Transmission fluid compositions for hybrid and electric vehicle applications

A transmission fluid composition comprising:

• a major amount of a lubricating oil basestock comprising a Group III basestock, a Group IV basestock, or a combination thereof;
• and
• a minor amount of an additive package comprising:
• (iv) a basic nitrogen-containing ashless dispersant comprises one or more compounds of structure (III):
• wherein:
• R8 and R9 are each independently a hydrocarbon group made by the metallocene-catalyzed polymerization of an α-olefin feedstock comprising 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-octadecene, or mixtures thereof;
• each R10 is independently hydrogen, an acetyl moiety, or a moiety formed by reaction between ethylene carbonate and >N—R10;
• and
• x is from 1 to 10 and is the same for all molecules of structure (III) or is an average of all molecules of structure (III) in a mixture of molecules of structure (III);
• wherein component (iv) is present in the composition in an amount from 0.75% to 2.0% by mass, based on the total mass of the composition;
• and
• (v) one or more dihydrocarbyl hydrogen phosphite compounds having a structure H—P(═O)—(OR39)2, in which each R39 independently comprises an alkyl group having 12 to 24 carbon atoms,
• wherein component (v) provides the composition from 100 to 300 ppm by mass of phosphorous, based on the total mass of the composition;
• and
• wherein the transmission fluid composition comprises no intentionally added components of:
• (i) a mixture comprising two or more compounds of structures (I):
• wherein groups R1, R2 and R3 are independently alkyl groups having 1 to 18 carbon atoms or alkyl groups having 1 to 18 carbon atoms where the alkyl chain is interrupted by a thioether linkage, provided that, in the mixture (i), at least some of groups R1, R2 and R3 are alkyl groups having 1 to 18 carbon atoms in which the alkyl chain is interrupted by a thioether linkage;
• (ii) one or more compounds of structures (II) of structures (II):
• wherein groups R4 and R7 are independently alkyl groups having 1 to 12 carbon atoms and R5 and R6 are independently alkyl linkages having 2 to 12 carbon atoms;
• (iii) a detergent comprising calcium salicylate;
• and
• (iv) a borated polyisobutenyl succinic anhydride (PIBSA)—polyamine (PAM) dispersant.