JP2006144627A - Decompression device of engine and motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To extend time during which compression pressure in a cylinder is reduced in a process of rotating a cam for moving a decompression pin. <P>SOLUTION: The device is equipped with a decompression shaft 24 freely turnably fitted in a hollow hole 21 of an exhaust cam shaft 7, a turning device 25 for turning the decompression shaft 24, and a decompression pin 22 projected from a radial end of the exhaust cam shaft 7 by turning the decompression shaft 24. A recessed groove 42 is formed in the decompression pin 22. An eccentric projection 32 is formed on an end surface in an axial direction of the decompression shaft 24. A cam mechanism 45 for changing the turning of the decompression shaft 24 into the reciprocating motion of the decompression pin 22 by bringing the eccentric projection 32 into slide contact with a wall surface of the recessed groove 42. A projected curved surface 33 with a cross sectional circular arc shape taking the shaft core of the decompression shaft 24 as a center is formed in a part coming into contact with the wall surface of the recessed groove 42 in the eccentric projection 32. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an engine decompression device and a motorcycle for reducing the compression pressure in a cylinder at the beginning of engine startup.

  As a conventional decompression device, for example, there is one disclosed in Patent Document 1. The decompression device disclosed in Patent Document 1 includes a decompression shaft that is rotatably supported in an axial direction in an engine valve camshaft, and a state in which the decompression shaft extends in a radial direction on the valve camshaft. A configuration is adopted in which an exhaust valve is opened by a decompression pin supported in a movable manner to reduce the compression pressure in the cylinder.

  The decompression shaft is rotatably inserted into an insertion hole that is drilled so as to extend in the axial direction in the axial center portion of the valve camshaft. A driving means having a centrifugal weight is connected to one end side of the decompression shaft, and a cam for changing the position of the decompression pin is provided on the other end side.

  The drive means is configured to rotate the decompression shaft from the initial position to the normal operation position by a centrifugal weight rotating integrally with the valve camshaft being displaced radially outward by centrifugal force. Further, this drive means returns the decompression shaft from the normal operation position to the initial position together with the centrifugal weight by the elastic force of the return spring when the rotation of the valve camshaft decreases. By this drive means, the decompression shaft is positioned at the initial position by the resilient force of the return spring until the valve camshaft rotates at a low speed from the stopped state when the engine is started. After rising to a predetermined number of revolutions, it is rotated by the centrifugal weight and positioned at the normal operation position.

The decompression shaft cam is constituted by an outer peripheral portion of a decompression shaft having a circular cross section and a flat surface formed at a part of the outer peripheral portion.
The decompression pin is movably fitted in a pin hole extending in the radial direction of the cam shaft. The pin hole is formed to extend from the decompression shaft insertion hole to one side in the radial direction. That is, this conventional decompression device is configured such that the extension line of the axis of the decompression pin passes through the axis of the decompression shaft when viewed from the axial direction of the decompression shaft.

  In the decompression pin, a pressing portion that protrudes in the vicinity of the cam of the valve camshaft and pushes the exhaust valve is formed at one end, and a flat surface that forms a cam follower with which the cam of the decompression shaft is slidably contacted is formed at the other end. The decompression pin is engaged with a C-shaped spring formed on the outer peripheral portion of the valve camshaft so as to extend in the circumferential direction, and is biased toward the decompression shaft by the spring.

In the conventional decompression device configured as described above, the decompression shaft is positioned at the initial position, and the outer peripheral portion of the decompression shaft constituting a part of the cam contacts the flat surface of the decompression pin, thereby pressing the decompression pin. The part protrudes from the valve camshaft. In this state, the exhaust valve is opened by the decompression pin, and the compression pressure in the cylinder is reduced.
In this decompression device, the decompression shaft rotates from the initial position to the normal operation position, and the flat portion of the cam contacts the flat surface of the decompression pin, so that the decompression pin moves back into the valve camshaft. In this state, the engine is in a normal operating state.
In addition, the applicant could not find prior art documents closely related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification. .
Japanese Patent Laid-Open No. 5-26017 (page 2-4, FIG. 7)

In the conventional decompression device disclosed in Patent Document 1, the period during which the compression pressure in the cylinder is reduced may be shortened. In such a case, the load at the time of cranking when the engine is started becomes large, and the startability is remarkably deteriorated.
In the conventional decompression device, the period during which the compression pressure in the cylinder is reduced is shortened because the cam (decompression shaft) is the elasticity of the valve spring for the exhaust valve when the decompression pin rotates from the initial position to the normal operation position. This is forcibly turned to the normal operation position.

  This decompression device is configured so that the extension line of the decompression pin axis passes through the axis of the decompression shaft when viewed from the axial direction of the decompression shaft, so that when the decompression shaft is located at the initial position, The contact point with the pin is located on an extension of the axis of the decompression pin. In this state, the elastic force of the exhaust valve spring acts from the decompression pin to the decompression shaft along the axis.

  However, when the decompression shaft starts to rotate from the initial position toward the normal operation position, the boundary between the outer peripheral portion of the cam and the flat surface comes into contact with the decompression pin and further rotates, so that this contact point is removed from the axis of the decompression pin. The decompression shaft moves in the direction of rotation. As described above, when the contact point deviates from the axis of the decompression pin, a rotational torque that rotates the cam toward the normal operation position is generated.

  The cam (decompression shaft) rotates in response to the difference between the centrifugal force acting on the centrifugal weight and the elastic force of the return spring. Will rotate. As a result, in this decompression device, as described above, the period during which the exhaust valve is opened by the decompression pin is shortened.

  The present invention has been made to solve such problems, and provides an engine decompression device capable of taking a long period of time during which the compression pressure in the cylinder can be reduced during the stroke of the decompression pin moving cam rotating. Objective.

  In order to achieve this object, a decompression device for an engine according to the present invention includes a valve train cam shaft having a hollow hole, a decompression shaft rotatably fitted in the hollow hole of the valve train cam shaft, An engine decompression device comprising: a turning device for turning the decompression shaft relative to the valve drive camshaft; and a decompression pin protruding from a radial end of the valve drive camshaft by turning the decompression shaft. In the decompression pin, a concave groove extending in a direction orthogonal to the axial direction of the valve operating camshaft is formed on the side facing the axial end portion of the decompression shaft, and the axial direction end surface of the decompression shaft is formed on the decompression pin. Is formed with an eccentric protrusion protruding at a position eccentric in the radial direction with respect to the axis of the decompression shaft, and the eccentric protrusion is in sliding contact with the wall surface of the concave groove, thereby A cam mechanism that changes the movement of the decompression pin into a reciprocating motion, and a convex curved surface having an arcuate cross section centering on the axis of the decompression shaft at a portion of the eccentric projection that slides on the wall surface of the concave groove of the decompression pin. Formed.

  An engine decompression device according to a second aspect of the present invention is the engine decompression device according to the first aspect, wherein the decompression pin has a radial end of a valve camshaft in a rotation stroke of the decompression shaft. In the first half of the stroke from the initial position where the amount of protrusion from the portion is maximum to the normal operation position where the amount of protrusion is minimum, the convex curved surface having an arc-shaped cross section is in sliding contact with the concave groove.

  A motorcycle according to a third aspect of the present invention is equipped with the engine decompression device according to the first aspect of the present invention.

According to the present invention, since the contact point between the convex curved surface of the eccentric protrusion and the wall surface of the concave groove is located on the axis of the decompression pin when viewed from the valve operating cam shaft direction, the convex curved surface contacts the wall surface of the concave groove. In this state, the rotational torque that rotates the eccentric protrusion is not generated by the elastic force of the valve spring applied to the decompression pin. For this reason, since a so-called dead zone is formed in the rotation range of the decompression pin, the feedback that the decompression pin projects from the valve camshaft can be lengthened.
Therefore, when the engine is started, the decompression pin always protrudes from the valve camshaft for a certain period, thereby reducing the compression pressure in the cylinder and improving the engine startability.

According to the second aspect of the present invention, the decompression pin can be reliably projected from the valve camshaft until the decompression shaft rotates by about half the total rotational angle of the decompression shaft after the engine is stopped.
Therefore, the pressure in the cylinder is always low at the start of cranking of the engine, making it easier to start the engine.

  According to the third aspect of the present invention, since the compression pressure in the cylinder is always reduced for a certain period when the engine is started, a motorcycle that can easily start the engine can be provided.

Hereinafter, an engine decompression device and a motorcycle according to an embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 1 is a structural view showing a cylinder head portion of a motorcycle engine equipped with a decompression device according to the present invention, FIG. 2 is a view showing a decompression shaft, FIG. 1 (a) is a side view thereof, and FIG. FIG. 3C is a rear view. 3 is a front view of the rotation device, FIG. 4 is a longitudinal sectional view of the decompression device according to the present invention, FIG. 5 is a sectional view for explaining the operation of the decompression shaft and decompression pin, and FIG. (B) shows a state where the end of the convex curved surface of the eccentric protrusion comes into contact with the decompression pin, and (c) shows a normal operation state. In addition, the fracture | rupture position of FIG. 5 is shown by the VV line in FIG. FIG. 6 is a graph showing the relationship between the rotation angle of the decompression shaft and the force pressing the decompression pin toward the initial position (decompression pin moving force), and FIG. 7 is a rotational torque (rotation torque for rotating the decompression shaft in the reverse direction). It is a graph which shows the relationship with a decompression shaft reverse rotation torque.

  In these drawings, reference numeral 1 denotes a cylinder head of a motorcycle engine according to this embodiment. The cylinder head 1 is provided with a valve operating device 4 for opening and closing the intake and exhaust valves 2 and 3. The cylinder head 1 is also provided with a decompression device 5 that reduces the compression pressure in the cylinder when the engine is started.

The valve operating device 4 is configured to open and close two intake valves 2 and two exhaust valves 3 provided for each cylinder by an intake cam shaft 6 and an exhaust cam shaft 7. The intake valve 2 and the exhaust valve 3 are closed by the resilient force of a valve spring (not shown) mounted between the valve lifter 8 and the cylinder head 1, and the valve lifter 8 resists the resilient force of the valve spring. Is opened by being pressed by the cam 9 of the intake camshaft 6 or the cam 10 of the exhaust camshaft 7.
The intake camshaft 6 and the exhaust camshaft 7 have sprockets 11 and 12 attached to one end in the axial direction (hereinafter, this one end is referred to as a base end), and a timing chain 13 wound around the sprocket 11 and 12. The rotation of a crankshaft (not shown) is transmitted by

  As shown in FIG. 4, the exhaust camshaft 7 is formed in a hollow shape with a hollow hole 21 formed in an axial center portion, and a cam 10 is provided at a tip portion and a central portion in the axial direction. . Of these cams 10, the cam located at the tip of the exhaust camshaft is designated by reference numeral 10a, and the cam located at the center is designated by reference numeral 10b. The exhaust camshaft 7 constitutes a valve operating camshaft referred to in the present invention, and the hollow hole 21 constitutes a hollow portion referred to in the present invention. Further, a pin hole 23 through which a decompression pin 22 of the decompression device 5 described later is inserted is formed at a central portion in the axial direction of the exhaust cam shaft 7 and adjacent to the central cam 10b. The pin hole 23 extends in a direction perpendicular to the axial direction of the exhaust cam shaft 7.

  The pin hole 23 is a position adjacent to the cam 10b located at the center of the exhaust camshaft 7 out of the two cams 10a and 10b provided on the exhaust camshaft 7, and the exhaust cam from the cam 10b. It is formed on the base end side of the shaft 7. Further, as shown in FIG. 5, the pin hole 23 is formed so that the center line L passes through the axis C <b> 1 of the exhaust cam shaft 7 when viewed from the axial direction of the exhaust cam shaft 7. Only the shaft portion of the exhaust cam shaft 7 shown in FIG. 5 is drawn.

  As shown in FIGS. 3 and 4, the decompression device 5 includes a decompression shaft 24 inserted into the hollow hole 21 of the exhaust cam shaft 7, and one end portion of the decompression shaft 24 (the base end portion of the exhaust cam shaft 7. And the decompression pin 22 connected to the other end of the decompression shaft 24.

  As shown in FIG. 2, the decompression shaft 24 includes a disc 26 located at one end (the end on the proximal end side of the exhaust camshaft 7), a disc 27 located at the other end, A small-diameter rod 28 is formed integrally with the disks 26 and 27 and connects the two disks. The decompression shaft 24 is formed so as to extend from the base end portion of the exhaust cam shaft 7 to the exhaust valve cam 10b on the center side.

The outer diameters of the discs 26 and 27 at both ends of the decompression shaft 24 are formed so as to be able to fit in the hollow hole 21 of the exhaust camshaft 7 in a freely rotatable manner.
On the outer end surface of the disk 26 located on one end side of the decompression shaft 24, an engaging groove 30 is formed which is connected to a centrifugal weight 29 (see FIGS. 3 and 4) of the rotating device 25 described later. A stopper 31 for determining the initial position of the centrifugal weight 29 is provided. As shown in FIG. 2A, the engaging groove 30 is formed so as to extend radially inward from the outer peripheral portion of the disk 26. As shown in FIGS. 2A and 3, the stopper 31 has a fan shape when viewed from the axial direction of the decompression shaft 24, and has an outer peripheral portion that protrudes from the disk 26.

The disc 27 at the other end of the decompression shaft 24 is provided with an eccentric projection 32 connected to a decompression pin 22 described later so as to extend outward in the axial direction.
As shown in FIG. 2, the eccentric protrusion 32 is formed in a columnar shape having a shorter length than the outer diameter, and is an outer end surface of the disk 28, and is formed with respect to the axis of the decompression shaft 24. It is provided at a position eccentric in the radial direction. A convex curved surface 33 having a radius of curvature different from that of the other portion is formed on a part of the outer peripheral surface of the eccentric protrusion 32 (a portion that slides on a lower wall (lower wall surface) 43 of a groove 42 described later). Has been.

  As shown in FIG. 2 (c), the convex curved surface 33 is formed in a cross-sectional arc shape centering on the axis of the decompression shaft 24 (center of the disk 27). The radius of the circular arc constituting the convex curved surface 33 is indicated by a symbol r in FIG. In this embodiment, since the decompression shaft 24 is located on the same axis as the exhaust cam shaft 7, the center C2 of the convex curved surface 33 (the axis center of the decompression shaft 24) is the axis C1 of the exhaust cam shaft 7 { This corresponds to that in FIG.

  As shown in FIGS. 3 and 4, the rotating device 25 for driving the decompression shaft 24 includes a centrifugal weight 29 rotatably supported by a support shaft 34 on the sprocket 12 of the exhaust camshaft 7, and the support shaft. The return spring 35 is held by a shaft 34. As shown in FIG. 4, the support shaft 34 is arranged at a position eccentric in the radial direction from the axis of the sprocket 12.

  As shown in FIG. 3, the centrifugal weight 29 includes a weight main body 36 formed so as to extend in an arc shape from the support shaft 34 when viewed from the axial direction of the exhaust cam shaft 7, and the axis of the sprocket 12 from the support shaft 34. And a drive arm 37 formed so as to extend to the side, and is accommodated in a circular recess 38 formed on the outer end surface of the sprocket 12.

  The centrifugal weight 29 is configured to rotate clockwise around the support shaft 34 with respect to the sprocket 12 in FIG. 3 due to centrifugal force generated by rotating integrally with the exhaust camshaft 7. An outer edge portion 36 a that is one side portion in the rotational direction of the centrifugal weight 29 and faces the peripheral wall surface of the circular recess 38 is formed in an arc shape along the peripheral wall as viewed from the axial direction of the sprocket 12. As shown in FIG. 3, the centrifugal weight 29 is restricted from moving due to the centrifugal force when the outer edge portion 36 a formed in an arc shape comes into contact with the peripheral wall.

  As shown in FIG. 4, the driving arm 37 of the centrifugal weight 29 is provided with a driving pin 39 protruding inward of the exhaust cam shaft 7 along the axial direction of the exhaust cam shaft 7. The drive pin 39 is formed in a columnar shape that fits into the engagement groove 30 formed at one end of the decompression shaft 24. In the decompression device 5 according to this embodiment, the driving pin 39 rotates with respect to the sprocket 12 together with the centrifugal weight 29, so that the rotational force is transmitted from the centrifugal weight 29 to the decompression shaft 24 via the driving pin 39. Then, the decompression shaft 24 rotates between the initial position shown in FIG. 5 (a) and the normal operation position shown in FIG. 5 (c).

  More specifically, when the centrifugal weight 29 is moved to the position shown by the solid line in FIG. 3, the decompression shaft 24 is positioned at the normal operation position shown in FIG. Further, in a state where the centrifugal weight 29 is at the position indicated by the two-dot chain line in FIG. 3, the decompression pin 22 is positioned at the initial position shown in FIG.

  The return spring 35 is a torsion spring. As shown in FIGS. 3 and 4, one end 35 a is engaged with the outer edge 36 a of the centrifugal weight 29 and the other end 35 b is engaged with the sprocket 12. The centrifugal weight 29 is urged counterclockwise in FIG. The movement of the centrifugal weight 29 biased by the return spring 35 is restricted by coming into contact with the stopper 31 of the decompression shaft 24 positioned at the initial position, as indicated by a two-dot chain line in FIG.

  In the rotating device 25, when the rotational speed of the exhaust camshaft 7 is lower than a predetermined rotational speed, the centrifugal weight 29 is moved to the initial position indicated by a two-dot chain line in FIG. Retained. The centrifugal weight 29 increases the rotation of the exhaust camshaft 7 and increases the applied centrifugal force, so that the sprocket 12 resists the elastic force of the return spring 35 as shown by the solid line in FIG. Oscillates clockwise with respect to. As the centrifugal weight 29 swings in this manner, the position of the driving pin 39 changes, and the decompression shaft 24 having the engaging groove 30 that engages with the driving pin 39 rotates with respect to the exhaust cam shaft 7. .

  The direction in which the decompression shaft 24 rotates at this time is clockwise in FIG. The eccentric protrusion 32 of the decompression shaft 24 according to this embodiment is located at the initial position shown in FIG. 5A when the engine is stopped, and rotates clockwise in FIG. 5 immediately after the start of engine cranking. Is held at the normal operation position shown in FIG.

  As shown in FIG. 5, the decompression pin 22 connected to the eccentric protrusion 32 is formed in a cylindrical shape having a length substantially equal to the outer diameter of the exhaust camshaft 7, and the pin hole of the exhaust camshaft 7 23 is movably inserted. At one end of the decompression pin 22, a pressing surface 41 made of a spherical surface that is in sliding contact with the valve lifter 8 is formed. In the middle of the decompression pin 22 in the axial direction, a concave groove 42 with which the eccentric protrusion 32 of the decompression shaft 24 comes into sliding contact is formed.

  The concave groove 42 extends in a direction orthogonal to the axial direction of the exhaust cam shaft 7 on the side facing the shaft end of the decompression shaft 24 and opens into the hollow hole 21 of the exhaust cam shaft 7. 22 is formed on the outer peripheral portion. The opening width (groove width) between one side wall (hereinafter, this side wall is referred to as the lower wall 43) located on one end side having the pressing surface 41 of the decompression pin 22 in the concave groove 42 and the other side wall 44 is as follows. The eccentric protrusion 32 is formed so as to be slightly larger than the outer diameter (the maximum diameter of a portion different from the convex curved surface 33).

  The concave groove 42 and the eccentric protrusion 32 that is in sliding contact with the concave groove 42 constitute a cam mechanism 45 that changes the rotation of the decompression shaft 24 into the reciprocating motion of the decompression pin 22. That is, when the decompression shaft 24 is pivoted with respect to the exhaust camshaft 7 by the pivoting device 25, the decompression pin 22 is pinned by the cam mechanism 45 as shown in FIGS. 5 (a) to 5 (c). Reciprocates within. As shown in FIG. 5A, the eccentric protrusion 32 and the decompression pin 22 are such that one end portion of the convex curved surface 33 of the eccentric protrusion 32 is below the concave groove 42 in a state where the decompression shaft 24 is located at the initial position. The pressing surface 41 of the decompression pin 22 is configured to protrude from the exhaust camshaft 7 in contact with the wall 43.

  The one end portion of the convex curved surface 33 is a front end portion in the rotational direction of the convex curved surface 33 when the decompression shaft 24 rotates from the initial position shown in FIG. 5A to the normal operation position shown in FIG. In the initial position, the contact point A between the convex curved surface 33 and the lower wall 43 is the axial direction of the decompression pin 22 because the convex curved surface 33 is formed in a circular arc shape with the axis C2 of the decompression shaft 24 as the center. As viewed from the center line L of the pin hole 23 (on the axis line of the decompression pin 22).

  When the exhaust camshaft 7 rotates with the decompression shaft 24 positioned at the initial position, the valve lifter 8 is pushed by the decompression pin 22, and the exhaust valve 3 is opened during the compression stroke, thereby reducing the compression pressure in the cylinder. . At this time, the decompression pin 22 is pressed upward in FIG. 5A by the resilient force of the valve spring because the pressing surface 41 contacts the valve lifter 8. This pressing force is applied to the eccentric protrusion 32 from the decompression pin 22 through the contact point A.

  As the decompression shaft 24 rotates in the clockwise direction in FIG. 5 from the initial position toward the normal operation position, the position of the convex curved surface 33 relative to the lower wall 43 also changes. However, since the center of the circular arc constituting the convex curved surface 33 is the axis C2 of the decompression shaft 24, the contact point A between the convex curved surface 33 and the lower wall 43 is as shown in FIGS. The position on the center line L does not change when viewed from the axial direction of the exhaust camshaft 7.

  That is, as shown in FIG. 5A, the initial position where one end portion of the convex curved surface 33 contacts the lower wall 43, and the other end portion of the convex curved surface 33 is the lower wall 43 as shown in FIG. The intermediate compression pin 22 is held at the initial position regardless of the rotation of the decompression shaft 24. In this embodiment, the decompression shaft 24 is configured to be positioned at the intermediate position when rotated about 40 ° from the initial position.

  When the decompression shaft 24 further rotates from the intermediate position shown in FIG. 5B, the outer peripheral surface 32 a adjacent to the convex curved surface 33 of the eccentric protrusion 32 comes into contact with the lower wall 43, and the eccentric protrusion 32 moves. Accordingly, the contact point A moves to the left in FIG. 5 and the amount of protrusion of the decompression pin 22 from the exhaust camshaft 7 gradually decreases. The decompression device 5 is configured such that the amount of protrusion of the decompression pin 22 becomes zero when the decompression shaft 24 is positioned at the normal operation position shown in FIG. That is, when the decompression shaft 24 rotates to the normal operation position, the exhaust valve 3 does not open in the compression stroke, so that the engine can be operated normally.

  The decompression device 5 according to this embodiment is configured such that the decompression shaft 24 is positioned at the normal operation position by rotating about 80 ° from the initial position. For this reason, the convex curved surface 33 has a minimum protruding amount from an initial position where the protruding amount of the decompression pin 22 from the radial end portion of the exhaust cam shaft 7 is maximized during the rotation stroke of the decompression shaft 24. In the first half of the stroke up to the driving position, it comes into sliding contact with the lower wall 43 of the groove 42.

  For this reason, according to the decompression device 5 according to this embodiment, the eccentric protrusion 32 until the decompression shaft 24 rotates from the initial position shown in FIG. 5A to the intermediate position shown in FIG. 5B. Since the contact point A between the convex curved surface 33 and the lower wall 43 of the concave groove 42 is located on the axis of the decompression pin 22 (on the center line L of the pin hole 23), the spring of the valve spring applied to the decompression pin 22 Rotational torque that rotates the eccentric protrusion 32 toward the normal operation position by force is not generated. Therefore, the decompression device 5 can hold the decompression pin 22 at the same position (initial position) in the axial direction in the first half of the stroke in which the decompression shaft 24 rotates from the initial position to the normal operation position.

  In the decompression device 5 according to this embodiment, the force (decompression pin 22 movement force) by which the decompression pin 22 is pushed by the rotation of the decompression shaft 24 changes as shown in FIG. Further, in this decompression device 5, when the decompression pin 22 is pressed by the valve lifter 8, the rotational torque (decompression shaft 24 reverse rotational torque) generated to rotate the decompression shaft 24 to the normal operation position side is as shown in FIG. Change. 6 and 7, the case where the eccentric protrusion 32 is provided with the convex curved surface 33 is indicated by a broken line, and the case where the eccentric protrusion 32 is not provided with the convex curved surface 33 is indicated by a solid line.

  As is apparent from FIGS. 6 and 7, when the convex curved surface 33 is not provided, a force that presses the decompression pin 22 in the direction in which the protrusion amount decreases from the initial rotation of the decompression shaft 24 acts. By providing the convex curved surface 33 as described above, it can be seen that no force for moving the decompression pin 22 is generated until the decompression shaft 24 rotates about 40 ° from the initial position.

  Therefore, in the decompression device 5 according to this embodiment, a so-called dead zone is formed in the rotation range of the decompression shaft 24, so that the decompression pin 22 projects from the exhaust camshaft 7 by that amount. Can be made longer than the conventional decompression device. For this reason, in the decompression device 5 according to this embodiment, the decompression pin 22 always protrudes from the exhaust camshaft 7 for a certain period when the engine is started, and the compression pressure in the cylinder can be reduced. As a result, by mounting this decompression device 5 on the engine of a motorcycle, a motorcycle with good engine startability can be manufactured.

  In addition, the decompression device 5 according to this embodiment is configured so that the decompression pin 22 is moved from the state where the engine is stopped until the decompression shaft 24 rotates by about half of the total rotational angle of the decompression shaft 24 (about 40 °). It can be reliably projected from the exhaust camshaft 7. For this reason, according to the decompression device 5 according to this embodiment, when the cranking of the engine starts, the compression pressure in the cylinder is always in a low state, so that the engine can be started more easily.

It is a block diagram which shows the cylinder head part of the engine for motorcycles equipped with the decompression apparatus which concerns on this invention. It is a figure which shows a decompression shaft. It is a front view of a rotation apparatus. It is a longitudinal cross-sectional view of the decompression apparatus which concerns on this invention. It is sectional drawing for demonstrating operation | movement of a decompression shaft and a decompression pin. It is a graph which shows the relationship between the rotation angle of a decompression shaft, and decompression pin moving force. It is a graph which shows the relationship between the rotation angle of a decompression shaft, and decompression shaft reverse rotation torque.

Explanation of symbols

3 ... exhaust valve, 5 ... decompression device, 7 ... exhaust camshaft, 8 ... valve lifter, 21 ... through hole, 22 ... decompression pin, 23 ... pin hole, 24 ... decompression shaft, 25 ... rotating device, 29 ... centrifugal weight, 32 ... Eccentric protrusion, 33 ... Convex curved surface, 42 ... Concave groove, 43 ... Lower wall.

Claims (3)

  A valve operating camshaft having a hollow hole, a decompression shaft rotatably fitted in the hollow hole of the valve operating camshaft, and a rotating device for rotating the decompression shaft relative to the valve operating camshaft And a decompression pin for an engine that protrudes from a radial end portion of the valve camshaft by the rotation of the decompression shaft, wherein the decompression pin faces the shaft end portion of the decompression shaft. A concave groove extending in a direction perpendicular to the axial direction of the valve camshaft is formed on the side, and the axial end surface of the decompression shaft protrudes at a position eccentric in the radial direction with respect to the axis of the decompression shaft. And a cam mechanism for changing the rotation of the decompression shaft into the reciprocating motion of the decompression pin when the eccentric projection is in sliding contact with the wall surface of the concave groove. A portion which slides on the wall surface of the groove of the decompression pin in section, the decompression device of the engine, characterized in that the formation of the arcuate cross section of a convex curved surface centered on the axis of the decompression shaft.   2. The decompression device for an engine according to claim 1, wherein the amount of projection of the decompression pin is minimized from an initial position where the amount of projection of the decompression pin from the radial end of the valve camshaft is maximized during the rotation stroke of the decompression shaft. The decompression device for an engine according to the first aspect, wherein the convex curved surface having an arcuate cross section is in sliding contact with the concave groove in the first half of the stroke up to the operating position. A motorcycle equipped with the engine decompression device according to claim 1.

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