Grease composition for resin lubrication and electric power steering apparatus

Abstract

An object of the present invention is to provide a grease composition for resin lubrication which is capable of keeping good the sliding lubrication between a resin member and a metal member, and between a metal member and another metal member over the long term. The present invention provides a grease composition for resin composition which is characterized by including a base, a thickener, and at least one of a nonpolar wax and a polar wax. Further, the grease composition for resin lubrication is applied to a telescopic shaft for vehicle steering or an electric power steering apparatus, thereby to improve the durability, and to achieve a longer life.

1 . A grease composition for resin lubrication comprising a base oil, a thickener and at least one of a nonpolar wax and a polar wax.  
     
     
         2 . A grease composition for resin lubrication comprising a base oil, a thickener, and both of a nonpolar wax and a polar wax, 
 characterized in that the nonpolar wax is in an amount of 3 mass % or more based on the total amount of the grease,    the polar wax is in an amount of 2 mass % or more based on the total amount of the grease and    the total amount of the polar wax and the nonpolar wax is in an amount of 10 mass % or less based on the total amount of the grease.    
     
     
         3 . The grease composition for resin lubrication according to  claim 1  or  2 , characterized in that the nonpolar wax is a polyolefin wax.  
     
     
         4 . The grease composition for resin lubrication according to  claim 1  or  2 , characterized in that the polar wax is a wax of a montanic acid derivative.  
     
     
         5 . The grease composition for resin lubrication according to any one of  claims 1  to  4 , characterized in that the thickener is a diurea compound or a metallic complex soap.  
     
     
         6 . The grease composition for resin lubrication according to  claim 5 , characterized in that the thickener is a diurea compound represented by following formula (I), and R 1  and R 3  are each n-octylamine or a straight chain aliphatic amine having 12 to 20 carbon atoms, and the mole ratio of n-octylamine and the straight chain aliphatic amine having 12 to 20 carbon atoms is 1:4 to 4:1.  
       
         
           
           
               
               
           
         
       
     
     
         7 . The grease composition for resin lubrication according to any one of  claims 1  to  6 , characterized in that 70 mass % or more of the base oil is a poly α-olefin oil.  
     
     
         8 . The grease composition for resin lubrication according to any one of  claims 1  to  7 , characterized in that the base oil is at least one of dialkyl diphenyl ether, an ester type synthetic oil, and a highly refined mineral oil.  
     
     
         9 . The grease composition for resin lubrication according to anyone of  claims 1  to  8 , characterized in that the base oil kinematic viscosity is 15 to 200 mm 2 /s at 40° C.  
     
     
         10 . The grease composition for resin lubrication according to anyone of  claims 1  to  9 , characterized in that as a rust inhibitor, a sulfonic acid metal salt or a sulfonic acid calcium salt has been added in an amount of 0.3 to 4.0 mass % based on the total amount of the grease.  
     
     
         11 . The grease composition for resin lubrication according to any one of  claims 1  to  10 , characterized in that the grease composition is used for sliding lubrication between a resin member and a metal member.  
     
     
         12 . An electric power steering apparatus for transferring an auxiliary power by an electric motor to a steering mechanism of a vehicle via a speed reduction gear mechanism, 
 characterized in that a driven gear of the speed reduction gear mechanism includes a resin portion made of a resin composition, and having gear teeth formed on its outer peripheral surface, integrally provided around the outer periphery of a core tube made of metal, and the driving gear is made of metal, and lubrication is applied between the driven gear and driving gear with the grease composition according to any one of  claims 1  to  11 .    
     
     
         13 . The electric power steering apparatus according to  claim 12 , characterized in that the tooth surface roughness of the driving gear is 0.008 to 0.15 μm in terms of the arithmetic average roughness (Ra).  
     
     
         14 . The electric power steering apparatus according to  claim 12  or  13 , characterized in that the driving gear has been subjected to a palsonite treatment.  
     
     
         15 . A telescopic shaft for vehicle steering, to be incorporated into a steering shaft of a vehicle, having a male shaft and a female shaft unrotatably and slidably fitted to each other, 
 characterized in that a resin film is formed on a fitted portion surface of either one or both of the male shaft and the female shaft and the grease composition according to  claims 1  to  11  is allowed to lie between the male shaft and the female shaft, and a wax has been mixed in the grease composition in an amount of 2 to 10 mass % based on the total amount of the grease.    
     
     
         16 . The telescopic shaft for vehicle steering according to  claim 15 , characterized in that a mineral oil or a synthetic hydrocarbon oil is contained in an amount of 70 mass % or more based on the total amount of the base oil as a base oil, 
 a base oil kinematic viscosity is 15 to 200 mm 2 /s at 40° C.,    the wax is at least one selected from polyethylene, a montanic acid derivative, oxidized polyethylene, fatty acid amide, ketone, and polytetrafluoroethylene and    a worked penetration is 220 to 340.    
     
     
         17 . An electric power steering apparatus, characterized in that the grease composition for resin lubrication according to  claim 11  is applied as the lubrication of a speed reduction gear mechanism, and 
 the telescopic shaft for vehicle steering according to  claim 15  or  16  is used in the electric power steering apparatus.