement of the variator pump and the degree of engagement of the clutch in response to data received from the plurality of sensors.