What is the working principle of ABS?
4 Answers
ABS system, also known as the Anti-lock Braking System, works as follows: During braking, the ABS closes the normally open input solenoid valve on the wheel that begins to lock based on the speed signals from each wheel speed sensor, keeping the braking force constant. If the wheel continues to lock, the normally closed output solenoid valve is opened. This keeps the braking state at the optimal point, ensuring the best braking performance and maximum driving safety. ABS, short for Anti-lock Braking System, automatically controls the braking force during vehicle braking to prevent wheel lock-up, maintaining a state where the wheels are both rolling and slipping (with a slip ratio of about 20%). This ensures maximum traction between the wheels and the road surface. The ABS system mainly consists of four components: wheel speed sensors, the electronic control unit (ECU), the hydraulic unit, and the ABS warning light. The wheel speed sensors detect the motion state of the wheels and generate sinusoidal electronic pulse signals. These signals are processed by a modulator, converted into digital signals, and transmitted to the electronic control unit. The electronic central control unit (ECU) receives input signals from the wheel speed sensors and calculates parameters such as wheel speed, vehicle speed, and slip ratio. Based on the slip ratio, it determines the wheel state and issues control commands to the hydraulic unit. The hydraulic unit adjusts the pressure in the brake lines according to the control commands, with the adjustment process including pressure holding, pressure increase, and pressure decrease. The ABS warning light alerts the driver to any system malfunctions. If the ABS warning light comes on, it is recommended not to continue driving. An illuminated ABS light indicates a fault in the vehicle's anti-lock braking system. During emergency braking, if the wheels lock up, the vehicle may skid uncontrollably, making it difficult for the driver to slow down or adjust the vehicle's trajectory, posing significant safety risks.
Last time I drove on icy roads, ABS saved my life—this system is incredibly smart! It's like stomping on the brake pedal while it rapidly pulses the brakes for you, operating over a dozen times per second. Sensors on all four wheels monitor rotation speed, and the moment any wheel is about to lock up, it instantly releases brake pressure to let it spin. The most amazing part is feeling the brake pedal pulsate underfoot—that’s the ABS hydraulic pump at work. Now, the infotainment screen even shows real-time intervention status. Last time I saw it flicker, I decisively slammed the brakes, and the car stopped firmly without skidding.
As a frequent visitor to modification shops, I've disassembled ABS pump assemblies to share some insights: The wheel speed sensors act as the system's eyes, monitoring the rotational status of each tire. The control computer serves as the brain, issuing commands within 0.1 seconds when it detects abnormal sudden deceleration in any wheel. The most critical actuators are the solenoid valve sets, which rapidly switch between pressurization and depressurization states, transforming traditional braking's rigid output into pulsed braking. This entire process cycles over 15 times per second, essentially performing ultra-high frequency cadence braking to prevent wheel lock-up.
In twenty years of car repairs, I've encountered all sorts of ABS failures. The most common is wheel speed sensors clogged with mud, which can cause signal distortion and system misjudgment. When the solenoid valve gets stuck, the brake pedal becomes as hard as a rock, while water damage to the control module typically results in the ABS warning light staying on. Once, a customer complained about severe pedal vibration during hard braking—turns out the sensor wiring harness had been scorched by the exhaust pipe. Remember, don't release the brake when ABS is active; that pulsating pedal feedback is completely normal.
