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The BMW Sauber F1 team is using new regenerative braking technology to prove racing can be green and fast.
When it comes to most high-volume vehicle applications, brake systems have become more of a commodity than a specialty. It's almost as if it is about checking the box on repurposing an existing disc and caliper design, while adding an upgraded anti-lock sensor or two. That approach, however, doesn't work when you're trying to stop a $6.8 million racecar.
Formula One Goes Green
Common wisdom would say that race brake system engineers are focused on two goals: reducing weight and improving grip. That's partially true. In what most would consider the most grueling and competitive automotive racing circuit in the world, Formula One, changed the rules governing brake systems to promote energy efficiency. The 2009 season brought with it the introduction of the Kinetic Energy Recovery System (KERS), which recovers the heat normally wasted during braking maneuvers and converts that into power that can be used by the driver to boost acceleration.
Most 2009 F1 KERS systems use a motor-generator housed in the transmission to convert the mechanical energy into electrical energy and vice versa. When the energy has been captured, it is stored in a battery and released when required via a boost button on the steering wheel, which activates a small flywheel that can spin up to 80,000 rpm. The rules limit the power output to 60 kW (80 hp), with storage limited to 400 kilojoules. The FIA estimates the use of the added power cuts lap times by upwards of 0.3 seconds.
The downside of the KERS system centers around the additional weight required to add the electrical componentry, which adds as much as 77 lb. to the car. In a sport where every ounce is scrutinized, this technology could be tough to adopt. Brake system developer Brembo (brembo.com) has worked with several teams on integrating the KERS system. Surprisingly, engineers determined the introduction of KERS requires a smaller rear brake caliper, which helped cut some of the weight penalty. Advanced carbon-based friction materials are used to construct pads and discs, while new materials designed to reduce rear brake glazing—a symptom that reduces brake performance through excessive heating and cooling—have also been developed.
Caliper Design Critical
Arguably the most critical part of any vehicle's brake system is the caliper. For racing applications, caliper designs must be optimized to provide maximum performance for stiffness, fluid displacement, deflection, and pad wear/taper. These exacting specifications differ depending on the size and weight of the racecar and the track on which it will operate. In the recent past, race caliper design erred on the side of over-engineering to save time and reduce prototype builds.
As regulating bodies developed ever exacting standards for vehicle weight and performance, engineers and designers began to focus on improving the accuracy of caliper designs to help reduce weight and improve stiffness. Alcon Components (alcon.co.uk), which provides braking systems to F1, Rally Car, NASCAR and IndyCar racing league teams, has developed a proprietary caliper design system called Optimized Structure Caliper Architecture (OSCA), which tailors each caliper design to the exacting standards of the racing teams using finite element analysis (FEA) tools to develop the precise geometry and five-axis machining to produce it.
brake caliper design optimization
"Traditionally, caliper manufacturers design the caliper to meet a certain size and then we use that for as many applications as possible, which ends up being a compromise. We are taking specific vehicle data from the track testing and using that to optimize the caliper design," says Phil Stubbs, President of Alcon Components USA, which supplies calipers to NASCAR's Joe Gibbs racing team and is the sole caliper supplier to the IndyCar racing league.
"The optimization process is all done using software. The whole process can be done on the screen and we manufacture the finished part using five-axis machining, which is the key to our ability to cut development time and improve the overall design," Stubbs adds.
Alcon is using FEA software to virtually test new material applications, including composites. Stubbs says the rapid advancements in software development are allowing companies like his to show those who govern the various racing circuits how changes in regulations could help improve driver safety through advanced material applications in brake systems.
The lessons gained from the technologies and processes used by companies like Brembo and Alcon will not be limited to the racetrack. As governments increase regulatory pressure on passenger vehicles to become more fuel efficient and safer, it's likely the advancements made in F1 and NASCAR will end up on Main Street.