【正文】 is a danger that the car will skid. The mechanical linkage on the rear brakes is a system of rods or cables connecting the handbrake lever to the brakeshoe mechanism, which work entirely independently of the hydraulic system. Drum brakes are prone to a reduction in the braking effort, known as “fade”, caused by the overheating of the brake linings and the drum. Fade can affect all or only some of the brakes at a time, but it is not permanent, and full efficiency returns as soon as the brakes have cooled down. However, fading is unlikely to occur except after the brakes have been used repeatedly in slowing the car from a high speed or after braking continuously down a steep hill. Descending such a hill, it would have been preferable to use engine braking by changing down into a lower gear. Drum brakes can be made less prone to fade by improving the cooling arrangements, by arranging for more air to be deflected over them, for example.2 Disc BrakesThe disc brake consists of a steel disc with friction pads operated by slave hydraulic cylinders. The steel disc is attached to the road wheel and rotates with it. Part of this steel disc is enclosed in a caliper. This caliper contains two friction pads，one on each side of the disc, and two hydraulic cylinders, one outside each pad. The pads are normally held apart by a spring, but when the driver depresses the brake pedal, pistons from the hydraulic cylinders force the pads against the sides of the disc. Because the disc is not enclosed all the way round, the heat generated when the brakes are applied is dissipated very much more quickly than it is from brake shoes which are entirely enclosed inside a drum. This means that disc brakes are less prone to fade than drum brakes.()3 、Antilock Brake System (ABS) The function of an antilock, or antiskid, braking system is to prevent the wheels from locking under hard braking. Maximum braking force is obtained just before the wheels lock and skid. Such antiskid system ate useful on slippery surfaces, such as ice and snow, where the wheels may lock easily. Locked wheels are dangerous because the car needs a much longer distance to stop. Locked wheels also can cause the driver to lose control.The system uses a sensor that knows when one wheel (or a pair of wheel) is skidding. () The sensor sends a signal to a puter, which signals a modulator valve. The modulator connects into the hydraulic system and can momentarily release the brake pressure and prevent the wheels from locking.(The pressure release is so fast that a driver is seldom aware of it.) pressure is then reapplied until the sensor again senses that the wheel is about to lock up. Thus, this system keeps the wheels as close to lock up as possible, without actually allowing the wheels to lock up and skid. This is called incipient lock up. Maximum braking occurs at that point. If any part of the system should fail to work, the system goes into a “failsafe” mode. The brakes operate normally, as they would on a car that is not equipped with ABS. Today , ABS is an optional or standard feature that typically is found on expensive luxury cars and sports cars. In the future, ABS may be available for all cars.、ABS overview Antilock braking system is using the body of a rubber balloon, while hitting the brakes, will give brake oil pressure, feeding through to the ABS body, using of the air in the middle of the air layer to return the pressure, make wheels evade the locked points. When the wheel will arrive next locked point, brake oil pressure makes balloon in a repeat function, so can function eight to thirty times in one second equivalent constantly brake, relax, namely, similar to the mechanical braking . Therefore, ABS antilock braking system, can avoid the orientation losing control , the wheel’s lateral sliding ing up and the wheels rubbing on one point with the ground without being locked in the emergency brake，so it can make the brake friction efficiency achieves ninety percent. It also can reduce the braking consumption and prolong the brake wheel drum, disc and tire twice with the service life of the vehicle in the ABS. On the dry tarmac road or on snowy or on rainy days, the slippery performance reached 80% 90%, 30% 10%, 15% 20%. Ordinary braking system on a wet road surface brake, or in the emergency brake, it’s easy for wheels to be locked owing to the braking force exceeds the friction force of the tires and ground. In recent years, the consumers of the vehicle emphasis on the safety , so most of the cars have ABS listed as standard. Without ABS, emergency brake usually cause tire locked, then, the rolling friction bees sliding friction, as a result, braking force dramatically decreased. And if front wheels are locked first, the vehicle will lose the steering ability。 if the rear tires are first locked, the vehicle is easy to slide laterally , so the direction bees impossible to control. Through electronic or mechanical control, the ABS system controls the braking fluid pressure at a fast speed to avoid the wheels locked. Insure the tire have the biggest braking force and the turning ability when braking, and make the vehicle have the ability to evade the obstacles in emergency braking. With the rapid development of the automotive industry, safety increasingly bee the important basis of that people choose and buy cars. At present the widespread adoption of holding brake system (ABS) that people can fully meet the safety of requirements. Automobile brake prevent embrace system, referred to as the ABS, is to improve the car an important device passive safety. Someone said brake prevent embrace system is auto safety measures relay belts after another major progress. Automobile braking system is the bus passengers safety is the most important relationship to one of the second systems. With the rapid development of the automotive industry, automo