Power transmission apparatus for a vehicle

1. A power transmission apparatus for a vehicle, the power transmission apparatus comprising:

an engine output shaft to which a torque of an engine is transferred;

a first transmission shifting the torque input from the engine output shaft to two shift stages and outputting the torque shifted to the two shift stages to a central output shaft; and

a second transmission shifting the torque input from the central output shaft through two input paths to multiple shift stages and outputting the torque shifted to the multiple shift stages,

wherein the second transmission includes:

a first input shaft disposed on the same shaft line as that of the central output shaft, selectively connected to the central output shaft through a first clutch, and including one drive gear fixedly connected thereto and two drive gears selectively synchronously connected thereto through a first synchronizer;

a second input shaft disposed on an outer circumference of the first input shaft so as to overlap the first input shaft without rotation interference, selectively connected to the central output shaft through a second clutch, and including a central drive gear fixedly connected thereto;

a third input shaft disposed in parallel with the first and second input shafts wherein the third input shaft is spaced apart from the first and second input shafts by predetermined intervals and including a central driven gear fixedly connected thereto and two drive gears selectively synchronously connected thereto through a second synchronizer;

an idle shaft disposed in parallel with the first and second input shafts wherein the idle shaft is spaced apart from the first and second input shafts by predetermined intervals and including an idle gear transferring a torque of the second input shaft to the third input shaft and a reverse drive gear selectively synchronously connected thereto through a third synchronizer; and

an output shaft disposed in parallel with the first and third input shafts and the idle shaft between the first and third input shafts and the idle shaft and including four driven gears externally connected, respectively, to the respective drive gears configured on the first and third input shafts and the idle shaft and an output gear transferring the shifted torque to a final reduction differential.

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

the first transmission includes a single pinion planetary gear set outputting the torque of the engine as two shift stages including a torque reduced as compared with the torque of the engine and the same torque as the torque of the engine.

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

the single pinion planetary gear set includes a sun gear fixedly connected to the engine output shaft and selectively connected to a planetary carrier through a first engine clutch, the planetary carrier fixedly connected to the central output shaft, and a ring gear selectively connected to a transmission housing through a first brake.

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

the first transmission includes a single pinion planetary gear set outputting the torque of the engine as two shift stages including the same torque as the torque of the engine and including a torque increased as compared with the torque of the engine.

5. The power transmission apparatus of claim 4 , wherein:

the single pinion planetary gear set includes a sun gear fixedly connected to the central output shaft, a planetary carrier fixedly connected to the engine output shaft and selectively connected to the sun gear through a first engine clutch, and a ring gear selectively connected to a transmission housing through a first brake.

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

the first input shaft has a 1-speed drive gear fixedly connected to a distal end portion of a portion thereof penetrating through the second input shaft, and has a 3/7-speed drive gear and a 5/9-speed drive gear disposed between the 1-speed drive gear and the second input shaft and selectively synchronously connected thereto by the first synchronizer.

7. The power transmission apparatus of claim 6 , wherein:

the second input shaft has the central drive gear connected integrally therewith at a distal end portion thereof to be externally gear-meshed with the idle gear on the idle shaft.

8. The power transmission apparatus of claim 7 , wherein:

the third input shaft has the central driven gear fixedly connected to a front end portion thereof, and has a 2/6-speed drive gear and a 4/8-speed drive gear disposed behind the central driven gear and selectively synchronously connected thereto by the second synchronizer.

9. The power transmission apparatus of claim 8 , wherein:

the idle shaft has the idle gear fixedly connected to a front end portion thereof to be externally gear-meshed to the central drive gear of the second input shaft and the central driven gear of the third input shaft, and has the reverse drive gear disposed behind the idle gear and selectively synchronously connected to the idle shaft by the third synchronizer.

10. The power transmission apparatus of claim 9 , wherein:

the output shaft has a 1-speed driven gear, a 2/3/6/7-speed driven gear, a reverse driven gear, a 4/5/8/9-speed driven gear, and the output gear disposed thereon,

the 1-speed driven gear is externally gear-meshed to the 1-speed drive gear of the first input shaft and is connected to the output shaft through a one-way clutch,

the 2/3/6/7-speed driven gear is fixedly connected to the output shaft to be externally gear-meshed to the 3/7-speed drive gear and the 2/6-speed drive gear,

the reverse driven gear is fixedly connected to the output shaft to be externally gear-meshed to the reverse drive gear,

the 4/5/8/9-speed driven gear is fixedly connected to the output shaft to be externally gear-meshed to the 5/9-speed drive gear and the 4/8-speed drive gear, and

the output gear is fixedly connected to a front end portion of the output shaft to be externally gear-meshed to a final reduction gear of the final reduction differential.

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

the first transmission further includes a motor/generator which is fixedly connected to the planetary carrier.

12. The power transmission apparatus of claim 5 , wherein:

the first transmission further includes a motor/generator which is fixedly connected to the sun gear.

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

the first transmission further includes a motor/generator which is fixedly connected to the engine output shaft, and a second engine clutch is disposed on the engine output shaft between the motor/generator and the engine.