[Diy_efi] CIS EFI via Fuel Pump PWM

Mike erazmus at iinet.net.au
Thu Aug 8 16:40:21 GMT 2002


At 10:19 PM 7/8/2002 +0100, you wrote:
>I'm forgetting nothing, instant in this case is relative to having pump near
>rail, I just can't see the extra length doing anything.

Well if someone knows the spring constant for the pipes/hoses etc
Then I'd be interested to see the delta volume from say 30 to 60psi ?

Re: Your first comment, it *will* take time to build pressure from
idle to WOT - heaps of factors, the rotational intertia of the fuel
pump rotor is one reason and re my 1st para above - the other factor
is the delta volume of the fuel rail (in total) - a quick check in
my lab suggests this is definitely *not* instant ! And is therefore
a factor to include in any PID algorithm and an indication of
what sort of current you want to dump into a pump from a boost mode
SMPS, but of course, empirical evidence aside - I just haven't
done a delta volume calc taking into account srping constant of
steel - but I *have* done a quick test, looks like anything from
0.1 to 0.2 secs but not sure - I got other more important things
to do ;-)


rgds

mike


>    Huw
>----- Original Message -----
From: "Mike" <erazmus at iinet.net.au>
>To: <diy_efi at diy-efi.org>
>Sent: Wednesday, August 07, 2002 12:48 PM
>Subject: Re: [Diy_efi] CIS EFI via Fuel Pump PWM
>
>
>> At 11:39 PM 5/8/2002 +0100, you wrote:
>> >Erm, how will it take time to build up? Unless a "long" length of rubber
>> >hose is used, it will be instant.
>>
>> No - instant is not very likely, what does that mean micro seconds ?
>>
>> You are forgetting the rotational
>> inertia of the pump rotor... and the propensity for the fuel pressure
>> regulator to oscillate during a step change in flow/pressure, most outlets
>> of high pressure fuel pumps have a damper - mostly for the injectors
>> but also of value in reducing fuel pressure diaphragm flutter...
>>
>> rgds
>>
>> mike
>>
>>
>>
>>
>>  There might be an issue with dynamic flow,
>> >but given adequately sized solid tubing I would suggest this would be
>> >minimal.
>> >    Huw
>> >----- Original Message -----
>> >From: "Bernd Felsche" <bernie at innovative.iinet.net.au>
>> >To: <diy_efi at diy-efi.org>
>> >Sent: Monday, August 05, 2002 1:44 AM
>> >Subject: Re: [Diy_efi] CIS EFI via Fuel Pump PWM
>> >
>> >
>> >> ARKK tapped away at the keyboard with:
>> >>
>> >> > I asked this a week or two ago. I'm still hoping someone will ut in
>> >> > their two cents about the viability.
>> >>
>> >> > The idea was that CIS injectors could adequately be controlled via
>> >> > fuel pump modulation for pressure control.
>> >>
>> >> Unlikely to be successful unless the pump is quite close to the
>> >> injector. System delays will be the source of control problems;
>> >> it'll take a while for the pressure to build up over a couple of
>> >> metres of fuel line.
>> >>
>> >> What will you do to _reduce_ the pressure when load reduces?
>> >>
>> >> --
>> >> /"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
>> >> \ /  ASCII ribbon campaign | I'm a .signature virus!
>> >>  X   against HTML mail     | Copy me into your ~/.signature
>> >> / \  and postings          | to help me spread!
>> >>
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