JPH076372B2 - Exhaust valve made of titanium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a titanium exhaust valve used for an exhaust port of a four-cycle engine for vehicles and the like, and more particularly to a titanium exhaust valve provided with an antioxidation measure.

[Prior Art] A valve made of titanium is used as an intake / exhaust valve for a four-cycle engine. This titanium valve has advantages such as light weight and high heat resistance. Therefore, when used in a high-speed engine, such as an engine for a motorcycle, the inertial weight at the time of high-speed opening / closing of the valve is reduced,
It is particularly advantageous. The titanium valve is composed of an umbrella portion and a shaft portion connected to the umbrella portion, and both are integrally connected at a rounded joint portion formed on the umbrella portion. Moreover, the whole is formed using a titanium alloy or the like. Special consideration is required when using this titanium valve on the exhaust side. That is, the heat resistant temperature of a general titanium valve is about 500 ° C, while the temperature in the exhaust port rises to about 800 ° C due to the combustion of the air-fuel mixture. Therefore, measures such as using a more heat-resistant grade titanium alloy are usually adopted.

[Problems to be Solved by the Invention] By the way, a large stress concentrates on the joint portion of the titanium valve due to high-speed opening and closing of the valve. Therefore, it is a part that requires a considerably high strength. In addition, as a characteristic of titanium, since it has a strong affinity for oxygen and is in constant contact with the burnt high-temperature exhaust gas containing a large amount of oxide, the joint portion and the like existing in the exhaust port are
It is susceptible to oxidation. When the surface is oxidized, an oxide layer having high hardness is formed, and this oxide layer gradually diffuses to the inside. As a result, the physical properties such as strength are gradually changed. Therefore, the oxidation of the joint has a great influence on maintaining the strength of this portion, and is a major factor that affects durability.

On the other hand, the existing titanium exhaust valve can secure a certain durability by adopting the above-mentioned heat-resistant grade titanium alloy and other measures. However, the strength of the joint portion must be maintained or strengthened when it is desired to further improve durability or when it is used under more severe conditions. As an example of use under such severe conditions,
There are cases where the engine is used in a super-high-speed rotation state for a relatively long time, such as in a car with special racing specifications. in this case,
The joint portion is exposed to the high temperature in the exhaust port and the burnt high temperature exhaust gas containing a large amount of oxide, and excessive stress concentration occurs.

Therefore, the present invention aims to further improve the durability of the titanium exhaust valve, focusing on the oxidation prevention of the joint portion.

[Means for Solving Problems] The titanium exhaust valve of the present invention has the following configuration.
That is, in an exhaust valve made of titanium having an umbrella portion, a shaft portion, and a joint portion integrally connecting the umbrella portion and the shaft portion in a round shape, an oxidation preventing layer is formed on the surface of the joint portion and The protective layer is formed by a diffusion reaction with aluminum or tin.

[Operation of the Invention] The joint portion of the titanium exhaust valve is covered with an antioxidant layer formed by a diffusion reaction with aluminum or tin. Therefore, even if the joint portion is exposed to the burned high-temperature exhaust gas containing a large amount of oxide in the exhaust port, the titanium layer in this portion is prevented from coming into contact with the exhaust gas by the antioxidation layer. Therefore, the titanium layer is not subject to oxidation by the exhaust gas. Therefore, the strength of the joint is not affected by oxidation, and the initially set strength is maintained for a long time.

In addition, aluminum and tin have a high affinity for titanium,
A diffusion reaction is surely caused to form a strong antioxidant layer on the surface side of the base material.

[Embodiment] An embodiment of the present invention will be described with reference to FIGS. FIG. 1 schematically shows a valve mechanism of a 4-cycle engine E for a motorcycle. Inside the engine E, a piston P is provided so as to be able to reciprocate, and a crankshaft C
It is connected to and is rotating. A mixture of air and fuel is introduced into the combustion chamber R in the cylinder head H above the piston P.
An intake port 1 for sucking into the inside is provided, and an intake valve 2 for opening and closing an opening portion into the combustion chamber R is provided in the intake port 1.
Is provided. A shaft portion of the intake valve 2 slides in a tubular valve guide 3, and a retainer 4 is taperly coupled to a shaft end of the intake valve 2 via a cotter pin. A valve spring 5 is arranged between the retainer 4 and the valve guide 3 to urge the intake valve 2 to be pushed upward. The rocker arm 6 is provided above the intake valve 2.
Is rotatably provided. An adjust screw 7 is provided at the tip of the rocker arm 6 so that the lift amount of the intake valve 2 can be adjusted. A cam shaft 8 is provided in the vicinity of the rocker arm 6, and the rocker arm 6 is rotated by the cam profile of the cam 9 to vertically move the intake valve 2 to open and close the intake port 1. ing. 10 is a spark plug.

On the other hand, symmetrically with the exhaust valve 2, an exhaust valve 12 is provided in an exhaust port 11 provided in the cylinder head H. The shaft portion of the exhaust valve 12 is passed through the tubular portion of the valve guide 13, and the retainer 14 is joined to the shaft end. A valve spring 15 is arranged between the valve guide 13 and the retainer 14. A rocker arm 16 is provided above the exhaust valve 12, and an adjust screw 17 is provided at the tip of the rocker arm 16.
Is provided, and the rocker arm 16 is rotated by the cam 19 of the cam shaft 18. In addition, valve guide 1
3, retainer 14, valve spring 15, rocker arm 1
6, adjust screw 17, camshaft 18, turtle 19
Both have the same function as the member on the intake valve 2 side.

When the cam 9 pushes down the rocker arm 6 due to the rotation of the cam shaft 8, the intake valve 2 causes the valve spring 5 to move.
Is pushed down in the direction of piston P against the intake port 1
Opens and the mixture is inhaled. On the other hand, the exhaust gas generated by burning the air-fuel mixture is compressed by the piston P. At this time, when the valve spring 15 is pushed down by the cam 19 of the cam shaft 18, the exhaust valve 12 is pushed down in the piston P direction, and the exhaust port 11 is opened. Then, the exhaust gas passes through the exhaust port 11 and is discharged into the atmosphere through an exhaust pipe (not shown). At the time of this exhaust, the exhaust valve 12
The portion inside the exhaust port 11 is exposed to burnt high-temperature exhaust gas rich in oxides. Further, the inside of the exhaust port 11 becomes hot as the engine speed increases.

Next, the structure of the exhaust valve 12 will be described with reference to FIG. The exhaust valve 12 is entirely formed of a titanium alloy having a composition of Ti-6A1-4V. However, Ti-6A1-2Sn-4Z
Other appropriate materials such as an alloy composition of r-2M can be selected. The exhaust valve 12 has a substantially trumpet tubular shape, and includes an umbrella portion 20, a shaft portion 21, and a joint portion 22 formed on the umbrella portion 20 to connect the shaft portion 21 in a round shape. Umbrella part 20 is an exhaust port
11 is a part that opens and closes, and a peripheral portion thereof is a part that is in close contact with a valve seat (not shown) fitted into the cylinder head H to seal the exhaust port 11. The joint portion 22 is a portion that connects the umbrella portion 20 and the shaft portion 21, and is formed into a rounded shape. Further, an antioxidant layer 23 is formed on this surface. However, the film thickness of the anti-oxidation layer 23 shown in the drawing is exaggerated and is actually thinner. Reference numeral 24 is a groove for the cotter pin.

The oxidation preventing layer 23 in this embodiment is formed by spraying aluminum powder on the surface of the titanium valve. First, an aluminum layer is formed on the joint part 22 by thermal spraying. After that, a diffusion reaction occurs between the aluminum layer and the titanium surface to form a compound layer of aluminum and titanium. As a result, the antioxidant layer 23 in which both layers are firmly diffusion bonded is formed. Moreover, since the antioxidation layer 23 covers the titanium layer of the joint portion 22 and prevents the titanium layer of this portion from being directly exposed to the exhaust gas, the oxidation of the titanium layer is prevented. In addition, as another metal forming the antioxidant layer 23, there is Sn or the like, which is appropriately selected and used. The method for forming the antioxidant layer is not limited to thermal spraying. The point is that it suffices that the titanium layer can be firmly integrated by diffusion bonding or the like to form the coating film. The range of the joint portion 22 in which the antioxidant layer 23 is to be formed is
At least, the stress concentration is maximum. The minimum radius portion near the bases of the umbrella portion 20 and the shaft portion 21 is included.

FIG. 3 shows the oxidation resistance characteristics of the antioxidant layer 23 thus formed. This graph shows the change in hardness from the surface of each joint part using a titanium valve (made of Ti-6A1-4V alloy) having no antioxidation layer as a comparative example. When titanium is oxidized, an oxide film is formed, and the surface hardness of the oxide film is high. Therefore, in the illustrated comparative example, it can be seen that the hardness increases sharply toward the surface and is strongly oxidized. On the other hand, it can be seen that the one according to the present invention maintains almost constant hardness from the surface to the inside and is hardly oxidized. Therefore joint part 22
By forming the oxidation prevention layer 23 on the titanium layer, the titanium layer of the joint portion 22 can be prevented from being affected by the oxidation. Therefore, it is clear that at least the influence of oxidation can be avoided among the changes in physical properties such as strength due to use under severe conditions. If the antioxidant layer 23 is formed in a wider area, the area that is not affected by the oxidation can be expanded.

[Advantages of the Invention] The joint portion of the titanium exhaust valve of the present invention is a stress concentration portion, and an oxidation preventing layer formed by a diffusion reaction between titanium and aluminum or tin is formed in the joint portion exposed to high temperature exhaust gas. There is. Therefore, even in the high temperature exhaust gas, the titanium layer in the joint portion is not oxidized, and the strength change due to the oxidation of this portion can be prevented. Therefore, even under severe operating conditions, the initial set strength can be maintained for a relatively long period of time, and the durability of the exhaust valve can be further improved.

Further, aluminum and tin have a high affinity for titanium, and the diffusion reaction is surely caused. Also, these metals are inexpensive. Therefore, the anti-oxidation layer firmly bonded to the surface of the base material in the joint part of the titanium valve is surely secured.
Moreover, it can be advantageously formed.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a partial sectional view of an engine to which the present invention is applied, FIG. 2 is a partially cutaway external view, and FIG. It is a graph which shows a grade. (Explanation of symbols) 11 …… Exhaust port, 12 …… Exhaust valve, 20 …… Umbrella part, 21
…… Shaft part, 22 …… joint part, 23 …… Antioxidant layer.

Claims (1)

[Claims] 1. An exhaust valve made of titanium comprising an umbrella portion, a shaft portion, and a joint portion integrally connecting the umbrella portion and the shaft portion in a round shape, wherein an oxidation preventing layer is formed on a surface of the joint portion. An exhaust valve made of titanium, characterized in that the antioxidant layer is formed by a diffusion reaction with aluminum or tin.