The rotating element in the disc brake friction pair is a metal disc that works on the end face, called a brake disc. The friction element clamps the brake disc from both sides to generate braking. The fixing element has various structural forms. Generally, the disc brake can be divided into a caliper disc type and a full disc type.
Disc brakes are hydraulic and controlled by hydraulics. The main components are brake discs, sub-pumps, brake calipers, oil pipes, etc. The disc brake has fast heat dissipation, light weight, simple structure and convenient adjustment. Especially under high load, it has good high temperature resistance performance, stable braking effect, and is not afraid of muddy water. When driving in winter and harsh road conditions, the disc brakes used by many cars are flat brake discs, punched brake discs and paddles The linear brake disc, among which the braking effect and ventilation and heat dissipation ability of the line brake disc are relatively good.
Caliper disc brake In the caliper disc brake, the brake pad is composed of a friction block with a small working area and its metal back plate. There are usually 2 to 4 pieces in each brake. These brake pads and their actuators are housed in caliper-shaped brackets that span the sides of the brake disc, called brake calipers. The caliper disc brake has strong heat dissipation and good thermal stability, so it is widely used in most cars and light trucks. The caliper disc brake can be divided into fixed caliper disc type and floating caliper disc type according to the structure of the caliper. The caliper of a floating caliper disc brake is floating and can move axially relative to the brake disc.
Full disc brake On heavy-duty trucks, greater braking force is required, and full disc brakes are used for this purpose. The fixed and rotating elements of the full disc brake friction pair are both disc-shaped, which are called fixed discs and rotating discs, respectively. All working surfaces of the brake disc can be in contact with the friction lining at the same time. Its structural principle is similar to that of a friction clutch.
Compared with the drum brake, the working surface of the disc brake is flat and heat transfer on both sides. The disc rotates easily to cool, it is not easy to deform greatly, and the braking performance is stable. The effect is enhanced; while the drum brake transmits heat on one side, the temperature difference between the inner and outer sides is large, which causes the brake drum to be easily deformed. At the same time, after a long period of braking, the brake drum expands due to high temperature and the braking efficiency is weakened. In addition, the disc brake has a simple structure, convenient maintenance, and easy automatic adjustment of the brake clearance.
The disadvantage of the disc brake is that the friction plate directly acts on the disc, there is no automatic friction boosting effect, and the braking efficiency is low. Therefore, if it is used in a hydraulic braking system, the pressure of the brake actuation pipeline is high. A power assist device must be installed separately; when it is also used for parking brake, the added parking brake transmission is more complicated than the drum brake, so its application on the rear wheels is limited.
Generally there is no friction boosting effect, so the brake efficiency is less affected by the friction coefficient, that is, the efficiency is more stable; the efficiency decreases less after immersion in water, and it only needs to be braked once or twice to return to normal; the output braking torque is the same Under normal circumstances, the size and mass are generally small; the thermal expansion of the brake disc in the thickness direction is extremely small, which does not cause the brake gap to increase significantly and cause the brake pedal stroke to be too large as the thermal expansion of the brake drum; it is easier to achieve the gap Automatic adjustment, other maintenance and repair operations are also simpler. 1. Good thermal stability. Because the size of the brake friction pad is not long, the area of its working surface is only 12% to 6% of the area of the brake disc, so the heat dissipation is better. 2. Good water stability. Because the brake pad has a high unit pressure on the disc, it is easy to squeeze out water, and it is also easy to throw off after being wet with water under the action of centrifugal force, plus the wiping effect of the pad on the disc. The first and second braking can return to normal; while the drum brake needs more than ten braking to restore normal braking performance. 3. The braking torque has nothing to do with the forward and backward driving of the car. 4. Under the condition of outputting the same braking torque, the quality and size of the disc brake are smaller than that of the drum type. 5. The disc-type friction lining is easier to replace than the drum-type friction lining after wear, the structure is simpler, and the maintenance is easier. 6. The gap between the brake disc and the friction pad is small (0.05-0.15mm), which shortens the operating time of the cylinder piston and increases the force transmission ratio of the brake drive mechanism. 7. The thermal expansion of the brake disc will not cause the brake pedal stroke loss like the thermal expansion of the brake drum, which will also simplify the design of the automatic gap adjustment device.
Disc brakes have been widely used in cars. Now most cars are used on all wheels. A few cars are only used as front wheel brakes. They are used in conjunction with drum brakes on the rear wheels to ensure high directional stability during braking . In commercial vehicles, disc brakes are currently being adopted in new and high-end models.