Can someone explain how the low impedance injector controller on the S8 works?
Cheers,
Tony
Low impedance injector control
Re: Low impedance injector control
Hiya Tony,
Are you working out if you need to keep the peak&hold driver?
Are you working out if you need to keep the peak&hold driver?
96 MKIV Supra, S6GP, 591bhp & 523ft/lbs
Re: Low impedance injector control
I'm pretty sure I can get rid of it. I'm just interested in how I would set-up the software to drive the injectors correctly. 
Re: Low impedance injector control
Have you downloaded the S8 default calibration, there are lots of settings in the IO configuration for injector setup.TLicense wrote:I'm pretty sure I can get rid of it. I'm just interested in how I would set-up the software to drive the injectors correctly.
96 MKIV Supra, S6GP, 591bhp & 523ft/lbs
Re: Low impedance injector control
Yeah, that's what I'm trying to figure out how to set up. In particular the low impedance injector hold duty and low impedance injector open time.
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pat
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Re: Low impedance injector control
Tony,
The hold duty cycle is designed to try to maintain the injector current at its rated value. In other words, say your injectors have a DC resistance of 2 ohms, and they need to be driven with 4A current, this would require that there be 8V present across the injector (according to Ohm's Law). If we work off a nominal 13.8V running voltage, we would require 8/13.8 = 0.58 or 58% of the supply voltage. This is the hold duty, in theory. In practice it may need to be different because it isn't a "perfect" system, it is a REAL system and has other inherent characteristics that haven't been modeled in my simple explanation above. There will be a slew rate on the switching transistors. There is capacitance and inductance. The real value will need to be measured with a True RMS meter.
Injectors use a coil to generate a magnetic field to move a magnetic pintle to turn on the flow of fuel. Coils have inductance. Unlike resistors where if you suddenly apply 12V to a 2 ohm resistor, you could immediately expect a 6A current to flow, with an inductor the build up of the magnetic field results in a change in coil flux linkage which generates an EMF to oppose the change. This EMF is the product of the coil's inductance and the rate of change of current. That's the important bit... RATE OF CHANGE. For the current to change instantaneously, you would need to apply infinite voltage to it. But you only have 13.8V to play with, so it will take time for the current to build up. Of course we want it to build up, but only to 4A not to the full 6.9A it could; at some point it will have built up to 4A, this is what the low impedance opening time is about; how long we apply full drive to the injector before dropping back to our 58%. If we specify too little time then we won't have gotten to 4A yet, and the remaining current build up will be hampered by the reduction in drive voltage, whereas if we specify too long then the current will go beyond 4A and it will settle back down again once we move on to hold mode. Of the two, the lesser evil is too little opening time, as true injection pulse width will be unpredictable, whereas too much current will just generate a little more heat; we're not talking about continuously driving the injectors at 6.9A though, maybe for 0.1ms too long every 40ms (at 3000RPM), a 0.25% "excess", hardly worth losing sleep over.
In the real world the only way to get the figures "perfect" is to measure a real engine. A good DSO is your friend (or at least someone who has one that's willing to help, LOL).
Hope this helps / answers your question.
Cheers,
Pat.
The hold duty cycle is designed to try to maintain the injector current at its rated value. In other words, say your injectors have a DC resistance of 2 ohms, and they need to be driven with 4A current, this would require that there be 8V present across the injector (according to Ohm's Law). If we work off a nominal 13.8V running voltage, we would require 8/13.8 = 0.58 or 58% of the supply voltage. This is the hold duty, in theory. In practice it may need to be different because it isn't a "perfect" system, it is a REAL system and has other inherent characteristics that haven't been modeled in my simple explanation above. There will be a slew rate on the switching transistors. There is capacitance and inductance. The real value will need to be measured with a True RMS meter.
Injectors use a coil to generate a magnetic field to move a magnetic pintle to turn on the flow of fuel. Coils have inductance. Unlike resistors where if you suddenly apply 12V to a 2 ohm resistor, you could immediately expect a 6A current to flow, with an inductor the build up of the magnetic field results in a change in coil flux linkage which generates an EMF to oppose the change. This EMF is the product of the coil's inductance and the rate of change of current. That's the important bit... RATE OF CHANGE. For the current to change instantaneously, you would need to apply infinite voltage to it. But you only have 13.8V to play with, so it will take time for the current to build up. Of course we want it to build up, but only to 4A not to the full 6.9A it could; at some point it will have built up to 4A, this is what the low impedance opening time is about; how long we apply full drive to the injector before dropping back to our 58%. If we specify too little time then we won't have gotten to 4A yet, and the remaining current build up will be hampered by the reduction in drive voltage, whereas if we specify too long then the current will go beyond 4A and it will settle back down again once we move on to hold mode. Of the two, the lesser evil is too little opening time, as true injection pulse width will be unpredictable, whereas too much current will just generate a little more heat; we're not talking about continuously driving the injectors at 6.9A though, maybe for 0.1ms too long every 40ms (at 3000RPM), a 0.25% "excess", hardly worth losing sleep over.
In the real world the only way to get the figures "perfect" is to measure a real engine. A good DSO is your friend (or at least someone who has one that's willing to help, LOL).
Hope this helps / answers your question.
Cheers,
Pat.
Re: Low impedance injector control
Many thanks for that Pat. 
I'm sure I'll have more questions on this but that'll keep me going for a while!
I'm sure I'll have more questions on this but that'll keep me going for a while!