JP3450996B2 - Engine decompression device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine decompression device.

[0002]

2. Description of the Related Art As is well known, in a small portable engine, when the engine valve arranged in the combustion chamber is opened and closed at the time of starting, the pressure in the compression stroke is reduced to reduce the compression resistance of the piston. Some are equipped with a decompression device and are provided with a configuration that reduces the labor of an operator (for example, Japanese Patent Laid-Open No. Hei 9 (1999) -96945).
-184410). Conventionally, as a principle of this type of decompression device, the opening amount of the engine valve used in the normal combustion cycle is increased to some extent only at the time of starting, and the compression pressure acting on the piston in the rising process is released to reduce the compression resistance. It is designed to reduce. As an apparatus using the above principle, there is an apparatus having the configuration shown in FIG. Figure 6
FIG. 2 is a schematic diagram showing the decompression device described in the above publication, in which the decompression device D is arranged in the direction orthogonal to the axial direction of the cam shaft C1 in the vicinity of the shaft C1 of the cam C (hereinafter referred to as the cam shaft) C1. A decompressor F having a support shaft E having an axial direction as a fulcrum is provided. One end of the decompressor F, which sandwiches the support shaft E, is bent in such a direction that it can face the cam surface of the cam C to form an operating piece F1.
The other end is bent in the opposite direction to the actuating piece 4A to form a driving piece F2. Below the decompressor F, a centrifugal lever H which is swingable around a fulcrum shaft G supported by a part of a cam C is arranged, and a driving piece F2 of the decompressor F is disposed on the swing end side. Has been inserted. In the above structure, one end of the coiled spring J wound around the fulcrum shaft G is hooked on the centrifugal lever H, so that the centrifugal lever H is swingably biased in a direction against centrifugal force.
As a result, the decompressor F is biased counterclockwise in FIG. 6 with the support shaft E as a fulcrum, and the operating piece F1 is projected so as to face the cam surface of the cam C.
On the other hand, the centrifugal lever H swings to the opposite side to the previous one when the centrifugal force acts more than the biasing force of the coil spring J when the cam shaft C1 reaches a predetermined rotational speed or more. Therefore, the decompressor F swings clockwise in FIG. 6 around the support shaft E as a fulcrum, and retracts the operating piece F1 from a position facing the cam surface to a position not facing as shown by a chain double-dashed line.
The state where the operating piece F1 of the decompressor F faces the cam surface corresponds to the engine startup, and the action of centrifugal force is not large. The state where the operating piece F1 of the decompressor F retracts from the cam surface is This is the state after the start of the engine where the action of centrifugal force is large. Therefore, when the engine is started, the operating piece F1 of the decompressor F faces the cam surface, so that the lift amount of the cam C in the normal combustion process is slightly increased and the engine valve is slightly opened. Therefore, the compression pressure can be reduced. After the engine is started, the centrifugal lever H is adjusted as the centrifugal force increases as the engine speed increases.
Spreads outwards against the bias of the helical spring G, so that the operating piece F1 of the decompressor F withdraws from the cam surface and the opening / closing control of the engine valve according to the normal combustion cycle is performed.

[0003]

On the other hand, the conventional decompression device has the following problems. That is, as is clear from the configuration shown in FIG. 6, the structure becomes large and the structure becomes complicated due to the large number of parts. In particular,
Not only the number of parts is increased by requiring the support shaft E and the support shaft G in addition to the cam shaft C1, but also the decompressor F attached to the support shaft E moves in the direction parallel to the cam shaft C1. Since the F1 and the driving piece F2 are provided, the space occupied by the cam shaft C1 in the axial direction becomes large. Regarding the space occupied in the axial direction of the cam shaft C1, the shape of the cover used to close the back side of the centrifugal lever H also affects. That is, the decompressor F is attached to the inner surface of the cover.
Since the ends of the support shaft E face each other, it is necessary to prevent the support shaft E and the cover from interfering with each other. For this reason, the shape of the cover is determined in order to avoid the end portion protruding from the decompressor F. Therefore, the cover of the so-called so-called parallel shape to the back surface of the decompressor F is used to form the cover. The space between the cover and the cover cannot be reduced. From this also, the occupied area in the axial direction of the cam shaft C1 in the decompression device D becomes large,
Miniaturization is hindered.

An object of the present invention is to provide a decompression device having a simple structure and a structure that can be easily miniaturized in view of the problems in the conventional decompression device.

[0005]

In order to achieve this object, the invention according to claim 1 reduces the opening amount of the intake valve (7) and / or the exhaust valve (8) at the time of starting the small engine (1). A decompression device for setting the compression pressure to a pressure lower than that during a normal combustion cycle by increasing
The cam (20) is integrally molded with the cam gear (24) to form a cam block.
A recess (30A) forming a lock (30), which is formed on a surface of the cam gear (24) on the side opposite to the cam (20) in the axial direction, and a cam (2) facing the recess (30A).
0) communicates with the inside of the cam (20) to form an opening (30B) facing the contour surface (20A) of the cam (20), and a cutout portion that can be exposed to the opening (30B) in a part of the peripheral surface. (31
The flyweight (31) having a shaft portion (31A) formed with B) and whose swing amount is variable according to the rotation speed of the cam (20) is provided in the opening (30B). ) Is swingably supported in a direction parallel to the camshaft (19), and when the engine (1) is started, a part (3) of the cutout portion (31B) of the flyweight (31).
1B1) is provided on the contour surface (20A) of the cam (20) with an elastic member (32) for giving a habit, and the concave portion is provided.
If it has a peripheral height corresponding to the depth of the place (30A)
Plural pieces, both of which are formed on the cam block (30).
Locking claw (33
B) having a flat surface when fitted in the recess (30A)
The bottom surface (33A) formed on the side surface of the cam gear (24)
The recess (30A) is covered with a cap member (33) having the same flat surface as that of the cap member (33).
Is the elastic member (32) and the flyweight (3).
It is characterized in that it is configured to prevent the removal of 1).

The invention according to claim 2 is characterized in that the cap member (33) is provided so as not to protrude outside of a side surface of the cam gear (24) provided with the recess (30A). There is.

[0007]

According to the first aspect of the invention, the contoured surface of the cam is formed by communicating the recess formed in the surface of the cam opposite to the axial cam surface with the inside of the cam facing the recess. A flyweight whose shaft part is swingably supported in the opening facing the opening, and a cutout part which can be exposed to the opening is formed in a part of the shaft part of the flyweight to form a contour surface of the cam. Since they can face each other, a part of the flyweight is used as a member for changing the outer dimension of the contour surface of the cam, which requires a special member for changing the outer dimension of the contour surface. Therefore, the number of constituent parts can be reduced. Moreover, the flyweight is swingably supported in the opening facing the contour surface of the cam by the communication of the recess and the inside of the cam facing the recess, and the flyweight is prevented from coming off by the cap member. Concave
When fitted easily in place, it is flush with the side of the cam gear
Since the flyweight is partially stored in the recess and the inside of the cam in the axial direction of the cam, the space occupied in the axial direction of the cam can be reduced. .

According to the second aspect of the present invention, the bottom surface of the cap member does not protrude from the side surface of the cam gear, so that the axial length of the cam gear including the cam and the cap member is not excessively increased. Can be

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the invention described in the claims will be described below with reference to illustrated embodiments. FIG. 1 is a diagram showing a main structure of a portable engine to which a decompression device according to the claimed invention is applied. The portable engine 1 shown in the same figure is a cylinder housed inside a case 2. It is configured by an overhead valve type four-cycle engine that includes a head 3, a cylinder block 4, a crankcase 5, and a valve gear 6 to be described later in detail. That is,
The cylinder head 3 is provided with an intake valve 7, an exhaust valve 8 and an ignition plug 9 as in this type of 4-cycle engine.
Is provided with a crankshaft 10 whose axial ends are supported by these members. A drive shaft 12 of the work machine is connected to one end of the crankshaft 10 in the axial direction via a cooling rotary blade 11, and an engaging disc 14 that can be linked to a starter 13 is connected to the other end of the crankshaft 10 in the axial direction. The crankshaft 10 has a connecting rod 1
5, the piston 16 is attached, and the piston 16
Are slidable in the cylinder 4A in the cylinder block 4. An intake port and an exhaust port that communicate with a carburetor and an exhaust muffler (not shown) are formed at the top of the cylinder head 3, and the intake valve 7 and the exhaust valve 8 are arranged for each of these ports.

On the other hand, the valve operating device 6 is attached to a rocker arm 18 arranged in the cylinder head cover 3A located above the cylinder head 3 and a cam shaft 19 parallel to the rotation center of the crankshaft 10. The cam 20, two lifters 21 forming a cam follower member, a part of which contacts the cam surface of the cam 20, and the lifter 2
1 and two push rods 22 located between the rocker arms 18. The rocker arm 18 is
It is rockably supported by a rocker shaft 18A arranged in the cylinder head cover 3A, and is in a positional relationship capable of pressing the stem ends of the intake valve 7 and the exhaust valve 8.

In FIG. 1, the cam 20 is rotationally driven by a cam gear 24 having a rotation ratio of 1: 2 with respect to a cam drive gear 23 mounted on the crankshaft 10. .

On the other hand, the cam 20 described above is provided with a decompression device. The decompression device is shown in FIGS.
As shown in, the cam block 30 is integrally formed with the cam 20 and the cam gear 24, the fly weight 31, the elastic member 32, and the cap member 33. Hereinafter, each member will be described. In the cam block 30,
As shown in FIGS. 2 and 3 (A), a recess 30A is formed on a surface of the cam 20 opposite to the contour surface of the cam 20 in the axial direction (hereinafter, indicated by reference numeral 20A), and the recess 30A and the cam are formed. An opening 30 </ b> B facing the contour surface 20 </ b> A of the cam 20 is formed at a position where the cam 20 communicates with the position facing the recess 30 </ b> A.

2 and 3A, the opening 30
The shaft portion 31A of the flyweight 31 is arranged at B so as to be exposed. That is, the flyweight 31 has a shaft portion 31A in a direction parallel to the camshaft 19, and a cutout portion 31B is formed in a part of the shaft portion 31A. As shown in FIG. 4 (A), the cutout portion 31B has a surface along the diameter of the shaft portion 31A, and the rotation direction of the cam 20 (FIG. 4 (B)) at the end of the surface. The end portion 31B1 located on the downstream side (in the direction indicated by the reference symbol R) has the cam 20.
It is cut so as to be approximately parallel to the contour surface 20A. Therefore, when the end portion 31B1 protrudes in a state of being approximately parallel to the contour surface 20A of the cam 20,
As shown by the solid line in FIG. 4 (B) and as shown in FIG. 3 (B), the cutout portion 31B continuous to the end portion 31B1 thereof is in the rotational direction of the cam 20 with respect to the contour surface 20A (direction indicated by arrow R). The inclined surface is formed in a state where the height increases from the upstream side to the downstream side.

The flyweight 31 has a structure shown in FIGS.
As shown in (A), an elastic member 32 composed of a helical spring is wound around the shaft portion 31A. Elastic member 32
Is a recess 30A of the cam block 30 as shown in FIG.
The flyweight 31 is provided with the stopper S formed on the inner wall surface and the end face of the flyweight 31 in the vicinity of the shaft portion 31A, respectively. The flyweight 31 is oscillated and urged counterclockwise in FIG. There is. Due to this swinging bias, the flyweight 31 causes the end portion 31B1 of the cutout portion 31B to protrude from the opening 30B of the cam block 30 as shown by the solid line in FIGS. 3 (A) and 4 (B). It overlaps the surface of the contour surface 20A. As a result, the outer dimension of the contour surface 20A of the cam 20 is increased by the extent that the end portion 31B1 of the cutout portion 31B of the flyweight 31 overlaps the contour surface 20A.

As a biasing force of the elastic member 32 described above, the cutout portion 31B, particularly the end portion 31B1 of the flyweight 31 is made to face the contour surface 20A of the cam 20 when the engine is started. It is said that it can be a biasing force. In other words, it is an urging force that enables the flyweight 31 to swing when a centrifugal force obtained by the number of revolutions during normal operation after the engine is started acts. For this reason, after the engine is started, at the stage when the engine is in normal operation, the flyweight 31 swings against the urging of the elastic member 32, so that the end portion 31B1 of the cutout portion 31B rotates and the cutout portion 31B1 rotates. The direction of 31B changes. In this case, the cutout portion 31B is oriented so that a state in which the cutout portion 31B is retracted from the contour surface 20A of the cam 20 can be set, as indicated by a chain double-dashed line in FIGS. Note that FIG.
Is a cam block 3 excluding a cap member 33 described later.
0 shows a bottom view of 0.

On the other hand, as shown in FIGS. 2 and 3, the cap member 33 is formed of a molded part made of a flexible resin material, the surface of the cam block 30 facing the recess 30A being open. ing. The end surface of the cap member 33 opposite to the open surface is formed as a bottom surface 33A, and the bottom surface 3A
3A is a flat surface. The peripheral edge of the cap member 33 is formed at a height corresponding to the depth of the recess 30A of the cam block 30, and locking claws 33B are provided at a plurality of locations along the circumferential direction. The locking claw 33B can penetrate to the surface of the cam block 30 on the cam gear 24 side and can engage with the engagement hole 24A formed in the surface, whereby the cap member 33 can be recessed in the cam block 30. It is fitted in the place 30A and is prevented from coming off. The cap member 33 has a peripheral edge height of the recess 30A of the cam block 30.
3A, the bottom surface 33A is flush with the side surface of the cam gear 24 when fitted into the recess 30A, as shown in FIG. 3A. .
The bottom surface 33A may be located in the recess 0A of the cam gear 24 so that it does not protrude outside the side surface of the cam gear 24.

Since this embodiment has the above-mentioned structure,
Fly weight 31 is provided at the opening 30B of the cam block 30.
Is pivotally supported. That is, the shaft portion 31 of the flyweight 31
A is placed in the opening 30B of the recess 30A, and its shaft portion 31
By inserting A into the side surface of the cam gear 24, it is swingably supported. The flyweight 31 supported in the opening 30B is held between the flyweight 31 and the stopper S (see FIG. 5) located in the recess 30A of the cam block 30.
2, the end portion 31B1 of the cutout portion 31B has an opening 30B.
Emerge from. As a result, as shown by the solid line in FIGS. 2 and 3B, the end portion 31B1 of the cutout portion 31B is arranged on the surface of the contour surface 20A of the cam 20 in a protruding state, and the outer shape of the contour surface 20A. The dimensions are slightly increased. When the fly weight 31 is incorporated into the cam block 30, the cap member 3 is attached to the open surface of the recess 30A.
3 is attached. The cap member 33 is prevented from coming off from the recess 30A by the locking claw 33B being inserted into the engaging hole 24A of the cam block 30 and being hooked, so that the flyweight 31 and the elastic member 32 can be prevented from coming off.

As shown in FIGS. 3 (B) and 4 (B), the above-mentioned end portion 31B1 is made different from the direction in which the cutout portion 31B is formed. Therefore, when the cam 20 rotates, it is against the lifter 21. The notch 31B forming the inclined surface is the end 31
Since it abuts before B1, unlike the so-called step that collides with the lifter 21, the end portion 31B can be smoothly moved.
Can be listed in 1. Opening 30 at the end 31B1
By advancing from B, the amount of movement of the lifter 21 increases, the intake valve 7 and the exhaust valve 8 are slightly opened, and the compression resistance during compression of the piston is reduced. Either the intake valve 7 or the exhaust valve 8 may be slightly opened, and preferably only the exhaust valve 8 may be slightly opened.

On the other hand, when the engine speed increases and the rotation speed of the camshaft 19 increases after the start, the centrifugal force acting on the flyweight 31 also increases. For this reason,
The flyweight 31 swings against the biasing force of the elastic member 32, so that the flyweight 31 keeps its swinging end away from the camshaft 19 as shown by the chain double-dashed line in FIGS. 4 (B) and 5. Rock to. As a result, the shaft portion 31
A also rotates in conjunction with the end portion 31B1 of the cutout portion 31B.
Retract inside the opening 30B. As a result, the contour surface 20A of the cam 20 has an outer dimension used for a normal combustion cycle, so that the stroke of the intake valve 7 and / or the exhaust valve 8 can correspond to the normal combustion cycle.

According to the above embodiment, the end portion 31B1 continuous with the cutout portion 31B gradually pushes up the lifter 21 from the upstream side to the downstream side in the rotation direction of the cam 20 when it comes out from the opening 30B. Therefore, the lifter 21 is not subjected to an excessive impact force.
The durability of No. 1 can be improved. Further, since the cap member 33 reliably prevents the cap member 33 from coming off in the axial direction by engaging the locking claw 33B with the engagement hole 24A, the flyweight 31 simply causes the shaft portion 31A to move to the side surface of the cam gear 24. The cutout portion 31B of the flyweight 31 in the axial direction is inserted even though it is supported so as to be swingable.
The positional relationship between the opening and the opening 30B can be accurately maintained.

[0021]

As described above, according to the first aspect of the invention, the recess formed in the surface of the cam opposite to the axial cam surface and the inside of the cam facing the recess. A flyweight whose shaft is swingably supported in the opening facing the contour surface of the cam by communicating with each other, and a cutout portion that can be exposed in the opening in a part of the shaft of the flyweight. Since it is formed so as to be able to face the contour surface of the cam, a part of the flyweight is used as a member for changing the outer dimension of the contour surface of the cam.
Since no special member is required to change the outer dimensions of the contour surface, it is possible to reduce the number of constituent parts and make the structure simple. Moreover, an opening communicating the recess with the inside of the cam facing the recess is formed so as to face the contour surface of the cam, and the flyweight is swingably supported in the opening and is prevented from coming off by the cap member. As a result, the flyweight is partly housed in the recess and the inside of the cam in the axial direction of the cam, and the space occupied in the axial direction of the cam is reduced to reduce the entire decompression device. Miniaturization is possible.

According to the second aspect of the present invention, the bottom surface of the cap member does not protrude from the side surface of the cam gear, whereby the length of the cam gear including the cam and the cap member in the axial direction is excessively increased. You can choose not to. This makes it possible to prevent the length of the cam shaft including the cam and the cam gear in the axial direction from becoming excessively large. As a result, it is possible to easily reduce the size with a simple structure.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a main part of a portable engine to which a decompression device according to the first and second aspects of the invention is applied.

FIG. 2 is an exploded perspective view for explaining a main part configuration of a decompression device according to an embodiment of the invention described in claims 1 and 2. FIG.

3A and 3B are views for explaining an assembled state of the main part configuration shown in FIG. 2, in which FIG. 3A is a cross-sectional view, and FIG. 3B is a view in the direction of the arrow B in FIG. is there.

FIG. 4 is a diagram showing a configuration of a flyweight used in the configuration of the main parts shown in FIGS. 2 and 3, (A) being a perspective view and (B) being a plan view.

5 is a bottom view for explaining the operation of the main part configuration shown in FIG. 4. FIG.

FIG. 6 is a schematic diagram for explaining a conventional example of a decompression device.

[Explanation of symbols]

1 Portable engine 6 Valve drive 10 crankshaft 18 rocker arms 19 camshaft 20 cams 20A contour surface 24 cam gear 30 cam blocks 30A recess 30B opening 31 fly weight 31A shaft 31B Notch 31B1 end 32 Elastic member 33 Cap member 33A bottom 33B locking claw

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-177437 (JP, A) JP-A-9-184410 (JP, A) Actually open 2-87912 (JP, U) Actually open 60- 97308 (JP, U) Actual development Sho 50-128531 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01L 13/08

Claims (2)

(57) [Claims] 1. When the small engine (1) is started, the intake valve (7) and / or the exhaust valve (8) are slightly opened to set the compression pressure to a pressure lower than that in a normal combustion cycle. A decompression device for a cam cam (24) integrally formed with a cam (20).
A recess (30A ) that constitutes a lock (30) and is formed on a surface of the cam gear (24) opposite to the cam (20) in the axial direction, and the recess (30A).
The opening (30) which faces the contour surface (20A) of the cam (20) by communicating with the inside of the cam (20) facing A).
B) is formed, and a shaft portion (31A) having a notch portion (31B) that can be exposed to the opening (30B) is formed in a part of the peripheral surface, and the rotation speed of the cam (20) is increased. Accordingly, a flyweight (31) having a variable swing amount is swingably supported in the opening (30B) in a direction parallel to the cam shaft (19) of the cam (20), and the engine (1) is At the start of, the fly weight (3
1) An elastic member (32) for giving a habit of exposing a part (31B1) of the cutout portion (31B) to the contour surface (20A) of the cam (20) is provided, and the elastic member (32) is provided in the recess (30A). Has a peripheral height that corresponds to the depth
And is formed on the cam block (30).
Locking claws that can be attached to and detached from a plurality of engaging holes (24A)
(33B), when fitted in the recess (30A)
The bottom surface (33A) formed on the flat surface is the cam gear (24).
To the cap member (33) that forms the same flat surface as the side surface of
More covering the recess (30A), the cap member (33), said elastic member (32) and the flyweight (31) of the dropout decompression device of the engine, characterized by being configured to perform a stop . 2. The cap member (33) according to claim 1, wherein the cap member (33) is provided so as not to project outward from a side surface of the cam gear (24) provided with a recess (30A). Engine decompression device.