Lubricating oils are commonly used to reduce friction between moving parts, especially in internal combustion engines. As friction is reduced, fuel economy is improved.
It has been estimated that an average automobile loses 20 percent of the energy available for propulsion (7.5 percent of the total energy released in fuel combustion) due to engine friction. If these friction losses, occurring mainly around the piston ring and skirt area, could be eliminated, a fuel savings of up to about 6.5 miles per gallon could be realized. For this reason, the oil industry has spent considerable time and effort to develop superior lubricants capable of reducing engine friction without compromising the levels of performance and protection that the consumer has come to expect. This invention thus relates to a friction reducing lubricating oil composition which maintains the level of protection available in present commercially available lubricating oils while reducing friction.
It is known that glycerol monooleate is a friction reducer for crankcase lubricating oils. However, it is also known that when the glycerol monooleate is used as part of an automotive crankcase lubricating formulation in concentrations adequate to provide a significant decrease in friction, e.g., at concentrations greater than about 0.2 percent by weight, substantial difficulties are encountered in terms of composition instability and/or adverse performance in tests which measure other aspects of lubricating oil quality, e.g., the ASTM tests used to qualify an oil for satisfactory commercial use.
Lubricating oils are commonly modified to include various additives which increase the stability of the oil and increase the capacity of the oil to maintain contaminants properly dispersed. More particularly, conventional lubricating oils are well known to contain dispersants, viscosity index improvers, overbased sulfonates, phenates, zinc dithiophosphates, antioxidants, pour point depressants, and other components as needed to meet relevant viscosity targets and/or engine test performance requirements. These conventional lubricating oils exhibit reduced friction when they contain glycerol partial esters; however, the usual glycerol monooleates, when present, degrade the normally acceptable properties of the conventional oils and make them unacceptable.