CL idle initial values, CLT/MAT

Testing and development of Megasquirt 3

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elaw
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CL idle initial values, CLT/MAT

Post by elaw »

As some folks know, there's been quite a bit of debate here about whether the CL idle initial value table should be based on CLT or MAT.

Can I toss out a different idea? My feeling is it should be based on both!

Here's my rationale:
An engine's RPM is fundamentally dependent on two things: how much power it is making, and how much is being taken from it.

The amount of power an engine makes mostly depends on the mass of fuel being burned which is tied to the mass of air it is ingesting - or more correctly the *rate* of same. The amount of power being taken from an idling engine is the sum of its internal losses and any external loads such as accessories since at idle there is no power being used to propel the vehicle.

So taking accessories etc. out of the equation, at idle, RPM = mass flow rate of air and fuel vs. internal losses.

The mass of fuel is proportional to the mass of air which is dependent on idle valve position and the temperature of said air... MAT. The internal losses depend on many factors but correlate fairly well to CLT. It's really the oil temperature that matters because colder oil is thicker and creates more drag, but CLT is the best approximation of oil temperature that the Megasquirt has available.

Based on the above, I'd argue that both CLT and MAT should be factored into the idle valve position. So how about making the idle initial value table have MAT on one axis and CLT on the other? In my opinion the target RPM doesn't need to be in that table since it's already tied to CLT.
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nathaninwa
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Re: CL idle initial values, CLT/MAT

Post by nathaninwa »

It already kinda is based on coolant when using MAT, or even CLT for that matter. The idle speed target table is based coolant and the initial value table is based on rpm, which relates to coolant temp
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muythaibxr
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Re: CL idle initial values, CLT/MAT

Post by muythaibxr »

What Nathan said is both correct and the reason why I say using CLT is useless.
Megasquirt is not for use on pollution controlled vehicles. Any advice I give is for off road use only.
VcrMiata
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Re: CL idle initial values, CLT/MAT

Post by VcrMiata »

It is true that the RPM is based on the Idle Target RPM, but this is not necessarily based on CLT.

I find that on entry to closed loop, the initial value for the expected {MAT, CLT based Target RPM} value is never used.

What I have found is that the Idle Target RPM is not static based on only the CLT, after closed loop idle activates, the Idle Target RPM shoots up to the engine RPM at that time and then ramps down to the CLT based Idle Target RPM. This means the Initial Value table will always be initially accessed at an RPM coordinate that is too high.

For example: entry into the Initial Value table for my tune is usually around 1300 RPM - no matter what the CLT is.

I don't think this was the intention.
When it's very cold and the engine is up to temperature (CLT 90C corresponds to Target RPM 850), when closed loop is entered at MAT 0C, I would expect the entry to the Initial Value table to be at {0, 850} and that PWM duty cycle value should be used. What I find is: my initial idle RPM is usually around 1300 which means a PWM duty cycle value from {0,1300} is used, which now corresponds to an engine that is not up to temp (quite cold in-fact) and reports a PWM Duty Cycle value which is much too high.

If MAT is higher, like in the summer then this all washes out because the Initial Value table tends to have less variation across the RPM range at higher MATs.
But in the winter ...

Is this expected?
If so, then the Initial Value table is not really combining MAT and CLT values.
I may as well revert to using CLT only as this will allow me to reduce winter initial closed loop idle RPMs when the engine is up to temp and the ambient temp is very low.
Note: this behaviour occurred in 1.4.1 and also exists in 1.5.

By the way - I'm luv'n 1.5. Entry into idle has been fantastically reliable.
Djovani_jr
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Re: CL idle initial values, CLT/MAT

Post by Djovani_jr »

Why the table of Closed-Loop Idle Initial Values doesn"t match the reading of the MAT?
MS3 FW 1.5.2 RC12
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CL Idle initial values.png
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pit_celica
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Re: CL idle initial values, CLT/MAT

Post by pit_celica »

Djovani_jr wrote:hy the table of Closed-Loop Idle Initial Values doesn"t match the reading of the MAT?
MS3 FW 1.5.2 RC12
Please post your tune. Do you have something other than "0" in the "MAT/CLT Correction"?

Sam
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