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Monday, January 28, 2008

Speed Transmission

Manual Transmission Early transmission were all manually operated. There were two shaft, each with several gears of different sizes. One shaft could be moved or shifted, with respect to the other in order to mesh, or engage, a gear on one shaft with a gear on the other.

For most cars a transmission with three forward gears and one reverse gear is adequate. In some smaller car with small engines, four or five speed transmissions are used to compensate for the lower torque available from the engine. Truck designed to haul heavy loads may have as many as 20 forward speeds and four speeds in reverse. The part of the transmission that houses the gears is called gearbox.

A manual transmission has a clutch to disconnect the engine crankshaft from the gearbox while shifting gears. The driver shifts gear by manipulating a shift lever, which is connected to the transmission by a mechanical linkage. In the newer synchromesh transmission, synchronizers allow the gear teeth to be in constant mesh, turning freely on their shaft. The selected combination is first synchronized (the teeth on the two gears are brought to the same speed of rotation) and then locked together so that power is transmitted to ther drive shaft and then to the differential. Automatic Transmission Automatic transmissions use a torque converter – to couple the engine and the gearbox. It is a form of fluid coupling in which one rotating member indirectly imparts a rotating motion to another rotating member on another shaft that is connected to the gearbox.

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