Hybrid electro-mechanical transmission with single motor/generator and method of control

A method of operating an electro-mechanical transmission having an input member to receive power from an engine, an output member for delivering power from the transmission, a single motor/generator operatively connected to a battery for receiving power from the battery to act as a motor and for delivering power to the battery to act as a generator, wherein the battery is characterized by a maximum and a minimum charge, wherein the transmission is characterized by an absence of another motor/generator affecting power flow through the transmission, at least one differential gear set having a plurality of members, wherein the input member and said motor/generator are each operatively connectable with a different respective one of the members of said at least one differential gear set, a plurality of torque-transmitting mechanisms, wherein different ones of the torque-transmitting mechanisms are selectively engagable to establish different respective operating modes including at least one continuously variable mode characterized by a range of speed ratios and at least one fixed ratio mode having the same engaged torque-transmitting mechanisms as said at least one continuously variable mode, the method comprising:

• determining values of pre-selected vehicle operating characteristics in a current operating state of the transmission characterized by one of said operating modes, one of said speed ratios, a motor speed and a motor torque, said vehicle operating characteristics including vehicle speed, vehicle load and vehicle operator inputs;
• analyzing the determined values to thereby identify a target operating state characterized by one of said operating modes and one of said speed ratios and at which the vehicle will be characterized by optimal energy efficiency for said determined values;
• if the operating mode of the current operating state is different than the operating mode of the target operating state, engaging all of the torque-transmitting mechanisms that establish the operating mode of the target operating state and that are not engaged in the current operating state and disengaging all of the torque-transmitting mechanisms that establish the first operating state and that are not engaged in the operating mode of the target operating state to establish the operating mode of said target operating state;
• and
• controlling power flow between the battery and the motor/generator to target the speed ratio of the target operating state, thereby causing the battery to reach one of the maximum and the minimum charge and the transmission to be characterized by a fixed speed ratio established by the engaged torque-transmitting mechanisms of the operating mode of the target operating state.

A method of operating an electro-mechanical transmission on a vehicle, the transmission having a single motor/generator in power flow communication with a battery and having continuously variable modes, each including a range of speed ratios, and fixed ratio modes, comprising:

• determining values of pre-selected vehicle operating characteristics at a current time when the vehicle is characterized by a current operating state characterized by one of said modes;
• analyzing the determined values to thereby identify a target operating state characterized by one of said continuously variable modes and a speed ratio within the range of speed ratios of the continuously variable mode of the target operating state;
• if the mode of the current operating state is different than the mode of the target operating state, changing the engaged torque-transmitting mechanisms to establish the mode of the target operating state;
• and
• controlling power flow between the battery and the motor/generator to target the speed ratio of the target operating state, thereby causing the charge of the battery to be one of a minimum and a maximum level wherein net battery power flow is zero and the transmission is therefore characterized by a fixed speed ratio established by the engaged torque-transmitting mechanisms of the target operating state.