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Subject: Re: How to drive a solenoid fuel injector?
X-Newsreader: Microsoft Outlook Express 6.00.2800.1123
Date: Fri, 20 Dec 2002 19:43:00 GMT
NNTP-Posting-Date: Sat, 21 Dec 2002 06:43:00 EST
Organization: BigPond Internet Services (http://www.bigpond.net.au)
"Christopher R. Carlen" wrote in message
> Looks like I may have to make a driver for a fuel injector, the solenoid
> driven needle type.
> The existing system comes from Fiat, and it can only pulse the injector
> once or twice per cycle. We want to be able to pulse any number of times.
> I have not yet been informed of the numerical specs. needed. At this
> point, I am interested in some conceptual descriptions of how to drive
> solenoid actuated injectors.
> My first idea is to use a current source that is able to sink and source
> current, and swing the output voltage positive as well as negative.
> The current source can be commanded with a logic level pulse input to
> produce the desired needle lift and hold current. Since it is a current
> source, it will swing immediately (limited of course by its risetime) to
> it's maximum compliance voltage, and then the current will ramp up in
> the solenoid coil until it hits the desired level, at which the current
> source will level off it's voltage output so as to satisfy V=IR for the
> coil DC resistance.
> When the voltage input current control command switches to zero, the
> current source will swing to it's maximum negative voltage, until the
> coil current ramps down to zero.
> There doesn't seem to be anything one can do other than increase the
> coil voltage to speed up the current risetime, so I will have the
> compliance voltage of the source as the main parameter controlling
> overall lift time performance. The injector drivers that we have which
> are actual "under the hood" injector electronics packages, seem to
> charge a capacitor to a high voltage (about 50V), and connect it to the
> injector. But they can't give multiple pulses because they need too
> much time to recharge.
> Our research injector driver need not be small to fit under the hood.
> So if it has a bit of oversized hardware in order to implement a "brute
> force" current sourse, that would be Ok.
> The main desires here are relatively simple circuitry that can be tested
> and put in service quickly, as opposed to requiring lengthy theoretical
> investigations in order to understand how to even get started.
> What other approaches might I consider other than what I'm picturing? I
> am even considering making this thing linear, instead of PWM. I have
> had squirly experiences with PWM drive techniques in my limited
> experience, and so I'd like to do more labs on that for developing my
> abilities before putting PWM into something that has to be used to do
> real work. I am reasonably comfortable with making high power linear
> amplifiers though.
> The other thing I don't know at this point besides numbers, is if it is
> necessary to have the pull-in current be one level, and then if the
> injection pulse is much longer than the pull in time, should there be a
> lower holding current value, and how I might go about implementing this
> all, while presenting the user with the simplest interface possible,
> just a TTL level inject pulse. I suppose I can figure this out myself.
> I'm mainly interested in if there is a better way than a current source.
> Comments appreciated.
> Good day!
How about something like this???
The LM1949 linear integrated circuit serves as an excellent control of fuel
injector drive circuitry in modern automotive systems.
The IC is designed to control an external power NPN Darlington transistor
that drives the high current injector solenoid.
The current required to open a solenoid is several times greater than the
current necessary to merely hold it open; therefore, the LM1949, by
directly sensing the actual solenoid current, initially saturates the driver until
the "peak" injector current is four times that of the idle or "holding" current.
Greg the Grog
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