JP4536697B2 - Cam mechanism with decompression device - Google Patents

Description

  The present invention relates to a cam mechanism with a decompression device (decompression device) that relieves the compression pressure in a combustion chamber when the engine is started.

2. Description of the Related Art Conventionally, in the above cam mechanism, a decompression support portion provided with at least a camshaft for driving an exhaust valve and a decompression shaft having a decompression cam portion and a centrifugal weight portion on a rotating shaft, and provided integrally with the outer periphery of the camshaft. A support hole is formed along the cam shaft direction, and the rotation shaft of the decompression shaft is pivotally supported in the support hole, and the centrifugal force acting on the centrifugal weight portion as the cam shaft rotates. In response to this, there is a type in which the decompression shaft rotates to cause the decompression cam portion to appear and disappear on the cam surface of the exhaust cam of the camshaft (see, for example, Patent Document 1). The decompression support portion is integrally formed on the outer periphery of the camshaft.
JP 2004-278410 A

By the way, in recent engines, the use of titanium for the camshaft in the cylinder head has been studied in order to reduce the weight and lower the center of gravity. In this case, it is desirable to form a sprayed film by linear explosion spraying on each sliding part due to the sliding characteristics of titanium, but in a relatively fine part such as a decompression support part, the sliding characteristics There is a demand for a configuration that can easily improve the above.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a cam mechanism with a decompression device that relieves the compression pressure in the combustion chamber when the engine is started, and to easily improve the sliding characteristics of the decompression support portion while reducing the weight of the camshaft. .

As a means for solving the above-mentioned problem, the invention described in claim 1 is a cam mechanism with a decompression device for releasing the compression pressure in the combustion chamber when starting the engine, and at least the camshaft (13) for driving the exhaust valve (6 ). And a decompression shaft (33) having a decompression cam portion (36) and a centrifugal weight portion (35) on the rotating shaft (34) , and a decompression support portion provided on the outer periphery of the camshaft (13) so as to be integrally rotatable. (31) is formed with a support hole (32) along the camshaft direction, and a rotation shaft (34) of the decompression shaft (33) is rotatably supported in the support hole (32). depending on the centrifugal force acting on the centrifugal weight part with the rotation (35) of the camshaft (13), the said decompression cam portion (36) said decompression shaft (33) is rotated Kamusha Preparative the exhaust decompression device with a cam mechanism for infested on the cam surface of the cam (22) of (13), said cam shaft (13) outer circumference collar member (45) integrally attached to rotatable from its one axial end of the the provided, together with the decompression supporting portion to said collar member (45) (31) is formed, integrally rotatably mounted Following the camshaft (13) from said said axially one end side on the outer peripheral collar member (45) A cam sprocket (14), and movement of the collar member (45) in the mounting direction relative to the camshaft (13) is restricted by a first positioning portion (13c) provided on the camshaft (13), Movement of the cam sprocket (14) in the mounting direction with respect to the camshaft (13) is performed via the collar member (45). The second positioning portion (15b) provided on the cam sprocket (14) is controlled by the first positioning portion (13c), and the cam sprocket (14) is moved in the removal direction with respect to the cam shaft (13). Regulated by contacting the cam support (16) of the engine structure (2),
Further, the cam shaft (13) is made of titanium, and the central collar portion (15) through which the cam shaft (13) of the collar member (45) and the cam sprocket (14) is inserted is made of iron. And

According to a second aspect of the present invention, the exhaust cam (22 ) is formed with a recess (41) in which a part of the outer cam surface is cut out, and the decompression cam portion (36 ) is formed in the recess (41) . ) with is arranged rotatably, the decompression cam support portion for supporting the decompression cam portion (36) at least in the non-decompression upon actuation (49) is provided, the decompression cam support (49) is, the exhaust cam (22) It is characterized by being formed by a support member (48) attached to the head.

According to a third aspect of the present invention, a recess (41) is formed on one end side of the exhaust cam (22) in the axial direction so as to cut out a part of the outer cam surface, and the recess (41) A groove portion (47) is formed by cutting out at least a part of the inner peripheral side bottom surface (41a) , and an annular support member (48) that matches the groove portion (47) is attached from one end side in the axial direction. The decompression cam portion (36) is rotatably disposed in the recess (41) , and at least during the non-decompression operation, the decompression cam portion (36) is the support member on the inner peripheral bottom surface (41a) . (48) is supported at a site where it is formed.

The invention described in claim 4 is characterized in that the camshaft (13) is made of titanium, and the collar member (45) and the support member (48) are made of iron.

According to the present invention , the decompression support portion is formed of a collar member that is separate from the camshaft, so that the camshaft is made of titanium and the weight is reduced, and the collar member is made of iron and the sliding characteristics of the decompression support portion. Can be easily improved, the wear resistance of the decompression support portion can be ensured, and even if wear or the like occurs in the decompression support portion, it can be appropriately replaced.

According to the present invention , the collar member and the cam sprocket can be relatively positioned in the axial direction only by sequentially assembling the collar member and the cam sprocket to the camshaft, and after the assembly to the engine structure, Through this, the camshaft can receive thrust, and the assembling work of the valve mechanism can be facilitated.

According to the present invention , by forming the decompression cam support portion with a support member separate from the camshaft, the camshaft is made of titanium and the weight is reduced, and the decompression cam support portion is made of iron and the sliding characteristics are simplified. It is possible to improve the wear resistance of the decompression cam support portion, and it is possible to replace the decompression cam support portion as appropriate even if wear occurs in the decompression cam support portion. Further, only a part of the pole around the concave portion may be a separate member having different sliding characteristics, and the camshaft can be sufficiently reduced in weight.

According to this invention , the camshaft is made of titanium to reduce the weight by forming the inner peripheral side bottom surface which is a decompression cam support portion with a support member separate from the camshaft, and the decompression cam support portion is made of iron. The sliding characteristics can be easily improved, the wear resistance of the decompression cam support portion is ensured, and even if wear or the like occurs in the decompression cam support portion, it can be appropriately replaced. In addition, since the annular support member is attached to the camshaft from the one end side in the axial direction together with the collar member and the cam sprocket, the assembly operation of the valve mechanism is facilitated.

According to the present invention , the camshaft is made of titanium to reduce the weight of the valve mechanism, and the collar member, the central collar portion, and the support member that require wear resistance are made of iron to improve the durability of the valve mechanism. be able to. The above-mentioned titanium includes titanium and titanium alloys, and the iron includes various steels and alloyed irons.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a side view of the periphery of a cylinder head 2 of a four-stroke OHC single-cylinder engine (internal combustion engine) 1 used for a prime mover of a vehicle such as a motorcycle. As shown in FIG. A valve operating chamber 4 is formed together with the head cover 3, and a valve operating mechanism 7 for operating the intake and exhaust valves 5 and 6 is accommodated in the valve operating chamber 4.

  Intake and exhaust ports 8 and 9 are formed in the cylinder head 2, and the combustion chamber side openings of the intake and exhaust ports 8 and 9 are opened and closed by the intake and exhaust valves 5 and 6, respectively. The intake and exhaust valves 5 and 6 are formed by extending rod-shaped stems 5a and 6a from the umbrella-shaped valve body to the head cover 3 side, and valve springs are provided at the stem tip portions of the valves 5 and 6 via retainers 11. 12 spring force is applied, and the valves 5 and 6 are urged to close the combustion chamber side openings of the ports 8 and 9 by the spring force. The stems 5a, 6a of the intake / exhaust valves 5, 6 are arranged in a V shape when viewed from the side, and the camshaft 13 for driving the intake / exhaust valves is arranged between the stems 5a, 6a along the left-right direction. In the figure, the symbol C indicates the rotation center (axis) of the camshaft 13.

  As shown in FIG. 2, the left side portion of the camshaft 13 (the left side in the figure is indicated by an arrow LH) is inserted into the central collar portion 15 of the cam sprocket 14 that is coaxial with the camshaft 13 so as not to be relatively rotatable by spline fitting. Is done. The left side portion of the central collar portion 15 is rotatably supported by the left side wall 2a of the cylinder head 2 via the left ball bearing 16. In other words, the left end portion of the camshaft 13 is rotatably supported by the left side wall 2 a of the cylinder head 2 via the left ball bearing 16 while being held in the central collar portion 15. The through hole 17 for holding the left ball bearing 16 in the left side wall 2a of the cylinder head 2 is oil-tightly closed by a cap 17a from the outside of the valve operating chamber.

  On the other hand, the right end portion of the camshaft 13 is rotatably supported by the right side wall 2b of the cylinder head 2 via the right ball bearing 18. The right ball bearing 18 is held in a cup-shaped bearing support portion 19 that opens to the valve operating chamber side in the right side wall 2 b of the cylinder head 2.

  The engine 1 is a four-valve type and has a pair of left and right intake and exhaust valves 5 and 6, and these valves 5 and 6 are arranged so as to be distributed at the left and right centers of the cylinder. The camshaft 13 is disposed offset to the left as a whole so that the right end portion thereof is positioned between the pair of left and right intake and exhaust valves 5 and 6 (so as to be generally positioned at the center of the left and right sides of the cylinder). The outer diameter of the right end portion of the camshaft 13 and the outer diameter of the left side portion of the central collar portion 15 are substantially the same. Hereinafter, the cylindrical surface having the outer diameter may be referred to as a reference surface of the camshaft 13.

  Intake and exhaust cams 21 and 22 for driving intake and exhaust valves are integrally formed on the outer periphery of the right half of the camshaft 13. Each of the cams 21 and 22 forms an outer peripheral surface (cam surface) whose diameter is larger than that of the reference surface. Cylindrical portions 21a and 22a that form a coaxial cylindrical cam surface with the cam shaft 13 (see FIG. 4). ) And cam crests 21b and 22b (see FIG. 4) that project to the outer peripheral side of the cylindrical portions 21a and 22a to form a crest-shaped cam surface. The intake cam 21 is located on the right side of the right half and the exhaust cam 22 is located on the left side of the right half, and these are spaced apart from each other in the cam shaft direction.

  Referring also to FIG. 1, intake or exhaust rocker arms 23 and 24 are swingably provided between the intake and exhaust cams 21 and 22 and the distal end portions of the intake and exhaust valves 5 and 6, respectively. Cam rollers 23a and 24a that are in contact with the cam surfaces on the outer circumferences of the intake and exhaust cams 21 and 22 are rotatably provided at the cam side ends (input end portions) of the rocker arms 23 and 24, respectively. On the other hand, the valve side end portions (output end portions) of the rocker arms 23 and 24 are provided with contact portions 23b and 24b that contact the stem tips of the intake and exhaust valves 5 and 6 via shims, respectively.

  The camshaft 13 is driven to rotate in synchronization with the crankshaft of the engine 1 via a cam chain wound around the cam sprocket 14. When the camshaft 13 is driven to rotate, the rocker arms 23, 24 are appropriately swung according to the cam patterns of the intake / exhaust cams 21, 22, and the intake / exhaust valves 5, 6 are reciprocated to reciprocate the intake / exhaust ports 8, 9 combustion chamber side opening is opened and closed. In addition, the code | symbol 25 in FIG. 2 shows the cam chain chamber which accommodates the said cam chain.

  The cam rollers 23 a and 24 a of the rocker arms 23 and 24 abut on the cam surfaces of the intake and exhaust cams 21 and 22 from the head cover 3 side and roll on the cam surfaces as the camshaft 13 is driven to rotate. Hereinafter, the positions where the cam rollers 23a, 24a contact the outer periphery of the intake / exhaust cams 21, 22 are referred to as roller contact positions.

  When the cylindrical portions 21a and 22a are located at the roller contact positions, the intake / exhaust cams 21 and 22 keep the openings on the combustion chamber side of the intake / exhaust ports 8 and 9 closed without lifting the intake / exhaust valves 5 and 6 When the cam crests 21b and 22b are positioned at the roller contact position, the intake and exhaust valves 5 and 6 are lifted to open the combustion chamber side openings of the intake and exhaust ports 8 and 9. Hereinafter, the cylindrical cam surfaces on the outer circumferences of the cylindrical portions 21a and 22a are referred to as zero lift surfaces 21c and 22c.

Here, the engine 1 includes a decompression device (decompression device) 30 that opens the exhaust valve 6 to release the compression pressure in the combustion chamber when the engine 1 is started.
As shown in FIG. 3, the decompression device 30 is provided between the cam sprocket 14 and the exhaust cam 22 in the camshaft 13, and the decompression support portion 31 is rotatable on the outer peripheral side of the camshaft 13. A support hole 32 is formed in the decompression support portion 31 along the cam shaft direction. A rotation shaft 34 of a decompression shaft 33 in the decompression device 30 is pivotally supported in the support hole 32. The

4 and 8 together, the decompression support portion 31 protrudes to the outer peripheral side between the cylindrical portion 22a of the exhaust cam 22 and the cam sprocket 14, and the support hole 32 is formed through the tip side thereof. Is done.
Referring to FIG. 3, the decompression shaft 33 is formed by integrally forming a centrifugal weight portion 35 at the left end portion of the rotation shaft 34 and a decompression cam portion 36 at the right end portion, and the rotation shaft 34 is connected to the decompression support portion 31. The support hole 32 is rotatably supported while being inserted from the left side. At this time, the decompression cam portion 36 of the decompression shaft 33 is accommodated in the recess 41 formed on the left side surface of the exhaust cam 22.

  A cylindrical portion 37 that is coaxial with the rotating shaft 34 protrudes from the left end of the rotating shaft 34, and a torsion coil spring 38 that applies a biasing force to the decompression shaft 33 in one rotating direction is attached to the outer periphery of the cylindrical portion 37. . The decompression shaft 33 is slidably brought into contact with the left side surface of the decompression support portion 31 at the stepped portion 34a on the left side of the rotation shaft 34, and the cylindrical portion 37 is placed on the right side surface of the sprocket body 14a of the cam sprocket 14. By causing the left end surface to slidably contact, the decompression support portion 31 is pivotally supported in a state where movement in the cam shaft direction is restricted.

  The centrifugal weight portion 35 has an arm portion 35 with a relatively small left-right width extending from the left end portion of the rotating shaft 34 to the outer peripheral side, and a weight main body with the left-right width expanded toward the left side at the distal end side of the arm portion 35. 35b is integrally formed. The centrifugal weight portion 35 is positioned in the rotational drive direction of the camshaft 13 (in the direction of arrow F in FIG. 4) relative to the decompression support portion 31. When the decompression shaft 33 rotates about the rotation shaft 34, the centrifugal weight portion 35 responds to the centrifugal force. Thus, the weight main body 35b is movable to the inner peripheral side or the outer peripheral side of the camshaft 13.

  The decompression shaft 33 is biased toward the side that moves the weight main body 35b to the inner peripheral side by the spring force of the torsion coil spring 38. At this time, when one side of the centrifugal weight portion 35 comes into contact with the outer periphery of the collar member 45 described later, a rotation limit position of the decompression shaft 33 toward the side on which the weight main body 35b is moved to the inner peripheral side is defined. The rotation limit position at this time is defined as an inner peripheral rotation limit position. The centrifugal weight portion 35 is formed to bend so as to go around the outer periphery of the collar member 45 at the inner peripheral side rotation limit position.

  A relatively short stopper piece 39 extends from the portion of the left end portion of the rotating shaft 34 opposite to the centrifugal weight portion 35 to the outer peripheral side. The stopper piece 39 defines a rotation limit position when the decompression shaft 33 is rotated to the side that moves the weight main body 35 b to the outer peripheral side against the spring force of the torsion coil spring 38. Let the rotation limit position at this time be an outer periphery side rotation limit position.

  Referring also to FIG. 5, the decompression cam portion 36 is formed by chamfering, for example, two places on the outer peripheral side of the cylindrical body on the distal end side of the rotating shaft 34 in a flat shape. Hereinafter, the chamfered portions are referred to as first and second flat portions 36a and 36b, and the cylindrical portions remaining therebetween are referred to as first and second cam crest portions 36c and 36d. The flat portions 36 a and 36 b and the cam crest portions 36 c and 36 d are alternately arranged in the circumferential direction of the rotation shaft 34.

  As shown in FIGS. 3 and 6, the concave portion 41 is formed on the left side surface of the cylindrical portion 22a of the exhaust cam 22 by cutting out a part of the cam surface (zero lift surface 22c). The concave portion 41 has a U-shape (square shape) that opens to the outer peripheral side when viewed in the cam shaft direction, and is disposed opposite to the support hole 32 of the decompression support portion 31 in the cam shaft direction. The decompression cam portion 36 of the decompression shaft 33 is rotatably accommodated in the recess 41. The concave portion 41 and the decompression cam portion 36 are located at the roller contact position when the engine 1 is in the latter half of the compression process. Hereinafter, the cam surface notch portion of the exhaust cam 22 by the concave portion 41 is denoted by reference numeral 42.

5A and 7A, the first cam crest portion 36c of the decompression cam portion 36 is located in the cam surface notch portion 42 when the decompression shaft 33 is in the inner peripheral side limit position. . At this time, the decompression cam portion 36 (first cam crest portion 36c) projects a predetermined amount on the cam surface (zero lift surface 22c) of the exhaust cam 22.
On the other hand, referring to FIG. 5B and FIG. 7B, the first flat portion 36a of the decompression cam portion 36 is located in the cam surface notch portion 42 when the decompression shaft 33 is at the outer peripheral side limit position. To do. At this time, the decompression cam portion 36 (first flat portion 36a) does not protrude on the cam surface (zero lift surface 22c) of the exhaust cam 22.

The decompression shaft 33 rotates in accordance with the centrifugal force acting on the centrifugal weight portion 35 (weight body 35b) as the camshaft 13 rotates, and the decompression cam portion 36 is camped from the cam surface notch portion 42 to the cam of the exhaust cam 22. Invade on the surface.
Specifically, the decompression shaft 33 is urged to the inner peripheral rotation limit position by the spring force of the torsion coil spring 38 when the camshaft 13 stops or rotates at a speed lower than a predetermined speed, and the decompression cam portion 36 is exhausted. It protrudes on the cam surface of the cam 22. On the other hand, when the camshaft 13 rotates at a predetermined speed (rotational speed when the engine starts) or higher, the decompression shaft 33 rotates toward the outer rotation limit position against the spring force of the torsion coil spring 38. The decompression cam portion 36 is not projected on the cam surface of the exhaust cam 22.

When the cam roller of the exhaust rocker arm 24 rolls on the cam surface notch portion 42, the left side of the cam roller passes over the cam surface notch portion 42, and the right side is the cam surface remaining on the right side of the cam surface notch portion 42 ( Passes over the zero lift surface 22c). Accordingly, when the cam roller rolls on the cam surface notch portion 42 with the decompression cam portion 36 projecting on the cam surface, the cam roller rides on the decompression cam portion 36 and swings the exhaust rocker arm 24, so that the exhaust valve 6 It operates to open a predetermined amount of the combustion chamber side opening of the exhaust port 9 to release the compression pressure in the combustion chamber.
Thereby, the rotation suppression force of the crankshaft due to the pressure increase before the compression top dead center is suppressed, and the rotation of the crankshaft is sufficiently accelerated.

Thereafter, when the rotation of the camshaft 13 is accelerated together with the crankshaft, the decompression shaft 33 rotates against the urging force of the torsion coil spring 38 by the centrifugal force, and the decompression cam portion Eliminate protrusions on 36 cam surfaces.
When the cam roller rolls on the cam surface notch 42 in this state, the cam roller rolls on the zero lift surface 22c without riding on the cam portion, and the exhaust valve 6 does not operate and the exhaust port 9 does not operate. The opening is kept closed, allowing a normal compression process. That is, it is possible to easily and reliably start the engine 1 while reducing the initial input of engine starting means such as a starter motor.

As shown in FIG. 3, the left half of the camshaft 13 is provided with a diameter smaller than that of the reference surface. A central collar portion 15 and a collar member 45 of the cam sprocket 14 are attached to the outer periphery of the left half portion so as to be integrally rotatable.
The collar member 45 is attached to the right outer periphery of the left half of the camshaft 13 so as not to be relatively rotatable by press-fitting or spline fitting from the left end side. The right side portion of the collar member 45 is formed with a slightly larger diameter, and a part of the outer periphery of the right side portion bulges to the outer peripheral side, whereby the decompression support portion 31 is integrally formed. That is, the decompression support portion 31 is provided separately from the main body of the camshaft 13.

  A stepped portion 13c is formed on the left and right intermediate outer periphery of the camshaft 13 along with the reduced diameter of the left half, and the right end surface of the collar member 45 abuts on a surface orthogonal to the axial direction of the stepped portion 13c. The movement of the collar member 45 to the right, that is, the movement in the direction of attachment to the camshaft 13 is restricted.

  The central collar portion 15 is attached to the left outer periphery of the left half portion of the camshaft 13 so as not to rotate relative to the collar member 45 from the left end side by press-fitting or spline fitting. A left support surface 15a is formed on the outer periphery of the left side of the central collar portion 15 and is fitted into the inner race of the left ball bearing 16, and a left annular protrusion 15b adjacent to the right side of the left support surface 15a. Is formed. The left annular protrusion 15b abuts on the right side surface of the inner race of the left ball bearing 16 when the camshaft 13 is assembled to the cylinder head 2, and the cam sprocket 14 moves to the left, that is, in the direction of removal from the camshaft 13. Regulate the movement of At this time, the movement of the collar member 45 to the left (withdrawal direction) via the cam sprocket 14 is restricted. A disc-shaped sprocket body 14 a is integrally formed on the outer periphery of the right side portion of the central collar portion 15.

  The right end surface of the central collar portion 15 abuts on the left end surface of the collar member 45, thereby restricting movement of the entire cam sprocket 14 to the right, that is, movement in the direction of attachment to the camshaft 13. When the cam sprocket 14 is assembled to the cylinder head 2, the left annular projection 15 b restricts the leftward movement of the cam sprocket 14. Thus, the cam sprocket 14 moves to the left of the entire camshaft 13 via the cam sprocket 14 and the collar member 45. Movement is restricted.

  A right support surface 13a that fits into the inner race of the right ball bearing 18 is formed on the outer periphery of the right end portion of the camshaft 13, and a right annular protrusion 13b is adjacent to the left side of the right support surface 13a. It is formed. The right annular protrusion 13b abuts against the left side of the inner race of the right ball bearing 18 when the camshaft 13 is assembled to the cylinder head 2, and restricts the camshaft 13 from moving to the right. The right annular protrusion 13b and the left annular protrusion 15b restrict the movement of the entire camshaft 13 relative to the cylinder head 2 in the axial direction and position the camshaft 13 and support the thrust load of the entire camshaft 13. .

Here, the camshaft 13 and the cam sprocket 14 are made of titanium made of titanium or a titanium alloy, and the collar member 45 and the decompression shaft 33 are made of iron made of various steels or alloy irons.
In addition, the left and right support surfaces 13a and 15a of the camshaft 13 and the cam surfaces of the intake and exhaust cams 21 and 22 and the teeth of the cam sprocket 14 are improved in their sliding characteristics to ensure wear resistance. A sprayed film is formed by wire explosion spraying.

  As shown in FIGS. 3 and 6, the left side surface of the exhaust cam 22 is formed with an annular groove 47 that is coaxial with the camshaft 13. The groove portion 47 has a U-shaped (square shape) constant cross section that opens to the left and extends in a circumferential shape, and the groove portion 47 is positioned immediately on the inner peripheral side of the concave portion 41. The left side (or the whole) of the inner peripheral side bottom surface 41a of the recess 41 is cut away.

  An annular support member 48 that matches the groove 47 is attached from the left end side of the camshaft 13. The support member 48 has a substantially same rectangular cross section as the groove portion 47 and extends circumferentially. When the support member 48 is fitted in the groove portion 47, the left side surface is the left side of the exhaust cam 22. A part of the outer peripheral surface forms a portion where the groove portion 47 in the inner peripheral side bottom surface 41a of the recess 41 is cut out. Hereinafter, the portion (inner peripheral side bottom surface 41 a) formed by the support member 48 in the recess 41 is referred to as a decompression cam support portion 49.

  When the decompression camshaft 13 is at the inner circumferential side rotation limit position (when the decompression function is activated, hereinafter, sometimes referred to as decompression operation), the decompression camshaft 13 is placed in the cam surface notch portion 42. A first cam peak portion 36c is disposed and protruded by a predetermined amount from the zero lift surface 22c of the exhaust cam 22, and a support member 48 on the inner peripheral side bottom surface 41a of the recess 41 is provided on the outer peripheral surface of the second cam peak portion 36d. The portion to be formed, that is, the decompression cam support portion 49 is brought into contact (see FIG. 7A). Thereby, the support rigidity with respect to the load when the cam roller of the exhaust rocker arm 24 rides on the decompression cam portion 36 is increased.

  On the other hand, when the decompression shaft 33 is in the outer periphery side rotation limit position (when the decompression function is not activated, hereinafter, sometimes referred to as non-decompression operation), the cam surface notch portion 42 is One flat portion 36a is arranged to eliminate the protrusion of the exhaust cam 22 from the zero lift surface 22c, and one end side of the first cam peak portion 36c retracted in the recess 41 is brought into contact with the decompression cam support portion 49 (FIG. 7). (See (b)). As a result, the decompression cam portion 36 can be supported by the decompression cam support portion 49 in the recess 41 even during non-decompression operation.

  The support member 48 is also made of iron similar to the collar member 45 and the decompression shaft 33 to ensure wear resistance. When the decompression shaft 33 rotates between the decompression operation and the non-decompression operation, the decompression cam support portion 49 faces the second flat portion 36b. At this time, the decompression cam support portion 49 and the decompression cam portion 36 do not come into contact with each other, and the rotation of the decompression shaft 33 becomes smooth. Further, the flat portions 36a and 36b are disposed so as to be inclined with respect to each other in the axial direction so that the second cam peak portion 36d is narrower than the first cam peak portion 36c.

  As described above, the cam mechanism in the above embodiment includes the decompression device 30 that releases the compression pressure in the combustion chamber when the engine is started, and includes the camshaft 13 that drives the intake and exhaust valves 5 and 6, and the rotation. The dynamic shaft 34 includes a decompression cam portion 36 and a decompression shaft 33 having a centrifugal weight portion 35, and a support hole 32 is formed in the decompression support portion 31 provided on the outer periphery of the camshaft 13 so as to be integrally rotatable. A rotation shaft 34 of the decompression shaft 33 is pivotally supported in the support hole 32, and the decompression shaft 34 is rotated according to the centrifugal force acting on the centrifugal weight portion 35 as the camshaft 13 rotates. The shaft 33 rotates so that the decompression cam portion 36 protrudes and retracts on the cam surface of the exhaust cam 22 of the camshaft 13. Comprising a periphery to collar member 45 integrally attached to rotatable from its one axial end of the Yafuto 13, in which the decompression supporting portion 31 in the collar member 45 is formed.

  According to this configuration, by forming the decompression support portion 31 with the collar member 45 separate from the camshaft 13, the camshaft 13 is made of titanium and the weight is reduced, and the collar member 45 is made of iron and the decompression is supported. The sliding characteristics of the portion 31 can be easily improved, the wear resistance of the decompression support portion 31 is ensured, and even if wear or the like occurs in the decompression support portion 31, it can be replaced as appropriate.

  Further, the cam mechanism includes a cam sprocket 14 that is attached to the outer periphery of the camshaft 13 so as to be integrally rotatable from the one axial end side to the collar member 45, and the mounting direction of the collar member 45 with respect to the camshaft 13 The movement of the cam sprocket 14 in the mounting direction with respect to the camshaft 13 is restricted by the stepped portion 13c via the collar member 45. The movement of the cam sprocket 14 in the detaching direction with respect to the cam shaft 13 is restricted by the contact of the left annular protrusion 15b provided on the cam sprocket 14 with the left ball bearing 16 of the cylinder head 2. .

  According to this configuration, the collar member 45 and the cam sprocket 14 are sequentially assembled to the camshaft 13 to perform relative positioning in the axial direction, and after the assembly to the cylinder head 2, the collar member The thrust receiving of the camshaft 13 can be performed via the camshaft 45 and the cam sprocket 14, and the assembling work of the valve mechanism 7 can be facilitated.

Further, in the cam mechanism, a recess 41 is formed on one end side in the axial direction of the exhaust cam 22, and a part of the outer peripheral cam surface is cut out, and a part of the inner peripheral bottom surface 41 a of the recess 41 is formed. A groove portion 47 is formed in the groove portion 47. An annular support member 48 that matches the groove portion 47 is attached from one end side in the axial direction, and the decompression cam portion 36 is rotatable in the recess portion 41. The decompression cam portion 36 is supported by a portion (decompression cam support portion 49) formed by the support member 48 on the inner peripheral bottom surface 41a.
According to this configuration, by forming the inner peripheral side bottom surface 41a which is the decompression cam support portion 49 with the support member 48 separate from the camshaft 13, the camshaft 13 is made of titanium, and the decompression cam is reduced. Since the support portion 49 is made of iron, the sliding characteristics can be easily improved, the wear resistance of the decompression cam support portion 49 can be ensured, and even if wear or the like occurs in the decompression cam support portion 49, it can be appropriately replaced. In addition, since the annular support member 48 is attached to the camshaft 13 from the one axial end side together with the collar member 45 and the cam sprocket 14, the assembling work of the valve mechanism 7 is facilitated.

  In the cam mechanism, the camshaft 13 and the cam sprocket 14 are made of titanium, and the collar member 45 and the support member 48 are made of iron, so that the camshaft 13 and the cam sprocket 14 are made of titanium. It is possible to sufficiently reduce the weight of the valve mechanism 7 and to improve the durability of the valve mechanism 7 by making the collar member 45 (decompression support portion 31) and the support member 48 that are relatively fine and wear-resistant and made of iron. it can.

The present invention is not limited to the above-described embodiment. For example, the cam sprocket may be composed of a central collar portion and a sprocket body that are separate from each other. In this case, if the central collar portion is made of iron and the sprocket body is made of titanium, it is possible to easily achieve both the weight reduction of the cam sprocket and the wear resistance of the decompression support portion.
Here, the product made of titanium is an alloy containing at least Ti, and may contain, for example, Al, V, or the like. Moreover, iron is an alloy containing at least Fe, and may contain an appropriate amount of other elements such as C, Si, Mn, P, S, Cr, Mo, and O.

Further, the groove and the support member may have an arc shape having a predetermined length instead of an annular shape over the entire circumference of the camshaft. In this case, the iron support member is reduced in size and the camshaft is further reduced in weight. Moreover, the structure which the one end part of the collar member 45 fits in a groove part may be sufficient. In this case, the number of parts is reduced and assembly is facilitated.
Furthermore, the support member may be configured to form each side surface of the recess. Further, the concave portion may have a trapezoidal shape or a triangular shape instead of the axial direction view shape.
And the structure in the said Example is an example of this invention, and it cannot be overemphasized that a various change is possible in the range which does not deviate from the summary of the said invention.

It is the side view which looked around the cylinder head of the engine in the Example of this invention from the cam shaft direction. It is AA sectional drawing of FIG. FIG. 3 is an enlarged view around the camshaft of FIG. 2. It is A arrow directional view of FIG. FIG. 5 is an operation explanatory diagram of the decompression shaft of FIG. 4, (a) shows a state where the decompression shaft is at the inner circumferential side rotation limit position, and (b) shows a state where the decompression shaft is at the outer circumference side rotation limit position. . It is BB sectional drawing of FIG. FIG. 7 is an operation explanatory diagram of the decompression cam portion of FIG. 6, (a) shows a state where the decompression shaft is at the inner circumferential side rotation limit position, and (b) shows a state where the decompression shaft is at the outer circumferential side rotation limit position. . It is DD sectional drawing of FIG.

Explanation of symbols

2 Cylinder head (engine structure)
6 Exhaust valve 13 Camshaft 13c Step part (first positioning part)
14 Cam sprocket 15 Center collar 15b Left annular projection (second positioning part)
16 Left ball bearing (cam support)
22 Exhaust cam 30 Decompression device 31 Decompression support section 32 Support hole 33 Decompression shaft 34 Rotating shaft 35 Centrifugal weight section 36 Decompression cam section 41 Recess 41a Inner peripheral side bottom surface 45 Color member 47 Groove section 48 Support member 49 Decompression cam support section

Claims (4)

A cam mechanism with a decompression device that releases the compression pressure in the combustion chamber when the engine is started,
It includes a cam shaft for driving at least the exhaust valve (6) (13), the decompression cam portion pivot shaft (34) (36) and the centrifugal weight part and a decompression shaft (33) having (35), the camshaft ( 13) A support hole (32) along the cam shaft direction is formed in the decompression support (31) provided on the outer periphery of the decompression support (31) , and the rotation of the decompression shaft (33) is formed in the support hole (32). A shaft (34) is pivotally supported, and the decompression shaft (33) rotates in response to a centrifugal force acting on the centrifugal weight portion (35) as the camshaft (13) rotates. In the cam mechanism with a decompression device that causes the decompression cam portion (36) to protrude and retract on the cam surface of the exhaust cam (22) of the camshaft (13) ,
A collar member (45) attached to the outer periphery of the camshaft (13) so as to be integrally rotatable from one end side in the axial direction thereof is provided, and the decompression support portion (31) is formed on the collar member (45) ,
A cam sprocket (14) is attached to the outer periphery of the camshaft (13) so as to be integrally rotatable from the one axial end side to the collar member (45), and the collar member (45) with respect to the camshaft (13) Movement in the mounting direction is restricted by a first positioning portion (13c) provided on the camshaft (13), and movement of the cam sprocket (14) in the mounting direction with respect to the camshaft (13) A movement of the cam sprocket (14) in the removal direction with respect to the camshaft (13) is regulated by the first positioning portion (13c) via a member (45), and the cam sprocket (14) is provided with a first movement. The two positioning portions (15b) are regulated by contacting the cam support portions (16) of the engine structure (2).
Further, the cam shaft (13) is made of titanium, and the central collar portion (15) through which the cam shaft (13) of the collar member (45) and the cam sprocket (14) is inserted is made of iron. A cam mechanism with a decompression device. It said exhaust cam (22), the recess cutting away a portion of the cam surface of the outer peripheral (41) is formed, in the recess (41), the decompression cam portion (36) is arranged rotatably In addition, a decompression cam support portion (49 ) for supporting the decompression cam portion (36) at least during non-decompression operation is provided, and the decompression cam support portion (49) is a support member (48) attached to the exhaust cam (22). The cam mechanism with a decompression device according to claim 1 , wherein the cam mechanism is formed. A recess (41) is formed on the exhaust cam (22) at one end side in the axial direction, and a part of the outer peripheral cam surface is cut out, and at least the inner peripheral bottom surface (41a) of the recess (41). A groove portion (47) is formed by cutting out a part thereof, and an annular support member (48) that matches the groove portion (47) is attached from one end side in the axial direction, and in the recess portion (41) . The decompression cam portion (36) is rotatably arranged, and at least during non-decompression operation, the decompression cam portion (36) is supported by a portion formed by the support member (48) on the inner peripheral bottom surface (41a) . The cam mechanism with a decompression device according to claim 1 . The cam mechanism with a decompression device according to claim 2 or 3 , wherein the camshaft (13) is made of titanium, and the collar member (45) and the support portion (48) are made of iron.

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