Barometric correction - a suggestion

Testing and development of Megasquirt 3

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Barometric correction - a suggestion

Postby Marek » Tue Oct 25, 2011 12:33 am

Here's a halfway house suggestion for barometric correction without using a second sensor.

There are plenty of 12v solenoids available out there from vacuum piping used to control emissions setups on cars. Why not incorporate a switchable barometric correction, enabled by a momentary (push to enable) switch, which could divert the MAP sensor to the engine bay rather than to the inlet manifold while the button is pressed. If available to be used only at idle speed (and perhaps because MS had noticed that idle speed/settings had changed sufficiently), the engine could continue to let MS use the curent MAP setting to idle, whilst it samples a new ambient barometric pressure. Once the button is released, MS continues as per normal, sampling manifold vacuum, but has a new reference point rather than that that it has had from startup if it needs it - i.e. if barometric correction is needed , it'll implement it.

In theory, it could be implemented any time the revs/engine load are constant.

There are no hills where I live, but it was just an idea.

kind regards
Marek
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Re: Barometric correction - a suggestion

Postby jsmcortina » Tue Oct 25, 2011 3:09 am

Whilst that is innovative, it would likely be easier to just add an internal or external baro sensor.

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Re: Barometric correction - a suggestion

Postby Marek » Tue Oct 25, 2011 5:00 am

Dear James,
Agreed, but the result could also likely be backported for all MS2 users, who are very short of extra inputs. Cost wise, it is also a favourable solution by comparison to the doubling up of components.
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Re: Barometric correction - a suggestion

Postby Matt Cramer » Tue Oct 25, 2011 5:19 am

I've seen this strategy used on certain late '90s Nissans, FWIW.
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Re: Barometric correction - a suggestion

Postby jsmcortina » Tue Oct 25, 2011 5:41 am

Marek wrote:Dear James,
Agreed, but the result could also likely be backported for all MS2 users, who are very short of extra inputs. Cost wise, it is also a favourable solution by comparison to the doubling up of components.
kind regards
Marek

The point is moot though - you still require a pin (input or output) to use your feature and surely the cost of a relay and solenoid valve is similar or more than the cost of a MAP sensor ?

James
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Re: Barometric correction - a suggestion

Postby Marek » Tue Oct 25, 2011 8:54 am

On the contrary, solenoids and relays are ten a penny and sitting in spares boxes everywhere. I'd bet people don't stock map sensors. Wiring up a relay would be within everyone's capabilities, but wiring up and configuring a map sensor is definitely more work. Were the code to be there, it's a no brainer as to which is the easier and cheaper to implement.
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Re: Barometric correction - a suggestion

Postby Black99rt » Wed Nov 09, 2011 4:58 pm

You can use a digital input and keep an ADC for another function. (like an ambiant temperature sensor!)

Turbododges use this scheme.
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