So What Are Closed Loops? How Modern-Day Engine Management Systems Function

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BYLINE: Ken Corkett

ENGINE management systems are brilliant engineering concepts, but unfortunately, as most of us are neither brilliant nor engineers, engine management may be difficult to fully appreciate or understand. For example, terms such as closed loop or open loop mean little to the layman.

So, before I try to explain, let us go back in history to those dim and distant days when adjustments to ignition timing and fuelling were mainly mechanical. If you had a screwdriver and a spanner, chances are that you could handle most problems.

In the days of the magneto, or CB points system in general, the points opening could be set with a battery and bulb, or even by inserting a cigarette paper between the points and noting when it became free to determine the exact point of breaking. All that was then necessary was to measure the distance of the piston crown before the top of its compression stroke and set the opening to the manufacturer's specification.

Mixture setting was normally via a screw on the carburettor and this was simply screwed in or out until correct idle speed was achieved.

Now we have performance mapping. During development the engine is mounted on a dynamometer so that all its loads are measured along with exhaust by-products. The mapping itself consists of three dimensional graphs showing performance information, ignition advance, air-fuel ratio. One set of sensors and a microprocessor can control ignition and fuelling.

As for open and closed loop, the results of dynamometer tests are stored in the microprocessor's permanent memory and the engine will perform according to the stored data. …