Along with the development of various mechanism for transmitting power has arisen the need for suitable liquids which perform essential functions in the operation of those mechanisms. Operation of these complex mechanisms often requires that the liquid function in several different capacities. The liquid not only serves as a lubricant and coolant in reducing the friction and heat developed during operation of the mechanism, but also performs other key functions. In the case of automatic transmissions for automotive vehicles, for example, the liquid functions hydrokinetically in the liquid coupling or torque converter, depending upon the type of transmission, and in the hydraulic operation of the various mechanical components of the driving unit.
In most hydraulic systems the hydraulic liquid must lubricate the frictional parts of the system in addition to performing the primary function of transmitting power. The parts which are so lubricated include the frictional surfaces of the liquid pump, operating pistons, cylinders, valves and liquid motors. Many of these components are complex mechanical devices.
Automatic transmissions, industrial hydraulic systems, gear reducers, collision bumpers and the like, employ functional liquids having base stocks selected from naturally occurring oils of mineral origin or synthetic liquids such as that described in U.S. Pat. No. 3,577,361, W. C. Hammann et al, May 4, 1971. However, such liquids by themselves do not possess the characteristics which enable them to perform satisfactorily in such demanding applications. Thus, it is a general practice to add small amounts of other materials to these base stocks to affect one or more of the properties thereof. Among these latter materials are viscosity index improvers, detergent-inhibitors and swelling agents. These additives are described in U.S. Pat. No. 3,389,088, W. C. Schar et al, June 18, 1968.
While the aforementioned power transmission liquids perform satisfactorily, there has been a need to improve their properties with respect to freedom from leakage. This leakage, for example, from vehicle automatic transmission systems, pollutes our environment. The principal reason for the leakage is the deterioration of the elastomeric seals or gaskets or other similar devices. The deterioration can be defined as a change in the dimensions of a seal caused by mechanical wear and/or the liquid through a chemical-physical means.
As a result of this there have been numerous attempts to develop a material that can be added to the liquid that is present in power transmissions to revitalize the leaking seals or gaskets by swelling and softening the elastomer in those seals. An additive for this purpose must not be too potent in its elastomeric swelling properties because excessive swelling and softening of the transmission seals will cause seal failure. Also, the additive must not lower the viscosity of the automatic transmission liquid nor impair its oxidation stability.
As an alternative, the material could be present in the power transmission fluid when it was initially placed in the transmission equipment.