Piston with keystone second ring groove for high temperature internal combustion engines

Abstract

A piston for a high temperature internal combustion engine is provided. The piston includes an upper wall, base wall, outer rib, and inner rib defining a cooling chamber therebetween, and a plurality of ring grooves formed in the outer rib. Only the second ring groove is formed with the keystone cross-section, and all of the other ring grooves are formed with the conventional rectangular cross-section. Thus, the piston can be formed with low manufacturing costs and can also provide exceptional performance when used in high temperature combustion engines, wherein the temperature at the first ring groove is greater than 280° C., and thus prevents carbon from depositing or burns off any carbon deposits, but the temperature at the second ring groove is between 200° C. and 280° C., in which case carbon deposits can form and cause the piston ring to stick.

What is claimed is: 
     
         1 . A piston, comprising:
 an upper wall surrounding a center axis and presenting a combustion surface;   an outer rib extending from said upper wall to a base wall and presenting an outer surface;   an inner rib disposed between said outer rib and said center axis and extending from said upper wall to said base wall;   said upper wall and said ribs and said base wall presenting a cooling chamber therebetween;   said outer rib including a plurality of ring grooves;   said plurality of ring grooves including a first ring groove being the ring groove closest to said combustion surface and a second ring groove being the ring groove second closest to said combustion surface;   each of said ring grooves including a pair of side flanks extending inwardly from said outer surface to a base flank;   said side flanks of said first ring groove extending perpendicular to said base flank of said first ring groove; and   at least one of said side flanks of said second ring groove being disposed at an angle greater than 90 degrees relative to said base flank of said second ring groove.   
     
     
         2 . The piston of  claim 1 , wherein said plurality of ring grooves include a third ring groove being the ring groove third closest to said combustion surface; and said side flanks of said third ring groove extend perpendicular to said base flank of said third ring groove. 
     
     
         3 . The piston of  claim 2  including not more than three of said ring grooves in said outer rib. 
     
     
         4 . The piston of  claim 1 , wherein said side flanks of all of said ring grooves except said second ring groove extend perpendicular to said base flank. 
     
     
         5 . The piston of  claim 1 , wherein said side flank of said second ring groove closest to said combustion surface is disposed at an angle greater than 90 degrees and not greater than 135 degrees relative to said base flank of said second ring groove. 
     
     
         6 . The piston of  claim 5 , wherein both of said side flanks of said second ring groove are disposed at an angle greater than 90 degrees and not greater than 135 degrees relative to said base flank of said second ring groove. 
     
     
         7 . The piston of  claim 1 , wherein said ring grooves are axially aligned with one another and axially spaced from one another by said outer surface of said outer rib; and each of said ring grooves extends radially inwardly from said outer surface toward said center axis and circumferentially around said center axis. 
     
     
         8 . The piston of  claim 1 , wherein each of said ring grooves is disposed axially along and radially outwardly of said cooling chamber. 
     
     
         9 . The piston of  claim 1  including an upper piston part and a lower piston part welded together and together forming said outer rib, wherein one of said side flanks and said base flank of said second ring groove is provided by said upper piston part and the other side flank of said second ring groove is provided by said lower piston part. 
     
     
         10 . The piston of  claim 1 , wherein said base flanks of said ring grooves extend parallel to said center axis and parallel to said outer surface;
 said base flanks are axially aligned with one another;   each of said base flanks has a length extending parallel to said center axis from one of said side flanks to the other side flank of said ring groove;   each of said base flanks is spaced from said cooling gallery by a distance of not greater than three times the length of said base flank;   said outer surface presents a first distance between said combustion surface and said first ring groove and a second distance between said first ring groove and said second ring groove and a third distance between said second ring groove and said third ring groove;   said first distance is not greater than five times the length of said base flank of said first ring groove; and   said second distance and said third distance are each not greater than three times the length of said base flank of said first ring groove.   
     
     
         11 . The piston of  claim 1 , wherein said first ring groove is at a temperature greater than 280° C. and said second ring groove is at a temperature between 200° C. and 280° C. during operation of said piston in an internal combustion engine. 
     
     
         12 . A piston, comprising:
 an upper piston part formed of a metal material and extending annularly around a center axis and longitudinally along said center axis from an upper wall to a first upper joining surface and a second upper joining surface;   said metal material of said upper piston part being a steel, cast iron, or aluminum material;   said upper wall of said upper piston part including a combustion surface presenting a bowl rim extending annularly around said center axis and a combustion bowl extending inwardly and downwardly from said bowl rim toward said center axis;   said combustion surface of said upper wall presenting an apex at said center axis and surrounded by said combustion bowl;   said upper piston part including an upper outer rib depending from said bowl rim of said upper wall and extending annularly around said center axis and longitudinally along said center axis to said first upper joining surface;   said upper outer rib presenting an upper outer surface extending annularly around said center axis and facing away from said center axis;   said upper piston part including an upper inner rib disposed between said upper outer rib and said center axis;   said upper inner rib depending from said upper wall beneath said combustion bowl and extending annularly around said center axis and longitudinally along said center axis to said second upper joining surface;   said first and second upper joining surfaces being flat and extending perpendicular to said center axis;   a lower piston part formed of a metal material and extending annularly around said center axis and longitudinally along said center axis;   said metal material of said lower piston part being steel, cast iron, or aluminum material;   said lower piston part including a lower outer rib extending from a base wall to a first lower joining surface, said first lower joining surface and said first upper joining surface including a weld therebetween;   said base wall extending perpendicular to and surrounding said center axis said lower outer rib extending annularly around said center axis and upwardly from said base wall to said first lower joining surface;   said lower outer rib presenting a lower outer surface extending annularly around said center axis and aligned with said upper outer surface;   said lower piston part including a lower inner rib spaced from said lower outer rib by said base wall and disposed radially inwardly of said lower outer rib;   said lower inner rib extending from said base wall to a second lower joining surface, said second lower joining surface and said second upper joining surface including a weld therebetween;   said lower inner rib extending annularly around said center axis and upwardly from said base wall to said second lower joining surface;   said first and second lower joining surfaces being flat and perpendicular to said center axis;   said welded inner ribs and said welded outer ribs and said upper wall and said base wall forming a cooling chamber therebetween;   said cooling chamber being closed and extending annularly around said center axis;   said inner ribs surrounding said center axis and forming a cooling gallery at said center axis;   said cooling gallery being closed along said upper wall and open in a direction facing away from said upper wall;   said lower piston part including a pair of pin bosses extending downwardly from said base wall away from said upper piston part;   each of said pin bosses presenting a pin bore, said pin bores being aligned with one another along a second axis perpendicular to said center axis;   said lower piston part including a pair of skirt sections each depending from said base wall and spaced from one another by one of said pin bosses;   said outer ribs together including three ring grooves each extending radially inwardly from said outer surface toward said center axis and circumferentially around said center axis for retaining a piston ring;   said outer ribs together including no more than three ring grooves;   said three ring grooves including a first ring groove and a second ring groove and a third ring groove being axially aligned and spaced from one another by said outer surface of said outer ribs;   said first ring groove being the ring groove closest to said combustion surface;   said second ring groove being the ring groove second closest to said combustion surface and disposed between said first ring groove and said second ring groove;   said third ring groove being the ring groove farthest from said combustion surface and being disposed between said second ring groove and said base wall;   each of said ring grooves being disposed axially along and radially outwardly of said cooling chamber;   each of said ring grooves including a pair of side flanks extending inwardly from said outer surface to a base flank;   said side flanks of said first ring groove extending perpendicular to said base flank of said first ring groove for retaining a piston ring having a rectangular shape;   said side flanks of said third ring groove extending perpendicular to said base flank of said third ring groove for retaining a piston ring having a rectangular shape;   at least one of said side flanks of said second ring groove being disposed at an angle greater than 90 degrees relative to said base flank of said second ring groove for retaining a piston ring having a keystone shape;   one of said side flanks and said base flank of said second ring groove being provided by said upper piston part and the other one of said side flanks of said second ring groove being provided by said lower piston part;   said base flanks of said ring grooves being axially aligned with one another and extending parallel to said center axis and parallel to said outer surface;   each of said base flanks having a length extending parallel to said center axis from one of said side flanks to the other of said side flanks, the length of said base flank of said third ring groove being greater than the length of said base flank of said second ring groove and greater than the length of said base flank of said first ring groove;   each of said base flanks being spaced from said cooling chamber by a distance of not greater than three times the length of said base flank;   said outer surface presenting first land extending a first distance from said combustion surface to said first ring groove, a second land extending a second distance from said first ring groove to said second ring groove, and a third land extending a third distance from said second ring groove to said third ring groove;   said first distance being no greater than five times the length of said base flank of said first ring groove; and   said second distance and said third distance being no greater than three times the length of said base flank of said first ring groove.   
     
     
         13 . A method of forming a piston, comprising the steps of:
 providing a piston including an upper wall surrounding a center axis and presenting a combustion surface, an outer rib extending from the upper wall to a base wall and presenting an outer surface, and an inner rib extending from the upper wall to the base wall and disposed between the outer rib and the center axis, the upper wall and the ribs and the base wall presenting a cooling chamber therebetween; and   forming a plurality of ring grooves in the outer rib;   the step of forming the ring grooves including forming a first ring groove being the ring groove closest to the combustion surface and a second ring groove being the ring groove second closest to the combustion surface; and   the step of forming the ring grooves including forming each ring groove with a pair of side flanks extending inwardly from the outer surface to a base flank, the side flanks of the first ring groove extending perpendicular to the base flank of the first ring groove, and at least one of the side flanks of the second ring groove extending at an angle greater than 90 degrees relative to the base flank of the second ring groove.   
     
     
         14 . The method of  claim 13 , wherein the step of forming the ring grooves includes forming a third ring groove being the ring groove farthest from the combustion surface; and
 forming the third ring groove with side flanks extending perpendicular to the base flank of the third ring groove.   
     
     
         15 . The method of  claim 13 , wherein the step of forming the ring grooves includes forming not more than three of the ring grooves in the outer rib. 
     
     
         16 . The method of  claim 13 , wherein the step of forming the ring grooves includes forming side flanks of all of the ring grooves extending perpendicular to the base flank except for the at least one side flank of the second ring groove. 
     
     
         17 . The method of  claim 13 , wherein the step of forming the ring grooves includes forming the side flank of the second ring groove closest to the combustion surface at an angle greater than 90 degrees and not greater than 135 degrees relative to the base flank of the second ring groove. 
     
     
         18 . The method of  claim 17  including forming both of the side flanks of the second ring groove an angle greater than 90 degrees and not greater than 135 degrees relative to the base flank of the second ring groove. 
     
     
         19 . The method of  claim 13 , wherein the step of forming the ring grooves includes machining or casting. 
     
     
         20 . The method of  claim 13  including providing an upper piston part and a lower piston part, and welding the upper piston part to the lower piston part, wherein each of the piston parts provide a portion of the outer rib and a portion of the inner rib.