JPH0730686B2 - Engine valve - Google Patents

Description

TECHNICAL FIELD The present invention relates to an engine valve that is lightweight and has improved heat resistance.

(Prior Art) Lighter intake and exhaust valves are required in order to respond to higher engine speeds that accompany higher engine output requirements.
Therefore, it has been conventionally known to reduce the diameter of the valve stem portion or to make it hollow so as to reduce the weight. However, there is a limit in terms of rigidity to reduce the weight in this way. Therefore, it has been proposed to reduce the weight by changing the material forming the valve. That is, as an example in which this material is changed, there has been proposed one in which the entire valve is made of titanium or a titanium alloy which is a relatively lightweight metal. However, since this titanium or titanium alloy does not have a good thermal conductivity, there is a risk that heat will not be dissipated on the exhaust side and heat deformation or seizure of the exhaust valve will occur especially when used for the exhaust valve. .

In addition, since the former is required to have high heat resistance for the valve head and the valve stem of the intake and exhaust valves, and the latter is required to have good thermal conductivity, heat resistant steel made of different metals suitable for each member is used. It is known that a valve is constructed by using both of them and joining them, but the requirement for weight reduction has not been sufficiently satisfied.

Therefore, heat-resistant steel is used from the viewpoint of good heat conduction, titanium or titanium alloy is used from the viewpoint of weight reduction, and it is possible to construct a valve by joining both of them, but it is possible to use titanium or titanium by simply combining them. Since the titanium alloy has poor thermal conductivity, problems such as thermal deformation still remain. That is, when a metal having a relatively high thermal conductivity and a metal having a considerably lower thermal conductivity are joined to form an intake / exhaust valve, the heat transmitted through the metal having a high thermal conductivity is It will be stopped at the joint surface, and thermal stress will occur there, which may lead to problems such as breakage due to thermal deformation and thermal fatigue.

(Object of the Invention) The present invention has been made in view of the above conventional problems,
According to the requirements of heat resistance, weight reduction, etc., both the valve stem and the valve stem are made of two kinds of metal with different thermal conductivity. An object of the present invention is to provide an engine valve capable of preventing heat fatigue.

(Structure of the Invention) In the present invention, the valve stem portion and the valve stem portion are made of different metals, and the metal forming the valve stem portion has a lower thermal conductivity than the metal forming the valve stem portion. A valve of an engine in which both parts are joined, wherein a metal layer having a higher thermal conductivity than the both metals covers a range including the valve stem part and a joint part of the both parts, and the valve umbrella part It is formed so as to overlap at least a part of the surface of the metal constituting the, and heat is transferred from the valve head portion to the metal layer.

The metal layer is, for example, a metal molybdenum sprayed layer.

According to this configuration, even if the thermal conductivity of the valve stem portion is low, the heat of the valve umbrella portion is transferred to the metal layer and is dissipated through the portion that is in sliding contact with the valve stem portion. The heat is prevented from accumulating in the joint, and the thermal stress at this joint is reduced.

(Example) As one example of the valve of the engine of the present invention, the case where it is applied to an exhaust valve will be described with reference to the drawings.

In the drawings, reference numeral 1 denotes a cylinder head, which has a combustion chamber 1a and an exhaust passage 1b opening to the combustion chamber 1a. 2 is an exhaust valve, and this exhaust valve 2 has a valve head portion 2a and a valve stem portion 2b.
And are composed of dissimilar metals with different thermal conductivity.
It is joined at the 2c part. As a specific structure, the valve head portion 2a has SUH1 which is a metal having a relatively high thermal conductivity or
Heat-resistant steel such as SUH3 is used, and the valve stem 2b is made of titanium or titanium alloy, which is a metal with a relatively low thermal conductivity, and both are joined by electrical resistance welding, friction welding or brazing at the joint 2c. Has been done. In addition, as a metal layer made of a metal having a higher thermal conductivity than the two kinds of metals forming the both portions 2a, 2b on almost the entire surface of the valve stem portion 2b made of titanium or a titanium alloy,
A metal molybdenum sprayed layer 2d is formed. The molybdenum sprayed layer 2d is formed so as to cover the range including the joint portion 2c and to overlap at least a part of the surface of the metal forming the valve umbrella portion 2a, that is, at least a part thereof is made of heat-resistant steel. It is provided across the valve umbrella portion 2a.

3 is a valve seat for receiving the valve umbrella portion 2a, 4 is a sliding member for guiding the valve stem portion 2b, 5 is a cam shaft for opening and closing the exhaust valve 2, 6 is the cam shaft 5 and the valve stem portion 2b. A tappet located between the upper end of the exhaust valve 2 and the upper end of the spring is a spring for urging the exhaust valve 2 in the closing direction.

As described above, by using titanium or titanium alloy for the valve stem portion 2b, it is possible to achieve weight reduction and high corrosion resistance, and heat resistance is good by using heat-resistant steel as the valve umbrella portion 2a, and the valve umbrella portion The heat of 2a is dissipated through the sliding member 4 through the valve seat 3 and the molybdenum sprayed layer 2d having good thermal conductivity formed on the surface of the valve stem 2b across the valve umbrella 2a. To be
Therefore, the transfer of heat from the valve head portion 2a side is not affected by the joint portion 2c.
Therefore, it is possible to prevent thermal fatigue, thermal deformation of the valve canopy portion 2a, and the like from occurring because the thermal stress is reduced.

Further, the molybdenum sprayed layer 2d is generally porous and rich in oil lubricity. Therefore, by forming the molybdenum sprayed layer 2d on the surface of the valve stem portion 2b, the lubricity of the sliding member 4 becomes good. .

(Effects of the Invention) As described above, according to the present invention, both the valve umbrella portion and the valve stem portion are made of different metals for heat resistance, weight reduction, etc. When the stem portion has a lower thermal conductivity, the metal layer having a higher thermal conductivity than the both metals covers the range including the valve stem portion and the joint portion of the both portions, and the valve umbrella portion. By being formed so as to overlap at least a part of the surface of the metal constituting the, the overall heat conduction is good, suppressing the occurrence of thermal stress in the above-mentioned joints, thermal deformation of the valve,
It is possible to prevent the occurrence of thermal fatigue and the like, and it is possible to cope with higher engine output and higher engine speed.

[Brief description of drawings]

The drawings are sectional views showing an embodiment of an exhaust valve of an engine of the present invention. 2 ... Exhaust valve, 2a ... Valve head, 2b ... Valve stem, 2c ... Joint, 2d ... Molybdenum sprayed layer.

Claims (2)

[Claims] 1. A valve stem portion and a valve stem portion are made of different metals, the metal forming the valve stem portion has a lower thermal conductivity than the metal forming the valve stem portion, and the both portions are joined. In the valve of the engine described above, the metal layer having a higher thermal conductivity than the both metals covers the range including the valve stem portion and the joint portion of the both portions, and constitutes the valve umbrella portion. A valve for an engine, wherein the valve is formed so as to overlap at least a part of the surface of the valve, and heat is transferred from the valve head portion to the metal layer. 2. A valve for an engine according to claim 1, wherein the metal layer is a sprayed layer of molybdenum metal.