Formula 1 Racer Gears Up With Carbon Fiber
Toughened prepreg design provides structural durability for highly loaded Honda gearbox.
By Sara Black, Technical Editor | March 2006
Of the myriad forms of motorsports, Formula 1 auto racing is the most advanced in terms of both technology and money. Budgets consume on the order of $300 million to $400 million (USD) per year, and teams numbering in the hundreds labor to build, maintain, test and race the complex machines. Although the FIA (Federation Internationale de l'Automobile) issues specific rules each year that govern the "formula" for these sleek, extremely high-powered cars, a team's success depends on making room within those rules for ingenuity and innovation.
Illustration by Karl Reque
One recent innovation is a composite gearbox developed by the B.A.R. Honda Formula 1 design team, now the Honda Racing F1 Team (Honda Motor Co. purchased British American Tobacco's share of the team in October 2005). Introduced during the 2004 season, the gearbox — not a first for F1 but by far the most successful example of the technology — won the prestigious Simms Medal, presented by the U.K.'s Royal Auto Club for the best innovation in motorsports.
"We consider the composite gearbox to be the 'jewel in the crown' in terms of our race car design," says Honda Racing F1 Team's deputy technical director Gary Savage, who holds a Ph.D in mechanical engineering and is a 16-year veteran of Formula 1 car design. The gearbox's design has continued to evolve from the first 2004 version and is now even lighter and easier to manufacture, he asserts.
Performance required
The gearbox is a roughly pyramidal enclosure, approximately 46 cm long by 22 cm high by 30 cm at its widest point (18 inches by 9 inches by 12 inches), which encases the car's high-grade steel gears that are responsible for transmitting the engine's rotational power to the rear wheels. Made from a monolithic, uncored laminate that varies in thickness from 2 mm to 4 mm (0.08 inch to 0.16 inch), the gearbox case includes two interior "bulkheads" that support the gears and half-shafts. A number of high-grade titanium exterior fittings and attachment points (chemically treated to enhance bonding) allow the gearbox to be mounted to the engine and rear axle/suspension elements. Because of the high loads it has to endure and the various car parts that connect to it, the gearbox is considered a primary structural element of the car's overall chassis design.
Source: Honda Racing
The 2006 version of Honda's F1 car incorporates an all-composite gearbox made with a toughened, high-temperature prepreg from Cytec Engineered Materials.
Savage says the composite solution came about because of the lackluster performance of previous aluminum versions (some teams also use titanium or magnesium). Because weight and low inertia are so critical at this level of racing, aluminum castings for the gearbox had to be extremely thin and, as a result, rapidly developed fatigue cracks due to imposed vibrational and torsional stresses. "The original metal box didn't have sufficient fracture toughness and fatigued too easily — it would last anywhere from 1,200 km to maybe 8,000 km before needing repair or replacement," says Savage. "We would go through 30 or 35 gearboxes each season."
A replacement composite gearbox, however, would have to withstand extreme loads. It would need not only to hold up under the stress of transmitting 900 hp from the engine to the rear wheels, but also have sufficient stiffness to resist huge cornering, acceleration and braking loads imposed by the wheels, axles and suspension — loads up to 5G are commonplace. In addition to the operational stresses, the gearbox also would have to survive the peak loads imposed by the FIA-required rear crash test — a 14 m/sec impact with a 780 kg/1,700 lb weight, equivalent to being hit from behind by a fully loaded car. Operating temperatures in excess of 150°C/302°F would be likely because of gearbox proximity to the engine exhaust and the frictional heat generated by the gears. Designing the part for such daunting performance requirements required a combination of sophisticated modeling capabilities and a good measure of composites savvy, says Savage.
Pushing materials to the limits
"The design procedure used in Formula 1 is 'semi-quantitative' — a combination of finite element stress analysis and prior knowledge and experience, coupled with laboratory testing," says Savage. Purely theoretical numerical analysis isn't practical, he explains, because of limited materials and structural data and the severe time pressures of the sport. Team engineers, therefore, came up with a best estimate for the gearbox's configuration, given the shape and volume of the internal gears, the required attachment points, the need to transition from the three-dimensional shape at the rear crash structure down to a simplified engine mount area and, very importantly, concern for part manufacturability. Unigraphics NX CAD design software supplied by UGS (Plano, Texas) was the primary design tool.
Source: Honda Racing
Polished, high-grade titanium fittings, chemically treated to enhance bonding, allow the gearbox to be attached to the engine and suspension elements.
MSC.Software Corp. (Santa Ana, Calif.) supplied the NASTRAN and PATRAN finite element modeling programs used to refine the design. Engineers subjected the resulting computer model to a wide range of load cases to determine the margin of safety (MoS) to first ply failure. "Any MoS value greater than zero was good," notes Savage.
