Piston with engineered crown coating and method of manufacturing

Abstract

A steel piston with an engineered coating is provided. A high thermal conductivity material, for example copper, is disposed on first regions of a combustion bowl to reduce hot spots in the piston. A low thermal conductivity material, for example a ceramic, is disposed on second regions of the combustion bowl to reduce loss of heat through the piston. The high thermal conductivity material disposed on the combustion bowl has a surface roughness (R a ) of less than 5 μm to help reflect IR radiation and promote fuel flow. The low thermal conductivity material disposed on the combustion bowl has a surface roughness (R a ) of less than 3 μm to promote fuel flow. The low thermal conductivity material is also disposed on the bowl rim and top ring land, and has a surface roughness (R a ) of greater than 8 μm on the bowl rim and top ring land to retard gas flow.

1 . A method of manufacturing a piston, comprising the steps of:
 applying a high thermal conductivity material to at least one first region of a combustion bowl of a piston body, the high thermal conductivity material having a thermal conductivity of at least 100 W/mK; and   applying a low thermal conductivity material to at least one second region of the combustion bowl different from the at least one first region, the low thermal conductivity material having a thermal conductivity of not greater than 1 W/mK.   
     
     
         2 . The method of  claim 1  including smoothing the high thermal conductivity material disposed on the combustion bowl to a surface roughness (R a ) of less than 5 μm; and smoothing the low thermal conductivity material on the combustion bowl to a surface roughness (R a ) of less than 3 μm. 
     
     
         3 . The method of  claim 1  including applying the low thermal conductivity material to the bowl rim. 
     
     
         4 . The method of  claim 3  including smoothing the low thermal conductivity material on the bowl rim to a surface roughness (R a ) of greater than 8 μm. 
     
     
         5 . The method of  claim 1  including applying the low thermal conductivity material to a top ring land of the piston body. 
     
     
         6 . The method of  claim 5  including smoothing the low thermal conductivity material disposed on the top one of the ring lands to a surface roughness (R a ) of greater than 8 μm. 
     
     
         7 . The method of  claim 1 , wherein the steps of applying the high thermal conductivity material and the low thermal conductivity material include spraying the material from a plasma torch onto the piston body. 
     
     
         8 . The method of  claim 1 , wherein the high thermal conductivity material has a thermal conductivity of at least 300 W/mK; and the low thermal conductivity material includes ceramic. 
     
     
         9 . The method of  claim 1  including wrapping the piston body in a protective covering and leaving only regions to be coated exposed;
 grit blasting the exposed regions of the piston body to be coated with alumina; 
 blowing the piston body with dry compressed air; 
 washing the piston body with solvent; 
 disposing the piston body in a fixture of a plasma spray booth; 
 the steps of applying the high thermal conductivity material and the low thermal conductivity material including spraying the material from a plasma torch onto the piston body and moving a plasma torch along the piston body; 
 polishing the high thermal conductivity material and the low thermal conductivity material on the piston body; and 
 cleaning the polished piston with solvent.