Vehicle drive and method with electromechanical variable transmission

1. A vehicle drive comprising:

a first gear set and a second gear set, wherein each gear set comprises a sun gear, a ring gear, and planetary gears, the planetary gears coupling the sun gear to the ring gear, wherein the planetary gears are rotatably supported by a planetary gear carrier;

a first motor/generator coupled to the sun gear of the first gear set;

a second motor/generator selectively coupled to at least one of (a) the planetary gear carrier of the first gear set and (b) the ring gear of the first gear set, wherein the second motor/generator is electrically coupled to the first motor/generator by an electrical power transmission system, wherein the first motor/generator and the second motor/generator are electrically coupled without an energy storage device configured to at least one of (a) provide electrical energy to the first motor/generator or the second motor/generator to power the first motor/generator or the second motor/generator and (b) be charged by electrical energy from the first motor/generator or the second motor/generator;

an engine coupled to the ring gear of the first gear set and selectively coupled to the second motor/generator;

a first clutch configured to selectively engage the second motor/generator to the planetary gear carrier of the first gear set; and

a second clutch configured to selectively engage the second motor/generator to the engine.

2. The vehicle drive of claim 1 , wherein the first motor/generator generates all of the electrical energy required by the second motor/generator and the electrical energy required to offset power losses.

3. The vehicle drive of claim 2 , wherein the second motor/generator generates all of the electrical energy required by the first motor/generator and the electrical energy required to offset power losses.

4. The vehicle drive of claim 3 , wherein the second motor/generator generates the power required by the first motor/generator when a speed of the first motor/generator is less than a threshold speed.

5. The vehicle drive of claim 1 , wherein the first clutch and the second clutch are configured to couple the second motor/generator to the engine and the first gear set in more than one configuration.

6. The vehicle drive of claim 5 , wherein, in a first configuration, the second motor/generator is coupled to an output of the first planetary gear set, and wherein, in a second configuration, the second motor/generator is coupled to the engine.

7. The vehicle drive of claim 6 , wherein the configuration changes when the speed of the second motor/generator is greater than a first threshold speed.

8. The vehicle drive of claim 6 , wherein the configuration changes when the difference of the speed of the second motor/generator in the first configuration and the speed of the second motor/generator in the second configuration is greater than a second threshold speed.

9. The vehicle drive of claim 8 , wherein the second threshold speed is a function of a fixed speed and a percentage of a throttle input.

10. The vehicle drive of claim 6 , wherein the configuration changes when the difference of the speed of the second motor/generator in the first configuration and the speed of the second motor/generator in the second configuration is less than a third threshold speed.

11. A vehicle drive comprising:

a first gear set and a second gear set, wherein each gear set comprises a sun gear, a ring gear, and planetary gears, the planetary gears coupling the sun gear to the ring gear, wherein the planetary gears are rotatably supported by a planetary gear carrier;

a first motor/generator coupled to the first gear set;

a second motor/generator selectively coupled to at least one of (a) the planetary gear carrier of the first gear set and (b) the ring gear of the first gear set, wherein the second motor/generator is electrically coupled to the first motor/generator by an electrical power transmission system, wherein the first motor/generator and the second motor/generator are electrically coupled without an energy storage device configured to at least one of (a) provide electrical energy to the first motor/generator or the second motor/generator to power the first motor/generator or the second motor/generator and (b) be charged by electrical energy from the first motor/generator or the second motor/generator;

an engine coupled to the first gear set and selectively coupled to the second motor/generator;

a first clutch configured to selectively engage the second motor/generator to the planetary gear carrier of the first gear set;

a second clutch configured to selectively engage the second motor/generator to the engine; and

a controller of the vehicle comprising a processing circuit configured to:

operate the first clutch and the second clutch, wherein selectively engaging and disengaging the first clutch and the second clutch changes a configuration of the vehicle drive;

operate the engine at a calculated speed;

operate the first motor/generator at a calculated torque; and

operate the second motor/generator to maintain a voltage on the electrical power transmission system.

12. The vehicle drive of claim 11 , wherein operating the first clutch and the second clutch comprises:

measuring a plurality of inputs from the vehicle, wherein the inputs indicate an output power requested from the vehicle drive;

determining a desired configuration of the vehicle drive, wherein the vehicle drive in the desired configuration provides the output power requested; and

selectively engaging and disengaging the first clutch and the second clutch to configure the vehicle drive in the desired configuration.

13. The vehicle drive of claim 11 , wherein operating the engine at a calculated speed comprises:

determining a current configuration of the vehicle drive;

measuring current speeds of the vehicle, the engine, the first motor/generator, and the second motor/generator;

calculating a maximum power that can be provided at the current engine speed;

calculating a total power requested to be provided by a vehicle operator;

calculating a range of engine speeds that can provide the total power; and

operating the engine at an optimized speed, wherein the optimized speed is within the calculated range.

14. The vehicle drive of claim 11 , wherein operating the first motor/generator at the calculated torque comprises:

determining a current configuration of the vehicle drive;

measuring current speeds of the vehicle, the engine, the first motor/generator, and the second motor/generator;

calculating a total power requested to be provided;

calculating an electrical power from the motor/generators requested to be provided;

selecting the first motor/generator to provide the required torque to produce the electrical power;

calculating a torque that can provide the electrical power; and

operating the first motor/generator at the calculated torque.

15. The vehicle drive of claim 14 , wherein operating the second motor/generator comprises:

determining a current configuration of the transmission;

measuring current speeds of the vehicle, the engine, the first motor/generator, and the second motor/generator;

calculating a total power requested to be provided;

calculating an electrical power from the motor/generators requested to be provided;

selecting the second motor/generator to maintain a voltage on the electrical power transmission system between the second motor/generator and the first motor/generator; and

operating the second motor/generator to maintain the voltage on the electrical power transmission system.