Unit Injector C11 and C13 - Caterpillar Electronic Engine
Unit Injector
(31) Solenoid
(32) Tappet
(33) Plunger
(34) Barrel
(35) Nozzle assembly
Operation of the Electronic Unit Injector
The operation of the Electronic Control Unit (EUI) consists of the following four stages: Pre-injection, Injection, End of injection and Fill. Unit injectors use a plunger and barrel to pump high pressure fuel into the combustion chamber. Components of the injector include the tappet, the plunger, the barrel and nozzle assembly. Components of the nozzle assembly include the spring, the nozzle check, and a nozzle tip. The cartridge valve is made up of the following components: solenoid, armature, poppet valve and poppet spring.
The injector is mounted in an injector bore in the cylinder head which has an integral fuel supply passage. The injector sleeve separates the injector from the engine coolant in the water jacket. Some engines use a stainless steel sleeve. The stainless steel sleeve fits into the cylinder head with a light press fit.
Pre-Injection
(A) Fuel supply pressure
(B) Injection pressure
(C) Moving parts
(D) Mechanical movement
(E) Fuel movement.
Pre-Injection metering starts with the injector plunger and the injector tappet at the top of the fuel injection stroke. When the plunger cavity is full of fuel, the poppet valve is in the open position and the nozzle check is in the open position. Fuel leaves the plunger cavity when the rocker arm pushes down on the tappet an the plunger. Fuel flow that is blocked by the closed nozzle check valve flows past the open poppet valve to the fuel supply passage in the cylinder head. If the solenoid is energized, the poppet valve remains open and the fuel from the plunger cavity continues flowing into the fuel supply passage.
Injection
(A) Fuel supply pressure.
(B) Injection pressure
(C) Moving parts
(D) Mechanical movement
(E) Fuel movement.
To start injection, the ECM sends a current to the solenoid on the cartridge valve. The solenoid creates a magnetic field which attracts the armature. When the solenoid is energized, the armature assembly will lift the poppet valve so the poppet valve contacts the poppet seat. This is the closed position. Once the poppet valve closes, the flow path for the fuel that is leaving the plunger cavity is blocked. The plunger continues to push fuel from the plunger cavity and the fuel pressure builds up. When the fuel pressure reaches approximately 34500 kPa (5000 psi), the force of the high pressure fuel overcomes the spring force. This holds the nozzle check in the closed position. The nozzle check moves off the nozzle seat and the fuel flows out of the injector tip. This is the start of injection.
End of injection
(A) Fuel supply pressure
(C) Moving parts
Injection is continuous while the injector plunger moves in a downward motion and the energized solenoid holds the poppet valve closed. When injection pressure is no longer required, the ECM stops current flow to the solenoid. When the current flow to the solenoid stops, the poppet valve opens. The poppet valve is opened by the fuel injector spring and the fuel pressure. High pressure fuel can now flow around the open poppet valve and into the fuel supply passage. This results in a rapid drop in injection pressure. When the injection pressure drops to approximately 24000 kPa (3500 psi), the nozzle check closes and injection stops. This is the end of injection.
Fill
(A) Moving parts
(B) Mechanical movement
(C) Fuel movement.
When the plunger reaches the bottom of the barrel, fuel is no longer forced from the plunger cavity. The plunger is pulled up by the tappet and the tappet spring. The upward movement of the plunger causes the pressure in the plunger cavity to drop below fuel supply pressure. Fuel flows from the fuel supply passage around the open poppet and into the plunger cavity as the plunger travels upward. When the plunger reaches the top of the stroke, the plunger cavity is full of fuel and fuel flow into the plunger cavity stops. This is the beginning of pre-injection.
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(31) Solenoid
(32) Tappet
(33) Plunger
(34) Barrel
(35) Nozzle assembly
Operation of the Electronic Unit Injector
The operation of the Electronic Control Unit (EUI) consists of the following four stages: Pre-injection, Injection, End of injection and Fill. Unit injectors use a plunger and barrel to pump high pressure fuel into the combustion chamber. Components of the injector include the tappet, the plunger, the barrel and nozzle assembly. Components of the nozzle assembly include the spring, the nozzle check, and a nozzle tip. The cartridge valve is made up of the following components: solenoid, armature, poppet valve and poppet spring.
The injector is mounted in an injector bore in the cylinder head which has an integral fuel supply passage. The injector sleeve separates the injector from the engine coolant in the water jacket. Some engines use a stainless steel sleeve. The stainless steel sleeve fits into the cylinder head with a light press fit.
Pre-Injection
(A) Fuel supply pressure
(B) Injection pressure
(C) Moving parts
(D) Mechanical movement
(E) Fuel movement.
Pre-Injection metering starts with the injector plunger and the injector tappet at the top of the fuel injection stroke. When the plunger cavity is full of fuel, the poppet valve is in the open position and the nozzle check is in the open position. Fuel leaves the plunger cavity when the rocker arm pushes down on the tappet an the plunger. Fuel flow that is blocked by the closed nozzle check valve flows past the open poppet valve to the fuel supply passage in the cylinder head. If the solenoid is energized, the poppet valve remains open and the fuel from the plunger cavity continues flowing into the fuel supply passage.
Injection
(A) Fuel supply pressure.
(B) Injection pressure
(C) Moving parts
(D) Mechanical movement
(E) Fuel movement.
To start injection, the ECM sends a current to the solenoid on the cartridge valve. The solenoid creates a magnetic field which attracts the armature. When the solenoid is energized, the armature assembly will lift the poppet valve so the poppet valve contacts the poppet seat. This is the closed position. Once the poppet valve closes, the flow path for the fuel that is leaving the plunger cavity is blocked. The plunger continues to push fuel from the plunger cavity and the fuel pressure builds up. When the fuel pressure reaches approximately 34500 kPa (5000 psi), the force of the high pressure fuel overcomes the spring force. This holds the nozzle check in the closed position. The nozzle check moves off the nozzle seat and the fuel flows out of the injector tip. This is the start of injection.
End of injection
(A) Fuel supply pressure
(C) Moving parts
Injection is continuous while the injector plunger moves in a downward motion and the energized solenoid holds the poppet valve closed. When injection pressure is no longer required, the ECM stops current flow to the solenoid. When the current flow to the solenoid stops, the poppet valve opens. The poppet valve is opened by the fuel injector spring and the fuel pressure. High pressure fuel can now flow around the open poppet valve and into the fuel supply passage. This results in a rapid drop in injection pressure. When the injection pressure drops to approximately 24000 kPa (3500 psi), the nozzle check closes and injection stops. This is the end of injection.
Fill
(A) Moving parts
(B) Mechanical movement
(C) Fuel movement.
When the plunger reaches the bottom of the barrel, fuel is no longer forced from the plunger cavity. The plunger is pulled up by the tappet and the tappet spring. The upward movement of the plunger causes the pressure in the plunger cavity to drop below fuel supply pressure. Fuel flows from the fuel supply passage around the open poppet and into the plunger cavity as the plunger travels upward. When the plunger reaches the top of the stroke, the plunger cavity is full of fuel and fuel flow into the plunger cavity stops. This is the beginning of pre-injection.
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