Piston and method of making a piston

Abstract

A one-piece piston including a combustion bowl which is cast to its final form and includes at least one irregularity spaced from a central axis. The piston is initially fabricated of an upper crown member and a lower crown member, which are joined together. The piston is then chucked into a machine tool, such as a CNC lathe, which locates either the piston's top surface or a portion of the combustion bowl and establishes its location as a datum plane. It is this datum plane which serves as a reference location for subsequent machining operations of the piston.

What is claimed is: 
     
         1 . A method of making a piston comprising the steps of:
 preparing a single piece upper crown member of steel having a top surface and a combustion bowl recessed in said top surface, wherein the combustion bowl has a final finish form that is produced by other than machining;   preparing a lower crown member as a discrete component separate from the upper crown member;   joining the upper and lower crown members together; and   machining at least a portion of said jointed upper and lower crown members other than said combustion bowl.   
     
     
         2 . The method of  claim 1 , wherein the final finish form of the combustion bowl is produced by casting. 
     
     
         3 . The method of  claim 1 , wherein at least a portion of the piston is produced by forging. 
     
     
         4 . The method of  claim 3 , wherein at least portions of the forged piston are in the final finished form. 
     
     
         5 . The method of  claim 1 , wherein the top surface has a final finish form produced by other than casting. 
     
     
         6 . The method of  claim 1  wherein the upper and lower crown members are joined by friction welding. 
     
     
         7 . The method of  claim 6  wherein the friction welded upper and lower crown members are formed with an annular oil gallery. 
     
     
         8 . The method of  claim 1  including forming the final finished form of the combustion bowl to have a complex shape lacking rotational symmetry. 
     
     
         9 . The method of  claim 8  wherein the complex shape is asymmetric in the circumferential direction of the combustion bowl. 
     
     
         10 . A method of making a piston comprising the steps of:
 preparing a single piece upper crown member of cast steel having a top surface, a combustion bowl recessed in said top surface and an undercrown opposite the combustion bowl, wherein the combustion bowl and the undercrown has a final finish form that is produced by casting;   preparing a lower crown member as a discrete component separate from the upper crown member;   joining the upper and lower crown members together;   machining at least a portion of said jointed upper and lower crown members other than said undercrown and said combustion bowl; and   wherein the combustion bowl includes at least one irregularity spaced radially from a central axis and extending less than circumferentially around the central axis.