How It Works: The Transmission

How-To, Technology on May 8, 2018

We often hear about our vehicle’s transmission system, and sometimes have problems requiring parts to be replaced – but have you ever been curious about how the transmission actually works? Let’s break it down for you. The transmission provides controlled application of the power in the vehicle. Sometimes, when we refer to the transmission, we are talking about the gearbox. The gearbox uses gears and gear trains to facilitate speed and torque conversions.

The gearbox works on the principle of circular motion around a point at variable distance. A good example are bicycle gears: when you pedal while the chain is on the smallest front gear, the effort applied to push the pedal and turn the rear tire is very low. While the chain is on the largest gear, the effort applied is more but distance covered is much more. The smaller gears are great for effortlessly pushing your bicycle at slower speeds and it is easier to use the larger gears while traveling at a higher speed. This is the principle that applies to the gears of a vehicle. There are various discs of different diameters that connect/disconnect to allow for the change of gears.

When power comes from the engine to the transmission through the clutch (either manually done by the driver, or automatically done by the vehicle depending on your transmission type), a gear is chosen and sent to the differential which turn the wheels.

A clutch is needed to disconnect the engine from the transmission / gearbox for smooth transition between gears.

Automatic transmissions have certainly become the most popular choice in recent years because of how easy they are to drive. To best understand how a gearbox works though, we’ll first talk about the manual as this is more helpful in understanding the transmission’s functionality for your vehicle.

In the picture given above, you can see the numbers in the circles signify the position of the gear lever. The first frame shows the standard view we see on a stick shift, which is a reflection of where to shift when changing gears. When a gear is selected, it pushes a rod in the opposite direction which in turn shifts a ‘gear wheel.’ The rod is called the “selector rod.”

In a five-speed transmission, there are basically three different selector rods. When you shift vertically, position of a single selector rod changes but when you move the gear lever sideways, a different selector rod is chosen.

Now that you know how a selector rod works, the next picture will explain how it changes the ‘gear’.

This gif gives a better understanding of the workings of a gearbox.

As you can see, choosing a selector rod controls which gear is engaged.

Now let’s discuss automatic transmissions. The basic difference between a manual and an automatic is their way of cutting off engine’s power. A manual, uses a traditional clutch while an automatic uses a torque converter.

Next, the gear system in an automatic looks different than on a manual transmission, using a different layout and setup of gears to get the job done. The principle is same: a planetary gear set lets you change gear ratios without having to engage different gears. They’re all already engaged, by being in the same position. All you have to do is use your brakes and the gas pedal to change which components rotate and which stay stationary. Unlike in manual transmission where you have to push different gears, gears are already aligned, and your actions control how the vehicle engages them.

Hopefully this has been a helpful explanation of how a transmission system works, as well as the differences between a manual and an automatic vehicle.

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