FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Back to site

resistor boxes for injectors, why ?
Goto page 1, 2  Next
 
Post new topic   Reply to topic    EFI University Forum Index -> Other
View previous topic :: View next topic  
Author Message
stevieturbo



Joined: 29 Aug 2006
Posts: 1235
Location: Norn Iron

PostPosted: Thu Oct 06, 2011 12:56 pm    Post subject: resistor boxes for injectors, why ? Reply with quote

Recently been wondering why OEM manufacturers do this ?

Honda, Toyota, Mitsubishi and others.

What is the point in having to run a resistor box for their injectors ? Surely it adds cost, wiring, more parts to fail ?

What possible benefit can there be ? They are obviously doing it for a reason though ?
_________________
got blown

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0
Back to top
View user's profile Send private message Visit poster's website
Grocerius Maximus



Joined: 02 Apr 2006
Posts: 300
Location: McKinney TX USA

PostPosted: Thu Oct 06, 2011 1:45 pm    Post subject: Reply with quote

True P&H driver circuits are much more expensive.

The answer to the question 'Why do OEM's do this?'
is always

a) Money.

b) Emissions (or other mandated regulations).
Back to top
View user's profile Send private message
Roberto Arano



Joined: 22 Nov 2005
Posts: 503
Location: colorado

PostPosted: Thu Oct 06, 2011 1:55 pm    Post subject: Reply with quote

Also they don't need to run big injectors at small pulsewidths.
Which a P&H low Z combo ,no resistor, combo is better at.

external resistors(heat outside ecu) with simple drivers is debatably more reliable
_________________
www.circuitse7en.net
http://stores.ebay.com/Circuit-Se7en

it's named efi UNIVERSITY not efi "Bragging" Smile
Back to top
View user's profile Send private message Visit poster's website
Warpspeed



Joined: 05 Jun 2006
Posts: 549
Location: Melbourne

PostPosted: Thu Oct 06, 2011 2:48 pm    Post subject: Reply with quote

As above, the way to make a really fast opening and closing injector is to use plenty of current and a low inductance injector.
The problem with that is, you need to limit the current somehow once it has built up far enough to hold the injector open.
Two ways to do that, either fit an external resistor, or use a much more complex driver system to initially pulse a high current, then hold the injector open at a much lower current.
A resistor is cheap, simple, and it works. So that is what you so often see on mass produced systems.
Back to top
View user's profile Send private message
stevieturbo



Joined: 29 Aug 2006
Posts: 1235
Location: Norn Iron

PostPosted: Thu Oct 06, 2011 3:53 pm    Post subject: Reply with quote

So using the external resistor still allows the low z injector to operate "fast" compared to a high z injector ? Even though they dont actually implement a proper P&H strategy ?
_________________
got blown

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0
Back to top
View user's profile Send private message Visit poster's website
Warpspeed



Joined: 05 Jun 2006
Posts: 549
Location: Melbourne

PostPosted: Thu Oct 06, 2011 4:09 pm    Post subject: Reply with quote

Yes, a low Z, low inductance injector will have a much faster buildup of current at turn on, and a lower inductive "kick" at turn off, and so will be faster both on and off.

The problem is, if you just switch twelve volts directly across a low impedance injector, the final steady state current would be far too great. The current needs to be limited somehow, and a resistor is the crude and simple way to do that.

The peak and hold drivers do switch the full twelve volts, but only for an instant. After that the current is held at a figure just above where the injector will release. The peak and hold drivers give the best of both worlds, very fast opening and very fast closing.

A resistor is not quite as good, but it is a solution that certainly works well enough for a mass produced production vehicle with sensibly sized injectors.
Back to top
View user's profile Send private message
stevieturbo



Joined: 29 Aug 2006
Posts: 1235
Location: Norn Iron

PostPosted: Fri Oct 07, 2011 5:18 am    Post subject: Reply with quote

I had always thought using resistors was a cheap bandaid for people stuck with low-z and no other way to control them. But did think it strange when so many OEM use that setup.

Didnt realise it still allowed the injector to perform well.
_________________
got blown

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0
Back to top
View user's profile Send private message Visit poster's website
keithmac



Joined: 14 Nov 2010
Posts: 233

PostPosted: Tue Jul 09, 2013 12:39 pm    Post subject: Reply with quote

Would a peak and hold circuit provide a big advantage at low opening times/ idle on low impedance PTE 1200cc injectors running with a resistor pack at present?.

Would it be worth the cost to upgrade the drivers, struggling with idle tune stability and lowl load afr repeatability with the big 1200s?.
Back to top
View user's profile Send private message
stevieturbo



Joined: 29 Aug 2006
Posts: 1235
Location: Norn Iron

PostPosted: Tue Jul 09, 2013 3:14 pm    Post subject: Reply with quote

Good question. I guess it should improve things, but never something Ive tried.

But then with the cost of the box and time spent wiring it in....you might be able to buy some of the modern high impedance ID or Bosch injectors, which even in 2000cc form, really do perform well at the low end.
That way no boxes required.

I assume you are fully sequential and have tinkered with injector timing too to try and get it to run better ?

Also, what fuel pressure ?
_________________
got blown

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0
Back to top
View user's profile Send private message Visit poster's website
Warpspeed



Joined: 05 Jun 2006
Posts: 549
Location: Melbourne

PostPosted: Tue Jul 09, 2013 3:55 pm    Post subject: Reply with quote

You don't see many peak and hold drivers around these days, they were the best engineering solution available at one time.

Even top end aftermarket engine management systems don't use peak and hold anymore.
The trend now is to better performing high impedance injectors, along with software corrections for opening and closing delays corrected for battery voltage.

If you think about it, if you know exactly what the opening and closing delays of the particular injector are, then you can arrange for the software to switch slightly ahead of the required event without very much difficulty.

The trick is to know the injector characteristics and how that changes with applied voltage. The manufacturers of the engine management unit often provide extensive libraries of all known injector characteristics and all you need to do is enter the injector part number when initially programming the system to suit your engine.

This dynamic time correction is probably the biggest single reason why top end management systems can provide a much more consistent idle quality, especially with huge injectors.
Back to top
View user's profile Send private message
joe90



Joined: 19 Mar 2013
Posts: 382
Location: under the car

PostPosted: Tue Jul 09, 2013 8:07 pm    Post subject: Reply with quote

You can't use software to correct deficiencies in hardware.
There's always going to be some minimum IDC,based on the injectors deadtimes, below that, you're out of control.

Maybe your fuel pressure is too high at idle?
Top end systems now use ECU control of fuel pressure.

GDI use peak and hold, 48 volt or something like that?

Ballast resistors on low impedence injectors give better control than a high impedence injector with a saturated driver (quicker to open)
but maybe not quite as good as a peak and hold driver with the low impedence injector.
Back to top
View user's profile Send private message
Warpspeed



Joined: 05 Jun 2006
Posts: 549
Location: Melbourne

PostPosted: Tue Jul 09, 2013 8:42 pm    Post subject: Reply with quote

Have to disagree with you Joe.

Delays in hardware certainly can be corrected by software, but only if you know what those delays are, and if they are constant.

It works exactly like ignition advance in your engine.
Fire the ignition some known time before you want max peak combustion pressure.
Apply the voltage to the injector some time before you need it to open.
Switch off the injector current some time before you want it to close.

Now the electrical part of injector operation involves the rise and fall of magnetic flux in an inductor.
We will ignore fuel pressure, spring pressure and inertia within the injector.

Flux buildup is entirely dependent on inductance and the net applied voltage after any resistance is taken into account.
Flux rundown is entirely dependent on inductance and how high the back EMF across the inductor is allowed to rise.

Flux buildup will always be limited by the available battery voltage, but flux rundown can be made many times faster than buildup by allowing the back EMF to rise to a much higher voltage.

Its only limited by the safe maximum voltage of the electronics switching the current to the injector.
Back to top
View user's profile Send private message
joe90



Joined: 19 Mar 2013
Posts: 382
Location: under the car

PostPosted: Tue Jul 09, 2013 9:31 pm    Post subject: Reply with quote

OK so suppose you've got an injector with an opening time of say 1msec at 12V and a closing time of 0.5 msec

Then.....if you're firing 0.9 msec pulses into it, it won't ever open.
If you then use software to make the pulses longer, say 1.1 msec, it'll open and stay open for ...how long? Probably giving too much fuel for proper idle.

How can you correct that and make it fully controllable with nothing other than software?
Most modified cars with huge injectors have terrible idle quality.



BTW a simple peak and hold driver is nothing more than an added capacitor, done correctly. It's like an LC filter circuit. A ballast resistor on an injector behaves like an RL filter circuit.
The downside to an LC filter circuit (peak/hold) is that it's more affected by frequency(RPMs) than a RL filter (ballast)


It's not a lot different from top end ECUs that have the ability to trim the AFR of individual cylinders.
If your intake manifold/ exhaust is so badly designed that you don't get the same airflow into each cylinder, you'll need it, but redesigning the hardware can be a better option in the long term, then you won't need it. Not if done right, then each cylinder should make the same power.
Software is often just a bandaid for bad hardware.
Back to top
View user's profile Send private message
Warpspeed



Joined: 05 Jun 2006
Posts: 549
Location: Melbourne

PostPosted: Tue Jul 09, 2013 9:56 pm    Post subject: Reply with quote

joe90 wrote:
OK so suppose you've got an injector with an opening time of say 1msec at 12V and a closing time of 0.5 msec

Then.....if you're firing 0.9 msec pulses into it, it won't ever open.

Yes you are right, 0.9mS would never open the injector...

But it will open with 1.4mS wide pulses giving an open time of 0.9 mS which I am assuming is what you want.

Apply 12v power at zero time.
Injector opens zero time + 1mS later
Remove power at zero time + 1.4mS
Injector closes 0.5mS after that, or at zero time + 1.9mS.

Total injector open time 0.9mS.
If the fuel map asks for 0.9mS, its pretty easy for software to number crunch that into a 1.4mS actual output pulse.

Lazy opening is not really a problem, provided you know exactly how much earlier to hit the power.
As opening delay varies with the available battery voltage, that too is taken into account during number crunching.
Minimum injector time is essentially set by the closing delay, which fortunately can be made much shorter than the opening delay by using a high voltage switching semiconductor.
Back to top
View user's profile Send private message
keithmac



Joined: 14 Nov 2010
Posts: 233

PostPosted: Wed Jul 10, 2013 12:08 am    Post subject: Reply with quote

Would best bet be to go with smaller primary injectors for low load idle and bigger secondaries to cover high load demand (all for best drivability?).

Would be a bit gutted to upgrade to peak and hold with little gain at the end..

Notice a fair few bikes now come from the factory with primary and secondary injectors..
Back to top
View user's profile Send private message
stevieturbo



Joined: 29 Aug 2006
Posts: 1235
Location: Norn Iron

PostPosted: Wed Jul 10, 2013 12:54 am    Post subject: Reply with quote

joe90 wrote:
You can't use software to correct deficiencies in hardware.
There's always going to be some minimum IDC,based on the injectors deadtimes, below that, you're out of control.

Maybe your fuel pressure is too high at idle?
Top end systems now use ECU control of fuel pressure.


Maybe his fuel pressure is too low ?

How many systems routinely use ecu to control fuel pressure ? It can be done, but it still isnt the done thing

joe90 wrote:

GDI use peak and hold, 48 volt or something like that?

Ballast resistors on low impedance injectors give better control than a high impedance injector with a saturated driver (quicker to open)
but maybe not quite as good as a peak and hold driver with the low impedance injector.


Modern high impedance injectors perform better than their ancient low impedance counterparts. That's why we can easily have 2000cc injectors running on normal petrol idle perfectly well.

joe90 wrote:

Most modified cars with huge injectors have terrible idle quality.



A very sweeping and wrong statement these days.


@ Keith, if you have the ability to run 2 inj per cylinder then yes it is the best of both worlds. Obviously it is a fair amount of work and cost if your intake doesnt already support it though. And does whatever ecu you are using support it ?
_________________
got blown

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0
Back to top
View user's profile Send private message Visit poster's website
keithmac



Joined: 14 Nov 2010
Posts: 233

PostPosted: Wed Jul 10, 2013 5:20 am    Post subject: Reply with quote

Sorry, I'm running 43psi base fuel pressure with manifold reference line.

Both setups will come out at similar money so if twin injectors is the better option I will go for that option!.

I can run 6 extra injectors with some wiring mods so not too difficult.

Got some 550 lucas injectors in now, will see how engine behaves then go for a second set for high load if alls well.

Cheers for all the advice!.
Back to top
View user's profile Send private message
Pantera EFI



Joined: 12 Feb 2005
Posts: 1718
Location: So. California

PostPosted: Wed Jul 10, 2013 9:01 am    Post subject: Fuel Injector Speed/Fuel Pressure Reply with quote

The concept of "low fuel pressure to help Idle Quality" is not always correct as are many of Joe's remarks.

Steve stated "raise fuel pressure" which in MOST cases will help the operational speed of a fuel injector.
Then the IDLE PW can be reduced with result in LOWER idle fuel flow.

Again, Steve's remark, overlooked it seems, is MOST valid. (MODERN fuel injectors).

Your choice of Lucas "old school" fuel injectors will lead you astray.

We sell the modern Delphi, Denso, Siemens fuel injectors most at 14 Ohms.
We have taken part of the design of the magnetic circuit of Deka fuel injectors.
These other manufactures also use similar art internally to create high speed fuel injectors with SMALL fuel droplet size.
The requirement of HIGH CURRENT for a modern fuel injector is obsolete.
Thus the choice of the "doner" fuel injector body for increased flow modification could be should be observed.

Now another well stated item for Idle Quality is WHEN the Injection Instant takes place.
There are some "high end" EMS the get this wrong for best Idle Quality.

We inject fuel into the port when the valve is FULL OPEN, at low engine speed.

Lance
Back to top
View user's profile Send private message Send e-mail Visit poster's website
rvengineering



Joined: 28 Feb 2010
Posts: 129
Location: Holland

PostPosted: Wed Jul 10, 2013 10:06 am    Post subject: Reply with quote

Well about peak and hold an correcting for dead time.

Most modern OEM ECU have a shunt resistor on the injector outputs and that not only used for fault indication or short circuit protection. The ECU can monitor current build-up over time per injector this way and it?s able to correct for dead time while the injector coil resistance changes while getting hot or colder for example.

Now for peak and hold even on hi impedance injectors running very short duration and hi RPM. Well we all know if you charge a battery we can use the battery to power for other things later on, well it the same with an injector coil. We need some power (voltage and amps) to charge the injector coil to open the injector valve and in order to close the valve fast we have to get almost the same amount of power/energy out of the injector coil so some circuit in the ECU is working overtime to do this on Hi RPM and some aftermarket ECU will fail even to do so getting the AFR all over the place with a constant fuelmap.
Well what if you are able to open the injector with some current and than step the current down limiting power and heat build up in the injector coil. You will get a more consistent open and closing time from the injector and are able to step up injector duration and RPM a lot more if wanted or needed.

As for most top end aftermarket ECU not having peak and hold. Well I think it not there as there is no marked demand for it but I assume all top en ECU monitor for current build-up on the injector outputs so peak and hold should be a small step to implement then.
All the ECU we sell (port injection or direct injection) have peak and hold and this only makes it easier to install and get better results as well as the type of injector used is not so critical any more and it also limits heat build up from both ECU and injectors.
Also the part used for the injector driver (FET and diodes) make a big difference on heat build up and accuracy.

Point taken on new type of fuel injectors.
_________________
RV Engineering.
Doktervermetstraat 14
4681 CD Nieuw-Vossemeer.
TEL: +31(0)6 13 90 61 94
E-mail adaptronic@gmail.com
www.adaptronic.nl
www.facebook.com/ruudvisserengineering
www.facebook.com/DieselEngineTestSystems
Back to top
View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
FPSeth



Joined: 03 May 2010
Posts: 52
Location: Right next to YUL

PostPosted: Tue Aug 13, 2013 9:47 pm    Post subject: Re: Fuel Injector Speed/Fuel Pressure Reply with quote

Pantera EFI wrote:

Now another well stated item for Idle Quality is WHEN the Injection Instant takes place.
There are some "high end" EMS the get this wrong for best Idle Quality.

We inject fuel into the port when the valve is FULL OPEN, at low engine speed.

Lance


Can you give us a quick run down on your theory of this? I am assuming something like spraying into maximum air velocity therefore better turbulence and therefore better wet flow through the head and better atomization in the chamber?
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    EFI University Forum Index -> Other All times are GMT - 7 Hours
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group

©2007 EFI University
Website designed and maintained by 3LizardsMedia.com