汽车专业英语 教学课件 ppt 作者 廖忠诚 杨晓波 主编Chapter6 Electrics and Electronics.ppt

chapter 6 Electics and Electronics yanganjie 6.1.2 Wires （ fig.6-1） Electric wires are used to conduct electric current around the motor vehicle. The wire is commonly braided multi-stranded copper core wrapped with plastic insulation. Copper is used as it offers low resistance and remains flexible even after years of use. Other wire configurations are shielded wires and ribbon. Twisted or shielded wires have the same construction but are harnessed in pairs and twisted to cancel the effect of electromagnetic interference. Ribbon cable is found inside computers and other electronic components. It is used for connecting between printed circuits 6.1.3Fuses circuit breakers Fuses and circuit-breakers are designed to break the circuit if current flow is excessive. The most common kinds are fuses, fusible links, and circuit breakers. They are all rated in amperes. Their ratings are usually marked on them.Fuses are typically used in lighting and accessory circuits where current flow is usually moderate. [1]Typically, a fuse contains a metal strip which is designed to overheat and melt when subjected to a specified excessive level of current flow, breaking the circuit and stopping the excessive current flow from potentially damaging more valuable components. A fusible link is typically placed near the battery, and, except for the starter motor, it carries the current needed to power an individual circuit, or a range of circuits.Circuit breakers are not destroyed by excess current. A bimetallic strip heats up and bends, opening a set of contacts and breaking the circuit. In most types, as the strip cools, it resumes its original shape. The contacts close, completing the circuit once more. 6.1.6 Batteries（fig.6-4） The wet cell lead acid battery is the main storage device in automotive use. An automotive battery can supply very high discharge currents while maintaining a high voltage - useful for cold starting. It gives a high power output for its co