Engine piston assembly and forged piston member therefor having a cooling recess

Abstract

Present day diesel engines having aluminum piston assemblies are limited to combustion chamber pressures of approximately 12,410 kPa (1,800 psi) whereas the desire is to increase such pressures up to the 15,170 kPa (2,200 psi) range. To reach such levels the instant piston assembly includes a steel piston member having an upper cylindrical portion defining a top surface, a depending tubular wall and an annular cooling recess having one or more machined surfaces of revolution about a central axis. The cooling recess is located beneath the top surface and juxtaposed to the top ring groove for removing heat away therefrom in use. The piston member is preferably forged and subsequently machined to precisely controllable dimensions. Moreover, the piston assembly is preferably of the articulated type and includes a forged aluminum piston skirt connected to the piston member through a common wrist pin.

What is claimed: 
     
       1. .[.AΘ .Iadd.An articulated piston assembly comprising an upper .Iaddend.forged .Iadd.one piece .Iaddend.steel piston member.Iadd., a lower aluminum skirt member, and a pin articulately mounting the members .Iaddend.for reciprocating movement in an engine.Iadd., the upper piston member .Iaddend.comprising: an upper portion of substantially cylindrical shape and having a central axis, a top surface, a tubular wall depending from the top surface and .Iadd.forged integral with the upper portion, the tubular wall .Iaddend.having a peripheral groove .Iadd.having a bottom surface and .Iaddend.adapted to receive a sealing ring.Iadd., the peripheral groove being spaced a preselected minimal elevational distance TRH from the top surface.Iaddend., a lower end surface, and an inwardly facing wall surface extending upwardly from the lower end surface;   the upper portion further including an outwardly facing wall surface spaced radially inwardly from the inwardly facing wall surface and a downwardly facing transition portion blendingly associated with the inwardly and outwardly facing wall surfaces to collectively define an annular cooling recess, the transition portion being .[.elevational.]. .Iadd.elevationally .Iaddend.spaced a relatively short distance "E" from the top surface.Iadd., the top of the cooling recess being in juxtaposed elevational relation with the peripheral groove to provide for removing heat from around the peripheral groove.Iaddend.; and   the inwardly facing wall surface being a machined surface of revolution about the central axis .[.integral or one piece forging.]. .Iadd.to maintain dimensional control and concentricity between the bottom surface of the peripheral groove and the inwardly facing wall surface.Iaddend..   
     
     
       2. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston .[.member.]. .Iadd.assembly .Iaddend.of claim 1 wherein the outwardly facing wall surface and the downwardly facing transition portion are machined surfaces of revolution about the central axis. 
     
     
       3. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston .[.member.]. .Iadd.assembly .Iaddend.of claim 1 .Iadd.wherein the upper piston member .Iaddend.further .[.including.]. includes a lower portion having a pair of depending pin bosses blendingly associated with the cooling recess and individually defining a bore, and the bores being aligned along a common axis. 
     
     
       4. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston .[.member.]. .Iadd.assembly .Iaddend.of claim 3 wherein the upper portion and lower portion are an integral or one-piece forging. 
     
     
       5. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston .[.member.]. .Iadd.assembly .Iaddend.of claim 4 wherein the material used for the .[.forging.]. .Iadd.upper piston member .Iaddend.is a chromium-molybdenum steel. 
     
     
       6. The forged steel piston member of claim 1 wherein the elevational distance "E" between the top surface and the top of the cooling recess is approximately 6 mm. 
     
     
       7. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston .[.member.]. .Iadd.assembly .Iaddend.of claim 1 wherein the upper portion defines a recessed crown surface which contains machined surfaces of revolution about the central axis so that a relatively uniform web is defined between the crown surface and the cooling recess. 
     
     
       8. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston .[.member.]. .Iadd.assembly .Iaddend.of claim 1 wherein the minimum radial thickness between the cooling recess and the innermost portion of the peripheral groove is about 1.74 mm. 
     
     
       9. The piston .Iadd.assembly .Iaddend.of claim 7 wherein the upper and lower portions are an integrally formed forging. 
     
     
       10. The piston assembly of claim 7 including an aluminum piston skirt, and a wrist pin connecting the piston member to the piston skirt. 
     
     
       11. The piston assembly of claim 10 wherein the outwardly facing wall surface and the downwardly facing transition portion are machined surfaces of revolution about the central axis. 
     
     
       12. An .[.engine.]. .Iadd.articulated .Iaddend.piston assembly for an engine of the type having a block defining a bore, a cylinder liner supported in the block and defining a piston bore, and a cylinder head connected to the block, wherein the improvement comprises: a forged steel .Iadd.piston .Iaddend.member .[.piston.]. having an upper portion of substantially cylindrical shape and having a central axis, a peripheral top surface, a tubular wall depending from the top surface and defining an outwardly facing top land, a top ring groove .Iadd.spaced .Iaddend.a preselected minimal elevational distance TRH .Iadd.of about 5 mm .Iaddend.from the top surface, a lower end surface, and an annular inwardly facing wall surface extending upwardly from the lower end surface;   the upper portion further including an annular outwardly facing wall surface spaced radially inward from the inwardly facing wall surface and a downwardly facing transition portion blendingly associated with the inwardly and outwardly facing wall surfaces to collectively define an annular cooling recess located in juxtaposed relation with to the top ring groove, the inwardly facing wall surface being a machined surface of revolution about the central axis; .[.and.].   a lower portion including a pair of depending pin bosses blendingly associated with the cooling recess and individually defining a bore and with the bores being aligned on a common axis;   .Iadd.a piston skirt defining a pair of wrist pin receiving bores aligned with the bores of the pin bosses; and   a wrist pin in the aligned bores for articulately connecting the piston skirt and the piston member.Iaddend..