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An Electronic Control Unit or ECU (also known as an "engine management system") is an
electronic device, basically a computer, in an internal combustion engine that reads several sensors in the engine and uses the information to control the fuel injection and ignition systems of the
engine. This approach allows an engine's operation to be controlled in great detail, allowing greater fuel efficiency, better
power and responsiveness, and much lower pollution levels than earlier generations of engines. Because the ECU is dealing with
actual measured engine performance from millisecond to millisecond, it can compensate for many variables that traditional systems
cannot, such as ambient temperature, humidity, altitude (air density), fuel octane rating, as well as the demands made on it by the driver. In addition, it
is able to a large degree to compensate for the gradual wearing of the engine as it ages, which in practice allows it to extend
engine life to two or three times that of engines of twenty years ago.
Modern ECUs use a microprocessor which can process the inputs from
the engine sensors in real time. An electronic control unit contains the hardware
and software (firmware). The hardware consists of electronic components on a
printed circuit board (PCB). The main component on this
circuit board is a micro-controller chip (CPU). The software is stored in the microcontroller
or other chips on the PCB, typically in EPROMs or Flash-Memory so the CPU can be
re-programmed by uploading updated code. This is also referred to as an (electronic) Engine Management System (EMS).
Earlier ECU designs were based more on analogue computer
circuitry, due to the fact that for analogue circuits processing speed is not an issue. It was not until around 1987 that digital electronics and embedded microprocessor systems became fast enough to process engine
parameters in real time. The first such systems were introduced into racing engines such as those used for Formula One, but it was not long before these found their way into everyday cars.
A halfway house type of design was popular in the mid-80s. This used analogue techniques to measure and process input
parameters from the engine, then used a look-up table stored in a digital ROM chip to yield precomputed output
values. Later systems compute these outputs on the fly. The ROM type of system is amenable to tuning if one knows the system well. The disadvantage of such systems is that the precomputed values
are only optimal for an idealised, new engine. As the engine wears the system is less able to compensate than a CPU based
system.
Sophisticated engine management systems receive inputs from other sources, and control other parts of the engine; for
instance, some variable valve timing systems are electronically controlled, turbocharger wastegates can also be managed. They also may interface with electronically-controlled automatic transmissions, traction control systems, and the like.
Such systems are used for many internal combustion engines in other applications. In aeronautical applications, the systems
are known as "FADECs" (Full Authority Digital Engine Controls). This kind of electronic control is less common in piston-engined
aeroplanes than in automobiles, because of the large costs of certifying parts for aviation use, relatively small demand, and the
consequent stagnation of technological innovation in this market.
Today there is more than one open source engine managments system in development. Some of these are:
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