Solenoid

TM 9-2320-312-24-2

Systems Operation Section

Solenoid

Barrel

The solenoid (1) is an electromagnet. When the

The barrel (9) is the cylinder that holds plunger (7).

solenoid is energized, the solenoid creates a very

The plunger moves inside the barrel. The plunger

strong magnetic field. This magnetic field attracts

and barrel together act as a pump. Both the

the armature (2) which is connected to the poppet

plunger and the barrel are precision components

valve (4) by an armature screw. When the armature

that have a working clearance of only 0.0025 mm

moves toward the solenoid, the armature lifts the

(.00010 inch). These tight clearances are required in

poppet valve off the poppet valve's lower seat (5).

order to produce injection pressures over 162 MPa

Energizing the solenoid and lifting the poppet valve

(23500 psi) without excessive leakage.

off the poppet valve's lower seat is the beginning of

the fuel injection process.

Note: A small amount of controlled leakage is

required in order to lubricate the plunger which

prevents wear.

Poppet Valve

The barrel (9) also contains the PRIME spill port.

The poppet valve (4) has two positions which are

opened and closed. In the closed position, the

The PRIME spill port is a small hole with a high

poppet is held on the lower poppet seat (5) by a

precision tolerance. The PRIME spill port is

spring. The closed lower poppet seat prevents high

machined through the side of barrel (9) into plunger

pressure actuation oil from entering the unit injector.

(7). This port momentarily vents fuel injection

The open upper poppet seat (3) vents oil in the

pressure during the downward stroke of the plunger.

cavity that is above the intensifier piston (6) to the

atmosphere. The oil is vented to the atmosphere

through the upper portion of the unit injector. In the

open position, the solenoid (1) is energized and the

poppet valve is lifted off the poppet valve's lower

seat. When the poppet valve is lifted off the poppet

valve's lower seat, the lower poppet seat opens

allowing high pressure actuation oil to enter the

unit injector. When the high pressure actuation oil

enters the unit injector, the high pressure actuation

oil pushes on the top of intensifier piston (6). The

upper poppet seat (3) of poppet valve (4) closes

and upper poppet seat (3) of poppet valve (4)

blocks the path to the drain. Blocking the path to

the drain prevents the leakage of high pressure

actuation oil from the unit injector.

Intensifier Piston

The surface area of intensifier piston (6) is six times

larger than the surface area of plunger (7). This

larger surface area provides a multiplication of

force. This multiplication of force allows 27.5 MPa

(4000 psi) of actuation oil to produce 162 MPa

(23500 psi) of fuel injection pressure. When poppet

valve (4) moves away from lower poppet seat (5),

high pressure actuation oil enters the unit injector.

When the high pressure actuation oil enters the unit

injector, the high pressure actuation oil pushes on

the top of intensifier piston (6). Pressure rises on

top of the intensifier piston and the pressure pushes

down on intensifier piston (6) and plunger (7). The

downward movement of the plunger pressurizes the

fuel in plunger cavity (8). The pressurized fuel in

the plunger cavity causes nozzle assembly (10) to

open. When the nozzle assembly opens, the fuel

delivery into the combustion chamber begins. A

large O-ring around the intensifier piston separates

the oil above the intensifier piston from the fuel

below the intensifier piston.