AUTOMOTIVE GEAR LUBRICANTS
The requirements for automotive gear lubrication have changed over the years, yet vehicle owner awareness has not. Gear lubrication has been commonly considered elementary, but, in fact, it is a dynamic process that requires sophisticated technology.The differentials that house the gears are out of sight, out of mind. They are neglected. But differentials are just as important to the operation of a vehicle as the engine. An engine without a functioning differential will not move the vehicle. Gear lubrication needs to be taken more seriously than before. There are several forces driving the need for better gear lubrication. First, is improved fuel economy. Modern vehicle aerodynamics, with lower level air dams, is decreasing the air flow over differentials. Fuel economy is improved, but reduced air flow increases differential operating temperatures. Also, lubricant fill volumes in differentials have been reduced in order to lower fluid drag on the gears and bearings for further improvement in fuel economy. However, lubricants cool components, and with less fluid in the sump, operating temperatures rise.
Improvements in vehicle performance have created additional need for more sophisticated gear lubrication. There has been a 34% increase in engine horsepower over the last decade, while axle gear sizes have remained constant, sump capacities have been lowered and drain intervals extended. In the light truck segment there has been a 93% horsepower increase since 1981.
Most vehicles operate under severe service as defined by vehicle manufacturers, but the majority of vehicle owners are unaware of this. Severe service applications include towing, hauling, plowing, off-road use, frequent stop-and-go driving, steep-hill driving and temperature extremes. Severe service applications are on the rise. Severe service increases the need for better gear lubrication.
OPERATING CONDITIONS AND LUBRICATION REQUIREMENTS
Differentials contain many different components, each having its own requirements for lubrication. The ring and pinion gears operate under extreme pressure and sliding contact that require extreme-pressure additives for protection. The bearings operate under rolling motion where lubricant film strength is particularly important, and limited-slip clutches require special friction additives for proper operation. It is essential, therefore, that gear lube formulations be carefully balanced to protect all components. Too much emphasis on the needs of one component can detract from the needs of another.