Basics of Design Engineering - Bearings
Richard Childress Racing's NASCAR Busch Grand National Chevrolet runs on Timken RacePac wheel hubs. The car recently finished third at Daytona. Childress fields five cars in the NASCAR Winston Cup and Busch Grand National Series.
An exploded view shows what goes inside Timken RacePac wheel hubs. Conventional lip seals are replaced with steel rings that ride close to rotating hubs. The arrangement keeps out contaminants by using heat from bearing friction to build a pressure differential inside hubs. The units come preassembed, pregreased, and ready to install.
"Proper wheel-bearing preload helps win races," says David Holden, an engineer with the Richard Childress Racing NASCAR team. "We have crew devoted to the task, though getting the adjustment right can be tricky and consumes valuable time on race day." Not enough preload and handling and controllability suffer. Excessive amounts rob horsepower and overheat bearings, possibly leading to early failure.
Now racing teams have another option. RacePac wheel-bearing hubs from Timken, Canton, Ohio (www.timken.com), come preassembled and race-ready. The tapered-roller-bearing front and rear hubs are lubed with a proprietary amount of high-end synthetic grease, sealed, and preloaded to Timken specs. "Sophisticated equipment and machinery precisely apply loads and measure gaps to levels unreachable by manual methods trackside," explains Timken's James W. Skelly. Teams use hubs for one race then send them back to Timken for refurbishing.
Developing RacePac hubs took about two years. One key to making it all work is proper lubrication. Bench tests revealed too little grease caused overheating and early bearing failure while excessive amounts raised parasitic losses. The data helped the group tweak grease charge based on bearing size. Proper grease load, combined with more efficient bearing rollers that rely on point contact rather than elliptical face contact, and reshaped roller ends, reduce friction, wear, and lower operating temperatures.
The use of special seals further lowers operating temperatures. A patented seal design, borrowed from the company's railroad bearings, does away with torque-sapping lip seals and instead works off positive air pressure. Here, heat from bearing friction builds a pressure differential to keep grease in and contaminants out. The no-contact arrangement consumes negligible torque so cars put more horsepower to the ground.
The result: RacePac hubs run about 30% cooler than those with standard bearing setups or roughly cooler by 53°F. This is significant given bearings can reach 300°F during a race and grease life drops precipitously with elevated temperature. Best of all, chassis dynamometer tests show cars equipped with RacePac hubs gain about 6 hp. That's enough for about 0.3 sec/lap. News of such competitive advantages travels fast. Nine cars at a recent race in Talladaga sported RacePac hubs.