文档介绍：UNIT 4 Introduction to Drive Train
Part ITechnical and Practical Reading
Passage A
Drive Train (I)
The drive train serves two functions: it transmits power from the engine to the drive wheels, and it varies the amount of torque.
“Power” is the speed at which work is performed. “Torque” is twisting force.
The drive train includes: transmission that is connected to the back of the engine and sends the power from the engine to the drive wheels; driveshaft that transmits the power from transmission to differential; and differential that sends the power to the two wheel axles. See figure 4-1.
Figure 4-1
Some types of drive train layouts use a “transaxle”, which is simply bination of the transmission and the differential. These are usually found on front wheel drive cars, but are also used on rear-engine cars. See figure 4-2.
Figure 4-2 Front wheel drive layout
Transmission Type
There are two types of transmissions: manual and automatic.
If you have a manual transmission, you have to shift the gears yourself, usually with a stick located on your console and the clutch pedal.
If you have an automatic transmission, the mechanism changes without any help from you.
This is plished through a system that works by oil pressure.
Each shift of the gears is controlled by a shift valve; and the gear changes depend on speed, the road, and load conditions.
Both manual transmission (with its clutch) and automatic transmission (plus its torque converter) plish exactly the same thing, but they do it in totally different ways. See figure 4-3.
Figure 4-3