Understanding Vehicle Brake Systems: Types, Functionality, and Safety

Posted on Jan 15, 2025 in Technology

Brake Service

The brake service allows the driver to reduce vehicle speed during normal driving, enabling them to slow down and stop.

Features:

  • Number of circuits: One mixed brake circuit for the front and rear channels independently.
  • Force on the foot: Maximum 800 Newtons.
  • Maximum pressure circuit: 20-50 Bar.
  • Pedal mechanical relationship: 8:1 to 5:1.

Auxiliary Brake

The auxiliary brake complements and supports the service brake in case of failure or damage, allowing the vehicle to slow down and come to a stop.

Parking Brake

Characteristics:

  • Drive: Mechanical with transponder by notches (ratchet).
  • Maximum actuating force: Maximum 400 Newtons.
  • Lever ratio: 15:1.
  • Braking value: Must produce 20% of the total braking deceleration.
  • Average deceleration: Minimum 1.2 m/s2.
  • Power brake: Must be able to stop the vehicle completely on a slope.

Long-Term Brake

Employed in buses and trucks, the long-term brake maintains the vehicle at a constant speed on slopes without overheating, avoiding service brake issues. The most commonly used are:

  • Engine: Acts upon the exhaust, braking departure with a butterfly valve.
  • Retarder: The most used are hydrodynamic (hydraulic gears) and electromagnetic.

Stopping or Braking Distance

The stopping distance is the distance traveled from the moment the braking system is activated until the vehicle comes to a complete stop. It depends on:

  • Braking force.
  • Adhesion.
  • Velocity of the vehicle.

Formula: e = v2 / (E * 254) = meters

Effects on Stability During Braking

  • Tilt to the front axle: An increase in load on the front axle and a decrease in adhesion on the rear axle. In hard braking, the rear axle can lock up, necessitating a braking spell.
  • Front-wheel lock and loss of trajectory: Locking the front wheels produces a deviation of trajectory in a curve, causing understeer and the vehicle to move towards the outside of the curve.
  • Rear-wheel lock: In a curve, this causes oversteer, with the rear axle pivoting around the front exterior.
  • Uneven braking without wheel lock: In this case, the uneven braking effect increases at a faster rate.

Cooling Circuit Elements

During braking, kinetic energy is converted into heat, which can produce the fading effect (above 400oC), causing components to expand and lose effectiveness.

Cooling solutions:

  • Ventilated discs.
  • Drums with small wings.
  • Bodywork with specific channels for air ducting.

Auxiliary Braking Force Circuit

  • With hydraulic auxiliary force: Utilizes pressure sources (pump) driven by the engine. The pump pedal is replaced by a metering and balancing valve.
  • Pneumatic auxiliary: Used to open a cylinder, allowing air pressure to pass to the cylinder with a diaphragm.

Brake Legislation

II, X, HI, LL, HH.

Components of a Drum Brake

  • Brake backing plate.
  • Brake drums.
  • Brake tensioning devices:
    • Cam.
    • Expansion wedge.
  • Brake cylinder:
    • Single-piston cylinder.
    • Dual-piston cylinder.
    • Staggered-piston cylinder.
    • Integrated compensator cylinder.
  • Retaining springs and safety devices.
  • Adjustment devices:
    • Manual adjustment (Girling system): Adjusting the brake cylinder thread.
    • Manual adjustment (Bendix system): A cam per caliper.
    • Automatic adjustment: Ratchet adjustment or friction washer adjustment.