Product Description Multec 3.5 Fuel Injector Application Manual
3-12 Delphi Energy and Chassis Systems
Revision: 11/05-1
3.6 Injector Controls – Controller Drive Circuit
There are two principal types of injector drivers: saturated switch and
peak-and-hold. All Multec 3.5 injectors are designed to use the saturated
switch driver.
A saturated switch drive circuit is used with injectors having relatively
high resistance, generally 11 to 16 ohms.
• Multec 3.5 injector resistance is nominally 12.0 Ohms at 20
o
C (68
o
F) [Test current not to exceed 10 mA]
Maximum current is limited by the circuit resistance: I=V/R. When the
injector driver is de-energized, return spring force and fuel pressure push
the ball on its seat and shut off fuel flow. A saturated switch driver is a
low-cost driver with low injector energy dissipation rates.
3.6.1 Minimum Operating Voltage (MOV)
Injectors need to function reliably and predictably at low battery voltage
conditions. Low battery voltage conditions are caused by low
temperatures, battery/alternator malfunctions, engine cranking and high
temperature/high load conditions.
Minimum operating voltage is the lowest voltage that will provide fuel
flow (i.e., open valve).
Static minimum operating voltage (SMOV) is defined as the minimum
level of applied voltage level where actuation of the injector first occurs.
(See SAE J1832 Section 4.1.23.1.1 for SMOV measurement procedure.)
Dynamic minimum operating voltage (DMOV) is defined as the applied
voltage where the injector dynamic flow rate (at a duty cycle of 10.0 / 20.0
ms PW/RR) is 50% of the injector dynamic flow rate at normal operating
voltage. (See SAE J1832 Section 4.1.23.2.1 for DMOV measurement
procedure.)
Note
Minimum operating voltage, system pressure, and linear range are
injector performance trade-offs.
3.6.2 Driver Considerations
In high percentage alcohol fuel applications, it is necessary to completely
remove power from the injector when the vehicle is not running to avoid
potential internal corrosion. This can be accomplished by using a “high
side” drive circuit, or powering the injector from ignition rather than
battery with the normal “low side” drive circuit. (A “low side” driver
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