The Transmission and Transaxle

An automobile must be able to reach a wide variety of speeds over varying terrain. A car must be able to travel at slow speeds through city streets, at high speeds along expressways, and at steady speeds when traveling uphill. The automobile's transmission system helps the vehicle change speeds to operate efficiently under all these conditions.

In order to better understand what the transmission does, let's look at the operation of a bicycle. A car's transmission can be compared to the gears on a bicycle, and the car's engine can be compared to the bike's rider. Most modern bicycles allow the rider to change gears as the bike is being ridden. So, when you ride your bike on a flat road, the higher you set the gear, the faster the bike will go. However, if you want to go uphill when the bike is in high gear, you'll have to apply a lot more effort to the pedals. To make it easier to pedal up the hill, you would need to change to a lower gear.

The same is true for an automobile. In order to drive a car uphill in high gear, the car's engine will have to produce an excessive amount of power. Shifting the car to a lower gear will make it much easier for the engine to move the vehicle uphill.

The opposite of this explanation also applies. If a bicycle is traveling downhill or along a flat road in low gear, you'll have to pedal very fast to produce any kind of speed. This will put a lot of strain on you. Therefore, to make it easier to move the bike along, you would need to change to a higher gear. This allows the bicycle to travel faster with less pedaling.

This same action occurs in an automobile. As you increase the speed of your car, the engine has to operate at higher and higher speeds in order to move the car along. If the engine was left in a low gear, the speed could become so excessive that it might damage the engine. To prevent this from occurring, you would simply shift the vehicle into a higher gear to reduce the required speed of the engine.

Two types of transmissions are commonly used in automobiles: the automatic transmission and the manual transmission. Most vehicles today contain automatic transmissions, although manual transmissions are available on most new car models. An automatic transmission usually has either three or four gear selections. The gears are shifted automatically with only a limited amount of input from the driver. In contrast, a manual transmission usually has either four or five gear selections, and the shifts must be performed manually by the driver.

The type of transmission a vehicle contains is generally a buyer option. Most new vehicles can be purchased with either type of transmission. However, because automatic transmissions are easier to operate than manual systems, most customers prefer them.

Many modern automobiles (especially vehicles with front-wheel drive) use a special type of transmission called a transaxle. A transaxle is a device that combines a transmission and a drive train all in one unit. (We'll discuss drive trains in a moment.) When both systems are combined in one unit, space is saved, the device is lighter in weight, and it's easier to maintain. This makes a transaxle a good choice for use in smaller or compact cars. Transaxles can contain either manual or automatic transmission components.