The Clutch

Some type of clutch is found in every car. The clutch may be operated by means of a foot pedal, or it may be automatic or semi-automatic. The friction clutch and the fluid coupling are the two basic varieties. The friction clutch, which depends on solid contact between engine and transmission, consists of: the rear face of the fly­wheel; the driving plate, mounted to rotate with the fly­wheel; and the driven plate, between the other two. When the clutch is engaged, the driving plate presses the driven plate against the rear face of the flywheel. Engine power is then delivered through the contacting surfaces to the transmission.

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Fluid coupling may be used either with or without th(friction clutch. When it is the sole means of engaging the engine to the transmission, power is delivered exclu sively through an oil medium without any contact of solic parts. In this type, known as a fluid drive, an engine-driven, fan-bladed disc, known as the fluid flywheel, agitates the oil with sufficient force to rotate a second disc that is connected to the transmission. As the rota­tion of the second disc directly depends on the amount oi engine power delivered, the prime result of fluid coupling is an automatic clutch action, which greatly simplifies the requirements for gear shifting.

Manual and Automatic Transmissions

The transmission is a mechanism that changes speed and power ratios between the engine and the driving wheels. Three general types of transmission are in cur­rent use: conventional or sliding-gear, Hydra-Matic, and torque-converter systems.

The conventional transmission provides for three or four forward speeds and one reverse speed. It consists of two shafts, each with gears of varying diameters. One shaft drives the other at a preselected speed by meshing the appropriate set of gears. For reverse speed, an extra gear, known as the idler gear, is required to turn the driven shaft in the opposite direction from normal rota­tion. In high gear, the two shafts usually turn at the same speed. In low, second, and reverse gears, the driven shaft turns more slowly than the driving shaft. When a pair of gears permits the driven shaft to turn more rapidly than the driving shaft, the transmission is said to have overdrive. Overdrive is designed to increase the speed of a car.

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The Hydra-Matic type of transmission combines the automatic clutch provided by fluid coupling with a semi­automatic transmission. A mechanical governor, control­led by the pressure exerted on the accelerator pedal, regu­lates gear selection through a system of hydraulically controlled shift valves. Hydra-Matic transmission pro­vides for several forward gears.

The torque-converter type of transmission provides an unlimited number of gear ratios with no shifting of gears. The torque converter is a hydraulic mechanism using engine power to drive a pump, which impels streams of oil against the blades of a turbine. The tur­bine is connected to the drive shaft and causes it to ro­tate.

Both Hydra-Matic and torque-converter systems are controlled by a selector lever on the steering column, which provides also for reverse and sometimes for emer­gency-low gears.