汽车专业英语课件.ppt

(最新整理)汽车专业英语
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UNIT 4 Introduction to Drive Train
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Part ITechnical and Practical Reading
nsmissions with more speeds provide better fuel economy and smoother shifting, but they cost more to manufacture, so small sub-compact cars will often have optional 4 speed transmissions, while more upscale cars will have 5 or 6 speed transmissions. See figure 4-4.
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Figure 4-4
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Automatic Transmission
The modern automatic transmission is by far the most complicated mechanical component in today’s automobile.  Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony.
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All automatic transmissions have a shifter that has at least 4 positions, park, reverse neutral and drive. 
Many units also have a low range to assist in engine braking on long downhill runs. 
Others have special positions where the driver can manually shift if desired. See figure 4-5.
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Figure 4-5
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Automatic transmissions contain many gears in various combinations. 
In a manual transmission, gears slide along shafts as you move the shift lever from one position to another, engaging various sized gears as required in order to provide the correct gear ratio.
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In an automatic transmission, however, the gears are never physically moved and are always engaged to the same gears. 
This is accomplished through the use of planetary gear sets. See figure 4-6.
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Figure 4-6 Planetary Gear System Side View
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The basic planetary gear set consists of a sun gear, a ring gear and two or more planet gears, all remaining in constant mesh. 
The planet gears are connected to each other through a common carrier that allows the gears to spin on shafts called “pinions” attached to the carrier.
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Notes：
1. The drive train includes: transmission that is connected to th