Hybrid bearing boosts IndyCar clutch life

Peterborough, NH--Nasty, brutish, and short sums up the life of key components of IndyCar(R) drivetrains. The engines rev from a few hundred rpm at idle to 13,000 rpm in the blink of an eye, accelerating the lightweight cars to speeds exceeding 200 mph in less than five seconds. In fact, drivers say that the Indy 500 serves as a respite of sorts for transmissions. There isn't as much shifting on the big oval as on the road courses that make up the bulk of the racing season.

Team mechanics have learned to live with the component attrition caused by racing, but a recently introduced clutch throw-out bearing has made their lives easier. Its hybrid ceramic/steel construction and aerospace-derived lubricant give the unit two to three times the life of conventional all-steel bearings, often enabling a car to practice, qualify, and race without a transmission tear-down.

Developed by New Hampshire Ball Bearings, Inc. (NHBB), in concert with the Rahal/Hogan IndyCar team, the hybrid bearing cuts operating temperature 25C compared to previous designs. In addition, the bearing's reduced mass and decreased friction reduce drivetrain parasitic losses, thus improving acceleration and delivering greater torque to the cars' rear wheels.

NHBB core business comes from military, aerospace, and specialty markets. It got into IndyCar racing initially as a simple product sponsorship, supplying rod ends and spherical bearings to the Rahal/Hogan team. "The relationship worked well," explains Sales and Marketing VP Jack Langridge, "So we asked them what their toughest anti-friction bearing applications were." Short-lived clutch bearings was the reply.

The new bearing represents the end product of 18 months of development and five design iterations. "It's not an easy application," says Phil Parmenter, NHBB's chief engineer. "It's a high thrust load, almost instantaneous acceleration, and there's no real pattern to the loading."

Still, the basic configuration for the bearing was well defined. Ceramic balls, used on high performance turbine engines, would reduce the bearing's mass and torque requirements. But because the silicon nitride balls chosen for the design are so hard, they deform less than typical steel balls under load. For that reason, the curvature of the bearing's steel races must conform to the balls more closely than usual to evenly distribute stress and prevent premature failure.

Engineers modeled the bearing using industry-standard software from AB Jones. The software allowed simulated accelerations and calculation of centrifugal forces on bearing components. Early designs used stainless-steel races to forestall corrosion problems, but data from the highly instrumented Rahal/Hogan car showed they didn't deliver the desired increase in life.

  • Harsh-environment machinery

  • Superchargers

  • Turbine engines

The current design employs AISI 52100 steel for the outer race and M50 high-speed tool steel on the inner one. After an intensive evaluation program, NHBB engineers selected Braycote 601 grease from Bray Oil Co, Irvine, CA, as the bearing lubricant. The grease combines unusually low viscosity with relatively constant viscosity stability over the bearing's temperature range, reports Parmenter.

Because operating conditions on the IndyCar circuit vary so widely, Parmenter hesitates to claim a specific life-improvement figure for the new bearing over the old ones. "You can expect double to triple the life," he says, but actual values depend on the engine it's used in, weather conditions, and even the individual driver. Suffice it to say that Rahal/Hogan's experience led several other teams to use the bearing in their cars this season.

For NHBB, the hybrid bearing's development has led to better understanding of materials and lubricants that may result in smaller, higher-performance aerospace components, specifically electrical generators. More subtly, the program boosted team spirit at the company. As Langridge explains, "Our people don't often get to see a missile or an F-16 in flight, but they can see this application every weekend during racing season."

Additional details...Contact Robyn Nattila, NHBB, Inc., Route 202 South, Peterborough, NH, 03458-0805, (603) 924-4100.

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