Motor-assisted transmission

1. A powertrain comprising:

an engine;

a layshaft transmission having an input shaft and an output shaft;

an electric motor/generator;

a transfer gear set having a first transfer gear and a second transfer gear meshing with the first transfer gear and mounted for rotation with the output shaft; wherein the transfer gear set is configured so that the second transfer gear rotates slower than the first transfer gear;

a planetary gear set having a first member fixed to the input shaft for rotation at a common speed with the input shaft, a second member fixed to the motor/generator for rotation at a common speed with the motor/generator, and a third member fixed to the first transfer gear for rotation at a common speed with the first transfer gear;

a first clutch selectively engageable to directly connect the engine for rotation with the input shaft so that the engine is fixed to the input shaft for rotation at a common speed with the input shaft;

a second clutch selectively engageable to ground the input shaft to a stationary member;

first and second gear pairs each operable for transferring torque from the input shaft to the output shaft at a respective fixed speed ratio by selectively engageable synchronizers when the first clutch is engaged, the engine is on and the motor/generator is not powered; wherein each of the first and the second gear pairs are configured to increase the speed of the output shaft relative to the speed of the input shaft; and

the powertrain being operable in an electrically-variable operating mode in which the motor is controlled to add torque to the output shaft through the planetary gear set while the first clutch is engaged and the engine is operated at a predetermined speed, the fixed speed ratios providing speeds of the output shaft greater than speeds of the output shaft in the electrically-variable operating mode.

2. A powertrain comprising:

an engine having an engine crankshaft;

a planetary gear set having a first member, a second member, and a third member, the members including a sun gear member, a carrier member, and a ring gear member;

an input member; wherein the first member is fixed to the input member for rotation at a common speed with the input member;

a first clutch selectively engageable to directly connect the engine crankshaft with the input member so that the engine crankshaft is fixed to the input member for rotation at a common speed with the input member, and the first member and the third member of the planetary gear set rotate at different speeds when the first clutch is engaged; wherein the engine is completely disconnected from the planetary gear set when the first clutch is not engaged;

a second clutch selectively engageable to ground the input member with a stationary member;

an electric motor/generator having a rotor continuously fixed to the second member for rotation at a common speed with the second member;

an output member;

a set of intermeshing gears including a first transfer gear continuously fixed to the third member for rotation at a common speed with the third member; wherein the set of intermeshing gears is configured to increase torque from the third member to the output member;

a first gear pair having a first gear continuously fixed to the input member for rotation at a common speed with the input member, and having a second gear meshing with the first gear and rotatable about the output member; wherein the first gear pair is configured to reduce torque from the input member to the output member;

a second gear pair having a third gear connected for rotation with the input member and a fourth gear meshing with the third gear and rotatable about the output member; wherein the second gear pair is configured to reduce torque from the input member to the output member;

a first synchronizer selectively engageable to connect the second gear for common rotation with the output member;

a second synchronizer selectively engageable to connect the fourth gear for common rotation with the output member;

wherein the first clutch is engaged, the second clutch is not engaged, the motor is not powered, and the synchronizers are alternately engaged to provide two different fixed speed ratios between the input member and the output member;

wherein the transmission is operable in an electrically-variable operating mode when the first clutch is engaged, the engine is on, and the motor/generator provides torque to the second member; and

wherein the electrically-variable operating mode is established to provide speeds of the output member greater than speeds of the output member during launch of the transmission and less than speeds of the output member during the two different fixed speed ratios.

3. The powertrain of claim 2 , wherein the transmission is operable in an electric-only operating mode when the second clutch is engaged and the motor/generator is operated as a motor to provide torque to the output member.

4. The powertrain of claim 2 , wherein the transmission is operable at a first of the two different fixed speed ratios when the first clutch is engaged, the engine is on, the motor/generator is off, and the first synchronizer is engaged, and is operable at a second of the two different fixed speed ratios when the first clutch is engaged, the engine is on, the motor/generator is off, and the second synchronizer is engaged.

5. The powertrain of claim 2 , wherein the first member is the sun gear member, the second member is the ring gear member, and the third member is the carrier member.

6. The powertrain of claim 2 , wherein the motor/generator is operated as a generator to receive torque from the second member and thereby slow the output member in a regenerative braking mode.

7. The powertrain of claim 2 , wherein the motor/generator is operated as a motor to provide torque to the second member, the second clutch is engaged, and the first clutch and the synchronizers are not engaged to launch the transmission.

8. The powertrain of claim 7 , wherein the engine provides a predetermined amount of torque at the crankshaft and the motor/generator is controlled to provide a varying amount of torque to meet varying output torque requirements at the output member in the electrically-variable operating mode.

9. The powertrain of claim 8 , wherein the motor/generator is controlled to provide torque or receive torque as necessary to dampen engine vibrations.

10. The powertrain of claim 2 , wherein the motor/generator is controlled to vary torque at the output member during a shift between the fixed speed ratios.

11. A powertrain comprising:

an engine having an engine crankshaft;

a transmission having:

a planetary gear set having a sun gear member, a carrier member, and a ring gear member;

an input shaft; wherein the sun gear member is fixed to the input shaft for rotation at a common speed with the input shaft;

a first clutch selectively engageable to directly connect the engine crankshaft with the input shaft so that the engine crankshaft is fixed to the input shaft for rotation at a common speed with the input shaft;

a second clutch selectively engageable to ground the input shaft with a stationary member;

an electric motor/generator having a rotor fixed to the ring gear member for rotation at a common speed with the ring gear member;

an output shaft generally parallel with the input shaft;

a set of intermeshing gears configured to increase torque from the carrier member to the output shaft;

a first gear pair having a first gear connected for rotation with the input shaft and a second gear meshing with the first gear and rotatable about the output shaft; wherein the first gear pair is configured to reduce torque from the input shaft to the output shaft;

a second gear pair having a third gear connected for rotation with the input shaft and a fourth gear meshing with the third gear and rotatable about the output shaft; wherein the second gear pair is configured to reduce torque from the input shaft to the output shaft;

a first synchronizer selectively engageable to connect the second gear for common rotation with the output shaft;

a second synchronizer selectively engageable to connect the fourth gear for common rotation with the output shaft; wherein the first synchronizer and the second synchronizer are arranged adjacent to one another and integrated as a dual synchronizer;

wherein the engine, the motor/generator, the clutches and the synchronizers are operable to provide a launch mode using torque provided by only the motor/generator, an electrically-variable mode using torque provided by both the engine and the motor/generator; and fixed ratio modes using torque provided by only the engine; and

wherein the electrically-variable mode provides speeds of the output member less than speeds of the output member provided in the fixed ratio modes.