JP2019056340A - Piston of internal combustion engine and manufacturing method of piston - Google Patents

Abstract

To provide a piston which can obtain a characteristic corresponding to performance which is required to respective regions of the piston.SOLUTION: A piston contains an aluminum alloy. The piston has a piston head part, a first piston pin boss part and a second piston pin boss part. The piston head part has T6-treated hardness. The first piston pin boss part has a first piston pin hole into which a piston pin is inserted, and has T6-treated hardness which is higher than that of the piston head part. The second piston pin boss part has a second piston pin boss hole into which the piston pin is inserted, and has T6-treated hardness which is higher than that of the piston head part.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piston.

  Conventionally, a piston manufactured using an aluminum alloy as a material is known. For example, the piston disclosed in Patent Document 1 is subjected to heat treatment such as cooling to the atmosphere or oil cooling after casting and heating at 480 to 520 ° C. for 1 to 8 hours.

JP-A-55-24784

  With conventional pistons, it has not been possible to realize characteristics corresponding to the performance required for each part of the piston.

  The piston according to an embodiment of the present invention preferably includes a piston head portion having a T6-treated hardness and a piston pin boss portion having a T6-treated hardness and higher than the piston head portion.

  Therefore, the characteristic according to the performance each requested | required of a piston head part and a piston pin boss | hub part is realizable.

2 shows a cross section of the piston of the first embodiment, taken along a plane perpendicular to the axis of the piston pin hole and passing through the axis of the piston. The cross section cut along the plane which passes along the axis of a piston along the axis of a piston pin hole of the piston of a 1st embodiment is shown. FIG. 2 shows a cross section (similar to FIG. 1) of the piston immersed in the cooling liquid in the cooling step of the first embodiment. FIG. 5 shows a cross section (similar to FIG. 1) of a piston partially covered with a masking member and immersed in a cooling liquid in the cooling process of the second embodiment. FIG. 7 shows a cross section (similar to FIG. 2) of a piston in a state where a cooling liquid is injected on an inner peripheral surface in a cooling step of a third embodiment. FIG. 6 shows a cross section (similar to FIG. 2) of a piston of different hardness for each region (delimited by a broken line) in the third embodiment. 9 shows a cross section (similar to FIG. 1) of a piston of a seventh 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 is used in an internal combustion engine (engine) of a vehicle such as an automobile. The engine is, for example, a 4-stroke gasoline engine. The piston 1 is accommodated in the cylinder so as to be reciprocally movable. As shown in FIGS. 1 and 2, the piston 1 has a bottomed cylindrical shape, and includes a piston head part 2, apron parts 31, 32, piston pin boss parts 41, 42, and piston skirts (skirt parts) 51, 52. Have one.

  The piston head part 2 has a crown part 20 and a land part 21. The cross section of the piston head portion 2 (crown portion 20) cut along a plane orthogonal to the moving direction of the piston 1 inside the cylinder is substantially circular. A line passing through the center of the circle and parallel to the moving direction is referred to as an axis of the piston 1. The direction in which the axis extends is called the axis direction. The crown portion 20 is on one side in the axial direction of the piston head portion 2. A piston crown surface (top surface) 22 is provided on one side in the axial direction of the crown portion 20. The piston crown 22 defines a combustion chamber together with the cylinder head of the engine and faces the combustion chamber. On the other side in the axial direction of the crown portion 20, there is a surface (piston back surface) 23 on the back side of the piston crown surface 22.

  The land portion 21 extends from the outer peripheral side of the crown portion 20 to the other side in the axial direction. On the outer periphery of the land portion 21, there are three annular piston ring grooves 211, 212, and 213. Each of the grooves 211, 212, 213 extends in the direction around the axis of the piston 1 (circumferential direction) and surrounds the entire circumference of the land portion 21. The grooves 211, 212, and 213 are arranged in this order from one side in the axial direction to the other side. A piston ring is installed in each groove 211, 212, 213. The groove 211 is a top ring groove, and a top ring is installed as a first pressure ring (compression ring). The ring groove 212 is a second ring groove, and a second ring as a second pressure ring is installed. The ring groove 213 is an oil ring groove, and an oil ring is installed as an oil control ring.

  The apron parts 31, 32, the piston pin boss parts 41, 42 and the skirt parts 51, 52 extend from the piston head part 2 to the other side in the axial direction. The inner peripheral sides of these portions 31 to 52 are hollow. The piston pin boss portions 41 and 42 are on both sides in the radial direction with respect to the axis. The piston pin boss portion 41 has a piston pin hole 410 in the cylindrical boss portion. The piston pin hole 410 extends in the radial direction through the piston pin boss portion 41. Similarly, the piston pin boss portion 42 has a piston pin hole 420 in the cylindrical boss portion. The piston pin holes 410 and 420 face each other in the radial direction. End portions of the piston pins are inserted and fitted into the piston pin holes 410 and 420, respectively. 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. The skirt portions 51 and 52 are on both sides in the radial direction. The outer periphery of the skirt portions 51 and 52 is in sliding contact with the inner wall of the cylinder. The apron portion 31 includes a piston pin boss portion 41 and is connected to the skirt portions 51 and 52 at both ends in the circumferential direction. The apron portion 32 includes a piston pin boss portion 42 and is connected to the skirt portions 51 and 52 at both ends in the circumferential direction. The piston pin boss portions 41 and 42 are connected to the skirt portions 51 and 52 via the apron portions 31 and 32.

  The top ring groove 211 is formed by an anti-abrasion ring 6 embedded in the piston 1. The anti-abrasion ring 6 is an annular member including Ni-resist cast iron, is fixed inside the piston head portion 2, and surrounds the outer periphery of the piston head portion 2. At least a part of the anti-ring 6 is wrapped in the piston head part 2 and joined integrally with the piston head part 2. The anti-ring 6 has a joint surface 60. The anti-wear ring 6 is a joining member that joins the piston head portion 2 at the joining surface 60. The thermal expansion coefficient (linear expansion coefficient) of the anti-abrasion ring 6 containing Ni-resist cast iron is different from the thermal expansion coefficient of the piston head part 2 containing an aluminum alloy.

  Hereinafter, a method for manufacturing the piston 1 will be described. The piston 1 is formed by casting using an aluminum alloy. The aluminum alloy is an aluminum Al-silicon Si system, specifically, AC8A defined by Japanese Industrial Standards (JIS), and includes at least silicon and copper. The manufacturing process of the piston includes a casting process, a machining process, and a heat treatment process.

  In the casting process, the prototype (intermediate workpiece) of the piston 1 is cast by gravity casting, and the wear-resistant ring member is cast into the intermediate workpiece. The wear-resistant ring member is a prototype of the anti-abrasion ring 6 and is cast into the prototype (the outer periphery) of the piston head portion 2.

  In the machining process, the intermediate workpiece is machined with a lathe or the like to form the piston 1. The piston crown surface 400 is formed by cutting. Further, the outer diameter of the piston 1 such as the outer periphery of the piston head portion 2 and the skirt portions 51 and 52 is finished. Along with the outer periphery of the piston head portion 2, a part (outer peripheral side) of the wear resistant ring member is cut to form the wear resistant ring 6. In other words, the outer peripheral surface of the piston head part 2 including the outer peripheral surface of the wear resistant ring 6 as a part thereof is finished. Further, the piston pin holes 410 and 420 and the piston ring grooves 211 to 213 are formed by cutting (the top ring groove 211 is formed in the wear-resistant ring 6). Thus, the piston 1 (including the wear resistant ring 6) as shown in FIGS. 1 and 2 is formed. The groove 211 may be formed in the wear resistant ring member before the casting process. Of the surface of the piston 1 thus molded, for example, the inner peripheral surface 10 remains the casting surface formed during casting.

  In the heat treatment step, the molded piston 1 is heat treated. As a result, the properties of each part of the piston 1 are improved and adjusted to appropriate strength and hardness. The heat treatment step includes a solution treatment step, a cooling step, and an artificial aging treatment step, and corresponds to a T6 treatment defined by JIS.

  In the solution treatment step, the solution treatment of the molded piston 1 (in the state before the heat treatment, that is, in the first state) is performed. As a result, the atoms of the additive element in the aluminum alloy constituting the piston 1 are dissolved in the aluminum crystal to form a solid solution (change to the piston in the second state).

  The cooling process corresponds to a quenching process, and the solid solution piston 1 obtained by the solution treatment is rapidly cooled to obtain a supersaturated solid solution. In the present embodiment, the cooling method, speed, and degree are changed depending on the portion of the piston 1. Of the piston 1 in solution, at least a part of the piston head part 2 is not cooled, and at least a part of the piston pin boss parts 41 and 42 is cooled (local cooling). As shown in FIG. 3, a part of the region of the piston 1 in solution is immersed in the coolant 70 that has entered the cooling tank 7. The region to be immersed includes the region where the piston pin holes 410 and 420 are formed in the piston pin boss portions 41 and 42, and is a region on the opposite side of the piston head portion 2 with respect to the piston pin holes 410 and 420 in the axial direction. When these areas come into contact with the cooling liquid 70, they are rapidly cooled. The region not immersed is the region on the piston head portion 2 side with respect to the piston pin holes 410 and 420 in the axial direction, including the wear-resistant ring 6 and a region in the vicinity thereof. Since these regions do not contact the coolant 70, they are not cooled more rapidly than the soaked regions. However, when the temperature of the soaked area is lowered, the non-soaked area is also indirectly cooled by the heat conduction inside the piston 1, so that it is cooled more rapidly than the air cooling.

  The artificial aging treatment process corresponds to the tempering treatment, and the additive dissolved in the aluminum alloy is artificially given a temperature of normal temperature or higher to the supersaturated solid-state piston 1 obtained by the cooling treatment. Deposit elements. Thereby, hardness becomes high. Note that the machining step may be performed after the heat treatment step.

  The characteristics of the piston 1 manufactured by the above steps are listed below. Crystals (crystallized products) that are precipitates from the aluminum alloy appear in the aluminum alloy beyond the limit amount where the additive elements are uniformly mixed. The average particle diameter of the crystal including the crystals that have not been dissolved by the solution treatment is determined by the solution treatment. Therefore, the average grain size of crystals in the piston 1 is smaller than the average grain size of crystals precipitated from, for example, the same aluminum alloy treated with T5. For example, in the piston 1, the average length in the longitudinal direction of the silicon crystal is, for example, several tens of μm, which is shorter than the average length in the longitudinal direction of the silicon crystal precipitated from the same aluminum alloy treated with T5. Similarly, in piston 1, the average particle size of the (intermetallic) compound of aluminum and copper precipitated from the aluminum alloy is smaller than the average particle size of the compound precipitated from the same aluminum alloy treated with T5.

  An oxide film is formed on the surface of the piston 1 by solution treatment of the piston 1 after casting. This oxide film covers at least the casting surface (for example, the inner peripheral surface 10). When the machining process is performed before the heat treatment process, the oxide film covers the entire surface of the piston 1. The thickness of this oxide film by solution treatment is thicker than that of the oxide film covering the surface of the same aluminum alloy that has been subjected to the T5 treatment. Also, the color density of the surface of the piston 1 treated with T6 is higher than the color density of the surface of the same aluminum alloy treated with T5.

  The piston head portion 2 and the piston pin boss portions 41 and 42 have T6-treated strength (for example, the tensile strength of AC8A defined by JIS: 270 or more and the Brinell hardness: about 110). The T6 treated hardness has a certain range. Each part 2, 41, 42 has a hardness within this range.

  The piston pin boss portions 41 and 42 are higher in cooling speed or degree in the cooling process than the piston head portion 2. Accordingly, the piston pin boss portions 41 and 42 have higher hardness than the piston head portion 2. In the piston head part 2, the hardness of the crown part 20 (particularly the part radially inward of the land part 21 having the piston ring groove 211) and the land part 21 (including the part joined to the anti-abrasion ring 6) is (the piston (Including the region where the pin holes 410 and 420 are formed) The hardness of the piston pin boss portions 41 and 42 is lower.

  The piston pin boss portions 41 and 42 have a strength higher than the strength subjected to the T5 treatment (for example, the tensile strength of AC8A defined by JIS: 190 or more and Brinell hardness: about 90). The T5 treated hardness has a certain range. The range of the hardness of the piston pin boss portions 41 and 42 is higher than the maximum value of the hardness subjected to the T5 treatment. The range of the hardness of the piston head portion 22 is within the range of the hardness subjected to the T6 treatment, but may include a value lower than the maximum value of the hardness subjected to the T5 treatment.

  Next, the function and effect will be described. During the operation of the engine, the piston 1 reciprocates in the cylinder by receiving the combustion pressure generated in the combustion chamber during the expansion stroke on the piston crown surface 22. This reciprocating movement is converted into a rotational motion by the connecting rod and output to the crankshaft. If the hardness of the piston head part 2 (crown part 20) that receives the combustion pressure on the piston crown surface 22 is too high, the piston head part 2 may be cracked. That is, the piston head portion 2 (crown portion 20) needs to have appropriate flexibility. On the other hand, the piston pin connected to the connecting rod fits into the piston pin holes 410 and 420 of the piston pin boss portions 41 and 42. The piston pin boss portions 41 and 42 that receive the load from the piston pin on the inner peripheral surfaces of the piston pin holes 410 and 420 require high strength against compressive stress.

  As shown in the above characteristics, the piston 1 has the required performance of each part in the piston pin boss portions 41 and 42 that require high strength as described above and the piston head portion 2 that requires moderate flexibility. Depending on the characteristics. That is, the piston pin boss portions 41 and 42 have a T6 treated hardness. Specifically, it has a hardness higher than the hardness treated with T5. Therefore, high strength can be secured. The piston head portion 2 has a T6-treated hardness, while the crown portion 20 has a lower hardness than the piston pin boss portions 41 and 42. This is because the piston 1 is locally cooled in the cooling step. That is, the piston head portion 2 including the crown portion 20 is not cooled (not in contact with the coolant 70) and is indirectly cooled (via heat conduction inside the piston 1). Therefore, moderate flexibility can be obtained while ensuring the necessary strength.

  In the piston 1 including the piston head portion 2, the average grain size of crystals precipitated from the aluminum alloy is smaller than the average grain size of crystals precipitated from the T5 treated aluminum alloy. Therefore, since the structure is improved and the spreadability of the material is improved, moderate flexibility can be obtained in the piston head portion 2 including the crown portion 20. For example, in the piston 1 including the piston head portion 2, the average length in the longitudinal direction of the silicon crystal is shorter than the average length in the longitudinal direction of the silicon crystal precipitated from the T5 treated aluminum alloy. Therefore, the spreadability of the material is good. Similarly, in the piston 1 including the piston head portion 2, the average particle size of the precipitated aluminum and copper compound is smaller than the average particle size of the compound precipitated from the T5 treated aluminum alloy. Therefore, the spreadability of the material is good.

  The wear-resistant ring 6 is made of a material different from that of the aluminum alloy, and has a different thermal property (thermal expansion coefficient) from the piston head portion 2. For this reason, in the heat treatment step (cooling step or cooling in the aging treatment step), peeling occurs at the interface (joint surface 60) where the wear-resistant ring 6 and the piston head part 2 are joined due to thermal shock during cooling. There is a fear. On the other hand, the hardness of the land portion 21 (including the portion joined to the anti-abrasion ring 6) is lower than the hardness of the piston pin boss portions 41 and 42. This is because the piston 1 is locally cooled in the cooling step. That is, the piston head portion 2 including the land portion 21 is not cooled (not in contact with the coolant 70) and indirectly cooled (through heat conduction inside the piston 1). As described above, since the cooling process is performed in a region excluding the portion where the anti-abrasion ring 6 is provided, the thermal shock at the time of cooling in the portion where the anti-wear ring 6 is provided is mitigated, and interface peeling occurs. The product can be prevented from being damaged.

  In the cooling process of the present embodiment, the region of the piston 1 opposite to the piston head portion 2 is simply immersed in the coolant 70 including the piston pin holes 410 and 420. Therefore, a large amount of the piston 1 can be efficiently and locally cooled.

  The oxide film that covers the surface of the piston 1 including the outer peripheral surface of the piston head portion 2 is formed by solution treatment, and has a relatively small thermal expansion coefficient (linear expansion coefficient). The oxide film is thicker than the oxide film covering the surface of the T5 treated aluminum alloy. Therefore, when the coefficient of thermal expansion of the wear resistant ring 6 is smaller than that of the aluminum alloy that is the base material of the piston 1, the oxide film suppresses the difference in coefficient of thermal expansion between the piston 1 and the wear resistant ring 6. The Therefore, generation | occurrence | production of interface peeling at the time of cooling can be suppressed more. This is the same when the machining process is performed after the heat treatment process.

  The color density on the surface of the piston 1 is higher than the color density on the surface of the T5 treated aluminum alloy. Therefore, since the emissivity of heat from the surface of the piston 1 becomes high, an excessive increase in the temperature of the piston 1 can be suppressed during engine operation.

  Hereinafter, the effect of this embodiment will be described in comparison with the comparative example. Comparative Example 1 is a piston in which an anti-abrasion ring is cast, and as a heat treatment after casting, the whole piston is subjected to a solution treatment, and then cooled to the atmosphere or oil-cooled. In Comparative Example 1, peeling of the anti-abrasion ring is suppressed, but the cooling rate becomes insufficient and no quenching occurs, so there is a risk of insufficient strength and wear. On the other hand, the piston 1 of the present embodiment has hardness that the land portion 21 is lower than the hardness of the piston pin boss portions 41 and 42, but the whole piston 1 is T6 treated. For this reason, the required strength can be ensured while preventing the anti-abrasion 6 from peeling. Comparative Example 2 is a piston in which an anti-abrasion ring was cast, and as a heat treatment after casting, the entire piston was subjected to T5 treatment and then subjected to T6 treatment only around the piston pin boss portion. In Comparative Example 2, peeling of the anti-abrasion ring is suppressed, and the strength of the piston pin boss portion is improved. However, the piston head portion is insufficient in flexibility of the crown portion and may be cracked. In addition, since the piston pin boss portion is repeatedly subjected to the T5 process and the T6 process, it is troublesome twice. On the other hand, the piston 1 of the present embodiment has hardness that the crown portion 20 is lower than the hardness of the piston pin boss portions 41 and 42, but the whole piston 1 is T6 treated. For this reason, moderate flexibility of the crown portion 20 can be realized while ensuring the strength of the piston pin boss portions 41 and 42. Moreover, since the T6 process is performed only once, the manufacturing process is simple.

[Second Embodiment]
Only differences from the first embodiment will be described. The heat treatment process of this embodiment includes a masking process. In the masking step, after the solution treatment step and before the cooling step, a predetermined region including the wear resistant ring 6 on the surface of the piston 1 is covered with a member other than the piston 1. Specifically, a region of the surface of the piston 1 (excluding the inner peripheral surface 10) that is not immersed in the coolant 70 in the first embodiment is covered with the masking member 8. The masking member 8 is formed of a heat insulating material and has a heat insulating property. The masking member 8 covers at least the outer peripheral surface of the land portion 21 including the piston crown surface 22 and the piston ring grooves 211 to 213. In addition, you may perform a masking process before a solution treatment process. Thereafter, as shown in FIG. 4, in the cooling step, the entire piston 1 partially covered by the masking member 8 is immersed in the coolant 70 that has entered the cooling tank 7. The portion covered by the masking member 8 is in contact with the coolant 70, and the portion not covered by the masking member 8 is not in contact with the coolant 70.

In this way, the piston crown surface 22 is not cooled by the masking member 8 (indirect cooling without being exposed to the coolant 70), thereby obtaining an appropriate flexibility in the region adjacent to the piston crown surface 22. Can do. Further, the outer peripheral surface of the land portion 21 is not cooled by the masking member 8 (it is indirectly exposed to the heat conduction inside the piston 1 without being exposed to the coolant 70), so that the joint surface with the anti-ring 6 is joined. It can suppress that the predetermined area | region containing is rapidly cooled, and generation | occurrence | production of interface peeling at the time of cooling can be suppressed. The range in which the masking member 8 covers the surface of the piston 1 is preferably set to a range in which the above-described effects can be obtained.
In addition, the same effect as the first embodiment can be obtained by the same configuration as the first embodiment.

[Third embodiment]
Only differences from the first embodiment will be described. As shown in FIG. 5, in the cooling process of the present embodiment, the coolant 70 is injected onto the inner peripheral surface 10 of the piston 1. Specifically, the cooling liquid 70 is water, and the mist-like cooling liquid 70 is sprayed from the spray nozzle 9 onto the inner peripheral surface 10. At this time, the piston 1 is disposed such that the axis of the piston 1 is along the vertical direction and the piston crown surface 22 side is on the upper side in the vertical direction. The coolant 70 is sprayed from the lower side in the vertical direction toward the upper side. The injected coolant 70 adheres to the back surface of the piston crown surface 22 of the piston back surface 23 and the inner surface of the piston pin boss portions 41 and 42 in the radial direction with respect to the axis of the piston 1, and also to the piston pin holes 410 and 420. After adhering to the inner peripheral surface, etc., it flows out by gravity. The coolant 70 is not sprayed on the surfaces (the crown surface 22 and the outer peripheral surface of the piston 1) excluding these surfaces. For example, the cooling rate is set to a rate at which the sprayed portion of the coolant 70 decreases from 500 ° C. to 300 ° C. in about 180 seconds. The coolant 70 is not limited to water but may be oil or the like. Water is advantageous for cooling because of its high specific heat.

  As shown in FIG. 6, the cooling speed of the piston 1 as it moves away from the surface α to which the coolant 70 adheres and the region α adjacent to the surface inside the piston 1 to the regions β and γ inside the piston 1. Or less. Therefore, the hardness of the piston 1 has a gradient corresponding to the part, and decreases in the order of α, β, γ. The piston pin boss portions 41 and 42 including the regions α and β have higher hardness than the crown portion 20 (including the vicinity of the piston ring surface 22) including the region γ and the land portion 21 (including the vicinity of the anti-ring ring 6). .

  In the cooling process of the present embodiment, in order to locally cool the piston 1, the coolant 70 is sprayed onto a portion (piston pin boss portions 41, 42) that requires rapid cooling. Thereby, a local cooling process can be performed easily. Instead of immersing the piston 1 in the coolant 70, the coolant 70 is injected into the piston 1, so that the masking member does not cover part of the surface of the piston 1 as in the second embodiment. The local cooling process can be easily performed. The coolant 70 may be sprayed after a part of the surface of the piston 1 is covered with the masking member.

  In the cooling step, the coolant 70 is sprayed from the lower side in the vertical direction toward the upper side. Therefore, effective cooling is possible. That is, when the coolant 70 is injected from the upper side to the lower side in the vertical direction, the coolant 70 may remain on the surface of the piston 1 and not flow out. For example, there is a possibility that cooling (quenching) cannot be performed sufficiently, for example, the coolant 70 accumulates on the inner peripheral side of the piston 1 and boils. On the other hand, by injecting the coolant 70 from the lower side, the coolant 70 once adhered to the surface of the piston 1 flows out of the piston 1 due to gravity. Therefore, the cooling liquid 70 is unlikely to stay on the surface of the piston 1, so that cooling can be performed more effectively.

  Specifically, in the cooling step, the mist-like coolant 70 is sprayed by spraying. Therefore, it is easy to cool the (local) surface of the piston 1 uniformly and gradually. In addition, the occurrence of the Leidenfrost phenomenon can be suppressed, and cooling can be performed more effectively. 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]
Only differences from the first embodiment will be described. The cooling process of this embodiment injects cooling gas with respect to the piston pin boss parts 41 and 42. For example, air as a cooling gas is injected into a region (including the piston pin holes 410 and 420) opposite to the piston head portion 2 in the piston 1 in the axial direction. In this case, the cooling gas is not injected to the regions other than the region. Alternatively, the cooling gas is injected onto the inner peripheral surface 10 of the piston 1 as in the third embodiment. In this case, the cooling gas is not injected to the surfaces other than the inner peripheral surface 10 and the inner peripheral surfaces of the piston pin holes 410 and 420 (part of them). The cooling gas is not limited to air but may be carbon dioxide. The cooling gas may be intensively injected onto the surfaces of the piston pin boss portions 41 and 42 including the inner peripheral surfaces of the piston pin holes 410 and 420. Further, a masking member may be used as in the second embodiment.

  Thus, by injecting the cooling gas, the local cooling process can be easily performed as in the third embodiment. Further, the equipment can be simplified as compared with the case of using the coolant. In addition, problems such as coolant remaining on the surface of the piston 1 and Leidenfrost phenomenon can be avoided. 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]
Only differences from the first embodiment will be described. In the cooling process of the present embodiment, a cooling process is performed on all of the solutionized piston 1, and the cooling temperature (temperature of the cooling fluid) is changed for each part of the piston 1. The cooling temperature of the piston pin boss portions 41 and 42 is set to a temperature that has a higher cooling effect than the cooling temperature of the piston head portion 2. Particularly, in the piston pin boss portions 41 and 42, the cooling temperature of the region where the piston pin holes 410 and 420 are formed (inner peripheral surfaces of the piston pin holes 410 and 420) is set to a temperature T1 having a high cooling effect. Of the piston head portion 2, the cooling temperature of the crown portion 20 (the region radially inward from the vicinity of the anti-ring 6 and adjacent to the piston crown surface 22) is set to a temperature that has a lower cooling effect than T1. Further, the cooling temperature of the land portion 21 (near the anti-rotation ring 6) in the piston head portion 2 is set to a temperature having a cooling effect lower than that of T1.

  Thus, by changing the cooling temperature for each part of the piston 1, cooling (quenching) according to the characteristics required for each part of the piston 1 can be performed individually. High strength can be secured in the piston pin boss portions 41 and 42 (regions where the piston pin holes 410 and 420 are formed). In the crown portion 20 (region adjacent to the piston crown surface 22) of the piston head portion 2, moderate flexibility can be obtained. In the land portion 21, it is possible to suppress peeling of the anti-abrasion ring 6 during cooling. Note that any one of the first to fourth embodiments may be used as a specific cooling method. In this way, when the cooling temperature is changed for each part of the piston 1, a part of the piston 1 may not be subjected to the cooling process. In addition, the same effect as that of the first embodiment can be obtained by the same configuration as that of the first embodiment.

[Sixth embodiment]
Only differences from the first embodiment will be described. In the cooling process of the present embodiment, the cooling process is performed on all of the solution-formed piston 1, but the start timing of the cooling process is changed for each part of the piston 1. By accelerating the start of the cooling process, the cooling effect of the part can be enhanced, and by delaying the start of the cooling process, the cooling effect of the part can be lowered. Specifically, the cooling process for the piston pin boss parts 41 and 42 is started earlier than the cooling process for the piston head part 2. In particular, in the piston pin boss portions 41 and 42, the region where the piston pin holes 410 and 420 are formed (inner peripheral surfaces of the piston pin holes 410 and 420) is started earlier. Of the piston head portion 2, the cooling processing of the crown portion 20 (the region radially inward from the vicinity of the anti-ring 6 and adjacent to the piston crown surface 22) is started slower than the piston pin boss portions 41 and 42. . Further, the start of the cooling process of the land portion 21 (near the anti-rotation ring 6) in the piston head portion 2 is made slower than the piston pin boss portions 41 and 42. In addition, the cooling process of the piston head part 2 may be started before the cooling process of the piston pin boss parts 41 and 42 is finished, or the cooling of the piston head part 2 is finished after the cooling process of the piston pin boss parts 41 and 42 is finished. Processing may be started.

  Thus, by changing the start timing of the cooling process for each part of the piston 1, cooling (quenching) according to the characteristics required for each part of the piston 1 can be performed individually. High strength can be secured in the piston pin boss portions 41 and 42 (regions where the piston pin holes 410 and 420 are formed). In the crown portion 20 (region adjacent to the piston crown surface 22) of the piston head portion 2, moderate flexibility can be obtained. In the land portion 21, it is possible to suppress peeling of the anti-abrasion ring 6 during cooling. Note that any one of the first to fourth embodiments may be used as a specific cooling method. As described above, when the start timing of the cooling process is changed for each portion of the piston 1, the cooling process may not be performed on a part of the piston 1. Further, the length of the cooling time may be adjusted not with the start timing of the cooling process or with the start timing. In addition, the same effect as that of the first embodiment can be obtained by the same configuration as that of the first embodiment.

[Seventh embodiment]
Only differences from the first embodiment will be described. As shown in FIG. 7, the piston 1 of the present embodiment has a low thermal conductive film 11 as a joining member that joins the piston head portion 2 instead of the anti-ring 6. There is a recess 220 in a region of the piston crown surface 22. The recess 220 stores and holds the low thermal conductive film 11. At least a part of the film 11 is wrapped in the piston head part 2 and joined integrally with the piston head part 2. The surface on one side in the axial direction of the coating 11 faces the combustion chamber, and the surface on the other side in the axial direction of the coating 11 is in contact with the bottom surface of the recess 220. The outer surface (outer peripheral surface) of the coating 11 in the radial direction with respect to the axis is in contact with the inner peripheral surface (inner wall) of the recess 220. The film 11 includes zirconia (zirconium dioxide) and other low thermal conductivity materials, and a binder. The binder is a metal, and includes, for example, aluminum (pure aluminum or the same aluminum alloy as the piston 1). The thermal conductivity of the film 11 is smaller than the thermal conductivity of the piston head portion 2. The coating 11 only needs to have a lower thermal conductivity than the piston head 2, and may be, for example, a sintered body of aluminum powder. Any one of the first to sixth embodiments may be used for the heat treatment step. In short, the vicinity of the low thermal conductive film 11 (recess 220) is indirectly cooled (by heat conduction inside the piston 1). Alternatively, when the cooling process in the vicinity of the low thermal conductive film 11 (concave portion 220) is performed, it is sufficient that the cooling effect is lower than the cooling process of the piston pin boss portions 41 and.

  The low thermal conductive film 11 is formed of a low thermal conductive material, and is different in thermal properties (thermal conductivity) from the piston head portion 2. For this reason, in the heat treatment step, there is a possibility that peeling occurs at the interface where the low thermal conductive film 11 and the piston head part 2 are joined due to thermal shock during cooling. On the other hand, the hardness of the crown portion 20 (including the portion joined to the low thermal conductive film 11) is lower than the hardness of the piston pin boss portions 41 and 42. This is because the cooling process is performed in a region excluding a portion where the low thermal conductive film 11 is provided. By performing such a cooling process, the thermal shock during cooling is alleviated, so that it is possible to suppress the occurrence of interface peeling and damage to the product. 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. An engine mounted on a ship or the like is not limited to a vehicle. Moreover, you may apply the piston of this invention, and its manufacturing method to apparatuses other than an internal combustion engine.

[Technical ideas that can be grasped from the embodiment]
The technical idea (or technical solution, the same applies hereinafter) that can be understood 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 for an internal combustion engine containing an aluminum alloy,
A piston head portion having a T6 treated hardness;
A first piston pin hole into which the piston pin is inserted; a first piston pin boss portion having a hardness that is T6 treated and higher than the piston head portion;
A second piston pin hole into which the piston pin is inserted, and a second piston pin boss portion having a T6-treated hardness and higher than the piston head portion.
(2) In a more preferred embodiment, in the above embodiment,
The first piston pin boss part and the second piston pin boss part have a hardness higher than the hardness subjected to the T5 treatment.
(3) In another preferred embodiment, in any of the above embodiments,
A member joined to the piston head portion, the member having a thermal property different from that of the piston head portion;
The hardness of the portion of the piston head portion joined to the member is lower than the hardness of the first piston pin boss portion and the second piston pin boss portion.
(4) In still another preferred embodiment, in any of the above embodiments,
The average grain size of crystals precipitated from the aluminum alloy is smaller than the average grain size of crystals precipitated from the T5 treated aluminum alloy.
(5) In still another preferred embodiment, in any of the above embodiments,
The aluminum alloy includes silicon;
The average length in the longitudinal direction of the silicon crystals precipitated from the aluminum alloy is shorter than the average length in the longitudinal direction of the silicon crystals precipitated from the T5 treated aluminum alloy.
(6) In still another preferred embodiment, in any of the above embodiments,
The aluminum alloy includes copper;
The average particle size of the compound of aluminum and copper precipitated from the aluminum alloy is smaller than the average particle size of the compound precipitated from the aluminum alloy treated with T5.
(7) In still another preferred embodiment, in any of the above embodiments,
Having a casting surface formed during casting,
The oxide film covering the casting surface is thicker than the oxide film covering the surface of the aluminum alloy that has been T5 treated.
(8) In still another preferred embodiment, in any of the above embodiments,
The color density of the surface is higher than the color density of the surface of the aluminum alloy treated with T5.
(9) Moreover, in one aspect of the manufacturing method of the piston of the present technical idea,
A first step of molding the piston in the first state;
The piston in the first state is inserted with a piston head portion, a first skirt portion and a second skirt portion, a first piston pin boss portion having a first piston pin hole into which the piston pin is inserted, and the piston pin. A second piston pin boss having a second piston pin hole.
The first step;
A second step of changing to a piston in the second state by solutionizing the piston in the first state;
A third step of cooling the first piston pin boss part and the second piston pin boss part without cooling at least a part of the piston head part of the piston in the second state.
(10) In a more preferred embodiment, in the above embodiment,
The piston in the second state is a joining member joined to the piston, and has a joining member whose thermal properties are different from those of the piston,
In the third step, among the pistons in the second state, the joining member and the vicinity thereof are not cooled.
(11) In another preferred embodiment, in any of the above embodiments,
Prior to the third step, there is a step of covering a predetermined region including the joining member on the surface of the piston with a member other than the piston.
(12) In still another preferred embodiment, in any of the above embodiments,
The third step includes a region in which the first piston pin hole is formed in the first piston pin boss portion and a region in which the second piston pin hole is formed in the second piston pin boss portion, A region opposite to the piston head portion with respect to the first piston pin hole and the second piston pin hole is immersed in a coolant.
(13) In still another preferred embodiment, in any of the above embodiments,
In the third step, a coolant is sprayed onto the first piston pin boss portion and the second piston pin boss portion.
(14) In still another preferred embodiment, in any of the above embodiments,
In the third step, the coolant is injected from the lower side in the vertical direction toward the upper side.
(15) In still another preferred embodiment, in any of the above embodiments,
In the third step, the mist-like coolant is sprayed by spraying.
(16) In still another preferred embodiment, in any of the above embodiments,
The third step includes a region in which the first piston pin hole is formed in the first piston pin boss portion and a region in which the second piston pin hole is formed in the second piston pin boss portion, A region on the opposite side of the piston head portion with respect to the first piston pin hole and the second piston pin hole is immersed in a coolant.
(17) In still another preferred embodiment, in any of the above embodiments,
In the third step, a cooling gas is injected to the first piston pin boss portion and the second piston pin boss portion.
(18) In still another preferred embodiment, in any of the above embodiments,
In the third step, the inner peripheral surface of the first piston pin hole in the first piston pin boss portion and the inner peripheral surface of the second piston pin hole in the second piston pin boss portion are cooled, and then another Cool the area.
(19) In still another preferred embodiment, in any of the above embodiments,
In the third step, the cooling temperature is changed for each portion of the piston in the second state.

DESCRIPTION OF SYMBOLS 1 Piston 2 Piston head part 41 1st piston pin boss part 410 1st piston pin hole 42 2nd piston pin boss part 420 2nd piston pin hole 51 1st skirt part 52 2nd skirt part 6 Wear-resistant ring (joining member)
11 Low thermal conductive film (joining member)

Claims (19)

A piston for an internal combustion engine containing an aluminum alloy,
A piston head portion having a T6 treated hardness;
A first piston pin boss portion having a first piston pin hole into which the piston pin is inserted and having a T6-treated hardness and higher than the piston head portion;
A piston for an internal combustion engine, having a second piston pin hole into which the piston pin is inserted, and a second piston pin boss portion having a T6-treated hardness and higher than the piston head portion. The piston of the internal combustion engine according to claim 1,
The first piston pin boss portion and the second piston pin boss portion are pistons of an internal combustion engine having a hardness higher than a hardness subjected to T5 treatment. The piston of the internal combustion engine according to claim 1,
A member joined to the piston head portion, the member having a thermal property different from that of the piston head portion;
The hardness of the part joined to the member in the piston head part is lower than the hardness of the first piston pin boss part and the second piston pin boss part,
Piston for internal combustion engine. The piston of the internal combustion engine according to claim 1,
A piston for an internal combustion engine, wherein an average particle diameter of crystals precipitated from the aluminum alloy is smaller than an average particle diameter of crystals precipitated from the T5 treated aluminum alloy. The piston of the internal combustion engine according to claim 4,
The aluminum alloy includes silicon;
The average length in the longitudinal direction of the silicon crystals precipitated from the aluminum alloy is shorter than the average length in the longitudinal direction of the silicon crystals precipitated from the T5 treated aluminum alloy,
Piston for internal combustion engine. The piston of the internal combustion engine according to claim 4,
The aluminum alloy includes copper;
The average particle size of the compound of aluminum and copper precipitated from the aluminum alloy is smaller than the average particle size of the compound precipitated from the aluminum alloy treated with T5.
Piston for internal combustion engine. The piston of the internal combustion engine according to claim 1,
Having a casting surface formed during casting,
The oxide film covering the casting surface is thicker than the oxide film covering the surface of the aluminum alloy that has been T5 treated.
Piston for internal combustion engine. The piston of the internal combustion engine according to claim 1,
The piston of an internal combustion engine, wherein the color density of the surface is higher than the color density of the surface of the aluminum alloy treated with T5. A piston manufacturing method comprising:
A first step of molding the piston in the first state;
The piston in the first state is inserted with a piston head portion, a first skirt portion and a second skirt portion, a first piston pin boss portion having a first piston pin hole into which the piston pin is inserted, and the piston pin. A second piston pin boss having a second piston pin hole.
The first step;
A second step in which the piston in the first state is changed into a piston in the second state by solutionizing;
A third step of cooling the first piston pin boss part and the second piston pin boss part without subjecting at least a part of the piston head part to the cooling process among the pistons in the second state. Method. In the manufacturing method of the piston according to claim 9,
The piston in the second state is a joining member joined to the piston, and has a joining member having a thermal property different from that of the piston,
In the third step, among the pistons in the second state, the joining member and its vicinity are not cooled.
Piston manufacturing method. In the manufacturing method of the piston according to claim 10,
Prior to the third step, a method of manufacturing a piston, comprising a step of covering a predetermined region including the joining member on the surface of the piston with a member other than the piston. In the manufacturing method of the piston according to claim 11,
The third step includes a region in which the first piston pin hole is formed in the first piston pin boss portion and a region in which the second piston pin hole is formed in the second piston pin boss portion, A method for manufacturing a piston, wherein a region opposite to the piston head portion with respect to the first piston pin hole and the second piston pin hole is immersed in a coolant. In the manufacturing method of the piston according to claim 9,
The third step is a method of manufacturing a piston, wherein a coolant is injected to the first piston pin boss portion and the second piston pin boss portion. In the manufacturing method of the piston according to claim 13,
The third step is a method for manufacturing a piston, wherein the coolant is injected from the lower side to the upper side in the vertical direction. In the manufacturing method of the piston according to claim 13,
The third step is a method for manufacturing a piston, wherein the mist-like coolant is sprayed by spraying. In the manufacturing method of the piston according to claim 9,
The third step includes a region in which the first piston pin hole is formed in the first piston pin boss portion and a region in which the second piston pin hole is formed in the second piston pin boss portion, A method for manufacturing a piston, wherein a region opposite to the piston head portion with respect to the first piston pin hole and the second piston pin hole is immersed in a coolant. In the manufacturing method of the piston according to claim 9,
The third step is a method of manufacturing a piston, wherein a cooling gas is injected to the first piston pin boss portion and the second piston pin boss portion. In the manufacturing method of the piston according to claim 9,
The third step starts the cooling process of the inner peripheral surface of the first piston pin hole in the first piston pin boss part and the inner peripheral surface of the second piston pin hole in the second piston pin boss part. The manufacturing method which starts the cooling process of the area | region of this. In the manufacturing method of the piston according to claim 9,
The third step is a method of manufacturing a piston, wherein the cooling temperature is changed for each portion of the piston in the second state.

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