In addition to calculating the fueling based on driver demand, temperature has a considerable part to play in the equations used. Conversely, a fueling strategy or a fault that results in less than a normal quantity of fuel being injected would result in a ‘lean mixture’. For best power levels and safe combustion, the ECU must change the ratio of the mixture and inject more fuel under full throttle than it would during cruising – this is called a ‘rich mixture’. The increase in airflow to the engine is measured by the Mass Air Flow sensor (MAF) so the ECU can change the amount of fuel that’s injected, keeping the mixture ratio within limits. When you press the accelerator pedal, your throttle flap will open to allow more air in to the engine. Because of the combustion characteristics of the fuels in use, it also requires a change in the ratio of this mixture. These require a number of sensors to measure such variables and apply them to logic in the programming of the ECU to determine how to correctly compensate for them.Īn increase in engine demand (such as accelerating) will require an increase in the overall quantity of mixture. The ECU has the job of controlling the fuel injection, ignition and ancillaries of the engine using digitally stored equations and numeric tables, rather than by analogue means.Īn ECU has to deal with many variables when deciding the correct mixture ratio. The only way to meet these strict requirements is to hand over control of the engine to an ECU, the Engine Control Unit. With the demands of modern vehicles focusing on fuel efficiency and lower emissions, the mixture must be more tightly controlled. Too little fuel - too much oxygen makes the combustion slow and weak.Įngines used to have this mixture quantity and ratio controlled by an entirely mechanical metering device called a carburetor, which was little more than a collection of fixed diameter holes (jets) through which the engine ‘sucked’ the fuel. Too much fuel - too little oxygen, and the combustion is dirty and wasteful. Not only is the amount of mixture important, but the ratio of that mixture has to be correct. Too much mixture and the engine will be full throttle, too little and the engine will not be able to power itself or the car. This combination of air and fuel is called a ‘mixture’. As the air is sucked in, enough fuel has to be provided to create power to sustain the engine’s operation while having a useful amount left over to propel the car when required. While this sounds like something that can be done mechanically (and was in the past), there’s now a bit more to it than that.Īn internal combustion engine is essentially a big air pump that powers itself using fuel. It determines the position of the engine’s internals using a Crankshaft Position Sensor so that the injectors and ignition system are activated at precisely the correct time. If this unit controls both an engine and a transmission, it is often described as a Powertrain Control Module (PCM).įor the purposes of this article, we will discuss the ECU as an Engine Control Unit.įundamentally, the engine ECU controls the injection of the fuel and, in petrol engines, the timing of the spark to ignite it. In the Automotive industry, the term ECU often refers to an Engine Control Unit (ECU), or an Engine Control Module (ECM). The use of the term ECU may be used to refer to an Engine Control Unit, however ECU also refers to an Electronic Control Unit, which is a component of any automotive mechatronic system, not just for the control of an engine.
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