Patent ID: 7282008

Claim:
A mode switch control system for a hybrid transmission for a powertrain, the powertrain including an engine, a motor/generator, and an output shaft, the hybrid transmission including a stationary rotating element, and a differential unit including a plurality of rotating elements to connect the engine, the motor/generator, and the output shaft to each other, the mode switch control system comprising: a first torque-transmitting mechanism selectively engageable to connect specific two of the rotating elements to establish a high speed mode to set a speed ratio of an output speed to the output shaft to an input speed from the engine to an infinitely variable high speed ratio in which a torque of the motor/generator is needed to be a first torque to serve for torque balance in the hybrid transmission near a mode-switch speed ratio which is a boundary point between the high speed mode and a low speed mode, and disengageable to disconnect the specific two rotating elements to establish the low speed mode to set the speed ratio to an infinitely variable low speed ratio in which the torque of the motor/generator is needed to be a second torque opposite in direction to the first torque, to serve for the torque balance near the mode-switch speed ratio; an actuator to adjust a torque capacity of the first torque-transmitting mechanism; a motor/generator controller to adjust a torque of the motor/generator; and a control unit in operative communication with the actuator and the motor/generator controller, to perform the following: determining an operating condition of the hybrid transmission; issuing a command indicative of switching the transmission mode from the high speed mode to the low speed mode, in accordance with the operating condition of the hybrid transmission; and performing the following, in response to the command: reducing the torque capacity of the first torque-transmitting mechanism, to disengage the first torque-transmitting mechanism; and varying the torque of the motor/generator to the second torque, in connection with the reduction of the torque capacity of the first torque-transmitting mechanism.