When braking, the wheel cylinder piston pushes the brake shoe outward under the action of the brake fluid pressure. The brake shoe overcomes the elastic force of the return spring and expands outward, pressing against the brake drum, generating braking torque to make the car brake. The working principle of the drum brake is to push the piston of the brake master cylinder to move when the brake pedal is stepped on, and then generate pressure in the oil circuit. The brake fluid transmits the pressure to the brake shoe to open outwards and presses the brake drum, the components of drum brakes that generate braking torque include brake wheel cylinders, brake shoes, brake drums, friction linings, return springs, etc. Drum brakes have gradually withdrawn from the car field, and are mainly used for braking load comparison The working principle of the drum brake also includes the effect of self-increasing or self-decreasing force. The friction torque of the lead shoe is 2 to 2.5 times that of the shoe