Overheating of the lining and friction surface on a brake causes a significant reduction in the coefficient of friction and therefore a decrease in braking effect. This effect is referred to as fading due to changes in the lining material's properties. Friction brakes are used as the wheel brakes in commercial vehicles. They convert kinetic energy from the parts that rub against each other into thermal energy and to a lesser extent into mechanical material abrasion. A distinction is made between two types of friction brakes: drum brakes and disc brakes. Fading is substantially less pronounced on disc brakes than on drum brakes.
Friction and heat
The parts firmly attached to the wheels (brake drums or discs) rub against the non-rotating components (brake shoes or linings). Friction causes the vehicle's kinetic energy to be converted into heat. The better the braking effect, the greater the heat that is generated. The contact surfaces are subject to very high loads due to heat and friction. So commercial vehicle brake discs are mostly internally ventilated.
Fundamentals
Friction brakes are used as the wheel brakes in commercial vehicles. They convert kinetic energy from the parts that rub against each other into thermal energy and to a lesser extent into mechanical material abrasion. A distinction is made between two types of friction brakes: drum brakes and disc brakes. The greater the force required for a particular braking effect, the worse the efficiency of the brake. The brake coefficient C* gives information about the efficiency of a brake, but says nothing about the brake's quality. That includes above all the attainable braking performance, responsiveness and sensitivity. Despite a worse C* value for the disc brake, it is superior to drum brakes in all three areas. Confirmation is provided by the following braking distances from 80 kilometres per hour: 60 metres with drum brakes and brake pressure of 8 bar, 45 metres with disc brakes and brake pressure of 10 bar, 42 metres with disc brakes and an EBS electronic braking system.
