JPH0452452Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Technical Field of the Invention] The present invention relates to an improvement of a cast iron cylinder head having a cast-in exhaust insulation port. [Prior art] Exhaust ports are formed in the cylinder head of an engine by casting, and the exhaust port is kept at a high temperature and uses its energy to drive a turbocharger. Various methods have been proposed for treating exhaust gas, such as re-burning the gas to purify it. Therefore, in order to maintain the exhaust gas as high as possible, the so-called "exhaust port" is constructed by casting the exhaust port into the cylinder head as a hollow double pipe structure with a space between the inner pipe and the outer pipe. "insulated ports" are used. This exhaust heat insulating port having a hollow double pipe structure has an air layer formed in the middle thereof or a heat insulating material is laminated to increase the heat insulating effect, and is effectively used. Hollow 2 for conventionally used exhaust insulation port
For heavy pipes, austenitic heat-resistant steel (stainless steel) is used to improve heat resistance and corrosion resistance.
is used. On the other hand, in the case of a cylinder head that is cast by encasing the exhaust heat insulating port as a core, it is necessary to press fit the valve guide into the cylinder head after casting to support the exhaust valve and intake valve.
In this case, it is necessary to machine a hole through the cast iron part that makes up the cylinder head and the exhaust heat insulation port, and press fit the valve guide into the hole. In machining this hole, it is easy to drill a hole in cast iron, but drilling a hole in the double pipe that makes up the exhaust insulation port is quite difficult, and the drill may slip and penetrate the exhaust insulation port. The current situation is that productivity is declining because of this. [Purpose of the invention] In order to solve the problem of workability when the exhaust insulation port is made of cast iron, the inventors of the present invention used a microscope to examine the hole for inserting the valve guide in the exhaust insulation port. When we examined its structure, we found that if the machined surface of the exhaust heat insulation port that comes in contact with the cast iron part is made of austenitic stainless steel, the main component, Cr, will combine with carbon on the cast iron side during casting. However, it turned out to be a highly hard Cr carbide. Moreover, the hardness of this Cr carbide is quite high, _Hv 700, and it has been found that this causes a significant decrease in workability as described above. On the other hand, in order to confirm this fact, when a metal containing no Cr or Ni was cast into cast iron, it was found that the hardness of the metal hardly increased. This invention provides the excellent heat resistance and corrosion resistance of austenitic steel to the surface that comes into contact with engine exhaust gas, and the carbon contained in the cast iron that makes up the cylinder head is replaced by the presence of chromium contained in the austenitic steel. The purpose is to prevent the increase in hardness of the exhaust heat insulation port due to the "carburization phenomenon" in which chromium carbide is transferred to the austenitic steel side during casting, and to provide a cylinder head with excellent machinability. be. [Summary of the invention] To achieve the above object, the cylinder head according to the present invention is a cylinder head made of cast iron having an exhaust insulation port of a double pipe structure fixed by casting and perforated. The outer tube of the port is cast in cast iron and is made of mild steel, and the inner tube that is placed in contact with the exhaust gas and has a space between it and the outer tube is made of austenitic heat-resistant steel. In the present invention, the mild steel and austenitic heat-resistant steel that constitute the exhaust heat insulation port consisting of a double pipe are metal materials that are commonly used, and no special materials are used. Therefore, mild steel generally has a carbon content of 0.12 to 0.25%.
This refers to ordinary steel at the front and rear, and when these are represented by symbols, steel materials with low carbon content such as SPCC, SS41P, SPHC, SAPH, etc. fall under this category. In addition, a typical example of austenitic heat-resistant steel is 18−
8 stainless steel (SUS304), which exhibits a similar carburizing phenomenon, is a heat-resistant and corrosion-resistant material. Next, the melting points of these metal materials will be explained as follows. The melting point of ordinary cast iron (C=3.4%, Si=2.1%) is
The temperature of the molten metal when melted during casting is approximately 1240°C. In addition, the melting temperature of mild steel (SPCC) is about 1530℃, and the melting point of austenitic steel (SUS304) is 1530℃.
Before and after. Therefore, the difference between the melting point of cast iron during casting and the melting points of the mild steel pipe, austenite steel pipe, and molten metal that form the exhaust heat insulation port is about 300°C, and the exhaust heat insulation port is placed inside the cylinder head by casting. It can be seen that it is extremely easy to provide. [Example] Next, an example of the present invention will be described with reference to the drawings. Fig. 1 is a sectional view showing the upper structure of a cast iron cylinder head for a gasoline engine.A combustion chamber 2 is formed on the lower surface of the cylinder head 1, and a double pipe structure is continuous to the combustion chamber 2. The exhaust heat insulation port 3 is formed by casting. Inside the combustion chamber 2, an ignition plug 4, an exhaust valve 5, and an intake valve (not shown) are provided. The stem 5A of the exhaust valve 5 is supported by a valve guide 6 provided through the cylinder head 1 and the exhaust port 3, and is operated by being pressed at the upper end by a rocker arm 8 driven by a cam 7. is configured to do so. In the exhaust port 3 according to the present invention, the inner tube 3A that contacts the exhaust gas is made of an austenitic heat-resistant steel tube, the outer tube 3B is made of a mild steel plate tube, and both ends 8 are made of an austenitic heat-resistant steel tube. Either the end of the inner tube 3A is bent to wrap the outer tube 3B so that hot water during casting does not enter into the space 9 of the exhaust heat insulation port 3, or both ends 8 are closed by welding. are doing. A flat surface 10 is formed on the upper surface of the intermediate portion of the exhaust heat insulation port 3, and the valve guide 6 is provided to penetrate this flat surface 10. FIG. 2 is a sectional view showing the main parts of the cylinder head 1 before machining.
A heavy tubular exhaust insulation port 3 is mounted within the cast iron section 15 by a cast-in. When the cylinder head 1 is cast with the exhaust heat insulation port 3 made of cast iron as described above, the hole 13 for the valve guide 6 is formed on the flat surface 10 using a tool 14, as shown in FIG. Processed by. Then, the valve guide 6 is press-fitted and fixed into the hole 13 as shown in FIG. 1, and the stem 5A of the exhaust valve 5 is inserted into the valve guide 6 and supported so as to be reciprocatable. Note that since the intake valve has a similar structure, its explanation will be omitted. In the machining of the exhaust heat insulation port 3, the part of the exhaust heat insulation port 3 having a structure using a conventional double pipe was made of austenitic heat-resistant steel in contact with the cast iron part 15. It is characterized in that the outer tube 3B that contacts the cast iron portion 15 is made of a mild steel tube, and the inner tube 3A is made of austenitic heat-resistant steel. [Effects of the invention] Next, in order to clarify the effects of the invention, the thermal conductivity coefficients of three types of materials: air, austenitic heat-resistant steel (stainless steel), and carbon steel are compared as shown in Table 1. It becomes like this. [Table 1] Air Austenitic Carbon Heat Resistant Steel Steel thermal conductivity coefficient 0.050 14 46 (cal/mh℃, 500℃) Furthermore, the relationship between the material of the cast-in material and the hardness after casting using cast iron is shown in the second table. Shown in the table.

【table】

[Table] As described above, the present invention uses a mild steel pipe on the outer pipe 3B side of the exhaust heat insulation port that contacts the cast iron part 15, and uses austenitic heat-resistant steel on the inner pipe 3A side that contacts the exhaust gas. The following effects can be achieved. (a) Since a soft steel pipe (such as SPCC) is used for the outer pipe 3B constituting the exhaust heat insulation port 3 with a double pipe structure, even if it comes into contact with the cast iron part 15, there will be a large amount of Cr, Cr, etc. in this material. Since it does not contain Ni, it does not generate Cr carbide, and as shown in Table 2, the hardness after casting is Hv100, but even after casting it is about Hv250, which is a low value. On the other hand, if austenitic heat-resistant steel (SUS304, etc.) is used on the outer tube 3B side,
It can be seen that the hardness increases significantly from Hv200 to 700. As described above, according to the present invention, since the hardness of the outer tube 3B has not increased significantly even after being cast-in, the machinability when drilling the hole 13 for the valve guide in the exhaust heat insulation port 3 is improved, especially when using the drill 14. The cutting performance is significantly improved, and this drill 1
4. Positioning and drilling can be performed easily, significantly improving productivity. (b) Since a tube made of austenitic heat-resistant steel is used on the inner tube 3A side, the thermal conductivity coefficient of this tube is 14 kcal/mh℃, as shown in Table 1, compared to 46 kcal/mh℃ of carbon steel. Approximately 1/3 compared to mh℃
In addition, since a heat insulating layer made of an air layer or a heat insulating material is formed in the space 9 between the outer tube 3B and the inner tube 3A, an effective heat insulating effect cannot be obtained. I can do it. In addition, in the example, a cast iron cylinder head for a gasoline engine was explained.
It is clear that a cast iron cylinder head for a diesel engine would have similar effects.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the upper structure of a cylinder head according to an embodiment of the present invention, FIG. 2 is a sectional view showing an exhaust port formed by casting, and FIG. FIG. 3 is a sectional view showing a state in which the exhaust heat insulation port of the cylinder head shown in the figure is being drilled with a tool. 1... Cylinder head, 2... Combustion chamber, 3...
Exhaust insulation port, 3A... Inner pipe (made of austenitic heat-resistant steel), 3B... Outer pipe (made of mild steel), 5... Exhaust valve, 6... Valve guide, 8... End, 9
...Space part, 14...Tool, 15...Cast iron part.

Claims (1)

[Scope of utility model registration request] In a cast iron cylinder head that has an exhaust insulation port with a double pipe structure that is fixed by casting and perforated, the exhaust insulation port has an outer pipe that is cast in the cast iron and is made of mild steel, and there is a gap between the outer pipe and the outer pipe. A cylinder head characterized in that an inner tube arranged with a space provided therein is made of austenitic heat-resistant steel.