What does a transmission do

What Transmissions Do

Have you ever wondered why cars with gas or diesel engines need transmissions? Every car that has an internal combustion engine needs one, but electric cars and steam engines don’t. Why is that? Let’s find out!

Speed vs Torque

Before we dig into the operational characteristics of internal combustion engines, we need to have a good understanding of two important parameters:  Speed and Torque. Let’s start with speed; It’s the easy one. When an engine is running, the crankshaft is spinning and this can be measured in Revolutions Per Minute, or RPM. Speed is simply how many times the crankshaft turns in a minute. Torque is a little more complex. Engine torque is how much “twisting force” the engine generates. An engine with low torque won’t have enough twisting force to make a car accelerate very fast. There just isn’t enough rotational power. In order to move a car efficiently, the speed and torque need to be optimum within the engine’s “Power Band.”

Here’s a good analogy that might help to explain. Let’s consider a carpenter who is pounding a nail. We know that it takes a certain amount of power to drive a nail into a piece of wood. Now let’s imagine that your arm is an engine (which technically it is) and you need to pound a nail.

Speed = How many times you hit the head of the nail per minute.

Torque = How hard you hit the nail each time you strike it.

Think back to the last time you were hammering nails. You hit the nail several times (speed) and each strike was delivered with good force (torque.) You were working efficiently. If you were hammering really fast, you probably noticed that you weren’t striking the nail with much force and this was fatiguing and wasn’t getting you far. You also didn’t try to pound the nail in with one swing which would be difficult. Essentially the rate that a seasoned carpenter swings the hammer, and force he applies, is his/her Power Band. Its where the engine is working optimally.

Internal combustion engines

Does the carpenter analogy above make sense? Well, we want an internal combustion engine to do the same thing. We want it to spin at the speed that allows it to deliver the needed torque to make the car move, without working so hard that it destroys itself. When the engine rotates at the optimum speed, Kims Nissan of Laurel, a local Nissan dealer in Laurel, MS, says we are operating within it’s Power Band.

Enter the transmission

Transmissions ensure that engines spin at optimal speeds within the power band so they provide wheels with the right amount of power needed to move and accelerate a car. It’s able to do this by driving a series of different sized gears.

Transmissions have a series of variously sized gears. Because the gears that mesh with each other are different sizes, the speed of a car can be varied without changing the speed of the engine’s rotational power all that much. This is thanks to gear ratios.

Hopefully this gives you an idea of how transmissions work. If you find yourself ever explaining this to someone, use the carpenter nail analogy to illustrate how speed and torque interact when optimum power is needed. We’d like to take credit for the analogy, but we found it during our research too.