JPH116407A - Engine valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine valve excellent in abrasion resistance and lubricity. SOLUTION: In a valve element, made of heat resistant steel, comprised of a poppet part provided in range with a stem part; an engine valve is provided by forming a nitriding layer, including a sulfide by nitrosulphurizing treatment, on an iron alloy layer, provided on the upper surface of heat resistant steel finished on the annular back surface edge part of the poppet part. Lubricity and abrasion resistance can be kept by using liquid fuel too.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an engine valve used as an intake valve or an exhaust valve of an engine of an internal combustion engine such as an automobile.

[0002]

2. Description of the Related Art In general, an internal combustion engine is configured to put a combustible substance (fuel) into a combustion chamber, and take out a change in volume when the combustible substance is burned by a piston provided in the combustion chamber as a reciprocating motion. At this time, the one that performs each of the steps of fuel intake, compression, expansion, and exhaust four times is called a four-stroke engine, and the one that performs it twice is called a two-stroke engine.

[0003] An intake valve seat and an exhaust valve seat of a valve train of a four-stroke engine for an automobile are arranged and mounted at an intake inlet and an exhaust outlet of a cylinder head of the engine, respectively. The intake and exhaust valves, which reciprocate with the operation of the engine, come into contact with and separate from the respective valve seats, causing the combustion chamber and the intake passage,
The combustion chamber and the exhaust passage are configured to be shut off and communicate with each other.

[0004] In recent years, from the viewpoint of protection of the global environment and resources, the requirements for exhaust gas regulations and fuel efficiency regulations for automobile engines have become strict. For this reason, car engines
High temperature, high speed, reduction of engine oil consumption, etc.
It has become inevitable to withstand harsh use environments more than ever before. In addition, since the number of automobile users has increased, the time and effort required to maintain those automobiles and the required life have also been increasing.

In order to cope with such severe use environment conditions, heat-resistant steel valves are often used as valves of valve train parts. In order to improve abrasion resistance of a valve face portion in contact with a valve seat. , On the back edge of the valve head
Co with high hardness at high temperature and high resistance to high temperature corrosion
A base metal layer or a Ni-base alloy has been provided by overlay welding to provide a metal layer.

Further, as a valve seat material used as a mating material of a valve, Fe-C-Co-Ni-based materials and Fe-C-based materials are used to improve the wear resistance.
o, a sintered alloy to which an Fe-C-Cr-Mo-V alloy or the like is added is used. Alternatively, after adding and mixing a hard alloy powder of a specific composition in a specific ratio to an alloy powder of a specific composition, compression molding, and infiltrating copper or a copper alloy at a high density, it has excellent wear resistance and sliding characteristics. Used as material.

[0007]

In the case of gaseous fuel such as LPG, unlike the case of liquid fuel such as gasoline or light oil, lubrication between the valve and the valve seat is small, Adhesion occurs between the valve seats, causing excessive wear. Therefore, some valve seats used in gas-fueled engines have a lubricant (Pb or the like) added thereto. The purpose of lubricants is to reduce the amount of wear between the valve and the valve seat by reducing the adhesion between the surface where the valve and the valve seat contact. For this purpose, the most desirable location for the lubricant is between the valve and the valve seat. However, valves and valve seats are
They are not always in contact, but are constantly in contact and withdrawal. Moreover, the combustion gas is blowing through the detached surface, and as a result, it is very difficult to keep the liquid lubricant between the valve and the valve seat. This means that the lubricant melted out of the valve seat is blown off by the exhaust gas due to the heat of combustion during the use of the valve. After a situation in which little lubricant remains in the valve seat, adhesion occurs between the valve and the valve seat,
The current situation is that excessive wear eventually occurs.

Therefore, it is necessary that the supplied lubricant can be easily and continuously provided on the surface of the valve or the valve seat even while the valve and the valve seat are repeatedly contacted and separated. For this purpose, it is necessary to use a lubricant whose use state is not liquid. Further, in the current infiltration into a substrate, there is a possibility that the lubricant will be lost during use. Therefore, instead of supplying the lubricant by infiltration to the base material, the presence of the lubricant on the surface,
It is desirable to be present so as to be dispersed in the substrate.

The present invention has been made in view of the above circumstances, and has as its object to provide an engine valve with further improved wear resistance.

[0010]

An engine valve according to the present invention is a heat-resistant steel valve body in which a stem portion is connected to a valve head portion, and a ring-shaped rear edge of the valve head portion is finished. An iron alloy layer is provided on the upper surface of the heat-resisting steel formed as described above, and a nitride layer containing sulfide is formed on the iron alloy layer by sulphonitriding.

[0011] The nitrided layer containing sulfide formed by the nitrosulphurizing treatment has a nitrided layer having a surface hardness of at least Hv450.
It is preferable to have a layer made of a sulfide and a nitride having a hardness of not less than μm and a hardness of Hv 350 to 450 of not less than 5 μm. It is desirable that a plating layer containing 80% by weight or more of iron exists on the upper surface of the heat-resistant steel formed by finishing the annular rear edge of the valve head.

In addition, it is preferable that a ferrite layer or a thermal spray layer containing 50% by weight or more of iron element exists in place of the plating layer.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the engine valve of the present invention, the effect of the lubricant is always exerted by the presence of sulfide (FeS), which acts as a lubricant, in the contact portion of the valve surface with the valve seat. Is done. Further, by including iron nitride in the layer containing sulfide, the hardness can be increased and the wear resistance of the valve can be improved.

By performing the nitrosulphurizing treatment for the above-mentioned purpose, a nitrided layer and a nitrided layer containing sulfide can be simultaneously formed due to a difference between a production rate of iron nitride and a production rate of iron sulfide. Furthermore, in this nitrosulphurizing treatment, a nitrided layer can be formed between the nitrided layer, the layer containing sulfide, and the substrate. The wear resistance can be improved by utilizing the hardness of the nitrided layer.

Normally, heat-resistant steel containing a large amount of chromium, which is a material for forming a valve, has a relatively small thickness of a nitride layer containing sulfide formed on the surface in the sulphonitriding treatment. Therefore, in order to increase the effect of the hardness of the nitrided layer and to make sulfides and nitrides more easily formed, the proportion of the Fe element on the surface of the valve base material is increased, and the proportion of the element that hinders the treatment is increased. It is desirable to lower it. For this reason, it is preferable that the surface of the valve to be subjected to the sulfur-nitriding treatment be subjected to plating, metal plating, thermal spraying or the like in advance to increase the amount of iron element.

This makes it possible to form a protective film having sufficient lubricity and high hardness on the valve surface,
Since the material of the valve and the valve seat directly comes out of the surface and does not hit, the wear can be reduced. Regarding the thickness of the sulfide and nitride layers, there is no lubricating effect when the film thickness is small, and there is almost no difference in the effect when the layer thickness is 5 μm or more. If the sulphinitriding treatment time is short, the thickness of the layer composed of sulfide and nitride becomes thin, and considering the treatment time for securing the thickness of the nitrided layer existing under this layer, the hardness is reduced. It is preferable that the layer composed of sulfide and nitride having an Hv of 350 to 450 has a thickness of 5 μm or more.

In this sulphonitriding treatment, a mixed layer can be formed on the upper surface side of the nitrided layer because the diffusion of elements into the base material is different between nitrogen and sulfur. As a result, the wear resistance of the base material can be ensured by the lower nitride layer, and the lubricity of the base material can be ensured by the mixed layer of sulfide and nitride thereon. FIGS. 5, 6, 7, and 8 show the relationship between the oxynitriding treatment time and the hardness and the film thickness, and the relationship between the treatment time and the wear. After each plating on the valve base material, a nitrosulphurizing treatment was performed for 30 minutes.
Minutes, 90 minutes and 180 minutes. Further, in order to check the hardness, what was subjected to the treatment for 90 minutes was subjected to a heat treatment of holding at 600 ° C. for 2 hours to reduce the hardness of the portion near the surface. The wear amount was evaluated using the tester shown in the examples. As a result, as shown in FIG. 6, it is necessary that a layer having a hardness of Hv450 or more is 30 μm or more as a surface treatment. That is, the amount of wear is small in the 90-minute treatment and the 180-minute treatment, but is large as shown in FIG. 7 in the 30-minute treatment and the heat-treated product. Therefore, the hardness H of the heat-treated product
It can be seen that v450 and a thickness of 30 μm or more have the effect of reducing the wear amount of the valve.

If the thickness of the layer made of sulfide and nitride is small, the amount of wear is large as shown in FIG. If the processing time is short, the thickness of the layer composed of sulfide and nitride becomes thin, and the hardness increases only with the nitride layer as shown in FIG. In order to maintain a balance with the thickness of the nitride layer and the layer containing sulfide, the hardness of the surface layer is 350 to 45 in Hv.
It is desirable that the zero thickness be 5 μm or more.

If the iron content of the steel material of the valve subjected to the nitrosulphurizing treatment is less than 50% by weight, the sulfide layer formed by the treatment cannot be made thicker than 5 μm. Also,
The larger the iron content, the deeper the sulphinitriding treatment layer, and the greater the effect of the treatment. However, when the iron content is 100% by weight, the abrasion resistance of the plating layer is weakened. Therefore, it is preferable to add P (phosphorus) up to 10% by weight. If the P content is less than 8% by weight, the hardness of the plating layer is low and the wear resistance is poor,
If it exceeds 10% by weight, the toughness of the plating layer becomes low and the coating becomes brittle, which is not preferable. Except for P and impurities other than P, the iron content is specified to be 80% by weight or more in order to increase the iron content.

[0020] As a material for the banking, general Fe-Cr is used.
The use of a -Mo-Ni-C alloy is preferred. If the amount of iron in the substrate subjected to the nitrosulphurizing treatment is less than 50% by weight, the sulfide layer formed by the treatment cannot be made thicker than 5 μm. Therefore, the iron content of the base material is 50 to 80% by weight.
Is preferred. If the amount is too large, the strength of the base material is reduced and the wear resistance is also reduced, such being undesirable.

The amount of Fe—C is a rule for easily producing particles for thermal spraying and for ensuring abrasion resistance.
If the amount of C is small, the particles are not stable and particles suitable for thermal spraying cannot be obtained. If the amount of C is large, abrasion resistance deteriorates. The amount of Cr is to ensure corrosion resistance. If the amount is small, abrasion resistance and corrosion resistance are deteriorated. If the amount is large, particles are not stable and particles suitable for thermal spraying cannot be obtained.

If the amount of iron in the substrate by thermal spraying is less than 50% by weight, the sulfide layer formed by the
m or more, so that it is not preferable. Therefore, the amount of iron on the surface to be treated of the substrate is preferably 50 to 70% by weight. Also, by forming a hard layer on the valve surface, it becomes possible to reduce the wear of the valve,
As a result, wear of the valve can be reduced.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on an example in which the present invention is applied to an exhaust valve / valve seat. Heat-resistant steel (S
UH35) was hot forged, machined into a valve shape, and then Example 1 was iron-phosphorous plated (C: 0.3% by weight, P:
9% by weight, the composition of the residual iron), and Example 2 was made of ferrous metal (Cr: 19% by weight, Mo: 10% by weight, Ni: 19% by weight, C: 1.7% by weight, Example 3 was subjected to thermal spraying of iron (C: 1% by weight, composition of residual iron), and was used as a base for the sulfur-nitrided portion. After finishing the annular back edge of the valve head, the entire valve is subjected to sulphonitriding (sodium cyanide (NaCN) 30%, sodium carbonate (Na ₂ C)
O ₃ ) 30%, sodium chloride (NaCl) 30% as a base material, and a reducing salt bath agent using sodium sulfate (Na ₂ SO ₄ ) and sodium thiosulfate (Na ₂ S ₂ O ₃ ) as a few percent of a sulfurizing agent is 580. C., and the object to be treated was immersed in this for 180 hours to form a highly lubricated sulfide film on the metal surface and a hard nitride layer as a base thereof.

Comparative Example 1 is a material having the composition of Example 1 which is not subjected to the oxynitriding treatment. Comparative Example 2 was obtained by performing a nitrosulphurizing treatment without a base treatment. Comparative Example 3 is one obtained by only plating. Comparative Example 4 was a processed one.
In Comparative Example 5, a thermal spraying treatment was performed.

[0025]

[Table 1]

[0026]

[Table 2]

The mating member used in the evaluation was a conventional valve seat material having excellent wear resistance. Each of the test samples prepared above was evaluated for wear resistance using a valve seat tester that simulated actual movements of a valve and a valve seat of an engine. The outline of the test machine is shown in Fig. 1 (1 valve and 2 valve seats are abutted, and the valve reciprocates up and down. The flame is blown by a burner from above the valve to load the temperature of the combustion gas of the engine). .

As a result of the evaluation, as shown in FIGS. 2 and 3, the wear depth (a (μm)) of the valve face portion, which is the contact surface of the valve with the valve seat, was evaluated. The amount of wear of the valve seat is represented by the difference between the position of the valve shaft end face when the valve is brought into contact after the wear test and the position of the valve shaft end face when the new valve is brought into contact (b (μm)). Measure,
The respective abrasion resistances were used. The results are shown in FIGS.

The valve abrasion was most frequent in Comparative Example 1 in which no treatment was performed, followed by Comparative Examples 3 and 5 in which only the plating layer and the sprayed layer were used, and in Comparative Example 2 in which only the nitrosulfurizing treatment was performed, and in the ferrous metal. Although only the wear amount of Comparative Example 4 is almost the same as that of Comparative Example 4, each of them is larger than that of the present embodiment. Further, it can be seen that the valve seat wear amount is large in all of the comparative examples, and that the present embodiment is small in all, and the wear resistance is improved.

[0030]

According to the engine valve of the present invention, since the coating of the iron nitride layer containing sulfide is formed on the contact surface of the valve with the valve seat, wear of the main body is suppressed and lubricity is improved. Therefore, even in the case of gaseous fuel, wear can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a valve seat tester.

FIG. 2 is a schematic view showing a position of a worn surface of a valve.

FIG. 3 is a schematic diagram showing a change in the position of a shaft end surface of a valve.

FIG. 4 is a bar graph showing a wear amount of a valve after a wear test.

FIG. 5 is a bar graph showing a wear amount of a valve seat after a wear test.

FIG. 6 is a graph showing the relationship between hardness and film thickness depending on the time of the nitrosulphurizing treatment of the valve substrate.

FIG. 7 is a bar graph showing the amount of wear of the valve subjected to the processing of FIG. 6;

8 is a graph showing the relationship between the hardness and the thickness of the nitrided layer containing sulfide of the nitrosulfurized product of FIG. 6;

FIG. 9 is a graph showing a relationship between a thickness of a nitride layer containing sulfide and a wear amount of a valve seat.

Claims (1)

[Claims] 1. A heat-resistant steel valve body having a stem portion connected to a valve head portion, wherein an iron alloy layer is formed on an upper surface of the heat-resistant steel formed by finish-finishing an annular back edge of the valve head portion. A valve for an engine, wherein a nitride layer containing sulfide is formed thereon by sulphonitridation treatment.