Transportation is one of the major consumers of petroleum products and thus efficient transportation is a focus of government legislation throughout the world. Original Equipment Manufacturers (OEMs) are responding with innovations in engine design delivering unprecedented levels of fuel economy and low carbon emissions. As the engines become more efficient and more sophisticated so do the oils that lubricate them. While the increase in fuel efficiency from these specialty lubricants is significantly smaller than what one can expect from the specially designed engine, so is the investment in developing and producing such a lubricant. Moreover, the lubricant can be applied in existing engines improving fuel economy and thereby decreasing CO2 emissions. By reducing friction energy losses in the engine the lubricant can be capable of improving fuel consumption by a few percent.
The main additive components in the lubricant that deliver reduced friction and improved fuel economy are friction modifiers and viscosity modifiers. Friction modifiers reduce friction in the boundary lubrication regime where metal on metal contact is present; viscosity modifiers work in the hydrodynamic regime where reduced viscosity results in reduced frictional losses. Base oil viscosity is also very important for fuel economy in this regime.
Viscosity modifiers have been viewed as important fuel economy enablers for several years. A number of chemistries and architectures have been explored in the quest to get fuel economy without sacrificing durability and wear protection. One of the viscosity modifier classes is self-assembled molecules. These molecules can be tuned to form aggregates (micelles) under certain temperature and/or shear conditions, disassemble under other conditions and then self-repair the micelle. These VMs provide very good thickening in the assembled state. They can be designed to partially disassemble under shear to provide reduced viscosity for better fuel efficiency and resistance to permanent mechanical degradation by the self-repair mechanism. Other performance features to increase engine wear protection by the lubricant can also be built in this class of VM.
We present the examples of the use of the self-assembled VMs in top tier lubricants and their performance in engine and field tests. Several unique features of these VMs such as shear stability, soot dispersancy credits, and formulation flexibility are discussed.