C-9 HUEI Fuel System (1) Oil pump (9) Sensor for the Injection Actuation Pressure (IAP) (17) Fuel pressure regulator (18) Boost pressure sensor (2) Hydraulic electronic unit injectors (10) Fuel filter (19) Oil pressure sensor (3) Oil filter (4) Oil cooler (11) Primary fuel filter and water separator (20) Coolant temperature sensor (5) High pressure oil (12) Fuel tank (21) Throttle position sensor (6) Fuel (13) Camshaft gear (22) Inlet air temperature sensor (7) Connector for the Injection Act
Introduction The operation of the Hydraulic Electronic Unit Injector fuel system is completely different from any other fuel system that is actuated mechanically. The HEUI fuel system is completely free of adjustment. Adjustments to the components that are mechanical can not be made. Changes in performance are made by installing different software in the ECM.
ECM The ECM is located on the left side of the engine. The ECM is a powerful computer that provides total electronic control of engine performance. The ECM uses data from engine performance that is gathered by several sensors. The ECM uses this data in order to make adjustments to the fuel delivery, injection pressure and injection timing. The ECM contains programmed performance maps (software) in order to define horsepower, torque curves and rpm. The ECM logs faults of engine performance.
Fuel Transfer Pump (1) Unit injector hydraulic pump (2) Fuel transfer pump The fuel transfer pump is mounted on the back of the unit injector hydraulic pump. The fuel transfer pump is the only serviceable part of the unit injector hydraulic pump. The fuel transfer pump is used in order to draw fuel from the fuel tank . Also, the fuel transfer pump is used in order to pressurize the fuel to 450 kPa (65 psi). The fuel transfer pump has an internal relief valve in order to protect the system.
Injection Actuation Pressure Sensor (IAP) The IAP Sensor monitors injection actuation pressure. The IAP Sensor sends a continuous voltage signal back to the ECM . The ECM interprets the signal. The ECM is aware of the injection actuation pressure at all times. The ECM analyzes the voltage from the sensor. The ECM then adjusts the current to the solenoid.
The primary fuel filter/water separator will not trap these small contaminants. Very small abrasive particles in the fuel cause abrasive deterioration of the unit injectors. The secondary fuel filter removes particles in the size of two microns in size or particles that are greater than two microns in size. The use and regular maintenance of this two micron filter will provide a significant improvement in injector life.
Oil that is drawn from the sump is pressurized to the lubrication system oil pressure by the engine oil pump. Oil flows from the engine oil pump through the engine oil cooler, through the engine oil filter, and then to the main oil gallery. A separate circuit from the main oil gallery directs a portion of the lubrication oil in order to supply the unit injector hydraulic pump. A steel tube on the left side of the engine connects the main oil gallery with the inlet port of the unit injector hydraulic pump.
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.
• • • ECM Sensor for the Injection Actuation Pressure (IAP) Pump control valve The closed loop circuit works in the following manner: • • • The ECM determines a desired actuation pressure by gathering information from sensor inputs and software maps. The ECM monitors actual actuation pressure through a constant signal voltage from the IAP sensor. The ECM constantly changes control current to the pump control valve. This changes the pump outlet flow.
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.
HEUI Injector (Components) The HEUI injector serves four functions. The HEUI injector pressurizes supply fuel from 450 kPa (65 psi) to 175 MPa (25382 psi). The HEUI injector functions as an atomizer by pumping high pressure fuel through orifice holes in the unit injector tip. The HEUI injector delivers the correct amount of atomized fuel into the combustion chamber and the HEUI injector disperses the atomized fuel evenly throughout the combustion chamber.
The HEUI injector consists of three major parts: • • • Upper end, or actuator (A) Middle, or pumping unit (B) Lower end, or nozzle assembly (C) The upper end (A) consists of the following items: • • • • • • • Solenoid (1) Armature spring (2) Armature (3) Seated pin (4) Spool spring (5) Spool valve (6) Check ball for intensifier piston (7) The middle of the injector (B) contains the following items: • • • • Intensifier piston (8) Return spring (9) Plunger (10) Barrel (11) The lower end of the injector
Pre-Injection Cross section of pre-injection cycle (2) Armature spring (3) Armature (4) Seated pin (5) Spool spring (6) Spool valve (8) Intensifier piston (10) Plunger (16) Check piston (19) Nozzle check The injector is in the phase of preinjection when the engine is running and the injector is between firing cycles. Plunger (10) and the intensifier piston (8) are at the top of the piston bore. The cavity below the plunger is full of fuel.
Pilot Injection Cross section of pilot injection cycle (1) Solenoid (3) Armature (4) Seated pin (6) Spool valve (7) Check ball for intensifier piston (8) Intensifier piston (10) Plunger (15) Nozzle spring (16) Check piston (19) Nozzle check (20) Nozzle tip (21) Drain Pilot injection occurs when the ECM sends a control current to the solenoid (1) . The current creates a magnetic field which lifts the armature (3) and the seated pin (4) . The seated pin has a lower seat and an upper seat.
Actuation oil now flows past the open spool and to the top of the intensifier piston. The downward movement of the piston and plunger (10) pressurizes the fuel in the plunger cavity to the nozzle tip (20) . Pilot injection begins when the injection pressure increases in order to overcome the force of the nozzle spring (15) which lifts the nozzle check (19) . Pilot injection will continue if the following conditions exist: • • • The solenoid is energized. The spool remains open.
Actuation pressure increases under the spool valve (6) that creates the balance of hydraulic force on the top and bottom of the spool. The weak spool spring (5) now acts on the spool. This closes the spool very slowly. As the spool remains open, actuation pressure continues to flow past the spool to intensifier piston (8) and to plunger (10) . The injection pressure in the nozzle and in the plunger cavity increases very quickly when the nozzle check is held in the closed position.
Fill Cross section of fill cycle (1) Solenoid (2) Armature spring (3) Armature (4) Seated pin (5) Spool spring (6) Spool valve (7) Check ball for intensifier piston (8) Intensifier piston (9) Return spring (10) Plunger (16) Check piston (18) Reverse flow check valve (19) Nozzle check (22) Drain The fill cycle begins when the solenoid (1) is deenergized. The armature (3) and the seated pin (4) are forced down by the armature spring (2) .
