Assembly of internal combustion engine valve and valve seat

Abstract

In an assembly of a hollow poppet valve and a valve seat insert, the hollow poppet valve's head is integrally formed with a stem end, a hollow part is formed from the head to a stem, and coolant is filled into the hollow part along with an inert gas. The valve seat insert is formed of iron base sintered alloy and obtained by integrating two layers of a supporting material side layer and a valve contact face side layer. The hollow poppet valve is formed of a material having thermal conductivity of 5-45 (W/m.Math.K) at 20-1000 C. The valve seat insert includes the supporting material side layer having thermal conductivity of 23-50 (W/m.Math.K) at 20-300 C. and a valve contact face side layer having thermal conductivity of 10-22 (W/m.Math.K) at 20-300 C. This enables a valve temperature decrease throughout an engine's entire RPM range compared with the prior art.

Claims

1. An assembly comprising: a valve; and a valve seat insert for an internal combustion engine, wherein the valve is comprised of a material having thermal conductivity of 5 to 45 (W/m.Math.K) at 20 to 1000 C., the valve comprises a stem and a head integral at an end of the stem, the valve has a hollow part formed from the head to the stem, and the hollow part is filled with a coolant and an inert gas, and wherein the valve seat insert has a double-layer structure comprised of a supporting material side layer and a valve contact face side layer, the supporting material side layer has thermal conductivity of 23 to 50 (W/m.Math.K) at 20 to 300 C., and the valve contact face side layer has thermal conductivity of 10 to 22 (W/m.Math.K) at 20 to 300 C., the supporting material side layer and the valve contact face side layer each being an iron base sintered alloy, wherein the hollow part of the valve comprises i) a large-diameter hollow part provided inside the head, the large-diameter hollow part having an overall substantial disk shape with an upper surface and a lower surface, ii) a small-diameter hollow part provided in the stem, the small-diameter hollow part having a substantially linear shape, and iii) an opening between the large-diameter hollow part and the small-diameter hollow part, wherein the large-diameter hollow part communicates with the small-diameter hollow part through the opening, the large-diameter hollow part being substantially orthogonal to the small-diameter hollow part, wherein the opening between the large-diameter hollow part and the small-diameter hollow part is located along a top planar portion of the upper surface of the large-diameter hollow part, the top planar portion being in a plane substantially orthogonal to a center axis line of the valve, wherein the upper surface includes an eave-shaped annular step part located around the top planar portion, wherein the large-diameter hollow part has an overall conical trapezoid shape having a tapered outer peripheral face substantially similar to the outer shape of the head, wherein the material of the valve is one of heat-resistant steel and the equivalent thereof or Ni base alloy and the equivalent thereof, wherein the valve seat insert formed of the iron base sintered alloy is formed so that a boundary face between the valve contact face side layer and the supporting material side layer is formed within an area surrounded by a face having an angle of 45 formed with respect to a valve seat insert axis and having a circular line distant by 0.5 mm from a valve contact face toward a supporting material in a direction perpendicular to the valve contact face at a center position of the valve contact face in the width direction and a face having a circular line of of a valve seat insert height as a distance from a valve seat insert seating face on the outer peripheral face of the valve seat insert and an intersection line between the valve seat insert seating face and the inner peripheral face of the valve seat insert, wherein the valve contact face side layer is 10 to 60% as a volume % with respect to the entire valve seat insert, wherein the valve contact face side layer is formed of iron base sintered alloy having a base matrix in which hard particles are dispersed in a base matrix phase, the base matrix has a base matrix composition containing 0.2 to 2.0% of C, 40% or less of one or two or more selected from Co, Mo, Si, Cr, Ni, Mn, W, V, and S in total and the balance being Fe and inevitable impurities by a mass %, and the base matrix has a base matrix structure in which 5 to 40% of the hard particles are dispersed in the base matrix phase with respect to the entire valve contact face side layer by a mass %, and wherein the supporting material side layer is formed of iron base sintered alloy having a base matrix composition containing 0.2 to 2.0% of C and the balance being Fe and inevitable impurities by a mass %, wherein the valve contact face side layer has a base matrix structure in which 0.5 to 4% of solid lubricant particles are dispersed in the base matrix phase with respect to the entire valve contact face side layer by a mass % in addition to the base matrix structure, and wherein the coolant is a material having higher thermal conductivity than the material of the valve.

2. An assembly comprising: a valve; and a valve seat insert for an internal combustion engine, wherein the valve is comprised of a material having thermal conductivity of 5 to 45 (W/m.Math.K) at 20 to 1000 C., the valve comprises a stem and a head integral at an end of the stem, the valve has a hollow part formed from the head to the stem, and the hollow part is filled with a coolant and an inert gas, and wherein the valve seat insert has a double-layer structure comprised of a supporting material side layer and a valve contact face side layer, the supporting material side layer has thermal conductivity of 23 to 50 (W/m.Math.K) at 20 to 300 C., and the valve contact face side layer has thermal conductivity of 10 to 22 (W/m.Math.K) at 20 to 300 C., the supporting material side layer and the valve contact face side layer each being an iron base sintered alloy, wherein the hollow part of the valve comprises i) a large-diameter hollow part provided inside the head, the large-diameter hollow part having an overall substantial disk shape with an upper surface and a lower surface, ii) a small-diameter hollow part provided in the stem, the small-diameter hollow part having a substantially linear shape, and iii) an opening between the large-diameter hollow part and the small-diameter hollow part, wherein the large-diameter hollow part communicates with the small-diameter hollow part through the opening, the large-diameter hollow part being substantially orthogonal to the small-diameter hollow part, wherein the opening between the large-diameter hollow part and the small-diameter hollow part is located along a top planar portion of the upper surface of the large-diameter hollow part, the top planar portion being in a plane substantially orthogonal to a center axis line of the valve, wherein the upper surface includes an eave-shaped annular step part located around the top planar portion, wherein the large-diameter hollow part has an overall conical trapezoid shape having a tapered outer peripheral face substantially similar to the outer shape of the head, wherein the material of the valve is one of heat-resistant steel and the equivalent thereof or Ni base alloy and the equivalent thereof, wherein the valve seat insert formed of the iron base sintered alloy is formed so that a boundary face between the valve contact face side layer and the supporting material side layer is formed within an area surrounded by a face having an angle of 45 formed with respect to a valve seat insert axis and having a circular line distant by 0.5 mm from a valve contact face toward a supporting material in a direction perpendicular to the valve contact face at a center position of the valve contact face in the width direction and a face having a circular line of of a valve seat insert height as a distance from a valve seat insert seating face on the outer peripheral face of the valve seat insert and an intersection line between the valve seat insert seating face and the inner peripheral face of the valve seat insert, wherein the valve contact face side layer is 10 to 60% as a volume % with respect to the entire valve seat insert, wherein the valve contact face side layer is formed of iron base sintered alloy having a base matrix in which hard particles are dispersed in a base matrix phase, the base matrix has a base matrix composition containing 0.2 to 2.0% of C, 40% or less of one or two or more selected from Co, Mo, Si, Cr, Ni, Mn, W, V, and S in total and the balance being Fe and inevitable impurities by a mass %, and the base matrix has a base matrix structure in which 5 to 40% of the hard particles are dispersed in the base matrix phase with respect to the entire valve contact face side layer by a mass %, and wherein the supporting material side layer is formed of iron base sintered alloy having a base matrix composition containing 0.2 to 2.0% of C and the balance being Fe and inevitable impurities by a mass %, wherein the supporting material side layer has a structure in which 0.5 to 4% of solid lubricant particles are dispersed in the base matrix phase with respect to the entire supporting material side layer by a mass %, and wherein the coolant is a material having higher thermal conductivity than the material of the valve.

3. The assembly of the valve and the valve seat insert for the internal combustion engine according to claim 1, wherein the valve is padded on at least a contact area with respect to the valve seat insert on the valve face.

4. The assembly of the valve and the valve seat insert for the internal combustion engine according to claim 2, wherein the valve is padded on at least a contact area with respect to the valve seat insert on the valve face.

5. The assembly of the valve and the valve seat insert for the internal combustion engine according to claim 1, wherein a width of the lower surface of the large-diameter hollow part is greater than twice a maximum height of the large-diameter hollow part.

6. The assembly of the valve and the valve seat insert for the internal combustion engine according to claim 2, wherein a width of the lower surface of the large-diameter hollow part is greater than twice a maximum height of the large-diameter hollow part.

7. The assembly of the valve and the valve seat insert for the internal combustion engine according to claim 2, wherein the valve contact face side layer has a base matrix structure in which 0.5 to 4% of solid lubricant particles are dispersed in the base matrix phase with respect to the entire valve contact face side layer by a mass % in addition to the base matrix structure.

8. The assembly of the valve and the valve seat insert for the internal combustion engine according to claim 2, wherein the supporting material side layer contains 20% or less of one or two or more selected from Mo, Si, Cr, Ni, Mn, W, V, S, and P in total by a mass % in addition to the base matrix composition.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a longitudinal sectional view illustrating a shape of a hollow poppet valve used in the invention and a state where the hollow poppet valve is assembled with a valve seat insert and is fitted into a cylinder head.

(2) FIGS. 2(a) and 2(b) are explanatory views schematically illustrating a flow of coolant inside a hollow part when the hollow poppet valve used in the invention is opened and closed.

(3) FIG. 3 is a longitudinal sectional view illustrating another example of the hollow poppet valve used in the invention.

(4) FIGS. 4(a) and 4(b) are explanatory views schematically a shape of the valve seat insert used in the invention, where FIG. 4(a) is a high thermal conduction type and FIG. 4(b) is a standard type.

(5) FIGS. 5(a) and 5(b) are longitudinal sectional views illustrating an example of a shape of the valve seat insert used in the invention, where FIG. 5(a) is a high thermal conduction type and FIG. 5(b) is a standard type.

(6) FIG. 6 is a graph showing an influence of an assembly of the valve and the valve seat insert on a relation between a valve face temperature and an engine rotation speed.

(7) FIG. 7 is a graph showing an influence of an assembly of the valve and the valve seat insert on a valve face temperature decrease rate.

(8) FIGS. 8(a) and 8(b) are longitudinal sectional views illustrating a shape of a valve used as comparison.

DESCRIPTION OF EMBODIMENTS

(9) First, as illustrated in FIG. 1, an assembly 1 of a valve and a valve seat insert of the invention means, for example, an assembly of a valve 10 of which a face part 14 contacts a valve contact face 8a of a valve seat insert 8 and the valve seat insert 8 press-fitted into an opening peripheral portion of an exhaust passage 6 toward a combustion chamber 4 at a cylinder head 2 of an internal combustion engine (an engine). Further, Reference Numeral 3 indicates a valve insertion port also provided in the cylinder head 2 and a valve guide 3a is disposed on the inner periphery thereof. Further, Reference Numeral 9 indicates a spring that energizes the valve 10 in a valve opening direction.

(10) First, a valve used herein will be described.

(11) In the assembly 1 of the valve and the valve seat insert of the invention, the hollow poppet valve (the hollow valve) 10 in which a head 13 is integrally formed with an end of a stem 11, a hollow part S is formed from the head to a stem, and coolant 19 is filled into the hollow part S along with an inert gas, is used.

(12) In the hollow poppet valve 10, the tapered face part 14 is provided in an outer periphery of a head 13 in the valve in which the head 13 is integrally formed with one end side of a stem 11 through an R-shaped fillet part 12 having a gradually increasing outer diameter. Coolant 19 is filled (enclosed) in the hollow part S along with an inert gas such as an argon gas. As the coolant (the refrigerant), it is desirable to use a material, for example, metallic sodium or metallic potassium having higher thermal conductivity than a valve material from the viewpoint of the heat transfer effect. Further, it is desirable that the amount of the enclosed coolant be 50% or more of the volume of the hollow part.

(13) The hollow poppet valve used in the invention is set to a valve formed of a material of which the thermal conductivity is 5 to 45 (W/m.Math.K) from 20 to 1000 C.

(14) As the valve material having such thermal conductivity, one of heat-resistant steel and the equivalent or Ni-base super alloy and the equivalent is desirable.

(15) As the heat-resistant steel, martensite-type or austenite-type heat-resistant steel defined in JIS G 4311 can be exemplified. Among the heat-resistant steel defined in JIS G 4311, austenite-type heat-resistant steel is desirable from the viewpoint of heat resistance strength.

(16) Further, as the Ni-base super alloy, Inconel 751, Nimonic 80 A, or the like can be exemplified.

(17) As illustrated in FIG. 1, the hollow valve 10 used in the invention is desirably formed as a valve in which a hollow part S comprises a large-diameter hollow part S1 which has a substantial disk shape and is provided inside the head 13 and a small-diameter hollow part S2 which has a substantial linear shape and is provided in the stem 11, the large-diameter hollow part S1 and the small-diameter hollow part S2 communicate with each so as to be substantially orthogonal to each other, and the opening peripheral portion of the small-diameter hollow part S2 in the large-diameter hollow part S1 is formed as a plane 13b substantially orthogonal to the center axis line L of the valve. That is, an eave-shaped annular step part 15 is formed by the inner peripheral face of the small-diameter hollow part S2 and the opening peripheral portion of the small-diameter hollow part S2. By the existence of the annular step part 15, a circulation of coolant inside the hollow part S occurs so as to rotate inwardly in the longitudinal direction as indicated by the arrow of FIGS. 2(a) and 2(b) and a turbulent flow of coolant inside the small-diameter hollow part S2 also occurs when the valve is opened and closed. Accordingly, the upper layer part to the lower layer part of the coolant 19 inside the hollow part S are actively mixed and hence the heat transfer effect of the valve is further improved. Further, FIG. 2(a) indicates a case where the valve moves down and FIG. 2(b) indicates a case where the valve moves up.

(18) Further, it is desirable that the large-diameter hollow part S1 is formed in a conical trapezoid shape having a tapered outer peripheral face substantially similar to the outer shape of the head 13. Accordingly, the volume of the large-diameter hollow part S1 can be increased and hence a large amount of coolant can be charged. Further, since the conical upper face and the conical outer peripheral face form an obtuse angle, coolant smoothly flows (like F1, F2, F6, and F8 of FIGS. 2(a) and 2(b)) so as to activate the circulation when the valve is opened and closed and hence the heat transfer effect of the valve is further improved.

(19) Further, as illustrated in FIG. 3, the large-diameter hollow part S1 may be formed in a substantially conical trapezoid shape in which a ceiling face 13b is offset from the above-described conical upper face toward the stem of the valve by a predetermined amount H. Accordingly, the amount of the filled coolant can be increased.

(20) Further, in the hollow poppet valve used in the invention, padding may be performed on a contact area (a face plane) with respect to the valve seat insert by welding or the like for the purpose of improving wear resistance, corrosion resistance, and the like. As the material of padding, CoCrMoC-type alloy represented as stellite (trade mark) or Co-based face hardened alloy such as CoMoSi-type alloy represented as TRIBALLOY (trade mark) can be exemplified.

(21) In addition, it is needless to limit the manufacturing method of the hollow poppet valve having the above-described structure used in the invention particularly as long as a manufacturing method capable of forming the above-described structure.

(22) The hollow poppet valve used in the invention may be formed a predetermined dimension shape by general processing such as cutting and grinding while a casting material, a forging material, or a rolling material having a predetermined composition are used as the valve material. However, in the hollow poppet valve used in the invention, it is desirable to use, for example, the following steps of the manufacturing method from the viewpoint of improving the productivity.

(23) That is, it is desirable to manufacture the hollow poppet valve having a structure illustrated in FIG. 1 from a valve material by sequentially performing a forming step of forming a concave part corresponding to a large-diameter hollow part at the inside of a head outer shell by, for example, forging using a mold, a hole drilling step of drilling a hole corresponding to a small-diameter hollow part in a bottom face of the concave part, a coolant filling step of filling a predetermined amount of coolant (solid) into the concave part corresponding to the large-diameter hollow part, and a hollow part sealing step of sealing the hollow part by welding a cap to an opening of the concave part under the atmosphere of an inert gas. However, it is needless to mention that a method of manufacturing the hollow poppet valve used in the invention is not limited thereto.

(24) Next, the valve seat insert used in the assembly of the invention will be described.

(25) The valve seat insert 8 used in the invention is a valve seat insert formed of iron base sintered alloy. The valve seat insert 8 which comprises a supporting material side layer 81 provided at a contact side with respect to a seat face of the cylinder head 2 and a valve contact face side layer 82 provided at a contact side with respect to the valve 10, has a double-layer structure in which two layers, that is, the supporting material side layer 81 and the valve contact face side layer 82 are integrated with each other as illustrated in FIG. 1.

(26) Further, the valve seat insert used in the invention is set as a valve seat insert in which the thermal conductivity measured at 20 to 300 C. by a laser flash method satisfies 23 to 50 W/m.Math.K at the supporting material side layer and 10 to 22 W/m.Math.K at the valve contact face side layer.

(27) When the thermal conductivity of the supporting material side layer is smaller than 23 W/m.Math.K, desired high thermal conductivity can be ensured. For this reason, the thermal conductivity of the supporting material side layer is set to 23 W/m.Math.K or more. Further, when the supporting material side layer has a composition so that the thermal conductivity exceeds 50 W/m.Math.K, the strength needs to be improved separately and the productivity is degraded. Further, when the thermal conductivity of the valve contact face side layer is smaller than 10 W/m.Math.K, the content of alloy increases and hence desired strength cannot be ensured. Meanwhile, when the valve contact face side layer has a composition so that the thermal conductivity exceeds 22 W/m.Math.K, desired wear resistance cannot be ensured.

(28) In the invention, as the valve seat insert assembled with the hollow valve having the above-described structure, an iron base sintered alloy valve seat insert having a double-layer structure and satisfying the thermal conductivity of the valve seat insert used in the related art can be appropriately used.

(29) Further, in the invention, it is desirable to use the hollow poppet valve having the above-described structure by assembling particularly a high thermal conduction type valve seat insert having high thermal conductivity with the hollow poppet valve. In the assembling of the valve and the valve seat insert, the heat transfer effect of the assembly of the valve and the valve seat insert is remarkably improved in addition to the heat transfer effect of the valve. Particularly, the heat transfer effect at the low-middle rotation speed zone of the engine is remarkably improved.

(30) For the high thermal conduction type valve seat insert having high thermal conductivity, the valve contact face side layer having a large content of alloy and low thermal conductivity is formed as thin as possible, the supporting material side layer having a small content of alloy and excellent thermal conductivity is formed so as to be thick, and the contact face between the cylinder head and the supporting material side layer of the valve seat insert is enlarged. For that reason, in the high thermal conduction type valve seat insert used in the invention, as illustrated in FIG. 4(a), it is assumed that a boundary face between the valve contact face side layer 82 and the supporting material side layer 81 is formed within an area surrounded by a face (a face A) which includes a circular line (A1) distant from the valve contact face toward the supporting material by 0.5 mm in a direction perpendicular to the valve contact face at the center position of the valve contact face in the width direction and forms an angle of 45 with respect to the valve seat insert axis and a face (a face B) which has an intersection line (B1) between the valve seat insert seating face and the inner peripheral face of the valve seat insert and a circular line (B2) having a distance from the valve seat insert seating face on the outer peripheral face of the valve seat insert set to of the valve seat insert height h. FIG. 4(a) is a longitudinal sectional view schematically illustrating a shape of the high thermal conduction type valve seat insert. Further, in FIG. 4(b) illustrates a shape of the standard valve seat insert used in general. In the standard valve seat insert, the boundary face is set a face forming an angle of 90 with respect to a valve seat insert axis.

(31) Regarding the boundary face between the valve contact face side layer and the supporting material side layer, the valve contact face side layer is thin too much at the valve contact face in relation to the above-described face (the face A) and hence the durability of the valve seat insert is degraded. From the viewpoint of the durability, it is more desirable that the boundary face is located at a position of 1 mm or more near the supporting material from the valve contact face in a direction perpendicular to the valve contact face at the center position of the valve contact face in the width direction.

(32) Furthermore, when the boundary face is near the supporting material in relation to the above-described face (the face B), the valve contact face side layer is thickened too much and hence the thermal conductivity of the valve seat insert is degraded. In order to maximally increase the contact area between the supporting material side layer and the cylinder head, it is desirable to adjust the boundary face between the valve contact face side layer and the supporting material side layer as a face having a circular line and formed so that an angle formed with respect to the valve seat insert axis is 60 or less and desirably 40 to 50 and a distance from the valve seat insert seating face on the outer peripheral face of the valve seat insert is or more of the valve seat insert height h and is desirably or more.

(33) Regarding the manufacturing of the above-described high thermal conduction type valve seat insert, the balance between the molding pressure and the molding face shape of the provisional pressing punch when mixed powder for the supporting material side layer is provisionally pressed and the adjustment of the molding pressure of the punch obtained when mixed powder for the valve contact face side layer is compressed are important when a desired boundary face is stably formed. Specifically, it is desirable to adjust the molding face shape of the provisional pressing punch so that an angle with respect to the axis is set to 20 to 50 and the molding pressure of the provisional pressing punch is 0.01 to 3 ton/cm.sup.2.

(34) When the angle of the molding face shape of the provisional pressing punch with respect to the axis exceeds 50, desired high thermal conductivity cannot be ensured. Meanwhile, when the angle of the molding face shape of the provisional pressing punch with respect to the axis is smaller than 20, powder moves too much in a molding process and hence a desired boundary face shape cannot be molded. Further, when the molding pressure of the provisional pressing punch is smaller than 0.01 ton/cm.sup.2, the boundary face changes in the circumferential direction or the radial direction and hence desired boundary face precision cannot be ensured. Meanwhile, when the molding pressure of the provisional pressing punch increases so as to exceed 3 ton/cm.sup.2, the adhesion between the supporting material side layer and the valve contact face side layer decreases and hence the strength of the valve seat insert decreases. Due to this reason, the molding face shape of the provisional pressing punch is adjusted so that an angle with respect to the axis is 20 to 50 and the molding pressure of the provisional pressing punch is adjusted in the range of 0.01 to 3 ton/cm.sup.2.

(35) Further, in the high thermal conduction type valve seat insert used in the invention, the boundary face is adjusted within the above-described range and desirably the valve contact face side layer is adjusted so that the volume % with respect to the entire valve seat insert is 10 to 60%. When the volume % of the valve contact face side layer with respect to the entire valve seat insert is smaller than 10%, the valve contact face side layer is thin and durability is not sufficient. Meanwhile, when the volume exceeds 60%, the valve contact face side layer is thickened too much and hence thermal conductivity is degraded.

(36) Further, in the standard valve seat insert used in the invention, it is desirable to adjust the boundary face so that an angle with respect to the valve seat insert axis is set to 90 and the volume % of the valve contact face side layer with respect to the entire valve seat insert is 40 to 60%.

(37) The valve contact face side layer of the valve seat insert used in the invention is formed of iron base sintered alloy having base matrix in which hard particles are dispersed in a base matrix phase. When the hard particles are dispersed in the base matrix phase, the wear resistance of the valve seat insert is remarkably improved. As the hard particles dispersed in the base matrix phase, Co-base intermetallic compound particles are desirable. The Co-base intermetallic compound particles have a feature that intermetallic compound having high hardness is dispersed in a comparatively soft Co base matrix and opposite material aggressiveness is low. Further, as desirable Co-base intermetallic compound particles, SiCrMo-type Co-base intermetallic compound particles and MoNiCr-type Co-base intermetallic compound particles can be exemplified.

(38) In the valve contact face side layer, it is desirable to disperse hard particles by 5 to 40% by a mass % with respect to the entire valve contact face side layer. When the hard particle dispersion amount is smaller than 5%, desired wear resistance cannot be ensured. Meanwhile, even when a large amount of hard particles are dispersed so as to exceed 40%, the effect is saturated and hence an effect matching an addition amount cannot be expected. For this reason, it is desirable that the hard particle dispersion amount in the valve contact face side layer is 5 to 40% by a mass % with respect to the entire valve contact face side layer. More desirably, the mass % is 20 to 30%.

(39) Further, 0.5 to 4% of solid lubricant particles may be contained in the valve contact face side layer by a mass % with respect to the entire valve contact face side layer in addition to the above-described hard particles. When the content is smaller than 0.5%, a desired lubricating effect cannot be expected and hence machinability is degraded. Meanwhile, when the content exceeds 4%, the effect is saturated and hence the strength is degraded. For this reason, it is desirable to limit the content in the range of 0.5 to 4%. As the solid lubricant particles, MnS and CaF.sub.2 can be exemplified.

(40) In the valve contact face side layer, it is desirable that the base matrix comprising the base matrix phase, the hard particles, and/or the solid lubricant particles have a base matrix composition containing 0.2 to 2.0% of C, 40% or less of one or two or more selected from Co, Mo, Si, Cr, Ni, Mn, W, V, and S in total and the balance being Fe and inevitable impurities by a mass %.

(41) C: 0.2 to 2.0%

(42) C is an element that improves the strength and the hardness of the sintered body and easily diffuses a metallic element in a sintering process and is desirably contained by 0.2% or more in order to obtain such an effect. Meanwhile, when the content exceeds 2.0%, cementite is easily generated inside a base matrix, a liquid phase is easily generated in a sintering process, and dimensional precision is degraded. For this reason, it is desirable to limit C in the range of 0.2 to 2.0%. Further, the range is desirably from 0.7 to 1.3%.

(43) One or Two or More Selected from Co, Mo, Si, Cr, Ni, Mn, W, V, and S: 40% or Less in Total

(44) Co, Mo, Si, Cr, Ni, Mn, W, V, and S are all elements which improve the strength and the hardness of the sintered body and improve the wear resistance thereof. In order to obtain such an effect, it is desirable to contain at least one of the elements including hard particles by 5% or more in total. Meanwhile, when the content exceeds 40% in total, formability and strength are degraded. For this reason, it is desirable that one or two or more selected from Co, Mo, Si, Cr, Ni, Mn, W, V, and S are limited to 40% or less in total. Desirably, the content is 30% or less in total.

(45) The rest of the valve contact face side layer other than the above-described examples consists of Fe and inevitable impurities.

(46) Meanwhile, the supporting material side layer of the valve seat insert used in the invention is formed of iron base sintered alloy and is integrated with the valve contact face side layer through the boundary face. It is desirable that the supporting material side layer have a composition capable of ensuring desired strength as the valve seat insert while supporting the contact face side layer without contacting the valve.

(47) Further, the supporting material side layer may contain 0.5 to 4% of solid lubricant particles in the base matrix with respect to the entire supporting material side layer by a mass % if necessary. When the content is smaller than 0.5%, a desired lubricating effect cannot be expected and hence machinability is degraded. Meanwhile, when the content exceeds 4%, the effect is saturated and hence the strength is degraded. For this reason, it is desirable to limit the content in the range of 0.5 to 4%. As the solid lubricant particle, MnS and CaF.sub.2 can be exemplified. More desirably, the content is 0.5 to 3%.

(48) The base matrix phase composition (the base matrix composition including solid lubricant particles when the solid lubricant particles are dispersed) of the supporting material side layer of the valve seat insert used in the invention contains 0.2 to 2.0% of C, 20% or less of one or two or more selected from Mo, Si, Cr, Ni, Mn, W, V, S, and P in total and the balance being Fe and inevitable impurities by a mass %.

(49) C: 0.2 to 2.0%

(50) C is an element which improves the strength and the hardness of the sintered body and is desirably contained by 0.2% or more in order to ensure the desired strength and the desired hardness as the valve seat insert. Meanwhile, when the content exceeds 2.0%, cementite is easily generated inside a base matrix phase, a liquid phase is easily generated in a sintering process, and dimensional precision is degraded. For this reason, it is desirable to limit C in the range of 0.2 to 2.0%. More desirably, the range is 0.7 to 1.3%.

(51) The above-described elements are basic elements of the supporting material side layer, but may further contain one or two or more selected from Mo, Si, Cr, Ni, Mn, W, V, S, and P by 20% or less in total in addition to the basic composition.

(52) One or Two or More Selected from Mo, Si, Cr, Ni, Mn, W, V, S, and P: 20% or Less in Total

(53) Mo, Si, Cr, Ni, Mn, W, V, S, P are all elements which improve the strength and the hardness of the sintered body and one or two or more thereof can be contained if necessary. In order to obtain such an effect, the content of 5% or more in total is desirable, but the content needs to be decreased as small as possible from the viewpoint of the thermal conductivity. Meanwhile, when the content exceeds 20% in total, formability is degraded. For this reason, it is desirable to limit the content of one or two or more selected from Mo, Si, Cr, Ni, Mn, W, V, S, and P to 20% or less in total.

(54) The rest of the supporting material side layer other than the above-described examples consists of Fe and inevitable impurities.

(55) Further, it is important that the supporting material side layer is a layer having high thermal conductivity in which the thermal conductivity measured at 20 to 300 C. by a laser flash method is 23 (W/m.Math.K) or more. For that reason, it is desirable to form the supporting material side layer by iron base sintered alloy having a base matrix composition containing 0.2 to 2.0% of C and the balance being Fe and inevitable impurities by a mass % so that a particularly expensive alloy element does not need to be contained even within the above-described composition range.

(56) Next, a desirable method of manufacturing the valve seat insert used in the invention by iron base sintered alloy will be described.

(57) It is desirable to mold the valve seat insert made of iron base sintered alloy and used in the invention by a press-molding machine having a die, a core rod, an upper punch, a lower punch, two kinds of separately driven feeders, and an independently driven provisional pressing punch.

(58) First, as the raw material powder for the supporting material side layer, iron-based powder, graphite powder, alloy powder as the other alloy element powder, lubricant particle powder, and/or solid lubricant particle powder are blended and mixed by a predetermined amount so as to obtain the above-described desired supporting material side layer composition and are kneaded so as to obtain mixed powder for the supporting material side layer.

(59) As the raw material powder for the valve contact face side layer, iron-based powder, graphite powder, alloy powder as the other alloy element powder, hard particle powder, lubricant particle powder, and/or solid lubricant particle powder are blended mixed by a predetermined amount so as to obtain the above-described desired valve contact face side layer composition and are kneaded so as to obtain mixed powder for the valve contact face side layer.

(60) The mixed powder for the supporting material side layer is charged into a first feeder and the mixed powder for the valve contact face side layer is charged into a second feeder. First, after the first feeder is moved, the die and the core rod are relatively moved up with respect to the lower punch, and the mixed powder for the supporting material side layer is charged into a charging space for the supporting material side layer while the charging space is formed. Then, the provisional pressing punch is moved, the molding face shape and the molding pressure of the provisional pressing punch are adjusted so that an upper face as the boundary face with respect to the valve contact face side layer is formed in a predetermined shape, and the mixed powder for the supporting material side layer is provisionally pressed.

(61) In order to manufacture the high thermal conduction type valve seat insert used in the invention, it is desirable to perform a provisional pressing operation so that the molding face shape of the provisional pressing punch is formed in a shape in which an angle with respect to the valve seat insert axis becomes 20 to 40% smaller than the angle of the boundary face of the obtained green compact and the molding pressure of the provisional pressing operation becomes 0.01 to 3 ton/cm.sup.2.

(62) Next, after the second feeder is moved, the die and the core rod are relatively moved with respect to the lower punch, and the mixed powder for the valve contact face side layer is charged into a charging space for the valve contact face side layer while the charging space is formed. Then, the upper punch is moved down and the mixed powder for the valve contact face side layer and the mixed powder for the supporting material side layer are integrally pressed so as to obtain a green compact. When the mixed powder for the valve contact face side layer and the mixed powder for the supporting material side layer are integrally pressed, it is desirable to adjust the molding pressure so that the green compact density is in the range of 6.5 to 7.5 g/cm.sup.3.

(63) Next, the obtained green compact is heated and sintered at 1100 to 1200 C. under the protection atmosphere of an ammonia decomposing gas and vacuum by a general sintering method so as to obtain a sintered body. The sintered body obtained in this way is formed as a valve seat insert for an internal combustion engine having a predetermined dimensional shape by processing such as cutting and grinding.

EXAMPLES

(64) A valve material was set as austenite-type heat-resistant steel SUH35 (having thermal conductivity of 18 W/m.Math.K at 20 C.) and the valve material was sequentially subjected to a forging step, a hole drilling step, a coolant filling step, and a hollow part sealing step so as to manufacture a hollow poppet valve having a structure illustrated in FIG. 1. Further, coolant filled into a hollow part was set as metallic sodium (having thermal conductivity of 142 W/m.Math.K at 0 C.). Further, the valve material was subjected to cutting and polishing so as to manufacture a solid valve having a structure illustrated in FIG. 8(a).

(65) Further, raw material powder was blended, mixed, and kneaded so as to have a sintered body composition and a sintered body structure of a valve seat insert illustrated in Table 2, thereby obtaining mixed powder for a valve contact face side layer and mixed powder for a supporting material side layer. The mixed powder was compression-molded by a press-molding machine having a die, a core rod, an upper punch, a lower punch, two kinds of separately driven feeders, and an independently driven provisional pressing punch so as to obtain a green compact having a double-layer structure and was subjected to a sintering process so as to obtain a sintered body. The obtained sintered body was subjected to cutting, grinding, or the like so as to obtain a valve seat insert for an internal combustion engine formed of iron base sintered alloy and having a double-layer structure comprising a valve contact face side layer and a supporting material side layer with a predetermined dimensional shape (having an outer diameter of 30 mm, an inner diameter of 25 mm, and a height of 6 mm). The obtained valve seat insert corresponds to a high thermal conduction type valve seat insert having a structure illustrated in FIG. 5(a) and a standard valve seat insert having a structure illustrated in FIG. 5(b).

(66) Further, in the high thermal conduction type valve seat insert having a structure illustrated in FIG. 5(a), the boundary face between the valve contact face side layer and the supporting material side layer is a face that includes a circular line of 5 mm from the valve seat insert seating face at the outer peripheral face of the valve seat insert and a circular line of 2.5 mm from the seat face at the inner peripheral face of the valve seat insert and an angle formed with respect to the valve seat insert axis is 45. Further, the boundary face is a face distant by 1.0 mm in a direction perpendicular to the valve contact face at the center position of the valve contact face in the width direction. The boundary face is within an area surrounded by a face having a circular line of 0.5 mm in a direction perpendicular to the valve contact face at the center position of the valve contact face in the width direction and forming an angle of 45 with respect to the valve seat insert axis and a face having a circular line of of the valve seat insert height as a distance from the upper end face of the valve seat insert on the outer peripheral face of the valve seat insert and an intersection line between the valve seat insert seating face and the inner peripheral face of the valve seat insert.

(67) Further, in the high thermal conduction type valve seat insert having a structure illustrated in FIG. 5(a), the thermal conductivity at 20 to 300 C. was 13 W/m.Math.K at the valve contact face side layer and was 37 W/m.Math.K at the supporting material side layer. In the standard valve seat insert having a structure illustrated in FIG. 5(b), the thermal conductivity at 20 to 300 C. was 13 W/m.Math.K at the valve contact face side layer and was 37 W/m.Math.K at the supporting material side layer.

(68) Further, in the high thermal conduction type valve seat insert, the molding process was performed while the molding face shape of the provisional pressing punch in the powder compression-molding process was adjusted to so as to have an angle of 25 to 40 with respect to the axis and the molding pressure of the provisional pressing punch was adjusted in the range of 0.02 to 1 ton/cm.sup.2. In the process of manufacturing the standard valve seat insert, the molding face shape of the provisional pressing punch was set to be flat (an angle of 90 with respect to the axis).

(69) TABLE-US-00001 TABLE 1 SINTERED BODY COMPOSITION (MASS %) SUPPORT MATERIAL SIDE LAYER (BASE MATRIX) VALVE VALVE OTHERS SEAT SEAT VALVE CONTACT FACE SIDE LAYER (BASE MATRIX) Mo, Si, Cr, INSERT INSERT OTHERS SUM OF Ni, Mn, W, SUM OF No. TYPE C Co Mo Si Cr Ni Mn W, V, S OTHERS REST C V,, S, P OTHERS REST Sa STANDARD 1.1 14.1 6.2 0.6 2.1 2.0 0.6 W: 0.6, 26.8 Fe 1.00 Mn: 0.3, 0.5 Fe TYPE** V: 0.2, S: 0.2 S: 0.4 Sb HIGH 1.1 14.1 6.2 0.6 2.1 2.0 0.6 W: 0.6, 26.8 Fe 1.00 Mn: 0.3, 0.5 Fe THERMAL V: 0.2, S: 0.2 CONDUCTION S: 0.4 TYPE* SINTERED BODY STRUCTURE SUPPORT MATERIAL SIDE LAYER VALVE VALVE CONTACT FACE SIDE LAYER (BASE MATRIX) SEAT HARD SOLID THERMAL SOLID THERMAL INSERT PARTICLES*** LUBRICANT**** CONDUC- LUBRICANT**** CONDUC- No. (MASS %) (MASS %) TIVITY***** RATIO****** (MASS %) TIVITY***** Sa I: 20 i: 1.0 13 51 i: 0.5 37 Sb I: 20 i: 1.0 13 26 i: 0.5 37 *FIG. 5(a) **FIG. 5(b) ***HARD PARTICLES (I): Co-Mo-Si-TYPE Co-BASE INTERMETALLIC COMPOUND PARTICLE ****SOLID LUBRICANT PARTICLES (i): MnS *****THERMAL CONDUCTIVITY AT 300 C. MEASURED BY LASER FLASH METHOD ******VALVE CONTACT FACE SIDE LAYER RATIO (VOLUME %): VOLUME % WITH RESPECT TO ENTIRE VALVE SEAT INSERT

(70) By assembling the above-described valve and the above-described valve seat insert, the assembly of the valve and the valve seat insert was obtained. The assembly was set as an assembly (A) of a solid valve (No. Ba) and a standard valve seat insert (No. Sa), an assembly (B) of a solid valve (No. Ba) and a high thermal conduction type valve seat insert (No. Sb), an assembly (C) of a hollow valve (No. Bb) and a standard valve seat insert (No. Sa), and an assembly (D) of a hollow valve (No. Bb) and a high thermal conduction type valve seat insert (No. Sb).

(71) The assembly of the valve and the valve seat insert was assembled to a gasoline engine (having a capacity of 1.8 liter and an in-line four cylinder) for an automobile. Further, a thermocouple was welded at the neck part of the valve so as to measure the valve face temperature.

(72) After a heating operation was performed for a predetermined time, a high-load operation was performed at a predetermined rotation speed under predetermined operation condition, and the valve face temperature was measured. The predetermined rotation speed was set to 1000 to 5500 rpm.

(73) The obtained result is illustrated in FIG. 7 by calculating the valve face temperature decrease rate of each assembly (={(the valve face temperature of the reference assembly)(the valve face temperature of the said assembly)}/(the valve face temperature of the reference assembly)) based on the assembly No. A.

(74) From FIG. 7, the assembly (the assembly Nos. C and D) of the valve and the valve seat insert of the invention is formed as the assembly of the valve and the valve seat insert in which the valve temperature decreases largely and an increase in valve temperature can be suppressed remarkably compared with the reference assembly (No. A).

REFERENCE SIGNS LIST

(75) 1: assembly of valve and valve seat insert 2: cylinder head 4: combustion chamber 6: exhaust passage 8: valve seat insert 9: valve spring 10: valve 11: stem 12: fillet area 13: head 15: annular step part 18: cap 19: coolant S: hollow part