Application of different brake drives in automobile
????The brake driving mechanism and braking force adjustment mechanism of the automobile are transmitted from the driver or other force sources to the brake, so that it generates a braking torque. According to different braking force sources, the front axle front axle brake drive mechanism can be generally divided into three categories: simple brake, dynamic brake and servo brake.
?????Simple braking only depends on the pedal or handle applied by the driver as the source of braking force, so it is also called manual braking. Among them, it is divided into mechanical type and hydraulic type. The mechanical type is completely transmitted by the lever system. Due to its low mechanical efficiency, small transmission ratio, and many lubrication points, it is difficult to ensure the correct ratio of the front and rear axle braking forces and the balance of the left and right wheel braking forces. The brakes were eliminated. However, due to its simple structure, low cost, and reliable operation (less failures), it is also widely used in parking brake devices for medium and small cars. Hydraulic simple brakes (commonly referred to as hydraulic brakes) are used for service brakes. The advantages of hydraulic brakes are: short action lag time (0.1 ~ 0.3s); high working pressure (up to 10 ~ 20MPa), so the size of the wheel cylinder is small, can be installed inside the brake, directly as the opening of the brake shoe The mechanism (or the pressing mechanism of the brake block), without the need for transmission parts such as the brake arm, makes it simple in structure and small in quality; high in mechanical efficiency (the hydraulic brake system has a self-lubricating effect). The main determination of the hydraulic brake is that after excessive heating, part of the brake fluid vaporizes and forms bubbles in the pipeline, which seriously affects the hydraulic transmission and reduces the efficiency of the brake system, or even completely fails.
?????Power braking is the transformation of the engine's power, and the potential energy in the form of air pressure or hydraulic pressure is used as the entire source of power for automobile braking. The force applied by the driver to the pedal or handle is only used for the manipulation of the control elements in the circuit. Therefore, the inverse proportional relationship between the pedal force and the pedal stroke in simple braking will no longer exist in the dynamic braking, so that the pedal force can be made smaller, while at the same time having an appropriate pedal stroke. Air brake is one of the most widely used dynamic brakes. Its main advantages are light handling, workable light truck front axle assembly design is reliable, not easy to fail, and easy maintenance; in addition, its air source can be used for other devices in addition to braking. Its main disadvantage is that it must have air compressor, air reservoir, brake valve and other devices, the structure is complex, cumbersome, and high cost; the establishment and removal of pressure in the pipeline are slow, that is, the action lag time is long (0.3 ~ 0.9s) Therefore, the idling distance and the stopping distance are increased. For this reason, if the distance from the brake valve to the brake air chamber and the air reservoir is too far, it is necessary to add a pneumatic second-level element. The working pressure of the pipeline is low, generally 0.5 ~ 0.7MPa, so the diameter of the brake air chamber must be designed to be larger, and can only be placed outside the brake, too. The brake shoe is driven by the lever and the cam or wedge, which is Increased unsprung mass; there is a lot of noise in the brake chamber exhaust. Pneumatic braking is widely used in trucks and buses with a total mass of more than 8 tons.