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Strong and consistent stopping power has always been a Porsche strength. The last 30 years of its progressive development in brake system design makes Porsche an undisputed leader in the field. With the debut of the Porsche Ceramic Composite Brake (PCCB) system, Germany's premier sports car manufacturer has taken a significant leap into the future. For not only does the new material offer better outright performance, fade resistance and a remarkably low wear rate, it is also much lighter.
The mass of each brake, wheel and tyre assembly affects the ride and handling of a car. Lower unsprung weight and you improve ride and handling. In the overall scheme of things, lower weight means better acceleration and stopping, and quicker change of direction. The PCCB discs are half the weight of grey cast iron, equating to a saving of 16.5kg.
Cooling is one of the most important aspects of brake efficiency. If you can conduct heat away fast and keep the brake fluid from boiling, that is half the battle won. Porsche patented involuted cooling and cross-drilling in 1967, and has filed a total of 300 patents on brake systems since 1960! The involuted cooling channels involved the use of angled rather than radial internal cooling veins to direct cooling air to the discs. This reduced temperatures by 40°C, and cross-drilling dropped temperatures a further 60°C.
Ceramic technology is still a black art to most car makers. So far only Porsche and Mercedes-Benz have gone public with the technology, but Porsche is undoubtedly ahead in the race to bring it to customers. Silicon is used to conduct heat in the ceramic composite. It is vital that the silicon is evenly distributed within the disc or differential coefficients of expansion will crack the material.
Production of the discs is an elaborate process that takes more than one day. The base materials are a special carbon fibre and silicon carbide, and the process of baking the discs in a furnace to achieve the right results requires all of SGL's 100 years of experience with high temperature processes. Each involuted cross-drilled disc is made in two halves before being united as a single unit in a high temperature furnace.
At one point in production, each disc would be ready for use as a carbon disc for motorsport. But the production of a stable and inert ceramic disc requires the process to continue with siliconisation in a high-vacuum furnace fired to a temperature above silicon's 1420°C-melting point.
After cooling off, the finished disc is almost as hard as a diamond -the silicon carbine generated in the process has a hardness of 9.7. Yet the material has a high impact strength. That hardness gives the Ceramic Composite discs amazing durability. In a whole day's testing where journalists subjected both stock and ceramic brakes to abuse that few owners will approach, the new technology shone through.
While the standard discs showed the scoring and ripple patterns that owners who do track sessions are used to seeing, the ceramic discs had no visible signs of wear. Incidentally, the PCCB discs are also immune to road salt corrosion, which helps eliminate rubbing noises when the car is driven after being left idle for some time. It is thus no wonder Porsche is happy to endorse a 300,000km-service life (practically the lifespan of the car itself) for these new discs! Pad life is around double that of conventional linings.
On the new 911 Turbo, the PCCB installation uses 350mm diameter discs, 20mm larger than standard. To put things in perspective, if they were to increase the cast iron discs to this diameter, the weight saving would have been 22kg! The calipers are also larger. These have six pots rather than four, and two of these are smaller to ensure progressive action when you apply the brakes. The pistons feature a ceramic heat shield to help keep the brake fluid cool. This is said to be 2.5 times more effective than the titanium shield used on a Formula One racer!
PCCB is a bolt-on retro-fit for existing Turbos as well, as the larger front and rear discs and calipers are still proportionately sized in relation to one another. However, Porsche says that they are working to recalibrate the ABS system to take full advantage of the lower unsprung mass. They also told us that they were working with tyre manufacturers to further braking performance with PCCB.
Right now all the technological challenges have been successfully met, but at a price. Porsche wants DM15,000 for the PCCB system on a new Porsche Turbo, and a cheaper set-up with smaller discs and calipers will soon be available for normally aspirated Porsches.
As always, it is now up to the mass manufacturers to pick up the technology and run with it so that the obvious advantages of ceramic composite brakes can be offered to everyone.
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Last edited by Supercharger; 03-28-2003 at 09:50 PM.
Hey, thanks! I'm in a composites class right now in school. It's fun to read about exotic ceramic matrix composites in applications I actually care about! Too bad I'll never have the dough to buy a car with such sweet brakes!
Smooth is fast, fast is smooth.