With few exceptions, disc brakes are used as wheel brakes on the front axle
of passenger cars. Depending on the load, disc or drum brakes are used on the
rear axle. The following remarks are limited to the disc brake.
High mechanical and thermal stress exerted on the brake system
The foot force exerted on the brake pedal, supported by the system, acts as
tensioning force in the wheel brakes that presses the brake pads onto the brake
discs. As a result of the friction force created by this, the greater portion of
the kinetic energy of the vehicle is converted to heat within a short time. The
mechanical and thermal stresses acting on the brake disc and brake pads are
very high. In extreme cases, the braking power occurring during deceleration
can be many times the maximum engine power.
Essential requirements with regard to the brake system
The essential requirements placed on a brake system can be summarised
as follows:
• Minimum stopping distance under all operating conditions
• Good brake comfort (no judder, no squealing, good pedal feel)
• Adequate service life of the wearing parts.
As far as brake discs and brake pads as essential co-functioning elements
for the braking procedure are concerned, this means:
• Frictional stability over a very wide temperature range
• Low dependence of the coefficient of friction on the contact pressure,
speed and environmental influences
• Good mechanical strength and resistance to deformation
• Wear status within the specified limit values
• Component tolerances within the specified limit values
• Adequate wear behaviour of the brake pads and brake discs.
Brake discs and brake pads are co-functioning key safety elements. The
requirements placed on them can only be met with components developed
for/adapted to the vehicle concerned. Safety risks, as well as losses of
comfort and a reduced service life can be avoided by correct maintenance.
