Thursday, August 30, 2012
Corvette’s Chassis Innovations Refined on the Race Track
“Candidly, Corvette was not a high-performance car until Zora Arkus-Duntov fitted it with a V-8, and began campaigning Corvettes in racing,” said Tadge Juechter, Corvette’s vehicle chief engineer. “Today, the Corvettes competing in the 24 Hours of Le Mans use many of the same components as Corvettes rolling off the assembly line at Bowling Green.”
The Corvette C6.R is built on the same aluminum frame rails that underpin production Corvette Z06 and ZR1 models. Other production chassis structures in the race car include the windshield frame, the hoop around the rear of the passenger compartment, the door hinge pillars, the drivetrain tunnel, the firewall and the floor pan. Corvette C6.R also uses the production steering column out of the ZR1, with a fully adjustable steering wheel, as well as production rack-and-pinion steering.
For the production Corvette ZR1, the racing influence is also evident in the rear transaxle design that helps achieve a near-perfect 51/49 weight distribution, as well as the racing-developed carbon ceramic brake rotors and Michelin® Pilot® Sport Cup Zero Pressure tires (developed by the same Michelin engineers who developed tires for Corvette Racing in the American Le Mans Series). These features contribute to the ZR1 running Germany’s legendary Nürburgring in 7:19.63.
Here’s an overview of the chassis technologies that have shaped Corvette performance on and off the track:
C2: Independent suspension, disc brakes and aluminum wheels
First-generation (1953-62) Corvettes used a modified passenger car frame and live rear axle, which worked well with the cars’ comparatively modest performance output. Substantially greater power was on the horizon for the second-generation Corvette and racing-derived development spearheaded by the legendary Zora Arkus-Duntov – Corvette’s first chief engineer – highlighted the need for a dedicated chassis system.
When the “C2” (Corvette second generation) launched in 1963, it featured a sturdy, ladder-type frame design that was 90 percent stiffer than the sedan-based “X”-frame of the first-generation models. It also featured an independent rear suspension held in place by a unique transverse leaf-spring design. Besides offering greater handling capability, the independent rear axle was lighter than the previous solid axle design.
The C2 also introduced disc brakes and aluminum wheels, based on designs Duntov refined on Corvette race cars.
“Duntov pioneered the model of technology transfer by applying what was learned on the race track to improve the production cars,” said Juechter, “That philosophy continues to play an integral role in vehicle development at Chevrolet.”
C4: Unitized structure, composite springs, antilock brakes and traction control
The C4 generation (1984-96) represented an even bigger leap in chassis technology than the C2. The ladder frame that had served the Corvette for about 20 years was replaced by a unitized “backbone” chassis that, again, was inspired by racing cars. It eliminated several cross members, allowing direct mounting of the rear differential and other components, which enabled greater interior room. It was also lighter than the previous ladder frame.
Integrated on the backbone chassis was a “cage” incorporating the windshield frame, door frames, rear wall of the “cockpit,” rocker panels and more. The Corvette’s body panels were attached to the chassis and cage, marking the first time in the car’s history that it didn’t use a conventional body-on-frame design.
When it came to the suspension, the C4 again used unequal-length upper and lower A-arms in the front suspended by a new, transverse spring design similar to the rear suspension. At the rear was another transverse composite spring, but used with a new five-link independent suspension design vs. the previous three-link setup. The reinforced fiberglass springs were exceptionally strong yet compliant, and they worked in two ways: They flattened as they flexed, but when the vehicle rolled in a turn, they effectively formed an S shape. That added roll stiffness, which minimized the size – and weight – of the stabilizer bars.
Additional C4 chassis/drivetrain innovations included rack-and-pinion steering (1984), aluminum driveshaft (1984), aluminum disc brake calipers (1984), antilock brakes (1986) and traction control (1992).
The C4 was an unqualified success on the track. In its first year of competition, the C4 Corvette went undefeated and captured the SCCA Showroom Stock GT-class championship. That launched a renewed effort on racing and the benefits of technology transfer.
C5: Hydroformed rails, rear transaxle, magnetic ride
The C5 generation (1997-2004) built on the success of the C4 with a new, unitized backbone chassis design, but it was lighter and stronger. Its construction employed a comparatively rare process called hydroforming, which used water pressure and heat to turn six-inch steel tubes into side rails for the Corvette chassis. Each tube replaced what formerly had comprised 36 separate, welded components in the C4 chassis.
The other big advancement with the fifth-generation Corvette was the use of a rear transaxle, which moved the transmission to the rear of the vehicle rather than the traditional position directly behind the engine. The tunnel between the engine and transaxle was enclosed with a panel that contributed to the chassis’ strength and rigidity.
“Weight distribution was a primary motivator,” said Juechter. “We were trying to get to 50/50, balancing the work load on the front and rear tires, which is extremely challenging to do with the front-engine, V-8 powered car. Moving to a rear transaxle dramatically improved the weight balance, as well as enabling a smoother ride and greater interior space.”
Additional C5 chassis/drivetrain innovations included run-flat tires (1997), Active Handling System (1998), magnesium wheels (2002) and Magnetic Selective Ride Control (2003).
The strength and performance capability delivered by the C5 chassis paid huge dividends on the race track. During six years of competition, Corvette Racing – the first factory-backed Corvette team in the car’s history – led the C5.R to an overall victory at the Daytona 24-hour race and three 1-2 finishes in the GTS class at the 24 Hours of Le Mans. During the 2004 season, Corvette Racing won every race the team entered and captured every pole position in the American Le Mans Series.
C6: Aluminum and magnesium structure
The success of the C5.R racing program directly influenced the design of the C6 Corvette (2005 – 2013) as designers and engineers further strengthened but lightened the proven backbone design.
At a glance, the C6 chassis looks similar to the C5, but it was shortened slightly and strengthened in key areas to enable greater performance and to enhance crashworthiness. And while it retained the same basic suspension design as the C5 – short/long arm front suspension and multi-link rear suspension with transverse composite springs – all of the components were redesigned. No C5 suspension parts were carried over to the C6.
For the first time, different chassis were available with different Corvette models. The higher-performance C6 Z06 and ZR1 models received a unique, aluminum-intensive backbone structure rather than the steel backbone used on other models. It was developed as a lighter foundation, featuring a magnesium roof structure and engine cradle, and weighed only 278 pounds – 49 percent less than the steel backbone’s 414 pounds. Like the steel frame, the aluminum chassis was created via hydroforming.
Corvette Racing immediately employed the C6 chassis with its C6.R race cars. Corvette Racing has won the 24 Hours of Le Mans seven times since 2001, most recently beating Ferrari to the checkered flag in 2011.
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