JPH066169Y2 - Automatic decompression device for starting internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a decompression device for an internal combustion engine, and more particularly to a flyweight for the decompression device.

[Conventional technology]

2 to 7 show a conventional device described in Japanese Utility Model Laid-Open No. 60-170009, in which the slide cam surfaces 6 and 7 of the flyweight 12 are planes or convex curved surfaces orthogonal to the decompression pin axis. There is.

FIG. 2 is a vertical sectional front view of the main part around the cam gear, and FIG.
FIG. 3 is a cross-sectional view taken along the line III-III in the figure, in which a crankshaft 31 is mounted in the center of the crankcase 30 of the overhead valve engine E,
Further, the valve gear cam shaft 2 is mounted above the crankshaft to
32 and the cam gear 5 are meshed with each other, and the crankshaft 31 and the valve operating camshaft 2 are interlocked.

By fixing the cam 3 formed on the valve operating cam shaft 2, the tubet 18 can be vertically driven, and the tubet 18 is connected to the valve operating mechanism 1 to drive the intake / exhaust valves in the head cover to be opened / closed.

Further, the cam shaft portion between the bearing 33 and the left cam 3 is a large-diameter rotating portion, and the cam gear 5 is rotatably fixed to this rotating portion, and the shaft portion between the cam gear 5 and the left cam 3 is fixed. A circular guide hole 8 is penetrated through the guide hole 8 in a transversely inclined shape so as to get closer to the cam gear 5 as it goes downward, and a decompression pin 10 is inserted into the guide hole 8 so as to be slidable forward and backward.

The side surface 11 of the cam gear 5 on the cam side is formed in a stepped shape, and a substantially U-shaped plate-shaped centrifugal weight 12 is located on the stepped side surface 11 at a fulcrum 34 located on the tabet 18 side when viewed from the cam axis D. As a result, the decompression spring 14 placed on the cam gear side surface 11 is engaged with the claw-shaped engaging portion 3 provided at the tip of the centrifugal weight to bias the centrifugal weight 12 in the centripetal direction C. To do.

The centrifugal weight 12 is formed by laminating two steel plates, and the tip output portion 15 is composed of a decompression cam surface portion 6 and a decompression releasing cam surface portion 7, and the decompression releasing cam surface portion 7 is made into a centrifugal weight 12. The decompression cam surface portion 6 is provided adjacent to the tip end of the above and adjacent to the base end side thereof.

The decompression cam surface portion 6 is formed on a flat surface that is substantially orthogonal to the virtual straight line H connecting the fulcrum pin 34 and the input end 16 of the decompression pin 10, and the decompression releasing cam surface portion 7 is used for the decompression. Camshaft 2 for cam surface portion 6
Is formed on a flat inclined surface that is distant from the axis D of, that is, an inclined surface that has a directionality that intersects the virtual straight line H at an acute angle.

Further, the decompression pin 10 is a cylindrical rod-shaped body in which a large-diameter cylindrical body is extended, and the tip of the rod-shaped body at one end and the tip of the large-diameter cylindrical body at the other end are each formed into a partially spherical shape, and the former is output. The end part 17 and the latter part form the input end part 16. Further, the output end portion 17 can be brought into contact with the tappet 18, and the input end portion 16 can be brought into contact with the output end portion 15 of the centrifugal weight 12, respectively, and a decompression position A for pushing up the tappet 18 by the tension of the spring 14, The decompression pin output end 17 can be switched and driven to the decompression releasing position B where the centrifugal force F of the centrifugal weight 12 overcomes the tension of the spring 14 and the tappet 13 is not pushed up.

At this time, the cam gear upper side of the left cam 3 is notched in a concave shape to bring the decompression pin 10 closer to the radial center side of the tappet 18 to accurately perform the upward movement of the tappet 18 to improve the accuracy of decompression operation. It is improving.

The function of the automatic decompression device thus constructed will be described. When the engine is started, the decompression spring 14 elastically biases the centrifugal weight 12 toward the centripetal side C, and the centrifugal weight output end 15 causes the decompression pin 10 to move.
Push the input end 16 of the, and then the output end above the decompression pin
17 pushes up the tappet 18 and fixes it at the decompression position A.

Therefore, since the pressure in the combustion chamber is reduced, the force required for starting can be reduced and the starting can be facilitated.

Moreover, the decompression pin 10 contacts the decompression cam face portion 6 of the centrifugal weight output end 15, and the imaginary straight line H connecting the fulcrum pin 34 and the input end 16 of the decompression pin 10 to this cam face portion 6
Since the connecting force of the decompression pin is almost perpendicular to the horizontal direction, that is, the centrifugal weight 12 rotates in the decompression releasing direction by the urging force of the valve closing spring through the decompression pin with almost no splitting of the force in the horizontal direction, that is, the lateral movement direction. To get rid of

On the other hand, if the engine rises above a certain speed, the centrifugal weight
Since the centrifugal force F acting on 12 overcomes the elastic force of the spring 14 to rotate the centrifugal weight 12 in the centrifugal direction, the decompression pin 10 has its input end 16 at the decompression releasing cam surface portion of the centrifugal weight output end 15. 7, and is pushed down in the decompression releasing direction by receiving the biasing force from the valve closing spring of the valve mechanism.

Also, the striking force that the decompression pin 10 imparts to the centrifugal weight 12 is
Since the horizontal component force acts on the cam surface portion 7 in proportion to the inclination angle between the virtual straight axis H and the decompression releasing cam surface portion 7, the centrifugal weight 12 receives the rotational moment in the decompression releasing direction F. , And can move quickly to the decompression release position together with its own centrifugal force.

[Problems to be solved by the device]

 The above-mentioned conventional technique has the following problems.

(1) Holding of the decompression pin 10 during decompression operation is uncertain.

For example, in FIG. 4 described above, although the decompression pin joint slide cam surface 6 of the flyweight 12 is orthogonal to the pin shaft 34, the flyweight 12 moves due to centrifugal force as the cam shaft 2 rotates. Especially when the engine suddenly rotates after stopping, the inertial force of the flyweight 12 is large and the decompression pin 10
Is likely to come off the slide cam surface 6 even when decompression is required.

(2) The lift amount of the decompression pin 10 lacks stability.

For example, in FIG. 4, there is a slight movement of the flyweight 12 due to a change in rotation even during decompression operation, but in this case, the plane orthogonal to the slide cam is a flyweight.
It moves in the direction of centrifugal force around the 12 fulcrum pins 34, but the distance from the center of the fulcrum pin 34 to the orthogonal surface 6 is not the same, and the amount of protrusion of the decompression pin 10 (the amount of pushing up the tappet) from the cam base changes. I will end up.

[Means for solving problems]

Place the flyweight operating center on the decompression pin axis,
The joint surface of the flyweight with the decompression pin is a concave circular arc having an equal distance R from the same center.

[Action]

Since the slide cam surface is concave and has an arc from the flyweight operation center, the pin is not disengaged and the lift amount does not change with a slight change in the flyweight movement, thus improving reliability.

〔Example〕

In FIG. 1, 50 is a decompression pin, 52 is a flyweight, 54 is a fulcrum pin, 56 is a concave slide cam during decompression,
57 is a pin contacting cam surface during non-decompression, 60 is a guide hole, 61 is a guide shaft, and 0 is a flyweight movement center.

The difference between the present invention and the conventional device will be described.

The flyweight 52 is rotatably supported by a fulcrum pin 54 on the axis line of the decompression pin 50, and a slide cam 56 is also provided.
A guide hole 60 is provided on the side for smooth and reliable movement of the weight 52 due to centrifugal force, and is rotatably held by a support tool 61 fixed to the camshaft 2 (see FIGS. 2 and 3). .

The slide cam 56 is formed by an arc R from the center of rotation 0, and is a smooth surface continuous with the cam surface 57 with which the decompression pin 50 makes contact when not decompressed.

[Effect of device]

The automatic decompression device of the present invention is a decompression device that operates a decompression pin by a flyweight (centrifugal weight) attached to a cam gear and pushes up a tappet to depressurize it at the time of starting. The following effects are brought about by making the circular shape of the slide cam an arc curved surface centered on the fulcrum of the flyweight arranged on the center line of the decompression pin axis.

(1) In the decompression state, the flyweight joint surface 56 of the decompression pin 50 is a concave surface, and even if the flyweight 52 slightly moves, the lateral movement component force due to the force P received from the valve train does not act. The decompression pin 50 is securely held.

(2) Similarly, during the process from the decompression operation to the non-decompression state, the decompression pin 50 makes the concave slide surface of the weight 52.
While in contact with 56, the lift amount of the tappet is constant due to the radius R, and the decompression amount can be stabilized.

[Brief description of drawings]

FIG. 1 is a front view of a main portion of an embodiment of the present invention, FIG. 2 is a front view of a vertical portion of a conventional cam gear, and FIG. 3 is a sectional view taken along the line III-III in FIG. Fig. 5 is a front view showing the rotating state of the fly weight 52 ... Fly weight, 0 point ... Weight moving center 56 ... Decompression concave surface stay cam 50 ... Decompression pin 57 ... Non decompression pin joining cam surface

Claims (1)

[Scope of utility model registration request] 1. A decompression device for actuating a decompression pin by a flyweight attached to a cam gear to push up a tappet to depressurize the engine at the time of starting. An automatic start-up decompression device for an internal combustion engine, characterized by having an arc curved surface centered on a fulcrum of a flyweight arranged on an axis centerline.