What is a Transmission and How does it work?
A transmission works like the gears on a bike. By adjusting the ratio between gears, you can achieve different speeds without the engine having to work as hard. A transmission makes it so that the engine can work at a more constant level of intensity than if, say, it tried to drive at many different speeds in one gear.
You wouldn’t pedal uphill in the third gear on your bike (unless you’re Lance Armstrong), and your engine doesn’t want to work that way either, because it would go kaput. If you’ve ever had a “single speed” or “fixed gear” bicycle, you’ll understand how great being able to adjust gear ratios is for long-term performance.
However, as we all know, there are two types of transmissions, automatic and manual and they work differently.
In cars with an automatic transmission, the car itself takes care of shifting between different gear ratios so you don’t have to. Ah, convenience! The engine, however, is not connected to the transmission directly. But don’t worry. The way it switches gears is through something in between the two called a torque converter.
Without getting too technical, the torque converter is what automatic cars use so you can come to a stop and not stall. It is a fluid coupling that lets the engine work somewhat independently of the transmission. When you press on the gas, power gets transferred from the engine to wheels because more fluid is pumped into the torque converter. Passing transmission fluid is what keeps the engine and transmission in communication.
Then, the “messages” (it’s not telepathy) about how hard the engine is working and which gear ratio to set are sent to a part called the planetary gear set. This is the part that holds the parts that act like the gears on your bike. The parts inside it (called the sun gear, the planetary gears and its carrier and the ring gear) adjust in different ways for first, second third, fourth and reverse. The spinning of the turbine is what tells these parts what to do. Since they know “automatically” what to do, you don’t have to press on a clutch or reach for a stick shift. That’s luxury!
In cars with manual transmissions, the clutch is what connects the transmission and the engine. By pressing the clutch pedal (that weird one over on the far left of your car), you disconnect the engine and the transmission momentarily. Meanwhile, lots of gears are turning, and by moving your stick shift (trying reaching down, to your right) you are actually moving parts that alter the gear ratio. There’s nothing like knowing you’re in control of the machine.
To simplify – automatic transmissions “communicate” with engines through the torque converter whereas manuals alter their gear ratios based on how you alter the various gears with your stick shift.
And the debate will continue forever as to which is better.