Chapter XI - The braking system

The braking system has the role of ensuring the car a rapid reduction of the travel speed, of braking efficiently on a downhill or uphill slope and to ensure the stopping of the motor vehicle on the public roads that present a maximum inclination.

According to the functional role the braking system can be:

• the main braking system (is represented by the foot brake or the main service brake);
• the stationary braking system (is represented by the parking brake, the one that keeps the motor vehicle immobilized on a slope, in the absence of the driver);
• the additional braking system (is represented by the deceleration device that keeps constant the descending speed of long slopes, without a prolonged use of the brakes).

The braking system is a complex system formed of:

• the actuation system: is that system that regulates the braking force. The pressing force of the foot is transmitted from the pedal to the brake booster and the brake pump transforms the force amplified by the brake booster into hydraulic pressure with the help of the brake fluid;
• the transmission system: takes over the braking force through the brake fluid with the help of the system pipes and hoses;
• the mechanical wheel braking system: ensures the actuation of the braking devices for pressing the pads and the shoes on the discs, respectively brake drums.

The disc brake consists of:

• the brake discs;
• the pads;
• the wear sensors;
• the calipers.

The drum brake is composed of:

• the shoes;
• the brake drums;
• the brake cylinders;
• accessories.

The electronic safety system: has the role of helping the driver in critical situations:

• the ABS system prevents the wheels from locking at the moment of braking;
• the ASR system prevents the wheels from skidding at the moment of starting from standstill;
• the ESP system intervenes when the tendency to skid appears, stabilizing the trajectory desired by the driver.

The components of the braking system:

• the main brake pump: transforms the force applied on the pedal into pressure. The obtained pressure is transferred to the pistons in the calipers through the pipes and hoses;
• the disc brake: are universally used on automobiles for their stability as well as for the good thermal absorption and cooling capacity. The discs, made of cast iron, are generally ventilated on the front axle and are sized so as not to exceed temperatures of 600 - 700 °C in the case of successive severe brakings, such as: alpine descents, which require the thermal capacity of the discs and their cooling possibilities, or the accelerations-brakings chains that implicitly require the thermal capacity of the discs;
• the brake booster: uses a part of the vacuum created by the engine, in the intake manifold. When the brake pedal is actuated, the pressing force is amplified through valves;
• the drum brake: is limited due to its modest thermal performance, especially regarding the increase of the brake absorption that accompanies the expansion of the drum when hot.