Pilot injection

Pilot injection

Pilot injection circulation cross section (1) Solenoid valve (3) Armature (4) Seat pin (6) Slide valve (7) Intensifier piston check ball (8) Intensifier piston (10) Plunger (15) Nozzle Spring (16) Check valve piston (19) Nozzle check valve (20) Nozzle tip (21) Oil discharge port

When the ECM sends a control current to the solenoid valve (1), pilot injection occurs. The current generates a magnetic field that lifts the armature (3) and the seat pin (4). The seat pin has a lower base and an upper base. When the armature lifts the seat pin, the upper base cuts off the drive pressure flow to the one-way valve. The lower base opens. This allows the drive oil on the top of the check valve piston (16) to flow to the drain port (21). The driving oil trapped under the spool valve (6) also flows to the drain port (21). The driving oil is discharged through the drain hole on the side of the fuel injector.

The pressure drop below the spool valve creates a hydraulic pressure differential acting on the spool valve. When hydraulic pressure acts on the top of the slide valve, the slide valve moves into the open position. The hydraulic pressure pushes the slide valve downward. When the spool valve and pin push the one-way ball (7) of the intensifier piston to the ball seat in the closed position, the spool valve stops moving downward. This prevents the drive pressure from escaping from the chamber of the intensifier piston (8). The driving pressure drop can also eliminate the downward force on the check valve piston.

At this time, the driving oil flows through the open slide valve to the top of the intensifier piston. The piston and plunger (10) move down to push the fuel in the plunger chamber to the nozzle tip (20). When the injection pressure increases to overcome the force of the nozzle spring (15) that lifts the nozzle check valve (19), the pilot injection starts.

If the following conditions exist, the pilot injection will continue:

The solenoid valve is energized.

The spool valve remains open.

There is no driving pressure on the top of the check valve piston.