User Manual

In order to start the engine quickly, the injection actuation pressure must rise quickly. Because the unit injector
hydraulic pump is being turned at engine cranking speed, pump flow is very low. The ECM sends a strong
current to the control valve solenoid in order to keep the poppet valve closed. With the poppet valve in the
closed position, all of the flow to the drain is blocked. The hydraulic forces that act on each side of the actuator
piston are equal. The actuator spring holds the actuator to the left. The pump produces maximum flow until the
6 MPa (870 psi) desired pressure is reached. Now, the ECM reduces the current to the pressure regulator
solenoid in order to reduce control pressure. The reduced control pressure allows the actuator piston to move to
the right. This reduces pump outlet flow in order to maintain the 6 MPa (870 psi) desired pressure.
Note: If the engine is already warm, the pressure that is required to start the engine may be higher than 6 MPa
(870 psi). The values for the desired actuation pressures are stored in the performance maps of the ECM. The
values for desired actuation pressures vary with engine temperature.
Once the unit injectors begin to operate, the ECM controls the current to the control valve. The ECM and the
control valve solenoid will maintain the actuation pressure at 6 MPa (870 psi) until the engine starts. The ECM
monitors the actual actuation pressure through the IAP Sensor that is located in the high pressure oil manifold.
The ECM establishes desired actuation pressure by monitoring several electrical input signals and the ECM
sends a predetermined current to the control valve solenoid. The ECM also compares the desired actuation
pressure to the actual actuation pressure in the high pressure oil passage. The ECM adjusts the current levels to
the control valve solenoid in order to make the actual actuation pressure equal to the desired actuation pressure.
Valve Operation (RUNNING ENGINE)
Once the engine starts, the ECM controls the current to the pump control valve in order to maintain the desired
actuation pressure. The IAP Sensor monitors the actual actuation pressure in the high pressure oil passage in the
cylinder head. The ECM compares the actual actuation pressure to the desired actuation pressure 67 times per
second. The ECM adjusts the current levels to the pump control valve when the actual actuation pressure and
the desired actuation pressure do not match. These adjustments make the actual injection actuation pressure
equal to the desired injection actuation pressure.
Oil Flow (ENGINE RUNNING)
A small amount of pump outlet flow flows through the actuator piston and into the control pressure cavity.
Control pressure increases and the increased pressure unseats the poppet valve. The open poppet valve allows
flow to the drain. The ECM changes control pressure by increasing or reducing the current to the control valve
solenoid and resultant force on the poppet.
The following items create a closed loop system:
• ECM
• IAP
• Pressure Regulator
This closed loop system provides infinitely variable control of pump outlet pressure. This pump outlet pressure
has a range from 6 MPa (870 psi) to 28 MPa (4061 psi).