Injector driver board- bosch and siemens injectors

[Rich Mauruschat]

At 20:45 18/07/97 -0700, you wrote:
>Hello all-
>
>First of all, I want to thank everyone out there for my help with this 
>project ( the staged injection for a VW golf using a 68HC11F1) without 
>your help, I would never have tried.  
>
>I tested the injector driver board today. Using a National Semiconductor 
>LM 1940 voltage regulator and LM1949 injector drivers.  I set the timer 
>to 1.5 ms with a 15k resistor and a .1uf cap.  Tried 0.09, .18 and .47 ohm 
>resistors for the sensing.  I tried this with chrysler injectors- two 
>styles which are bosch and siemens.  Bosch are 280155703   12.3 ohm, like 
>the siemens/deka which  is a 4612402.  The bosch goes in an early (pre- 
>production) neon, I can't imagine they changed injectors, but who knows?  
>The siemens deka comes from a 1995 or 1996 3.3liter  grand voyager SE 
>van.  Canadian spec, I think. 
>
>With the 0.47 ohm resistor, i got the 4:1 difference in injector current 
>from peak to hold for both injectors.  I didn't with the 0.18 and 0.09 
>ohm resistance.  The .18 ohm had about a 2:1 current difference.  The 
>0.09 sense resistor wound up running the injectors saturated.  ( I think) 
>In a discussion with my electronics prof. ( he was helping me)  he seemed 
>to think that a notch in the initial voltage rise was the beginning of 
>injector motion.  By varying the pulse width to the injector, we 
>determined audibly that the injector didn't open if this point (typically 
>1.08 to 1.2ms, and about 550 ma) wasn't crossed. We figured that the 
>opening current for both the injectors was about 550 ma, the Bosch opened 
>about 0.1 ms faster.  Perhaps the pintle is smaller with less inertia?  I 
>don't know.
>
>At this point without actually observing fluid out of the injectors, we 
>canot be absolutely sure that the injectors are holding open after the 
>initial opening surge.  By dialing the duty cycle up to 96-99% the 
>injectors became quiet ( and the scope was showing some high voltages)  
>below 13% duty cycle at 100.0 Hz ( ~1.3 ms pulse) they were quiet.  I can 
>only assume that they were "holding".  
>
>My question-  does anyone have a definitive bench test for injector that 
>doesnt involve flowing fuel thru the injector?
>
>Thanks, 
>
>Seth Allen
>
>(graduating soon (again) and looking for an automotive job)
>
>
Seth,
Principally by observing the CURRENT waveform (ie connect a low value
resistor in series with the injector and monitor the voltage across this
resistor - 0R1 usually works ok), a discontinuity occurs in the current rise
slope at the point when the armature starts to move; this is caused by the
transient inductance change in the injector as the armature moves. The
discontinuity can be quite small and a decent 'scope is required to see it.
What may not be obviously clear is the point at which the armature actually
starts and stops, it depends how good a trace you can get to be able to spot
the precise start and finish of the discontinuity, although the 'hump'
itself is usually pretty obvious. This may well be the effect your prof.
refers to. 
Richard