CN112360588A

CN112360588A - Pressure reducing structure of motorcycle engine

Info

Publication number: CN112360588A
Application number: CN202011225739.4A
Authority: CN
Inventors: 郑林; 张立成; 程雪君; 郑海刚; 颜阳益
Original assignee: Zhejiang Qianjiang Motorcycle Co Ltd
Current assignee: Zhejiang Qianjiang Motorcycle Co Ltd
Priority date: 2020-11-05
Filing date: 2020-11-05
Publication date: 2021-02-12

Abstract

The invention provides a decompression structure of a motorcycle engine, and belongs to the technical field of motorcycles. The decompression structure solves the problem that decompression failure can occur in the decompression structure of the existing motorcycle engine. This motorcycle engine's decompression structure includes the decompression round pin and is used for driving decompression round pin pivoted and gets rid of the piece, the one end of getting rid of the piece articulates on the camshaft just get rid of the piece and can radially throw away along the camshaft under the effect of centrifugal force, it is connected with the elastic component that is used for ordering about to get rid of the piece and carries out the reseing to get rid of on the piece to get rid of, the supporting seat has still linked firmly the supporting seat on the camshaft, the supporting seat is located the both sides of getting rid of the piece respectively with exhaust cam, the supporting seat makes to get rid of the piece and obtains the location along the axial position of camshaft with exhaust cam combined action, be equipped with interior spacing portion on the supporting seat, it leans on including spacing portion to lean on under the effect of elastic component to get rid of the piece, still be. The invention effectively avoids the possibility of decompression failure.

Description

Pressure reducing structure of motorcycle engine

Technical Field

The invention belongs to the technical field of motorcycles, and relates to a decompression structure of a motorcycle engine.

Background

When the motorcycle engine is started, new gas needs to be sucked for compression, great compression resistance is generated near the compression end point, and at the moment, if decompression is not performed, the starting force is increased, and starting is very difficult, so that decompression needs to be performed by adopting a decompression structure to ensure that the engine is started smoothly.

The decompression structure is usually arranged on a camshaft, for example, an engine camshaft decompression valve (application number: CN201921559477.8) disclosed in Chinese patent document, which comprises a camshaft body, wherein an air inlet cam and an exhaust cam are arranged on the camshaft body, the outer end surface of the exhaust cam is provided with a decompression pin and a torsion spring mounting seat with a torsion spring, a decompression valve throwing block is arranged on the camshaft body and positioned outside the decompression pin, one end of the decompression valve throwing block is connected with the torsion spring mounting seat, and the other end of the decompression valve throwing block is matched with the decompression pin; a gasket is arranged on the camshaft body and close to the outer end face of the throwing block of the reducing valve; one end card of torsional spring is on the camshaft body, and the other end card is on the pressure reducing valve flail block. The pressure reducing valve has the following defects in the actual working process: 1. the pressure reducing valve throwing block is inserted into the track groove of the pressure reducing pin through a shaft to drive the pressure reducing pin to rotate. This relief pressure valve is after the flail piece is thrown away, lack the stroke that throws away the piece and carry out spacing structure, and because the engine is at the operation in-process, along with the change of speed, the rotational speed of camshaft is also indefinite, this leads to decompression flail piece long term to be in wobbling state, consequently can give decompression flail piece, parts such as decompression round pin bring unnecessary wearing and tearing, lead to decompression flail piece and the installation accuracy who subtracts the pressure pin, the cooperation precision between decompression flail piece and the decompression pin reduces, this in the past can lead to reducing the actual turned angle of pressure pin and set for turned angle appearance deviation, cause the condition that the decompression became invalid, it directly leads to the decompression to lose efficacy to even still can appear reducing the pressure flail piece from the decompression round pin internal separation. 2. In this relief pressure valve, when the piece resets is got rid of in the decompression, rely on and lean on the location that realizes the piece is got rid of in the decompression with the elasticity that overcomes the torsional spring mutually with the decompression round pin, this locate mode is because decompression round pin direct atress, also can appear the decompression and get rid of the condition that the piece breaks away from in the decompression round pin, perhaps appears the dead condition of decompression round pin card, leads to the decompression to lose efficacy.

Disclosure of Invention

The invention aims to solve the problems of the prior art, provides a decompression structure of a motorcycle engine, and solves the problem that the decompression structure of the prior motorcycle engine has decompression failure.

The purpose of the invention can be realized by the following technical scheme: a decompression structure of a motorcycle engine comprises a camshaft with an exhaust cam, the decompression structure comprises a decompression pin and a throwing block for driving the decompression pin to rotate, one end of the throwing block is hinged on the camshaft and can be thrown out along the radial direction of the camshaft under the action of centrifugal force, the throwing block is connected with an elastic piece for driving the throwing block to reset, it is characterized in that the camshaft is fixedly connected with a supporting seat, the supporting seat and the exhaust cam are respectively positioned at two sides of the throwing block, the supporting seat and the exhaust cam cooperate to position the throwing block along the axial direction of the camshaft, the supporting seat is provided with an inner limiting part, the throwing block is propped against the inner limiting part under the action of the elastic piece, the supporting seat is further provided with an outer limiting part which can be used for abutting against the throwing block after the throwing block is thrown out so as to limit the throwing stroke of the throwing block.

In the decompression structure of motorcycle engine, how to drive the decompression round pin to rotate when getting rid of the piece motion realizes that the decompression function is prior art. Roughly speaking, when the engine starts, the camshaft begins to rotate, and when the camshaft reaches certain rotational speed, the throwing block can be thrown out due to the effect of centrifugal force, and the throwing block can drive the decompression pin to rotate when throwing out, so that the decompression pin which is originally higher than the base circle of the exhaust cam becomes lower than the base circle of the exhaust cam, and the decompression valve does not play a role in decompression at the moment. When the engine stalls, get rid of the piece and reset because the effect of elastic component, make the effective operating position of decompression round pin higher than the cam base circle simultaneously, play the decompression effect, guarantee the validity of relief pressure valve when the engine starts next time.

The pressure reducing structure is additionally provided with the supporting seat on the side part of the throwing block on the camshaft, so that the position of the throwing block along the axial direction of the camshaft is positioned under the combined action of the supporting seat and the exhaust cam, and the throwing block cannot deviate along the axial direction of the camshaft in the working process; simultaneously, spacing portion and outer spacing portion in still being equipped with on the camshaft, the piece of getting rid of can supply to get rid of the piece and lean on outside spacing portion after throwing away, has injectd the biggest throw-out stroke that gets rid of the piece to guarantee that the camshaft is when surpassing certain rotational speed, get rid of the piece and lean on outside spacing portion all the time and can not the swing of making a round trip, avoid getting rid of parts such as piece, decompression round pin and appear the unnecessary wearing and tearing, guarantee the operation precision of decompression round pin. When the engine stops, the swinging block can be always abutted against the inner limiting part under the action of the elastic piece, and the situation that the decompression pin is blocked due to direct force application of the decompression pin is avoided. Obviously, the structure of present case makes to get rid of the piece and has obtained the location along camshaft axial position, has also carried out the injecing simultaneously along the radial swing range of camshaft for get rid of the piece and swing on the orbit of settlement all the time, job stabilization and running accuracy are high, and then can be stable and accurate drive decompression round pin rotate, have avoided the ability that decompression became invalid.

Moreover, get rid of the piece among this pressure reducing structure and throw away spacing of stroke, spacing of axial spacing and the spacing of resetting stroke all rely on single part to be the supporting seat and realize, such design can avoid realizing respectively through a plurality of parts under the different spacing circumstances, each spare part manufacturing easily appears, the problem that the installation accuracy that the assembly tolerance is great brings reduces, consequently this pressure reducing structure makes and gets rid of the piece can be stable, accurate drive decompression round pin rotates, thereby avoid the possibility that the decompression became invalid.

In the pressure reducing structure of the motorcycle engine, the camshaft comprises a shaft body, the outer limiting part and the side wall of the throwing block, which is back to the shaft body, are oppositely arranged, and after the throwing block is thrown out, the outer limiting part can be abutted against the side wall of the throwing block, which is back to the shaft body. When the camshaft reaches a certain rotating speed, the throwing block can be thrown out due to the action of centrifugal force, so that the throwing block is supported against the side wall of the shaft body in a back direction on the outer limiting part, and then the position of the throwing block after throwing out is positioned.

In the pressure reducing structure of the motorcycle engine, the throwing block is approximately arc-shaped, the inner concave surface of the throwing block faces the shaft body, the middle part of the supporting seat is provided with a shaft hole for the shaft body to pass through, the inner limiting part is arc-shaped and is arranged around the edge of the shaft hole, and the throwing block abuts against the inner limiting part through the inner concave surface of the throwing block. The supporting seat links firmly through the axis body of shaft hole with the camshaft for supporting seat installation stability is good, and moreover, this structure is because the supporting seat can be processed alone, and processing is comparatively convenient and machining precision is high, can guarantee the supporting seat and get rid of and have higher cooperation precision between the piece, thereby can be better to getting rid of the piece spacing, guarantee to get rid of the stability of a working process. When the supporting seat is installed, the supporting seat is only required to be sleeved on the camshaft from one end of the camshaft, and the assembly is more convenient.

In the pressure reducing structure of the motorcycle engine, one end of the throwing block, which is hinged to the cam shaft, is a hinged end, the other end of the throwing block is a swinging end, a through hole is formed in the hinged end of the throwing block, a support pin penetrates through the through hole, a first mounting hole is formed in the support seat, one end of the support pin penetrates through the first mounting hole, and the other end of the support pin is connected to the exhaust cam. Such structure makes to get rid of the piece and rely on the supporting pin to articulate on the camshaft, and the stability of supporting pin directly influences the stability of getting rid of a piece working process this moment. This decompression structure relies on the supporting seat to have still realized the fixed of backing pin tip through increasing the supporting seat on the camshaft for the both ends of backing pin have all received the support, and the stability of backing pin can promote, thereby has guaranteed to get rid of a working process and has better stability.

In the pressure reducing structure of the motorcycle engine, the support seat is plate-shaped, the support seat locally protrudes towards the side wall of the throwing block to form a first limiting protruding part, the hinged end of the throwing block locally protrudes towards the side wall of the support seat to form a second limiting protruding part, the surface of the first limiting protruding part and the surface of the second limiting protruding part are perpendicular to the axis of the camshaft, and the surface of the first limiting protruding part and the surface of the second limiting protruding part are attached to each other. The surface of the first limiting convex part and the surface of the second limiting convex part are perpendicular to the axis of the camshaft, so that the swinging block always swings back and forth along the radial direction of the camshaft in the swinging process. The first limiting convex part and the second limiting convex part are both formed by local protrusions, the structure not only well limits the axial position of the throwing block, but also enables the friction of the swinging process of the throwing block to be small, and the swinging process of the throwing block is stable and smooth.

In the pressure reducing structure of the motorcycle engine described above, the outer stopper portion is located on the edge of the support base. Such structure not only makes outer spacing portion be convenient for process, enables the radial size of supporting seat less moreover for this decompression structure has compact structure's advantage.

In the pressure reducing structure of the motorcycle engine, the outer convex surface of the throwing block is recessed inwards at the end part of the swinging end of the throwing block to form an inner concave part, the outer limiting part and the inner concave part are arranged oppositely, a gap is reserved between the outer limiting part and the inner concave part, the inner concave part is provided with a third limiting convex part, and the third limiting convex part can abut against the outer limiting part after the throwing block is thrown out. Concave part has formed the abdicating in through setting up for when getting rid of the piece and being in the reset state, the interval has between interior concave part and the outer spacing portion, guarantees that the camshaft when the rotational speed risees, gets rid of the piece and can throw away under the effect of centrifugal force. And outer spacing portion sets up with interior recess relatively for after the flail block is thrown away, spacing convex part three can support and lean on in outer spacing portion, prescribe a limit to throw the stroke that the piece was thrown away. The third limiting convex part is arranged, the surface abutted against the outer limiting part can be conveniently machined on the third limiting convex part, and the thickness of the third limiting convex part can be accurately controlled through accurate control in the machining process.

In the pressure reducing structure of the motorcycle engine, the side wall of the exhaust cam facing the throwing block is provided with the convex part, the side wall of the throwing block facing the exhaust cam is provided with the limit convex part four, and the side wall of the convex part facing the throwing block is a plane perpendicular to the axis of the camshaft and can be abutted against the plane by the limit convex part four. The lateral wall that the bellying faced the flail block is the plane perpendicular with camshaft axis for the flail block is at swing in-process, along the radial swing back and forth of camshaft all the time. The fourth limiting convex part is attached to the plane, so that the throwing block is positioned along the axial direction of the cam shaft, and the stability of the working process of the throwing block is ensured.

In the pressure reducing structure of the motorcycle engine described above, the boss portion is connected to the shaft body and formed into an integral structure. Through the design, the four-structure strength of the limiting convex part is high, and the manufacturing is convenient.

In the decompression structure of the motorcycle engine, the boss is provided with a second mounting hole, and one end of the support pin penetrates through the second mounting hole. Make supporting pin simple to operate through such structure, the mounting hole one on the cooperation supporting seat for the both ends of support receive the support, and supporting pin stability is good and then promote the stability of getting rid of a work process.

Compared with the prior art, the decompression structure of the motorcycle engine has the following advantages:

1. among this decompression structure of motorcycle engine, get rid of the piece and obtained injecing along the axial position of camshaft axial, also injecing along the radial amplitude of oscillation of camshaft simultaneously for get rid of the piece and swing on the orbit of design all the time, job stabilization and running accuracy are high, and then can be stable accurate drive the decompression round pin and rotate, have avoided the ability that the decompression became invalid.

2. In the pressure reducing structure of the motorcycle engine, the supporting seat is arranged on the outer side of the exhaust cam and sleeved on the cam shaft, and the supporting seat can be independently processed and formed, so that the pressure reducing structure is convenient to process.

3. The decompression structure of the motorcycle engine also has the advantages of compact structure and convenience in assembly.

Drawings

Fig. 1 is a partial view of the engine of the present motorcycle.

Fig. 2 is a schematic perspective view of the pressure reducing structure.

Fig. 3 is a schematic perspective view of the pressure reducing structure.

Fig. 4 is an exploded view of the present pressure relief structure.

Fig. 5 is an exploded view of the present pressure relief structure.

Figure 6 is a partial perspective view of the present pressure relief structure.

Fig. 7 is a third schematic perspective view of the pressure relief structure.

In the figure, 1, a camshaft; 11. an exhaust cam; 12. a shaft body; 13. a boss portion; 14. A second mounting hole; 2. a decompression pin; 3. throwing blocks; 31. a hinged end; 32. a swing end; 33. A via hole; 34. a second limiting convex part; 35. an inner concave surface; 36. a third limiting convex part; 37. a fourth limiting convex part; 4. an elastic member; 5. a supporting seat; 51. an inner limiting part; 52. an outer stopper portion; 53. a shaft hole; 54. a first mounting hole; 55. a first limiting convex part; 6. and (7) supporting the pin.

Detailed Description

The following are specific embodiments of the present invention and are further described with reference to the accompanying drawings, but the present invention is not limited to these embodiments.

Example one

As shown in fig. 1 to 3, in the decompression structure of the motorcycle engine, the engine includes a camshaft 1 having an exhaust cam 11, and the decompression structure includes a decompression pin 2, a thrower 3, a mount base, and the like. Specifically, the swinging block 3 is substantially arc-shaped, one end of the swinging block 3 is a hinged section, and the other end is a swinging end 32. The throwing block 3 is hinged on the exhaust cam 11 of the camshaft 1 through the hinged end 31, so that when the camshaft 1 exceeds a certain rotating speed, the throwing block 3 can be thrown out along the radial direction of the camshaft 1 under the action of centrifugal force. In order to realize throwing away the reset of piece 3, still be connected with on the throwing piece 3 and be used for driving about throwing the piece 3 and carry out the elastic component 4 that resets, elastic component 4 is the torsional spring in this embodiment. The supporting seat 5 is fixedly connected on the camshaft 1, the supporting seat 5 and the exhaust cam 11 are respectively positioned at two sides of the throwing block 3, the supporting seat 5 and the exhaust cam 11 jointly act to enable the position of the throwing block 3 along the axial direction of the camshaft 1 to be positioned,

as shown in fig. 4 to 6, the supporting seat 5 is provided with an inner limiting portion 51, the throwing block 3 abuts against the inner limiting portion 51 under the action of the elastic element 4, and the supporting seat 5 is further provided with an outer limiting portion 52 which can allow the throwing block 3 to abut against after the throwing block 3 is thrown out so as to limit the throwing stroke of the throwing block 3.

Specifically, as shown in fig. 4 to 6, the camshaft 1 includes the axis body 12, and the supporting seat 5 is platelike, gets rid of the interior concave surface of piece 3 towards the axis body 12, and the shaft hole 53 that supplies the axis body 12 to pass is seted up at the middle part of supporting seat 5, and interior spacing portion 51 is arc platelike and sets up around the border in shaft hole 53, and when getting rid of piece 3 and reseing, get rid of piece 3 and lean on with interior spacing portion 51 counterbalance through its interior concave surface. The outer limiting portion 52 is located at the edge of the supporting seat 5, the outer limiting portion 52 and the side wall of the throwing block 3, which faces away from the shaft body 12, are arranged oppositely, and the outer limiting portion 52 can be abutted against the side wall of the throwing block 3, which faces away from the shaft body 12, after the throwing block 3 is thrown out.

As shown in fig. 2, the outer convex surface of the throwing block 3 is recessed inward at the end of the swinging end 32 of the throwing block 3 to form an inner concave portion 35, the outer limit portion 52 is opposite to the inner concave portion 35 with a gap therebetween, the inner concave portion 35 is provided with a third limit convex portion 36, and the third limit convex portion 36 can abut against the outer limit portion 52 after the throwing block 3 is thrown out. Let a bit through setting up interior recess 35 for when throwing away piece 3 and being in the reset condition, interior recess 35 and spacing 52 outside have the interval, guarantee that camshaft 1 when the rotational speed risees, throw away piece 3 and can throw away under centrifugal force's effect. And set up spacing convex part three 36 here, can be convenient for process the surface that leans on with outer spacing portion 52 on spacing convex part three 36, moreover through the thickness of accurate control spacing convex part three 36, can grasp the stroke that gets rid of piece 3 accurately in the course of working.

In order to realize the positioning of the thrower 3 along the axial direction of the camshaft 1, as shown in fig. 4 and 6, the supporting seat 5 locally protrudes towards the side wall of the thrower 3 to form a first limit protrusion 55, the hinged end 31 of the thrower 3 locally protrudes towards the side wall of the supporting seat 5 to form a second limit protrusion 34, the surface of the first limit protrusion 55 and the surface of the second limit protrusion 34 are both perpendicular to the axial line of the camshaft 1, and the surface of the first limit protrusion 55 abuts against the surface of the second limit protrusion 34. The side wall of the exhaust cam 11 facing the throwing block 3 is provided with a convex part 13, and the convex part 13 is connected with the shaft body 12 and forms an integral structure. The side wall of the convex part 13 facing the throwing block 3 is a plane vertical to the axis of the camshaft 1, and the side wall of the throwing block 3 facing the exhaust cam 11 is provided with a limit convex part four 37 which can be attached to the plane.

As shown in fig. 4 to 6, in order to realize stable installation of the throwing block 3, a through hole 33 is formed in the hinged end 31 of the throwing block 3, a first installation hole 54 is formed in the support base 5, a second installation hole 14 is formed in the protruding portion 13, one end of the support pin 6 is inserted into the first installation hole 54, and the other end of the support pin 6 is inserted into the second installation hole 14. Through the structure, the supporting pin 6 is convenient to mount, the two ends of the supporting pin are supported by matching with the first mounting hole 54 on the supporting seat 5, and the stability of the supporting pin 6 is good, so that the stability of the working process of the swinging block 3 is improved.

The operation principle of the pressure reducing structure of the motorcycle engine will be briefly described with reference to fig. 7. as shown in fig. 7, when the engine is started, the camshaft 1 starts to rotate, and when the camshaft 1 reaches a certain rotation speed, the throwing block 3 is thrown out by the centrifugal force, so that the pressure reducing pin 2 which is originally higher than the base circle of the exhaust cam 11 becomes lower than the base circle of the exhaust cam 11, and the pressure reducing valve does not perform the pressure reducing function. In this state, the outer stopper portion 52 abuts against the slinger 3, and the maximum slinger stroke of the slinger 3 is limited. When the engine stalls, as shown in fig. 2, the effect of elastic component 4 enables to get rid of piece 3 and begins to reset and leans on including spacing portion 51 at last, makes the effective operating position of decompression round pin 2 exceed the cam base circle simultaneously, plays the decompression effect, guarantees the validity of relief pressure valve when the engine starts next time.

Example two

The structure and principle of the present embodiment are basically the same as those of the embodiment, and the difference is that the elastic element 4 for driving the swinging block 3 to reset is a tension spring, one end of the tension spring is hooked on the swinging end 32 of the swinging block 3, and the other end is hooked on the camshaft 1.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Although 1, camshaft is used more herein; 11. an exhaust cam; 12. a shaft body; 13. a limiting part; 14. a second mounting hole; 2. a decompression pin; 3. throwing blocks; 31. a hinged end; 32. a swing end; 33. a via hole; 34. a second limiting convex part; 35. an inner concave surface; 36. A third limiting convex part; 37. a fourth limiting convex part; 4. an elastic member; 5. a supporting seat; 51. an inner limiting part; 52. an outer limit portion; 53. a shaft hole; 54. a first mounting hole; 55. a first limiting convex part; 6. support pins, etc., but does not exclude the possibility of using other terms. These terms are used merely to more conveniently describe and explain the nature of the present invention; they are to be construed as being without limitation to any additional limitations that may be imposed by the spirit of the present invention.

Claims

1. A decompression structure of a motorcycle engine comprises a camshaft (1) with an exhaust cam (11), the decompression structure comprises a decompression pin (2) and a throwing block (3) used for driving the decompression pin (2) to rotate, one end of the throwing block (3) is hinged on the camshaft (1), the throwing block (3) can be thrown out along the radial direction of the camshaft (1) under the action of centrifugal force, an elastic piece (4) used for driving the throwing block (3) to reset is connected onto the throwing block (3), the decompression structure is characterized in that a supporting seat (5) is fixedly connected onto the camshaft (1), the supporting seat (5) and the exhaust cam (11) are respectively positioned at two sides of the throwing block (3), the supporting seat (5) and the exhaust cam (11) jointly act to enable the throwing block (3) to be positioned along the axial position of the camshaft (1), and an inner limiting portion (51) is arranged on the supporting seat (5), the throwing block (3) is abutted against the inner limiting part (51) under the action of the elastic piece (4), and the supporting seat (5) is further provided with an outer limiting part (52) which can be abutted against the throwing block (3) after the throwing block (3) is thrown out so as to limit the throwing stroke of the throwing block (3).

2. A decompression arrangement for a motorcycle engine according to claim 1, wherein the camshaft (1) comprises a shaft body (12), the outer limiting portion (52) is disposed opposite to a side wall of the thrower (3) facing away from the shaft body (12), and the outer limiting portion (52) can abut against the side wall of the thrower (3) facing away from the shaft body (12) after the thrower (3) is thrown away.

3. The decompression structure of the motorcycle engine according to claim 2, wherein the thrower (3) is substantially arc-shaped, an inner concave surface of the thrower (3) faces the shaft body (12), a shaft hole (53) for the shaft body (12) to pass through is formed in the middle of the support base (5), the inner limit portion (51) is arc-plate-shaped and is arranged around the edge of the shaft hole (53), and the thrower (3) abuts against the inner limit portion (51) through the inner concave surface of the thrower.

4. The decompression structure of a motorcycle engine according to claim 1, 2 or 3, wherein one end of the throwing block (3) hinged to the camshaft (1) is a hinged end (31), the other end of the throwing block is a swinging end (32), a through hole (33) is formed in the hinged end (31) of the throwing block (3), a support pin (6) penetrates through the through hole (33), a first mounting hole (54) is formed in the support seat (5), one end of the support pin (6) penetrates through the first mounting hole (54), and the other end of the support pin (6) is connected to the exhaust cam (11).

5. A decompression structure of a motorcycle engine according to claim 1, 2 or 3, wherein the support seat (5) is plate-shaped, the support seat (5) is locally protruded towards the side wall of the thrower (3) to form a first limit protrusion (55), the hinge end (31) of the thrower (3) is locally protruded towards the side wall of the support seat (5) to form a second limit protrusion (34), and the surface of the first limit protrusion (55) is abutted against the surface of the second limit protrusion (34).

6. A decompression structure of a motorcycle engine according to claim 2 or 3, wherein the outer stopper portion (52) is located on an edge of the support base (5).

7. A decompression arrangement for a motorcycle engine according to claim 2 or 3, wherein the outer convex surface of the thrower (3) is recessed at the end of the swing end (32) of the thrower (3) to form an inner concave surface (35), the outer stopper (52) is disposed opposite to the inner concave surface with a space therebetween, the inner concave surface (35) has a third stopper protrusion (36), and the third stopper protrusion (36) can abut against the outer stopper (52) when the thrower (3) is thrown out.

8. A decompression arrangement for a motorcycle engine according to claim 4, wherein the exhaust cam (11) has a boss (13) on the side wall facing the thrower (3), the thrower (3) has a fourth limit boss (37) on the side wall facing the exhaust cam (11), the side wall of the boss (13) facing the thrower (3) is a plane perpendicular to the axis of the camshaft (1) and the fourth limit boss (37) can abut against the plane.

9. A decompression structure of a motorcycle engine according to claim 8, characterized in that the boss portion (13) is connected to the shaft body (12) and formed in an integrated structure.

10. A decompression structure of a motorcycle engine according to claim 8, wherein a second mounting hole (14) is opened in the boss (13), and one end of the support pin (6) is inserted into the second mounting hole (14).