What Does A Transmission Do?


Five Fluids You Should Check to Keep Your Car Running Smoothly

In cars, what transmissions do is convert speed and torque along the drive train. The sole purpose is to maximize the efficiency of your engine to achieve lower fuel consumption while at the same time giving you the most amount of torque possible. Basically, your transmission keeps your cars performance in check and makes your wheels turn. If you didn't have your transmission, your car would not be able to drive or fuction properly. Your transmission is what converts the engines power to turn the wheels at a controlled rate for the best fuel economy.



How Automatic Transmissions Work


If you have ever driven a car with an automatic transmission, then you know that there are two big differences between an automatic transmission and a manu­al transmission:


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Most modern automatic gearboxes have a set of gears called a planetary or epicyclic gear train.

A planetary gear set consists of a central gear called the sun gear, an outer ring with internal gear teeth (also known as the annulus, or ring gear), and two or three gears known as planet gears that rotate between the sun and ring gears.


The drive train is coupled to a mechanism known as a torque converter, which acts as a fluid drive between the engine and transmission.


If the sun gear is locked and the planets driven by the planet carrier, the output is taken from the ring gear, achieving a speed increase.


If the ring gear is locked and the sun gear is driven, the planet gears transmit drive through the planet carrier and speed is reduced.


To achieve direct drive without change of speed or direction of rotation, the sun is locked to the ring gear and the whole unit turns as one.


How Manual Transmissions Work


If you drive a stick-shift car, then you may have several questions floating in your head.


How does the funny "H" pattern that I am moving this shift knob through have any relation to the gears inside the transmission? What is moving inside the transmission when I move the shifter?

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Cars need transmissions because of the physics of the gasoline engine. First, any engine has a redline -- a maximum rpm value above which the engine cannot go without exploding. Second, engines have narrow rpm ranges where horsepower and torque are at their maximum. For example, an engine might produce its maximum horsepower at 5,500 rpm. The transmission allows the gear ratio between the engine and the drive wheels to change as the car speeds up and slows down. You shift gears so the engine can stay below the redline and near the rpm band of its best performance.


Ideally, the transmission would be so flexible in its ratios that the engine could always run at its single, best-performance rpm value. That is the idea behind the continuously variable transmission (CVT).

The function of any transmission is transferring engine power to the driveshaft and rear wheels.

Gears inside the transmission change the vehicle's drive-wheel speed and torque in relation to engine speed and torque. Lower (numerically higher) gear ratios serve as torque multipliers and help the engine to develop enough power to accelerate from a standstill.


Initially, power and torque from the engine comes into the front of the transmission and rotates the main drive gear (or input shaft), which meshes with the cluster or counter shaft gear -- a series of gears forged into one piece that resembles a cluster of gears. The cluster-gear assembly rotates any time the clutch is engaged to a running engine, whether or not the transmission is in gear or in neutral.




French inventors Louis-Rene Panhard and Emile Levassor are credited with the development of the first modern manual transmission. They demonstrated their three-speed transmission in 1894 and the basic design is still the starting point for most contemporary manual transmissions.


Panhard and Levassor used a chain drive on their original transmission. In 1898 auto maker Louis Renault used their basic design, but substituted a drive shaft for the drive chain and added a differential axle for the rear wheels to improve performance of the manual transmission.


Manual transmissions were the standard on most vehicle for the first half of the 20th century, but automatic transmissions were being developed as far back as 1904. General Motors introduced the clutchless automatic transmission under the moniker, Hydra-Matic, in 1938, but the first true fully automatic transmission didn't appear until 1948 with the Buick Dynaflow transmission.