Patent ID: 8414436

Claim:
A method of operating a hybrid powertrain; wherein the hybrid powertrain includes an engine and a transmission; wherein the transmission has an input member connected with the engine, an output member, a stationary member, a first and a second motor/generator, a first planetary gearing arrangement, and a second planetary gearing arrangement; wherein the input member is connected for common rotation with a first member of the first planetary gearing arrangement; wherein the output member is connected for common rotation with a first member of the second planetary gearing arrangement; wherein the first motor/generator is connected for common rotation with a second member of the first planetary gearing arrangement; wherein the second motor/generator is connected for common rotation with a second member of the second planetary gearing arrangement; an interconnecting member continuously connecting a third member of the first planetary gearing arrangement for common rotation with a third member of the second planetary gearing arrangement; a plurality of torque-transmitting mechanisms including a first torque-transmitting mechanism selectively engagable to ground the first motor/generator to the stationary member, a second torque-transmitting mechanism selectively engagable to connect the interconnecting member for common rotation with the output member, a third torque-transmitting mechanism and a fourth torque-transmitting mechanism, the third and fourth torque-transmitting mechanisms being selectively engagable to connect different members of the second planetary gearing arrangement to the stationary member or for common rotation with one another; the method comprising: establishing three different electrically-variable operating modes by engaging only one respective different one of the second, third and fourth torque-transmitting mechanisms in response to different respective vehicle operating conditions; establishing at least two different fixed ratio modes by engaging the first torque-transmitting mechanism in addition to said only one respective different one of the second, third and fourth torque-transmitting mechanisms engaged to establish the electrically-variable operating modes; wherein the at least two different fixed ratio modes are established in response to different respective vehicle operating conditions requiring greater torque at the output member than the respective different vehicle operating conditions of the electrically-variable operating modes.