Table of contents: Coordinated operation of individual… ↓ Launch ↓ Warm engine ↓ Idling ↓ Partial load ↓ Accelerations ↓ Full load ↓ Forced idle mode ↓ Speed limitation ↓
Coordinated operation of individual parts
When the engine is running, the pistons rising and falling in the cylinders suck in air. If you fully depress the gas pedal, the engine sucks in the maximum amount of air, since in this case both throttle valves are fully open. For the engine to run cleanly, it is necessary that the fuel is mixed with the sucked air in a precise proportion. To determine the proportion of air and gasoline in the working mixture, MPI uses the mass of the sucked air. In MPFI, the comparative value is information about the pressure in the intake manifold and temperature.
The control unit can now send the correct signals to open and close the injection valves. Long opening is provided for a large amount of fuel, short opening is provided for a small amount of fuel.
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 injection duration of the valves is increased. Factors such as coolant temperature and engine speed affect the injection duration. After a certain engine speed, the amount of fuel required to start a cold engine slowly decreases and begins to match the standard.
Warm engine
After starting, the engine needs a richer working mixture for some time, because a certain amount of fuel still condenses in the intake area. For this purpose, there is a "post-start boost". Depending on the temperature, more fuel is supplied for some time. The control unit receives the necessary information about the engine temperature from the coolant temperature sensor.
Motor oil, which is quite viscous when the engine is cold, causes increased internal friction in the car. Increased effort is required to maintain engine speed. The already mentioned idle stabilization valve is designed to ensure the supply of this increased amount of working mixture.
Idling
When the throttle valve is closed, a small amount of air is drawn through a bypass channel around the throttle valve. This air is detected by the air flow meter, or pressure sensor, and is therefore supplemented in the idle mixture with the required amount of fuel. In general, the idle mixture contains more gasoline than in normal operation, so that the engine runs smoothly and without interruptions in ignition.
The amount of air passing through the bypass channel (and, therefore, the engine idle speed), 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 fuel-air mixture is enriched, which is necessary for acceleration, when the increase in the intake quantity/mass of air per second exceeds a certain value. The throttle potentiometer also signals acceleration. When the engine is cold, more fuel is required for acceleration. Therefore, the control unit evaluates each pulse from the fresh air flow meter or pressure sensor and the throttle potentiometer as an acceleration signal and increases the fuel supply.
Full load
The throttle 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 working mixture (enrichment of the working mixture at full load).
Forced idle mode
When driving downhill with the gas pedal released, there is no need to supply fuel to the engine. The car itself rolls due to its weight or acceleration. At high engine speeds and throttle position (from its potentiometer) the control unit knows when the forced idle mode occurs and can "save fuel".
Speed limitation
The injection system compares the engine speed at the moment with the maximum speed of 6500 rpm and, if it is exceeded, simply closes the "fuel tap".
(Text provided by the online resource: «audimanual.ru»)