Vehicle drive and method with electromechanical variable transmission

1. A vehicle drive comprising:

a gear set comprising 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 gear set;

a second motor/generator selectively coupled to at least one of (a) the planetary gear carrier of the gear set and (b) the ring gear of the 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 gear set and selectively coupled to the second motor/generator;

a 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 clutch is configured to couple the second motor/generator to the engine and thereby change a configuration of the vehicle drive.

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

a second motor/generator selectively coupled to at least one of (a) the planetary gear carrier of the gear set and (b) the ring gear of the 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 gear set and selectively coupled to the second motor/generator; and

a controller including a processing circuit configured to:

operate the engine at a calculated speed;

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

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

12. The vehicle drive of claim 11 , further comprising a clutch configured to selectively engage the second motor/generator to the engine, wherein the controller is configured to operate the clutch, wherein selectively engaging and disengaging the clutch changes a configuration of the vehicle drive.

13. The vehicle drive of claim 12 , wherein operating the engine at the 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 12 , wherein operating one of the first motor/generator and the second 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 one of the first motor/generator and the second motor/generator to provide a required torque to produce the electrical power;

calculating the required torque for providing the electrical power; and

operating the selected motor/generator at the required torque.

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

determining the current configuration of the vehicle drive;

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

calculating the total power requested to be provided;

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

selecting the other of the first motor/generator and 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 selected motor/generator to maintain the voltage on the electrical power transmission system.

16. The vehicle drive of claim 14 , wherein calculating the total power requested to be provided comprises:

calculating a maximum power deliverable to the vehicle drive at a current vehicle speed;

measuring a proportion of throttle input of the vehicle drive; and

calculating the total power requested to be provided by multiplying the maximum power deliverable and the proportion of throttle input.

17. The vehicle drive of claim 14 , wherein calculating the electrical power from the motor/generators requested to be provided comprises:

calculating a ratio of the electrical power from the motor/generators to the total power, wherein the ratio is a function of engine speed and vehicle speed; and

calculating the electrical power from the motor/generators by multiplying the ratio and the total power requested to be provided.

18. The vehicle drive of claim 12 , wherein operating the clutch comprises:

measuring a plurality of inputs from the vehicle, wherein the plurality of 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 clutch to configure the vehicle drive in the desired configuration.