Spark plug and method of manufacturing same

Abstract

A spark plug and a method of manufacturing same is provided a spark plug for an internal combustion engine comprising, a center electrode 2 , a ground electrode 3 is formed a spark discharge gap G with the center electrode 2 , a housing welded to the end portion 31 of the ground electrode 3 . The surface of the housing 4 is formed a plated layer 5 whose melting point is lower than the melting point of the housing 4 and is lower than the melting point of the ground electrode 3 . There is substantially no the plated layer 5 on a junction boundary face between the housing 4 and the ground electrode 3 . The burr including constituents of the plated layer 5 lies next to the junction boundary face 11.

1 . A spark plug comprising: 
 a center electrode;    a ground electrode forming a spark discharge gap with said center electrode;    a housing welded to an end portion of said ground electrode;    a plated layer formed on a surface of said housing, said plated layer having a melting point lower than a melting point of said housing and lower than a melting point of said ground electrode;    substantially no plated layer exists on either of a junction boundary face between said housing and said ground electrode, or on a surface of said ground electrode; and    constituents of said plated layer exists in a welding burr formed next to said junction boundary face.    
   
   
       2 . A spark plug according to  claim 1 , wherein said melting point of the plated layer is 1000° C. or less.  
   
   
       3 . A spark plug according to  claim 1 , wherein said plated layer is made of electroless nickel plating.  
   
   
       4 . A spark plug according to  claim 1 , wherein said housing is made of metal including iron and the outermost layer of the ground electrode is at least made of heat-resistant nickel alloy.  
   
   
       5 . A spark plug according to  claim 1 , wherein said housing is sunk into said ground electrode by about 0.3 mm or more, and welded to the housing.  
   
   
       6 . A method of manufacturing a spark including a center electrode; a ground electrode forming a spark gap with said center electrode; and a housing welded to an end portion of said ground electrode; the method including: 
 forming a plated layer on a surface of said housing, said plated layer having a melting point in lower than a melting point of the housing and lower than a melting point of the ground electrode;    welding between said housing and said ground electrode by resistance welding while contacting an end portion of said ground electrode with a top surface of said housing via said plated layer; and    extruding out constituents said plated layer from a junction boundary face between said housing and said ground electrode during said welding.    
   
   
       7 . A method for manufacturing a spark plug according to  claim 6 , wherein the welding burr is formed next to the junction boundary face between the housing and the ground electrode and the resistance welding is carried out so that welding burr includes all the constituents of said plated layer.  
   
   
       8 . A method for manufacturing a spark plug according to  claim 6 , wherein a projecting portion is formed on said top surface of said housing and, said ground electrode is welded to said housing by resistance welding with said projection portion contacts said end portion of said ground electrode.  
   
   
       9 . A method for manufacturing a spark plug according to  claim 6 , wherein a projection portion is formed on said end portion of said ground electrode and, said projection portion of said ground electrode contacts said top surface of said housing while said ground electrode is welded to said top surface of said housing by resistance welding.  
   
   
       10 . A method for manufacturing a spark plug according to  claim 6 , wherein said plated layer is made of electroless nickel plating.  
   
   
       11 . A method for manufacturing a spark plug according to  claim 6 , wherein said housing is sunk into said ground electrode by about 0.3 mm or more, and welded to said housing.