Gail Mattson, age 13, of Tonawanda, N.Y., for her question:
HOW DOES A TRANSMISSION WORK?
A transmission is an assembly of parts which carries, or transmits, power from an engine to a drive shaft. The transmission may use a set of gears and shafts and it may also carry the power hydraulically or electrically.
Transmissions are used in automobiles, buses, trucks, tractors, airplanes, ships and other vehicles.
An engine provides power in the form of a twisting force, called torque. This is the same force you use when you unscrew the lid of a jar of honey. Torque must be carried to the wheels of a car, or to the propeller of a ship or airplane. The transmission is designed to change the twisting force of an engine so that a driver can select the amount and direction of force he needs.
The power of the engine reaches the transmissions by means of a turning shaft coming from the clutch. On the end of this shaft is a small gear engaged with a larger gear on the countershaft of the transmission. This is part of a three speed manual control transmission.
In a constant mesh transmission, gears are meshed all the time. The gears do not turn the shafts on which they are mounted until a geared clutch inside the transmission is moved either forward or backward.
Many cars today use an automatic gear transmission. When the driver wants to go forward, he moves a selector to the driving position. Then all he has to do is push the accelerator. As the car increases speed, the automatic transmission shifts from low to high gear.
Most automatic gear transmissions in automobiles use a fluid clutch
,and a set of planetary gears, or gears which revolve about each other like planets around a sun.
Planetary gears are particularly useful because the power can flow through them in a wide range of twisting forces when the hydraulic valves lock or hold the gears.
Here's a good idea: go to a garage in your neighborhood and ask the mechanic to show you a transmission and to point out how it works. You'll see that it is a complicated mechanical device.
Perhaps he will have a fluid transmission, or hydraulic torque converter for you to see. This type of transmission carries the torque directly from the engine to the drive shaft. The twisting force of the engine is built up or reduced by placing a set of fixed, or stationary, blades in the middle of a fluid clutch.
The advantages of a hydraulic torque converter is that it moves slowly from one speed to another as the car picks up power.
Many variations and combinations of torque converters and planetary gears are used in automobile automatic transmissions.