High energy engagement strategy for automatic transmission clutches and brakes

A control strategy and method for controlling torque transfer from a throttle-controlled automotive vehicle engine through geared torque flow paths in a transmission to vehicle traction wheels, the engine having an output torque controller for any given throttle position and engine speed including a torque reducer whereby torque is truncated, the transmission having fluid pressure-operated friction clutch and brake elements for establishing and disestablishing forward and reverse torque flow paths, a transmission fluid temperature sensor, an engine coolant temperature sensor, a traction wheel speed sensor, an engine throttle position sensor, a driver-operated range selector for establishing a forward drive torque flow path and a reverse drive torque flow path, the strategy and method comprising the steps of:

• determining the duration of a torque truncation when the range selector is repeatedly cycled between positions corresponding to the reverse torque flow path and the forward torque flow path as a function of transmission fluid temperature;
• verifying whether entry conditions are met for entry into a torque truncation mode, the entry conditions including a determination of whether the transmission fluid temperature is below a calibrated value;
• determining the magnitude of the torque truncation as a function of engine load and engine coolant temperature;
• setting the maximum engine torque truncation as determined by a calibration factor that ensures engine stability;
• and
• modifying the engine torque during movement of the range selector lever between forward and reverse positions when the entry conditions are met, whereby friction element distress is avoided as one friction element is released and another friction element is applied during repeated cycling of the range selector lever between positions corresponding to forward drive and reverse drive.