GB2424458A

GB2424458A - A continuously variable transmission with a centrifugal clutch and a plate clutch

Info

Publication number: GB2424458A
Application number: GB0601138A
Authority: GB
Inventors: Chun-Hsien Wu; Chi-Nan Yeh
Original assignee: Sanyang Industry Co Ltd
Current assignee: Sanyang Industry Co Ltd
Priority date: 2005-03-25
Filing date: 2006-01-20
Publication date: 2006-09-27
Also published as: JP2006275288A; GB0601138D0; TW200633873A; ES2293817B1; ITMI20060243A1; DE102006002363A1; FR2883618A1; ES2293817A1; TWI265107B

Abstract

A transmission system comprises a belt type continuously variable transmission 23, a gearshift transmission 3 and a centrifugal clutch 6 mounted on a first end 221 of an output shaft 22 of the continuously variable transmission 2. A plate clutch 4 is mounted on a second end 222 of the output shaft 22 and is engaged to transfer rotary motion from the output shaft 22 to power output shaft 32 by a gearshift speed-change procedure. When engine speed reaches a certain level the centrifugal clutch 6 engages and power is transferred from the continuously variable transmission 2 to the gearshift transmission 3 and then to rear wheels 11 via the power output shaft 32. If a manual gear-change is required the plate clutch 4 is disengaged and gears in the gearshift transmission 3 are shifted by a gearlever which moves gears 351-354 or gears 361-364 to alter the gear ratio. In another embodiment the plate clutch 4 may be on the same end of the output shaft 22 as the centrifugal clutch 6.

Description

POWER TRANSMISSION SYSTEM

BACKGROUND OF THE INVENTION

I.Field of the Invention

The present invention relates to a power transmission system and more particularly, to a power transmission system specifically designed for use in a vehicle, for example, scooter or all-terrains vehicle.

2.Description of Related Art

Regular commercial vehicles include two types subject to their power transmission mechanisms, i.e., the continuously variable transmission and the gearshift transmission. The former is the so-called automatic transmission vehicle, and the later is the so-called manual trnasmission vehicle.

Due to the use of different transmission methods, the aforesaid two types of vehicles have the respective advantages and drawbacks. For example, a belt continuously variable transmission vehicle works smoothly when changing the speed, and is easy to operate without a special gearshift mechanism. Therefore, a belt continuously variable transmission vehicle is suitable for moving on regular planar roads. On the contrary, a gearshift transmission vehicle uses a gearshift mechanism to match with the action of the clutch. It can be changed to different gearshift positions, showing a high performance at low speed, medium speed as well high speed.

However, the advantages of the aforesaid belt continuously variable transmission are the drawbacks of the gearshift transmission. On the contrary, the drawbacks of the belt continuously variable transmission are the advantages of the gearshifi transmission. It is unable to make up one's mind as to which of the aforesaid two designs to choose. To a motorcyclist, it is unable to obtain a vehicle that fits different road conditions comfortably.

Therefore, conventional designs are still not satisfactory in function.

Further, the clutch of a conventional gearshift transmission is an integrated design. This integrated arrangement limits the installation space for the engine or other parts of the vehicle, not allowing for flexible mounting arrangement of parts.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstances in view. The power transmission system according to one embodiment of the present invention comprises a continuously variable transmission, a gearshift transmission, a centrifugal clutch, and a plate clutch. The continuously variable transmission comprises an input shaft coupled to a crankshaft of a vehicle engine to receive a rotary driving force from the vehicle engine, an output shaft, which has a first end and a second end, and a continuously variable transmission mechanism coupled between the input shaft and the output shaft for transferring the rotary driving force from the input shaft to the output shaft by means of a continuously variable transmission action.

The gearshift transmission comprises a power output shaft and a gearshift mechanism.

The centrifugal clutch is coaxially mounted on the first end of the output shaft of the continuously variable transmission and selectively coupled to the output shaft of said continuously variable transmission.

The plate clutch is coaxially mounted on the second end of the output shaft of the continuously variable transmission and coupled to the gearshift mechanism for transferring the rotary driving force from the output shaft of the continuously variable transmission to the power output shaft by the gearshift mechanism.

By means of the aforesaid stTucture, the rotary driving force of the vehicle engine can be simultaneously transferred through the continuously variable transmission when the gearshift transmission is at either one of the available gearshift positions, i.e., the rotary driving force of the vehicle engine is transferred through the continuously variable transmission and the gearshift transmission that match each other to fit the speed change of the vehicle engine. Therefore, the power transmission system fits all different road conditions and terrains that require a high or low torque or a high or low speed, i.e., the aforesaid structure provides both the function of the continuously variable transmission and the function of the gearshift transmission, enabling the performance of the vehicle engine to be fully carried out.

Further, because the centrifugal clutch and the plate clutch are separately arranged, there is a free space for selective arrangement of the parts of the vehicle engine and other parts of the vehicle.

The aforesaid continuously variable transmission mechanism of the continuously variable transmission can be a centrifugal type continuously variable transmission mechanism. Further, the continuously variable transmission mechanism comprises a drive face, a movable drive face, and a roller. The drive face and the movable drive face are respectively axially mounted on the input shaft. The roller is adapted to produce a centrifugal force to drive the movable drive face axially sliding along the input shaft upon rotation of the input shaft.

Further, the continuously variable transmission mechanism comprises a driven face, a movable driven face, and a driven face spring.

The driven face and the movable driven face are respectively axially mounted on the output shaft. The driven face spring is adapted to impart a spring force to the movable driven face to drive the movable driven face axially sliding along the output shaft.

The centrifugal clutch is coaxially mounted on the first end of the output shaft of the continuously variable transmission at the same side relative to the movable driven face. The plate clutch is coaxially mounted on the second end of the output shaft of the continuously variable transmission at the same side relative to the driven face.

Further, the gearshift mechanism comprises a first shaft and a second shaft. The first shaft is coaxially coupled to a rear end of the power output shaft. The first shaft has a plurality of first gears mounted thereon.

The second shaft has a plurality of second gears mounted thereon and selectively engageable to the first gears to form different gear ratios.

Further, the power output shaft is coupled to a vehicle rear wheel.

According to an alternate form of the present invention, the power transmission system comprises a continuously variable transmission, a gearshift transmission, a centrifugal clutch, and a plate clutch. The continuously variable transmission comprises an input shaft coupled to a crankshaft of a vehicle engine to receive a rotary driving force from the vehicle engine, an output shaft, which has a first end, and a continuously variable transmission mechanism coupled between the input shaft and the output shaft.

The gearshift transmission comprises a power output shaft and a gearshift mechanism. The centrifugal clutch is coaxially mounted on the first end of the output shaft of the continuously variable transmission.

The plate clutch is coaxially mounted on the first end of the output shaft of the continuously variable transmission adjacent to the centrifugal clutch.

The continuously variable transmission transfers the rotary driving force from the input shaft to the centrifugal clutch by a continuously variable transmission action. The centrifugal clutch is selectively coupled to the plate clutch, and the plate clutch is selectively coupled to the output shaft for enabling the gearshift mechanism to transfer the rotary driving force from the output shaft to the power output shaft by a gearshift position changing action.

This alternate form achieves the same various effects of the aforesaid first embodiment of the present invention. Further, because the plate clutch and the centrifugal clutch are arranged at the same side, a space is provided at one side of the gearshift transmission for the arrangement of the vehicle engine, i.e., there is a free space for selective arrangement of the parts of the vehicle engine and other parts of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a power transmission system according to the present jn\Tentjon FIG. 2 is a schematic drawing showing an idle- running status of the vehicle engine according to the present invention.

FIG. 3 is a schematic drawing showing the operation of the power transmission system according to the present invention.

FIG. 4 is a schematic drawing showing the gearshifting action of the power transmission system according to the present invention.

FIG. 5 is an engine speed-vs-vehicle speed curve obtained from the

present invention and the prior art design.

FIG 6 is a sectional view of a sectional view of an alternate form of the present invention.

FIG 7 is a schematic drawing showing the action of the plate clutch of the power transmission system shown in FIG. 6 (I).

FIG. 8 is a schematic drawing showing the action of the plate clutch of the power transmission system shown in FIG 6 (II).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG 1 and FIG 2, a vehicle engine 1 is shown comprising a crankshaft 12, a left cover 51, and a right cover 52. The left cover 51 and the right cover 52 are abutted against each other. The right cover 52 has an axle hole 53. The left cover 51 accommodates a continuously variable transmission 2 and a centrifugal clutch 6. The right cover 52 accommodates a gearshift transmission 3 and a plate clutch 4.

The continuously variable transmission 2 comprises an input shaft 21, an output shaft 22, and a continuously variable transmission mechanism 23. The output shaft 22 is axially mounted in the axle hole 53 of the aforesaid right cover 52. The input shaft 21 is coupled to the crankshaft 12 of the aforesaid vehicle engine I to receive a rotary driving force from the crankshaft 12. Further, the continuously variable transmission mechanism 23 is coupled between the input shaft 21 and the output shaft 22, and adapted to transfer inputted rotary driving force from the input shaft 21 to the output shaft 22 by means of a continuously variable transmission procedure.

According to this embodiment, the continuously variable transmission mechanism 23 is a centrifugal type continuously variable transmission mechanism, comprising a drive face 231, a movable drive face 232, a roller 233, a drive belt 230, a driven face 234, a movable driven face 235, and a driven face spring 236. The drive face 231 and the movable drive face 232 are respectively axially mounted on the input shaft 21.

During rotary motion of the input shaft 21, the roller 233 produces a centrifugal effect to drive the movable drive face 232 axially sliding along the input shaft 21.

Further, the driven face 234 and the movable driven face 235 of the continuously variable transmission mechanism 23 are respectively axially mounted on the output shaft 22, and the driven face spring 236 is adapted to drive the movable driven face 235 axially sliding long the output shaft 22.

Further, the drive belt 230 is mounted on the drive face 231, the movable drive face 232, the driven face 234 and the movable driven face 235, and adapted to transfer the inputted rotary driving force from the input shaft 21 to the output shaft 22 by a centrifugal continuously variable transmission way.

As stated above, the movable drive face 232 and the movable driven face 235 of the continuously variable transmission mechanism 23 are movable in axial direction by means of a centrifugal force, i.e., the drive belt 230 which is mounted on the drive face 231, the movable drive face 232, the driven face 234 and the movable driven face 235 will be forced to change the position in radial direction upon movement of the movable drive face 232 and the movable driven face 235, thereby causing a change of the radius ratio among the drive face 231, the movable drive face 232, the driven face 234 and the movable driven face 235 to achieve the desired continuously variable transmission function. For example, when at a relatively lower speed status, the drive belt 230 is supported on the drive face 231 and the movable drive face 232 at a relative lower position and close to the center, and at the same time the drive belt 230 is supported on the driven face 234 and the movable driven face 235 at a relatively higher position and close to their periphery, therefore a relatively greater radius ration is produced to form the low speed status, and vise versa.

Referring to FIG. 1 and FIG. 2 again, the gearshift transmission 3 comprises a power output shaft 32 and a gearshift mechanism 33. The power output shaft 32 is coupled to the vehicle's rear wheel 11. The gearshift mechanism 33 comprises a first shaft 35 and a second shaft 36.

The first shaft 35 is coaxially coupled to the rear end of the power output shaft 32. However, the first shaft 35 does not rotate with the power output shaft 32. Further, the first shaft 35 comprises five first gears 351--355. The second shaft 36 comprises five second gears 361-365. The second gears 361-365 are selectively engageable to the first gears 351-355 to form different gear ratios, i.e., the first gears 351-355 (or the second gears 361-365) can be moved axially subject to the control of a gearshifi lever (not shown) to change the engagement between the first gears 351-355 and the second gears 361-365, thereby achieving the desired change of gearshift position. The change of the gearshift position of the gearshift transmission 3 will be described further.

Further, the centrifugal clutch 6 is coaxially mounted on one end, namely, the first end 221 of the output shaft 22 of the continuously variable transmission 2, and selectively coupled to the output shaft 22 of the continuously variable transmission 2. The plate clutch 4 is coaxially mounted on the other end, namely, the second end 222 of the output shaft 22 of the continuously variable transmission 2, and coupled to the gearshift mechanism 33 for transferring the rotary driving force from the output shaft 22 of the continuously variable transmission 2 to the power output shaft 32 by a gearshift speed-change procedure.

According to this embodimeht, the centrifugal clutch 6 is coaxially mounted the first end 221 of the output shaft 22 of the continuously variable transmission 2, and the first end 221 of the output shaft 22 and the movable driven face 235 are disposed at the same side; the plate clutch 4 is coaxially mounted on the second end 222 of the output shaft 22 of the continuously variable transmission 2, and the second end 222 of the output shaft 22 and the driven face 234 are disposed at the same side. The movable driven face 235 and the driven face 234 may be reversed in position, therefore the centrifugal clutch 6 and the plate clutch 4 can also be reversed in position.

In the same manner, the movable driven face 235 and the driven face 234 can be made immovable, however the centrifugal clutch 6 can be set between the plate clutch 4 and the driven face 234.

The aforesaid plate clutch 4 comprises a clutch plate 41, a clutch friction disk 42, and a clutch cam plate 43. The clutch plate 41 can be pressed on the clutch friction disk 42. The clutch cam plate 43 is adapted to push the clutch plate 41 away from the clutch friction disk 42.

The aforesaid gearshift mechanism 33 further comprises an intermediate gear 34 engaged between the plate clutch 4 and one first gear 351.

Referring to FIG. 2 again, when the vehicle engine 1 is started, the input shaft 21 is at a low speed status, the centrifugal clutch 6 is in a separated position, and therefore the output power of the vehicle engine 1 is transferred by the continuously variable transmission 2 to the centrifugal clutch 6 and ended at the centrifugal clutch 6.

Referring to FIG. 3, when the revolving speed of the input shaft 21 is gradually increasing, i.e., the drive belt 230 is rotated the output shaft 22, and the revolving speed of the output shaft 22 is gradually increasing. When the speed reaches a certain level, the centrifugal clutch 6 starts to rotate due to the effect of a centrifugal force. At this time, the driving force that comes from the continuously variable transmission 2 is transferred through the centrifugal clutch 6 to the gearshift transmission 3 and then to the vehicle's rear wheel 11 via the power output shaft 32 to cause the vehicle to move.

Referring to FIG 4, when the speed of the vehicle is gradually increasing, the continuously variable transmission 2 carries out the designed continuously variable transmission function. When moving on a different land and when a change of the gearshift position is necessary, drive the clutch cam plate 43 to push the clutch plate 41 away from the clutch friction disk 42, thereafter operate the gearshift lever (not shown) to move one of the first gears 351-354 at the first shaft 35 or one of the second gears 361-364 at the second shaft 36 axially into engagement with an adjacent one of the first gears 351-354 or second gears 361-364, achieving the change of the desired gearshift position, for enabling the rotary driving force to be transferred through the power output shaft 32 to the vehicle's rear wheel 11 by means of the engagement between the second gear 365 at the second shaft 36 with the first gear 355 at the first shaft 35.

The gearshift position changing operation is outlined hereinafter. As stated above, the five first gears 351-355 at the first shaft 35 include four first gears 351-354 that are mounted on the first shaft 35 and one first gear 355 mounted on the rear end of the power output shaft 32. Further, the No. 3 first gear 353 of the first shaft 35 is axially movable along the first shaft 35 and rotatable with the first shaft 35; the No. 1 first gear 351 of the first shaft is meshed With the intermediate gear 34 and rotatable with the first shaft 35; the No. 2 first gear 352 and No. 4 first gear 354 of the first shaft 35 run idle; the No. 5 first gear 355 of the first shaft 35 is rotatable with the power output shaft 32; the No. 3 first gear 353 of the first shaft 35 is axially movable along the first shaft 35 and engageable to the No. 2 first gear 352 or No. 4 first gear 354 of the first shaft 35 for rotation with the No. 2 first gear 352 or No. 4 first gear 354 of the first shaft 35.

Similarly, the five second gears 361-365 at the second shaft 36 have the No. 1 second gear 361 and the No. 3 second gear 363 run idle; the No. 2 second gear 362 of the second shaft 36 is axially movable along the second shaft 36 and rotatable with the second shaft 36; the No. 2 second gear 362 of the second shaft 36 is axially movable along the second shaft 36 and connectable to the adjacent No. 1 second gear 361 and No. 3 second gear 363 for synchronous rotation; the No. 4 second gear 364 and No. 5 second gear 365 of the second shaft 36 are rotatable with the second shaft 36; the No. 5 second gear 365 of the second shaft 36 is meshed with the No. 5 first gear 355 of the first shaft 35 at the rear end of the power output shaft 32.

When changing the gearshift position, the user can operate the gearshift lever (not shown) to move the No. 3 first gear 353 of the first shaft 35 or the No. 2 second gear 362 of the second shaft 36 leflwards or rightwards. For example, when moved the No. 2 second gear 362 of the second shaft 36 leftwards into engagement with the No. 1 second gear 361 of the second shaft 36, and this is the first gearshift position that allows the rotary driving force to be transferred in proper order through the intermediate gear 34, the No. 1 first gear 351 of the first shaft 35, the No. I second gear 361 of the second shaft 36, the No. 5 second gear 365 of the second shaft 36, and the No. 5 first gear 355 of the first shaft 35; when moved the No. 3 first gear 353 of the first shaft 35 rightwards into engagement with the adjacent No. 4 first gear 354 of the first shaft 35, and this is the second gearshift position that allows the rotary driving force to be transferred in proper order through the intermediate gear 34, the No. 1 first gear 351 of the first shaft 35, the No. 4 first gear 354 of the first shaft 35, the No. 4 second gear 364 of the second shaft 36, the No. 5 second gear 365 of the second shaft 36, and the No. 5 first gear 355 of the first shaft 35; when moved the No. 3 first gear 353 of the first shaft 35 leftwards into engagement with the adjacent No. 2 first gear 352 of the first shaft 35, and this is the third gearshift position that allows the rotary driving force to be transferred in proper order through the intermediate gear 34, the No. 1 first gear 351 of the first shaft 35, the No. 2 first gear 352 of the first shaft 35, the No. 2 second gear 362 of the second shaft 36, the No. 5 second gear 365 of the second shaft 36, and the No. 5 first gear 355 of the first shaft 35; when moved the No. 2 second gear 362 of the second shaft 36 rightwards into engagement with the adjacent No. 3 second gear 363 of the second shaft 36, and this is the fourth gearshift position that allows the rotary driving force to be transferred in proper order through the intermediate gear 34, the No. 1 first gear 351 of the first shaft 35, theNo. 3 first gear 353 of the first shaft 35, the No. 3 second gear 363 of the second shaft 36, the No. 5 second gear 365 of the second shaft 36, and the No. 5 first gear 355 of the first shaft 35.

As indicated above, by means of the aforesaid structure, the invention achieves gearshift position change. Further, when changing the gearshift position, the clutch cam plate 43 can be driven to push the clutch plate 41 away from the clutch friction disk 42 to interrupt the transfer of the rotary driving force temporarily, and the clutch cam plate 43 is released to have the clutch plate 41 be returned and pressed on the clutch friction disk 42 for transmission of the rotary driving force after change of the gearshifi position.

Referring to FIG. 5 and FIG. 1FIG 4 again, when the gearshift transmission 3 is at either one of the aforesaid gearshift positions, the rotary driving force of the vehicle engine 1 can be simultaneously transferred through the continuously variable transmission 2, i.e., the rotary driving force of the vehicle engine 1 is transferred through the continuously variable transmission 2 and the gearshift transmission 3 that match each other to fit the speed change of the vehicle engine 1. Therefore, the power transmission system fits all different road conditions and terrains that require a high or low torque or a high or low speed, i.e., the aforesaid structure provides both the function of the continuously variable transmission 2 and the function of the gearshift transmission 3, enabling the performance of the vehicle engine 1 to be fully carried out.

Further, because the centrifugal clutch 6 and the plate clutch 4 are separately arranged, there is a free space for selective arrangement of the parts of the vehicle engine 1 and other parts of the vehicle.

FIG 6-FIG 8 show an alternate form of the present invention. This embodiment is substantially to the aforesaid first embodiment with the exception that the plate clutch 71 and the centrifugal clutch 72 are arranged at the same side. During operation, the continuously variable transmission 73 transfers the rotary driving force from the input shaft 74 to the centrifugal clutch 72 through a continuously variable transmission action.

Thereafter, when the centrifugal clutch 72 reached a speed level, the centrifugal clutch 72 is coupled to the plate clutch 71, and the plate clutch 71 is coupled to the output shaft 75, enabling the gearshift transmission mechanism 76 to transfer the rotarydriving force from the output shaft 75 of the continuously variable transmission 73 to the power output shaft 77 by means of a gearshifting action, i.e., the output shaft 75 is rotated with the plate clutch 71. When changing the gearshift position, it simply needs to act the clutch plate 78 upon the plate clutch 71.

Therefore, this alternate form achieves the same various effects of the aforesaid first embodiment of the present invention. Further, because the plate clutch 71 and the centrifugal clutch 72 are arranged at the same side, a space is provided at one side of the gearshift transmission 79 for the arrangement of the vehicle engine, i.e., there is a free space for selective arrangement of the parts of the vehicle engine and other parts of the vehicle.

Although the present invention has been explained in relation to its preferred embodiments, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.

Claims

WHAT IS CLAIMED IS: 1. A power transmission system comprising: a

continuously variable transmission, said continuously variable transmission comprising an input shaft coupled to a crankshaft of a vehicle engine to receive a rotary driving force from said vehicle engine, an output shaft, said output shaft having a first end and a second end, and a continuously variable transmission mechanism coupled between said input shaft and said output shaft for transferring said rotary driving force from said input shaft to said output shaft by means of a continuously variable transmission action; a gearshift transmission, said gearshift transmission comprising a power output shaft and a gearshifi mechanism; a centrifugal clutch coaxially mounted on the first end of said output shaft of said continuously variable transmission and selectively coupled to said output shaft of said continuously variable transmission; and a plate clutch coaxially mounted on the second end of said output shaft of said continuously variable transmission and coupled to said gearshift mechanism for transferring said rotary driving force from said output shaft of said continuously variable transmission to said power output shaft by said gearshift mechanism.
2. The power transmission system as claimed in claim 1, wherein the continuously variable transmission mechanism of said continuously variable transmission is a centrifugal type continuously variable transmission mechanism.
3. The power transmission system as claimed in claim 2, wherein said continuously variable transmission mechanism comprises a drive face, a movable drive face, and a roller, said drive face and said movable drive face being respectively axially mounted on said input shaft, said roller being adapted to produce a centrifugal force to drive said movable drive face axially sliding along said input shaft upon rotation of said input shaft.
4. The power transmission system as claimed in claim 2, wherein said continuously variable transmission mechanism comprises a driven face, a movable driven face, and a driven face spring, said driven face and said movable driven face being respectively axially mounted on said output shaft, said driven face spring being adapted to impart a spring force to said movable driven face to drive said movable driven face axially sliding along said output shaft.
5. The power transmission system as claimed in claim 4, wherein said centrifugal clutch is coaxially mounted on the first end of said output shaft of said continuously variable transmission at the same side relative to said movable driven face.
6. The power transmission system as claimed in claim 4, wherein said plate clutch is coaxially mounted on the second end of said output shaft of said continuously variable transmission at the same side relative to said driven face.
7. The power transmission ystem as claimed in claim 1, wherein said gearshift mechanism comprises a first shaft and a second shaft, said first shaft being coaxially coupled to a rear end of said power output shaft, said first shaft having a plurality of first gears mounted thereon, said second shaft having a plurality of second gears mounted thereon and selectively engageable to said first gears to form different gear ratios.
8. The power transmission system as claimed in claim 1, wherein said power output shaft is coupled to a vehicle rear wheel.
9. A power transmission system comprising: a continuously variable transmission, said continuously variable transmission comprising an input shaft coupled to a crankshaft of a vehicle engine to receive a rotary driving force from said vehicle engine, an output shaft, said output shaft having a first end, and a continuously variable transmission mechanism coupled between said input shaft and said output shaft; a gearshift transmission, said gearshift transmission comprising a power output shaft and a gearshifi mechanism; a centrifugal clutch coaxially mounted on the first end of said output shaft of said continuously variable transmission; and a plate clutch coaxially mounted on the first end of the output shaft of said continuously variable transmission adjacent to said centrifugal clutch; wherein said continuously variable transmission transfers said rotary driving force from said input shaft to said centrifugal clutch by a continuously variable transmission action; said centrifugal clutch is selectively coupled to said plate clutch, and said plate clutch is selectively coupled to said output shaft for enabling said gearshift mechanism to transfer said rotary driving force from said output shaft to said power output shaft by a gearshift position changing action.
10. The power transmission system as claimed in claim 9, wherein the continuously variable transmission mechanism of said continuously variable transmission is a centrifugal type continuously variable transmission mechanism.
11. The power transmission system as claimed in claim 10, wherein said continuously variable transmission mechanism comprises a drive face, a movable drive face, and a roller, said drive face and said movable drive face being respectively axially mounted on said input shaft, said roller being adapted to produce a centrifugal force to drive said movable drive face axially sliding along said input shaft upon rotation of said input shaft.
12. The power transmission system as claimed in claim 10, wherein said continuously variable transmission mechanism comprises a driven face, a movable driven face, and a driven face spring, said driven face and said movable driven face being respectively axially mounted on said output shaft, said driven face spring being adapted to impart a spring force to said movable driven face to drive said movable driven face axially sliding along said output shaft.
13. The power transmission system as claimed in claim 12, wherein said centrifi.igal clutch is coaxially mounted on the first end of said output shaft of said continuously variable transmission at the same side relative to said movable driven face.
14. The power transmission system as claimed in claim 12, wherein said plate clutch is coaxially mounted on the first end of said output shaft of said continuously variable transmission at the same side relative to said movable driven face.
15. The power transmission system as claimed in claim 9, wherein said power output shaft is coupled to a vehicle rear wheel.

1 6. A power transmission system substantially as described herein with reference to and as illustrated in the accompanying drawings.