JP2019044735A - Piston of internal combustion engine, film thickness measurement method for piston of internal combustion engine, and manufacturing method for piston of internal combustion engine - Google Patents

Abstract

To provide a piston of an internal combustion engine where a film having thermal properties different from those of a piston body part is provided on a crestal plane on a combustion chamber side, and which can easily measure a thickness of a film.SOLUTION: A piston comprises a piston body part and a film. The film has a film body part and a recess part for film thickness measurement. The recess part for film thickness measurement is opened toward a combustion chamber, and has a bottom part, an opening edge part, and a peripheral wall part between the bottom part and the opening edge part. At least a part of the opening edge part and peripheral wall part is composed of the film body part. The bottom part has a reference surface for film thickness measurement in at least a part of which the film body part does not exist.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piston for an internal combustion engine.

  2. Description of the Related Art Conventionally, a piston for an internal combustion engine having a film having a thermal property different from that of a piston main body on the combustion chamber is known (for example, Patent Document 1).

JP 2015-2222060 A

  With a conventional piston, it was not easy to measure the thickness of the membrane.

  In the piston of the internal combustion engine according to the embodiment of the present invention, preferably, the membrane has a membrane main body portion and a thickness measurement concave portion. The film thickness measurement recess is open toward the combustion chamber and has a bottom, an opening edge, and a peripheral wall between the bottom and the opening edge. At least a part of the opening edge portion and the peripheral wall portion is formed of a membrane main body portion. The bottom portion has a film thickness measurement reference surface in which at least a part of the film main body does not exist.

  The thickness of the film can be easily measured using the reference surface for film thickness measurement.

FIG. 3 is a perspective view of the piston according to the first embodiment viewed from the crown surface side. FIG. 3 shows a cross section of the piston of the first embodiment cut along a plane including the axis of the piston (and the axis of the film thickness measuring recess). FIG. FIG. 3 schematically shows a cross section of a film portion including a film thickness measurement recess according to the first embodiment. FIG. 2 is a perspective view similar to FIG. 1 of a prototype of a piston main body formed in the casting process of the first embodiment. FIG. 5 is a cross-sectional view similar to FIG. 2 of the prototype of the piston main body portion of FIG. FIG. 2 is a perspective view similar to FIG. 1 of a prototype of a piston on which a sintered material is installed in the sintered body forming step of the first embodiment. FIG. 7 is a cross-sectional view similar to FIG. 2 of the prototype of the piston of FIG. The sintering process of the first embodiment is schematically shown using a cross section of a prototype of a piston. FIG. 2 is a perspective view similar to FIG. 1 of a prototype of a piston formed in the sintering process of the first embodiment. FIG. 10 is a cross-sectional view similar to FIG. 2 of the prototype of the piston of FIG. FIG. 6 is a perspective view similar to FIG. 1 of a piston according to a third embodiment. FIG. 6 is a cross-sectional view similar to FIG. 2 of a piston according to a third embodiment. FIG. 9 is a perspective view similar to FIG. 1 of a piston according to a fourth embodiment. FIG. 10 is a cross-sectional view similar to FIG. 2 of a piston according to a fourth embodiment. FIG. 10 is a schematic cross-sectional view similar to FIG. 3 of a fifth embodiment.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[First embodiment]
First, the configuration will be described. The piston 1 of this embodiment is accommodated in a cylinder of an internal combustion engine (engine) so as to be able to reciprocate. The engine is a 4-stroke gasoline engine. As shown in FIGS. 1 and 2, the piston 1 has a piston body 2 and a membrane 3. Each part of the piston main body 2 is integrally formed of an aluminum alloy (for example, Al-Si AC8A) as a material (raw material). The main material of the piston main body 2 may be iron or the like. The piston 1 (piston body 2) has a bottomed cylindrical shape, and includes a piston head 4, a piston pin boss (apron) 5, and a skirt (piston skirt) 6. The piston main body 2 is formed using an aluminum alloy as a material (raw material) for weight reduction or the like. Hereinafter, the direction in which the piston 1 moves inside the cylinder is referred to as the axial direction. In the axial direction, the piston head 4 side with respect to the piston pin boss part 5 and the skirt part 6 is called one side, and the opposite side is called the other side.

  The piston head 4 has a crown portion 40 and a land portion 41. The crown portion 40 is on one side in the axial direction of the piston head 4 and has a crown surface (top surface) 400. The crown surface 400 is on the one side in the axial direction of the crown portion 40, has a planar shape extending perpendicularly to the axial direction, and has a substantially circular outline when viewed from one side in the axial direction. The straight line extending in the axial direction through the center of the crown surface 400 is hereinafter referred to as the axis 10 of the piston 1. The crown surface 400 defines a combustion chamber with the cylinder head. The crown surface 400 is the surface of the piston head 4 on the combustion chamber side (the side facing the combustion chamber), and is directly exposed to the combustion gas inside the combustion chamber. The crown 40 has a recess 401. The recess 401 has a bottomed cylindrical shape (shallow dish shape whose bottom is a flat surface) that opens on one axial side of the crown 40, and includes a bottom 402, an opening edge, and a peripheral wall 403. The bottom 402 has a planar shape that extends perpendicular to the axial direction (substantially parallel to a plane perpendicular to the axis 10), and has a substantially circular outline when viewed from one side in the axial direction. The peripheral wall portion 403 extends in the axial direction between the bottom portion 402 and the opening edge portion. The recess 401 is in the approximate center of the crown 40. The axis of the recess 401 substantially coincides with the axis 10 of the piston 1 (within manufacturing error).

  The land portion 41 extends from the outer peripheral side of the crown portion 40 to the other side in the axial direction. On the outer periphery of the land portion 41, there are three annular piston ring grooves 410. A piston ring is installed in each groove 410. Inside the land portion 41 is an annular passage 411. The passage 411 extends in the circumferential direction of the piston 1 and overlaps the outer peripheral side of the recess 401 when viewed from the axial direction. The passage 411 overlaps at least a part of the region in which each groove 410 is formed in the axial direction (viewed from a direction orthogonal to the axis 10). In the passage 411, for example, oil injected from an oil jet flows. The piston head 4 (land portion 41) can be cooled by this oil flow.

  The piston pin boss portion 5 and the skirt portion 6 extend from the piston head 4 (land portion 41) to the other side in the axial direction, and are on the opposite side of the combustion chamber with respect to the piston head 4. The inner peripheral side of the skirt portion 6 and the piston pin boss portion 5 is hollow. A pair of piston pin bosses 5 is provided on both sides in the radial direction with respect to the axis 10 of the piston 1. Each piston pin boss portion 5 has a pin boss 50. Each pin boss 50 has a piston pin hole 51. The piston pin hole 51 extends through the pin boss 50 in the radial direction of the piston 1. In each piston pin hole 51, the end of the piston pin is inserted and fitted. The piston 1 is connected to the small end of the connecting rod via a piston pin. The large end of the connecting rod is connected to the crankshaft. A pair of skirt portions 6 are provided on both sides of the piston 1 in the radial direction. The skirt portion 6 is sandwiched between the piston pin boss portions 5 and 5 in the direction around the axis 10 (circumferential direction). Both sides of the skirt 6 in the circumferential direction are connected to the piston pin boss 5. The skirt portion 6 slides against the inner wall of the cylinder.

  The membrane 3 is a structure for reducing the thermal conductivity from the combustion chamber to the piston body 2. The film 3 is accommodated in the recess 401. The recess 401 functions as a film holding unit. One axial side of the membrane 3 faces the combustion chamber as part of the crown surface 400. The other axial side of the film 3 is in contact with the bottom 402 of the recess 401. The outer periphery of the film 3 is in contact with the peripheral wall 403 of the recess 401. The thickness of the film 3 (depth of the recess 401) is, for example, 0.1 to 0.2 mm. The film 3 has a film body 30 and a recess (film thickness measurement recess) 31.

  As shown in FIG. 3, the membrane main body 30 includes a binder 300 and hollow particles 301. The binder 300 is a metal and includes aluminum. Aluminum may be pure aluminum or an aluminum alloy. The hollow particle 301 is a material (low thermal conductivity material) having a lower thermal conductivity than the metal of the piston body 2. The hollow particle 301 has a spherical outer shell formed of metal or ceramics, and its maximum outer dimension is, for example, several tens of μm. There is a void inside the outer shell. For example, titanium, a titanium alloy, stainless steel, or the like can be used as a metal that is a material of the outer shell. For example, alumina, silica, a composite material of alumina and silica, or the like can be used as the ceramic material for the outer shell. A plurality of hollow particles 301 are dispersed inside the membrane body 30. Two or more kinds of hollow particles having different average particle diameters may be used. The film main body 30 is a sintered body. Inside the membrane body 30, there are a plurality of voids 302 formed by sintering between the binders 300 or between the binder 300 and the hollow particles 301.

  The recess 31 has a bottomed cylindrical shape (a shallow dish shape with a flat bottom surface) and opens toward the combustion chamber. The recess 31 has a bottom portion 310, an opening edge portion 311, and a peripheral wall portion 312. The bottom portion 310 has a planar shape extending orthogonally to the axial direction (substantially parallel to a plane orthogonal to the axis 10), and has a substantially circular outline when viewed from one side in the axial direction. The bottom part 310 is a part of the bottom part 402 of the recess 401. The bottom 310 does not have (but does not contact with) the membrane main body 30, and the membrane main body 30 does not cover the bottom 310. A part of the bottom 402 of the recess 401 is exposed as a bottom 310 to the combustion chamber side. The opening edge 311 has a substantially circular outline when viewed from one axial side. The entire opening edge 311 (entire circumference) is composed of the membrane main body 30. The peripheral wall portion 312 is a wall portion between the bottom portion 310 and the opening edge portion 311 and has a cylindrical inner peripheral surface extending in the axial direction. The entire peripheral wall portion 312 (entire circumference) is composed of the membrane body portion 30. In the radial direction of the piston 1, the concave portion 31 is slightly displaced from the center of the membrane main body portion 30 (concave portion 401), and the axis of the concave portion 31 is offset from the axis 10. A part of the peripheral wall 312 of the recess 31 overlaps the axis 10.

  Hereinafter, the manufacturing process of the piston 1 will be described with reference to FIGS. The manufacturing process includes a casting process, a first machining process, a sintered body forming process, a heat treatment process, a second machining process, and a film thickness measurement process.

  In the casting process, the prototype (intermediate workpiece) of the piston body 2 is cast. Specifically, a molten aluminum alloy as a base metal is poured into a mold and solidified. At this time, the inner periphery of the piston main body 2 and a part of the passage 411 are formed.

  In the first machining step, a prototype 2A of the piston body 2 as shown in FIGS. 4 and 5 is formed by machining using a lathe or the like. The prototype 2A has a prototype 401A of the recess 401. By machining, the bottom portion 402 of the original 401A is finished (surface treatment is performed on the bottom surface) so that the surface roughness, for example, the value of the arithmetic average roughness Ra becomes small. Note that the master 401A of the recess 401 may be formed in the casting process, and the bottom 402 of the master 401A may be finished in the first machining process.

  In the sintered body forming step, a prototype 1B of the piston 1 as shown in FIGS. 9 and 10 is formed. The prototype 1B has a prototype 3B of the film 3 formed as a sintered body inside the prototype 401A of the recess 401. The sintered body forming process includes a material preparation process, a material installation process, and a sintering process.

  In the material preparation step, a material for forming the film 3 as a sintered body (hereinafter referred to as a forming material 303) is prepared. The forming material 303 is obtained by mixing metal powder (aluminum powder) as the binder 300 and hollow particles 301 in a predetermined (weight or volume) ratio.

  In the material installation step, as shown in FIGS. 6 and 7, the forming material 303 is filled into the prototype 401A of the concave portion 401 in the prototype 2A of the piston main body 2. Specifically, the forming material is put up to the upper end (opening edge) of the prototype 401A. Note that it is arbitrary to which position of the original 401A the forming material 303 is put. Further, after the metal powder and the hollow particles 301 are separately put into the prototype 401A, they may be mixed inside the prototype 401A.

  In the sintering step, the filled forming material 303 (specifically, aluminum powder among them) is sintered. In this embodiment, the discharge plasma sintering method is used, and sintering is performed by mechanical pressurization and pulse current heating. As a preparation step, as shown in FIG. 8, carbon electrodes 81 and 82 are respectively arranged on both sides in the axial direction of the prototype 2A of the piston main body 2. The electrode 81 on one axial side has a protrusion 810. The protruding portion 810 has a cylindrical shape protruding in the axial direction from a part of the end face of the electrode 81. A columnar insulator 83 is installed so as to extend in the axial direction at a position inside the forming material 303 where the concave portion 31 of the film 3 is planned. The end surface on one side in the axial direction of the insulator 83 faces the end surface of the protruding portion 810, and the end surface on the other side in the axial direction of the insulator 83 is in contact with the bottom portion 402 of the prototype 401A of the recess 401. In this state, the end surface of the electrode 81 is brought into contact with the forming material 303, and the electrode 82 is brought into contact with the other axial side of the prototype 2A of the piston main body 2. Then, a pulse voltage (current) is applied from the power supply 80 while pressurizing the forming material 303. The forming material is sintered by heat generation of each aluminum powder by energization, discharge plasma energy generated between the particles, and the like. As shown in FIG. 9 and FIG. 10, a prototype 3B of the film 3 as a sintered body whose volume is smaller than that of the original forming material 303 is formed inside the prototype 401A of the recess 401.

  In the prototype 3B, the gap after the insulator 83 and the protruding portion 810 are removed becomes the prototype 31B of the recess 31 of the film 3. A part of the bottom 402 of the original 401A of the recess 401 is exposed as the bottom 310 of the recess 31. Thus, when the prototype of the film body 30 is formed by sintering using the forming material 303, the prototype 31B of the recess 31 is formed at the same time (in a common process), thus simplifying the manufacturing process. You can plan. By making the shape of the electrode 81 and the insulator 83 correspond to the recess 31, the recess 31 (original 31B) can be easily formed. Note that the protruding portion 810 may be an insulator instead of a conductor (electrode). Further, instead of the insulator 83, a cylindrical member (conductive or insulating) into which the protruding portion 810 can enter is installed so as to extend in the axial direction, and is located on the inner peripheral side of the cylindrical member and at the bottom 402 of the prototype 401A. And the gap between the end face of the protruding portion 810 may function as an insulator. In this case, the gap after the cylindrical member is removed becomes the prototype 31B of the recess 31.

  In the heat treatment step, heat treatment is performed on the prototype 1B of the piston 1. As a result, the properties of the prototype 1B (prototype 2A of the piston body 2) are improved and adjusted to appropriate strength and hardness. Note that the heat treatment step may be performed before the sintered body forming step or after the second machining step.

  In the second machining step, the prototype 1B of the heat-treated piston 1 is machined with a lathe or the like to form the piston 1 as shown in FIGS. A crown surface 400 is formed by cutting one axial side of the piston head 4 (the side facing the combustion chamber). The entire surface of one side of the piston head 4 in the axial direction is machined. By cutting a part (on the surface side) of the prototype 3B of the membrane 3 together with a part (outside in the radial direction) of the piston head 4, the crown surface 400 including the membrane 3 is planar while forming the membrane 3 Finish. A recess 31 is formed in the film 3 by leaving a part of the gap (original 31B) after the insulator 83 and the like are removed. In addition, the piston pin hole 51 and the piston ring groove 410 are processed, and the outer diameter of the piston main body 2 such as the outer periphery of the piston head 4 and the skirt 6 is finished.

  As described above, the sintered body forming process and the second machining process function as a film forming process for forming the film 3. An anodizing treatment may be applied to the surface on one side in the axial direction of the formed film 3. In this case, the strength of the film main body 30 is improved, and the thermal conductivity of the film main body 30 is reduced by oxidizing the binder 300. Since the porous anodic oxide film is formed, the thermal conductivity of the film body 30 is further reduced. In addition, it is preferable to perform a sealing treatment on the surface of the anodized film.

  In the film thickness measurement step, the thickness of the formed film 3 (film body 30) is measured. The measurement method of the present embodiment is a contact type, and a contact type surface roughness meter is used as a film thickness measuring instrument, for example. In FIG. 3, the movement of the stylus (contactor) 9 of the surface roughness meter is indicated by a dashed-dotted arrow. By electrically detecting the vertical movement (axial direction) of the contact 9 moved in the lateral direction (along the plane perpendicular to the axis 10) via the recess 31, and processing the electrical signal The thickness of the film 3 can be measured. The film thickness measurement process can be divided into a first process, a second process, and a third process. In the first step, the contact 9 is brought into contact with the surface of the bottom 310 in the recess 31 of the film 3. This corresponds to measuring the position of the surface of the bottom 310. In the second step, the contact 9 is brought into contact with the surface of the membrane main body 30 on one axial side (combustion chamber side). This corresponds to measuring the position of the surface of the membrane body 30. In the third step, the amount of vertical displacement of the contactor 9 is calculated based on the electrical signals detected in the first step and the second step. This corresponds to calculating the thickness of the film 3 based on the measurement results of the first step and the second step. Thereafter, it is determined whether or not the measured film thickness is between a predetermined upper limit value and a lower limit value (within a predetermined range). Note that the first and second steps may be reversed. Actually, the process of calculating the thickness of the film 3 may be performed by subtracting the measurement result of the first step from the measurement result of the second step.

  Thus, the recess 31 functions as a recess for measuring the film thickness. The surface of the bottom portion 310 functions as a reference surface for measuring the film thickness. Note that the film thickness measurement process is not limited to the manufacturing process of the piston 1, but may be performed in an inspection process after use of the piston 1.

  Next, the function and effect will be described. The membrane 3 is a functional layer having a thermal property different from that of the piston main body 2 and is located between the combustion chamber and the piston main body 2 and functions as a low thermal conductive film (heat insulating layer). Therefore, it is possible to improve the thermal efficiency and exhaust gas characteristics of the engine. That is, the membrane main body 30 has a lower thermal conductivity than the piston main body 2 due to the internal properties of the hollow particles 301 and the air gap 302 in addition to the thermal properties of the material. Therefore, heat transfer from the gas inside the combustion chamber to the piston head 4 (piston main body 2) is reduced, and the gas combustion efficiency is improved accordingly. Further, since the crown surface 400 is maintained at a high temperature by the film 3, the fuel adhering to the crown surface 400 is quickly vaporized and burned. The membrane 3 may have a lower heat capacity (per unit volume) than the piston body 2. In this case, since the followability of the temperature of the crown surface 400 to the gas temperature in the combustion chamber is improved, abnormal combustion (knocking) of the fuel can be suppressed. Further, the membrane 3 may be localized on a part of the crown surface 400. As a result, an excessive increase in the temperature of the crown surface 400 can be suppressed, and both improvement in heat insulation and suppression of knocking can be achieved. For example, when the piston 1 is applied to an in-cylinder direct injection engine, the membrane 3 corresponds to the fuel injection region on the crown surface 400 (the portion where the fuel collides / explodes and the temperature or pressure becomes highest). It may be localized in the vicinity thereof.

  The low thermal conductivity material in the membrane main body 30 may be a material other than the hollow particles 301. In the present embodiment, since the membrane body 30 includes the hollow particles 301, the porosity in the membrane body 30 is increased, and the thermal conductivity is further reduced. In addition, it is preferable to use a material having a lower thermal conductivity than the piston body 2 as the material of the hollow particles 301 (outer shell). The shape of the hollow particle 301 is not limited to a spherical shape, and may be a columnar shape (carbon nanotube or the like).

  The film main body 30 includes a binder 300. Therefore, even when the membrane main body 30 includes the hollow particles 301, the binder 300 improves the bonding strength (hardness) inside the membrane main body 30 and suppresses chipping and collapse thereof. In addition, the strength of the bonding between the membrane 3 and the piston body 2 is improved, and the force for holding the membrane 3 on the piston body 2 is improved. The binder 300 is a metal. Therefore, even if a relatively large void is formed inside by the hollow particles 301, the strength of the membrane body 30 can be improved. The metal of the binder 300 is not limited to aluminum, but may be titanium alloy, magnesium, etc., but the thermal conductivity should be equal to or lower than the material (base metal) of the piston main body 2 (low thermal conductivity material). Is preferred. Moreover, it is preferable that it is a metal with high heat resistance and durability. In the present embodiment, the binder 300 includes aluminum. Therefore, it is possible to improve the bonding force between the piston main body 2 including the aluminum alloy and the membrane main body 30.

  The film main body 30 is a sintered body formed by sintering. The sintered body includes more minute voids 302 than the piston main body portion 2 formed by casting. For this reason, the thermal conductivity of the membrane 3 can be made lower than that of the piston main body 2 efficiently. In addition, by sintering, the membrane body 30 can be efficiently formed even if the membrane body 30 is relatively thick. In other words, it is easy to make the film 3 thick. A second machining process is performed after the sintered body forming process. That is, before the crown surface 400 is formed by cutting, the prototype 3B of the film 3 is formed. Therefore, in the sintered body forming process, since there are few restrictions due to the shape of the crown surface 400, the work of forming the prototype 3B becomes easy. In other words, even when the crown surface 400 has a complicated shape, the film 3 can be easily formed on the crown surface 400.

  The piston head 4 has a recess 401 on the crown surface 400. The recess 401 surrounds the outer periphery of the membrane 3 with the peripheral wall portion 403 and functions as a holding portion of the membrane 3. Therefore, the membrane 3 can be prevented from falling off from the piston body 2. Further, even when the discharge plasma sintering method is used in the sintering process, it is advantageous because the forming material 303 is held in the recess 401 and can be energized by applying pressure thereto. In the sintering process, sintering may be performed by pressurization or heating that does not depend on energization. Alternatively, a preform formed by pressing the forming material 303 into a disk shape may be prepared, and this may be placed in the recess 401 and sintered. In this case, the prototype of the recess 31 of the film 3 can be formed in advance on the preform. Further, sintering may be performed using the principle of friction stir welding (joining). In this case, by pressing the forming material 303 with a rotating tool, the forming material 303 is mixed and heated by frictional heat to form a sintered body. Even in this case, if the piston head 4 has the concave portion 401, it is advantageous because the forming material 303 is held in the concave portion 401 and can be agitated by applying pressure thereto. Further, in this case, a member to be a mold of the concave portion 31 of the film 3 is not installed, or the forming material 303 is not installed in the concave portion 401 or a position adjacent to the concave portion 401 (a sintered body is not formed even by friction stirring). The recess 31 of the film 3 can be formed by providing a space.

  If the film 3 is too thin, the heat transfer cannot be sufficiently reduced. On the other hand, if the film 3 is too thick, the film 3 may cause the crown surface 400 to be too hot and cause knocking. Therefore, it is desirable that the thickness of the film 3 be controlled within a predetermined range that can sufficiently exhibit the function of reducing heat transfer and can suppress the occurrence of knocking. The necessity of management can be said not only when the piston 1 is manufactured, but also when it is used after manufacturing. On the other hand, the film 3 has a recess 31. Therefore, the film thickness can be easily measured by executing the film thickness measurement step at the time of manufacturing or after use of the piston 1, and the film thickness can be managed within the predetermined range based on the measurement result. The membrane main body 30 does not exist on the surface of the bottom 310 of the recess 31, and the surface of the piston main body 2 (the bottom 402 of the recess 401) is exposed. Therefore, the thickness of the membrane 3 (membrane body portion 30) can be measured by using the surface of the bottom portion 310 as a reference plane. Note that it is sufficient that the film main body 30 is not present on at least a part of the surface of the bottom 310, and there may be a region where the film main body 30 is partially present on the surface of the bottom 310.

  The film 3 is held by the recess 401, and the outer periphery of the film 3 is surrounded by the peripheral wall part 403. Therefore, it is difficult to measure the thickness of the film 3 unless the film 3 has the recess 31. On the other hand, since the film 3 has the concave portion 31, the film thickness can be easily measured even when the film 3 is held by the concave portion 401.

  Specifically, in the film thickness measurement step, the first step of measuring the position of the surface of the bottom 310 in the recess 31 of the film 3 and the position of the surface that is the surface on the combustion chamber side of the film main body 30 are measured. The second step and a third step of calculating the thickness of the film 3 (film main body portion 30) based on the measurement results of the first step and the second step. Therefore, by measuring the distance from the surface of the bottom 310 to the surface of the membrane body 30 (the surface facing the combustion chamber) (the height of the step between the surface of the bottom 310 and the surface of the membrane body 30) The thickness of the membrane 3 (membrane main body 30) can be measured. Note that the measurement of the film thickness is not limited to measuring the actual value of the film thickness, but may directly determine whether or not the film thickness is within a predetermined range.

  The surface of the bottom 310 in the recess 31 of the film 3 is a part of the surface of the bottom 402 in the recess 401 of the crown 40. The surface of the bottom portion 402 is processed so that the surface roughness becomes small in the first machining process. Therefore, the surface of the bottom portion 310 as a reference surface for film thickness measurement also has a small surface roughness, so that the film thickness measurement accuracy can be improved. When casting the piston main body 2, the surface of the bottom 402 in the original mold 2 </ b> A of the piston main body 2 initially becomes a casting surface. Since the surface (cast surface) is machined so as to reduce the surface roughness as described above, the adhesion between the bottom 402 (recess 401) and the film body 30 is improved. 3 retainability can be improved.

  The surface of the bottom 310 in the recess 31 of the film 3 is parallel to a plane orthogonal to the axial direction (axis line 10). Therefore, if the dimension in the axial direction from the surface of the bottom part 310 is measured, the thickness of the film 3 can be measured, so that the installation of the piston 1 in the film thickness measuring device, the film thickness measurement, and the like are facilitated. Note that the surface of the bottom portion 310 is “parallel to the plane orthogonal to the axial direction” does not mean that it is strictly parallel, and that the processing error of the surface of the bottom portion 310 is allowed, Needless to say, the accuracy of the installation position of the piston 1 to the film thickness measuring device is not guaranteed.

  The opening edge 311 of the recess 31 of the film 3 is formed by the film main body 30 on the entire circumference. Therefore, a location suitable for film thickness measurement can be selected as appropriate from the opening edge 311, so that measurement accuracy can be improved. For example, the film thickness may be measured at a plurality of locations around the opening edge 311 and the average value may be used as the final film thickness measurement value.

  The film thickness measuring method of the present embodiment is a contact type, and includes a step of bringing the contactor 9 of the film thickness measuring device into contact with the surface of the bottom portion 310, and a step of bringing the contactor 9 into contact with the surface of the membrane main body portion 30. . Therefore, it is less susceptible to the surface roughness of the measurement object than the non-contact measurement method. That is, even if there is a minute unevenness on the surface with which the tip (terminal) of the contact 9 abuts, it is difficult to affect the measurement result, so a stable measurement result can be obtained. . The film thickness measuring device is not limited to the surface roughness meter, and for example, a contact displacement meter (displacement sensor) may be used.

[Second Embodiment]
The method for measuring the thickness (film thickness) of the film 3 in this embodiment is a non-contact type, and a laser displacement meter (displacement sensor), for example, is used as a film thickness measuring instrument. In FIG. 3, the movement of the laser light irradiation position is indicated by a dashed-dotted arrow. The film thickness can be measured by detecting the reflection of the laser beam moved in the lateral direction via the concave portion 31 at the light receiving portion and processing the signal. As in the first embodiment, the film thickness measurement process can be divided into a first process, a second process, and a third process. In the first step, the surface of the bottom portion 310 is irradiated with laser light. The distance to the surface is measured by detecting the reflected light. This corresponds to measuring the position of the surface of the bottom 310. In the second step, a laser beam is irradiated on the surface of one side of the film main body 30 in the axial direction. The distance to the surface is measured by detecting the reflected light. This corresponds to measuring the position of the surface of the membrane body 30. In the third step, the thickness of the film 3 (membrane main body 30) is calculated by subtracting the measurement result (distance) of the second step from the measurement result (distance) of the first step. Note that the first and second steps may be reversed. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. The film thickness measurement method of the present embodiment is a non-contact method, and includes a step of irradiating the surface of the bottom portion 310 with a laser beam for film thickness measurement and a step of irradiating the surface of the film body 30 with the laser beam. Therefore, as compared with the contact-type measurement method, the contact does not contact the membrane main body 30, so that damage to the membrane 3 due to contact of the contact can be suppressed. Moreover, it is easy to make the spot diameter of the laser beam smaller than the diameter of the contact terminal in the contact-type measuring method. For this reason, the formation range of the recess 31 in the film 3 (the range in which the film main body 30 does not exist) can be reduced. Therefore, the influence on the function of the membrane 3 due to the portion where the membrane main body portion 30 does not exist can be suppressed. The light used for measurement is not limited to laser light. The measurement medium irradiated on the surface of the bottom portion 310 is not limited to light, and the film thickness may be measured by a non-contact displacement meter using ultrasonic waves or magnetism. Further, the film thickness may be measured using not only a displacement meter but also a non-contact type length measuring sensor. In addition, the cross-sectional shape (image, etc.) of the portion of the membrane 3 that straddles the concave portion 31 and the membrane main body 30 is acquired by laser light or X-ray irradiation, etc. May be. In addition, the same effect as that of the first embodiment can be obtained by the same configuration as that of the first embodiment.

[Third embodiment]
As shown in FIGS. 11 and 12, the concave portion 31 of the membrane 3 is located at the position (outer peripheral edge) farthest from the center of the membrane main body 30 (the concave portion 401) in the radial direction of the piston 1. A part of the opening edge 311 of the recess 31 (the part farthest from the axis 10) and a part of the peripheral wall 312 (the part farthest from the axis 10) form the recess 401 in the piston main body 2 (piston head 4). They overlap and coincide with the opening edge and the peripheral wall 403, respectively. The other part of the opening edge 311 of the recess 31 and the other part of the peripheral wall 312 are formed of the membrane body 30. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. In general, combustion (explosion) in the combustion chamber starts from the vicinity of the axis 10 of the piston 1. For this reason, it is effective to improve the heat insulation between the combustion chamber and the piston main body 2 by the membrane 3 at or near the center of the crown surface 400. On the other hand, in the film 3, since the film main body 30 does not exist in the recess 31, the heat insulating function of the film 3 is not exhibited in the recess 31. On the other hand, in the present embodiment, the opening edge 311 and the peripheral wall 312 of the recess 31 are an area composed of the membrane body 30 (first area) and an area composed of the recess 401 of the piston head 4 (second area). Including. That is, the concave portion 31 is at a position in contact with the concave portion 401 of the piston head 4, in other words, at the outer peripheral edge of the membrane 3. Therefore, the concave portion 31 can be easily avoided from being located in the central portion of the crown surface 400 or in the vicinity thereof, so that the influence on the function of the membrane by the portion where the membrane main body portion 30 does not exist can be suppressed. When the piston 1 is applied to an in-cylinder direct injection engine, if the concave portion 31 is disposed so as to avoid the portion corresponding to the fuel injection region on the crown surface 400, the function of the membrane 3 is more reliably deteriorated. Can be suppressed. In addition, the same effect as that of the first embodiment can be obtained by the same configuration as that of the first embodiment.

[Fourth embodiment]
As shown in FIGS. 13 and 14, the crown 40 does not have the recess 401 of the first embodiment. The other axial side of the membrane 3 is in contact with the surface of the crown 40 on the one axial side. The outer periphery of the membrane 3 constitutes a part of the outer periphery of the piston head 4. The surface of the bottom portion 310 in the concave portion 31 of the film 3 is the surface on one side of the crown portion 40 in the axial direction. The recess 31 is at the approximate center of the membrane body 30. The axis of the recess 31 substantially coincides with the axis 10 of the piston 1. The peripheral wall 312 of the recess 31 is inclined with respect to the axis 10. The diameter of the recess 31 gradually increases (becomes a large diameter) from the bottom 310 side (the other axial side) toward the opening edge 311 side (the one axial side). The thickness (axial dimension) of the membrane 3 in the peripheral wall portion 312 is such that the opening edge from the bottom 310 side (axis 10 side) in the direction orthogonal to the axial direction (axis 10) (the radial direction of the piston 1) It gradually increases as it goes toward 311 (the radially outer side of the piston 1). Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. When the peripheral wall 312 of the recess 31 extends along the axis 10 (in the axial direction), the angle formed by the inner peripheral surface of the peripheral wall 312 and the surface of one side of the membrane main body 30 in the axial direction is close to a right angle. Become. Therefore, the film 3 is easily damaged in the vicinity of the opening edge 313. In contrast, in the present embodiment, the thickness (axial dimension) of the film 3 in the peripheral wall portion 312 gradually increases from the bottom portion 310 side toward the opening edge portion 311 side. Since the peripheral wall portion 312 is inclined as described above, the angle formed by the inner peripheral surface of the peripheral wall portion 312 and the surface on one side in the axial direction of the membrane main body portion 30 is larger than a right angle. Therefore, damage to the film 3 in the vicinity of the opening edge 313 can be suppressed. Further, when the film 3 is formed by sintering and the concave portion 31 of the film 3 is formed by a mold at the time of sintering, the inner wall of the peripheral wall portion 312 is removed when removing a member (such as the insulator 83 of the first embodiment) serving as the mold. Since the peripheral surface is inclined as described above, the inclined surface becomes a draft angle of the member serving as the mold, and interference with the peripheral wall portion 312 can be suppressed. Similarly, when the film 3 is formed using the discharge plasma sintering method, the inclined surface of the peripheral wall portion 312 becomes a draft angle of the protruding portion 810 of the electrode 81, and interference between the peripheral wall portion 312 and the protruding portion 810 is suppressed. Can do. In addition, the same effect as that of the first embodiment can be obtained by the same configuration as that of the first embodiment.

[Fifth Embodiment]
As shown in FIG. 15, there is a second film 32 covering the film 3 (the film main body 30 and the recess 31) on the surface of the film 3 on one axial side. The membrane 32 covers the membrane main body 30 and also covers the bottom 310 of the recess 31, the opening edge 311 and the peripheral wall 312. Since the membrane 3 (membrane main body portion 30) is a sintered body and is porous, a large number of pores open on the surface of the membrane 3 (the same applies when the surface of the membrane 3 is subjected to anodization). The membrane 32 closes the opening of these holes. The film 32 is formed, for example, by plating the film 3 using a sealing agent after the second machining step (when the surface of the film 3 is anodized, it is sealed with pressurized steam or the like). Formed by hole treatment). The sealing agent contains silica having excellent heat resistance, for example. The film thickness measurement step is performed before the sealing treatment step, and the thickness of the film 3 is measured before the film 32 is formed. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. If unburned gas or fuel enters a hole opened on the surface of the membrane 3, the function (thermal insulation) of the membrane 3 and the exhaust gas performance of the engine may be deteriorated. On the other hand, the function of the membrane 3 and the exhaust gas performance can be improved by sealing the pores with the second membrane 32 covering the membrane 3.

  Here, when the film 32 covers not only the film main body 30 but also the recess 31, if the thickness of the film 32 is uniform, the thickness of the film 3 may be measured before the film 32 is formed. Even if it is performed later, the measurement result does not change. However, the thickness of the film 32 covering the film main body 30 may be different from the thickness of the film 32 covering the recess 31 (for example, the film 32 becomes thicker on the recess 31 side). As described above, if the thickness of the film 3 is measured in a state where the thickness of the film 32 is not uniform, the measurement accuracy may be lowered. In contrast, in the film thickness measurement step, the thickness of the film 3 is measured before the film 32 is formed. Thereby, it can suppress that the measurement precision of the thickness of the film | membrane 3 falls.

  It should be noted that the film thickness may be measured before and after the formation of the film 32 in any part of the film main body 30. Based on the difference between these measurement results, the thickness of the film 32 can be measured. Based on the measurement result of the thickness of the film 32, the functions of the film 3 and the film 32 can be appropriately exhibited by managing the thickness of the film 32 within a predetermined range. In addition, the same effect as that of the first embodiment can be obtained by the same configuration as that of the first embodiment.

[Other Embodiments]
As mentioned above, although the form for implementing this invention was demonstrated based on drawing, the specific structure of this invention is not limited to embodiment, The design change etc. of the range which does not deviate from the summary of invention are included. Even if it exists, it is included in this invention. For example, the engine format is arbitrary. The engine is not limited to a 4-stroke engine and may be a 2-stroke engine. Not only a gasoline engine but also a diesel engine may be used. The fuel supply method may be an in-cylinder direct injection type that directly injects into the cylinder (combustion chamber), or a port injection type that injects into the intake port. An engine mounted on a ship or the like is not limited to a vehicle. The shape of the piston is arbitrary. For example, there may be a recess or the like for suppressing interference with the bulb on the crown surface.

[Technical ideas that can be grasped from the embodiment]
A technical idea (or technical solution, the same applies hereinafter) that can be grasped from the embodiment described above will be described below.
(1) In one aspect of the piston of the internal combustion engine of the present technical idea,
A piston body comprising a metal and having a piston head and a skirt,
The piston head has a concave film holding portion on a crown surface which is a surface on the combustion chamber side of the internal combustion engine in the piston head.
A piston body,
In the film holding part, a film having a film body part and a film thickness measurement recess,
The membrane body is different in thermal properties from the piston body,
The film thickness measurement recess is open toward the combustion chamber, and has a bottom, an opening edge, and a peripheral wall between the bottom and the opening edge.
At least a part of the opening edge portion and the peripheral wall portion is composed of the membrane body portion,
The bottom has a reference surface for film thickness measurement in which the film main body does not exist at least in part.
And a membrane.
(2) In a more preferred embodiment, in the above embodiment,
The opening edge of the film thickness measurement recess is entirely formed of the film body.
(3) In another preferred embodiment, in any of the above embodiments,
The membrane body is a sintered body.
(4) In still another preferred embodiment, in any of the above embodiments,
The membrane body includes a binder that is a metal.
(5) In still another preferred embodiment, in any of the above embodiments,
The opening edge portion of the film thickness measurement recess includes a first region composed of the film body portion and a second region composed of the film holding portion.
(6) In still another preferred embodiment, in any of the above embodiments,
The membrane body is a sintered body.
(7) In still another preferred embodiment, in any of the above embodiments,
The membrane body includes a binder that is a metal.
(8) In still another preferred embodiment, in any of the above embodiments,
In the peripheral wall portion, the membrane has a thickness in an axial direction in which the piston main body moves in a cylinder of the internal combustion engine in a direction perpendicular to the axial direction from the bottom side to the opening edge side. Gradually increases toward
(9) In still another preferred embodiment, in any of the above embodiments,
The reference surface for film thickness measurement is a surface obtained by subjecting the surface of the film holding portion to surface processing by machining.
(10) In still another preferred embodiment, in any of the above embodiments,
A second film covering the film main body and the film thickness measurement recess of the film;
(11) In still another preferred embodiment, in any of the above embodiments,
The film thickness measuring reference plane is parallel to a plane orthogonal to the axial direction, which is the direction in which the piston body moves in the cylinder of the internal combustion engine.
(12) In one aspect of the method for measuring the film thickness of the piston of the internal combustion engine of the present technical idea,
The piston is
A piston body comprising a metal and having a piston head and a skirt,
The piston head has a film holding portion on a crown surface which is a surface on the combustion chamber side of the internal combustion engine in the piston head.
A piston body,
The film is in the film holding part and has a film main body part and a concave part,
The membrane body has a lower thermal conductivity than the piston body,
The concave portion is open toward the combustion chamber, and has a bottom portion, an opening edge portion, and a peripheral wall portion between the bottom portion and the opening edge portion,
At least a part of the opening edge portion and the peripheral wall portion is composed of the membrane body portion,
The bottom portion has a reference surface in which the membrane main body portion does not exist at least in part.
A piston having a membrane,
A first step of measuring the position of the reference plane;
A second step of measuring the position of the surface that is the surface on the combustion chamber side of the membrane body part;
And a third step of calculating the thickness of the film based on the measurement results of the first step and the second step.
(13) In a more preferred embodiment, in the above embodiment,
The first step includes a step of bringing a contact into contact with the reference surface,
The second step includes a step of bringing the contact into contact with the surface of the membrane main body.
(14) In another preferred embodiment, in any of the above embodiments,
The first step includes a step of irradiating the reference surface with laser light for film thickness measurement, ultrasonic waves, or magnetism,
The second step includes a step of irradiating the surface of the film main body with laser light, ultrasonic waves, or magnetism for measuring the film thickness.
(15) From another viewpoint, in one aspect of the method for manufacturing a piston of an internal combustion engine of the present technical idea,
A method of manufacturing a piston of an internal combustion engine to which the film thickness measurement method can be applied,
A film forming step of forming the film body by sintering;
(16) In a more preferred embodiment, in the above embodiment,
In the film forming step, the concave portion is formed when the film main body is formed using metal powder as a material.
(17) In another preferred embodiment, in any of the above embodiments,
In the film forming step, an electrode is brought into contact with the metal powder and energized to form a sintered body of the film main body.

DESCRIPTION OF SYMBOLS 1 Piston 2 Piston main-body part 3 Film | membrane 30 Film | membrane main-body part 300 Binder 31 Recessed part (recessed part for film thickness measurement)
310 bottom 311 opening edge 312 peripheral wall 32 second membrane 4 piston head 400 crown surface 401 recess (membrane holding portion)
6 Skirt

Claims (17)

A piston of an internal combustion engine,
A piston body comprising a metal and having a piston head and a skirt,
The piston head has a concave film holding portion on a crown surface which is a surface on the combustion chamber side of the internal combustion engine in the piston head.
A piston body,
In the film holding part, a film having a film body part and a film thickness measurement recess,
The membrane body is different in thermal properties from the piston body,
The film thickness measurement recess is open toward the combustion chamber, and has a bottom, an opening edge, and a peripheral wall between the bottom and the opening edge.
At least a part of the opening edge portion and the peripheral wall portion is composed of the membrane body portion,
The bottom has a reference surface for film thickness measurement in which the film main body does not exist at least in part.
A piston for an internal combustion engine having a membrane. The piston of the internal combustion engine according to claim 1,
The opening edge of the film thickness measurement recess is a piston of an internal combustion engine, the entire circumference of which is the film body. The piston of the internal combustion engine according to claim 2,
The piston of an internal combustion engine, wherein the membrane body is a sintered body. The piston of the internal combustion engine according to claim 3,
The membrane main body part is a piston of an internal combustion engine including a binder which is a metal. The piston of the internal combustion engine according to claim 1,
The piston of an internal combustion engine, wherein the opening edge of the film thickness measurement recess includes a first region made up of the membrane body and a second region made up of the membrane holding part. The piston of the internal combustion engine according to claim 5,
The piston of an internal combustion engine, wherein the membrane body is a sintered body. The piston of the internal combustion engine according to claim 6,
The membrane main body part is a piston of an internal combustion engine including a binder which is a metal. The piston of the internal combustion engine according to claim 1,
In the peripheral wall portion, the membrane has a thickness in an axial direction in which the piston main body moves in a cylinder of the internal combustion engine in a direction orthogonal to the axial direction from the bottom side to the opening edge side. The piston of an internal combustion engine that gradually increases toward The piston of the internal combustion engine according to claim 1,
The reference surface for film thickness measurement is a piston of an internal combustion engine, wherein the surface of the film holding portion is a surface treated by machining. The piston of the internal combustion engine according to claim 1,
A piston for an internal combustion engine, comprising: a second membrane that covers the membrane main body portion of the membrane and the film thickness measurement recess. The piston of the internal combustion engine according to claim 1,
The piston for an internal combustion engine, wherein the reference surface for measuring the film thickness is parallel to a plane orthogonal to an axial direction that is a direction in which the piston body moves in a cylinder of the internal combustion engine. A method for measuring the thickness of a piston of an internal combustion engine,
The piston is
A piston body comprising a metal and having a piston head and a skirt,
The piston head has a film holding portion on a crown surface which is a surface on the combustion chamber side of the internal combustion engine in the piston head.
A piston body,
The film is in the film holding part and has a film main body part and a concave part,
The membrane body has a lower thermal conductivity than the piston body,
The concave portion is open toward the combustion chamber, and has a bottom portion, an opening edge portion, and a peripheral wall portion between the bottom portion and the opening edge portion,
At least a part of the opening edge portion and the peripheral wall portion is composed of the membrane body portion,
The bottom portion has a reference surface in which the membrane main body portion does not exist at least in part.
A piston having a membrane,
A first step of measuring the position of the reference plane;
A second step of measuring the position of the surface that is the surface on the combustion chamber side of the membrane main body;
A method for measuring the thickness of a piston of an internal combustion engine, comprising: a third step of calculating the thickness of the film based on the measurement results of the first step and the second step. The method for measuring the thickness of a piston of an internal combustion engine according to claim 12,
The first step includes a step of bringing a contact into contact with the reference surface;
The second step includes a step of bringing the contact into contact with the surface of the membrane main body.
A method for measuring the thickness of a piston of an internal combustion engine. The method for measuring the thickness of a piston of an internal combustion engine according to claim 12,
The first step includes a step of irradiating the reference surface with laser light, ultrasonic waves, or magnetism for film thickness measurement,
The second step includes a step of irradiating the surface of the film main body with laser light, ultrasonic waves, or magnetism for measuring the film thickness,
A method for measuring the thickness of a piston of an internal combustion engine. A method for manufacturing a piston of an internal combustion engine to which the film thickness measuring method according to claim 12 can be applied,
A method for manufacturing a piston of an internal combustion engine, comprising a film forming step of forming the film body by sintering. The method for manufacturing a piston of an internal combustion engine according to claim 15,
The said film formation process is a manufacturing method of the piston of an internal combustion engine which forms the said recessed part, when forming the said film | membrane main-body part using metal powder as a material. The method for manufacturing a piston of an internal combustion engine according to claim 16,
The film forming step is a method of manufacturing a piston for an internal combustion engine, wherein an electrode is brought into contact with the metal powder and energized to form a sintered body of the film main body.

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