As vehicle speeds have increased, so too has the need for better braking systems. Over the past decade, components such as the rotor, calipers and pads have used a variety of materials including carbon-ceramics, with the use of aluminium alloys for components such as the caliper body also increasing. Attention has also been placed on improving the noise, vibration and harshness levels of the brake system.
Brake actuation has focused on improved capability of the technology in conjunction with ESC systems to control the car in critical conditions, particularly vehicle stability and a reduction in response times at high speeds.
OEMs are now asking suppliers such as Brembo to place greater focus on reducing weight further, giving systems zero-drag behaviour to help improve overall vehicle fuel efficiency, reducing squeal, and overall system cost.
Much of the weight reduction will come from new materials. In the future carbon-ceramics will be developed for higher volumes and, while it will not replace cast-iron discs, its use will become much more widespread, rather than being restricted to the luxury segment. New designs could also see greater use of aluminium, further reducing weight.
1. Lining material
The lining material generates friction with the brake disc, generating the brake torque. In both passenger and commercial vehicles it is an organic material – a mixture of powdered metal and rubber, bonded together with resin – while for high-performance applications ceramics and carbon materials are used.
2. Pad spring
The stainless or carbon steel pad spring keeps the pads near to the piston but maintains the narrow distance to the rotor when braking isn’t required. The spring is formed with an inclined plane that pushes the pads against the piston when braking isn’t required. NVH is a key design criteria for OEMs and the pad spring reduces brake noise and squeal.
The piston pushes the pads against the rotor, via high-pressure fluid, activating the brakes. The system fluid works at a pressure of up to 130bar. The piston is usually made from either aluminium, cast iron or steel.
Combined with the caliper, it is the main component when braking is initiated by the driver. It must dissipate heat generated during braking of between 700°C and 1,000°C, and, while cast iron is commonly used, for high-performance cars carbon-ceramic composite materials are used.
The rubber component stops brake fluid leakages between the piston and caliper. Durability is a key area for the seals and is guaranteed by numerous test cycles with low and high temperature extremes from –40°C up to 180°C.
Links the rotor to the wheel hub, and is made from cast iron or aluminium. It undergoes various test procedures, among them thermal shock tests, where the rotor and bell must overcome more than 100 braking events of deceleration at 1g from maximum vehicle speed to 0km/h.
7. Caliper body
The main function of the caliper body is to transfer hydraulic pressure to the piston and transform the pressure into force which is then applied to the pads. Materials can vary from aluminium for passenger vehicles to cast iron for commercial vehicles. Design varies based on braking forces – which in turn depend on the mass and speed of the vehicle.