JPH0353449B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a speed limiting mechanism for an internal combustion engine.

Generally speaking, the speed of general-purpose engines is controlled by a cabana to prevent so-called overrun and damage to the engine or to the other machine, and the speed is normally controlled at a crankshaft rotation speed of 3600 r/min. It is often used in the speed range below pm.

However, in order to improve work efficiency, users sometimes remove the cabana system and directly operate the throttle valve of the carburetor, forcing it to be fully opened. In such cases, the engine overruns.

By the way, even in the case of the above usage,
In order to prevent damage to the engine and other work equipment, the maximum rotation speed can be kept below the set value by
Design methods for exhaust valve systems, intake/exhaust systems such as carburetors, air cleaners, and mufflers, electrical system design methods, and methods using other devices have been adopted. In particular, OHV type general-purpose engines have a higher maximum rotation speed than SV (side valve) type engines due to their structure, so there is a strong demand for overrun prevention.

One of the design methods for the intake/exhaust valve system is to reduce the operating load of the valve spring to disrupt the operation of the valve system, thereby reducing valve jump, bounce, and
There is a method of lowering the rotational speed at which surging occurs, thereby keeping the maximum rotational speed below a certain value.

However, if the operating load of the valve spring is reduced, general-purpose engines are often left unused for long periods of time or degraded oil is used. There is a strong possibility of valve stuck.

The present invention has been made in order to effectively eliminate such inconveniences, and its purpose is to provide an internal combustion engine that can suppress the maximum rotation speed to a certain value or less without causing valve stuck on the exhaust valve. The engine is to provide a speed limiting mechanism.

In order to achieve such an object, the present invention aims to reduce the set load and maximum lift load of the intake side valve spring to the set load and maximum lift load of the exhaust side valve spring, which are set to be at least a sufficient load to prevent valve jumps and surging from occurring. Its feature is that it is set smaller than the load.

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

Fig. 1 is a partially cutaway side view of an internal combustion engine equipped with a mechanism according to the present invention, Fig. 2 is a cutaway plan development view of the same internal combustion engine, Fig. 3 is a cutaway side view of the intake/exhaust valve system, and Fig. 4 6 to 6 are relationship diagrams between engine speed and valve spring maximum load showing experimental results.

In the internal combustion engine shown in FIGS. 1 and 2,
1 and 2 are a cylinder block and a cylinder head, and a piston 3 is slidably fitted into the cylinder bore 1a of the cylinder block 1, and the piston 3 is connected to a crankshaft 5 via a connecting rod 4. There is. The crankshaft 5 has a ball bearing 7 in the crankcase 6.
It is rotatably supported via 7.

The cylinder head 2 is also provided with intake and exhaust ports 8 and 9, which are intermittently opened and closed by intake and exhaust valves 10 and 11, respectively. The intake and exhaust valves 10 and 11 are urged in a direction to close the intake and exhaust ports 8 and 9 by valve springs 12 and 13, respectively.

By the way, the set load of the intake valve spring 12, that is, the spring load when the intake valve 10 is fully closed, and the maximum lift load, that is, the spring load when the intake valve 10 is fully open, are set smaller than those of the exhaust side valve spring 13. ing. Specifically, the purpose is achieved by changing the thickness, diameter, length, etc. of both valve springs 12, 13. In this way, the intake/exhaust side bull springs 12, 13
Since the spring loads of the springs 12 and 13 are made different, there is a possibility that the springs 12 and 13 may be incorrectly assembled during actual assembly work. Therefore, for example, in the intake/exhaust valves 10 and ₁₁ as shown in FIG.
If the outer diameter of a is d ₂ , the inner diameter of the exhaust valve spring 13 is d ₃ , and the outer diameter of the retainer 14 is d ₄ , then the following relationship exists between these dimensions d ₁ , d ₂ , d ₃ , and d ₄ If d ₂ > d ₃ and d ₁ >d ₄ are established, incorrect assembly of the springs 12 and 13 can be effectively prevented.

By the way, one ends of swingable rocker arms 15 and 16 are in contact with the tops of the intake and exhaust valves 10 and 11, respectively.

On the other hand, a camshaft 17 is rotatably disposed diagonally below and parallel to the crankshaft 5, and the camshaft 17 and the crankshaft 5 are connected via gears 18 and 19 that mesh with each other. . The camshaft 17 is provided with cams 17a and 17b as shown in the figure, and each cam 17a and 17b is provided with a lifter 20 and 2.
Push rods 22 and 23 are interposed between the other ends of each lifter 20 and 21 and the rocker arms 15 and 16. 24 in the figure
is a spark plug, and S is a combustion chamber.

Thus, the reciprocating motion of the piston 3 within the cylinder block 1 is converted into a rotational motion of the crankshaft 5 via the connecting rod 4, and the rotation of the crankshaft 5 is further transmitted to the camshaft 17 via gears 18 and 19. , the camshaft 17 is driven to rotate. And this camshaft 1
A cam 17 that rotates together with the rotation of 7.
a, 17b are connected to rocker arms 15, 1 via lifters 20, 21 and push rods 22, 23.
Push up one end of 6 and open the intake/exhaust valves 10, 11.
Open at the right time. That is, when the piston 3 passes the top dead center and moves to the intake stroke, the intake valve 10 opens, and as the piston 3 descends, the negative pressure generated in the combustion chamber S is drawn and is generated by the carburetor (not shown). The resulting air-fuel mixture is drawn into the combustion chamber S. Then, when the piston 3 reaches near the dead center, the intake valve 10 is closed, the piston 3 rises and moves to the compression stroke, the air-fuel mixture sucked into the combustion chamber S is compressed, and the piston 3 reaches the top dead center. When the temperature reaches near the point, the air-fuel mixture is ignited and combusted by the spark generated by the spark plug 24. The piston 3, which receives the pressure generated in the combustion chamber S by the combustion of the air-fuel mixture, descends, passes the dead center, and then rises again due to its inertia and moves to the exhaust stroke. In this exhaust stroke, the exhaust valve 11 opens, and exhaust gas generated by combustion of the air-fuel mixture as the piston 3 rises is discharged to the atmosphere via the exhaust valve 11 and an exhaust pipe (not shown) following it. Ru.

The above is the operation of an engine, especially a four-cycle engine, and the engine repeats the same cycle thereafter.

Figures 4 to 6 illustrate the actual experimental results for the internal combustion engine described above in terms of the relationship between engine speed and maximum valve spring load. In each figure, the horizontal axis represents the intake valve spring 12. The maximum load and the vertical axis indicate the engine rotational speed at which valve jump occurs, the engine rotational speed at which valve bounce occurs, and the engine rotational speed at which surging occurs, respectively.

In each figure, curve A is the characteristic curve in the normal case, that is, when the valve spring is not modified as in the present invention, curve B is the characteristic curve in the case in which the valve spring is modified as in the present invention, and curve C (characteristic curve in the case where the valve spring is not modified as in the present invention). 6
(omitted in the figure) respectively indicate the logically calculated value characteristics of the maximum rotation speed.

As is clear from the comparison of curves A and B in each figure, by setting the valve spring load as in the present invention, it is possible to suppress the maximum engine speed to a certain value or less and prevent overline, and also to reduce the spring load. The smaller the setting, the lower the maximum rotation speed can be held down.

While the maximum engine speed is kept low, the load on the exhaust side valve spring is kept relatively high, making it possible to suppress the occurrence of the aforementioned disadvantageous phenomenon of valve stay.

In addition, when using the same spring on the intake side and exhaust side, the relationship between the set lengths h _IN and h _EX of the intake and exhaust side valve springs 12 and 13 is h _EX < h _IN in Fig. 3. so that each valve 10,1
1. It is possible to set the dimensional relationship between the retainers 14, 14' and the spring seat surfaces 2b, 2b' of the cylinder head 2. That is, in general, the valve lift on the exhaust side is often set to a smaller value than the valve lift on the intake side, but in order to achieve the purpose of the present invention, the difference in valve lift is taken into account and the value at the maximum lift is set. It goes without saying that it is necessary to make the load stronger on the exhaust side than on the intake side. One method for this purpose is to set the valve lift amount on the exhaust side to be larger than that on the intake side.

As is clear from the above description, according to the present invention, the set load and maximum lift load of the intake side valve spring are set to be at least a sufficient load to prevent valve jumps and surging from occurring. Since it is set smaller than the maximum lift load, the maximum engine speed can be kept below a certain value without causing valve stuck on the exhaust valve.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a partially cutaway side view of an internal combustion engine equipped with a mechanism according to the present invention, FIG. 2 is a cutaway plan development view of the same internal combustion engine, and FIG. 1 is a cutaway side view of the intake/exhaust valve system, and FIGS. 4 to 6 are relationship diagrams between engine speed and valve spring maximum load showing experimental results. In the drawing, 1 is the cylinder block, 2 is the cylinder head, 3 is the piston, 5 is the crankshaft, 10 and 11 are the intake and exhaust valves, respectively, and 12 and 1 are the cylinder heads.
3 is the intake and exhaust side valve springs, and 17 is the camshaft.

Claims (1)

[Claims] 1. The set load and maximum lift load of the intake side valve spring are set to be smaller than the set load and maximum lift load of the exhaust side valve spring, which are set to at least sufficient loads to prevent valve jumps and surging. Characteristic speed limiting mechanism for internal combustion engines.