Coordinated work of individual parts
When the engine is running, pistons that rise and fall in the cylinders suck in air. If you fully depress the gas pedal, then the engine sucks in the maximum amount of air, since in this case both throttle valves are fully open. For clean engine operation, fuel must be mixed with the intake air in the exact proportion. The MPI uses the mass of intake air to determine the proportion of air and gasoline in the working mixture. In the MPFI, the reference value is intake manifold pressure information and temperature.
Now the control unit can give the correct signals to open and close the injection valves. A long opening is provided for a large amount of fuel, a short time - when a small amount of fuel is needed.
Launch
To start a cold engine, a more saturated, i.e., fuel-rich working mixture is needed, since many droplets of fuel settle on the walls in the suction area on their way to the combustion chambers and no longer participate in the combustion process. Therefore, the proportion of fuel in the fuel-air mixture must be increased.
During cold start control, the duration of injection by the valves is increased. Factors such as coolant temperature and engine speed affect injection duration. After a certain engine speed, the amount of fuel needed to start a cold engine slowly decreases to match the standard amount.
Warm engine
After starting, the engine needs a rich mixture for a while, as a certain amount of fuel still condenses in the intake area. For this there is «post-launch promotion». Depending on the temperature, more fuel is delivered for a while. The control unit receives the necessary information about the engine temperature from the coolant temperature sensor.
Engine oil, which is quite viscous when the engine is cold, causes increased internal friction in the car. More effort is needed to keep the engine running. To ensure the supply of this increased amount of the working mixture, the already mentioned idling stabilization valve is designed.
Idling
When the throttle valve is closed, a small amount of air is passed through the bypass around the throttle valve. This air is detected by an air flow meter, or pressure sensor, and is therefore supplemented with the required amount of fuel in the idling mixture. In general, the idling mixture contains more gasoline than during normal operation in order to keep the engine running smoothly and without misfiring.
The amount of air passing through the bypass (and, consequently, the number of revolutions of the engine at idle), is determined by the idle speed stabilization valve.
Partial load
At partial load, the engine receives a standard amount of fuel. At the same time, importance is attached to minimizing fuel consumption.
Accelerations
If the accelerator pedal is suddenly depressed, the enrichment of the fuel-air mixture necessary for acceleration is caused when the increase in the intake/th amount/mass of air per second exceeds a certain value. The throttle potentiometer also signals acceleration. When the engine is cold, acceleration requires more fuel. Therefore, the control unit evaluates each pulse of the fresh air flow meter or pressure sensor and throttle potentiometer as an acceleration signal and increases the fuel supply.
Full load
The throttle valve potentiometer indicates to the control unit that the driver has fully depressed the gas pedal. To develop maximum power, the engine now receives a richer mixture (enrichment of the working mixture at full load).
Forced idle mode
When driving downhill with the gas pedal released, the engine does not need to be supplied with fuel. The car itself rolls due to weight or acceleration. By high engine speed and throttle position (from her potentiometer) the control unit learns when a forced idle mode occurs and can «save fuel».
RPM limit
The injection system compares the engine speed at the moment with a maximum speed of 6500 rpm and, if they are exceeded, simply closes «fuel tap».
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