【Listening】

【Vocabulary & Phrases】

drum brake（鼓式制动器）

return spring（回位弹簧）

self-adjusting system（自动调节系统）

master cylinder（主缸）

wheel cylinder（轮缸）

mechanical pressure（机械力）

hydraulic pressure（液压力）

brake line（制动管路）

brake hose（制动软管）

brake fluid（制动液）

【Reading】

BrakeSystem

Drumbrake

So if disk brakes are so great, how come we stillhave cars with drum brakes? The reason is cost. While all most vehicles formany years have disk brakes on the front wheels, drum brakes are cheaper toproduce for the rear wheels.

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

HydraulicBrake Systems

When the operator steps on the brake pedal, thebrake pedal operates a hydraulic system.

The typical brake system is composed of thefollowing basic components

（1）Master cylinder :That is directly connected to the brake pedal, converts your foot's mechanicalpressure into hydraulic pressure.

（2）Brake lines andbrake hoses : They connect the master cylinder to the wheel cylinders locatedat each wheel.

（3）Brake fluid : Thatis special oil that has special properties. It is designed to withstand coldtemperature without thickening as well as very high temperature withoutboiling.

In the brake system, master cylinder contains twoseparate sections, there is a piston in each section and both pistons areconnected to a brake pedal in the driver's compartment. When the brake ispushed down, brake fluid is sent from the master cylinder to the wheels. At thewheels, the fluid pushes shoes, or pads, against revolving drums or disks,which can slow and stop car.

拓展视频

【作业】