What is closed loop mean as in vehicle?

Answer 1

Closed loop, as applied to engine control, means as control changes are made, some variable is measured to determine whether the setpoint is reached, or whether more or less adjustment is required. For instance, in a typical fuel-injected vehicle, when you first start a cold engine, lots of fuel is required to keep it running until it warms up. The computer simply dumps a predetermined amount of fuel governed only by engine speed, throttle position, and engine temperature. There is no point in trying to fine tune the fuel delivered at this point, since the mixture needs to be soggy rich just to keep the engine running. This is called open-loop control. Once the engine has reached operating temperature, the computer switches to 'closed-loop' control. This means the computer receives feedback from an oxygen sensor as to whether the mixture is too lean or too rich, then it makes adjustments, then checks the sensor again, then makes adjustments, and on and on in an infinite loop. To understand the principle, imagine if you were to close your eyes and type words on your computer keyboard. If you are a good typist, the words are probably correct, but you have no way to know if you made a mistake. That's open loop control. There's no feedback as to whether the desired result was obtained, you simply have to assume that the correct words are there. Now open your eyes. if you mis-typed a word, you now have the feedback that you messed up, and you can type in a correction. That's closed-loop, from your fingers, to the keyboard, to the screen, to your eyes, which control the fingers. See the loop?