[Diy_efi] Timing Calculations

Mark Higgins nospam
Fri Jun 17 04:41:31 UTC 2005


That doesn't close or redefine anything.

Dwell is important, but dwell is only a small amount of time and wont 
overlap other ignition events.  I can sacrifice one timer for all 
ignition events and not need to worry about overlap.  Even if I plot 
'dwell on' and 'dwell off' angles, deviation will be minimal because of 
the short dwell time.

With ignition I can always use the last trigger tooth delay to calculate 
rpm, so I can calculate rpm as accurately as the last trigger before the 
ignition 'zone' for that cylinder.  An injection event can last up to a 
full engine cycle, so my rpm reading will deviate much more in that time.

As I have been saying, the angle that injection ends is the important 
part, not the starting angle.  This is why most aftermarket EFI let you 
specify end of injection angle, which is the point when injection should 
be finished.  I have more 16bit timers than usual on my uC, which is 4.  
I can't sacrifice a timer to each injector.  Even if I did, incorrectly 
guessing the start angle that will result in the proper pulse width 
before the ending angle will cause overshoots.  Then I might as well 
just go to batch injection.

Mark Higgins

Astrona wrote:

>Injection is time-based, but shooting-angle is also important.
>Ignition is angle-based, but dwell-period is also important.
>
>If you have big enough injectors to avoid 100% duty cycle in every case,
>you can just open the injector at desired angle and set the timer (no
>degrees!) to shut it.
>
>Should close the issue or redefine it.
>
>
>
>----- Original Message ----- 
>From: "Mark Higgins" <nospam at higginstribe.com>
>To: <diy_efi at diy-efi.org>
>Sent: Thursday, June 16, 2005 10:26 PM
>Subject: Re: [Diy_efi] Timing Calculations
>
>
>  
>
>>Has anyone actually made their own EFI on this list, cuz this is kinda
>>annoying.
>>
>>You are basing your idea of injector timing in sequential mode, that it
>>is a single event, when it is more accurately defined as two events.
>>One event opens the injector and one event closes the injector.  Both
>>the open and close points of the injector need to be calculated, unlike
>>in batch mode where you can just modulate the PWM and injection is not
>>an event at all,
>>
>>The ignition event is simple, since it's an instantaneous event that
>>only cares about it's own position.  The injector ON event doesn't care
>>about it's position, it only cares about trying to accurately determine
>>when to turn on so that the injector will be open for a set amount of
>>time before it reaches the injector off position.  The injector off
>>position cares about two things, it's position and whether the injector
>>has been on for the specified amount of time.
>>
>>Because of the acceleration I have to deal with the on and off event
>>coming closer together time wise, which will ultimately effect the
>>amount of fuel.  So, the acceleration/deceleration problem will
>>ultimately effect the amount of fuel , starving it on high acceleration,
>>which, yes, I'm more worried about that than 1 or 2 degrees of ignition
>>timing.  But, if I fix one, it will work towards fixing the other.  Yes,
>>I know about the importance of ignition timing, can we get over that now?
>>
>>Mark Higgins
>>
>>Adam Wade wrote:
>>
>>    
>>
>>>--- Mark Higgins <nospam at higginstribe.com> wrote:
>>>
>>>
>>>
>>>      
>>>
>>>>Of course for batch fire it doesn't mean much since
>>>>there's no individual injector timing.
>>>>
>>>>
>>>>        
>>>>
>>>That was the whole point.  Batch fire vehicles run
>>>just fine, and make excellent power; in fact, I doubt
>>>you could tell me whether a vehicle was batch or
>>>sequential fire, even looking at dyno data with
>>>four-gas analysis.
>>>
>>>Injector timing makes very little difference once you
>>>get very far above idle speed.
>>>
>>>
>>>| 82 Honda CX500 Turbo (Cassandra)  90 Kwak Zephyr 550 (Daphne) |
>>>| "It was like an emergency ward after a great catastrophe; it  |
>>>|   didn't matter what race or class the victims belonged to.   |
>>>|  They were all given the same miracle drug, which was coffee. |
>>>|   The catastrophe in this case, of course, was that the sun   |
>>>|     had come up again."                    -Kurt Vonnegut     |
>>>| M/C Fuel Inj. Hndbk. @ Amazon.com -  http://tinyurl.com/6o3ze |
>>>
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>>>
>>>
>>>
>>>
>>>      
>>>
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>>    
>>
>
>
>
>  
>




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