© 2005-2016 Nira Control AB 35
3.15.2 Type of Injectors
NIRA i7x is designed to drive up to eight fuel injectors sequentially. Injectors
for port fuel injection are ground controlled. Connect one of the injector
terminals to +12 V (terminal 15 via Main Relay) and the other to one of the
wires marked “-Fuel Injector 1-8” in the NIRA i7x harness. In sequential
mode, on engines up to eight cylinders, keep it simple by using the wire
marked “-Fuel Injector 1” for cylinder 1, the wire marked “-Fuel Injector 2”
for cylinder 2 and so on.
If the injector coil resistance is 8,5 Ohm or less, an additional, external
resistor needs to be added to each injector. This is necessary in order to
avoid overheating the injector.
Injectors with coil resistance in the range of 2-5 Ohm work well with a 3.3
Ohm, 15 W resistor in series.
If the series resistance is too high, the injector on-time precision decreases at
low-load conditions and it may be difficult to get the injectors to turn on if
the battery voltage is low.
If you would like to calculate the series resistance yourself, use Ohm’s Law
and size the resistance such that the power across the injector is in the range
of 10-25 Watt, assuming normal battery voltage with the engine running
(approx 14 Volt.) Do not go outside this range.
P = Power [Watt], V = voltage [Volt], I = current (Ampere)
(V/sqrt(P/R_injector)) – R_injector = R_series
E.g. R_injector = 3Ω, P = 15 Watt, V = 14 Volt
-> (14/sqrt(15/3))-3 = 3.3Ω.
If you would have chosen 6.8Ω, the injector would only see 6 Watt. At
low battery voltages, such as during cranking, this would result in long,
imprecise injector on times. NIRA i7x has negligible internal resistance
on the injector output lines.
3.16 Boost Pressure Actuator
NIRA i7x is connected to a boost pressure actuator that controls the air-flow
from the inlet to the turbo’s waste gate. By controlling the air-flow,
electronically, NIRA i7x can control the boost pressure in a very accurate
manner.
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