Celect System Operation
The ECI
(electronically controlled injection) Celect system uses an engine-driven gear pump to
pull fuel from the fuel tank. The fuel is passed through a primary filter or filter/water
separator unit, then to the ECM where the fuel is circulated through a cooling plate. The
cooling plate, mounted to the rear of-the ECM, ensures adequate cooling of the electronic
package.
The gear pump
is designed to deliver fuel to the fuel manifold at 140 psi, which supplies the
electronically controlled injectors. A spring-loaded bypass valve allows excess fuel under
pressure to return to the suction side of the pump to maintain maximum system pressure.
A rocker arm
and pushrod assembly mechanically operates the injector. The injector requires rocker arm
actuation of the plunger to create high fuel pressure for injection. To control both the
start of injection timing and the quantity of fuel metered, the ECM sends out a
pulse-width-modulated (PWM) electrical signal to each injector. The PWM signal determines
the start of injection, while the duration of this signal determines how long the injector
can effectively continue to spray fuel into the combustion chamber, as the plunger is
forced down by the rocker arm assembly. A shorter PWM signal means that the effective
stroke of the injector plunger will be decreased. A longer PWM signal means that the
effective stroke will be increased.
The start of
injection and the duration of the PWM signal is determined by the ECM, based on the
various input sensor signals and the preprogrammed PROM information within the ECM. Each
PROM is designed for a specific engine/vehicle combination, based on the desired
horsepower setting and rpm, the tire size, and gear ratios used in the vehicle.
Contained
within the injector are a timing plunger, a return spring, and an injector control valve—that
is the key to the operation. The control valve is electrically operated, receiving signals
from the ECM to energize/de-energize, which determines the start of injection. The length
of time that this solenoid is energized determines the quantity of metered fuel to be
injected into the combustion chamber. Also within the injector body is a metering spill
port which must be closed to allow injection, a metering piston, the bias spring, and the
spill-timing port. The injection sequence of events occur as follows:
- The
injector receives a signal from the ECM; the injector control valve will close and the
metering phase begins while the metering piston and timing plunger are bottomed in the
injector.
- As
the camshaft rotates, the injector pushrod cam follower will ride down the cam ramp,
thereby allowing the rocker arm and pushrod to be forced up by the energy of the timing
plunger return spring. Fuel at gear pump pressure of 140 psi can flow into the fuel supply
passage and unseat the lower check valve, allowing the metering chamber to be charged with
pressurized fuel as long as the timing plunger is being pulled upward by the force of the
large external spring. Fuel pressure, acting on the bottom of the metering piston, forces
it to maintain contact with the timing plunger within the bore of the injector body.
- Metering
ends when the ECM energizes the injector control valve, causing it to open. Pressurized
fuel can flow through the open injector control valve into the upper timing chamber, which
stops the upward travel of the metering piston. To ensure that the metering piston remains
stationary, the small bias spring in the timing chambers holds it in place, while the
timing plunger continues upward due to camshaft rotation. Fuel and spring pressure, acting
on the metering piston, will ensure fuel pressure is maintained below the piston to keep
the lower metering ball-check valve closed. This allows a precisely metered quantity of
fuel to be trapped in the metering chamber.
- As
long as the timing plunger moves upward due to the rotating camshaft lobe action and the
force of the external return spring on the ECI injector, the upper timing chamber will
continue to fill with pressurized fuel.
- When
the engine camshaft lobe starts to lift the injector cam follower roller, the pushrod
moves up and the rocker arm reverses this motion to push the timing plunger downward. On
the initial downward movement, the injector control valve remains open and fuel flows from
the timing chamber and through the control valve to the fuel supply passage. When the ECM
closes the control valve, fuel is trapped in the timing chamber; this fuel acts as a solid
hydraulic link between the timing plunger and metering piston. The downward movement of
the timing plunger causes a rapid pressure increase in the trapped fuel within the
metering chamber. At approximately 5,000 psi, the tapered needle valve in the tip of the
injector will be lifted against the force of its return spring and injection begins.
Injection
will continue until the spill passage of the downward-moving metering piston uncovers the
spill port. Fuel pressure within the chamber is lost and the needle valve reseats by
spring pressure. This terminates injection. Immediately after the metering spill port is
uncovered, the upper edge of the metering piston also passes the timing spill port to
allow fuel within the upper timing chamber to be spilled back to the fuel drain, as the
timing plunger completes its downward movement. Injection has now been completed. |
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