Lapinus recently posted an extensive look at trends in the automotive braking industry. The following is a peek at the first part of the story; the entire article, including images, can be found by clicking on this sentence.
Limburg, Netherlands – The key component of any car braking system is the disc brake pad. Stopping a 1300 kg car traveling at 100 km/hour in five seconds generates more than 100 kW of heat in an area of only 50 cm2. That heat is dissipated into the brake pads. Within seconds, temperatures can reach 600°C and in extreme cases even higher.
Despite that, braking must be safe and smooth. With an increasing focus on HSE (Health, Safety, Environment) these days, disc brake pad manufacturers (compounders) are having to look for alternatives to traditional raw materials like copper and other materials, which can give rise to health and safety issues.
A major trend: new friction materials must still perform well even under extreme braking conditions.
Brake pads must give the same pedal feel and deceleration in repeated city braking as well as sudden emergency stops down steep mountain roads. That must happen whether conditions are wet or dry, muddy or icy, acid or alkaline, and in temperatures from -40 to +50°C.
Braking trends are increasingly affecting not just compounders but also car manufacturers. Standards are on the way to ensure friction materials reduce emissions. Fine particulate emissions are becoming increasingly unwelcome in cities. And even electric vehicles, which use regenerative braking that reduces wear and emissions, place their own demands on braking systems.
Nothing must compromise braking performance. Safety is the priority, but brakes also have to work without NVH (noise, vibration and harshness) such as judder, groan or squeal. Doing all this thousands of times without fail needs leading-edge design, a consistent manufacturing process and extremely consistent base material. Compounders and car manufacturers alike must have confidence that the brake pads won’t disintegrate when they’re needed most – in an emergency. If there’s one part in a car that must not fail, it’s the brakes.
Global standards for braking systems
Strict braking performance requirements in Europe at the moment demand low-steel (LS) brake pads that incorporate steel fibers. These are needed to pass, amongst others, the extreme AMS (Auto Motor and Sport) braking test that simulates extreme braking conditions. Stresses are particularly high on the front brakes, which absorb most of the braking energy.
There are disadvantages to these materials, though. They may result in more corrosion issues and, because of the higher abrasiveness, they generate higher disc wear (the iron oxide wear particles can be found on the front wheel rims in particular). Also, these brakes can make more grinding or squealing noises when they wear down.
In the U.S. and Far East, Non-Asbestos Organic (NAO) friction materials dominate, with no steel fibers. These friction materials are less abrasive than low steel materials, have excellent NVH behavior and low disc wear resulting in clean wheel rims. Mineral fibers are normally used as reinforcement in NAO friction materials. The high aspect ratios for the fibers can give dimensional stability, and they stay stable despite high friction forces and high heat. Lapinus’ high-alumina low-silica mineral fibers are often used in NAO materials. These fibers are completely safe for humans and the environment. Uniquely, they are certified bio-soluble, with RCC, Fraunhofer ITEM, RAL and EUCEB certification and are not classed as a carcinogen. They therefore protect the public as well as factory workers.
High Performance NAO
Needing two or more brake designs for different geographic regions is not ideal for vehicle manufacturers. It means higher parts stocks, greater logistical complexity, and generally higher costs in an intensely cost-conscious industry. It’s even worse for brake pad manufacturers, since they have to cope with two very different formulations for the same car when it’s a model that’s available worldwide. That means at least two parallel and separate design and production paths for new materials and new products.
The solution will come from HP-NAO (High Performance NAO, also called ‘hybrid’) materials that can be used globally. Together with our partners, Lapinus is working on a research project to develop new products that can help give the high braking performance of LS but with the excellent characteristics of NVH (less corrosion and low disc wear) along with the smooth braking characteristics of NAOs.
Global standardization of materials and production will need pads with excellent heat resistance, mechanical integrity, NVH, wear and rotor cleanability, and a stable coefficient of friction (Figure 1). Progress on the standard has been good, with brake pad and car manufacturers showing interest. Hybrid friction materials will have lower or zero steel content, so helping to reduce corrosion. HP-NAOs should also bring reduced particulate emissions.