Oil Flow for ENGINE CRANKING

TM 9-2320-312-24-2

Systems Operation Section

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 IAP Control Valve.

The ECM and the IAP Control Valve maintain the

actual 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 IAP

Control Valve. 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 IAP Control Valve in order

to make the actual actuation pressure equal to the

desired actuation pressure.

Oil Flow for ENGINE CRANKING

Pump outlet pressure (1) enters the end of the

valve body and pump outlet pressure acts against

the valve spool. The pump outlet pressure tries to

push the valve spool to the right (open). A small

amount of oil also flows through the center of the

spool, through the spool control orifice and into the

spool spring chamber. The current from the ECM (2)

causes the solenoid to generate a magnetic field

which pushes the armature to the left. The armature

exerts a force on the push pin and the poppet

which holds the poppet closed. The poppet is the

only path to the drain for the oil in the spool spring

chamber. Pump outlet pressure (1) flows through

the spool control orifice and into the spool spring

chamber. This flow of pump outlet pressure allows

spring chamber pressure to build up. Because the

spring chamber path to the drain is blocked by the

poppet, the pressure in the spring chamber is equal

to pump outlet pressure (1).

The combination of spool spring force and spring

chamber pressure hold the spool to the left. When

the spool is held to the left, the drain ports are

closed. All pump flow is directed to the high

pressure oil manifold until an actual actuation

pressure of 6 MPa (870 psi) is reached.