Shift control system/method for vehicle equipped with driveline retarder

A control system for controlling shifting of an automated vehicular powertrain system (10) comprising a fuel-controlled engine (12) drivingly coupled to a multiple-speed mechanical transmission (14) having an output shaft (22) drivingly coupled to vehicular drive wheels (26) and a driveline retarder (28) effective to apply a selective level of retarding torque to said drive wheels, said control system including a control unit (30) for receiving input signals (32) including an input signal indicative of engine torque and an input signal indicative of vehicle acceleration and for processing same in accordance with predetermined logic rules to issue command output signals (34) to powertrain system actuators including a transmission actuator (50) and a retarder actuator (52), said control system characterized by said control unit operating under logic rules for:

• during a shift of said transmission into a target gear ratio (GR.sub.T), if engine torque is determined to be less than a first predetermined reference value and vehicle acceleration is greater than a second reference value, causing the retarder to apply increased retarding torque to said drive wheels.

A computer program for use with a computer-based onboard control unit for controlling shifting of an automated vehicular powertrain system comprising a fuel-controlled engine drivingly coupled to a multiple-speed mechanical transmission having an output shaft drivingly coupled to vehicular drive wheels, and a driveline retarder effective to apply a selective level of retarding torque to said drive wheels, said control unit having means for receiving input signals including an input signal indicative of engine torque and an input signal indicative of vehicle acceleration and for processing same in accordance with predetermined logic rules defined by said computer program to issue command output signals to system actuators including a transmission actuator and a retarder actuator, said computer program stored on a computer-usable medium and characterized by defining logic rules for:

• causing a determination of engine torque and vehicle acceleration;
• and
• during a shift of said transmission into a target gear ratio (GR.sub.T), if engine torque is determined to be less than a first predetermined reference value (TORQUE.sub.E <REF.sub.1) and vehicle acceleration is greater than a second reference value (dOS/dt>REF.sub.2), causing the retarder to apply increased retarding torque to said drive wheels.