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| Illustration 1 | g00418398 |
Fuel System Schematic (1) Fuel filter base (2) Siphon break (3) Vent plug (4) Unit injectors (5) Fuel supply manifold (6) Drain plug (7) Fuel priming pump (8) Fuel return manifold (9) Secondary fuel filter (10) Fuel regulator valve (11) Fuel return port (12) Electronic control module (ECM) (13) Fuel transfer pump (14) Pressure regulating valve (15) Check valve (16) Fuel tank | |
The fuel supply circuit is a conventional design for unit injector diesel engines. Fuel transfer pump (13) is a gear type pump. The clearance in the fuel transfer pump is constant. The fuel transfer pump delivers fuel from the tank to unit injectors (4). Fuel is pulled from the fuel tank by the fuel transfer pump. The fuel transfer pump incorporates check valve (15) in order to allow fuel flow around the gears for hand priming. Pressure regulating valve (14) is used to protect the system from extreme pressure. The fuel transfer pump creates excess fuel flow that cools the unit injectors. The excess fuel flow also purges the air from the unit injectors.
After the fuel transfer pump, the fuel flows through the cored passages in the electronic control module housing in order to cool the module. The fuel then flows through secondary fuel filter (9). Fuel priming pump (7) is located on the fuel filter base. The fuel priming pump is used to fill the system after draining the fuel supply and return manifolds. Fuel filter base (1) also incorporates siphon break (2) in order to prevent fuel from exiting the cylinder head during long periods of storage. Fuel priming pump (7) minimizes the fuel that returns to the tank by utilizing two check valves.
The fuel flows continuously from the fuel supply manifold through the unit injectors and excess fuel is returned to the tank by fuel return manifold (8). The plunger displaces some fuel that is not injected into the cylinder. This fuel is also returned to the tank by the fuel return manifold. Refer to Systems Operation/Testing and Adjusting, "Unit Injector" for an explanation of the injection process.
A flow control orifice is located in the fuel return manifold. The flow control orifice maintains sufficient system back pressure in order to fill the unit injectors. Superb fuel flow is provided to the unit injectors without excessive heating of the fuel tank.
Fuel transfer pump (13) is located at the left front lower corner of the engine. The fuel transfer pump is driven by the lower accessory drive gear.
The fuel supply and return manifolds are drilled passages in a common manifold which is mounted to the cylinder head. Fuel from fuel supply manifold (5) flows through drilled passages in the cylinder head, and into unit injectors (4).
Fuel return port (11) is located at the end of fuel return manifold (8). The fuel return port is a part of fuel filter base (1). The pressure regulating orifice maintains the needed back pressure in order to fill the unit injectors. The pressure regulating orifice also provides a constant fuel flow through the unit injectors.
Fuel System Electronic Control Circuit
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| Illustration 2 | g00549482 |
Logic for Engine Speed Control (A) Coolant temperature sensor (B) Cold mode operation (C) Logic for engine control (D) Customer parameters (E) Throttle position sensor (1) Engine speed in rpm (2) Desired RPM (3) Transmission clutch/brake pedal | |
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| Illustration 3 | g00549489 |
Electronic Governor (A) Fuel injection control (B) Electronic governor (C) FRC maps (D) Torque maps (E) Atmospheric pressure sensor (F) Coolant temperature sensor (G) Fuel temperature sensor (H) Fuel pressure sensor (I) Engine speed signal interpreter (J) Boost pressure sensor (K) Engine speed sensor (1) Signals to unit injectors (2) Fuel position (3) Desired RPM (4) Engine RPM (5) FRC fuel position (6) Rated fuel position (7) Atmospheric pressure (8) Coolant temperature (9) Fuel temperature (10) Fuel pressure (11) Top center for No. 1 cylinder (12) Boost pressure | |
The following traditional Caterpillar fuel system components have been replaced with an electronically controlled, mechanically actuated unit injector in each cylinder.
- Fuel injection pump
- Fuel injection lines
- Fuel injector nozzles
A solenoid on each unit injector controls the amount of fuel that is delivered by the unit injector. The Electronic Control Module (ECM) sends a signal to each unit injector solenoid in order to provide complete control of the engine.
Electronic Controls
The electronic control system for the engine consists of two main components:
- Electronic Control Module (ECM)
- Personality Module
The ECM is the computer. The personality module is the software for the computer. The personality module contains the operating maps. The operating maps define the following characteristics of the engine:
- Horsepower
- Torque curves
- Rpm
- Other characteristics
The ECM, the personality module, the sensors, and the unit injectors work together in order to control the engine. Neither of the four can control the engine alone.
The ECM determines a desired rpm that is based on the following criteria:
- Throttle signal
- Certain diagnostic codes
- Vehicle speed signal
The ECM maintains the desired engine rpm by sensing the actual engine rpm. The ECM calculates the fuel amount that needs to be injected in order to achieve the desired rpm.
Fuel Injection
The ECM controls the amount of fuel that is injected by varying the signals to the unit injectors. The unit injectors will inject fuel ONLY if the unit injector solenoid is energized. The ECM sends a 90 volt signal to the solenoid for energizing the solenoid. By controlling the timing of the 90 volt signal, the ECM can control injection timing. By controlling the duration of the 90 volt signal, the ECM can control the amount of fuel that is injected.
The ECM sets certain limits on the amount of fuel that can be injected. FRC Fuel POS is a limit that is based on boost pressure in order to control the fuel air mixture for the emission control. When the ECM senses an increase in the boost pressure, the ECM increases the FRC Fuel POS. Rated Fuel POS is a limit that is based on the horsepower rating of the engine. Rated Fuel POS is similar to the rack stops and the torque spring on a mechanically governed engine. Rated Fuel POS provides the horsepower and the torque curves for a specific engine family. Rated Fuel POS provides the horsepower and the torque curves for a specific horsepower rating. The limits are programmed by the factory into the Personality Module. The limits are not programmable in the field.
There are three levels of fuel to air ratio that can be selected by the customer.
- Level 1: Minimum smoke
- Level 2: Factory setting
- Level 3: Maximum acceleration
The injection timing relies on the engine rpm, on the engine load and on other engine data. The ECM senses the top center position of cylinder number 1 from the signal that is provided by the engine speed sensor. The ECM decides when the injection should occur relative to the top center position. The ECM provides the signal to the unit injector at the desired time.
Unit Injector Mechanism
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| Illustration 4 | g00418440 |
Unit Injector Mechanism (1) Adjusting nut (2) Rocker arm assembly (3) Unit injector (4) Pushrod (5) Cylinder head (6) Lifter (7) Camshaft | |
The unit injector mechanism provides the downward force that is required to pressurize the fuel in the unit injector. At the precise time, unit injector (3) allows the fuel to be injected into the combustion chamber. The camshaft gear is driven by an idler gear. The idler gear is bolted through the timing gear housing to the block. The idler gear is driven by the crankshaft gear. The timing marks on the crankshaft gear, on the idler gear and on the camshaft gear are aligned in order to provide the correct relationship between the piston and the valve movement. Camshaft (7) has three camshaft lobes for each cylinder. Two lobes operate the inlet and exhaust valves, and one operates the unit injector mechanism. Force is transferred from the unit injector lobe on the camshaft through lifter (6) to pushrod (4). From the pushrod, force is transferred through rocker arm assembly (2) to the top of the unit injector. Adjusting nut (1) allows setting of the unit injector adjustment. Refer to Systems Operation/Testing and Adjusting, "Unit Injector Adjustment" for the proper setting of the unit injector adjustment.
Unit Injector
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| Illustration 5 | g00418441 |
Unit Injector (1) Solenoid connection to the multiplex enable circuit (2) Solenoid valve assembly (3) Spring (4) Valve (closed position) (5) Plunger (6) Barrel (7) Seal (8) Seal (9) Spring (10) Spacer (11) Body (12) Check valve | |
Fuel at low pressure from the fuel supply manifold enters the unit injector at the fill port through drilled passages in the cylinder head.
As the unit injector mechanism transfers the force to the top of the unit injector, spring (3) is compressed and plunger (5) is driven downward. This action displaces fuel through valve (4) and into the return manifold to the tank. The passage into barrel (6) is closed by the outside diameter of the plunger. The passages within body (11) and along check valve (12) to the injector tip are filled with fuel as the plunger moves down. After the passage in the plunger barrel is closed, fuel can be injected at any time. The start of injection relies on the software in the electronic control module.
When solenoid valve assembly (2) is energized from a signal across solenoid connection (1), valve (4) closes and pressure is elevated in the injector tip. Injection starts at 37931 kPa (5500 psi) as force of spring (9) above spacer (10) is overcome. The check valve starts moving off the valve seat. The pressure continues to rise as the plunger cycles through the plunger's full stroke. After the correct amount of fuel has been discharged into the cylinder, the electronic control module signals across the solenoid connection. The solenoid valve assembly is de-energized and valve (4) is opened. The high pressure fuel is then dumped through the spill port and into the fuel return manifold. The fuel then goes to the fuel tank. The check valve in the injector tip seats. Injection has ended as the fuel pressure decreases to at least 25517 kPa (3700 psi).
The length of injection meters the fuel that is consumed during the fuel injection process. Injection length is controlled by the governor logic that is programmed into the electronic control module.
After reaching the maximum lifting point, the force to the top of the unit injector is removed as spring (3) expands. The plunger returns to the plunger's original position. This uncovers the fuel supply passage into the plunger barrel in order to refill the injector pump body. The fuel at low pressure then circulates through the fuel injector body. After circulating through the fuel injector body, the fuel goes out of the spill port. This happens until solenoid valve assembly (2) is again energized.