User Manual

The unit injector hydraulic pump is a variable delivery piston pump. The variable piston pump uses an angled
drive plate which rotates. The pistons do not rotate. The pistons move in relation to the angled drive plate. The
pistons move in the sliding sleeves.
The unit injector hydraulic pump is driven by the gear train on the front of the engine. The drive gear on the
front of the pump turns the common shaft. The angled drive plate is mounted on the common shaft. The rotation
of the angled drive plate causes the pump piston to move in and out within the sliding sleeves.
As the pistons move out of the sliding sleeves, oil is drawn into the inside of the pistons through the passage in
the drive plate. Oil is forced out of the piston when the piston is pushed back into the sliding sleeve and the
ports are exposed.
Changing the relative position of the sliding sleeve to the spill port changes the volume of oil in the piston. The
location of the sliding sleeve is continuously changing. The location of the sliding sleeve is determined by the
ECM. Changing the location of the sliding sleeves changes the flow of the pump. The result is the amount of oil
that can be pressurized.
The pressure of the injection actuation system is controlled by matching pump outlet flow and resulting pressure
to the pressure demand for the injection actuation system. The position of the sliding sleeves is changed in order
to control the pump outlet flow. Moving the sleeves to the left covers the spill port for a longer distance. This
increases effective pumping stroke and pump outlet flow. Moving the sleeves to the right covers the spill ports
for a shorter distance which reduces the effective pumping stroke. This also reduces the pump outlet flow.
The sliding sleeves are connected by an idler. One sleeve is connected to an actuator piston. Moving the
actuator piston right or left causes the idler and sleeves to move the same distance to the right or to the left.
Control pressure is determined by the amount of current from the ECM to the solenoid. A small amount of
pump outlet flow goes through a small passage in the actuator piston. This small amount goes out of an orifice
and into the control pressure cavity. The pressure in this cavity is limited by a small poppet valve. The opening
of the poppet valve allows a portion of the oil in the cavity to flow to drain. A force holds the poppet valve
closed. This force on the poppet valve is created by a magnetic field that acts on an armature. The strength of
the magnetic field determines the required pressure in order to overcome the force of the actuator spring.
An increase of current to the solenoid causes an increase to the following items:
• The strength of the magnetic field
• The force on the armature and poppet valve
• The control pressure which causes the actuator piston to move to a position that results in more flow
A reduction of current to the solenoid causes a reduction to the following items:
• The strength of the magnetic field
• The force on the armature and poppet valve
• The control pressure which causes the actuator piston to move to a position that results in less flow
The ECM monitors actuation pressure. The ECM constantly changes current to the pump control valve in order
to control actuation pressure. Three components work together in a closed loop circuit in order to control
actuation pressure: