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Common Applications Reference

R & O Lubricants

The primary function of a Rust and Oxidation lubricant is to provide satisfactory lubrication, remove heat and function as force-transmitting oils for control units. The R & O oil must combat extreme temperatures of 200 C and maintain an aging stability in order to dissipate the heat from the bearings. Foam and water seperability are extremely important especially in turbine oil applications
Along with being resistant to the elements of its environments it must also provide a good seal against water. Its viscosity must match that of specifications and maintain that viscosity grade throughout the oil’s life.

Gear Lubricants

The primary functions of a gear lubricant are the same as those for all lubricants. However, particular emphasis might be placed on friction reduction and heat removal. Contaminant containment, while important, is not as difficult as with crankcase lubricants because no fuel degradation products are present.

The principal types of additives used for gear lubricants are:

1. Antiwear and extreme pressure additives
2. Antifoam agents
3. Antioxidants
4. Antirust additives

The oxidation, rust and foam inhibitors used in gear lubricants are generally of the same type as those used in crankcase lubricants.

Of particular importance are antiwear and extreme pressure additives, which are activated only under specific temperature and pressure conditions and are inactive under other conditions. This property is necessary both to preserve the reagents and to avoid extraneous reactions that might be detrimental to the system. Examples of harmful side effects are excessive wear on gear teeth, ball and roller bearing parts, and other differential components, as well as possible deposits in oil passages and other critical areas.

Automatic Transmission Fluids

The principal functions of automatic transmission fluids (ATFs) are:

1. Power transmission in the fluid member (torque converter)
2. Hydraulic control medium
3. Heat transfer medium
4. Lubrication of transmission parts such as clutches, gears, bearings, and seals
5. Friction modification

The general types of additives used to enhance these functions are:

1. Antioxidants
2. Dispersants
3. Extreme pressure additives
4. Friction modifiers or "oiliness" agents
5. Pour point depressants
6. Viscosity modifiers
7. Seal conditioners
8. Corrosion inhibitors
9. Antifoam agents

A critical problem in developing an ATF is providing the desired frictional properties for proper clutch pack operation while still providing the other properties. Because of differences in transmission design among the major auto manufacturers, the required frictional properties vary considerably. One design may require a "slippery" fluid with a low coefficient of friction at lock-up to provide a smooth shift without the noise and wear produced by stick/slip. Another might require a higher coefficient of friction to ensure fast clutch plate lock-up that prevents wear due to excessive slippage.

ATFs must also have a sufficiently high viscosity at elevated temperatures to ensure against excessive leakage in hydraulic and control systems. This would result in low hydraulic pressures and degradation of shift characteristics. In addition, too high a viscosity at low temperatures causes reduced fluid flow, which causes reduced fluid efficiency, pump cavitation, extended shift time, possible clutch plate failures, and reduced starting capability.

Modern vehicle and transmission designs place increased stress on the automatic transmission fluid. The drive to improve fuel economy has led to more aerodynamic car designs that permit less airflow around transmission, thereby increasing operating temperatures. This, combined with reduced sump sizes, results in severe thermal stress on the fluid.

An important property of and ATF is compatibility with elastomer seals. The fluids can affect the tensile strength, elongation, hardness and volume of elastomers. Various immersion tests are generally used to evaluate the compatibility of ATFs with the different seal materials.