Power transmission device and vehicle including the same
A power train for a vehicle, the power train includes: a motor including a rotatable shaft; a reducer coupled to the motor; a gear train disposed at least partially inside the reducer, to transmit rotational force generated by the motor; and a wheel rotatable by receiving power from the reducer or by transmitting power generated by its rotation to the reducer, wherein the gear train is configured to transmit power from the motor to the reducer or to transmit power from the reducer to the motor based upon comparison of a rotational angular velocity of the rotatable shaft and a rotational angular velocity of the reducer.
1. A power train for a vehicle, the power train comprising:
a motor including a rotatable shaft;
a reducer selectively coupled to the rotatable shaft;
a gear train disposed at least partially inside the reducer to transmit rotational force generated by the motor; and
a wheel rotatable by receiving power from the reducer or by transmitting power generated by its rotation to the reducer,
wherein:
when a rotational angular velocity of the rotational shaft is greater than a rotational angular velocity of the reducer, the gear train is configured to transmit power from the motor to the reducer; and
when a rotational angular velocity of the reducer is greater than a rotational angular velocity of the rotational shaft, the gear train is configured to transmit power from the rotation of the wheel to the motor through the reducer.
2. The power train according to claim 1 , wherein the reducer comprises:
a sun gear engageable with the rotatable shaft of the motor;
a plurality of planetary gears engageable the outside of the sun gear; and
a carrier engageable with the planetary gears and revolvable with an orbital motion of the planetary gears about the sun gear, and
the gear train comprises:
a first unidirectional clutch between the rotatable shaft of the motor and the sun gear; and
a second unidirectional clutch between the rotatable shaft of the motor and the carrier.
3. The power train according to claim 2 , wherein when the rotational angular velocity of the rotatable shaft of the motor is higher than the rotational angular velocity of the carrier, the first unidirectional clutch is configured to transmit power generated by rotation of the rotatable shaft of the motor to the sun gear.
4. The power train according to claim 3 , wherein when the rotational angular velocity of the rotatable shaft of the motor is higher than the rotational angular velocity of the carrier, the second unidirectional clutch is configured to interrupt power transmission between the motor and the carrier.
5. The power train according to claim 2 , wherein when the rotational angular velocity of the carrier is higher than the rotational angular velocity of the rotatable shaft of the motor, the first unidirectional clutch is configured to interrupt power transmission between the sun gear and the motor.
6. The power train according to claim 5 , wherein when the rotational angular velocity of the carrier is higher than the rotational angular velocity of the rotatable shaft of the motor, the second unidirectional clutch is configured to transmit power generated by rotation of the carrier to the rotatable shaft of the motor.
7. The power train according to claim 2 , wherein the first unidirectional clutch and the second unidirectional clutch are spaced apart from each other in an axial direction of the power train.
8. The power train according to claim 2 , wherein the first unidirectional clutch and the second unidirectional clutch are spaced apart from each other in a radial direction of the power train.
9. The power train according to claim 7 , wherein the second unidirectional clutch symmetrically faces a wheel-facing side of the first unidirectional clutch in the axial direction.
10. The power train according to claim 9 , wherein the first unidirectional clutch and the second unidirectional clutch have substantially the same outer diameter.
11. The power train according to claim 8 , wherein an outer diameter of the first unidirectional clutch is larger than an outer diameter of the second unidirectional clutch.
12. The power train according to claim 9 , wherein the power train comprises a power transmission device, the gear train comprises a power transmission unit, and the carrier comprises:
a carrier body forming at least part of the carrier; and
a carrier head coupled to a side of the carrier body, and having an outer diameter smaller than that of the carrier body,
the first unidirectional clutch at least partially disposed in the carrier body, and
the second unidirectional clutch at least partially disposed in the carrier head.