JPH086574B2 - Decompression device for internal combustion engine - Google Patents

Description

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

(2) Prior Art As the above conventional decompression device, for example, the actual open sho 62-
As disclosed in Japanese Patent No. 14106, a spindle (14) planted on one side of the valve operating cam (4) usually has a predetermined decompression position, but the rotational speed of the valve operating cam (4) increases. It is known that the decompression weight (8) swings outward in the radial direction of the cam in accordance with the above and heads toward a predetermined decompression release position.

(3) Problems to be Solved by the Invention However, in the conventional decompression device, in order to perform the position regulation of the decompression weight (8) to the decompression position,
A flange part (26) having a direct part (29) and engageable with the decompression weight (8) is specially processed on the outer peripheral surface of the valve camshaft (2) adjacent to the weight (8), Further, the swing lever (5) with the decompression projection (35) that can be projected and retracted from the base circle of the valve cam (4) in conjunction with the swing of the decompression weight (8) is provided with the decompression weight (8) and the valve cam. (4)
The swing lever which is rotatably supported by a notch-shaped flat portion (31) specially processed on the outer peripheral surface of the valve camshaft (2) intermediate between and and driven by the decompression weight (8). The decompression projection (35) of (5) is projected and retracted from the cam base circle to switch between decompression release and decompression operation.

Therefore, in such a conventional decompression device, not only the number of parts is relatively large and the structure is complicated, but also in order to assemble these parts to the valve operating camshaft, complicated processing is specially applied to the camshaft at many places. There is a problem that it is necessary, and it is difficult to unitize the decompression device itself, the assembly work is troublesome, and the overall cost increases.

Therefore, an object of the present invention is to provide a decompression device for an internal combustion engine, which is capable of solving the problems of the above-mentioned conventional device and simplifying the structure and improving the workability of assembling.

B. Configuration of the Invention (1) Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides a base plate on one side of a valve cam so that the base plate can rotate integrally with the cam. The arc-shaped decompression weight, which is in the normal predetermined decompression position, swings radially outward of the valve cam in accordance with the increase in the rotational speed of the valve cam and moves toward the predetermined decompression release position. A decompression device for an inner edge engine, which is supported, wherein the decompression weight projects from the base circle of the valve cam when the decompression position is in the decompression position, and retracts from the base circle when in the decompression release position. A decompression projection is integrally provided at the free end of the decompression weight, and a return spring for urging the decompression weight toward the decompression position side is interposed between the decompression weight and the substrate. A stopper that can hold the decompression weight in the decompression position against the biasing force of the return spring by abutting against the decompression projection is provided on the side surface of the valve valve cam facing the substrate. It is characterized in that it is provided at a position corresponding to.

(2) Action When the rotation speed of the crankshaft is below the set value, such as when the engine is started, the decompression weight is biased to the decompression position by the elastic force of the return spring, and the decompression projection integrated with the decompression weight is the valve cam. Decompression is performed by projecting outward from the base circle of the exhaust side to lift the exhaust side cam follower, and after the engine starts, if the crankshaft speed exceeds the set value, the decompression weight returns due to the centrifugal force acting on it. The decompression cam is biased to the decompression releasing position against the elastic force of the spring, and the decompression cam is retracted inward from the base circle of the valve operating cam to release the decompression action.

(3) Examples Hereinafter, examples of the present invention will be described with reference to the drawings.

In FIGS. 1 to 3, a half reduction gear R is mounted on a crankshaft 1 rotatably supported by an engine body E via a ball bearing 2.
Is provided. The 1/2 reduction gear R is an eccentric drive cam Ca ₁ which is fixed to the crank shaft, and the eccentric driven cam Ca ₂ which is externally rotatably supported on the engine body E on the outer periphery of the eccentric driving cam Ca ₁ The rotation of the crankshaft 1 is transmitted to the eccentric driven cam Ca ₂ with a 1/2 reduction ratio. The configuration of the 1/2 reduction gear R will be described later in detail.

One valve cam 3 is integrally formed on the outer circumference of the eccentric driven cam Ca ₂ , and the slipper surfaces 4 ₁ , 5 ₁ of the conventionally known cam followers 4, 5 are brought into contact with the cam surface of the valve cam 3. It These cam followers 4 and 5 are interlocked with intake and exhaust valves provided in the combustion chamber via a conventionally known valve operating mechanism.

Crankshaft 1 of valve cam 3 integrated with eccentric driven cam Ca ₂
An annular substrate 7 is fixed to the outer periphery of the cylindrical portion 6 surrounding the
A decompression weight 8 having an arc shape and extending along the cam surface of the valve operating cam 3 is pivotally supported by a pivot shaft 9 on the base plate 7 so as to be rotatable in the radial direction. At the free end of the decompression weight 8, a decompression projection 10 made of a pin is integrally provided toward the side surface of the valve operating cam 3. A return spring 11 composed of a tension coil spring is stretched between the decompression weight 8 and the substrate 7, and the pulling force of the return spring 11 acts to pull the decompression weight 8 inward. Is biased so as to project outward from the base circle Cb of the valve cam 3.

On the side surface of the eccentric driven cam Ca ₂ facing the decompression weight 8, a fan-shaped recess 12 is formed at a position corresponding to the base circle Cb of the valve operating cam 3. The tip of the decompression projection 10 has entered the recess 12, and the decompression projection 10 has a stopper 13 formed of the wall surface of the recess 12.
The decompression weight 8 by returning to the return spring.
It can be held in the decompression position against the biasing force of 11, that is, the pulling force. Further, on the outer periphery of the substrate 7, a stopper piece 14 facing the outer intermediate portion of the decompression weight 8 is provided.
Are integrally formed, and the stopper piece 14 is formed on the substrate 7
Is rotated together with the decompression weight 8, and when the decompression weight 8 is swung outward in the radial direction by the centrifugal force, its swing position, that is, its decompression release position can be regulated.

Next, the structure of the 1/2 water reducer R will be described mainly with reference to FIGS. 3 and 4. The eccentric drive cam Ca ₁ has a pair of first and second
Eccentric wheels 15 ₁ and 15 ₂ are arranged in parallel as one unit. The pair of
1, the eccentric driven cam Ca ₂ circumscribing the second eccentric wheel 15 ₁ , 15 ₂
The second eccentric wheels 15 ₁ and 15 ₂ are rotatably supported by the engine body E with an eccentric amount equal to the eccentric amount e of the crankshaft 1. The outer peripheral surface of the eccentric driven cam Ca ₂ is sucked as described above.
One valve cam 3 for exhaust is formed, and this valve cam 3
The slipper surfaces 4 ₁ , 5 ₁ of the above-mentioned intake and exhaust cam followers 4, 5
Are abutted.

The first and second eccentric wheels 15 ₁ and 15 ₂ have a cylindrical outer peripheral surface with a circular cross section, and are eccentric from the central axis C ₀ of the crankshaft 1 in opposite directions when viewed in the diametrical direction of the crankshaft 1. Only eccentric.

Corresponding to the positions of the first and second eccentric wheels 15 ₁ and 15 ₂ , the central axis C ₁ eccentric from the central axis C ₀ of the crankshaft 1 by the eccentric amount e.
Forming a hollow portion of the eccentric driven cam Ca ₂ having
The inner peripheral surfaces 16 ₁ , 16 ₂ surround the outer peripheral surfaces of the first and second eccentric wheels 15 ₁ , 15 ₂ .

The first inner peripheral surface 16 ₁ is a pair of parallel facing surface portions 16 that are parallel to each other and rotate while circumscribing the first eccentric wheel 15 ₁ while the first eccentric wheel 15 ₁ is sandwiched with the rotation of the crankshaft 1. ₁ -1,16 ₁
-2, and the second inner peripheral surfaces 16 ₂ are parallel to each other and rotate while circumscribing the second eccentric wheel 15 ₂ while the second eccentric wheel 15 ₂ is sandwiched between the second inner peripheral surfaces 16 ₂ as the crankshaft 1 rotates. A pair of opposing surface portions 16 ₂ -1,16 ₂ -2, and each opposing surface portion 16 ₁ -1,16 ₁ -2 of the first inner peripheral surface 16 ₁ and each opposing surface portion of the second inner peripheral surface 16 ₂ 1
6 ₂ -1 and 16 ₂ -2 are formed in a state in which their phases are deviated from each other by 90 °.

Figure 5 (a) and Figure 6 (a), the opposing face portion 1 when the first eccentric ring 15 ₁ is in a state where the eccentric downwards
6 ₁ -1,16 ₁ -2 extend in the vertical direction, and at this time, the second
The eccentric wheel 15 ₂ is eccentric to the upper side, and at the same time, the facing surface portion 16 ₂
-1,16 _2-2 extends in the horizontal direction. When the crankshaft 1 rotates in the direction of the arrow f in this state, the central axis C of the crankshaft 1 among the pair of outer tangent lines of the pair of opposed surface portions and the first and second eccentric wheels 15 ₁ and 15 _{2 On} the outer tangent line on the side where the distance from ₀ increases, the first and second eccentric wheels 15 ₁ and 15 ₂ press the opposing surface portions to transmit torque to the eccentric driven cam Ca ₂ . That is, the first eccentric 15 _1, the second eccentric 15 ₂ while pressing the opposed surface portions 16 ₁ -2 presses the opposed face 16 ₂ -1. As a result, when the rotation of the _first and second eccentric wheels 15 ₁ and 15 ₂ advances by 90 °, the rotation of the eccentric driven cam Ca ₂ advances by 45 ° as shown in FIGS. 5 (b) and 6 (b). . The second eccentric 15 ₂ with pressing the first eccentric ring 15 ₁ further opposing surface portions 16 ₁ -2 hold the opposite surface portion 16 ₂ -1, first, second eccentric 15 _1, 15 ₂ rotate 180 As the angle advances, the rotation of the eccentric driven cam Ca ₂ advances by 90 ° as shown in FIGS. 5 (c) and 6 (c). At this point
When the first and second eccentric wheels 15 ₁ , 15 ₂ rotate further, the first eccentric wheel 15 ₁
Begins to push the facing surface portion 16 ₁ -1, and the second eccentric wheel 1
5 ₂ continues down the opposite surface portion 16 ₂ -1. 1st, 2nd eccentric wheel 1
When 5 ₁ and 15 ₂ further rotate to 270 °, the 5th
As shown in Fig. 6 (d) and Fig. 6 (d), the eccentric driven cam Ca ₂ is 135
Rotate only by °.

As described above, the eccentric drive cam is driven by the rotation of the crankshaft 1.
The rotation of the crankshaft 1 is caused by Ca ₁ and the eccentric driven cam Ca ₂ repeating the rotational movements shown in FIGS. 5 and 6 (a) to (d).
It is transmitted to the eccentric driven cam Ca ₂ with a reduction ratio of 1/2, and the pair of cam followers 4 and 5 are swung by the valve cam 3 on the eccentric driven cam Ca ₂ , and the push rod is included in the conventional publicly known art. The intake and exhaust valves are operated via the valve operating mechanism.

Next, the operation of this embodiment will be described. If the crankshaft 1 is cranked to start the engine, the crankshaft 1 is rotated. The rotational speed of the driven eccentric cam Ca ₂ of R is also low, and the decompression weight 8 is attracted to the crankshaft 1 side by the elastic force of the return spring 11, and the tip thereof is a valve cam as shown in FIG. 2 (A). The decompression projection 10 is abutted against the stoppers 13 on the three side surfaces to be in a fixed state, and the decompression projection 10 is projected outward from the base circle of the valve operating cam 3. During start-up of the engine thus decompression projections 10 of the valve operating cam 3 driven by 1/2 reduction ratio by the rotation of the crank shaft 1 and abuts against the sliding surface 5 ₁ of the exhaust-side cam follower 5 shown by lifting the cam follower 5 The exhaust valve during the compression stroke is opened through the valve operating mechanism to reduce the pressure in the combustion chamber to perform the decompression operation.

When the engine is started and the rotation speed of the crankshaft 1 exceeds the set value, the rotation of the driven eccentric cam Ca ₂ of the 1/2 speed reducer R is also accelerated, so that the decompression weight 8 can reduce the centrifugal force acting on it. As shown in FIG. 2 (B), the return spring 11
2 swings outwardly around the pivot shaft 9 against the resilience of the stopper to abut against the stopper piece 14 to be in a fixed state as shown in FIG. The decompression protrusion 10 immerses inward of the base circle Cb of FIG.

In the above embodiment, the case where the 1/2 reduction gear R is provided directly on the crankshaft and the driven eccentric cam Ca ₂ , that is, the valve actuation cam 3 is provided with the decompression device of the present invention has been described, but it is provided separately from the crankshaft 1. It goes without saying that the decompression device of the present invention may be provided in the valve operating cam on the valve operating cam shaft which is driven by the 1/2 reduction mechanism.

C. Effect of the Invention As described above, in the decompression device of the present invention, the decompression projection integrally provided at the free end of the decompression weight is set in and out of the base circle according to the increase / decrease in the rotation speed of the valve cam. By swinging so that the decompression can be directly switched by decompression release / decompression operation, it is not necessary to interpose a special functional part between the decompression weight and the decompression projection. The structure can be simplified accordingly. Further, since the decompression weight and the return spring can be integrated into a unit together with the base plate, and the valve cam only needs to be provided with a stopper to which the decompression projection can abut and a mounting portion of the base plate, the overall manufacturing, It is easy to assemble, and in combination with the simplification of the above-mentioned structure, it can greatly contribute to cost reduction.

[Brief description of drawings]

The drawings show one embodiment of the device of the present invention. FIG. 1 is a vertical sectional side view taken along the line II of FIG. 2 (A), FIG. 2 (A),
FIG. 2B is a sectional view taken along the line II-II in FIG.
Shows the state when the engine is started, and FIG. 2B shows the state after the engine is started. 3 is a sectional view taken along the line III-III in FIG. 1, FIG. 4 is a sectional view taken along the line IV-IV in FIG. 1, and FIGS. 5A to 5D are the first eccentric cams. And FIG. 6 (a) to FIG. 6 (d) show the second eccentric cam and the eccentric driven cam in relation to the change in the rotation angle of the crankshaft. FIG. 6 is an operation diagram corresponding to FIG. 4, showing the relationship between and in correspondence with changes in the rotation angle of the crankshaft. Cb …… base circle, 3 …… valve cam, 7 …… substrate, 8 …… decompression weight, 10 …… decompression projection, 11 …… return spring

Claims (1)

[Claims] 1. A base plate (7) is provided on one side of a valve cam (3) so as to rotate integrally with the cam (3), and the base plate (7) usually has a predetermined decompression position. However, the arcuate decompression weight (8) swings outward in the radial direction of the valve cam (3) in response to an increase in the rotational speed of the valve cam (3) and heads to a predetermined decompression release position (8). A decompression device for an internal combustion engine, in which the decompression weight (8) protrudes from a base circle (Cb) of the valve cam (3) when the decompression weight (8) is in the decompression position, and the decompression is released. The decompression protrusion (10), which is recessed from the base circle (Cb) when it is in the position, is integrally provided at the free end of the decompression weight (8), and between the decompression weight (8) and the substrate (7). Has
A return spring (11) for urging the decompression weight (8) toward the decompression position is interposed, and the decompression projection () is provided on a side surface of the valve cam (3) facing the substrate (8). A stopper (13) capable of holding the decompression weight (8) at the decompression position against the biasing force of the return spring (11) by abutting against the decompression spring.
Is provided at a position corresponding to the base circle (Cb), the decompression device for an internal combustion engine.