Under emergency braking conditions on a slippery surface, an Anti-lock Braking System (ABS) rapidly modulates braking force to prevent the road wheels from locking. In which sequential order does the system execute this automatic cycle?
- 1Wheel speed sensors detect that a road wheel is decelerating rapidly and is about to lock.
- 2The electronic control unit (ECU) signals the hydraulic modulator to reduce brake fluid pressure at the affected wheel.
- 3The released wheel accelerates back up toward vehicle speed, restoring rolling grip and steering control.
- 4The hydraulic modulator reapplies brake fluid pressure to decelerate the wheel again until slip is re-detected.
Answer
The correct sequence begins with wheel speed sensors detecting imminent wheel lockup, followed by the electronic control unit commanding the hydraulic modulator to reduce brake line pressure, allowing the wheel to regain rotational grip, and finishing with the modulator reapplying hydraulic pressure to maintain stopping power.
An Anti-lock Braking System (ABS) works as a closed feedback loop. First, magnetic or optical wheel speed sensors detect that a wheel is rapidly slowing down and about to stop turning entirely (wheel lock). Second, the ABS electronic control unit (ECU) directs solenoid valves inside the hydraulic modulator to reduce hydraulic fluid pressure to that specific brake. Third, this momentary release allows the tyre to roll freely again, restoring traction and directional control. Fourth, the system's electric pump and valves reapply hydraulic brake pressure to continue slowing down the car. This four-stage sequence repeats multiple times per second until the vehicle stops or footbrake pressure is released.
Step-by-Step Solution
Key Concept
Anti-lock Braking System (ABS) electronic-hydraulic modulation cycle
Estimated Time:1m 0s