汽车制动系统的日常维修保养毕业论文外文翻译

Routine brake system maintenance

The braking system is the most important system on a car. If the brakes don't work properly, the result can be disastrous. So the good brakes are essential for safety.

There are two completely independent braking systems on a car. One is the service brake, and the other is parking brake. The service brake acts to slow, stop, or hold the vehicle during normal driving. They are foot-operated by the driver depressing and releasing the brake pedal. The parking brake's purposes are to hold a car stationary while it is unattended, and to keep the car from rolling on unleveled ground. It is also called the handbrake.

Basically, all car brakes are friction brakes. When the driver applies the brake, the control device will force brake shoes or pads against the rotating brake drums or discs at wheels. Friction between the shoes or pads and the drums or disks then slows or stops the wheels so that the car is braked.

Disc brake

Disc brakes are used on the front wheels of most cars and on all four wheels on many cars.

The main components of a disc brake are the brake pads, the caliper which contains a piston, and the rotor which is mounted to the hub.

The disc brake is a lot like the brakes on a bicycle. Bicycle brakes have a caliper, which squeezes the brake pads against the wheel. In a disc brake, the brake pads squeeze the rotor instead of the wheel, and the force is transmitted hydraulically instead of through a cable. Friction between the pads and the disc slows the disc down.

A moving car has a certain amount of kinetic energy, and the brakes have to remove this energy from the car in order to stop it. The brakes convert the kinetic energy to heat generated by the friction between the pads and the disc, so the car stops.

Drum brake

So if disk brakes are so great, how come we still have cars with drum brakes? The reason is cost. While all most vehicles for many years have disk brakes on the front wheels, drum brakes are cheaper to produce for the rear wheels. Drum brake is shown in Fig.

Drum brakes consist of a backing plate, brake shoes, brake drum, wheel cylinder, return springs and an automatic or self-adjusting system. When you apply the brakes, the wheel cylinder pushes the brake shoes into contact with the machined surface on the inside of the drum. When the pressure is released, return springs pull the shoes back to their rest position. As the brake linings wear, the shoes must travel a greater distance to reach the drum. When the distance reaches a certain point, a self-adjusting mechanism automatically reacts by adjusting the rest position of the shoes so that they are closer to the drum.

Hydraulic Brake Systems