Power transmission apparatus for an electric vehicle

1. A power transmission apparatus for an electric vehicle including a motor as a power source, the power transmission apparatus comprising:

a compound planetary gear set formed as a combination of first and second planetary gear sets sharing a sun gear and a plurality of first pinion gears;

a first brake selectively connecting a first ring gear of the first planetary gear set to a transmission housing; and

a second brake selectively connecting the shared sun gear of the first and second planetary gear sets to the transmission housing,

wherein a second ring gear of the second planetary gear set is fixedly connected to a rotor of the motor and configured to continuously receive a torque of the motor, and

wherein the power transmission apparatus outputs a shifted torque through a planet carrier rotatably supporting the plurality of first pinion gears and a plurality of second pinion gears of the first planetary gear set.

2. The power transmission apparatus of claim 1 , wherein:

the first planetary gear set is a double pinion planetary gear set including the shared sun gear and the plurality of first pinion gears shared with the second planetary gear set, a plurality of second pinion gears, and the first ring gear; and

the second planetary gear set is a single pinion planetary gear set including the shared sun gear and the plurality of first pinion gears shared with the first planetary gear set, and the second ring gear.

3. The power transmission apparatus of claim 2 , wherein:

the plurality of first pinion gears are externally engaged with the shared sun gear;

each of the plurality of second pinion gears is externally engaged with two adjacent first pinion gears among the plurality of first pinion gears;

the planet carrier rotatably supports the plurality of first pinion gears and the plurality of second pinion gears; and

the plurality of second pinion gears are internally engaged with the first ring gear.

4. The power transmission apparatus of claim 3 , wherein the plurality of first pinion gears are internally engaged with the second ring gear of the second planetary gear set.

5. The power transmission apparatus of claim 4 , wherein the plurality of first pinion gears are formed as three first pinion gears, and the plurality of second pinion gears are formed as three second pinion gears.

6. The power transmission apparatus of claim 4 , wherein the plurality of first pinion gears are formed as four first pinion gears, and the plurality of second pinion gears are formed as four second pinion gears.

7. The power transmission apparatus of claim 4 , wherein the plurality of first pinion gears are formed as five first pinion gears, and the plurality of second pinion gears are formed as five second pinion gears.

8. The power transmission apparatus of claim 4 , wherein the plurality of first pinion gears are formed as six first pinion gears, and the plurality of second pinion gears are formed as six second pinion gears.

9. The power transmission apparatus of claim 4 , wherein an exterior circumference of the second ring gear is fixedly connected to the rotor of the motor.

10. The power transmission apparatus of claim 3 , wherein the planet carrier is fixedly connected to an output gear.

11. A power transmission apparatus for an electric vehicle including a motor as a power source, the power transmission apparatus comprising:

a first planetary gear set formed as a double pinion planetary gear set including a sun gear, a plurality of first pinion gears externally engaged with the sun gear, a plurality of second pinion gears externally engaged with the plurality of first pinion gears, each of the second pinion gears being externally engaged with two first pinion gears among the plurality of first pinion gears and disposed angularly both sides, a planet carrier rotatably supporting the plurality of first pinion gears and the plurality of second pinion gears, and a first ring gear internally engaged with the plurality of second pinion gears;

a second planetary gear set formed as a single pinion planetary gear set including the sun gear shared with the first planetary gear set, the plurality of first pinion gears shared with the first planetary gear set, the planet carrier shared with the first planetary gear set, and a second ring gear internally engaged with the plurality of first pinion gears and fixedly connected to a rotor of the motor;

a first brake selectively connecting a first ring gear of the first planetary gear set to a transmission housing; and

a second brake selectively connecting the shared sun gear of the first and second planetary gear sets to the transmission housing,

wherein the first and second planetary gear sets are combined to form a compound planetary gear set, and

wherein the power transmission apparatus outputs a torque through the planet carrier.

12. The power transmission apparatus of claim 11 , wherein the plurality of first pinion gears are formed as three first pinion gears, and the plurality of second pinion gears are formed as three second pinion gears.

13. The power transmission apparatus of claim 11 , wherein the plurality of first pinion gears are formed as four first pinion gears, and the plurality of second pinion gears are formed as four second pinion gears.

14. The power transmission apparatus of claim 11 , wherein the plurality of first pinion gears are formed as five first pinion gears, and the plurality of second pinion gears are formed as five second pinion gears.

15. The power transmission apparatus of claim 11 , wherein the plurality of first pinion gears are formed as six first pinion gears, and the plurality of second pinion gears are formed as six second pinion gears.

16. The power transmission apparatus of claim 11 , wherein an exterior circumference of the second ring gear is fixedly connected to the rotor of the motor.

17. The power transmission apparatus of claim 11 , wherein the planet carrier is fixedly connected to an output gear.