Components of the HEUI Injector

TM 9-2320-312-24-2

Systems Operation Section

Components of the HEUI Injector

The combined force of the mechanical spring and

reduced pressure oil in the spool spring chamber

try to move the spool to the left in order to block the

The HEUI injector serves four functions. The HEUI

drain port (3). When the drain port is blocked, pump

injector pressurizes supply fuel from 450 kPa

outlet pressure (1) rises and the increased pump

(65 psi) to 162 MPa (23500 psi). The HEUI injector

outlet pressure moves the spool to the right (open).

functions as an atomizer by pumping high pressure

fuel through orifice holes in the unit injector tip.

Because the mechanical spring has a fixed spring

The HEUI injector delivers the correct amount of

rate, the reduced pressure oil (5) in the spool must

atomized fuel into the combustion chamber and the

be adjusted in order to control pump outlet pressure

HEUI injector disperses the atomized fuel evenly

(1). The reduced pressure oil (5) in the spool can

throughout the combustion chamber.

be raised in order to control pump outlet pressure

(1) or the reduced pressure oil (5) in the spool can

be lowered in order to control pump outlet pressure

(1). The reduced pressure oil (5) is controlled by

the amount of electrical current from the ECM (2).

Most of the time, the poppet and the spool operate

in a partially open position. The poppet and the

spool are completely open or completely closed

only during the following conditions:

Acceleration

Deceleration

Rapidly changing engine loads

Oil Flow for RUNNING ENGINE

When pump outlet pressure (1) enters the end of

the valve body, a small amount of oil flows into the

spool spring chamber through the control orifice

in the spool. The pressure in the spool spring

chamber is controlled by adjusting the force on

the poppet (4). Adjusting the force on the poppet

(4) allows the poppet to drain off some of the oil in

the spool spring chamber. The force on the poppet

is controlled by the strength of the magnetic field

that is produced from the electrical current from the

ECM (2). The spool responds to pressure changes

in the spool spring chamber. The spool changes

positions in order to balance the force on the spool.

The spool tries to make the force on the right side

of the spool equal to the force on the left side of the

spool. The spool position dictates the amount of the

surface area of the drain ports (3) that is open.

The open area of the drain port controls the amount

of oil that is drained off from the pump outlet. The

oil is drained off from the pump outlet in order

to maintain the desired actuation pressure. The

process of responding to pressure changes on

either side of the spool occurs so rapidly that the

spool is held in a partially open position and pump

outlet pressure (1) is closely controlled. The IAP

Control Valve allows infinitely variable control of

pump outlet pressure (1) between 6 MPa (870 psi)

and 27.5 MPa (4000 psi).