disc brake Also known as disc brake, as the name implies, it is named after its shape. It is composed of hydraulic control The main parts include brake disc, wheel cylinder, brake caliper, oil pipe, etc. The brake disc is made of alloy steel and fixed on the wheel, which rotates with the wheel. The wheel cylinder is fixed on the bottom plate of the brake. The two friction plates on the brake caliper are respectively installed on both sides of the brake disc. The piston of the slave cylinder is driven by the hydraulic pressure transmitted from the oil pipe to push the friction plate to the brake disc for friction braking. It acts as if the rotating disc is clamped with pliers to force it to stop. The brake has the advantages of fast heat dissipation, light weight, simple structure and convenient adjustment. In particular, under high load, it has good heat resistance, stable braking effect, and is not afraid of mud and water. When driving in winter and bad road conditions, disc braking is easier to stop the car in a short time than drum braking. The biggest difference between the disc brake commonly used in the rear brake and the ventilation disc is that the ventilation disc is hollow, which is more conducive to heat dissipation. The thermal stability of the brake is very important, and it is the top priority of life when the vehicle brakes. As the temperature increases, the brake braking force decreases, and the higher the temperature is, the more severe the decrease is. Therefore, it is very beneficial to the ventilation and cooling of the brake disc.
Drum brake Is the earliest form Automobile brake , when disc brake Before its appearance, it has been widely used in all kinds of cars. However, due to its poor heat dissipation and drainage performance during braking due to structural problems, it is easy to reduce the braking efficiency. Therefore, in the past three decades, it has gradually withdrawn from the car field to give way to the disc brake. However, due to its low cost, it is still used in some economic cars, mainly for the rear wheel and parking brake with small braking load. Drum brake Generally used for rear wheels. Typical drum brake mainly consists of bottom plate, brake drum, brake shoe and wheel cylinder（ Brake wheel cylinder ）, return spring, locating pin and other components. The bottom plate is installed on the fixed position of the axle. It is fixed and fixed. It is equipped with brake shoes, wheel cylinders, return springs and locating pins to bear the rotating torque during braking. Each drum has a pair of brake shoes with friction lining. The brake drum is installed on the wheel hub and rotates with the wheel. It is made of a certain amount of cast iron and looks like a drum. When braking, the wheel cylinder piston pushes the brake shoe to press the brake drum, and the brake drum is reduced by friction, forcing the wheel to stop rotating. Drum brake In addition to low cost, it is also convenient to combine with parking (parking) brake Parking brake It is also combined on the rear wheel brake. This is a mechanical system, which is completely separated from the brake hydraulic system on the vehicle: use the hand lever or parking pedal (American cars) to tension the steel cable, and operate the lever of the drum brake to expand the brake shoe, playing the role of parking brake, so that the car will not slip; Loosen the steel cable, and the return spring will make the brake shoe return to its original position, and the braking force will disappear. From the point of view of economy and practicality, car designers generally adopt a hybrid form of front wheel disc brake and rear wheel drum brake. During the braking process of a four-wheel car, due to the effect of inertia, the load of the front wheels usually accounts for 70% - 80% of the total load of the car, so the braking force of the front wheels is much greater than that of the rear wheels. Most of the cars we drive today (such as Xiali, Fukang, Jetta, etc.) are not completely disc brake Instead, it is a front disc and rear drum hybrid brake (that is, the front wheel uses a disc brake, and the rear wheel uses a drum brake). As for the rear wheel, the non ventilated disc type is also the cost reason. After all, the manufacturing process of the ventilation plate is much more complicated, and the price is relatively expensive. With the development of material science and the reduction of cost, the disc brake has the tendency to gradually replace the drum brake in the automotive field. 
