JPS63306215A - Decompression device for internal combustion engine - Google Patents

Abstract

PURPOSE:To simplify the assembly of a decompression device by supporting a circular decomp weight pivotally on a base plate as one body with a tappet valve cam, and installing a stopper, regulating the decomp weight to a decomp position, in this tappet valve cam. CONSTITUTION:A decomp weight 8 is pivotally supported on a base plate 7 as one body with a tappet valve cam 3. A decomp projection 10 is installed in a free end of this decomp weight 8. A return spring 11, which energized the decomp projection 10 to a position to be projected from a base circle of the tappet valve cam 3, is connected to the decomp weight 8. A stopper, regulating the decomp weight 8 into a decomp position, is formed in the tapper valve cam 3. With this constitution, only when the stopper is formed in the tappet valve cam, a decompression device can be installed, thus installation can be done simply.

Description

DETAILED DESCRIPTION OF THE INVENTION A1 Object of the Invention (1) Industrial Field of Application The present invention relates to an improvement of a decompression device equipped with a decompression weight for an internal combustion engine.

(2) Prior Art A conventional decompression device for an internal combustion engine equipped with a decompression weight is disclosed, for example, in Japanese Patent Publication No. 53-37981.

(3) Problems to be Solved by the Invention However, in order to attach the decompression device to an engine part such as a valve train camshaft, the conventional decompression device requires complex machining of the part, or the assembly of the engine part. There is a problem in that it is troublesome to attach, leading to high costs.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a decompression device for an internal combustion engine with a simple structure that can be easily assembled to the valve cam by simply providing a slight stopper on the valve cam. It is something.

B9 Structure of the Invention (1) Means for Solving Problems In order to achieve the above-mentioned object, the present invention includes a base plate provided on a valve operating cam so as to be able to rotate integrally therewith; an arcuate decompression weight that swings in the radial direction of the valve cam in response to an increase or decrease in the rotational speed of the valve cam; a decompression protrusion that can protrude and retract from the base circle of the valve drive cam; a return spring that is connected to the decompression weight and biases the decompression protrusion to a decompression position that projects from the base circle of the valve drive cam; and a return spring that is provided on the valve drive cam; , a stopper that can collide with the decompression weight so that the decompression weight is regulated at the decompression position.

(2) Function When the rotation speed of the crankshaft is below a set value, such as when starting the engine, the decompression weight is biased to the decompression position by the elastic force of the return spring, and the decompression protrusion integrated with the decompression weight moves the valve. The decompression effect is performed by lifting the exhaust side cam follower by protruding outward from the base circle of the cam, and when the crankshaft rotation speed exceeds the set value after the engine has started, the decompression weight is activated by the centrifugal force acting on it. The decompression cam is biased to the decompression release position against the elastic force of the return spring, and the decompression cam is recessed inward from the base circle of the valve train cam, and the decompression action is released.

(3) Examples Embodiments of the present invention will be described below with reference to the drawings.

In Figs. 1 to 3, a crankshaft 1 rotatably supported by an engine body E via a ball bearing 2 has a 1/2 speed reducer R.
is provided. This 1/2 speed reducer R includes an eccentric drive cam Ca1 fixed to the crankshaft, and this eccentric drive cam Ca1.
It consists of an eccentric driven cam Caz circumscribed on the outer periphery of the engine body E and rotatably supported by the engine body E, and the rotation of the crankshaft 1 is transmitted to the eccentric driven cam Caz with a 1/2 reduction ratio. There is. The configuration of the 1/2 speed reducer R will be described in detail later.

One valve-driving cam 3 is integrally formed on the outer periphery of the eccentric driven cam Ca2, and the cam surface of this valve-driving cam 3 is provided with slimper surfaces 42, 5. is brought into contact. These cam followers 4 and 5 are cylindrical bodies that surround the crankshaft l of the valve drive cam 3 that is integrated with nine eccentric driven cams Caz that are interlocked with intake and exhaust valves provided in the combustion chamber through a conventionally known valve drive mechanism. An annular base plate 7 is fixed to the outer periphery of the portion 6, and the valve drive cam 3 is attached to the base plate 7 in an arc shape.
A decompression weight 8 extending along the cam surface is pivotably supported by a pivot shaft 9 so as to be rotatable in the radial direction. The free end of the decompression weight 8 has a decompression protrusion 1 made of a pin.
0 is integrally provided toward the side surface of the valve operating cam 3.

A return spring 11 made of a tension coil spring is stretched between the middle of the decompression weight 8 and the substrate 7, and the tensile force of this return spring 11 acts to pull the decompression weight 8 inward. The valve train cam 3
It is biased so as to protrude outward from the base circle cb of.

A fan-shaped recess 12 is formed on the side surface of the eccentric driven cam Ca facing the decompression weight 8, and the tip of the decompression protrusion 10 enters the recess 12.
This decompression protrusion 10 abuts against a stopper 13 made of the wall surface of the recess 12, so that the decompression weight 8 can be restricted to the decompression position. Further, a stopper piece 14 is integrally formed on the outer periphery of the substrate 7 and faces the outer intermediate portion of the decompression weight 8, and this stopper piece 14 allows the substrate 7 to rotate with the decompression weight 8,
When the decompression weight 8 swings outward in the radial direction due to centrifugal force, its swing position, that is, its decompression release position can be regulated.

Next, the structure of the 1/2 speed reducer R will be explained mainly with reference to FIG. The second eccentric wheels 15+ and 15□ are integrally arranged in parallel. The first of the pair. The eccentric driven cam Ca2 circumscribing the second eccentric wheels 151, 15□ is the first eccentric driven cam Ca2. Second eccentric wheel t5+, 15
It is rotatably supported on the engine body with an eccentricity equal to that of the eccentric wheel e with respect to the crankshaft 1 in □. Eccentric driven cam C
As mentioned above, one valve drive cam 3 for intake and exhaust is formed on the outer peripheral surface of a2, and the slipper surfaces 4+ and 5+ of the above-mentioned intake and exhaust cam followers 4.5 are applied to this valve drive cam 3. be touched.

1st. The second eccentric wheels 151, 15□ have a cylindrical outer circumferential surface with a circular cross section, and are eccentric by an eccentric amount e from the central axis C0 of the crankshaft 1 in opposite directions when viewed in the diametrical direction of the crankshaft l.

1st. Second eccentric wheel 15. ．． Corresponding to the position of 15□, the first. The second inner circumferential surface 161, 16□ is the first inner circumferential surface 161, 16□. Second eccentric wheel 15. ．． 15! surrounds the outer circumferential surface of.

First inner peripheral surface 16. As the crankshaft 1 rotates, the first eccentric wheel 15. is constantly sandwiching the first eccentric wheel 151.
A pair of mutually parallel opposing surfaces 16 that rotate while circumscribing the
．． -1.16□-2, and the second inner peripheral surface 16
□ is always the second eccentric wheel 15 as the crankshaft 1 rotates.
A pair of mutually parallel opposing surface portions 16□-1, 16□- rotate while circumscribing the second eccentric ring 15□ with g sandwiched therebetween.
2, and has a first inner circumferential surface 16. Each opposing surface portion 16°-1,
161-2 and each opposing surface portion 16□-1 of the second inner peripheral surface 16□
, 16□-2 are formed with a phase shift of 90° from each other.

In FIG. 5(a) and FIG. 6(a), when the first eccentric wheel 151 is in a downwardly eccentric state, the facing surface portion 16+1.16+2 extends in the vertical direction, and in this case, the second eccentric wheel 15□ is eccentric upward, and the opposing surface portions 16□-1 and 16□-2 extend in the horizontal direction. In this state, when the crankshaft l rotates in the direction of the arrow f, each pair of opposing surfaces and the first... Among each pair of external tangents to the second eccentric shafts 151 and 152, the first. Second eccentric wheel 15. ．． 15□ presses the opposing surface portion and transmits torque to the eccentric driven cam Caz. That is, the first eccentric wheel 15. is the facing surface portion 16. -2 and the second eccentric wheel 152 presses the opposing surface portion 16□-1.
Press. As a result, 1. 2nd eccentric transfer 15. ．． 15
．． When the rotation progresses by 90 degrees, Fig. 5 (b)
As shown in Figure (b), the eccentric driven cam Ca rotates by 45 degrees. The first eccentric wheel 15 further has an opposing surface portion 16. -2 while continuing to press the second eccentric wheel 15□.
Press and hold 1. Second eccentric wheel 15. ．． When the rotation of cam 152 progresses by 180°, the rotation of the eccentric driven cam Ca progresses by 90° as shown in FIGS. 5(C) and 6(C). At this point, the first. When the second eccentric wheels ts+ and tsz further rotate, the first eccentric wheel 15. starts pushing the opposing surface portion 161-1, and the second eccentric wheel 15□ continues to push the opposing surface portion 16□-1. 1st degree second eccentric wheel 15. ．． When the rotation of 15□ progresses further and rotates to 270°, Fig. 5 (d) and Fig. 6
As shown in Figure (d), the eccentric driven cam Caz rotates by 135°.

As described above, the rotation of the crankshaft 1 causes the eccentric drive cam C to
at and the eccentric driven cam Caz are shown in Figures 5 and 6 (a) ~
By repeating the rotational movement shown in (d), the rotation of the crankshaft 1 is transmitted to the eccentric driven cam Caz with a reduction ratio of 1/2, and the eccentric driven cam Ca and the upper valve drive cam 3,
As described above, the pair of cam followers 4.5 are oscillated, and the intake and exhaust valves are operated via a conventionally known valve operating mechanism including a bushing rod.

Next, to explain the operation of this embodiment, when the engine is started (cranked), the crankshaft 1 is rotated, but since the rotation speed is less than the predetermined set rotation speed, the 1/2 iA speed The rotational speed of the driven eccentric cam Caz of R is also low, and the decompression weight 8 is drawn toward the crankshaft 1 side by the elastic force of the return spring 11, and its tip touches the valve drive cam 3 as shown in FIG. The decompression projection 10 is brought into a fixed state by colliding with the stopper 13 on the side, and is projected outward from the base circle of the valve train cam 3. Therefore, when starting the engine, the rotation of the crankshaft 1 causes the decompression speed ratio to be reduced to 1/2. The decompression protrusion 10 of the valve drive cam 3 that is driven by the engine collides with the slimmer surface 51 of the exhaust side cam follower 5, lifts the cam follower 5, and opens the exhaust valve during the compression stroke via a valve drive mechanism (not shown). A decompression action is performed by reducing the combustion chamber pressure.

When the engine is started and the rotation speed of the crankshaft 1 exceeds the set value, the rotation speed of the driven eccentric cam Ca2 of the 1/2 reduction aR is also increased, so the decompression weight 8 is reduced due to the increase in the centrifugal force acting thereon. As shown in FIG. 2(B), it swings outward around the pivot shaft 9 against the elastic force of the return spring 11 and collides with the stopper piece 14, as shown in FIG. 2(B). , the decompression projection 10 is recessed inward from the base circle cb of the valve operating cam 3, and the decompression action described above is no longer performed by the decompression projection 10.

In the above embodiment, a case was explained in which the 1/2 residual speed gear R was provided directly on the crankshaft, and the decompression device of the present invention was provided on its driven eccentric cam Ca, that is, the valve drive cam 3. It goes without saying that the decompression device of the present invention may be provided on a valve operating cam on a valve operating camshaft which is provided and driven via a 1/2N speed mechanism.

C1 Effects of the Invention As described above, the decompression device of the present invention can be assembled into an engine by simply forming a stopper surface on the valve drive cam of the engine component, and is unitized. As a result, it is extremely easy to assemble, has a small number of parts, and has a simple configuration, resulting in a significant cost reduction as a whole.

[Brief explanation of the drawing]

The drawings show one embodiment of the device of the present invention, and FIG. 1 is a longitudinal cross-sectional side view taken along the line 1-1 in FIG.
(B) is a sectional view taken along the line ■-■ in Figure 1, and Figure 2 (A)
Figure 2 (CB) shows the state when the engine is started, and Fig. 2 (CB) shows the state after the engine has started. Figure 3 is a sectional view taken along line ■-■ in Figure 1;
Figure 4 is a sectional view taken along the line IV-IV in Figure 1, and Figure 5 (
a) to (d) are the third diagrams showing the relationship between the first eccentric cam and the eccentric driven cam in response to changes in the rotation angle of the crankshaft.
6(a) to 6(d) correspond to FIG. 4, which sequentially shows the relationship between the second eccentric cam and the eccentric driven cam in response to changes in the rotation angle of the crankshaft. This is an action diagram. cb...Base circle,

Claims (1)

[Claims] A base plate (7) is provided on the valve drive cam (3) so as to be able to rotate together with the valve drive cam (3); Valve cam (3
) is an arc-shaped decompression weight (8
) and: a decompression protrusion (10) provided at the free end of the decompression weight (8) and capable of retracting from the base circle (Cb) of the valve operating cam (3) as the decompression weight (8) swings; ; Connected to the decompression weight (8), the decompression protrusion (10) is connected to the base circle (
a return spring (11) protruding from Cb) biased to the decompression position; a return spring (11) provided on the valve drive cam (3) so as to restrict the decompression weight (8) to the decompression position; A stopper (1
3) A decompression device for an internal combustion engine, comprising: