Patent ID: 8255129

Claim:
An automobile powertrain comprising: an engine; a torque converter coupled to the engine; a drive shaft; an automatic transmission having an input shaft drivingly connected to the torque converter, an output shaft drivingly connected to the drive shaft, a plurality of gear ratios, a plurality of torque-transmitting mechanisms and a hydraulic control system; an engine control unit electrically connected to the engine; and a transmission control unit electrically connected to the hydraulic control system, wherein the transmission control unit has control logic operable to downshift the transmission from a fifth of the plurality of gear ratios to a third of the plurality of gear ratios by controlling engagement of the plurality of torque-transmitting mechanisms, the control logic including: a first control logic for demanding a downshift from the fifth of the plurality of gear ratios to the third of the plurality of gear ratios; a second control logic for reducing a main pressure of the hydraulic control system to a minimum pressure in order to allow a first of the plurality of torque-transmitting mechanisms to slip; a third control logic for retarding a torque output of the engine when the first of the plurality of torque-transmitting mechanisms begins to slip; a fourth control logic for calculating a value of the torque output of the engine required to accelerate the input shaft to achieve a third gear synchronous speed within a specified time; a fifth control logic for disconnecting the main pressure of the hydraulic control system from the first of the plurality of torque-transmitting mechanisms and connecting the main pressure to a second of the plurality of torque-transmitting mechanisms thereby exhausting a remaining hydraulic pressure from the first of the plurality of torque-transmitting mechanisms and partially pressurizing the second of the plurality of torque-transmitting mechanisms; a sixth control logic for controlling the torque output of the engine to the calculated value of the torque output required to accelerate the input shaft of the transmission to the third gear synchronous speed; and a seventh control logic for modulating the main pressure of the hydraulic control system to engage the second of the plurality of torque-transmitting mechanisms and establish the third of the plurality of gear ratios between the input shaft and the output shaft.