Unit injector hydraulic pump -807640093

TM 9-2320-312-24-2

Systems Operation Section

Unit injector hydraulic pump (1) is a fixed

ECM (15) selects the desired actuation pressure.

displacement axial piston pump. The pump is

The desired actuation pressure is based on both the

designed in order to generate adequate flow under

sensor input and the performance maps. The ECM

the conditions that are the most demanding.

sends a control current to IAP Control Valve (10)

in order to change the actual actuation pressure.

Under most operating conditions, unit injector

The IAP Control Valve reacts to the electrical

hydraulic pump (1) is producing excess flow. This

current from the ECM in order to change the actual

excess flow must be discharged to a drain in order

actuation pressure. The actual actuation pressure

to control the system's pressure. IAP Control Valve

is changed when the IAP Control Valve discharges

(10) regulates system pressure by discharging the

pump flow to the drain. The IAP Control Valve

precise amount of oil to the drain. This discharging

acts as an electrically controlled relief valve. IAP

of oil is required in order to maintain the desired

Sensor (6) monitors the actual actuation pressure

actuation pressure.

in the high pressure oil passage. The IAP Sensor

reports the actual actuation pressure to the ECM by

There are two types of actuation pressure:

sending a signal voltage to the ECM.

Desired actuation pressure

The injection actuation pressure control system

operates in a cycle. ECM (15) selects the desired

Actual actuation pressure

actuation pressure. Then, the ECM sends an

electrical current to IAP Control Valve (10) that

should produce that pressure. The IAP Control

Desired actuation pressure is the injection actuation

Valve reacts to the electrical current from the ECM

pressure that is required by the system for optimum

by changing the pressure relief setting, which

engine performance. The desired actuation

changes the actual actuation pressure. IAP Sensor

pressure is established by the performance maps

(6) monitors the actual actuation pressure and the

in ECM (15). The ECM selects the desired actuation

IAP Sensor sends a signal voltage back to the ECM.

pressure. The ECM bases the selection on the

The ECM interprets the signal voltage from the IAP

signal inputs from many sensors. Some of the

Sensor in order to calculate the actual actuation

sensors that are supplying signal inputs to the ECM

pressure. Then, the ECM compares the actual

are accelerator pedal position sensor (18), boost

actuation pressure to the desired actuation pressure

pressure sensor (16), speed/timing sensors (14),

in order to adjust the electrical current to the IAP

and coolant temperature sensor (20). The desired

Control Valve. The IAP Control Valve responds to the

actuation pressure is constantly changing due

change in electrical current by changing the actual

to changing engine speed and due to changing

actuation pressure. This process is repeated 67

engine load. The desired actuation pressure is only

times per second. This cycle of constant repetition

constant under steady state conditions (steady

is called a closed loop control system.

engine speed and load).

Most of the high pressure oil flow from unit injector

Actual actuation pressure is the actual system

hydraulic pump (1) is used in order to power unit

pressure of the actuation oil that is powering

injectors (7). Excess flow is the amount of pump

the injectors (7). IAP Control Valve (10) is

flow that is not required in order to meet the desired

constantly changing the amount of pump flow

actuation pressure. The excess flow is returned to

that is discharged to the drain. The pump flow

the drain through IAP Control Valve (10). Excess

is discharged to the drain in order to match the

flow from the IAP Control Valve flows upward

actual actuation pressure to the desired actuation

through a U-shaped tube in the pump reservoir. The

pressure.

excess flow travels through a drilled passage to the

front of the pump. Drain oil flows out of the front of

Three components operate together in order to

the pump over the pump drive gear and flows down

control injection actuation pressure:

the engine front gear train to sump.

ECM (15)

IAP Control Valve (10)

IAP Sensor (6)