Grease composition, machine component, and starter overrunning clutch

Abstract

A silicone grease composition having high friction characteristics and wear characteristics is disclosed. The silicone grease composition is provided by adding a zinc salt (B) containing, at a mass ratio from 1:99 to 99:1, a zinc dialkyldithiophosphate (B1) and a zinc dialkyldithiocarbamate (B2) as an extreme-pressure additive to a silicone oil (A).

1 . A grease composition comprising:
 a silicone oil (A); and   a zinc salt (B) containing, at a mass ratio from 1:99 to 99:1, a zinc dialkyldithiophosphate (B1) and a zinc dialkyldithiocarbamate (B2).   
     
     
         2 . The grease composition according to  claim 1 , wherein a content of the zinc salt (B) is not less than 5 mass % and not greater than 30 mass % relative to the entire grease composition. 
     
     
         3 . The grease composition according to  claim 1 , wherein the zinc salt (B) contains the zinc dialkyldithiophosphate (B1) and the zinc dialkyldithiocarbamate (B2) at a mass ratio from 2:98 to 50:50. 
     
     
         4 . The grease composition according to  claim 1 , further comprising one or more types of thickeners (C) selected from the group consisting of lithium soaps and lithium complex soaps. 
     
     
         5 . The grease composition according to  claim 1 , wherein a content of the silicone oil (A) is in a range of not less than 50 mass % and not greater than 95 mass % relative to the total amount of the grease composition, and the silicone oil (A) has an aromatic hydrocarbon group in a molecule. 
     
     
         6 . The grease composition according to  claim 1 , further comprising a partial ester (D) of a polyhydric alcohol. 
     
     
         7 . The grease composition according to  claim 1 , wherein the grease composition is a grease composition for a power transmission device. 
     
     
         8 . A machine component in which the grease composition according to  claim 1  is enclosed. 
     
     
         9 . The machine component according to  claim 8 , wherein the machine component is a clutch or a torque limiter mechanism. 
     
     
         10 . An overrunning clutch, wherein the grease composition according to  claim 1  is enclosed in a clutch cam chamber formed from an outer clutch and an inner clutch. 
     
     
         11 . The grease composition according to  claim 2 , wherein the zinc salt (B) contains the zinc dialkyldithiophosphate (B1) and the zinc dialkyldithiocarbamate (B2) at a mass ratio from 2:98 to 50:50. 
     
     
         12 . The grease composition according to  claim 11 , further comprising one or more types of thickeners (C) selected from the group consisting of lithium soaps and lithium complex soaps. 
     
     
         13 . The grease composition according to  claim 12 , wherein a content of the silicone oil (A) is in a range of not less than 50 mass % and not greater than 95 mass % relative to the total amount of the grease composition, and the silicone oil (A) has an aromatic hydrocarbon group in a molecule. 
     
     
         14 . The grease composition according to  claim 13 , further comprising a partial ester (D) of a polyhydric alcohol.