JP4637143B2 - In-cylinder injection internal combustion engine, piston for in-cylinder injection internal combustion engine, low heat conduction alloy for piston for in-cylinder injection internal combustion engine, low heat conduction member for piston for in-cylinder injection internal combustion engine, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a piston used in a direct injection internal combustion engine such as a diesel engine or a gasoline engine, a low heat conduction member used for the piston to promote atomization or vaporization of liquid fuel, and a low heat conduction alloy suitable therefor, The present invention relates to a method for producing such a low thermal conductive member.

  With increasing environmental awareness, internal combustion engines such as diesel engines and gasoline engines used in automobiles, motorcycles, industrial machines, and the like are strongly required to save fuel and clean exhaust gases. For example, from the viewpoint of fuel saving, a direct injection gasoline engine has recently been adopted for general commercial vehicles.

  By the way, in the case of a cylinder injection internal combustion engine, since the spray amount and spray timing of the fuel sprayed directly into the cylinder vary depending on the load of the internal combustion engine, it is always easy to completely atomize or vaporize the fuel. It wasn't. For this reason, incomplete combustion of the fuel or the like occurs slightly, and even if it is cold, the fuel consumption may deteriorate, or the hydrocarbon soot in the exhaust gas may increase. Certainly, recent automobiles are equipped with an exhaust gas catalyst device, but the catalyst does not activate unless the temperature rises to some extent, so if exhaust gas purification is insufficient when the internal combustion engine is cold, such as immediately after startup It was easy to happen.

  In particular, the direct injection gasoline engine enables stratified combustion in an ultra lean region with a high air-fuel ratio in addition to uniform mixed combustion. However, if the fuel is not sufficiently atomized or vaporized around the spark plug during stratified combustion, unburned gas will be discharged as the ignitability deteriorates, which adversely affects fuel efficiency and exhaust gas purification. obtain.

  Under such circumstances, in order to promote atomization or vaporization of the sprayed fuel, for example, it has been conventionally proposed to provide a low heat conduction region that is higher in temperature than the surroundings in the fuel collision region of the piston top surface. The following patent documents have specific disclosures related thereto.

JP-A-11-193721 JP 2000-186617 A (Patent No. 3551801)

  Patent Document 1 proposes to provide a low heat conduction member in the fuel collision area on the top surface of the piston for the in-cylinder spark ignition engine in order to promote fuel evaporation and reduce fuel adhesion. However, Patent Document 1 does not specify a specific material for the low thermal conductivity member, and merely presents thermal conductivity and specific heat.

  Patent Document 2 proposes placing a low heat conductive material plate on a fuel collision portion provided on the top surface of the piston for the same purpose as Patent Document 1. Specifically, it proposes to adjust the plate temperature moderately by forming an air layer with the joint interface between the plate and the piston main body being uneven, suppressing heat transfer from the plate to the piston main body. .

  However, Patent Document 2 substantially discloses only the uneven shape of the joint interface. Although there is a description of “sintered titanium alloy” or the like, there is substantially no detailed disclosure of the material of the plate. Incidentally, the thermal conductivity of the titanium alloy is about 1/20 of that of a general aluminum alloy as a piston material, and the linear expansion coefficient of the titanium alloy is about 1/2 of that of the aluminum alloy. When such a titanium alloy member is provided in the fuel collision area at the top of the piston, even if fuel vaporization is promoted due to low thermal conductivity, repeated thermal stress acts on the top of the piston due to the difference in linear expansion coefficient. In addition, reliability such as thermal fatigue failure is low and practicability is poor.

The present invention has been made in view of such circumstances. That is, an object of the present invention is to provide a low heat conduction alloy suitable for forming a low heat conduction region in a fuel collision region provided at the top of a piston of a direct injection internal combustion engine.
Moreover, it aims at providing the low heat conductive member using the low heat conductive alloy, and its manufacturing method. Furthermore, it aims at providing the cylinder injection type internal combustion engine using the low heat conductive member etc., and the cylinder injection type internal combustion engine using the piston.

Means for solving the problems and their effects

  As a result of extensive research and trial and error, the present inventor has made an alloy that has a very low thermal conductivity and a linear expansion coefficient that is very close to a general aluminum alloy that is a constituent material of a piston. Newly found. The inventor has also confirmed that the alloy can be excellent in mechanical properties. Thus, the present invention has been completed.

<Low heat conduction alloy of piston for in-cylinder internal combustion engine>
(1) That is, the low heat conductive alloy of the piston for the cylinder injection type internal combustion engine of the present invention is provided at the top of the piston made of aluminum alloy at the top of the piston main body that can reciprocate in the cylinder of the cylinder block of the internal combustion engine. A low thermal conductivity area that is at least part of a fuel collision area where liquid fuel injected into the cylinder from a fuel injection valve provided in a cylinder head on the cylinder block can collide and has a lower thermal conductivity than the surrounding area Is used for a low thermal conductive layer or a low thermal conductive member, and manganese (Mn): 5 to 35 mass% and carbon (C): 0.5 to 1.5 mass% when the whole is 100 mass% And the balance: iron (Fe) and inevitable impurities or incidental elements.

(2) In recent internal combustion engines, aluminum alloy pistons are used for diesel engines as well as gasoline engines from the viewpoint of reducing inertial mass. The thermal conductivity of the aluminum alloy for pistons is usually about 120 to 140 W / mK although it depends on the temperature range.

  On the other hand, although the reason for the low thermal conductive alloy of the present invention is not necessarily clear, the thermal conductivity is as small as 1/10 to 1/20 as compared with the aluminum alloy for pistons. For this reason, when the low heat conduction alloy of the present invention is used in the low heat conduction area of the fuel collision area of the piston for the cylinder injection type internal combustion engine, the heat received by the combustion of the fuel is very diffused or dissipated in the low heat conduction area. It becomes difficult to be done. For this reason, the low heat conduction region using the low heat conduction alloy of the present invention is likely to be heated to a higher temperature than the surrounding aluminum alloy.

Fuel that is newly sprayed toward the fuel collision zone and contacts the high-temperature, low heat conduction zone receives heat from the low-heat conduction zone, resulting in high temperature and high enthalpy of the fuel itself without being vaporized or vaporized immediately. To do.
As a result, in the case of a gasoline engine, for example, an air-fuel mixture with an appropriate concentration is easily formed at least around the spark plug, and stable combustion is possible even during ultra lean combustion. Even in the case of a diesel engine, the atomization and vaporization of the fuel are promoted, the enthalpy is increased, the afterburning is reduced, and the combustion is easily completed near the top dead center.
In any case, if the low heat conduction alloy of the present invention is used in the low heat conduction region of the piston, the stable operation range of the direct injection internal combustion engine is expanded, the fuel consumption of the direct injection internal combustion engine is reduced, the exhaust gas is purified, etc. Excellent effects can be obtained.

  Even if the portion made of the low heat conductive alloy of the present invention is hotter than the surrounding aluminum alloy, the portion is not overheated because it is cooled each time the fuel is sprayed. That is, the low heat conductive layer or the low heat conductive member made of the low heat conductive alloy of the present invention becomes a heat spot, and serious problems such as knocking and preignition that cannot be avoided are not caused.

(3) By the way, a general aluminum alloy for pistons has a high coefficient of linear expansion of about 20 × 10 ⁻⁶ / K. When a low heat conduction layer or a low heat conduction member made of a different alloy is provided in the fuel collision area at the top of the piston made of this aluminum alloy (base material), separation or Inconveniences such as fracture and thermal fatigue failure due to repeated thermal stress can occur.

  However, the low thermal conductive alloy of the present invention has a linear expansion coefficient substantially equal to that of the aluminum alloy for piston, although the reason is not necessarily certain. That is, there is substantially no difference between the linear expansion coefficients of the two. For this reason, even when a low heat conductive member made of the low heat conductive alloy of the present invention is provided at the top of the piston, there is almost no thermal stress due to the difference in linear expansion coefficient between the low heat conductive member and the piston top. Thus, when the low thermal conductive alloy of the present invention is used, a highly durable piston excellent not only in strength but also in thermal fatigue strength can be obtained.

  Note that the repeated thermal stress generated in the fuel collision zone at the top of the piston includes short-term repeated thermal stress caused by heating due to combustion of the fuel and cooling due to vaporization of the collided fuel, and when the internal combustion engine itself is cold. Long-term repeated thermal stress due to warm weather is considered. If the low thermal conductive alloy of the present invention is used, any thermal stress can be reduced, and a piston excellent in heat fatigue resistance in the short term and in the long term, that is, a cylinder injection type internal combustion engine can be obtained.

(4) By the way, in addition to the above-described thermal stress, a large explosion pressure repeatedly acts on the piston, and a large inertial force acts at a high speed. For this reason, mechanical properties such as excellent strength or toughness are required for alloys and members used for pistons. The low thermal conductive alloy of the present invention can be excellent in mechanical properties such as strength or elongation in addition to the above-described thermal conductivity and linear expansion coefficient. This has been confirmed by many test results.
Thus, it can be said that the low heat conductive alloy of the present invention is suitable for forming a low heat conductive region in the fuel collision region at the top of the piston from any viewpoint.

  However, the low thermal conductive alloy of the present invention is only required to have excellent thermal characteristics such as the above-described thermal conductivity and linear expansion coefficient, and is required to have mechanical characteristics such as strength or elongation. It is not intended to be construed as limited by its mechanical properties.

(5) The existence form of the low thermal conductive alloy of the present invention is not limited. That is, it may be a raw material such as powder or ingot, and may be in the form of a liquid (molten metal) as well as a solid. It may be an intermediate product (low thermal conductivity member) manufactured from the raw material. Further, it may be a low heat conductive layer or a low heat conductive member already applied to the top of the piston.
The “subsidiary element” in the present specification is an element other than Mn, C, and Fe described above, is not an inevitable impurity, and is within a range that does not fundamentally impair the characteristics of the low thermal conductive alloy of the present invention. An element that is allowed to be contained as a subordinate. It does not matter whether the incidental element improves the characteristics of the low thermal conductive alloy of the present invention. An element that does not impair the basic characteristics of the low heat conductive alloy of the present invention described above even if there is no effect of improving the characteristics is also a subsidiary element.

  In the present specification, the numerical range “x to y” includes the lower limit (x) and the upper limit (y) unless otherwise specified. In addition to the numerical values specified as the upper limit value or the lower limit value in the present specification, the upper and lower limit values of the numerical values specified for the range, the numerical values described in the [Example] column, and the numerical values shown in the attached table are arbitrary. It should be noted that a new upper / lower limit value or a new numerical value range can be set by appropriately combining these numerical values. These are common throughout this specification.

<Low heat conduction member of piston for in-cylinder internal combustion engine>
The present invention can be grasped not only as a low heat conductive alloy but also as a low heat conductive member using the low heat conductive alloy. That is, the present invention provides a fuel injection valve provided on the top of an aluminum alloy piston at the top of a piston main body that can reciprocate in a cylinder of a cylinder block of an internal combustion engine, and provided on a cylinder head on the cylinder block. Forming a low heat conduction region which is at least a part of a fuel collision region where the liquid fuel injected into the cylinder can collide and has a lower thermal conductivity than the surroundings, and is made of the low heat conduction alloy of the present invention described above. It is also a low heat conduction member of a piston for a cylinder injection type internal combustion engine which is characterized.

<Piston for in-cylinder internal combustion engine>
Moreover, this invention can be grasped | ascertained not only as a low heat conductive member but as a piston using it. That is, according to the present invention, a piston main body capable of reciprocating in a cylinder of a cylinder block of an internal combustion engine and a liquid fuel injected into the cylinder from a fuel injection valve provided in a cylinder head on the cylinder block collide with each other. A piston top made of an aluminum alloy having a low heat conduction layer or a low heat conduction member at the top of the piston main body which forms at least a part of the obtained fuel collision area and has a low heat conduction area having a lower thermal conductivity than the surroundings. A piston for a cylinder injection internal combustion engine, wherein the low heat conduction layer or the low heat conduction member is made of the low heat conduction alloy of the present invention described above.

<In-cylinder injection internal combustion engine>
Further, the present invention can be grasped not only as a piston but also as a direct injection internal combustion engine using the same. That is, the present invention provides a cylinder block having a cylinder, a cylinder head provided on the cylinder block, a fuel injection valve provided on the cylinder head, a piston main body capable of reciprocating in the cylinder, and the fuel injection A low heat conduction layer or a low heat conduction member that forms a low heat conduction area that is at least a part of a fuel collision area where liquid fuel injected from the valve into the cylinder can collide and has a lower thermal conductivity than the surroundings. An in-cylinder injection internal combustion engine comprising a piston made of an aluminum alloy piston at the top of the part, wherein the low heat conduction layer or the low heat conduction member is the low heat conduction according to claim 1 or 2. It is also a direct injection internal combustion engine made of an alloy.

<Method for producing low thermal conductive member of piston for in-cylinder internal combustion engine>
By the way, this invention can be grasped | ascertained also as a manufacturing method of the low heat conductive member suitable for manufacture of the low heat conductive member mentioned above. That is, the present invention includes a molding process in which a raw material powder filled in a cavity of a mold is pressed to form a powder compact, and a sintering process in which the powder compact is heated in a heating furnace to form a sintered compact. When the total amount of the raw material powder is 100% by mass, Mn: 5 to 35% by mass, C: 0.5 to 1.5% by mass, balance: Fe and inevitable impurities or incidental elements The low heat conductive member of the present invention described above is obtained from the sintered body. The method for producing a low heat conductive member for a piston for a cylinder injection internal combustion engine is also provided.

<Other invention>
(1) The present invention described above assumes a reciprocating engine. However, the essence of the present invention is that an Fe—Mn—C alloy having a specific composition exhibits a specific thermal conductivity and a linear expansion coefficient. Then, as long as the low heat conductive alloy of the present invention is used for a part or part that requires both of these characteristics, the effectiveness is clear.
When the present invention is considered in a high-level concept, the present invention has a Mn of 5 to 35% by mass, a C of 0.5 to 1.5% by mass, and a balance of Fe and 100% by mass. It is composed of inevitable impurities or ancillary elements, and is used for a low heat conduction part or a low heat conduction member that requires a thermal conductivity of 7 to 13 W / m · K and a linear expansion coefficient of 15 to 25 × 10 ⁻⁶ / K. It can be grasped as a characteristic low thermal conductive alloy.

  Furthermore, you may grasp | ascertain the low heat conductive alloy of this invention by adding tensile strength: 300-500 Mpa and / or elongation: 3-20% to said required characteristic. Furthermore, it has the composition, and is used for a specific part or a specific member that is required to satisfy at least two of the thermal conductivity, linear expansion coefficient, tensile strength, and elongation in the above range at the same time. It can be grasped as a low thermal conductive alloy.

When considered in this way, the low thermal conductive alloy of the present invention described above used for the low thermal conductive layer and the low thermal conductive member that forms a low thermal conductive area in the fuel collision area on the top of the piston specified the high-level conceptual application of the present invention. It can also be regarded as a subordinate conceptual invention.
(2) The use of the low thermal conductive alloy of the present invention is not limited to a reciprocating engine, and can be extended to a combustion engine including a rotary engine, an external combustion engine, etc., and more widely to a combustion apparatus including a boiler.

  Therefore, considering the present invention further, the present invention is at least a part of the fuel collision area on the aluminum alloy base material on which the liquid fuel injected from the fuel injection hole of the combustion apparatus can collide and is more thermally conductive than the surroundings. It is used for a low thermal conductive layer or a low thermal conductive member that forms a low thermal conductivity region with a low rate, and when the total is 100% by mass, Mn: 5 to 35% by mass and C: 0.5 to 1.5% by mass And the remainder: Fe and unavoidable impurities or incidental elements.

  Of course, the present invention provides at least a part of the fuel collision area on the aluminum alloy base material on which the liquid fuel injected from the fuel injection hole of the combustion apparatus can collide, and has a low thermal conductivity area having a lower thermal conductivity than the surrounding area. It can also be grasped as a low heat conductive member for a combustion device using the low heat conductive alloy for the combustion device. Furthermore, it can be grasped as a manufacturing method of the combustion apparatus itself or a low thermal conductive member for the combustion apparatus. These are the same as in the case of the cylinder injection internal combustion engine described above.

  The present invention will be described in more detail with reference to embodiments of the invention. It should be noted that the contents described in this specification including the following embodiments are applicable not only to the low thermal conductive alloy according to the present invention but also to the low thermal conductive member and the manufacturing method thereof.

  Of course, the following contents are not limited only to the in-cylinder injection internal combustion engine and the piston for the in-cylinder injection internal combustion engine of the present invention, but to the higher conceptual, intermediate conceptual, or lower conceptual invention. Needless to say, the present invention may be applied as appropriate without departing from the spirit of the invention. Furthermore, it should be noted that which embodiment is best depends on the target, required performance, and the like.

<Composition of low thermal conductive alloy>
(1) Mn
(a) Mn is an essential element important for obtaining the specific thermal conductivity and linear expansion coefficient that are the object of the present invention. In the present invention, the preferred amount of Mn is 5 to 35% by mass.
Here, the thermal conductivity of Mn alone is 7.8 W / mK, and the linear expansion coefficient is 21.6 × 10 ⁻⁶ / K. The thermal conductivity of Fe alone is 80.3 W / mK, and the linear expansion coefficient is 13.8 × 10 ⁻⁶ / K.

  However, the thermal conductivity and the linear expansion coefficient of the Fe—Mn—C alloy are not determined simply by the complex rule of the amount of constituent elements. As a result of the inventor's sincere and detailed experiments, it has been found that the thermal conductivity becomes very low even if the amount of Mn is relatively small. Conversely, it has also been found that even when the amount of Mn is relatively large, the linear expansion coefficient is far from the linear expansion coefficient of Mn alone. Based on such research results, in the present invention, the amount of Mn is set to the above range.

  When Mn is in the above range, desired thermal conductivity and linear expansion coefficient can be stably obtained. On the other hand, if Mn is too small, the thermal conductivity increases rapidly, which is not preferable. When Mn is excessive, the linear expansion coefficient is lowered and a desired linear expansion coefficient cannot be obtained. It is more preferable that Mn is 7 to 30% by mass.

  (b) According to the inventor's research, when the amount of Mn is in a more specific range within the above range, it has been revealed that the characteristics are more remarkable than before and after that. That is, it is a case where Mn is 5-18 mass% (especially when it is 5-15 mass%) or 20-30 mass%.

  First, when Mn is around 10% by mass, the thermal conductivity shows a minimum tendency and the linear expansion coefficient shows a maximum tendency even though the amount of Mn is relatively small.

  In this case, the lower limit of Mn is more preferably 7% by mass, 8% by mass, and further 9% by mass, and the upper limit of Mn is 18% by mass, 16% by mass, 14% by mass, 12% by mass, and further 11% by mass. % Is more preferable.

  Next, when Mn is 20 to 30% by mass, around 25% by mass, the tensile strength and the elongation tend to be maximized while the thermal conductivity and the linear expansion coefficient are within the desired ranges.

  In this case, the lower limit value of Mn is more preferably 22% by mass, 23% by mass, and further 24% by mass, and the upper limit value of Mn is more preferably 28% by mass, 27% by mass, and further 26% by mass.

(2) C
(a) C is also an essential element important for obtaining the specific thermal conductivity and linear expansion coefficient that are the object of the present invention. In the present invention, the preferred amount of C is 0.5 to 1.5% by mass.
According to the results of experiments conducted by the present inventors sincerely, when C is within the above range, desired thermal conductivity and linear expansion coefficient can be stably obtained. On the other hand, if C is too small, the thermal conductivity increases rapidly or the linear expansion coefficient becomes lower than the desired range, which is not preferable.

  On the other hand, as C increases, the thermal conductivity and the linear expansion coefficient are preferably close to the desired range, but when C is excessive, the tensile strength is rapidly reduced and the practicality becomes poor. Further, the elongation is not preferable because C decreases even if C is too little or too much. Based on such research results, in the present invention, the amount of C is within the above range.

  (b) According to the inventor's research, when C is around 1% by mass, the thermal conductivity and the linear expansion coefficient are stable within a desired range, and the tensile strength and elongation tend to be maximal. I understand. The reason for this tendency is not clear, but it can be considered as follows. That is, it is estimated that when C is too small, Mn oxide is generated, and when C is excessive, Fe and Mn-based carbides are generated, and tensile strength and elongation are lowered. When C is around 1% by mass, it becomes an austenite single phase and exhibits excellent tensile properties.

  In this case, the lower limit value of C is more preferably 0.7 mass%, 0.8 mass%, and further 0.9 mass%, and the upper limit value of C is 1.3 mass%, 1.2 mass%, It is more preferable in it being 1.1 mass%.

(3) The rest
(a) The main component of the balance is Fe, and Fe is an essential element that is important in obtaining the specific thermal conductivity and linear expansion coefficient that are the object of the present invention. Although the low thermal conductive alloy of the present invention is also an iron-based alloy (Fe-Mn-C alloy), the specific elements of Mn, C and Fe synergistically show characteristics far from general iron-based materials. . At least in terms of thermal conductivity and linear expansion coefficient, it exhibits excellent characteristics that cannot be considered as an iron-based alloy as described above.

  Only the surface layer of the low heat conductive alloy of the present invention can be modified as necessary by appropriately performing known carburizing treatment, nitriding treatment or the like for the low heat conductive alloy of the present invention. This purpose is not limited to the improvement of the strength of the low thermal conductive alloy, but can be used for, for example, a base treatment such as a DLC film.

  (b) The basic constituent elements of the low thermal conductive alloy of the present invention are three elements of Mn, C and Fe, but other elements (subsidiary) are within the range where desired characteristics of the low thermal conductive alloy of the present invention are obtained. There is no problem with the inclusion of the target element. Examples of such ancillary elements include Si, P, S, O, N, Cu, Ni, Cr, Mo, Nb, V, and Ti. Since the content of such ancillary elements is usually a trace amount (0.01 to 1% by mass), the ancillary element can also be called a trace element.

<Applications of low thermal conductive alloys>
(1) Low thermal conductive member or low thermal conductive layer
(a) The low thermal conductive member or the low thermal conductive layer made of the low thermal conductive alloy of the present invention has a low thermal conductive region on a base member made of a base material having a linear expansion coefficient of about 20 × 10 ⁻⁶ / K and a relatively high thermal conductivity. Used when partially forming. The form (size, thickness, film thickness, etc.) and manufacturing method of the low heat conductive member or low heat conductive layer are not limited. Moreover, as long as it is a low heat conductive member, a melting material or a sintered material may be sufficient. If a low heat conductive member is formed of a sintered material, the processing cost can be reduced by net shape, and the thermal conductivity can be increased or decreased by adjusting the porosity (density). The low thermal conductive layer is formed by, for example, thermal spraying. In any case, depending on the required specifications, the form and manufacturing method of the low heat conductive alloy can be selected as appropriate.

  (b) The low heat conduction member or the low heat conduction layer is provided in the fuel collision area at the top of the piston to form a low heat conduction area. For example, the low thermal conductive member is cast on the top of an aluminum alloy piston, and the low thermal conductive layer is formed by thermal spraying or the like on the piston top.

  The low heat conducting member or the like may have a minute uneven shape on the surface in order to promote vaporization of the liquid fuel that has come into contact, and the surface area thereof may be enlarged. In order to suppress heat transfer from the low heat conducting member or the like to the top of the piston, a heat insulating layer such as air may be partially formed at the interface between the two. In addition, when the low thermal conductive member is made of a sintered body having a high porosity, the thermal conductivity of the low thermal conductive member itself is decreased, and a minute uneven shape is formed on the surface, which facilitates fuel vaporization. .

  Of course, when the porosity is high, the vaporization of the fuel impregnated into the low heat conducting member may be hindered. In such a case, it is preferable to appropriately seal the surface of the low thermal conductive member.

(2) Expansion of usage
(a) The use of the low heat conductive alloy and the low heat conductive member or the low heat conductive layer according to the present invention is typically the above-described piston for a cylinder injection type internal combustion engine, but is not limited thereto. For example, the low thermal conductive alloy of the present invention is suitable for a member or part where one or more of thermal conductivity, linear expansion coefficient, strength and elongation are required to be in a specific range.

For example, it is a part or member having a thermal conductivity of 5 to 15 W / m · K, 7 to 13 W / m · K, 8 to 12 W / m · K, or 9 to 11 W / m · K. For example, the linear expansion coefficient of ^{15~25x10 -6 / K, 17~23x10 -6 /} K, 18~22x10 -6 / K even at sites or members such as 19~21x10 ^-6 / K. For example, it is a part or member having a tensile strength of 300 MPa to 500 MPa, 350 to 450 MPa, or 370 to 430 MPa. For example, it is a part or member having an elongation of 3 to 20%, 4 to 18%, 5 to 17%, 6 to 16%, or 8 to 14%.

  In addition, these ranges are an example which shows the required characteristic regarding uses, such as the low heat conductive member of this invention. The required characteristic is not limited to the above range, and the upper and lower limit values described can be arbitrarily combined to set a new range. Furthermore, a new required characteristic having only one of the upper limit value and the lower limit value as a boundary may be considered. For example, it is often sufficient to specify the characteristics in the case where the low thermal conductive alloy of the present invention is used such that the thermal conductivity is not more than a specific value and the tensile strength or elongation is not less than the specific value. This applies as well throughout the specification.

(b) In addition to the in-cylinder internal combustion engine piston, the following may be considered as specific applications of the low heat conductive alloy and the low heat conductive member of the present invention.
For example, it is a heat insulating material or a heat insulating member of a part forming a hot gas flow path in an internal combustion engine. Specifically, the outer peripheral portion of the intake port and the exhaust port.

<Manufacturing method of low thermal conductive member>
The manufacturing method of the low thermal conductive member of the present invention is not particularly limited. Therefore, the low thermal conductive member of the present invention may be a melted material or a sintered material. However, as a result of intensive studies by the present inventors, it has been found that when a low heat conductive member is manufactured by the sintering method of the present invention described above, the difference in the manufacturing conditions significantly affects the characteristics of the low heat conductive member. . Hereinafter, the low heat conductive member manufacturing method of the present invention will be described by being divided into a forming step and a sintering step.

(1) Molding process The molding process can be divided into a filling process in which a raw material powder is filled in a cavity of a molding die and a pressurizing process in which the filled raw material powder is pressed to form a powder compact.

  (a) As the raw material powder used in the filling step, it is possible to use atomized powder or the like that has been adjusted to a desired composition in advance. There are often. In the case of the present invention, it is conceivable that pure Fe powder, pure Mn powder, graphite powder, Fe-Mn powder, etc. are appropriately combined to form a raw material powder.

  According to the inventor's research, it has been found that the characteristics of the obtained low heat conducting member differ depending on the type of powder used. For example, when pure Fe powder, Fe-Mn powder and graphite powder are combined with pure Fe powder, pure Mn powder and graphite powder, the latter case has lower thermal conductivity, and The linear expansion coefficient tended to be closer to the desired value. The reason for this tendency is not clear, but it can be considered as follows. That is, when pure Mn powder is used, as compared with the case where Fe-Mn powder is used, as long as molding and sintering are performed under the same conditions, there is a portion where Mn is concentrated microscopically and locally. Because it exists, it is estimated that it will have a low thermal conductivity and a high coefficient of linear expansion.

  In addition, since pure Mn powder can be obtained at a lower cost than Fe—Mn powder, it is preferable to use pure Mn powder in terms of cost. Therefore, in the manufacturing method of the present invention, it is preferable that the raw material powder contains at least pure Mn powder composed of Mn and inevitable impurities. In particular, the raw material powder is more preferably composed of pure Fe powder, pure Mn, and graphite powder.

  In addition, when pure Mn powder was used, even if a sintered compact was produced under the same production conditions, the density was lowered, and the tensile strength was also lowered accordingly. However, even in this case, if re-compression / re-sintering (so-called 2P2S) is performed, it is easy to achieve high density and high strength. Moreover, the manufacturing cost increase due to the recompression and re-sintering can be sufficiently absorbed by the raw material cost reduction due to the use of pure Mn powder.

  (b) The characteristics of the obtained low heat conductive member can also be affected by the difference in molding pressure during the pressing step. However, when the molding pressure is 550 MPa or more, the linear expansion coefficient and elongation show almost stable values. Of course, as the molding pressure increases, the density and tensile strength tend to increase, but the tendency is small and the molding pressure becomes almost saturated when the molding pressure is 750 MPa or more. Similarly, the thermal conductivity is stable at a molding pressure of 550 MPa or more.

  Therefore, in the production method of the present invention, the molding pressure is preferably 550 MPa or more. The lower limit of the molding pressure is preferably 600 MPa, 700 MPa, 750 MPa or even 780 MPa. The upper limit of the molding pressure is preferably 2000 MPa, 1500 MPa, 1000 MPa, or even 850 MPa in consideration of the mold life and efficiency.

  Incidentally, it is not always easy to set the molding pressure to 800 MPa or more. Generally, when the molding pressure is increased, galling or the like occurs between the powder molded body and the inner wall surface of the molding die, and it is difficult to take out the powder molded body, the surface of the powder molded body is rough, Expensive molds can be damaged. In order to prevent this, conventionally, many internal lubricants have been mixed in the raw material powder. However, this is not preferable because a high-density sintered body cannot be obtained, and the discharged internal lubricant is carbonized to contaminate the sintering furnace.

  The present inventors have developed a mold lubrication warm pressure molding method that can perform ultra-high pressure molding without using such an internal lubricant, and have already obtained a patent (see Japanese Patent No. 3309970). ). By using this mold lubrication warm pressure molding method, it is possible to obtain a powder molded body and a sintered body molded with a wide range of molding pressures. In addition, according to this mold lubrication warm pressure molding method, it is not necessary to use an internal lubricant, so the density of the powder compact is easily reflected in the density of the sintered compact as it is, and the raw material cost and manufacturing cost can be reduced. Is possible.

  Even when the molding pressure is lowered, the linear expansion coefficient and the thermal conductivity of the obtained sintered body show almost stable values. For this reason, if it is a site | part and member in which high intensity | strength and high elongation are not requested | required, the sintered compact manufactured with comparatively low molding pressure can also be used. When the molding pressure is lowered, the density of the powder compact is usually lowered and the porosity of the sintered compact is increased, so that it is possible to obtain a low thermal conductivity member having a lower thermal conductivity. Thereby, the required characteristics of the low thermal conductive member of the present invention, and its application can be further expanded.

(2) Sintering process A sintering process is a process of heating the powder compact obtained after the forming process in a heating furnace (sintering furnace) to form a sintered body. In the sintering process, sintering conditions such as a sintering atmosphere, a sintering temperature, and a sintering time are important. It has been clarified by the inventor's sincere research that these differences in sintering conditions affect the characteristics of the low thermal conductive member of the present invention. Hereinafter, these sintering conditions will be sequentially described.

  (a) Sintering atmosphere

  The sintering atmosphere is usually performed in an antioxidant atmosphere. The oxidation prevention atmosphere is an inert gas atmosphere, a nitrogen atmosphere, a vacuum atmosphere, or the like. According to the inventor's research, it has been clarified that the difference in the sintering atmosphere affects the thermal conductivity and the linear expansion coefficient. In particular, it has also been clarified that the degree of the characteristic fluctuation of the low thermal conductive member generated according to the amount of Mn varies depending on the sintering atmosphere to be selected.

For example, a nitrogen (N ₂ ) atmosphere tends to be lower in thermal conductivity than an inert gas (Ar) atmosphere, and the linear expansion coefficient tends to be closer to a desired value (20 × 10 ⁻⁶ / K). . Also, the tensile strength tended to be higher in the nitrogen atmosphere than in the inert gas atmosphere. The reason for this tendency is not clear, but it can be considered as follows. That is, phonons are hindered by the stabilization of the austenite phase and the interstitial solid solution of N. The improvement in tensile strength is thought to be due to the solid solution strengthening of N.

Accordingly, in view of these characteristics and manufacturing costs, the sintering atmosphere in the sintering process is preferably a nitrogen (N ₂ ) atmosphere. When the sintering atmosphere is a nitrogen atmosphere, if Mn is in the vicinity of 10 to 25% by mass, 10 to 20% by mass, 11 to 17% by mass, or even 12 to 15% by mass, the thermal conductivity tends to be minimal. The linear expansion coefficient may show a maximum tendency.

  On the other hand, in terms of elongation, the inert gas atmosphere tends to be higher than the nitrogen atmosphere. The reason for such a tendency is not clear at present, but it is thought that a small amount of deposited nitride or carbonitride is the starting point of fracture and the elongation decreases.

  Therefore, if attention is paid to the elongation of the low thermal conductive member, the sintering atmosphere in the sintering step is preferably an inert gas atmosphere, particularly an Ar atmosphere. And when sintering atmosphere is inert gas atmosphere, if Mn is 15-35 mass%, 20-30 mass%, further 23-27 mass%, and if it is 24 to 26 mass% vicinity, elongation of a low heat conductive member will be carried out. Indicates a maximal trend.

(b) Sintering temperature It was found that the characteristics of the low heat conducting member are also affected by the difference in sintering temperature. That is, the higher the sintering temperature, the lower the thermal conductivity, and the linear expansion coefficient tends to be closer to the desired value (20 × 10 ⁻⁶ / K).

  The reason for this tendency is not clear at present, but it is considered that the higher the sintering temperature, the more the diffusion is promoted and the uniform austenite phase is obtained.

  Moreover, the tensile strength and elongation tended to increase as the sintering temperature increased. However, if the sintering temperature is too low, the tensile strength and elongation decrease rapidly and the practicality becomes poor. On the other hand, if the sintering temperature is excessively high, the manufacturing cost increases and the shape is liable to change. Therefore, the sintering temperature in the sintering step is preferably 1100 to 1300 ° C, more preferably 1150 to 1300 ° C.

  Here, when the present inventor earnestly experimented when the powder compact of Fe-25% Mn-1% C was sintered in Ar (that is, when “elongation” showed a maximum tendency), It was found that the density decreased, and the tensile strength and elongation showed a remarkable maximum tendency when the kneading temperature was around 1200 to 1300 ° C.

  The reason for this tendency is not clear, but it can be considered as follows. That is, if the sintering temperature is too high, liquid phase sintering occurs, and the structure becomes a coarse solidified structure, which is accompanied by segregation and solidification defects (minute voids), resulting in a decrease in density and tensile properties.

  Therefore, it is preferable that the sintering temperature in the sintering step is 1200 to 1300 ° C, further 1220 to 1280 ° C.

(b) Sintering time It was found that the difference in the sintering time does not significantly affect the thermal conductivity, linear expansion coefficient, tensile strength, density, etc. of the low thermal conductive member made of a sintered body. This tendency was not significantly affected by changes in the composition of the raw material powder. On the other hand, the elongation tended to increase as the sintering time increased.

  The reason for this tendency is not clear, but it can be considered as follows. That is, it is considered that when the sintering time is short, the formed pores are not rounded and easily become a starting point of fracture. On the other hand, if the sintering time is long, the formed pores are rounded and are unlikely to become the starting point of destruction.

  However, even when the sintering time was as short as 10 minutes or less, the elongation was practically sufficient. Further, even when the sintering time was longer than 120 minutes, no increase in elongation was observed, and the sample was almost saturated. Accordingly, the sintering time in the sintering process is preferably 120 minutes or less. From the viewpoint of shortening the manufacturing cycle time and securing the elongation, the sintering time is more preferably 10 to 120 minutes, and further preferably 30 to 90 minutes.

The present invention will be described more specifically with reference to examples.
<In-cylinder injection internal combustion engine>
FIG. 9 shows a direct injection spark ignition engine 1 (hereinafter simply referred to as “engine 1”) using gasoline as fuel, which is an example of the direct injection internal combustion engine of the present invention.

  The engine 1 is fitted in a cylinder block 30, a cylinder head 40 fixed on the cylinder block 30 with a head bolt (not shown) via a gasket (not shown), and a cylinder 31 of the cylinder block 30 so as to be able to reciprocate. It consists of the inserted piston 10.

The cylinder block 30, the cylinder head 40, and the piston 10 are made of an aluminum alloy. The aluminum alloy of the piston 10 is an AC8A alloy (JIS standard) having a thermal conductivity of 134 W / mK (room temperature) and a linear expansion coefficient of 20.9 × 10 ⁻⁶ / K (room temperature to 200 ° C.). The cylinder 31 of the cylinder block 30 is formed of a press-fit cast iron sleeve.

  The cylinder head 40 includes an intake port 41 and an exhaust port 42. The opening of the intake port 41 is opened and closed by an umbrella portion of an intake valve 71 driven by an intake side cam (not shown). The opening of the exhaust port 42 is opened and closed by an umbrella portion of an exhaust valve 72 driven by an exhaust side cam (not shown). A spark plug 80 is disposed substantially at the center between the intake valve 71 and the exhaust valve 72. Further, an injector 50 as a fuel injection valve is disposed on the intake port 41 side, and gasoline (liquid fuel) pressurized to a predetermined pressure is sprayed into the cylinder 31 from the opening 51 of the injector 50.

  A piston 10 that is a piston for a cylinder injection internal combustion engine includes a piston top 11 and a piston body 12. The piston 10 is swingably connected to the connecting rod 61 via a piston pin 61 fitted in a pin hole 113 provided in the piston body 12.

  The piston top 11 on the upper side of the piston 10 includes a top ring 112a, a second ring 112b, and an oil ring 112c on the outer peripheral side. A deep dish portion 111 is formed on the top surface side of the piston top portion 11. The gasoline is sprayed from the injector 50 toward the deep dish portion 111. The inner wall surface (particularly, the inner bottom surface) of the deep dish portion 111 forms the fuel collision area referred to in the present invention.

  Gasoline sprayed near the top dead center such as during ultra lean combustion is collected around the spark plug 80 by the deep dish portion 111. As a result, even if the air-fuel ratio is high, an air-fuel mixture having a concentration capable of ignition is formed around the spark plug 80. When a spark discharge is generated between the spark plug 80 gaps, stratified combustion occurs in the combustion chamber formed between the cylinder head 40 and the piston top 11. Of course, at high load, gasoline is sprayed from the injector 50 during the intake stroke in which the piston 10 descends, and uniform mixed combustion is performed in the stoichiometric region or the rich region.

  By the way, in the engine 1 of the present embodiment, the piston 10 in which the low heat conductive member 20 is cast into the deep dish portion 111 of the piston top portion 11 is used. The surface portion 21 of the low heat conducting member 20 corresponds to the low heat conducting region referred to in the present invention. As is clear from FIG. 9, the surface portion 21 of the low heat conducting member 20 forms only a part of the inner wall of the deep dish portion 111 instead of the entire inner wall. That is, it is limited to a portion where gasoline sprayed from the injector 50 can mainly collide or adhere. This promotes vaporization of the sprayed gasoline, while avoiding the formation of heat spots that cause knocking and the like.

<Manufacturing method of low thermal conductive member>
(1) Raw material powder The sintered compact which consists of a low heat conductive alloy used for the low heat conductive member 20 was manufactured as follows.
In order to mix and mix the raw material powder, pure Fe powder, graphite powder, pure Mn powder and Fe—Mn alloy powder (composition: Fe-50 mass% Mn) were prepared. The pure Mn powder is obtained by mechanically pulverizing a Mn lump to a particle size of 150 μm or less. The Fe—Mn alloy powder is a gas atomized powder and is classified to a particle size of 150 μm or less. These powders were blended into the component compositions shown in Tables 1 to 8 and uniformly mixed with a rotary mixer to obtain raw material powder for each test piece.

(2) Molding process
(a) First, a cemented carbide die (molding die) having the following three cavities was prepared. The inner wall surface of the cavity was previously subjected to TiN coating treatment, and the surface roughness was set to 0.4Z.

(i) Disc type test piece: diameter 23 mm x height 5 mm,
(ii) Flat plate test piece: parallel part 16 mm × 5 mm × 3 mm,
(iii) rectangular parallelepiped test piece: 30 mm × 30 mm × 5 mm

(b) The molding step was performed by the following mold lubrication warm pressure molding method.
Each of the molds was previously heated to 150 ° C. with a band heater. An aqueous solution in which lithium stearate (higher fatty acid-based lubricant) was dispersed was uniformly applied to the inner wall surface of the heated mold with a spray gun at a rate of about 1 cm ³ / second (application process).

Incidentally, the aqueous solution is obtained by adding a surfactant and an antifoaming agent to water. As the surfactant, polyoxyethylene nonylphenyl ether (EO) 6, (EO) 10 and borate ester Emulbon T-80 were added in an amount of 1% by volume based on the entire aqueous solution (100% by volume). . An antifoaming agent was added by 0.2% by volume to the entire aqueous solution (100% by volume) using FS Antifoam 80. The lithium stearate having a melting point of about 225 ° C. and an average particle size of 20 μm was used. The dispersion amount was 25 g with respect to 100 cm ^{3 of the} aqueous solution.

  Furthermore, this was refined by a ball mill type pulverizer (Teflon coated steel balls: 100 hours). The obtained stock solution was diluted 20 times to obtain a 1% aqueous solution having a final concentration. This aqueous solution was subjected to the aforementioned coating process.

  Various raw material powders were naturally filled in a mold in which this aqueous solution was applied to the inner wall surface (filling step). If the size of the test piece is large, the raw material powder may be heated at the same temperature as the mold.

  While holding the mold at 150 ° C., the raw material powder in the cavity was warm-pressed at the molding pressure shown in Tables 1 to 8 to obtain various powder compacts (molding process). In this molding, no galling or the like occurred between the mold and the powder molded body, and the powder molded body could be taken out from the mold with a low pressure.

(3) Sintering step Each obtained powder compact is sintered under the sintering conditions (sintering atmosphere, sintering temperature, sintering time) shown in Tables 1 to 8, and each of the sintered compacts. A specimen was obtained. The sintering atmosphere was 1 atm Ar or N2.

<Measurement of each specimen>
The following properties were measured using the obtained test pieces.
(i) The disk-shaped test piece was used for density measurement. The diameter and height were re-measured to determine the volume, and the weight was measured to determine the density.
(ii) Tensile strength and elongation were determined by conducting a tensile test according to JIS Z2241 using the flat plate test piece.
(iii) The thermal conductivity and the linear expansion coefficient were determined using test pieces appropriately cut out from the rectangular parallelepiped type test pieces. That is, the thermal conductivity was determined as the thermal conductivity at 50 ° C. according to JIS A1412-2. Moreover, the linear expansion coefficient calculated | required the average linear expansion coefficient to 20-200 degreeC according to JISZ2285.

<Evaluation>
(1) Effect of Mn content
(a) The influence of the amount of Mn on the characteristics of the low thermal conductive member (low thermal conductive alloy) is summarized in Table 1. Each characteristic with respect to the amount of Mn is shown in FIG. 1A. In order to clarify the influence of the amount of Mn on both the thermal conductivity (κ) and the linear expansion coefficient (α), the thermal characteristic index: 1 / κ (α _Al -Α) was calculated. The change in the thermal characteristic index with respect to the amount of Mn is shown in FIG. 1B.

(b) As is clear from FIGS. 1A and 1B, the thermal conductivity is low in the range of Mn: 5 to 35% by mass, and the linear expansion coefficient is sufficiently close to the linear expansion coefficient of the aluminum alloy: 20 × 10 ⁻⁶ / K. I understand that you are doing. In addition, it is understood that practical strength and elongation are secured within the range.

(c) Of these, especially in the vicinity of Mn: 15% by mass, the thermal conductivity, linear expansion coefficient and thermal characteristic index showed peak values. Further, in the vicinity of Mn: 25% by mass, the tensile strength and elongation showed peak values, and the thermal conductivity and the linear expansion coefficient were also within the desired ranges.
Therefore, when the thermal conductivity is kept as low as possible and the linear expansion coefficient is desired to be as close as possible to the linear expansion coefficient of the aluminum alloy: 20 × 10 ⁻⁶ / K, it can be said that Mn: 5 to 15% by mass is preferable. . Here, if strength and elongation are further taken into account, Mn: 10 to 15% by mass is preferable.

  On the other hand, when not only thermal conductivity and linear expansion coefficient but also high strength and high elongation are required, it can be said that Mn is 15 to 35% by mass, particularly 20 to 30% by mass.

(2) Effect of C content
(a) Table 2 summarizes the influence of the amount of C on the characteristics of the low thermal conductive member (low thermal conductive alloy). Each characteristic with respect to the amount of C is shown in FIG.

  (b) As apparent from FIG. 2, the thermal conductivity and the linear expansion coefficient were stable within the desired range in the range of C: 0.5 to 1.5% by mass. It also showed a favorable tendency that the thermal conductivity decreased with an increase in the amount of C and the linear expansion coefficient approached the linear expansion coefficient of the aluminum alloy.

(c) Among these, in particular, the tensile strength and elongation showed peak values in the vicinity of C: 1% by mass. This tendency is conspicuous when Mn is 25% by mass where the tensile strength and elongation reach a peak, but the same tendency is observed even when M is 15% by mass.
Therefore, it can be said that C is preferably 0.5 to 1.5 mass%, more preferably 0.7 to 1.3 mass%.

(3) Influence of sintering temperature
(a) The influence of the sintering temperature on the characteristics of the low thermal conductive member (low thermal conductive alloy) is summarized in Table 3. Each characteristic with respect to the sintering temperature is shown in FIG. The composition of the test piece used is Fe-25% Mn-1% C (unit: mass%).

  (b) As is clear from FIG. 3, the thermal conductivity and the linear expansion coefficient are stable within a desired range at a sintering temperature of 1100 ° C. or higher. It also shows a favorable tendency that the thermal conductivity decreases with increasing sintering temperature and the linear expansion coefficient approaches the linear expansion coefficient of the aluminum alloy.

  (c) Of these, the tensile strength and elongation peaked at a sintering temperature of about 1250 ° C. The increase in elongation is particularly remarkable, and the elongation (17%) at 1250 ° C. is more than four times the elongation (4%) at 1150 ° C. Therefore, it can be said that the sintering temperature is preferably 1150 to 1300 ° C. in consideration of practical elongation and manufacturing cost.

(4) Influence of sintering atmosphere
(a) The influence of the sintering atmosphere on the characteristics of the low thermal conductive member (low thermal conductive alloy) is summarized in Table 4. Each characteristic with respect to the sintering atmosphere is shown in FIGS. 4A and 4B. FIG. 4B shows the above-described thermal characteristic index. The composition of the test piece used is Fe-x% Mn-1% C (unit: mass%).

  (b) As is clear from FIGS. 4A and 4B, the thermal conductivity, the linear expansion coefficient, and the tensile strength are better in the nitrogen atmosphere than in the Ar atmosphere. The thermal characteristic index showed a peak in a nitrogen atmosphere when Mn was 12.5% by mass. Therefore, the nitrogen atmosphere is preferable to the sintering atmosphere rather than the inert gas (Ar) atmosphere. Moreover, in a nitrogen atmosphere, Mn: 10 to 20% by mass and further 10 to 15% by mass is preferable.

  (c) However, even in an Ar atmosphere, the thermal conductivity, linear expansion coefficient, and tensile strength were within the desired ranges. In addition, with regard to elongation, a peak prominent when Mn was 25% by mass in the Ar atmosphere than in the nitrogen atmosphere.

(5) Influence of sintering atmosphere and sintering temperature
(a) The influence of the sintering atmosphere and the sintering temperature on the characteristics of the low thermal conductive member (low thermal conductive alloy) is summarized in Table 5. FIG. 5A shows each characteristic in a nitrogen atmosphere, and FIG. 5B shows each characteristic in an Ar atmosphere. In both cases, ● represents a case where the sintering temperature is 1150 ° C., and ○ represents a case where the sintering temperature is 1250 ° C. The composition of the test piece used is Fe-x% Mn-1% C (unit: mass%).

  (b) As is clear from FIGS. 5A and 5B, it can be seen that in any atmosphere, the elongation is drastically reduced when the sintering temperature is low. Here, when the sintering temperature is 1150 ° C. and the elongation tends to peak, Mn: 25% by mass, the elongation is at most about 2% in the nitrogen atmosphere, whereas in the Ar atmosphere, The growth is 4%. Then, when the sintering temperature is low, it can be said that the Ar atmosphere is preferable to the nitrogen atmosphere at least with respect to elongation.

  However, as a whole, the nitrogen atmosphere is preferable to the Ar atmosphere as described above. Further, it can be said that the sintering temperature is more preferably 1250 ° C., which is a relatively high temperature.

(6) Influence of raw material powder
Table 6 summarizes the influence of the difference in the constituent powder of the raw material powder on the characteristics of the low thermal conductive member (low thermal conductive alloy). FIG. 6A and FIG. 6B show the influence on the characteristics due to the difference in the constituent powder. FIG. 6B shows the above-described thermal characteristic index. The composition of the test piece used is Fe-15% Mn-1% C and Fe-25% Mn-1% C (unit: mass%). Contrast constituent powders are Fe-50 mass% Mn alloy powder and pure Mn powder.

  (b) As is clear from FIGS. 6A and 6B, the thermal conductivity is lower when pure Mn powder is used than when Fe-Mn alloy powder is used, and the linear expansion coefficient is closer to the linear expansion coefficient of the aluminum alloy. . As a result, the thermal characteristic index shows a superior value when pure Mn powder is used.

  On the other hand, as apparent from the case of Mn: 25% by mass, with respect to tensile strength and elongation, it is preferable to use Fe—Mn alloy powder rather than pure Mn powder.

  However, even when pure Mn powder is used, practically sufficient strength and elongation are obtained, and it is preferable to use pure Mn powder in consideration of raw material costs as well as thermal conductivity and linear expansion coefficient.

  (c) When pure Mn powder is used, the density of the low thermal conductive member tends to decrease. However, the density can be increased by performing recompression and / or re-sintering as required. Each characteristic when recompressing and re-sintering is performed on a low thermal conductive member using pure Mn powder is shown in FIG. 6C. Thereby, even if recompression etc. are performed, it is clear that thermal conductivity and a linear expansion coefficient hardly change, and a density improves markedly with recompression pressure. The re-sintering was performed under a nitrogen atmosphere, a sintering temperature of 1250 ° C., and a sintering time of 30 minutes.

(7) Influence of molding pressure
Table 7 summarizes the influence of the molding pressure on the characteristics of the low thermal conductive member (low thermal conductive alloy). In addition, FIG. 7 shows changes in characteristics with respect to the molding pressure in both cases where the raw material powder was prepared with an alloy powder of Fe-50 mass% Mn and the raw material powder was prepared with pure Mn powder. The composition of the test piece used here is Fe-25% Mn-1% C (unit: mass%).

  (b) As apparent from FIG. 7, the density and the tensile strength increase as the molding pressure increases. However, when the molding pressure is 588 MPa or more, further 784 MPa or more, they are almost saturated. Further, when the molding pressure was 588 MPa or more, further 784 MPa or more, the linear expansion coefficient and elongation were hardly changed and stable within a desired range. These tendencies were almost the same regardless of the type of raw material powder.

Therefore, it can be said that the molding pressure is preferably 550 MPa or more, more preferably 750 MPa or more, regardless of the type of raw material powder.
(8) Influence of sintering time

  Table 8 summarizes the influence of the sintering time on the characteristics of the low thermal conductive member (low thermal conductive alloy). In addition, FIG. 8 shows changes in the characteristics with respect to the molding pressure for both the case where the raw material powder was prepared with an alloy powder of Fe-50 mass% Mn and the case where the raw material powder was prepared with pure Mn powder. The composition of the test piece used here is Fe-25% Mn-1% C (unit: mass%).

  (b) As is clear from FIG. 8, it can be said that the influence of the sintering time on the density, thermal conductivity, linear expansion coefficient and tensile strength is small regardless of the type of raw material powder. However, the elongation increases rapidly from the time when the sintering time is 30 minutes or more, and is saturated in about 120 minutes.

  Therefore, considering the production cycle time and the like, the sintering time is preferably 30 to 120 minutes. However, even if the sintering time is only 5 minutes, the elongation is around 10%, and the thermal conductivity, linear expansion coefficient and tensile strength are within the desired ranges, so the sintering time can be made relatively short. I understand that it is possible.

It is a graph which shows the influence which the amount of Mn has on the various characteristics of a low heat conductive alloy. It is a graph which shows the relationship between the amount of Mn, and a thermal characteristic index. It is a graph which shows the influence which C amount has on the various characteristics of a low heat conductive alloy. It is a graph which shows the influence which sintering temperature has on the various characteristics of a low heat conductive alloy. It is a graph which shows the influence which the amount of Mn has on the various characteristics of a low heat conductive alloy by the difference in sintering atmosphere. It is a graph which shows the relationship between sintering atmosphere and a thermal characteristic index | exponent. It is a graph which shows the influence which the amount of Mn exerts on the various characteristics of a low heat conductive alloy by the difference in the sintering temperature in nitrogen atmosphere. It is a graph which shows the influence which the amount of Mn exerts on the various characteristics of a low heat conductive alloy by the difference in the sintering temperature in argon atmosphere. It is a graph which shows the influence which the difference in the kind of raw material powder has on the various characteristics of a low heat conductive alloy. It is a graph which shows the relationship between the difference in the kind of raw material powder, and a thermal characteristic index | exponent. It is a graph which shows the relationship between the recompression pressure when a test piece (Fe-25% Mn-1% C) using pure Mn powder is recompressed and re-sintered, and various characteristics. It is a graph which shows the relationship between the forming pressure and the various characteristics of a low heat conductive alloy by the difference in raw material powder. It is a graph which shows the relationship between the sintering time and the various characteristics of a low heat conductive alloy by the difference in raw material powder. 1 is a partial cross-sectional view showing an embodiment of a direct injection internal combustion engine of the present invention.

Explanation of symbols

1 In-cylinder injection spark ignition engine (in-cylinder injection internal combustion engine)
DESCRIPTION OF SYMBOLS 10 Piston 11 Piston top part 12 Piston main-body part 111 Fuel collision area 20 Low heat conduction member 21 Low heat conduction area 30 Cylinder block 31 Cylinder 40 Cylinder head 50 Injector (fuel injection valve)

Claims (12)

It is provided at the top of an aluminum alloy piston at the top of a piston main body that can reciprocate in a cylinder block of an internal combustion engine, and is injected into the cylinder from a fuel injection valve provided at a cylinder head on the cylinder block. Used for a low thermal conduction layer or a low thermal conduction member that forms a low thermal conduction area that is at least part of a fuel collision area where liquid fuel can collide and has a lower thermal conductivity than the surroundings,
When the total is 100% by mass,
Manganese (Mn): 5 to 35% by mass;
Carbon (C): 0.5 to 1.5% by mass;
Balance: iron (Fe) and inevitable impurities or incidental elements;
A low heat conductive alloy for a piston for a cylinder injection type internal combustion engine.   The low thermal conductivity alloy for a piston for a direct injection internal combustion engine according to claim 1, wherein the Mn is 5 to 15 mass% or 20 to 30 mass%. It is provided at the top of an aluminum alloy piston at the top of a piston main body that can reciprocate in a cylinder block of an internal combustion engine, and is injected into the cylinder from a fuel injection valve provided at a cylinder head on the cylinder block. Forming a low thermal conductivity region that is at least part of the fuel collision area where liquid fuel can collide and has a lower thermal conductivity than the surroundings,
A low heat conduction member for a piston for a cylinder injection internal combustion engine, comprising the low heat conduction alloy according to claim 1. A piston main body capable of reciprocating in a cylinder of a cylinder block of an internal combustion engine;
A low heat conduction region is formed which is at least a part of a fuel collision region where liquid fuel injected into the cylinder from a fuel injection valve provided on a cylinder head on the cylinder block can collide and has a lower thermal conductivity than the surroundings. A piston for an in-cylinder internal combustion engine comprising a piston top made of an aluminum alloy having a low heat conduction layer or a low heat conduction member on the top of the piston main body,
The in-cylinder internal combustion engine piston according to claim 1, wherein the low heat conductive layer or the low heat conductive member is made of the low heat conductive alloy according to claim 1. A cylinder block having a cylinder;
A cylinder head provided on the cylinder block;
A fuel injection valve provided in the cylinder head;
Low thermal conductivity that is at least part of a fuel collision area where liquid fuel injected from the fuel injection valve into the cylinder can collide with the piston main body that can reciprocate in the cylinder and has lower thermal conductivity than the surroundings. A piston comprising an aluminum alloy piston top having a low heat conduction layer or a low heat conduction member forming a region at the top of the piston body, and a cylinder injection internal combustion engine comprising:
The in-cylinder injection internal combustion engine, wherein the low thermal conductive layer or the low thermal conductive member is made of the low thermal conductive alloy according to claim 1 or 2. A molding process in which the raw material powder filled in the cavity of the mold is pressed to form a powder compact; and
It comprises a sintering step in which the powder compact is heated in a heating furnace to form a sintered body,
When the raw material powder is 100% by mass as a whole,
Mn: 5 to 35% by mass,
C: 0.5 to 1.5 mass%,
The balance: Fe and inevitable impurities or incidental elements,
The method for producing a low heat conductive member for a piston for a cylinder injection internal combustion engine, wherein the low heat conductive member according to claim 3 is obtained from the sintered body.   The method for manufacturing a low heat conductive member for a piston for a direct injection internal combustion engine according to claim 6, wherein the raw material powder includes at least pure Mn powder composed of Mn and inevitable impurities.   The method for producing a low heat conductive member for a piston for a cylinder injection internal combustion engine according to claim 6, wherein the molding step has a molding pressure of 550 MPa or more.   The method for producing a low thermal conductive member for a piston for a cylinder injection internal combustion engine according to claim 6, wherein the sintering step has a sintering temperature of 1100 to 1300 ° C.   The method for producing a low heat conductive member for a piston for a cylinder injection internal combustion engine according to claim 6, wherein the sintering step is a nitrogen atmosphere.   The method for producing a low thermal conductivity member for a piston for an in-cylinder injection internal combustion engine according to claim 6, wherein the sintering step is an inert gas atmosphere.   The method for manufacturing a low heat conduction member for a piston for a cylinder injection internal combustion engine according to claim 6, wherein the sintering step has a sintering time of 120 minutes or less.

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