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Anti-lock braking system and EBD

Short answer

ABS prevents wheel lock-up by modulating brake pressure via wheel speed sensors and an ECU-controlled hydraulic unit, maintaining steering and reducing stopping distance on wet roads. EBD is an ABS software function that balances brake force between axles according to load, preventing early rear lock-up and replacing a mechanical proportioning valve.

Explain the working of an anti-lock braking system (ABS) with its main components. What is electronic brake force distribution (EBD)?

Anti-lock braking system (ABS)

ABS prevents the wheels from locking during hard braking. A locked wheel loses steering control and has less grip than a wheel that is still rolling with a little slip (about 10 to 20 % slip gives the maximum grip). ABS keeps the slip near this optimum.

 Wheel speed sensors (4) --> [ECU] --> [Hydraulic unit]
                                  |    valves + pump
                         Master cylinder -> brake lines

Main components

  1. Wheel speed sensors (magnetic or Hall type) with a toothed ring at each wheel.
  2. ECU, which compares the wheel speeds and calculates deceleration and slip.
  3. Hydraulic modulator with solenoid inlet and outlet valves for each wheel, and a return pump with accumulator.
  4. A warning lamp on the dashboard.

Working (three-phase cycle, 10 to 15 times per second)

  • Pressure build-up: normal braking; the inlet valve is open.
  • Hold: if the ECU senses that a wheel is decelerating too fast (about to lock), it closes the inlet valve so that the pressure is held.
  • Release: the outlet valve opens, the pressure falls and the wheel speeds up again.
  • The pressure is then raised again. The driver feels the pedal pulsate.

Advantages: shorter stopping distance on wet roads and steering control during braking.

Electronic brake force distribution (EBD)

EBD is an extension of the ABS software. During braking, weight shifts to the front axle, so the rear wheels can lock early. EBD uses the same sensors and valves to reduce the pressure on the rear brakes (and balance left and right) according to load, speed and road conditions, so that all four wheels use their available grip. It replaces the mechanical proportioning valve and gives shorter stopping distances, particularly when the vehicle is loaded.

✓ Answer checked by Claude Opus 5.5 (high effort)

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