Thursday June 12 2014

What is a crankshaft?

By Peter Mutimba defines a crankshaft or the crank as a system that converts linear energy into rotational energy. This enables the wheels to drive the car forward. To put it in a simpler way, a crankshaft is the device that converts explosions within the engine into the rotation of wheels, thus the forward motion of the car.

How does it accomplish this?
Consider for the moment what we discussed on the workings of an engine. A mixture of air and fuel is put under pressure within a cylinder and is then ignited by the spark plug. The resultant explosion is just fire in a cylinder and without the crankshaft, it is completely useless.
Before we continue, you should know what this device looks like. It is a bit like a roasting stick that has been stuck though pieces of meat. The protruding parts are where the pistons are attached. We call them crank pins. At they are attached to opposite sides of the crank, it means that as the crank rotates, one wide goes up, the other goes down, and the cycle continues. This will all make sense in a moment.
Ideally, each crank pin represents a cylinder in the engine.

Let’s break it down
Here is the science. Within this cylinder is a piston. The piston moves up and down within the cylinder depending on what is happening at that particular moment. When the air fuel mixture is put under pressure, the piston moves up…it actually does the pressurising. The explosion however, forces the piston back down and the process is repeated. And this is where the crankshaft is useful. The part of the piston that is not located inside the cylinder is attached to the crankshaft by a connecting rod.

Every time it moves up or down, it rotates the crankshaft. This rotational movement is the power that is eventually transferred to the tyres, moving the vehicle forward. If you have been alongside a truck and you happened to see a long metal rod running from front to back and rotating at a high speed, you know what I am talking about. The crankshaft is doing that. This should tell you how fast that rotation movement is. This is the origin of the word revs. It is not some complex petrol head term. It just means the number of the crankshaft’s revolutions per minute.