Transmission fluid

Abstract

A transmission fluid contains a base oil and calcium carbonate. The calcium carbonate is dispersed in a form of aggregations in the transmission fluid. A ratio of the aggregations having a particle diameter of 200 nm or more is in a range from 10 mass % to 35 mass % in terms of calcium based on a total amount of the aggregations. A base value of the transmission fluid is in a range from 0.5 mgKOH/g to 4 mgKOH/g by a hydrochloric acid method.

1 . A transmission fluid comprising:
 a base oil; and   calcium carbonate, wherein   the calcium carbonate is dispersed in a form of aggregations in the transmission fluid,   a ratio of the aggregations having a particle diameter of 200 nm or more is in a range of from 10 mass % to 35 mass % in terms of calcium based on a total amount of the aggregations, and   a base value of the transmission fluid is in a range of from 0.5 mgKOH/g to 4 mgKOH/g measured by a hydrochloric acid method.   
     
     
         2 . The transmission fluid according to  claim 1 , wherein
 the calcium carbonate is derived from an overbased organic acid calcium salt compound, and   a content of the calcium carbonate is in a range of from 0.001 mass % to 0.3 mass % in terms of calcium based on a total amount of the transmission fluid.   
     
     
         3 . The transmission fluid according to  claim 2 , wherein
 the overbased organic acid calcium salt compound is an overbased detergent, and   the overbased detergent is at least one of a sulfonate detergent, a salicylate detergent and a phenate detergent.   
     
     
         4 . The transmission fluid according to  claim 1 , wherein
 the base oil comprises polyalphaolefin.   
     
     
         5 . The transmission fluid according to  claim 4 , wherein
 a ratio of the polyalphaolefin in the base oil is 30 mass % or more.   
     
     
         6 . The transmission fluid according to  claim 4 , wherein
 the polyalphaolefin has a kinematic viscosity at 100 degrees C. in a range of from 2 mm 2 /s to 200 mm 2 /s.   
     
     
         7 . The transmission fluid according to  claim 1 , wherein
 the transmission fluid has a kinematic viscosity at 100 degrees C. in a range of from 3 mm 2 /s to 8 mm 2 /s, and   the transmission fluid has a viscosity index of 100 or more.   
     
     
         8 . The transmission fluid according to  claim 1 , wherein
 the transmission fluid is suitable for an automatic transmission or a continuously variable transmission.