ECU - (Engine Control Unit) All you need to know in simple.

ECU-Engine control unit, is a control unit that controls your engine. It determines the amount of fuel, ignition timing and other parameters whether a bike or a car needs to keep running smoothly.

 How it works-

Your bike or car equipped with it has got many sensors that continuously monitors the engine. The ECU reads the input values and decides what is the correct value required at the given condition. The input values can be collected from various sensors like crankshaft position sensor, air temperature sensor, oxygen sensor, Throttle position sensor and gives the data values to the ECU.

Sensors in a typical ECU

How it reads-
 

It reads value from multidimensional maps also known as Look up tables, It's just similar to our mathematical tables with some pre defined set of values. 

 

Look-up tables

Using these input values the engine speed, ignition timing and air/fuel mixture ratio is calculated from the signals coming from the sensors. In general we can say that it is the brain of the engine.

ECU of Yamaha YZF R-15

So a bike equipped with an ECU don't have a carburetor instead it uses a fuel injector to deliver the fuel. Suddenly if you raise the throttle, the ECU can sense it and can deliver the optimum amount of air/fuel required. 

Suppose If you ride your machine in a hilly terrain on higher altitudes more than 4000 metres, the oxygen level will be marginally less when compared to the sea level. The bike which uses an ECU will be more efficient when compared to a carburetted one, since it optimizes the right amount of fuel to be delivered for the changing conditions in environment. Optimum performance and efficiency - both can be obtained by using an ECU.

Depending upon other features the ECU can also be programmed to handle traction control system, ABS and electronic stability control system, dynamic damping control and many other components.