JP2011157845A - Valve seat for internal combustion engine, superior in cooling power - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a valve seat for an internal combustion engine, having a two-layer structure having superior wear resistance and high thermal conductivity. <P>SOLUTION: A face surface-side layer 1a has a base with hard particles dispersed into a base phase. The base is formed of iron-based sintered alloy having a composition containing C: 0.2-2.0 mass% and containing &le;40% in total of one or more kinds selected from among Co, Mo, Si, Cr, Ni, Mn, W, V, S, Ca and F and a composition formed by dispersing the hard particles into the base phase by 5-40 mass% with respect to the total amount of the face surface-side layer 1a. A seating surface-side layer 1b is formed of iron-based sintered alloy having a composition containing C: 0.2-2.0 mass% and composed of the residual Fe and unavoidable impurities. The face surface-side layer 1a is formed into a thin-walled shape occupying 10-45 vol% with respect to the total amount of a valve seat, and also a two-layer boundary surface is adjusted to a surface formed into a shape having an angle within a range from 20&deg; to 90&deg; at an average angle between a valve seat shaft and the two-layer boundary surface. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a two-layer type valve seat used for an internal combustion engine, and more particularly to improvement of thermal conductivity, that is, improvement of cooling performance of the valve seat.

  In an internal combustion engine, a valve seat on which a valve for opening and closing an intake port and an exhaust port is seated can maintain the airtightness of the combustion chamber, and can withstand wear due to repeated contact of the valve. Therefore, it is required to maintain excellent cooling ability that can suppress a temperature rise around the combustion chamber, such as heat radiation of the valve. In particular, the cooling capacity of the valve seat has a significant effect on the engine output, and is therefore an important performance to be retained by the valve seat.

  For this reason, in recent years, a valve seat having a two-layer structure made of different materials has been frequently used. In this two-layer valve seat, a face side layer made of a material having excellent wear resistance is provided on the face side on which the valve is seated, and a material having excellent thermal conductivity on the seat side in contact with the cylinder head. The seating surface side layer made of is arranged and integrated. Such a two-layered valve seat has recently been made of a sintered alloy using powder metallurgy because of its high dimensional accuracy and the use of a special alloy. However, the face side layer is usually made of a material having excellent wear resistance and contains a large amount of alloy elements, and thus is expensive. For this reason, from the viewpoint of reducing the material cost, it has been conventionally desired to make the face side layer as thin as possible in the two-layer valve seat.

  In response to such a demand, for example, Patent Document 1 describes a composite molded valve seat. In the valve seat described in Patent Document 1, a second sintered alloy, which is a special alloy, is disposed on the contact surface of the valve, and a first sintered alloy, which is a general low alloy sintered alloy, is disposed on the other part. The composite valve seat is characterized in that the boundary surface between the second sintered alloy and the first sintered alloy is substantially similar to the powder repose curve of the first sintered alloy. In the technique described in Patent Document 1, as shown in FIG. 3, a first space is formed by a die 10 having a stepped portion 10a, a lower punch 12, and a core rod 11 (FIG. 3A). After filling the space with the first powder P1 (FIG. 3 (b)), the die 10 and the core rod 11 are raised, and the upper surface of the first powder is shaped to resemble the powder repose curve to form the second space. (FIG. 3 (c)), the second space is filled with the second powder P2 (FIG. 3 (d)), and compression-molded by the upper press 13 having the shape of the valve contact surface (FIG. 3 (e)). . Thereby, the amount of the second sintered alloy made of a special alloy can be remarkably reduced. However, in the technique described in Patent Document 1, when the thickness of the second powder layer (face surface side layer) is extremely thin, the boundary surface with the first powder layer (seating surface side layer) is disturbed, and the second The thickness of the powder layer (face surface side layer) becomes extremely thin, and the first powder layer (sitting surface side layer) may be exposed on the face surface on the valve contact surface, and the wear resistance is significantly reduced. There was a problem of not functioning as a valve seat.

  Patent Document 2 describes a method for manufacturing a composite valve seat. The technique described in Patent Document 2 uses a press molding machine having a die, a core rod, an upper punch, and a lower punch, and a first compression space (filling space) formed by lowering the lower punch relatively. , Filling the first powder, then lowering the upper punch having a conical protrusion on the inner peripheral side to compress the first powder, forming a pre-compacted compact, and then raising the upper punch, After moving the lower punch relative to the die, forming a second space on the preliminary compacted body, and filling the second space with a second powder different from the first powder, the inner circumference This is a method of manufacturing a composite valve seat that is integrally compressed and molded into a green compact by an upper punch having a conical protrusion on the side, and then sintered into a two-layer valve seat (composite valve seat). In the technique described in Patent Document 2, the compression to the first powder by the upper punch is such that the shape of the upper punch remains on the upper surface of the pre-compacted compact, and no substantial molding is performed. . As a result, the relative amount of the second sintered alloy can be reduced. However, in the technique described in Patent Document 2, the punch used is the same in the compression molding to the first powder and the compression molding to the second powder, and the degree of freedom in designing the valve seat is low, There is a problem that the stroke of the punch becomes long, the molding time is long, and the productivity is lowered.

  In Patent Document 3, the valve contact layer 101 and the backup layer 102 are made of different materials, have a tapered portion 101a on the end surface on the valve contact layer side, and the boundary between the valve contact layer and the backup layer. A valve seat having a two-layer structure is described in which a slope along the tapered portion is formed on the surface. In the technique described in Patent Document 3, a green compact is produced using a powder molding apparatus having a die 10, a core rod 11, an upper punch 14, a lower first punch 12, and a lower second punch 13. The valve seat 100 having the above-described two-layer structure is manufactured by sintering. In the technique described in Patent Document 3, as shown in FIG. 4, first, the upper end surface of the lower second punch 13 is set to be lower than the lower end position of the tapered surface 12a of the lower first punch 12 having the upper end formed in a tapered surface shape. A filling space is formed by raising the first raw material powder P1 in the filling space on the lower first punch 12 (FIG. 4A). Next, the lower second punch 13 is lowered relative to the lower first punch 12 to move a part of the first raw material powder P1 on the lower first punch 12 onto the lower second punch 13. (FIG. 4B). Further, a filling space is formed on the lower first punch 12 and the lower second punch 13, and the second raw material powder P2 is filled in the filling space (FIG. 4C). Then, the raw material powder filled with the upper punch 14, the core rod 11 and the die 10 is compression-molded to form a green compact. The green compact can be sintered to produce a valve seat having a two-layer structure as described above. By adopting such a two-layer valve seat, the valve contact layer that requires wear resistance is not too thick, and the backup layer that requires high thermal conductivity has a sufficient volume. And a wear-resistant valve seat.

  Further, Patent Document 4 includes a step of filling a first layer of powder with a first feeder, a step of temporarily pushing the filled first layer with a temporarily pushing cylinder, and a second feeder with a first feeder. A powder forming method comprising a second layer filling step of filling a second powder and a pressure forming step of pressing the filled first layer metal and second layer metal is described. According to this method, since the first layer is filled and then temporarily pressed and then the second layer is filled, the boundary line is clear and the powder is not mixed.

JP-A-57-140802 JP 58-215299 A JP 2004-351453 A JP 2002-239793 A

However, in the technique described in Patent Document 3, when the thickness of the valve contact layer is extremely thin, the boundary surface with the backup layer is disturbed, and the thickness of the valve contact layer (face surface side layer) is extremely large. The back-up layer may be exposed on the valve contact surface (face surface), resulting in a problem that the wear resistance is remarkably reduced.
Further, when a two-layer valve seat having a thin second layer having a high alloy composition is manufactured using the technique described in Patent Document 4, the shape of the boundary surface between the two layers is not constant, and the face surface Since the thinning of the side layer cannot be stably achieved, for example, when compressed with a flat punch, the first layer may be exposed on the face surface, and the wear resistance of the valve seat is extremely reduced. Was leaving.

  The present invention advantageously solves the problems of the prior art, and has a much thinner face surface side layer than the conventional one, and is excellent in wear resistance and high thermal conductivity suitable for an internal combustion engine. An object is to provide a valve seat for an internal combustion engine having a two-layer structure. Here, the “thin face side layer” refers to a case where the face side layer is 10% to 45% by volume% with respect to the total amount of the valve seat.

  In order to achieve the above-mentioned object, the present inventors diligently studied various factors affecting the stable formation of the two-layer boundary surface. As a result, it has been found that in order to stably achieve the desired thinning of the face surface side layer, it is important to select an appropriate surface shape for the pressing surface of the temporary pressing punch. And it discovered that it was necessary to adjust the boundary surface of the face surface side layer and the seating surface side layer to an angle within an appropriate range of 20 ° to 90 ° with an average angle with respect to the valve seat axis. As a result, it is possible to reduce the thickness of the desired face side layer, and to manufacture a valve seat having both excellent wear resistance and excellent cooling ability. If the average angle of the boundary surface with respect to the valve seat axis is outside the above-mentioned appropriate range, the boundary surface is disturbed, the seating surface side layer is exposed to the valve contact surface (face surface), wear resistance is reduced, and the desired face It has also been found that the thickness reduction of the surface side layer cannot be achieved stably.

The present invention has been completed based on such findings and further investigations. That is, the gist of the present invention is as follows.
(1) A valve seat for an internal combustion engine made of an iron-based sintered alloy in which two layers of a face surface side layer and a seating surface side layer are integrated, and at least a valve contact surface of the valve seat is the face surface side layer A valve seat for an internal combustion engine having an excellent cooling capacity, wherein the face side layer is 10% to 45% by volume with respect to the total amount of the valve seat.

(2) In (1), the boundary surface between the face surface side layer and the seating surface side layer has an average angle α of not less than 20 ° and not more than 90 ° at an angle formed with the valve seat shaft at least in the valve contact surface corresponding region. A valve seat for an internal combustion engine, characterized in that the surface has a surface.
(3) The valve for an internal combustion engine according to (2), wherein the boundary surface is adjusted to ± 300 μm or less at each position perpendicular to the average position with reference to the average position of the boundary surface. Sheet.

  (4) In any one of (1) to (3), the face surface side layer has a base part in which hard particles are dispersed in a base phase, and the base part is in mass%, and C: 0.2 to Contains 2.0%, contains one or more selected from Co, Mo, Si, Cr, Ni, Mn, W, V, S, Ca, F in total, 40% or less, and the balance Fe And made of an iron-based sintered alloy having a base composition composed of unavoidable impurities and a base structure in which hard particles are dispersed in the matrix phase in a mass% with respect to the total amount of the face side layer by 5 to 40%. The valve seat for an internal combustion engine, wherein the seating surface side layer is made of an iron-based sintered alloy having a composition of C: 0.2 to 2.0% by mass and the balance Fe and unavoidable impurities. .

(5) In (4), in addition to the composition, the seating surface side layer is further in mass%, and is selected from Mo, Si, Cr, Ni, Mn, W, V, S, P, Ca, and F. A valve seat for an internal combustion engine characterized by comprising a composition containing at least 20% in total of one or more selected ones.
(6) In (4) or (5), the face surface side layer further includes a base portion in which solid lubricant particles are dispersed in addition to the hard particles in the base phase, and the base portion structure is In addition to the hard particles, a valve seat for an internal combustion engine having a base part structure in which solid lubricant particles are dispersed in an amount of 0.3 to 5.0% by mass% with respect to the total amount of the face side layer (7) (5) Alternatively, in (6), the seating surface side layer has a structure in which solid lubricant particles are dispersed in the matrix phase in an amount of 0.3 to 5.0% by mass based on the total amount of the seating surface side layer. Valve seat

  According to the present invention, a valve seat having a two-layer structure having a thin face side layer can be manufactured stably and easily at a low cost as compared with the prior art, and the industrial advantages are achieved. According to the present invention, it is possible to provide a valve seat having excellent cooling resistance and high heat conductivity, suitable for an internal combustion engine, and having a high cooling capacity, which contributes significantly to improvement in engine output. There is also an effect. Further, according to the present invention, the radial thickness of the valve seat can be reduced.

It is a schematic explanatory drawing which shows typically the cross section of the valve seat of this invention. It is a schematic explanatory drawing which shows typically the 2 layer structure of the valve seat of this invention. It is a schematic explanatory drawing which shows an example of the manufacturing process of the conventional 2 layer structure valve seat. It is a schematic explanatory drawing which shows an example of the manufacturing process of the conventional 2 layer structure valve seat. It is a schematic diagram which shows the outline | summary of a single rig testing machine.

  As shown in FIG. 1, the valve seat for an internal combustion engine of the present invention has a face surface side layer 1a on the face surface 1aa side in contact with the valve, and a seating surface side layer 1b on the side in contact with the seating surface 1ba. It is an iron-based sintered alloy valve seat formed by integrating two layers of a face surface side layer 1a and a seating surface side layer 1b. The valve seat 1 according to the present invention has a configuration in which at least a valve contact surface 1ca is formed by a face surface side layer 1a, and the face surface side layer 1a is 10% to 45% by volume% with respect to the total amount of the valve seat 1.

  If the volume ratio of the face surface side layer 1a is less than 10%, the face surface side layer becomes too thin, and desired wear resistance for an internal combustion engine cannot be ensured. On the other hand, if the amount of the face side layer exceeds 45%, the temperature around the cylinder head, especially around the combustion chamber, rises too much when the engine is running at a high speed and high load, causing knocking, etc. The engine output of can not be secured. In addition, when the amount of the face side layer exceeds 45%, the material cost becomes expensive, which is economically disadvantageous. In addition, the preferable volume ratio of the face side layer is 10% to 30% by volume% with respect to the total amount of the valve seat.

  In the valve seat of the present invention, the boundary surface between the face surface side layer and the seating surface side layer is at least an area corresponding to the valve contact surface, and an angle between the valve seat shaft and an average of 20 ° or more and 90 ° or less. A plane having an angle α is preferable. Thereby, a thin face side layer can be achieved, and the material cost can be further reduced. As shown in FIG. 2, the angle between the boundary surface and the valve seat axis is observed on the cross section including the valve seat axis, and the average shape (line) of the boundary surface in the cross section is approximated by a straight line. The average angle α with the valve seat shaft is obtained.

  If the angle α formed by the boundary surface and the valve seat shaft is less than 20 °, the face surface side layer becomes too thin, and desired wear resistance cannot be secured for an internal combustion engine. On the other hand, if it exceeds 90 °, the ratio of the seating surface side layer decreases, the thermal conductivity decreases, and the cooling ability by the valve seat decreases. For this reason, in the present invention, the boundary surface between the face surface side layer and the seating surface side layer is limited to a surface having an average angle α of 20 ° or more and 90 ° or less as an angle formed with the valve seat shaft.

  Further, in the valve seat of the present invention, ± 300 μm (= Δh) or less at each position perpendicular to the average position with reference to the average position of the boundary surface 1ab between the face surface side layer 1a and the seating surface side layer 1b. It is preferable to have a uniform boundary surface adjusted to the above. In the present invention in which the face surface side layer is thinned when the boundary surface of the two layers deviates from the above-described range (± 300 μm) (= Δh) in the height direction and is greatly disturbed such as in a wavy state, May be exposed to the contact surface of the valve or may be extremely thin, resulting in a problem that the wear resistance of the valve seat is significantly reduced.

Next, a preferred composition and structure of the valve seat according to the present invention will be described. Hereinafter, the mass% in the composition is simply expressed as%.
The face side layer of the valve seat according to the present invention is made of an iron-based sintered alloy having a base portion in which hard particles are dispersed in the base phase. By dispersing hard particles in the matrix phase, the wear resistance of the valve seat is significantly improved. In the present invention, the hard particles dispersed in the base phase of the face side layer are either Co-based intermetallic compound particles, stellite-based intermetallic compound particles, Fe-Mo-based intermetallic compound particles, or a composite thereof. It is preferable to do. Among them, the Co-based intermetallic compound particles are particles in which a high-hardness intermetallic compound is dispersed in a relatively soft Co matrix, and are characterized by low opponent attack. Examples of preferable Co-based intermetallic compound particles include Si—Cr—Mo-based Co-based intermetallic compound particles and Mo—Ni—Cr-based Co-based intermetallic compound particles.

  In the face side layer, it is preferable to disperse the hard particles in an amount of 5 to 40% by mass% based on the total amount of the face side layer. If the amount to be dispersed is less than 5%, desired wear resistance cannot be ensured. On the other hand, if the dispersion exceeds 40%, the effect is saturated and an effect commensurate with the amount added cannot be expected. For this reason, it is preferable to limit the dispersion amount of the hard particles in the face side layer to a range of 5 to 40% by mass% with respect to the total amount of the face side layer. More preferably, it is 15 to 25%.

In the face side layer, in addition to the hard particles described above, solid lubricant particles may be further contained in an amount of 0.3 to 5.0% by mass% based on the total amount of the face side layer. If the content is less than 0.3%, a desired lubricating effect cannot be expected, and the machinability deteriorates. On the other hand, if the content exceeds 5.0%, the machinability improving effect is saturated and the strength is reduced. For this reason, when it contains, it is preferable to limit to 0.3 to 5.0% of range. More preferably, it is 0.4 to 1.0% of range. As solid lubricant, MnS, CaF ₂ can be exemplified.

The base part including the base phase and the hard particles, or further the solid lubricant particles, includes C: 0.2 to 2.0%, among Co, Mo, Si, Cr, Ni, Mn, W, V, S, Ca, and F. It is preferable that one or two or more selected from the above be contained in a total of 40% or less, and have a composition composed of the remaining Fe and inevitable impurities.
C: 0.2-2.0%
C is an element that increases the strength and hardness of the sintered body and facilitates the diffusion of metal atoms during sintering. In the present invention, C is preferably contained in an amount of 0.2% or more. On the other hand, when the content exceeds 2.0%, cementite is likely to be generated in the matrix, and a liquid phase is likely to be generated during sintering, resulting in a problem that dimensional accuracy is lowered. For this reason, it is preferable to limit C to 0.2 to 2.0% of range. In addition, More preferably, it is 0.9 to 1.1%.

One or more selected from Co, Mo, Si, Cr, Ni, Mn, W, V, S, Ca, F: 40% or less in total
Co, Mo, Si, Cr, Ni, Mn, W, V, S, Ca, and F are all elements that increase the strength and hardness of the sintered body and further improve the wear resistance. In order to obtain such an effect, it is desirable to select at least one kind including hard particles and to contain 20% or more in total. On the other hand, when the content of these elements exceeds 40% in total, the formability is lowered and the strength is also lowered. For this reason, it is preferable to limit one or more selected from Co, Mo, Si, Cr, Ni, Mn, W, V, S, Ca, and F to a total of 40% or less. More preferably, the total is 25% or less.

The remainder of the face side layer other than those described above consists of Fe and inevitable impurities.
On the other hand, the seating surface side layer of the valve seat according to the present invention is made of an iron-based sintered alloy like the face surface side layer, and is integrated with the face surface side layer via the boundary surface by sintering. It is preferable that the seating surface side layer has a composition that does not contact the valve, supports the face surface side layer, and can simply secure a desired strength as a valve seat.

In the seating surface side layer, solid lubricant particles may be further contained in the matrix phase in an amount of 0.3 to 5.0% by mass with respect to the total amount of the seating surface side layer, if necessary. If the content is less than 0.3%, a desired lubricating effect cannot be expected, and the machinability deteriorates. On the other hand, when the content exceeds 5%, the machinability improving effect is saturated and the strength is reduced. For this reason, when it contains, it is preferable to limit to 0.3 to 0.5% of range. As solid lubricant, MnS, CaF ₂ can be exemplified.

The base phase composition of the seating surface side layer of the present invention (in the case where solid lubricant particles are dispersed, the base part composition including the base lubricant composition) includes C: 0.2 to 2.0%, or, further, Mo, A composition comprising one or more selected from Si, Cr, Ni, Mn, W, V, S, P, Ca, and F in a total of 20% or less, the balance being Fe and inevitable impurities It is preferable that
C: 0.2-2.0%
C is an element that increases the strength and hardness of the sintered body. In the present invention, in order to ensure desired strength and hardness as a valve seat, the seating surface side layer preferably contains 0.2% or more. However, when the content exceeds 2.0%, cementite is likely to be generated in the matrix, and a liquid phase is likely to be generated during sintering, resulting in a problem that dimensional accuracy is lowered. For this reason, it is preferable to limit C to 0.2 to 2.0% of range. In addition, More preferably, it is 0.9 to 1.1%.

The above-mentioned components are basic components of the seating surface side layer. In addition to the basic components, Mo, Si, Cr, Ni, Mn, W, V, S, P, Ca, and F can be used as selective elements. One or two or more selected from among them can be contained in a total of 20% or less.
One or more selected from Mo, Si, Cr, Ni, Mn, W, V, S, P, Ca, F: 20% or less in total
Mo, Si, Cr, Ni, Mn, W, V, S, and P are all elements that increase the strength and hardness of the seating surface side layer. Can be contained. In order to obtain such an effect, it is desirable to contain 10% or more in total. However, if the content of these elements exceeds 20% in total, the formability is lowered and the strength is also lowered. For this reason, when it contains, it is preferable to limit to 20% or less in total. In addition, More preferably, it is 5 to 15%.

The rest of the seating surface side layer other than those described above consists of Fe and inevitable impurities.
Below, the preferable manufacturing method of this invention valve seat is demonstrated.
In the present invention, a press molding machine having a die, a core rod, an upper punch, a lower punch, two types of feeders that can be driven independently from each other, and a temporary pressing punch that can be driven independently is used.
As the raw material powder for the face side layer, iron-based powder, graphite powder, alloy powder such as alloy element powder, hard particle powder, lubricant particle powder, or even solid lubricant particle powder, Is blended in a predetermined amount so as to have the above-described face surface side layer composition to obtain a mixed powder for the face surface side layer. The iron-based powder may be a pure iron powder or a steel-based powder having a specific composition. The steel powder having a specific composition is preferably a high speed steel powder. The iron-based powder used is preferably atomized powder.

The raw material powder for the seating surface side layer includes iron-based powder, graphite powder, alloy powder such as alloy element powder, lubricant particle powder, or further solid lubricant particle powder. A predetermined amount is blended so as to obtain a seating surface side layer composition to obtain a mixed powder for the seating surface side layer.
First, after moving the first feeder, the die and the core rod are raised relative to the lower punch to form a filling space for the seating surface side layer, while mixing for the seating surface side layer in the filling space Fill with powder. Then, by moving the temporary pressing punch and adjusting the pressing surface shape and pressing force of the temporary pressing punch so that the upper surface that becomes the interface with the face surface side layer has a predetermined shape, mixing for the seating surface side layer Temporarily press the powder. Next, after moving the second feeder, the die and the core rod are raised relative to the lower punch to form a filling space for the face side layer, while mixing the face side layer in the filling space. Fill with powder. Then, the upper punch is lowered to integrally pressurize the mixed powder for the face side layer and the mixed powder for the seat side layer to form a green compact. Incidentally, the pressure condition is not necessarily limited well, particularly if appropriately determined as desired, in conjunction with desired valve seat characteristics, the green compact density in the range of 5.0 to 7.5 g / cm ³ It is preferable to adjust so that it becomes.

The obtained green compact is then subjected to a sintering treatment to obtain a sintered body having an upper and lower two-layer structure. The conditions for the sintering process may be determined as appropriate according to the desired properties, except for performing in a reducing atmosphere, and need not be particularly limited. The sintering temperature is preferably 1100 to 1200 ° C. from the viewpoint of sintering diffusion.
From the viewpoint of securing strength, it is preferable to use a so-called 2P2S process in which the pressure molding and the sintering treatment are repeated at least twice. In the 2P2S process, the first sintering process is preferably presintering, and the second sintering process is preferably a sintered body having a desired density. Thereby, further improvement in density is expected.

  The raw material powder shown in Table 1 was mixed in the blending amounts shown in Table 1, and kneaded with a V-type mixer to obtain a mixed powder for the face side layer. Similarly, the raw material powders shown in Table 1 were mixed in the blending amounts shown in Table 1 and kneaded to obtain mixed powders for the seating side layer. In mixing, 0.8 parts by weight of zinc stearate powder as a lubricant particle powder was blended with 100 parts by weight of the total of the iron-based powder, graphite powder, alloy element powder, and solid lubricant particle powder.

  A press molding machine having a die, a core rod, an upper punch, a lower punch, two types of feeders that can be driven independently of each other, and a temporary pressing punch that can be driven independently of each other was used. First, the lower punch is lowered relatively to form a filling space for the seating surface side layer by the lower punch, the die and the core rod, and the first feeder is moved into the filling space to mix the seating surface side layer. Filled with flour. Subsequently, the temporary pressing punch was moved to temporarily press the filled mixed powder for the seating surface side layer. In the temporary pressing, the pressing surface shape and pressing force of the temporary pressing punch were adjusted to adjust the upper surface shape of the seating surface side layer serving as the boundary surface. Next, the die and the core rod are raised relative to the lower punch to form a filling space for the face surface side layer, and the second feeder is moved into the filling space to mix the mixed powder for the face surface side layer. Filled. Then, the upper punch was lowered, and the face surface side layer mixed powder and the seating surface side layer mixed powder were integrally pressure-molded to obtain various green compacts.

The obtained green compact is subjected to a preliminary sintering treatment, and further subjected to pressure molding (surface pressure: 6 to 10 ton / cm ² ) with a powder molding machine, followed by a sintering treatment (1100 to 1200 in a reducing atmosphere). The 2P2S process is performed to give a sintered body. In some sintered bodies, a 1P1S process in which molding and sintering are performed once is used.
Samples for analysis were taken from each layer of the obtained sintered body, and the content of each element was determined by emission analysis. The measurement was a cross section inside the boundary surface between the two layers.

  Further, the obtained sintered body (valve seat) was cut at the cross section (8 locations) including the valve seat axis, polished and corroded to reveal a boundary surface of two layers in each cross section. The shape of the boundary surface was observed using a video microscope (magnification: 100 times). As shown in FIG. 2, the average shape of the boundary surface in each cross section was approximated by a straight line, and the angle α formed with the valve seat axis was measured. The angle in each cross section was arithmetically averaged to calculate the average angle α. Further, the variation from the average shape of the boundary surface, that is, the difference in the height direction from the average shape position of the boundary surface is measured as shown in FIG. The difference was Δh.

Further, from the observation of the cross section of the sintered body, the cross sectional area of each layer was determined, and the volume ratio of each of the face surface side layer and the seating surface side layer in the valve seat was calculated in terms of the cross sectional area ratio.
Further, the obtained valve seat (sintered body) was inserted into a single rig wear tester shown in FIG. 5 and operated under the following test conditions, and the valve face was measured by a thermocouple attached to the valve face surface of the valve seat. The surface temperature was measured, and the saturated temperature was defined as the valve seat surface temperature.

Test conditions;
Test time: 9hr
Cam rotation speed: 3000 rpm
Valve speed: 10 rpm
Spring load: 35kgf (345N) (when set)
Lift amount: 7.5 mm
Valve material: SUH35
The amount of LPG + Air and the amount of cooling water were constant.

Based on the temperature of the valve face of sintered body No. 1, the difference between the temperature of the valve face of sintered body No. 1 and the temperature of the valve face of the sintered body was calculated. When the temperature of the sintered body No. 1 was lower than the temperature of the valve face surface, the cooling ability was excellent, and it was evaluated as ◯, and when it was elevated, the cooling capacity was lowered as x. .
Moreover, the shape of the test piece (valve seat) before and after the test was measured, and the difference between before and after the test was calculated and converted into the amount of wear (μm). Based on the wear amount of the sintered body No. 1, if the wear amount of the sintered body was within + 20%, the evaluation of wear resistance was “good”, otherwise it was “poor”.

  The obtained results are shown in Tables 2 and 3.

  Each of the examples of the present invention is a valve seat having excellent wear resistance, high thermal conductivity, and excellent cooling ability for an internal combustion engine. On the other hand, the comparative example which deviates from the scope of the present invention has a reduced cooling capacity or reduced wear resistance.

1 Valve seat
1a Face side layer
1b Seating surface side layer 2 Setting plate 3 Heat source (LPG + Air)
4 Valve
10 die
11 Core rod
12 Lower first punch
13 Lower second punch
14 Top punch
100 valve seat
101 valve contact layer
102 backup layer

Claims (7)

  A valve seat for an internal combustion engine made of an iron-based sintered alloy in which two layers of a face surface side layer and a seating surface side layer are integrated, and at least a valve contact surface of the valve seat is formed by the face surface side layer. The valve seat for an internal combustion engine having excellent cooling performance, wherein the face side layer is 10% to 45% by volume with respect to the total amount of the valve seat.   2. The internal combustion engine according to claim 1, wherein a boundary surface between the face surface side layer and the seating surface side layer has an average angle α of 20 ° or more and 90 ° or less with respect to a valve seat axis. Valve seat for   3. The valve seat for an internal combustion engine according to claim 2, wherein the boundary surface is adjusted to be ± 300 μm or less in a height direction with respect to an average position of the boundary surface. The face surface side layer has a base portion in which hard particles are dispersed in a base phase, and the base portion includes, in mass%, C: 0.2 to 2.0%, Co, Mo, Si, Cr, Ni, A base composition comprising one or more selected from Mn, W, V, S, Ca, and F in a total of 40% or less, the balance being Fe and inevitable impurities, and the base phase It is made of an iron-based sintered alloy having a base part structure in which hard particles are dispersed by 5 to 40% by mass% with respect to the total amount of the face side layer.
The seating surface side layer is made of an iron-based sintered alloy having a matrix phase composition composed of the balance Fe and unavoidable impurities, including C: 0.2 to 2.0% by mass%. 4. A valve seat for an internal combustion engine according to any one of 3 above.   The base phase composition of the seating surface side layer is 1% selected from Mo, Si, Cr, Ni, Mn, W, V, S, Ca, and F in addition to the matrix phase composition. The valve seat for an internal combustion engine according to claim 4, wherein the composition contains 20% or less of seeds or two or more kinds in total.   The face surface side layer has a base part in which solid lubricant particles are dispersed in addition to the hard particles in the base phase, and the base part structure further contains solid lubricant particles in addition to the hard particles. 6. The valve seat for an internal combustion engine according to claim 4, wherein the valve seat has a base part structure dispersed by 0.3 to 5.0% by mass% with respect to the total amount of the face side layer. 7. The structure according to claim 5, wherein the seating surface side layer has a structure in which solid lubricant particles are dispersed in the matrix phase in an amount of 0.3 to 5.0% by mass% based on the total amount of the seating surface side layer. Valve seat for internal combustion engine

Images