Powertrain with two planetary gear sets and two motor/generators for hybrid vehicle

1. A powertrain comprising:

an input member;

an output member;

a stationary member;

a first and a second electric motor/generator;

only two planetary gear sets each having a respective first, second, and third member;

an interconnecting member connecting one of the members of a first one of the planetary gear sets to one of the members of a second one of the planetary gear sets; the input member, the output member, the first motor/generator and the second motor/generator each being continuously connected for common rotation with a different one of the members of the planetary gear sets that is not connected by the interconnecting member;

four brakes each selectively engageable to ground a different respective one of the members of the planetary gear sets that is not connected by the interconnecting member to the stationary member; wherein engagement of a different one or ones of the brakes and operation of one or both of the motor/generators as a motor establishes three electric-only operating modes between the input member and the output member.

2. The powertrain of claim 1 , wherein one of the electrical-only operating modes is provided between the input member and the output member when a first one of the four brakes is engaged and the second motor/generator is operated as a motor.

3. The powertrain of claim 1 , wherein one of the electrical-only operating modes is provided between the input member and the output member when a second one of the four brakes is engaged and both of the motor/generators are operated as motors.

4. The powertrain of claim 1 , wherein one of the electrical-only operating modes is provided between the input member and the output member when a second one and a third one of the four brakes are engaged and the first motor/generator is operated as a motor.

5. The powertrain of claim 1 , further comprising:

an engine having an engine crankshaft connected for rotation with the input member; and

wherein an electrically-variable operating mode is provided between the input member and the output member when the engine is on, one of the four brakes is engaged, and the second motor/generator is operated as a motor.

6. The powertrain of claim 1 , further comprising:

an engine having an engine crankshaft connected for rotation with the input member; and

wherein an electrically-variable operating mode is provided between the input member and the output member when the engine is on, one of the four brakes is engaged, and the first motor/generator is operated as a motor.

7. The powertrain of claim 1 , further comprising:

an engine having an engine crankshaft connected for rotation with the input member; and

wherein a fixed speed ratio is established between the input member and the output member when the engine is on and two of the four brakes are engaged.

8. The powertrain of claim 1 , further comprising:

an engine having an engine crankshaft connected for rotation with the input member; and

wherein a series operating mode is established when the engine is on, one of the four brakes is engaged, the first motor/generator acts as a generator, and the second motor/generator acts as a motor.

9. A powertrain comprising:

an input member adapted for connection with an engine crankshaft;

an output member;

a stationary member;

a first electric motor/generator;

a second electric motor/generator;

a first planetary gear set having a first member, a second member, and a third member; wherein the input member is continuously connected for rotation with the first member of the first planetary gear set;

a second planetary gear set having a first member, a second member, and a third member;

an interconnecting member continuously connecting the second member of the first planetary gear set to the first member of the second planetary gear set for rotation at the same speed;

wherein the first motor/generator is continuously connected for rotation with the third member of the first planetary gear set;

wherein the output member is continuously connected for rotation with the second member of the second planetary gear set;

wherein the second motor/generator is continuously connected for rotation with the third member of the second planetary gear set;

a first brake selectively engageable to ground the first member of the second planetary gear set to the stationary member;

a second brake selectively engageable to ground the first member of the first planetary gear set to the stationary member;

a third brake selectively engageable to ground the third member of the second planetary gear set to the stationary member; and

a fourth brake selectively engageable to ground the third member of the first planetary gear set to the stationary member; wherein the brakes are engageable in different combinations and the motor/generators are operable as motors, as generators, or are off to establish different operating modes between the input member and the output member.

10. The powertrain of claim 9 , wherein an electrical-only operating mode is established between the input member and the output member when the first brake is engaged, and the second motor/generator is operated as a motor.

11. The powertrain of claim 9 , wherein an electrical-only operating mode is provided between the input member and the output member when the second brake is engaged, and both of the motor/generators are operated as motors.

12. The powertrain of claim 9 , wherein an electrical-only operating mode is provided between the input member and the output member when the second and third brakes are engaged and the first motor/generator is operated as a motor.

13. The powertrain of claim 9 , further comprising:

an engine having the engine crankshaft connected for rotation with the input member; and

wherein an electrically-variable operating mode is provided between the input member and the output member when the engine is on, the fourth brake is engaged, and the second motor/generator is operated as a motor.

14. The powertrain of claim 9 , further comprising:

an engine having the engine crankshaft connected for rotation with the input member; and

wherein an electrically-variable operating mode is provided between the input member and the output member when the engine is on, the third brake is engaged, and the first motor/generator is operated as a motor.

15. The powertrain of claim 9 , further comprising:

an engine having the engine crankshaft connected for rotation with the input member; and

wherein a fixed speed ratio is established between the input member and the output member when the third brake and the fourth brake are engaged.

16. The powertrain of claim 9 , further comprising:

an engine having the engine crankshaft connected for rotation with the input member; and

wherein a series operating mode is established when the engine is on, the first brake is engaged, the first motor/generator acts as a generator, and the second motor/generator acts as a motor.

17. A powertrain comprising:

an engine having an engine crankshaft;

a transmission having:

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

only one interconnecting member continuously connecting one of the members of the first planetary gear set for common rotation with one of the members of the second planetary gear set;

two motor/generators; wherein one of the motor/generators is connected for common rotation with one of the members of the first planetary gear set that is not connected by the interconnecting member, and the other of the motor/generators is connected for common rotation with one of the members of the second planetary gear set that is not connected by the interconnecting member;

a stationary member;

only four torque-transmitting mechanisms, each of which is a brake that grounds a different respective one of said members of the planetary gear sets to the stationary member; and

wherein the powertrain is operable to provide forward propulsion in seven different operating modes including three electric-only operating modes in which one or both of the motor/generators provides propulsion, and including a series operating mode in which the engine and one of the motor/generators provide forward propulsion and one of the motor/generators acts as a generator.