turbocharged engine

[silver343124]

Hi, I was wondering where is the place of pressure and temperature sensor (before or after throttle plate) in a gasoline turbocharged engine and if only wastegate valve is controled by the solenoid valve via ecu.

I made a simple scheme for better understanding...

[KiwiBacon]

Temperature sensors are often located in the MAF (if the engine has a MAF) which is before the throttle plate.

Pressure sensors are located after the throttle plate so they can read the intake manifold pressure.

Wastegates can be plumbed directly to the intake manifold or the line can be interrupted via a valve controlled by the ECU.

[Black Lotus]

Originally Posted by silver343124

Hi, I was wondering where is the place of pressure and temperature sensor (before or after throttle plate) in a gasoline turbocharged engine and if only wastegate valve is controled by the solenoid valve via ecu.

I made a simple scheme for better understanding...

I'm a bit confused as to why this scheme has a both a MAF sensor and a MAP sensor located in the intake. It's possible that someone would use both sensors but like Kiwi Fruit said, the MAP sensor would be located between the throttle valve(s) and the intake valve. For an intercooled engine the position you have for the air temp sensor is the best. Which is where it is at in both my turbo cars.
Back to the MAP sensor.
Typically, what I've seen is a MAF sensor with a barometric pressure sensor mounted somewhere in the car to tell the computer what the air density (or pressure) outside is.
Or, in the case of both my turbo cars, both use MAP sensors only (speed/density systems) mounted between the throttle valves and the intake valves, and no MAF.
One car, with the more deluxe OEM computer has a barometric sensor also to help the computer make on the fly adjustments in the injector pulse widths if the air density (pressure) changes. The other car takes an air density sample from the MAP sensor when you first switch the car on, and lives with that until it's turn off.

[silver343124]

Originally Posted by KiwiBacon

Temperature sensors are often located in the MAF (if the engine has a MAF) which is before the throttle plate.

Pressure sensors are located after the throttle plate so they can read the intake manifold pressure.

Wastegates can be plumbed directly to the intake manifold or the line can be interrupted via a valve controlled by the ECU.

I know that MAF sensor is a hot wire and that its electrical resistance changes with the air mass flow and air temperature and humidity. ECU don't know the humidity so it calculates the mass flow with presumption of 50% humidity (so the mistake is equal on the both side 0%-100% humidity).
So yes MAF also gives you a temperature data.
But I thought that turbo engines also have temp sensor behind IC so it can measure the temperature after IC.
This temp is important as gasoline turbos uses extra fuel to lower the temperature in the cylinder durring compression stroke, so I thought that with temp data after IC the ECU calculates how much extra fuel (rich mixture) should apply.

About pressure sensor I now see that its position must be before throttle plate to control the solenoid valve (which control the mechanical wastegate). As if pressure sensor will be mount after throttle plate then ECU won't know what kind of pressure the air compressor is making (when not runing under full throttle) and thus damage the intake system.

And one more question, Is BLOW OFF valve totaly mechanic or is it anyway controled by the ECU wia solenoid?

[UncleBob]

Originally Posted by Black Lotus

I'm a bit confused as to why this scheme has a both a MAF sensor and a MAP sensor located in the intake.

computers like to know what the boost level is. If for nothing else, to know when overboost is happening and to take measures to save the engine from damage (and set a light)

I would expect it to be after the TB though

[Black Lotus]

Originally Posted by silver343124

But I thought that turbo engines also have temp sensor behind IC so it can measure the temperature after IC.

Your picture DOES show the mass air temp sensor after the intercooler--where it can do the most good.

[KiwiBacon]

There are two ways for your engine to know how much air is going through it.

One is to read the airflow before turbos and all that junk (MAF sensor).
The other is to know the air pressure and temperature in the intake manifold (MAP sensor) and then perform some calculations.

[silver343124]

you all aren't reading the question and telling the stupidity.
PLEASE READ THE QUESTION, SEE THE SCHEME, THEN THINK AND ANSWER!

All newer cars have a hot wire MAF sensor and it is located behind air filter, noone use a pressure-temp method to calculate the air mass flow!

But we are talking about turbocharged engine. If engine is turbo/super charged then the temperature under compression will cause detonation, so ECU has to provide more fuel (than stoichiometric is) into cylinder under full throttle to lover this temp.

And because you can't know how efficient the IC is to determine the extra fuel needed the best way is to measure the intake temp after IC.
You also need a pressure sensor to control the solenoid bypass valve on the turbo side.

[2.2 Straight six]

temperature before throttle plate. assuming you want to know the ambient air temperature.

pressure sensor in the intake manifold.

EDIT

Originally Posted by silver343124

And because you can't know how efficient the IC is to determine the extra fuel needed the best way is to measure the intake temp after IC.
You also need a pressure sensor to control the solenoid bypass valve on the turbo side.

well done. you asked a question then you answered it after complaining about everyone else in the thread. real smooth.

you don't use a bypass. you use a wastgate, with a spring set to open at a certain pressure. or you use a pop-off valve to protect the engine should the boost pressure exceed what it should be.

[UncleBob]

Originally Posted by silver343124

stupidity.....

All newer cars have a hot wire MAF sensor and it is located behind air filter, noone use a pressure-temp method to calculate the air mass flow!

wrong. Not all cars are MAF controlled. There are still plenty of cars that are speed density. Honda has almost been exclusively speed density forever. Subaru was MAF for a long time, then switched to speed density

Just two examples.

[KiwiBacon]

Originally Posted by silver343124

But we are talking about turbocharged engine. If engine is turbo/super charged then the temperature under compression will cause detonation, so ECU has to provide more fuel (than stoichiometric is) into cylinder under full throttle to lover this temp.

And because you can't know how efficient the IC is to determine the extra fuel needed the best way is to measure the intake temp after IC.
You also need a pressure sensor to control the solenoid bypass valve on the turbo side.

Since Bob has already called you on the MAF vs MAP sensors.

If the ECU knows what the airflow is, it doesn't need to know what the intake temps are. It has knock sensors to sense detonation and retard timing accordingly.

There are many reasons for fuel enrichment at full throttle, lowering exhaust temps is only one of them.

Many vehicles don't have an ECU capable of varying boost. Hence don't care what intake pressure is.