Gear system

1. A gear system comprising:

a sun gear configured to be rotatable by a motor;

a ring gear disposed around a circumference of the sun gear;

a planetary gear configured to engage the sun gear and the ring gear and to rotate and revolve around the sun gear and within the ring gear;

a carrier coupled to the planetary gear and being configured to be rotated by the revolving planetary gear;

an output shaft comprising a hollow portion, the output shaft being selectively engaged with the carrier such that the output shaft is configured to rotate in accordance with the rotation of the carrier when the output shaft is engaged with the carrier, the output shaft including a circumferential outer surface facing an inner surface of the carrier over a specific range in an axial direction;

a first lubrication passage formed radially at a first point on the carrier within the specific range;

a second lubrication passage formed radially at a second point on the output shaft within the specific range; and

a third lubrication passage defined by a space between the outer surface of the output shaft and the inner surface of the carrier and configured to connect the first lubrication passage and the second lubrication passage;

wherein the third lubrication passage extends circumferentially around the outer surface of the output shaft over an angle of 360°, and

wherein the first point is coincident with the second point in the axial direction.

2. The gear system of claim 1 , wherein:

the first lubrication passage comprises three lubrication passages circumferentially spaced apart from each other at intervals of 120°, and

the second lubrication passage comprises three lubrication passages circumferentially spaced apart from each other at intervals of 120°.

3. The gear system of claim 2 , wherein the third lubrication passage extends along the circumferential boundary over an angle of at least 120°.

4. The gear system of claim 1 , wherein:

the hollow portion of the output shaft is connected to the second lubrication passage, and

the second lubrication passage extends radially from the hollow portion at the second point.

5. The gear system of claim 4 , wherein oil is introduced into the hollow portion by gear churning.

6. The gear system of claim 1 , wherein the carrier comprises a carrier plate provided at an end of the carrier disposed adjacent to the output shaft, the carrier plate being configured to cover a surface of the planetary gear disposed adjacent to the output shaft, and wherein the first point is on the carrier plate.

7. The gear system of claim 6 , wherein the carrier further comprises an inlet passage that axially extends from a radially outer end portion of the first lubrication passage to guide oil into an inner space of the carrier in which the planetary gear is located.

8. The gear system of claim 1 , wherein the second point is positioned at an end of the output shaft facing the carrier.

9. The gear system of claim 8 , wherein the hollow portion further comprises oil branch points configured to allow oil to flow into a needle roller bearing, a synchronizer, and a ball bearing, the branch points being sequentially arranged along the output shaft in a direction from the second point to an oil inlet.

10. The gear system of claim 1 , wherein an axial width of the third lubrication passage is greater than an axial width of the first lubrication passage and an axial width of the second lubrication passage.

11. The gear system of claim 1 , wherein a cross-sectional area of the third lubrication passage is greater than a cross-sectional area of the first lubrication passage and a cross-sectional area of the second lubrication passage.

12. The gear system of claim 1 , further comprising:

a rotor configured to rotate the sun gear, wherein:

when the gear system is in a driving mode, the carrier is engaged with the output shaft, and

when the gear system is in at least one of a neutral mode or a parking mode, the carrier in not engaged with the output shaft.

13. A gear system comprising:

a sun gear configured to be rotatable by a motor;

a ring gear disposed around a circumference of the sun gear;

a planetary gear configured to engage the sun gear and the ring gear and to rotate and revolve around the sun gear and within the ring gear;

a carrier coupled to the planetary gear and being configured to be rotated by the revolving planetary gear;

an output shaft comprising a hollow portion, the output shaft being selectively engaged with the carrier such that the output shaft is configured to rotate in accordance with the rotation of the carrier when the output shaft is engaged with the carrier, the output shaft including a circumferential outer surface facing an inner surface of the carrier over a specific range in an axial direction;

a first lubrication passage formed radially at a first point on the carrier within the specific range;

a second lubrication passage formed radially at a second point on the output shaft within the specific range; and

a third lubrication passage formed between the outer surface of the output shaft and the inner surface of the carrier and configured to connect the first lubrication passage and the second lubrication passage,

wherein the second point is positioned at an end of the output shaft facing the carrier.

14. The gear system of claim 13 , wherein the hollow portion further comprises oil branch points configured to allow oil to flow into a needle roller bearing, a synchronizer, and a ball bearing, the branch points being sequentially arranged along the output shaft in a direction from the second point to an oil inlet.