JPH0621527B2 - Valve seat insert and cylinder head using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a valve seat insert used in a cylinder head of a piston engine and a cylinder head using the same. More specifically, the present invention relates to a valve seat insert made of a ceramic member and a metal member, and a cylinder head of a piston engine equipped with the valve seat insert.

[Prior Art] A valve seat insert is a ring-shaped member that is mounted and fixed to a cylinder head of a piston engine, and has a function of holding pressure in the cylinder by abutting a valve. As such a valve seat insert, one made of a ceramic member from the viewpoint of excellent wear resistance, heat resistance, etc. is disclosed in JP-A-59-162345 and JP-A-60-1260.
It is proposed in Japanese Patent No. 3 publication.

JP-A-59-162345 discloses a valve seat made of partially stabilized zirconium oxide (PSZ).
On the other hand, Japanese Utility Model Application Laid-Open No. 60-12603 discloses a structure of a ceramic valve seat and a structure of the valve seat and the ceramic as a part of a structure for realizing a combustion chamber excellent in heat resistance. A mechanism for relieving an impact load when abutting on a valve is disclosed.

[Problems to be Solved by the Invention] However, the PSZ disclosed in JP-A-59-162345 has a small thermal conductivity and thus is excellent in adiabaticity, but has a large thermal expansion coefficient. If the entire valve seat is constructed and used in the presence of a temperature gradient, the PSZ will be damaged due to thermal stress. Furthermore, the attachment of the valve seat consisting of only the ceramic member to the cylinder head has a drawback that it requires careful handling because the toughness of the ceramic is insufficient.

On the other hand, in the device disclosed in Japanese Utility Model Laid-Open No. 60-12603, the valve seat has a complicated shape because the entire valve seat is made of a ceramic material and a mechanism for absorbing an impact load is incorporated. Since a ceramic material is difficult to machine and has poor toughness, a valve seat having such a complicated shape is difficult to manufacture and has a problem in reliability during use. Further, the attachment of the valve seat consisting of only the ceramic member to the cylinder head has the drawbacks that the toughness of the ceramics is insufficient, so that the handling is extremely careful and the automation is difficult.

In addition, the metal material forming the cylinder head generally has a coefficient of thermal expansion larger than that of the ceramic member. Therefore, if the temperature of the cylinder head rises after the valve seat consisting of only ceramic members is attached to the cylinder head, the thermal expansion difference between the cylinder head and the valve seat lowers the bonding force, resulting in insufficient fixation. The sheet comes off or rattles.

As described above, a valve seat made of only a ceramic member is not practical.

[Means for Solving Problems] Accordingly, the present invention has been made in view of the drawbacks of the above-described conventional valve seat inserts, and is not only excellent in wear resistance, thermal shock resistance, and heat resistance, but also manufactured by An object of the present invention is to provide a valve seat insert which is easy and highly reliable, and which is easy to handle and attach to a cylinder head, and a cylinder head which is equipped with the valve seat insert. According to the present invention, this object is composed of (a) a ceramic member, (b) a metal member integrally formed on the outer circumference of the ceramic member, and a valve of the piston engine. The contact surface with and is made of a ceramic member, the metal member has a metal structure made of austenite and spheroidal graphite, the coefficient of thermal expansion is equal to or greater than the coefficient of thermal expansion of the ceramic member and constitutes the cylinder head. It is achieved to provide a valve seat insert made of cast iron having a coefficient of thermal expansion smaller than that of the material and a cylinder head equipped therewith.

As the ceramic material forming the valve seat insert of the present invention, both oxide-based ceramics and non-oxide-based ceramics can be used. However, non-oxide ceramics are preferable because they have excellent high-temperature strength, wear resistance and thermal shock resistance, and at least one ceramic material selected from the group consisting of silicon nitride, silicon carbide and sialon is particularly preferable.

The coefficient of thermal expansion of the non-oxide ceramics is in the range of 3 to 5 × 10 ⁻⁶ / ° C. as shown in the table below.

Next, as a material for forming the cylinder head, aluminum alloy, cast iron, low alloy steel, etc. are generally used, and the thermal expansion coefficient of each of these materials is 10 × 10.
^-6 / ° C or higher.

On the other hand, as the metal member constituting the valve seat insert, austenitic spheroidal graphite cast iron, the thermal expansion coefficient of which is equal to or higher than the thermal expansion coefficient of the ceramic material, and more than the thermal expansion coefficient of the material forming the cylinder head. It must be cast iron that is small.

The metal member is cast iron, and the austenitic spheroidal graphite cast iron is a ring-shaped metal member that constitutes the valve seat insert of the present invention. That's why. Of the metallic materials for casting, cast iron is most suitable as a constituent member of the valve seat insert of the present invention. Iron-based materials other than cast iron are not preferable because they have high casting temperature, high material cost, and inferior castability to cast iron.

Further, the cast iron is austenitic cast iron, austenitic cast iron has the same crystal structure in the temperature range from high temperature to room temperature, because the expansion and contraction of the volume due to lattice transformation does not occur during heating or cooling, This is because the properties and dimensions do not change even when used in applications such as sheet inserts that are repeatedly subjected to heating and cooling temperature changes.

Cast iron is mainly austenitized by Ni and Mn in cast iron.
It is performed by adjusting the addition amount of. The thermal expansion coefficient of cast iron is also adjusted by adjusting the Ni content.

The reason why the cast iron is spheroidal graphite cast iron is that the shape of graphite existing in the cast iron is changed from a flake shape to a spherical shape to increase the mechanical strength of the cast iron.

Further, the graphite particles in the cast iron are dispersed spherically and discontinuously so that the dimensional change due to the oxidation of the graphite does not occur even in the use exposed to high temperature like the valve seat insert of the present invention.

The spheroidization of graphite is performed by adding at least one metal selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals to molten cast iron as a single substance or an alloy.

The above-mentioned metal member is at least one metal selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals: 0.02 to 0.5 wt%, Si: 1.0 to 7.
0 wt%, C: 1.0 to 3.0 wt%, Mn: 0.3 to
It is preferable to contain 6.0 wt%, Ni: 8 to 36 wt% and Fe.

Si is added to promote the graphitization of cast iron and to improve the oxidation resistance and growth resistance. The addition amount is 1.0
˜7.0 wt% is preferable, and 1.2˜5.0 wt% is particularly preferable. If the amount of Si added is less than 1.0 wt%, the oxidation resistance will be insufficient and the mechanical strength of the matrix will also decrease, such being undesirable. Further, if the amount of Si added exceeds 7.0 wt%, the austenite phase becomes unstable, and the toughness and mechanical strength decrease, which is not preferable.

C is added as a graphite forming element of cast iron, and the addition amount is preferably 1.0 to 3.0 wt%,
2.5 wt% is particularly preferred. Addition amount of C is 1.0wt
If it is less than%, ferrite is formed, which is not preferable.
Further, if the addition amount of C exceeds 3.0 wt%, the amount of graphite becomes excessive and the mechanical strength decreases, which is not preferable.

Mn is added to promote austenitization and toughness of cast iron, and the addition amount is preferably 0.3 to 6.0 wt%, more preferably 0 to 4 to 4.0 wt%,
5 to 2.0 wt% is particularly preferable. The addition amount of Mn is 0.
If it is less than 3 wt%, graphitization is delayed and chilling is promoted, which is not preferable. Further, if the addition amount of Mn exceeds 6.0 wt%, shrinkage of the casting and increase of casting stress are caused, which is not preferable.

Ni is added for casting austenitization, but it is also effective for promoting graphitization and spheroidizing graphite. Further, the amount of addition required to exert the effect of Ni is influenced by the amounts of addition of Si and Mn. The addition amount of Ni is preferably 8 to 36 wt%, more preferably 9 to 30 wt%, and particularly preferably 10 to 20 wt%. If the addition amount of Ni is less than 8 wt%, a complete austenite structure is not formed and ferrite is generated, which is not preferable. Further, if the addition amount of Ni exceeds 36 wt%, the thermal expansion coefficient increases, which is not preferable.

At least one metal selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals is added for spheroidizing graphite, and the addition amount is 0.02
0.5 wt% is preferable, and 0.05 to 0.2 wt% is particularly preferable. The addition of these metals is carried out by any one of a metal alone, a mixture, and an alloy of a metal and another metal.
If the amount of these metals added is less than 0.02 wt%, sufficient spheroidization of graphite cannot be obtained, which is not preferable. Further, if the addition amount exceeds 0.5 wt%, chilling is promoted, which is not preferable. The above-mentioned metals are Na, K and Li as alkali metals, and Mg and C as alkaline earth metals.
a, Ba, and Sr are preferable, and Ce and Misch metal (mixture of rare earth metals) are preferable as the rare earth metal.

The coefficient of thermal expansion of the metal member described above may be an intermediate value between the coefficients of thermal expansion of the ceramic member and the cylinder head constituent material at the operating temperature of the valve seat insert of the piston engine.

Since the cylinder head of the piston engine is cooled, the operating temperature of the valve seat insert is 200
℃ is expected to be about 300 ℃. Therefore, the coefficient of thermal expansion of the metal member is preferably 3 to 10 × 10 ⁻⁶ / ° C. in the temperature range of room temperature to 200 ° C., and 4 to 8 × 10 6.
^-6 / ° C is particularly preferred. In the temperature range of 200 ° C. or higher, the coefficient of thermal expansion may be 10 to 20 × 10 ⁻⁶ / ° C.

The shape of the valve seat insert of the present invention is not particularly limited, but is generally a cylindrical ceramic member integrally bonded to the outer periphery of a cylindrical ceramic member. A tapered contact surface is provided at one end of the inner surface of the ceramic member so as to be in close contact with the valve head portion and prevent gas leakage. Further, the wall thickness of the ceramic member and the metal member is appropriately determined according to the type of material used, the temperature used, the joining method or shape of both members.

Next, as a method of connecting both members, fitting, joining, cast gurney or caulking can be used.

Fitting includes shrink fit, cold fit or press fit.

Brazing and diffusion bonding can be used for bonding. In this case, it is preferable to preliminarily subject the surface of the joined portion of the ceramic member to the metal member to a metallizing treatment.

Further, by using a braze containing an active metal or using the active metal as a part of the insert, it is possible to join the ceramic member and the metal member without performing the metallizing treatment on the surface of the ceramic member.

Of these methods, the method by press fitting is the most preferable because it is easy to manufacture.

The outer diameters of both ends of the cylindrical ceramic member forming the valve seat insert are the same or different. When the above two members constituting the valve seat insert are made of a material having a small difference in thermal expansion coefficient, the outer diameters of both ends of the cylinder of the ceramic member are made the same, and the members are made of a material having a large difference in thermal expansion coefficient. It is preferable that the outer diameters of both ends of the cylinder of the ceramic member are different from each other. In order to make the outer diameters of both ends of the ceramic member different from each other, the outer circumference of the cylinder may be tapered. The size of the taper is such that the ceramic member does not fall off from the metal member at the operating temperature of the valve seat insert.

Further, the valve seat insert of the present invention is fixed to the cylinder head by utilizing the portion of the metal member joined to the outer periphery of the ceramic member. For this reason,
Usual joining methods of metal materials such as press fitting, screw mount, and welding can be used.

[Embodiment] An embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing an example of the usage of the valve seat insert of the present invention.

A valve seat insert 20 of the present invention composed of a ceramic member 8 and a metal member 9 is attached to the inlet of the exhaust port 4 provided in the cylinder head 2. A taper portion 5 is provided at one end of the valve seat insert 20 inside the ceramic member 8. The taper portion 5 abuts the cap portion 6 of the valve 1 as necessary to hold the pressure in the cylinder.

In this example, the upper end 7 of the valve seat insert 20 is
Since the ceramic member 8 is in contact with the cylinder head 2, the ceramic member 8 will not come off from the valve seat insert 20 even if the ceramic member 8 repeatedly contacts the valve 1.

2 to 4 are cross-sectional views showing specific examples of the structure of the valve seat insert of the present invention.

FIG. 2 shows a valve seat insert having a structure in which a cylindrical metal member 24 of the same shape is integrally joined on the outer periphery of a cylindrical ceramic member 21. Ceramic member 21
A tapered valve contact surface 27 is provided at one end on the inner side.

This valve seat insert can be made, for example, as follows.

First, a ceramic pipe and a metal pipe having an outer diameter and an inner diameter of predetermined dimensions are produced, and these pipes are cut into lengths of predetermined dimensions to obtain a ceramic member 21 and a metal member 24. After that, the metal member 24 is joined to the outside of the ceramic member 21 by a method such as press fitting, shrinkage fitting, brazing, diffusion bonding or caulking, so that the outside is the metal member 24 and the inside is the two layers of the ceramic member 21. The ring of the structure. After finishing the outer diameter of the ring to a predetermined size, it is cut into a predetermined length.

Alternatively, a molten metal is cast on the outer circumference of the ceramic pipe to form a two-layer structure pipe having an outer metal pipe and an inner ceramic pipe. After a while,
The pipe is cut into a length of a predetermined size to form a two-layer ring having a metal member 24 on the outside and a ceramic member 21 on the inside. Next, one end of the inside of the ceramic member 21 of these rings is processed into a taper shape to form a valve contact surface 27.

The valve seat insert of the present invention can also be used without finishing the inner surface of the ceramic member.

In FIG. 3, the outer surface 28 of the ceramic member 22 has a tapered shape, and a cylindrical metal member 25 is integrally coupled to the outer periphery of the cylindrical ceramic member 22 having different outer diameter dimensions at both ends. Figure 3 shows a valve seat insert of construction. A tapered valve contact surface 27 is provided inside the end of the ceramic member 22 having the smaller outer diameter.
Is provided.

This valve seat insert can be made, for example, as follows.

First, a ceramic pipe and a metal pipe having an outer diameter and an inner diameter of predetermined dimensions are made. After cutting the ceramic pipe into a predetermined length, the outer surface 28 is processed into a taper shape to form the ceramic member 22. In addition, the metal pipe is cut to a predetermined height to form a metal member 25. After that, the metal member 25 is joined to the outside of the ceramic member 22 by a method such as press fitting, shrinkage fitting, brazing, diffusion bonding or caulking to form a ring having a two-layer structure of a metal outside and a ceramic inside. . The outer diameter and height of the ring are finished into a predetermined dimension, and the ceramic member 22
One end of the inside of the valve is processed into a taper shape and the valve contact surface 2
Form 7. Alternatively, a molten metal is cast on the outer periphery of the ceramic member 22 processed into a predetermined size to form a two-layer structure having an outer metal member and an inner ceramic member. After that, the structure is finished into a predetermined shape.

FIG. 4 shows a valve seat insert having a structure in which a cylindrical ceramic member 23 is integrally connected to a recess 29 provided in the metal member 26. The ceramic member 23
A tapered valve contact surface 27 is provided at one end of the inner surface of the valve. This valve seat insert can be made, for example, as follows.

First, a metal member having a recess 29 having a predetermined shape and a ceramic member 23 having a predetermined shape are made. The outer diameter of the ceramic member 23 is determined according to the method of connecting the ceramic member 23 to the metal member. After that, the ceramic member 23 is joined to the concave portion 29 of the metal member 26 by a method such as press fitting, shrinkage fitting, brazing, diffusion bonding or caulking, and has a two-layer structure in which the outside is metal and the inside is ceramics. The body. The valve contact surface 27 is formed by finishing the outer diameter and height of the structure to predetermined dimensions and processing one end of the inside of the ceramic member 23 into a taper shape.

Alternatively, a molten metal is cast on the outer periphery of the ceramic member to form a two-layer structure structure in which the outer side is a metal member and the inner side is a ceramic member. After that, the structure is cut into a length of a predetermined size to form a two-layer structure having the metal member 26 on the outer side and the ceramic member 23 on the inner side. Next, the outer diameter, inner diameter and height of the structure are finished into predetermined dimensions, and one end of the inside of the ceramic member 23 is processed into a taper shape to form the valve contact surface 27.

Hereinafter, regarding the effect of the valve seat insert of the present invention,
The results of the implementation will be specifically shown.

First, a specific method for producing the austenitic spheroidal graphite cast iron used in the following Example 1 will be described. However, the method for producing austenitic spheroidal graphite cast iron is not limited to this method, and may be performed according to the method for producing alloyed cast iron and spheroidal graphite cast iron described in "Revised 3rd Edition, Foundry Handbook" issued by Maruzen Co., Ltd. it can.

First, a certain amount of carbon steel for machine structure steel (JIS: S15
C), nickel shot, and ferromanganese were melted in a high-frequency induction heating furnace, and then a predetermined amount of graphite electrode scrap was added to carry out carburization. Thereafter, a predetermined amount of ferrosilicon was added to the molten metal to adjust the Si amount. Next, after raising the temperature of the molten metal to 1500 ° C., the addition amount as Mg was reduced to 0.
Fe 45 wt%, Si so as to be 2 to 0.4 wt%
A predetermined amount of an alloy-like spheroidizing agent composed of 45 wt% and Mg 10 wt% is placed at the bottom of the ladle, and molten metal is poured into the ladle to perform the spheroidizing treatment. After the spheroidizing process is completed, 75
Ferrosilicon containing wt% Si is added to the molten metal, inoculated and cast into a mold.

The thus-obtained round bar having a diameter of 60 mm and a length of 150 mm was heated and annealed at 620 to 680 ° C. for 10 hours to remove stress, and used as a test material described in Examples.

A cupola, an electric furnace, and a reverberatory furnace can be used for melting the cast iron, but the electric furnace and the reverberatory furnace are preferable because the chemical components and the temperature can be easily controlled, and the electric furnace is more preferable. The cast iron can also be used for precision casting.

(Example 1) As a ceramic member, a cylinder having an inner diameter of 43 mm, an outer diameter of 48 mm, and a height of 10 mm was made of silicon nitride by an atmospheric pressure sintering method, and rounded with a radius of 1 mm on both edges of the outer periphery of the silicon nitride cylinder. A ceramic ring was prepared.

Room temperature of a test piece of the same composition produced at the same time as the ring to 8
The coefficient of thermal expansion in the temperature range of 00 ° C is 3.7 × 10 ^-6
/ ° C.

Further, as a metal member, Si is 1.9 wt% and C is 1.
7wt%, Mn 0.9wt%, Ni 12wt%, M
Austenitic spheroidal graphite cast iron with g of 0.1 wt% and balance of Fe, inner diameter 47.6 mm, outer diameter 52 mm, height 1
A 0 mm metal ring was made.

Room temperature of a test piece of the same composition produced at the same time as the ring to 8
The coefficient of thermal expansion in the temperature range of 00 ° C. is from room temperature to 200.
6 × 10 ^-6 / ° C at 17 ° C, 17 × 10 ^-6 at 200 to 800 ° C
/ ° C.

The above-mentioned metal ring was press-fitted into the outside of the above ceramic ring at room temperature to prepare a two-layer composite ring having a silicon nitride ring inside and an austenitic spheroidal graphite cast iron outside. Next, after cutting the composite ring to a height of 7 mm, the inside of one end of the silicon nitride ring was processed into a taper shape to form a valve seat insert having the same shape as in FIG.

With respect to the valve seat insert, the silicon nitride ring could not be extruded from the austenitic spheroidal graphite ring even when a load of 2 tons was applied at 300 ° C.

(Example 2) The valve seat insert manufactured in Example 1 was made of cast iron for a single-head diesel engine having a piston cylinder diameter of 141 mm (coefficient of thermal expansion: 13.3 x 10 ^-6 / ° C, 20
˜300 ° C.) Shrink-fitting was performed at the inlet of the exhaust port of the cylinder head to produce a cylinder head having the structure shown in FIG. The diesel engine with this cylinder head assembled was continuously operated at a rotation speed of 1900 rpm for 1000 hours, but no abnormality was found in both the exhaust valve and the valve seat insert.

[Effects of the Invention] As described above, in the valve seat insert of the present invention, since the metal member is bonded to the outer periphery of the brittle ceramic member, the ceramic member is damaged even when a strong impact force is applied during handling. There is nothing to do. On the other hand, valve
Since the contact surface with and is made of a ceramic member, the excellent wear resistance, thermal shock resistance, and heat resistance of the ceramic member can be utilized as it is. It can be easily fixed. Further, since the difference in thermal expansion coefficient between the ceramic member and the metal member on the outer periphery of the ceramic member is small, even if the temperature of the valve seat insert rises after being assembled in the cylinder head, the ceramic member is removed from the metal member. It does not come off or come loose. Furthermore, the valve seat insert of the present invention has a structure in which a metal member is bonded to a cylindrical ceramic member whose outer periphery is processed into a tapered shape even when the difference in thermal expansion coefficient between the ceramic member and the metal member is large. As a result, it is possible to prevent the decrease in the bonding force due to the difference in the thermal expansion coefficient of both members.

[Brief description of drawings]

FIG. 1 is a sectional view of a cylinder head of a piston engine incorporating the valve seat insert of the present invention, and FIGS.
Each of the drawings is a sectional view showing the structure of the valve seat insert of the present invention. 1 ... Valve, 2 ... Cylinder head, 4 ... Exhaust port, 5 ... Taper part, 6 ... Umbrella part, 8, 21, 22,
23 ... Ceramic member, 9, 24, 25, 26 ... Metal member, 20 ... Valve seat insert, 27 ... Valve contact surface.

Claims (7)

[Claims] 1. A valve seat insert used in a cylinder head of a piston engine, wherein the valve seat insert is (a) a ceramic member, and (b) a metal member integrally formed on the outer periphery of the ceramic member. , And the contact surface of the piston engine with the valve is made of a ceramic member, the metal member has a metal structure made of austenite and spheroidal graphite, and the coefficient of thermal expansion of which is the heat of the ceramic member. A valve seat insert, which is made of cast iron having a coefficient of expansion equal to or higher than that of the material forming the cylinder head. 2. The metal member comprises at least one metal selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals: 0.02-0.5 wt%, Si: 1.0-
7.0 wt%, C: 1.0 to 3.0 wt%, Mn: 0.
The valve seat insert according to claim 1, comprising 3 to 6.0 wt%, Ni: 8 to 36 wt% and Fe. 3. The valve seat insert according to claim 1 or 2, wherein both the ceramic member and the metal member have a cylindrical shape. 4. The valve seat insert according to claim 1, wherein the ceramic member has a tapered outer periphery. 5. The valve seat according to any one of claims 1 to 4, wherein the ceramic member is made of at least one ceramic material selected from the group consisting of silicon nitride, silicon carbide and sialon. insert. 6. A cylinder head of a piston engine, comprising: (a) a ceramic member, (b) a metal member integrally formed on the outer periphery of the ceramic member, and the piston engine. The contact surface with the valve is made of a ceramic member, the metal member has a metal structure made of austenite and spheroidal graphite, the coefficient of thermal expansion is equal to or greater than the coefficient of thermal expansion of the ceramic member and the cylinder head A cylinder head, characterized in that a valve seat insert made of cast iron having a coefficient of thermal expansion lower than that of the constituent material is mounted in the hole for the valve of the piston engine. 7. The metal member comprises at least one metal selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals: 0.02 to 0.5 wt%, Si: 1.0 to.
7.0 wt%, C: 1.0 to 3.0 wt%, Mn: 0.
The cylinder head according to claim 6, comprising 3 to 6.0 wt%, Ni: 8 to 36 wt% and Fe.