Grease composition and rolling bearing

Abstract

A grease composition containing base oil, a thickener, and an additive, wherein said additive contains at least one kind selected from among a phosphite ester shown by a chemical formula (1) or a phosphite ester shown by a chemical formula (2); a content of said phosphite ester is 0.5 to 4 parts by weight for 100 parts by weight which is a total of an amount of said base oil and that of said thickener; and said additive contains neither phosphite esters other than said phosphite ester shown by said formula (1) or by said formula (2) nor phosphate esters having organic groups whose carbon number is not less than three:

1 . A grease composition containing base oil, a thickener, and an additive, wherein said additive contains at least one kind selected from among a phosphite ester shown by a chemical formula (1) or a phosphite ester shown by a chemical formula (2); a content of said phosphite ester is 0.5 to 4 parts by weight for 100 parts by weight which is a total of an amount of said base oil and that of said thickener: 
       
         
           
           
               
               
           
         
         in chemical formulas (1) and (2), R 1 , R 2 , R 3 , R 4 , and R 5  denote a methyl group or an ethyl group; R 1  and R 2  are the same group or different groups; R 3 , R 4 , and R 5  are the same group or different groups. 
       
     
     
         2 . A grease composition according to  claim 1 , wherein said additive contains neither phosphite esters other than said phosphite ester shown by said formula (1) or by said formula (2) nor phosphate esters having organic groups whose carbon number is not less than three. 
     
     
         3 . A grease composition according to  claim 1 , wherein said phosphite ester is dimethyl phosphite, diethyl phosphite, trimethyl phosphite or triethyl phosphite. 
     
     
         4 . A grease composition according to  claim 1 , wherein said thickener is a urea compound shown by a chemical formula (3): 
       
         
           
           
               
               
           
         
         in chemical formula (3), R 7  denotes a divalent hydrocarbon group whose carbon number is 6 to 15, each of R 6  and R 8  denotes a monovalent aromatic hydrocarbon group and R 6  and R 8  are the same or different. 
       
     
     
         5 . A grease composition according to  claim 1 , wherein said base oil is at least one oil selected from among a mineral oil and synthetic oil, and a kinematic viscosity of said base oil at 40° C. is 20 to 150 mm 2 /s. 
     
     
         6 . A grease composition according to  claim 1 , wherein a worked penetration of said grease composition is 200 to 350. 
     
     
         7 . A rolling bearing, comprising an inner ring; an outer ring; a plurality of rolling elements interposed between said inner ring and said outer ring; and
 a grease composition being packed in circumferences of said rolling elements wherein said grease composition is as claimed in  claim 1 .   
     
     
         8 . A rolling bearing according to  claim 7 , wherein said rolling bearing is used as a hub bearing. 
     
     
         9 . A rolling bearing, which supports a rotor of a motor, said rolling bearing comprising an inner ring; an outer ring; a plurality of rolling elements disposed between said inner ring and said outer ring; a sealing member provided at openings disposed at both axial ends of said inner ring and said outer ring; and
 a grease composition being in circumferences of said rolling elements   wherein said grease composition is as claimed in  claim 1 .   
     
     
         10 . A rolling bearing according to  claim 9 , wherein the grease of the rolling bearing comprises a base oil having a kinematic viscosity at 40° C. of 20 to 50 mm 2 /s. 
     
     
         11 . A rolling bearing according to  claim 9 , wherein the grease of the rolling bearing comprises at least one base oil selected from among ester oil and poly-a-olefin oil. 
     
     
         12 . A rolling bearing according to  claim 9 , wherein said thickener is at least one selected from among lithium soap and a urea compound. 
     
     
         13 . A rolling bearing according to  claim 9 , which is a deep groove ball bearing. 
     
     
         14 . A rolling bearing according to  claim 9 , which supports rotors of motors for industrial machines and electric equipments and rotors of motors for driving electric cars.