Shift-feel durability enhancement

Abstract

Improved durability of shift-feel frictional characteristics in automotive transmission fluids is achieved by use of an initially substantially inert (friction-wise) compound--viz., an aliphatic tertiary amine having one long chain and two short chain groups--incorporated into a formulation which is otherwise balanced for initially good shift-feel frictional properties. When the fluid is subjected to the oxidative and thermal degradation conditions encountered under normal service conditions, the friction modifiers that give the fluid good initial shift-feel frictional properties degrade. However, as this occurs the aliphatic tertiary amine has itself been transformed by a mechanism that activates it so that in its new form it acquires the ability to provide good shift-feel properties. Thus this additive serves as a time-activated or delayed action substitute for the friction modifiers that have been degraded during service. The result is a continuation of good shift-feel performance over a long period of severe operation. In one embodiment of the invention, oil-soluble aliphatic diamines are used as the primary (i.e., initially effective) friction-reducing additives with which the delayed action tertiary amines are used. In another embodiment, the primary (i.e., initially effective) friction-reducing additives with which the delayed action tertiary amines are used are oil-soluble N-substituted dialkanolamines.