TIP- 3683769 - Caterpillar

Illustration 11 g00547599
Nozzle Assembly
(1) Inlet fill check ball
(2) Case
(3) Check
(4) Tip
(5) Tip orifice holes The nozzle assembly is similar to all other unit injector's nozzle assemblies. Fuel that has been pressurized to the injection pressure flows from the plunger cavity through a passage in the nozzle to the nozzle tip (4). Fuel flow out of the tip is stopped by check (3), which covers the tip orifice holes (5) in the end of the tip. The force of a spring holds the check down in the closed position. This prevents the leakage of fuel out of the tip and this prevents the leakage of combustion gas into the unit injector when the cylinder fires.When the injection pressure increases to approximately 28 MPa (4000 psi), the hydraulic force from the fuel overcomes the spring force. When the spring force is overcome by the hydraulic force, the check moves away from the tip. When the check moves away from the tip, the check is in the open position. The amount of pressure that is required to open the check is called the Valve Opening Pressure (VOP). The fuel flows out of the tip orifice holes in the end of the tip and the fuel flows into the combustion chamber. The check remains open and fuel continues to flow out of the tip until fuel injection pressure drops below 28 MPa (4000 psi). When the pressure drops, the check closes and fuel injection is stopped. The amount of pressure that allows the check to close is called the Valve Closing Pressure (VCP).Note: VOP and VCP will vary among applications and horsepower ratings in order to meet exhaust emission standards. The above values were used as illustrations only.The inlet fill check ball (1) unseats during upward travel of the plunger in order to allow the plunger cavity to refill. The inlet fill check ball seals during the downward stroke of the plunger in order to prevent fuel injection pressure leakage into the fuel supply.Operation of the HEUI Injector
There are three stages of injection with the HEUI injector:
Pre-injection
Injection
End of injectionPre-Injection
Illustration 12 g00988773
Pre-injection cycle
(1) Drain port
(2) High pressure oil inlet port
(A) Low pressure oil
(B) Fuel supply pressure
(C) Actuation oil pressure
(D) Mechanical movement of internal components During the pre-injection cycle, all internal components have returned to the spring loaded position. The solenoid is not energized and the lower poppet seat is closed. The lower poppet seat blocks high pressure oil inlet port (2). Actuation oil pressure is blocked from entering the unit injector. The plunger and the intensifier piston are at the top of the bore and the plunger cavity is full of fuel. Fuel pressure in the plunger cavity is equal to the fuel supply pressure. The fuel supply pressure is approximately 450 kPa (65 psi).Injection
Illustration 13 g00988788
Injection cycle
(1) Drain port
(2) High pressure oil inlet port
(A) Low pressure oil
(B) Fuel supply pressure
(C) Actuation oil pressure
(D) Mechanical movement of internal components
(E) Fuel flow
(F) Injection pressure While the solenoid is energized, the poppet valve remains open. While the poppet