3100 HEUI Diesel Truck Engine Hydraulic Electronic Unit Injector


Hydrauli c Electronic Unit Injector
(1) Poppet valve. (2) Lower seat (poppet valve). (3) Entry port (high pressure oil). (4) Solenoid return spring. (5) Solenoid. (6) Upper seat (poppet valve). (7) Plunger. (8) Intensifier piston. (9) Poppet cavity (oil). (10) Check ball (spring loaded). (11) Barrel. (12) Piston cavity (fuel). (13) Check ball (fuel inlet). (14) Reverse flow check. (15) Fill port(s) (Fuel). (16) Nozzle assembly. (17) Nozzle valve.

The injection pump, fuel lines and nozzles used in traditional Caterpillar Diesel Engines have been replaced with a hydraulic electronic unit injector for each cylinder. A solenoid (5) on each unit injector controls the amount of fuel delivered by the unit injector. An Electronic Control Module (ECM) sends a signal to each unit injector solenoid (5).

Low pressure fuel from the fuel supply manifold (through drilled passages in the cylinder head) enters the hydraulic electronic unit injector at the fill port(s) (15). Fuel can be injected at any time depending on the start of injection timing requirements programmed into the electronic control module.

A 110 volt DC electrical pulse from the fuel injection control circuits in the ECM energizes the solenoid (5) in the unit injector. The duration of this pulse determines the length of time that fuel is allowed to flow through the nozzle valve (17). The hydraulic oil pressure on the intensifier piston (8) determines injection pressure. The duration is determined from inputs to the ECM/Personality Module; rpm demand from the throttle position sensor or cruise control or PTO, power demand as determined by the electronic governor according to the load, and power/torque limitations as established by the rating limits, customer parameters, and AFRC circuits.

When the engine is in an “at rest” condition, the solenoid (5) is not energized, and the poppet valve (1) is held on its lower seat (2) by the solenoid return spring (4). In this “at rest” condition, high pressure inlet oil is blocked and the poppet cavity (9) is opened to drain. The intensifier piston (8) and the plunger (7) are at the top of their bore and the piston cavity (12) is full.

Unit injector oil flow
(2) Lower seat (poppet valve). (6) Upper seat (poppet valve).

When a pulse energizes the solenoid (5), the poppet valve (1) moves off the lower seat (2) and onto the upper seat (6). The path to the poppet cavity (9) is closed. High pressure oil enters the unit injector thru entry port (3) and acts on the top of the intensifier piston (8). Pressure builds, pushing the plunger (7) down. The downward movement of the plunger (7) pressurizes the fuel in the piston cavity (12), causing the nozzle valve (18) to open. The downward stroke of the piston during injection creates a positive pressure which moves intensifier piston (8) and plunger (7) downward, pressure increases on the fuel in the cavity of barrel (11) below plunger (7). Fuel flows past reverse flow check (14) down the fuel passage and pressurizes the nozzle. When valve opening pressure (VOP) is reached nozzle valve (17) opens and injection begins.

The intensifier piston (8) continues to move downward until the solenoid (5) is de-energized. The de-energized solenoid (5) permits the poppet valve (1), intensifier piston (8), and plunger (7) to return to its “at rest” condition. As the plunger (7) returns, it draws fuel into the piston cavity (12) through the fill port(s) (15) across a fuel inlet check ball (13). The unit injector is now ready to repeat the cycle.

The nozzle assembly (16) is of conventional design with the exception of the fuel inlet check ball (13) and reverse flow check (14). The fuel inlet check ball (13) unseats and seals during the downward stroke of the plunger (7) to allow the piston cavity (12) to refill. The reverse flow check (14) is a one way check plate which allows fuel to enter the nozzle assembly (16), but closes to prevent reverse flow at the end of injection. It traps fuel pressure in the nozzle to prevent combustion gas from entering the nozzle if there is leakage at the nozzle valve seat.

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