JPH0610091Y2 - Valve drive system for multi-cylinder internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a valve operating system of a multi-cylinder internal combustion engine in which intake and exhaust valves of each cylinder are opened and closed by a plurality of cams formed on a camshaft.

2. Description of the Related Art An intake / exhaust valve in a four-cycle internal combustion engine is opened / closed by each cam of a camshaft that rotates in synchronization with the engine, either directly or indirectly via a rocker arm. Therefore, in order to cope with thermal expansion of the valve stem and the like, it is necessary to provide an appropriate valve clearance in advance, as is well known. The valve clearance is usually adjusted by using a thickness gauge, and the valve clearance is adjusted under a predetermined temperature condition by adjusting the adjusting screw or replacing the shim. The adjustment value is generally different between the intake valve and the exhaust valve, but in the case of a multi-cylinder internal combustion engine, it does not differ between the cylinders, and the same valve clearance is given to all the cylinders.

However, even if adjustment is made so that the same valve clearance will be obtained in all cylinders during a certain temperature condition, such as when cold, during actual engine operation, due to uneven temperature distribution of the engine, etc. There is a risk that the valve clearances will have different values, and the valve opening / closing timing and thus the valve overlap and the like will be non-uniform in each cylinder.

FIG. 2 is a cam lift characteristic diagram showing a cam profile of a cam in the conventional valve operating system, and particularly shows the cam lift of the intake valve IN and the exhaust valve EX in the vicinity of the valve overlap. The scale attached to the vertical axis of the figure shows the valve lift amount when the valve clearance is set to a design value of 0.3 mm. Incidentally, in a multi-cylinder internal combustion engine, the cam profile of each cylinder is of course the same.

Here, for example, in an in-line four-cylinder engine, the valve in actual operation is composed of a # 1 cylinder that is close to the cooling water inlet, that is, the highest cooling effect, and a # 4 cylinder that is close to the cooling water outlet and lowest in the cooling effect. Clearance is likely to vary greatly. Therefore, for example, in the # 1 cylinder, even if the valve clearance during operation is an appropriate value of about 0.3 mm as shown in the figure, it may be expanded to about 0.4 mm in the # 4 cylinder. The valve opening / closing timing and the valve overlap between the cylinders and the # 4 cylinder become extremely uneven. This leads to non-uniform cylinder pressure in each cylinder, which causes, for example, an idle malfunction.

Incidentally, in recent years, many valve trains are equipped with a hydraulic lash adjuster that automatically adjusts the valve clearance to zero. Even in this case, however, the valve clearance amount to be absorbed by the lash adjuster is the same for each cylinder. For example, if the # 1 cylinder and the # 4 cylinder differ from each other, the leak down amount of the lash adjuster becomes non-uniform, and the valve opening / closing timing and the valve overlap cannot be evenly secured.

Therefore, conventionally, for example, in Japanese Patent Application Laid-Open No. 58-51204, many cases are adopted in which the base cycle diameters of the cams of the respective cylinders are different from each other so that a uniform and appropriate valve clearance can be obtained in each cylinder during actual operation. A valve train for a cylinder internal combustion engine has been proposed.

However, when the base cycles of the cams are set to different diameters in advance in this way, the valve clearance of each cylinder naturally becomes a different value for each cylinder when the engine is cold. . Therefore, if the valve clearance is adjusted during cold, it is necessary to use different thickness gauges for each cylinder so that the setting values are different, which is very troublesome and the adjustment error may occur. There is a problem that it tends to occur.

Means for Solving the Problems In order to solve the above problems, the present invention provides a valve operating system for a multi-cylinder internal combustion engine, which drives an intake / exhaust valve to open / close by a plurality of cams formed on a camshaft, The base circle of the cam is formed in each cylinder to have the same diameter, and the cam lift amount characteristic of the cylinder close to the cooling water outlet of the engine is increased by a predetermined amount in each phase compared to the cam lift amount characteristic of the cylinder close to the cooling water inlet. Therefore, the cam lift amount of the cam of each cylinder is different for each cylinder.

Action In the above configuration, since the base cycle has the same diameter, the same valve clearance is given to each cylinder when the engine is cold. Then, during the actual operation of the engine, the temperature of the valve operating device of the cylinder near the cooling water outlet becomes higher than that of the cylinder near the cooling water inlet, and the valve clearance becomes relatively large. Since the cam lift amount characteristic of the cam of the close cylinder is increased by a predetermined amount in each phase compared to the cam lift amount characteristic of the cam of the cylinder close to the cooling water inlet, the difference in valve clearance due to the temperature difference is canceled out. Thus, the valve opening / closing timing and valve overlap become uniform in each cylinder.

Embodiment FIG. 1 is a cam lift characteristic diagram similar to FIG. 2 showing a cam profile in a valve operating system according to the present invention.
In this figure, as an example of an in-line four-cylinder engine, the cam profiles of the # 1 cylinder having the highest cooling effect and the # 4 cylinder having the lowest cooling effect are shown as described above.

That is, as shown in the figure, the cam base circle diameters of the cam of the # 1 cylinder and the cam of the # 4 cylinder are set to be the same, while the profile of the cam lift portion is that of the # 4 cylinder cam. Is always set to exceed the cam lift of the # 1 cylinder by a fixed amount, for example, 0.1 mm. Further, although not shown in the figure, the cam event angle is also different according to the addition of the cam lift amount. It should be noted that the cam event angle is set to be the same in both cylinders by assuming that the # 1 cylinder cam and the # 4 cylinder cam have different inclinations of the buffer curve corresponding to the valve clearance that does not contribute to the actual lift of the intake / exhaust valves. You can also do it.

In this valve train, the valve clearance is adjusted when the engine is cold, and is uniformly adjusted for each cylinder with reference to the # 1 cylinder (the intake valve and the exhaust valve may have different values. Of course).

Then, in the state where the engine is actually operating, as described above, the vicinity of the # 4 cylinder near the cooling water outlet is more strongly affected by the heat than the vicinity of the # 1 cylinder near the cooling water inlet.
For example, the actual valve clearance of the # 1 cylinder is about 0.3 mm, while the actual valve clearance of the # 4 cylinder is expanded to about 0.4 mm. Therefore, the difference between the valve clearances of the two and the difference between the lift amounts of the # 1 cylinder cam and the # 4 cylinder cam described above are canceled out, and the valve opening / closing timing and the valve overlap during engine operation are as shown in the figure. The one cylinder and the # 4 cylinder are substantially uniform.

Although the cam profiles of the # 2 cylinder and the # 3 cylinder located in the middle are not shown, similarly, a predetermined valve opening / closing timing and valve overlap can be obtained in consideration of the actual valve clearance during engine operation. You can set it like this.

As described above, according to the valve operating system described above, the valve opening / closing timing and the valve opening / closing timing can be reduced even when the valve clearance becomes non-uniform due to the temperature distribution during operation such as the # 1 cylinder and the # 4 cylinder of the inline 4-cylinder engine. It is possible to ensure a uniform valve overlap. Since the cam base circle has the same diameter in each cylinder, the valve clearance of each cylinder becomes uniform when the engine is cold. In other words, when the valve clearance adjustment is performed, the value is the same for each cylinder. Can be Even when the hydraulic lash adjuster is used, the leak down amount of the lash adjuster in each cylinder can be maintained substantially uniform, and the in-cylinder pressure and the like can be made uniform.

It is needless to say that the specific numerical values and the like in the above embodiments are merely examples, and the present invention is not limited to these.

Effects of the Invention As is apparent from the above description, in the valve operating system for a multi-cylinder internal combustion engine according to the present invention, variations in valve clearance during operation due to non-uniformity of temperature distribution of the internal combustion engine among the cylinders occur. The cam profile can be offset, and the valve opening / closing timing and the valve overlap can be uniformly ensured to a predetermined value, and in particular, idle operation can be stabilized. Moreover, since the cam base circle has the same diameter in each cylinder, for example, when manually adjusting the valve clearance during cold, it is sufficient to adjust the same value in each cylinder, which may complicate the work. Absent.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing an embodiment of a cam profile in a valve operating system according to the present invention, and FIG. 2 is a characteristic diagram showing a cam profile in a conventional valve operating system.

Claims (1)

[Scope of utility model registration request] 1. A valve operating system for a multi-cylinder internal combustion engine in which intake and exhaust valves are opened and closed by a plurality of cams formed on a camshaft, and the base circle of the cam is formed in each cylinder to have the same diameter. The cam lift amount for each cylinder is set so that the cam lift amount characteristic of the cylinder near the cooling water outlet is increased by a predetermined amount in each phase as compared with the cam lift amount characteristic of the cylinder near the cooling water inlet. A valve operating system for a multi-cylinder internal combustion engine, characterized in that