Piston for an Internal Combustion Engine and Method for Its Production

Abstract

The present invention relates to a piston ( 10 ) for an internal combustion engine, having at least two hub bores ( 18 ) for holding a piston pin, wherein the hub bores ( 18 ) have at least one geometric deviation from a cylindrical inner contour. It is provided according to the invention that the hub bores ( 18 ) are formed from bores ( 21 ) with a cylindrical inner contour, that the bores ( 21 ) are provided with a coating ( 22 ) comprising a resin with solid lubricant particles embedded therein, and that the coating ( 22 ) forms the at least one geometric deviation from the cylindrical inner contour of the hub bores ( 18 ). The present invention also relates to a method for producing a piston of the type, in which method bores ( 21 ) with a cylindrical inner contour are initially produced, and a coating medium comprising a resin with solid lubricant particles embedded therein is subsequently applied to the inner faces of said bores ( 21 ) by means of a coating tool ( 30 ), such that the resulting coating ( 22 ) forms the at least one geometric deviation from the cylindrical inner contour of the hub bores ( 18 ).

1 : Piston ( 10 ) for an internal combustion engine, having at least two pin bores ( 18 ) for accommodating a piston pin, whereby the pin bores ( 18 ) have at least one geometric deviation from a cylindrical inside contour, wherein the pin bores ( 18 ) are formed from bores ( 21 ) having a cylindrical inside contour, that the bores ( 21 ) are provided with a coating ( 22 ) comprising a resin with solid lubricant particles embedded in it, and that the coating ( 22 ) forms the at least one geometric deviation from the cylindrical inside contour of the pin bores ( 18 ). 
   
   
       2 : Piston according to  claim 1 , wherein the at least one geometric deviation is configured as at least one stress relief pocket and/or ovality and/or as a shaped bore. 
   
   
       3 : Piston according to  claim 1 , wherein at least one oil collection chamber ( 24 ,  25 ) is provided in the coating ( 22 ). 
   
   
       4 : Piston according to  claim 3 , wherein the at least one oil collection chamber is configured as a channel ( 24 ) that runs in the pin boss axis direction. 
   
   
       5 : Piston according to  claim 3 , wherein the at least one oil collection chamber is configured as a channel that runs radially relative to the pin boss axis direction, surrounding it entirely or in part. 
   
   
       6 : Piston according to  claim 3 , wherein the at least one oil collection chamber is configured as a pocket-shaped recess. 
   
   
       7 : Piston according to  claim 1 , wherein the minimum thickness of the coating ( 22 ) amounts to 5 μm to 20 μm. 
   
   
       8 : Piston according to  claim 1 , wherein the resin is a thermally cured resin, particularly a polyamide imide resin. 
   
   
       9 : Piston according to  claim 1 , wherein the coating ( 22 ) contains 50 wt.-% to 60 wt.-% solid lubricant particles. 
   
   
       10 : Piston according to  claim 1 , wherein the solid lubricant particles consist of a material that is selected from the materials group that comprises graphite, molybdenum sulfide, tungsten disulfide, hexagonal boron nitride, and PTFE (polytetrafluoroethylene). 
   
   
       11 : Piston according to  claim 1 , wherein the solid lubricant particles have a particle size of 1 μm to 3 μm. 
   
   
       12 : Method for the production of a piston ( 10 ) for an internal combustion engine, having at least two pin bores ( 18 ) for accommodating a piston pin, whereby the pin bores ( 18 ) have at least one geometric deviation from a cylindrical inside contour, wherein first, bores ( 21 ) having a cylindrical inside contour are produced, and subsequently, a coating agent comprising a resin with solid lubricant particles embedded in it is applied to the inside surfaces of these bores ( 21 ), by means of a coating tool ( 30 ), so that the resulting coating ( 22 ) forms the at least one geometric deviation from the cylindrical inside contour of the pin bores ( 18 ). 
   
   
       13 : Method according to  claim 12 , wherein the at least one geometric deviation is configured by means of varying the amount of the coating agent given off by the coating tool ( 30 ) and/or by means of varying the advance of the coating tool ( 30 ). 
   
   
       14 : Method according to  claim 12 , wherein the coating agent is applied to inside surfaces of the bores ( 21 ) with a surface roughness of Ra (average roughness value)≦0.8 μm. 
   
   
       15 : Method according to  claim 12 , wherein the coating agent is applied by means of rotation atomization from a rotating nozzle ( 34 ) introduced into the bore ( 21 ). 
   
   
       16 : Method according to  claim 15 , wherein the rotation atomization is carried out at a rotation speed of the nozzle of 14,000 to 18,000 rotations per minute. 
   
   
       17 : Method according to  claim 12 , wherein the inside surfaces of the bores ( 21 ) are pre-heated before and/or during application of the coating agent, preferably up to a temperature of 50° C. to 80° C. 
   
   
       18 : Method according to  claim 12 , wherein a thermally curing coating agent is used, which is subjected to heat treatment immediately after completing the application, preferably at a temperature of 200° C.