JPH022882Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a mushroom valve for an internal combustion engine in which a metal valve stem is connected to a ceramic valve plate.

"Prior art and its problems" Mushroom valves are widely used as exhaust valves for internal combustion engines.

To explain the structure of a general mushroom valve, for example, as shown in FIG.
It is installed to block 4. A valve spring 15 is attached to the upper part of the valve stem 13, and the valve spring 15 urges the mushroom valve 11 in the direction of arrow A in the figure. A cam 16 is in contact with the upper end of the valve rod 13, and the rotation of the cam 16 causes the mushroom valve 11 to reciprocate to open and close the exhaust passage 14.

By the way, the conventional mushroom valve 11 is made of a wear-resistant and heat-resistant alloy because it must maintain a gas leakage prevention function while being exposed to high-temperature gas and being subjected to repeated impacts. However, for example, at high temperatures of 500 to 600℃, several hundred to
Under conditions of several thousand reciprocating movements, the valve plate 12
Wear of the contact area between the peripheral edge of the valve seat 17 and the valve seat 17 was unavoidable, and leaks often occurred from that area. For this reason, valve wear has generally been the biggest hindrance to the lifespan of internal combustion engines.

Therefore, in order to extend the life of the mushroom valve 11, it is known that the surface of the valve plate 12 is coated with stellite. However, simply coating with stellite was not very effective against wear, and had the disadvantage that once leakage occurred, it would rapidly wear out.

In order to further increase the lifespan of the mushroom valve 11, it is conceivable that the entire mushroom valve 11 be made of ceramic, which has excellent heat resistance and wear resistance. 17, a strong tensile force is applied to the valve stem 13, which causes the problem that the valve stem 13 may break due to the characteristics of ceramics, which are weak against tensile forces.

In order to solve this problem, it is conceivable to form the valve plate 12 from ceramics, form the valve stem 13 from metal, and connect the two. An example of a structure that is likely to be generally adopted as such a mushroom valve is the one shown in FIG. 5, for example. That is, this mushroom valve 11 has a flange portion 18 formed slightly closer to the base than the tip of the metal valve stem 13, and the tip of the valve stem 13 is attached to the ceramic valve plate 1.
The valve disk 12 is fixed by inserting the nut 19 into the center hole of the valve stem 13 and screwing the nut 19 onto the tip of the valve stem 13 and tightening the nut 19. However, in this mushroom valve 11, the strength of the part tightened by the nut 19 is weakened, so when closing the exhaust passage 14, the valve plate 12
When a strong impact force is applied to the nut 19, the threaded portion of the nut 19 is likely to be damaged and leakage may occur.

"Purpose of the invention" The purpose of the invention is to solve the problems of the prior art described above and to provide a mushroom valve with excellent durability and high performance.

``Structure of the invention'' The mushroom valve according to the invention has a center hole formed in a ceramic valve disk, a flange portion formed at the tip of a metal valve stem, and the valve stem is inserted from the base side into the center hole of the valve disk. The flange is inserted through the valve to prevent it from coming off, and the valve plate is tightened and fixed with a nut that is screwed onto the valve stem from the base side of the valve stem.

In this way, in this invention, a flange is formed at the tip of the valve stem to prevent it from coming off, and a nut is screwed from the base side of the valve stem to tighten and fix it. Even if an impact force is applied, the impact can be received by the flange portion of the valve stem, which is integrally formed of metal. Therefore, the stress applied to the tightening portion of the nut, which lacks strength, can be alleviated and durability can be improved. By using ceramics for the valve disc, it is possible to reduce wear on the valve disc, prevent leakage, and dramatically extend the life of the valve disc.

According to a preferred embodiment of the present invention, the contact surface between the flange portion of the valve stem and the valve disk and the contact surface between the nut and the valve disk are formed by two different imaginary apexes having a common apex at a point on the axis of the valve stem. It is considered to be the cone surface of a cone. According to this, when the metal valve stem and nut expand relatively more than the ceramic valve disk due to the difference in thermal expansion coefficients at high temperatures, the flange portion and nut expand into the cone of the virtual cone. Since it expands along the surface, it can maintain the same contact condition with the valve disk, preventing wobbling at the contact area with the valve disk and preventing large stress from being applied to the ceramic valve disk. It can be prevented. In this case, one virtual cone may be located outside or inside the other virtual cone, and the apex angle of one virtual cone is 180
The degree, that is, the conical surface of this virtual cone may be a plane. Furthermore, the virtual cone may be a cone or a pyramid.

In the present invention, ceramics constituting the valve disk can be appropriately selected from materials having the required heat resistance, wear resistance, and strength, such as silicon carbide, silicon nitride,
Preferred examples include sialon, alumina, and zirconia.

The mushroom valve of the present invention can be used as an exhaust valve for various internal combustion engines such as gasoline engines, but is particularly suitable as an exhaust valve for diesel engines, particularly for stationary equipment or marine diesel engines. In other words, in such an internal combustion engine, the compression ratio is high, and therefore the exhaust temperature is high, and the life of conventional mushroom valves was particularly short.However, by adopting the mushroom valve of the present invention, which uses a ceramic valve plate, Not only can this difficulty be greatly improved, but it also makes it possible to employ a larger compression ratio.

In addition, in this invention, after tightening the nut,
The nut may be welded to the valve stem or the threaded portion of the nut may be impregnated with a liquid seal.
In this way, leakage at the threaded portion of the nut can be more reliably prevented.

"Embodiment of the invention" According to an embodiment of the invention shown in FIG. is formed, and a flange portion 25 is formed at the tip of the valve stem 23. The valve rod 23 is inserted into the center hole 24 of the valve disk 22 from the base side, and is prevented from coming off by the flange portion 25 of the valve rod 23. Further, a nut 26, which is also inserted from the base side of the valve stem 23, is screwed onto the valve stem 23, and the valve disc 22 is tightened and fixed by this nut 26. In addition,
The nut 26 is welded to the valve rod 23 after the valve disk 22 is tightened and fixed.

Therefore, in this mushroom valve 21, when the exhaust passage is closed, the flange portion 25 of the valve stem 23, which is integrally formed with metal, can receive the impact that hits the valve seat, so that sufficient durability can be obtained. . Further, since the valve disk 22 is made of ceramics, wear resistance is improved, leakage is prevented, and the service life can be dramatically increased.

In another embodiment of the invention shown in FIG.
The contact surface between the flange portion 25 and the valve disk 22 and the contact surface between the nut 26 and the valve disk 22 have a common vertex at a point P that is on the axis of the valve stem 23 and coincides with the seat surface of the nut 26. It is formed to form the conical surface of a virtual cone (generating line is indicated by a two-dot chain line). (In this case, the contact surface between the nut 26 and the valve disc 22 is a flat surface, but in the present invention, the concept of a conical surface includes a flat surface.) In this embodiment, the difference in thermal expansion coefficient between metal and ceramics is Therefore, even if the valve stem 23, flange portion 25, and nut 26 expand relatively greatly compared to the valve disk 22 under high temperature, the contact state between the flange portion 25 and the valve disk 22 and the nut 26 and the valve disk 22 will be maintained.
The contact status can be kept the same. That is, when the metal part expands relative to the ceramic valve disc 22 under high temperature, the flange part 25 and the nut 26 become as shown by the dotted line in the figure, but the flange part 25 and the nut 26 become like the cone of an imaginary cone. Since it expands along the surface, the contact pressure against each valve disk 22 remains unchanged, and no rattling or unreasonable stress is generated on the valve disk 22.

In still another embodiment of the present invention shown in FIG. The conical surface of a virtual cone has a common vertex at a point P on the axis of the two. In this embodiment as well, due to the difference in thermal expansion coefficient between metal and ceramics, the valve stem 2
3. The flange portion 25 and the nut 26 are connected to the valve plate 22
Even if the valve expands relatively greatly compared to , the contact state between the flange portion 25 and the valve disc 22 and the contact state between the nut 26 and the valve disc 22 can be maintained the same, as shown by the dotted line in the figure.

"Effect of the invention" As explained above, according to the invention, a central hole is formed in a ceramic valve disk, a flange is formed at the tip of a metal valve stem, and the valve stem is inserted from the base side. The flange was inserted into the center hole of the valve plate to prevent it from coming out, and the valve plate was tightened and fixed with a nut that was screwed onto the valve stem from the base side of the valve stem, so that the impact of hitting the valve seat when closing the exhaust path was prevented. It can be received by the flange of the valve stem, which is integrally formed of metal, and provides sufficient durability. In addition, since the valve disc is made of ceramics, it has improved wear resistance, prevents leaks, and dramatically extends its life. Furthermore, by making the contact surfaces between the flange and the valve disk and the contact surfaces between the nut and the valve disk the conical surfaces of two different virtual cones whose apexes share a point on the axis of the valve stem, ceramics Even if the valve stem and nut expand relatively more greatly than the valve disk due to the difference in thermal expansion coefficient between the valve stem and the metal, the state of contact between them can be maintained the same.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the mushroom valve according to the present invention, FIG. 2 is a cross-sectional view showing another embodiment of the mushroom valve according to the present invention, and FIG. 3 is a cross-sectional view showing another embodiment of the mushroom valve according to the present invention. FIG. 4 is a sectional view showing a general aspect of a conventional mushroom valve, and FIG. 5 is a sectional view showing an example of a mushroom valve other than the present invention. In the figure, 21 is a mushroom valve, 22 is a valve disk, 23 is a valve stem, 24 is a center hole, 25 is a flange, and 26 is a nut.

Claims (1)

[Claims for Utility Model Registration] (1) In a mushroom valve for an internal combustion engine, which has a metal valve stem connected to a ceramic valve plate, a center hole is formed in the valve plate, and a center hole is formed at the tip of the valve stem. A flange portion is formed, the valve stem is inserted into the center hole of the valve disk from the base side thereof, the flange portion is used as a retainer, and a nut is screwed onto the valve stem from the base side of the valve stem. A mushroom valve for an internal combustion engine, characterized by a plate that is tightened and fixed. (2) In claim 1 of the utility model registration claim, the contact surface between the flange portion and the valve disk and the contact surface between the nut and the valve disk share one point on the axis of the valve stem. A mushroom valve for an internal combustion engine whose apex is the cone surface of two different virtual cones.