# US 2009/0266331 A1 · Piston for internal combustion engine and process for manufacturing the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2009/0266331 A1 - Document ID: US20090266331A1 - Status: Published application - Kind: A1 - Application number: 12/428,532 - Filed: 2009-04-23 - Published: 2009-10-29 - Earliest claimed: 2008-04-24 - Inventors: Kimihiko ANDO - Web page: https://patentgrep.com/patent/US20090266331A1 ## CPC - F02F 3/12: on piston heads - C21D 7/06: by shot-peening or the like - F02F 3/02: having means for accommodating or controlling heat expansion - Y10T 29/49249: Piston making - F02F: CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES - C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A piston for internal combustion engine includes a piston body, and a low thermal conductor. The piston body has a top that faces a combustion chamber of the internal combustion engine. The low thermal conductor is disposed in the top of the piston body. Moreover, the low thermal conductor has a superficial portion, and an interior portion. The superficial portion faces the combustion chamber. The interior portion is disposed on a more inner side in the low thermal conductor than the superficial portion is. In addition, the superficial portion exhibits a first porosity. The interior portion exhibits a second porosity. The first porosity is smaller than the second porosity. Moreover, the low thermal conductor's superficial portion has a combustion-chamber-side surface that faces the combustion chamber and is subjected to shot peening. ## Claims ### Claim 1 A piston for internal combustion engine, the piston comprising: a piston body having a top facing a combustion chamber of the internal combustion engine; and a low thermal conductor being disposed in the top of the piston body; the low thermal conductor having a superficial portion facing the combustion chamber, and an interior portion being disposed on a more inner side in the low thermal conductor than the superficial portion is; the superficial portion exhibiting a first porosity; the interior portion exhibiting a second porosity; and the first porosity being smaller than the second porosity. ### Claim 2 (depends on 1) The piston according to claim 1, wherein the low thermal conductor comprises a sintered body. ### Claim 3 (depends on 1) The piston according to claim 1, wherein the superficial portion of the low thermal conductor has a combustion-chamber-side surface facing the combustion chamber, and the low thermal conductor further has open pores that open in the combustion-chamber-side surface and exhibit an open porosity of 2% by volume or less. ### Claim 4 (depends on 1) The piston according to claim 1, wherein the low thermal conductor exhibits as a whole a porosity falling in a range of from 3 to 30% by cross-sectional area. ### Claim 5 (depends on 1) The piston according to claim 1, wherein the superficial portion of the low thermal conductor exhibits the first porosity that is less than 10% by cross-sectional area. ### Claim 6 (depends on 1) The piston according to claim 1, wherein the interior portion of the low thermal conductor exhibits the second porosity that falls in a range of from 10 to 40% by cross-sectional area. ### Claim 7 (depends on 2) The piston according to claim 2, wherein the sintered body comprises an alloy that includes Fe and Mn. ### Claim 8 A process for manufacturing piston for internal combustion engine, the piston comprising: a piston body having a top facing a combustion chamber of the internal combustion engine; and a low thermal conductor being disposed in the top of the piston body, and having a combustion-chamber-side surface to be disposed so as to face the combustion chamber; the manufacturing process comprising a step of: carrying out shot peening onto the combustion-chamber-side surface of the low thermal conductor. ### Claim 9 (depends on 8) The manufacturing process according to claim 8, wherein an open porosity, which open pores opening in the combustion-chamber-side surface of the low thermal conductor exhibit, is controlled to 2% by volume or less by means of the shot peening. ### Claim 10 (depends on 8) The manufacturing process according to claim 8, wherein the shot peening is carried out by means of ultrasonic shot peening. ### Claim 11 (depends on 10) The manufacturing process according to claim 10, wherein the ultrasonic shot peening comprises the steps of: disposing the low thermal conductor on the top of the piston body; enclosing an outer periphery of the combustion-chamber-side surface of the low thermal conductor with a housing; and colliding steel balls with the combustion-chamber-side surface within the housing.