JPH04311611A - Ceramic coated engine valve - Google Patents

Abstract

PURPOSE:To make a valve difficult to transmit heat applied to the bevel surface in the engine valve coated with a film of thermal sprayed ceramic to the back thereof while preventing the base metal from corrosion due to corrosive gas penetrating from the bevel surface. CONSTITUTION:The surface layer 2h of a film of thermal sprayed ceramic is adapted to have small porosity and the inner layer 2g large porosity. Thus, the conduction of heat from the surface of a bevel part to the back thereof is restrained to prevent the back of the bevel part from temperature-rising, so that the intake efficiency is not degraded and the output of an engine can be prevented from decreasing to improve the exhaust emission.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine valve for an internal combustion engine whose cap surface is coated with ceramic.

0002

2. Description of the Related Art An engine valve for intake or exhaust in an internal combustion engine is used as shown in FIG. Reference numeral 1 designates an engine valve, which is composed of an umbrella section 2 and a stem 3, and the umbrella section 2 is further composed of an umbrella front 2a, a face 2b, and an umbrella back 2c. 4 is a seat ring, 5 is a port, 6 is a stem guide, 7 is a valve spring, and 8 is a cam that opens the engine valve 1 against the valve spring 7.

[0003] The umbrella table of engine valve 1 is 850 to 900.
℃, and the heat input from the umbrella front 2a is conducted inside the umbrella part 2 and raises the temperature of the umbrella back 2c. Particularly in the case of an intake valve, when the temperature at the back of the valve increases, the temperature of the intake air-fuel mixture increases, deteriorating the intake efficiency, resulting in a decrease in engine output and deterioration in exhaust emissions. Further, when leaded gasoline is used as the fuel, the additives in the gasoline are decomposed at high temperatures to produce corrosive product gas, which corrodes the cap 2a.

[0004] Therefore, Japanese Utility Model Application Publication No. 59-141108 proposes an engine valve in which the umbrella surface of a metal base material is coated with a ceramic sprayed film.

[0005]

[Problems to be Solved by the Invention] In the above-mentioned conventional technology in which a ceramic sprayed film is coated on the umbrella surface of a metal base material, the ceramic sprayed film structure exhibits a uniform structure with almost constant porosity when viewed from a macroscopic perspective. Therefore, if the porosity of the sprayed ceramic film is increased to reduce heat conduction in order to suppress the rise in temperature at the back of the umbrella, there is a problem that corrosive gases will penetrate into the metal base material and corrode the base metal.

[0006] Furthermore, in order to improve the corrosion resistance, if the porosity of the ceramic sprayed film is reduced to create a dense structure, there is a problem that the heat conduction becomes better and the temperature at the back of the umbrella rises. Suppressing the temperature rise and improving corrosion resistance are contradictory to each other, and it has not been possible to satisfy both at the same time. In view of the above, an object of the present invention is to provide a ceramic coated engine valve that can suppress the temperature rise behind the umbrella and improve corrosion resistance at the same time.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an engine valve whose umbrella surface (2a) is coated with a ceramic sprayed film, in which the surface layer (2h) of the ceramic sprayed film has a small porosity. It is characterized by having a built-in part (2g) with a large porosity.

[0008]

[Operation] The ceramic sprayed coating on the surface layer (2h) with low porosity prevents the penetration of corrosive gases and improves corrosion resistance. In addition, since the ceramic sprayed film of the inner layer (2g) has low thermal conductivity, its heat insulating effect makes it difficult for the heat that has entered the umbrella front to be transmitted to the umbrella back, thereby suppressing the temperature rise on the umbrella back.

[0009]

Embodiment In the embodiment shown in FIG. 1, 2d is an engine valve base material made of metal, and a recess 2e with a depth h is formed in the umbrella surface 2a. First, shot blasting with #80 to #120 grain size is applied to the concave portion 2e to increase adhesion strength.
Pre-treatment is performed to achieve a predetermined surface roughness.

Next, as the undercoat 2f, NiCr
Spray Al-based metal powder. This undercoat 2f serves to increase the adhesion strength of the ceramic sprayed film. Next, 2 g of partially stabilized zirconia ZrO2.8% Y2 O3 is thermally sprayed as a top coat (first layer). This sprayed layer has a large porosity of 8 to 10%, and this layer has a heat insulating effect.

Next, a second top coat layer 2h is thermally sprayed using the same ceramic material. This sprayed layer has a porosity of 1
A small value of ~3% makes the structure of the sprayed film dense and strengthens the bonding force between particles, thereby preventing the penetration of corrosive gases and improving corrosion resistance. Furthermore, if necessary, the surface of the second top coat layer is ground or cut for finishing.

To change the porosity of the first and second top coat layers, the particle size of the thermal spray material is changed. For example, to obtain a sprayed film with a dense structure with relatively low porosity, 5 to 25
A material having a particle size distribution of about 60 to 80 μm is used to obtain a sprayed film with a high porosity. In the above example, the undercoat and both top coats were sprayed using plasma, but plasma was used for the first layer of the top coat (2 g), and oxygen-acetylene gas was used for the second layer of the top coat (2 h) at high speed and high temperature. By performing density spraying, the porosity of the second top coat layer 2h can be further reduced.

[0013] Furthermore, the material of each layer of the top coat need not be limited to the same material as in the above embodiment; for example, the first layer of the top coat may be made of alumina (Al2O3), which is relatively low cost and has a high porosity. , the second top coat layer is ZrO2 8% Y2, which has excellent heat resistance and low thermal conductivity.
O3 may also be used. Furthermore, magnesia (MgO) or the like may be used as the material for the first layer of the top coat, or a mixture of multiple types of ceramic materials may be used. May be used for eyes.

Further, as a heat source for thermal spraying, the plasma or oxygen-acetylene is not limited to being used alone, but may be used in combination. Furthermore, in the above embodiment, the second top coat layer 2h, which is the surface layer, and the first top coat layer 2g, which is the inner layer, have different porosity, so that the porosity of the surface layer is small and the porosity of the inner layer is small. Although the porosity is increased, the porosity may be made to change continuously as it moves from the surface layer to the inner layer. The porosity can be continuously changed, for example, by changing the amount of ceramic material supplied per unit time.

[0015]

[Effects of the Invention] Since the ceramic coated engine valve of the present invention is configured as described above, it is possible to suppress the conduction of heat input from the umbrella surface to the umbrella backside, and prevent a rise in the temperature of the umbrella backside. , there is no deterioration in intake efficiency, and a decrease in engine output can be prevented. Also, exhaust emissions are improved.

Furthermore, corrosion of the base metal due to corrosive gas can be prevented. In addition, the inner layer portion (first layer of top coat) has a high porosity and relieves strain caused by thermal stress, which has the effect of preventing peeling and cracking of the sprayed film due to thermal cycles.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical cross-sectional schematic diagram showing the main parts of an engine valve of the present invention.

FIG. 2 is a longitudinal sectional view of the valve train.

[Explanation of symbols]

1 Engine valve 2 Umbrella section 2a Umbrella table 2e Recessed part 2f Undercoat

Claims (1)

[Claims] Claim 1: In an engine valve whose umbrella surface (2a) is coated with a ceramic sprayed film, the surface layer (2h) of the ceramic sprayed film has a small porosity and the built-in part (2g
) Ceramic coated engine valve featuring a large porosity.