A brief guide to the control ECU of a diesel engine.
To control a modern diesel engine ? need to check:
Quantity? fuel injected
Advance Injection
Duration Injection
In order to control the injection of fuel ? need to know how much air is flowing into the engine and ? need to know the speed? of the engine.
In order to have the 5 factors that are closely connected.
Mass air flow (MAF)
Quantity? fuel injected
Advance Injection
Duration Injection
Speed? of the engine (rpm)
These factors are controlled by the accelerator pedal through the engine ecu.
The pedals electronic send a signal to the controller, which shows how much the driver is pushing the pedal.
The measure ? usually a percentage.
0% does not ? crushed so that the engine idles. 100% ? completely crushed.
Cos? 0% "choking us" the injectors to give a deal? fixed fuel, for a time determined by a fixed time. There? results in a fixed regime to a minimum. for example, 800 rpm. Cos? the idle speed ? been mapped to a specific value for the maf,quantity,duration and advance.
100% of the gas the injectors must give a deal? fixed fuel, for a time determined by a fixed time. Then at 100% throttle ? been mapped to a specific value for the MAF, quantity, duration and advance.
This means that any other percentage of from 1% to 99% will have? also be mapped to a specific value for the MAF, quantity, duration and advance.
Understand the facts and figures. (Based on engine 1.9 TDI PD VAG.)
AIR CONTROL
There ? no control air really in a diesel engine!
This is because the engine has a capacity? 1.9 litres or 1900 cubic centimeters (cm3 ).
The exact figure ? really? 1.897 cm3.
The engine ? a four-cylinder so that each cylinder ? 474 cm3 . (1897/4)
All four cylinders are identical, we only need to "deal" with one to simplify.
If a cylinder has a volume of 474 cm3,the amount? maximum of air and fuel that can? contain ? 474 cm3.
If we ignore the fuel for a moment, and also the volumetric efficiencies,means that the maximum amount? air the cylinder can? contain ? 474 cm3
If the air was a liquid, life would be easy. The quantity? of a liquid that you put in 474 cm3 ? 474 cm3.
The Air ? a gas, and then pu? "adapt to different quantity?" of the air in the same space, depending on pressure, temperature and density.
Cos? how much air you put in 474 cm3 of nonstro cylinder?
This ? determined by the density? of the air, and the density? of air depends on the ambient temperature and pressure.
The density? air ****llo of the sea, and on a hot day,say 20? C ? between 1milligrammmo/cm3 and 1.2 mg/cm3.
And 'pi? easy to think that it is 1.0 mg/cm3.
Cos? 474 cm3 of a cylinder contain? 474x1,0 mg of air, which ? 474 mg.
Cos? each stroke of the piston aspirareranno 474 mg of air. This ? referred to as 474 mg/stroke.
The engine or the ecu does not need to measure this data, why? this ? you get without trying.
Then why? the engine has a mass flow meter of air when you s? that being vacuumed 474mg/corsa air flow mass?
The MAF or (air mass meter) ? a means for the ecu to measure the exhaust gas recirculation (EGR).
The way pi? simple to measure the EGR flow ? to measure,through the MAF,the flow aspirated by the engine.
The ECU knows that the engine is sucking in 474mg/race we have said, then the measurement MAF must be 474mg/travel.But if the measurement MAF for? drops to 274mg/run while it must be still to 474 mg/stroke... where are the other 200 mg/stroke?
The other 200 mg/stroke "come" from the EGR valve as a gas of exhaust gas recirculation.
Therefore, the motor 200 mg/EGR/stroke + 274 mg/MAF/race sucked for a total of 474 mg/stroke.
Then, the control unit "knows" that the MAF should be 474 mg/stroke without the exhaust gas recirculation. (EGR valve) and less than 474 mg/stroke with the EGR valve open.
Then, if the digit MAF remains constantly high (close to 474 mg/stroke), the EGR valve ? stuck closed.
If the digit MAF remains constantly low (near 274 mg/stroke), the EGR valve ? locked open.
Then why? the engine has this EGR valve.
EGR helps to reduce oxides of nitrogen (NOx) which pollute the atmosphere.
The 474mg/stroke of air contains more? oxygen as the fuel pu? burn.
When the fuel consumption ? finished a part of the exhaust gas produced reacts with oxygen ****** that renderono oxides of nitrogen.
This problem can? be reduced by reducing the amount? oxygen 474 mg/stroke of air.
The way pi? simple to do that ? to have less air.
The way pi? easy to have less air ? to add exhaust gas.
That's why? it has a EGR valve and a MAF sensor.
PRESSURE CONTROL OF THE AIR - TURBOCHARGERS.
The pressure of the air and its temperature varies depending on where you live in the world,climate, humidity,altitude,etc...
The following assumes an air temperature of about 20? C has a pressure of 1000 millibars (mbar).
Suppose now that the cylinders receive air at a pressure of 1000 mbar and a temperature of 20? C at a flow of 474 mg/stroke. (To simplify things, we assume that the EGR is not ? involved)
A typical value of the boost of the turbo ? to add an extra 1000 - 1500 mbar of air pressure. Cos? a typical graph of pressure boost against rpm will run you? from 1000 mbar (without amplification of boost) up to 2500 mbar of boost max.
(Then the turbo "pushes" 1500 mbar)
The pressure of the air in the pi?,so if we have 474 mg of air at 1000 mbar can we have 948 mg of extra air to 2000 mbar. Then, with the air we have a pitch twice as high pi? pressure in the cylinder and pu? burn double the fuel much more efficiently than before.
The result ? the engine develops more? power.
You need to? check the turbo as the engine design pu? only withstand certain ****lli boost and this is through the MAP that informs the ecu of a certain ****llo boost.
The engine or the ecu has a sensor boost pressure on the manifold, said absolute pressure sensor (MAP) sensor intake air temperature (IAT).
These sensors allow the ecu to compare the actual pressure of the boost through the MAP, and to correlate the signal with the boost that is stored in the map ECU.
The control unit also has a single value Boost Limiter (SVBL), which acts as an emergency situation by cutting the boost in the case in which this portfolio? reached ? passed.
A MAP turbo will be? used by the ecu to increase the amount? injection in-line with the major thrust.
Another map turbo compares the actual increase of the boost(map sensor) with the increase in need of the boost to the achievement of a given pressure turbo. (BOOST LIMITER)
The effective thrust of the turbo must follow the approximate shape of the map turbo.
If the effective thrust is still too high or too low, the ecu v? in the recovery.
The recovery is active even if the effective thrust exceeds the single value Boost Limiter. (SVBL).
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Originally Written by dvdtuning
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