TANDEM ELECTRIC MOTOR VEHICLE DRIVE SYSTEM

1 . A vehicle drive system comprising:

a first electric motor including a first motor housing and a first motor shaft;

a second electric motor including a second motor housing and a second motor shaft; and

a gear system operatively connecting the first motor shaft and the second motor shaft, the gear system being configured and disposed to transmit torque from the first motor shaft to the second motor shaft to form a tandem electric motor drive system.

2 . The vehicle drive system according to claim 1 , wherein the gear system includes a first gear coupled to the first motor shaft and a second gear coupled to the second motor shaft, the first gear being axially off-set from the second gear.

3 . The vehicle drive system according to claim 2 , further comprising: a clutch member operatively connected to one of the first and second motor shafts, the clutch member being selectively activated to disengage the first motor shaft from the second motor shaft.

4 . The vehicle drive system according to claim 1 , wherein the gear system includes a planetary gear set.

5 . The vehicle drive system according to claim 1 , wherein the first motor shaft extends along a first axis and the second motor shaft extends along a second axis, the first axis being substantially identical to the second axis such that the first electric machine is axially aligned with the second electric machine

6 . The vehicle drive system according to claim 1 , wherein the gear system includes at least one idler shaft having mounted thereto a plurality of gears, the plurality of gears operatively connecting the first and second motor shafts.

7 . The vehicle drive system according to claim 1 , wherein the gear system comprises a transmission having multiple gear ratios.

8 . The vehicle drive system according to claim 7 , wherein the transmission includes a first gear and a second gear operatively connected to the first motor shaft, and a third gear and a fourth gear operatively connected to the second motor shaft, one of the first and second gears being operatively connected to one of the third and fourth gears.

9 . The vehicle drive system according to claim 1 , further comprising: a controller operatively connected to the first and second electric motors, the controller establishing a desired operational torque for each of the first and second electric motors.

10 . The vehicle drive system according to claim 9 , further comprising:

a first motor controller operatively coupled between the controller and the first electric motor; and

a second motor controller operatively coupled between the controller and the second electric motor.

11 . The vehicle drive system according to claim 1 , further comprising: a gear housing surrounding the gear system.

12 . The vehicle drive system according to claim 11 , wherein the gear housing joins the first motor housing and the second motor housing.

13 . A method of operating a tandem electric motor vehicle drive system, the method comprising:

activating a first electric motor having a first motor shaft; and

activating a second electric motor having a second motor shaft operatively connected to the first motor shaft through a gear system, output from the second electric motor adding to output from the first electric motor to provide a motive force to a vehicle.

14 . The method of claim 13 , further comprising: selectively activating a clutch connected to one of the first and second motor shafts to operatively disconnect the first electric motor and the second electric motor.

15 . The method of claim 13 , wherein activating the first electric motor comprises operating the first electric motor at a first parameter, and activating the second electric motor comprises operating the second electric motor at a second parameter.

16 . The method of claim 15 , further comprising: matching the first and second parameters.

17 . The method of claim 15 , further comprising: varying one of the first and second parameters from another of the first and second parameters.

18 . The method of claim 15 , wherein operating the first electric motor at the first parameter comprises establishing at least one of a first operational speed and a first output torque for the first electric motor and operating the second electric motor at the second parameter comprises establishing at least one of a second operational speed and a second output torque for the second electric motor.

19 . The method of claim 13 , further comprising: maintaining a fixed gear ratio between the first and second electric motors.

20 . The method of claim 13 , further comprising: varying a gear ratio between the first and second electric motors.