THE present state of the art regarding the formulation of automotive and aviation lubricants from the standpoint of protecting metal parts against mechanical and chemicalwear is outlined in this paper. The discussion is limited to four classes of lubricants, namely, (a) engine oils, (b) transmission oils, (c) rear-axle oils, and (d) greases.
By virtue of the wide variety of service conditions to which they are subjected, engine parts can be worn as the result of either mechanical or chemical action. Engine oils must be designed, therefore, to cope with both these types of wear. Oil viscosity and viscosity index are both important factors in engine wear. Various types of additives are being used to an increasing degree as “alloying” materials in engine oils to control their wear characteristics. A trend toward the use of specially synthesixed lubricants for both aviation and automotive service is in evidence.
In gear lubrication the pressure-viscosity characteristics of the lubricating oils may be important in preventing surface failure. In low-temperature operations low-viscosity, high-viscosity-index gear lubricants perform satisfactorily and. in addition, show increased efficiency at normal operating temperatures. Fluids for automatic transmissions must permit good friction coefficients between steel and the friction-band materials to achieve smooth operation of the unit.
For hypoid-gear service mineral oil must be fortified with additives which will react chemically with the gear surfaces to form solid film lubricants. In grease-lubricated automotive mechanisms fretting and means of alleviating this condition constitute the major problem.


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