VE / RPM dependency

Help on hobdrive connection with vehicle, parameters configuration

VE / RPM dependency

sascha » 24 май 2012, 23:17

Hi,

you said that initially Hobdrive showed you 1.3 l/h as idle consumption - and you calibrated it with the volume efficiency down to 0.7? Dis you set it then to 54% instead of the 92 (default).
Cail, is that the right way? My lupo 1.0 has also a 1.3l/h idle consumption but somehow I accepted/ consider that as roughtly corect because I think only more modern engines with e.g. eletrical servo steering go below 1 l/h. Does a VE of 55% not decrease the consumption then by 46% at any conditions?

Regards,
Sascha
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Re: Setting and calibration on Seat Ibiza

cail » 25 май 2012, 11:02

Sascha,
On small engines VE is often quite small. Think 60-70 should be good numbers for you.
But anyway - to know the real VE, you have to calibrate based on full tank consumption. Thats the best and the fastest method to know your VE.

VE of 55% is of course will reduce your overall consumption by 46%. Thats why you should look into the full tank real consumption and calibrate based on that.

If now your tank is emptied and hobdrive shows it is empty simultaneously, then you don't have to change anything.
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Re: Setting and calibration on Seat Ibiza

sascha » 26 май 2012, 16:54

Hi Cail,

Thanks for quick response - i have tried to set VE down and of course the consumption goes down. At the moment I drive the engine as much as possible at low rpm (1200-2200) and very high loads (<90%) and there setting VE to 75% might be OK for my small (I think 2 valve) engine but with the default value of 92 percent the overall consumption (when I went on the Motorway at 120km/h what is at about 3500 rpm - thanks to a longer 5th gear) was quite accurate. But I think, to set the VE to such a low (and fixed) value is quite a rought assumption, isnt´t? Wouldn´t it be better to define VE depending on RPMs - so that for both ways of operating (high loads at low rpm for daily driving in urban traffic where VE is low AND cruising at rpm with max torque/ hence fairly high VEs) HOBDRIVE would be as accurate as possible given the constraints of the MPG method we use?
Otherwise I can not further improve my setup because it would always be a compromise between both "extremes"
For information: I am now running on a 85% ethanol 15%gasoline blend. Stoich ratio (considering the slight desity change should be 11.2 which I have set)

Regards,
Sascha
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Re: Setting and calibration on Seat Ibiza

cail » 26 май 2012, 22:55

Sascha,
VE is not RPM dependent, so that would be physically incorrect assumption (although possible). Hobdrive now uses RPM dependant curve for EngineLoad method - but thats often used on diesels.

Using Ethanol mix means engine will dynamically change lambda in quite a wide range.
Suggest you to look to your Lambda value and LTFT in both driving conditions: city and highway. They could dynamically give a big difference and this could be a reason of difference you see.

If thats true, you then may use lambda/ltft fuel corrections in hobdrive (full version only) - this'll dynamically fix your AFR.

Another question after all this is how do you estimate the 'correctness' of the economy numbers you see. Comparing with official values may not be good. The only good way is to explicitly measure full tank, spent only in city, and full tank spent only on highway..
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Re: Setting and calibration on Seat Ibiza

sascha » 27 май 2012, 00:20

VE is not RPM dependent, so that would be physically incorrect assumption (although possible).

Are you sure? I thought that would be one of the fundamental problems in designing the intakes, valves and valve timing to get good VE over a broad rpm range ... even above 100% (even witout supercharging) for a high performance engine. What is your idea behind a rather constant VE over rpm?

Using Ethanol mix means engine will dynamically change lambda in quite a wide range.
Suggest you to look to your Lambda value and LTFT in both driving conditions: city and highway. They could dynamically give a big difference and this could be a reason of difference you see.

Lambda correction I do use exactly due to the fact that you mentioned. But LTFT (yes I have the registered version ;)) I do not use because I have replaced the fuel pressur eregulator by an adjustable one to increase througflow through the injectors - so LTFT doesn´t tell me any longer something about the delta to the normal gas operation. Thats why everything depends on the Stoich Ratio AND the VE ...

Another question after all this is how do you estimate the 'correctness' of the economy numbers you see. Comparing with official values may not be good. The only good way is to explicitly measure full tank, spent only in city, and full tank spent only on highway..


After I have now finished my transition phase where I mainly refilled from time to time different amounts of E85 and E10 I can now do a real full-to-empty measurements. And will keep you up to date.
The thing is that by using ethanol the part load consumption might have significantly changed so that any experience from pure gasoline operation can be useless. Nevertheless the actual MPG is somewhere around 7 liters/100km - hence that often cited 20% more compared to pure gas. Thats why I was concerned with reducing VE from 90% down to 55% (as suggested). I think that at the moment I slighly overestimate my high load consumption and are quite accurate when cruising. Complicated but very interesting. And great that there are people like you who can give support and provide us with that great application.
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Re: Setting and calibration on Seat Ibiza

sascha » 28 май 2012, 21:07

Изображение
[taken froseminarpaper.com]

thats the only thing what I have found regarding a quantitative comparison of VE for different rpms - it seems as there is really a variation of 15-20% along the engine speed - assuming a 95% VE for high rpms near max power I would end at 75% for my rpm range between 1200-2000 rpm. As said - an VE over rpm trendcurve would be great for the next version
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Re: Setting and calibration on Seat Ibiza

cail » 29 май 2012, 11:06

VE is not RPM dependent...
Are you sure?

I've searched abit and found other opinions:
For example http://answers.yahoo.com/question/index ... 518AA3rlat

Here also a good explanation on how to calculate VE, and some charts showing that VE/RPM curve can increase and then decrease:
http://www.bonnevillepro.com/forums/vie ... =36&t=6243
Изображение
Ultimately I think you are right, and introducing a VE/rpm tranlation would be good. Will consider this.
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