The ABS system is mainly composed of three parts: a sensor, an electronic control unit (ECU) and a solenoid valve. Its system principle structure is shown in Figure 3-2. The sensor is generally installed on the wheel to measure the rotation speed of the wheel, and the sensor is generally a magnetoelectric induction type. When the ABS is working, the ECU receives the wheel signal sent by the sensor, which is generally a rectangular voltage wave that meets the ECU voltage requirements, and then the program solidified in the ECU determines how to adjust the brake fluid pressure of each wheel according to the speed of each wheel and outputs The corresponding control signal is given to the hydraulic control unit of each wheel. The hydraulic control unit adjusts the pressure of the wheel cylinder after receiving the signal. The role of the sensor is to provide the wheel movement of the ECU. The ECU is the control center of the ABS system. The program solidified in the ECU is actually the control method of the ABS, and the hydraulic control unit is the actuator of the ABS control method.