Prev: Diode Array - anyone make them.....cheap?
Next: Which multi-PIC mid-range comms protocol?
From: Michael on 10 Aug 2010 19:16
Nowadays even economy cars (e.g.: 2010 Sentra) measure gas flow and
whatever may be derived from it (mpg, average mpg, "distance to empty"
etc). How do they do it? My (uneducated)guess is either of the
following :
1. accurate level meter in the gas tank (accuracy may be affected by
temperature and pressure - the tank is not stiff)
2. flow meter (how accurate are those things??)
3. count number of fuel injectors squirts (how accurate/repeatable is
the squirt size?)
Any comments/ideas/suggestions/referrals to articles will be
appreciated
P.S.: I understand that this is not automotive group, but it's the one
I regularly visit. Engineers are engineers after all.
From: Tim Wescott on 10 Aug 2010 19:25
On 08/10/2010 04:16 PM, Michael wrote:
> Nowadays even economy cars (e.g.: 2010 Sentra) measure gas flow and
> whatever may be derived from it (mpg, average mpg, "distance to empty"
> etc). How do they do it? My (uneducated)guess is either of the
> following :
> 1. accurate level meter in the gas tank (accuracy may be affected by
> temperature and pressure - the tank is not stiff)
> 2. flow meter (how accurate are those things??)
> 3. count number of fuel injectors squirts (how accurate/repeatable is
> the squirt size?)
> Any comments/ideas/suggestions/referrals to articles will be
> appreciated
> P.S.: I understand that this is not automotive group, but it's the one
> I regularly visit. Engineers are engineers after all.

I would guess 3, because for the EFI to work correctly the squirt size
_must_ be highly repeatable (and easily controllable), and is probably
at least fairly accurate. So the only thing that stands between you and
a fuel consumption estimate is software.

"Distance to empty" would require an accurate fuel sensor, but the other
two could just come from the odometer and the fuel flow.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: Joel Koltner on 10 Aug 2010 19:59
"Michael" <mk5778(a)yahoo.com> wrote in message
news:a50f0b14-de6b-4b3b-a919-0024e2501c53(a)h32g2000yqm.googlegroups.com...
> 1. accurate level meter in the gas tank (accuracy may be affected by
> temperature and pressure - the tank is not stiff)

I'd be surprised if the accuracy between "height of a float gauge" and
"gallons of fuel remaining" were worse than, e.g., 10% accuracy over
temperature and pressure. ...although since the software already corrects for
the arbitrary shape of the tank, correcting for temperature as well would be
straightforwrad anyway.

I also figure that their idea of "empty" is just like the idiot light's: You
still have perhaps a gallon or so left, it isn't the very last drop of
gasoline going into the engine right as the "distance 'til empty" gauge hits
0. :-)

From: Spehro Pefhany on 10 Aug 2010 19:59
On Tue, 10 Aug 2010 16:25:35 -0700, the renowned Tim Wescott
<tim(a)seemywebsite.com> wrote:

>On 08/10/2010 04:16 PM, Michael wrote:
>> Nowadays even economy cars (e.g.: 2010 Sentra) measure gas flow and
>> whatever may be derived from it (mpg, average mpg, "distance to empty"
>> etc). How do they do it? My (uneducated)guess is either of the
>> following :
>> 1. accurate level meter in the gas tank (accuracy may be affected by
>> temperature and pressure - the tank is not stiff)
>> 2. flow meter (how accurate are those things??)
>> 3. count number of fuel injectors squirts (how accurate/repeatable is
>> the squirt size?)
>> Any comments/ideas/suggestions/referrals to articles will be
>> appreciated
>> P.S.: I understand that this is not automotive group, but it's the one
>> I regularly visit. Engineers are engineers after all.
>
>I would guess 3, because for the EFI to work correctly the squirt size
>_must_ be highly repeatable (and easily controllable), and is probably
>at least fairly accurate. So the only thing that stands between you and
>a fuel consumption estimate is software.
>
>"Distance to empty" would require an accurate fuel sensor, but the other
>two could just come from the odometer and the fuel flow.

Distance to empty could be a sensor fusion problem-- use the level
sensor to detect the fuel remaining (it only needs to be accurate, and
a bit conservative, near the bottom) and use the fuel injectors and
speed reasdings to estimate average consumption.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff(a)interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Spehro Pefhany on 10 Aug 2010 20:02
On Tue, 10 Aug 2010 16:59:05 -0700, the renowned "Joel Koltner"
<zapwireDASHgroups(a)yahoo.com> wrote:

>"Michael" <mk5778(a)yahoo.com> wrote in message
>news:a50f0b14-de6b-4b3b-a919-0024e2501c53(a)h32g2000yqm.googlegroups.com...
>> 1. accurate level meter in the gas tank (accuracy may be affected by
>> temperature and pressure - the tank is not stiff)
>
>I'd be surprised if the accuracy between "height of a float gauge" and
>"gallons of fuel remaining" were worse than, e.g., 10% accuracy over
>temperature and pressure. ...although since the software already corrects for
>the arbitrary shape of the tank, correcting for temperature as well would be
>straightforwrad anyway.
>
>I also figure that their idea of "empty" is just like the idiot light's: You
>still have perhaps a gallon or so left, it isn't the very last drop of
>gasoline going into the engine right as the "distance 'til empty" gauge hits
>0. :-)

Well, the "distance to empty" gauge on a Nissan I'm familiar with cuts
out when the distance drops below 60km = 38 miles. Too close to call,
or whatever.



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff(a)interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 |  Next  |  Last
Pages: 1 2 3 4 5 6 7
Prev: Diode Array - anyone make them.....cheap?
Next: Which multi-PIC mid-range comms protocol?