How is load actually calculated?

[Torque]

Just wondering what the ECU actually uses to calculate load?

I read that the air being sucked in (so passing the AFM) is basically 'it' to calculate load.

However if you rev the engine in neutral, load is actually not going anywhere (which make sense)
So what other parameters are there in order to calculate load

[Matt]

Have to look up the Nissan patents again for that one exactly

TP is calculated from VQ map (based on AFM input) multiplied by K constant and current values in the fuel map (yes adjusting fuel map values will affect TP) and then enrichment factors

[Torque]

My question was more a general one, since I always marvelled how the actual load is computed.
So how does the ECU know that I'm actually on the road accelerating hard and not in neutral revving the engine?

[Matt]

neutral switch input

[crans]

What is the maximum TP is it 128? or 256?
My car is reaching 5.085v on the afm but the tp is only 103

[KillerB]

Max TP is 255, standard maximum for an 8 bit number.

Basically for the ecu, Load = air flow.
Load is calculated by taking the AFM voltage, linearizing it (through the VQ map) and multiplying it by a fixed constant.

So how does the ECU know that I'm actually on the road accelerating hard and not in neutral revving the engine?

it doesnt 'know' that. It just sees the amount of air getting sucked into the engine and responds by supplying the right amount of fuel.

[Eric]

taken from Nissan patent 4,787,358:

Tp during a coming fuel injection stroke in accordance with the air flow rate Qa and the engine speed N by referring to the following equation:
where K is a preset constant.

Tp=K Qa/N

final desired fuel injection quantity Ti during a coming fuel injection stroke in accordance with the basic desired fuel injection quantity Tp and the corrective factors KMR, KAC, KTw, a, and Ts by referring to the following equation.

Ti=a Tp(1+KMR+KAC+KTw)+Ts

[Torque]

Interesting ..

But how is it explained then that that the car has (naturally) no load condition in neutral gear revving?
Is it actually down to the neutral switch?

[Croustibat]

Because the flow is not the same when revving neutral, and when revving with a gear engaged. The EGT will be lower, the boost pressure will be lower. The ECU does not "know" anything else than flow (actually it is the MASS of the flow that matters, hence "mass airflow sensor" )

Just check how boost kicks in at 3500 rpm on 1st gear and on 5th gear. While you will barely hit full boost on 1st before hitting the rev limit, if you even hit full boost, you will reach it on the 5th on a very short time/rpm increase. because the load is more important.

[Torque]

Hi there,

Thanks for your answer

I gave the whole issue another thought:

I would define load as the difference between throttle position and actual rpm.
(DELTA)
The ECU knows that under zero load a particular throttle position corresponds to an rpm number.

So if the engine follows (rpm-wise) your throttle position the load the low.

However if you are in a gear and floor the pedal, the engine will have to work harder to overcome load.
(thus not following the throttle rev-wise)

And yes, I can actually hit full boost in first gear, but things become very crazy then



P.S:
In a N/A engine load would be measured by the inlet-track vacuum)

[PL]

It really is just airflow.

I think you're maybe just underestimating how big the difference is between airflow under load and airflow when "free revving". An engine really uses very little air unloaded. It's only once it sees some load that you really see some airflow.

PL

[Torque]

Hi ...

But what is airflow? ->

Airflow is displacement times rpm/2 (this is simplified)
(I am not talking forced induction)

But maybe we have to define 'Load' first.


To me 'Load' is how hard the engine has to work against a resistance
(Probably measured by the delta between throttle position and actual engine speed)

From your answerers I gather that by 'Load' you mean how much air is sucked into the engine?

[PL]

Yes, load is how much air is sucked into the engine. I guess that's simplified somewhat cos RPM has to come into it too. But airflow is certainly the key input.

But load is not "displacement times rpm/2" because this assumes 100% cylinder filling. What determines load is how far the throttle is open - which gives you your partial cylinder filling.

Have a good read of those Nissan ECCS patent documents. They detail how TP is derived in considerable detail.

PL

[Torque]

Hi Pete,

Yes .. of course, there is no +100% filling unless you have a very good setup or forced induction (but that is another story)

I will have a read ...