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| Illustration 1 | g01017623 |
(1) Fuel supply line (2) Electronic unit injectors (3) Fuel gallery (4) Pressure regulating valve (5) Fuel filter (6) Fuel priming pump (7) Distribution block (8) Fuel temperature sensor (9) Fuel transfer pump (10) Relief valve (11) Check valve (12) Fuel tank | |
The fuel supply circuit is a conventional design for electronic unit injector diesel engines. Fuel transfer pump (9) of the circuit is a gear type pump with fixed clearance. The fuel transfer pump delivers fuel from fuel tank (12) to electronic unit injectors (2). Fuel is pulled from the fuel tank by the fuel transfer pump. The fuel transfer pump incorporates a check valve (11) in order to permit a fuel flow around the gears for hand priming. The fuel transfer pump also incorporates a relief valve (10) in order to protect the system from extreme pressure. The excess fuel flow that is provided by the fuel transfer pump cools the electronic unit injectors. The excess fuel flow also purges the air from the electronic unit injectors.
The fuel in the fuel transfer pump flows through the cored passages in distribution block (7) and through a 2 micron fuel filter (5). Fuel priming pump (6) is positioned on the fuel filter base in order to prime the system when air has entered the fuel system. For more information on priming the fuel system, refer to Testing and Adjusting, "Fuel System - Prime".
The fuel enters the fuel manifold at the rear of the cylinder head. The fuel flows continuously from the fuel supply through the electronic unit injectors. This fuel then returns to the tank by the return line for the fuel manifold. Fuel is displaced by the plunger when the fuel is not being injected into the cylinder. This fuel returns to the tank by the fuel return manifold. For more information, refer to the topic on electronic unit injectors in Systems Operation, "Fuel System".
Pressure regulating valve (4) is located in the distribution block. The pressure regulating valve maintains a sufficient amount of back pressure in the system in order to fill the electronic unit injectors.
Fuel transfer pump (9) is located in the front of the engine at the lower left corner. The fuel transfer pump is mounted to either the front timing gear cover or a plate. The fuel transfer pump is driven by the gear train.
Fuel Heaters
Fuel heaters prevent the plugging of the fuel filters in cold weather. This plugging is called waxing. The engine will not dissipate enough heat in order to prevent waxing. Heaters that are not thermostatically controlled can heat the fuel in excess of 65°C (149°F). High fuel temperatures will reduce the engine performance, the transfer pump check valve, and the system reliability.
Note: Fuel heaters without some type of temperature regulator must never be used.
Two types of fuel heaters can be used: thermostatically controlled and self-adjusting.
Fuel System Electronic Control Circuit
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| Illustration 2 | g00597197 |
Logic for engine speed control (A) Logic for CRUISE/PTO (B) Control for CRUISE/PTO (C) Engine control logic (D) Coolant temperature sensor (E) Cold mode operation (F) Customer parameters (G) Accelerator pedal position sensor (1) Signal for enabling the engine retarder (2) Cruise control (mph) or PTO (rpm) (3) Transmission clutch/brake pedal (4) Cruise control set/resume switch (5) Cruise control on/off switch (6) PTO on/off switch (7) Vehicle speed (mph) (8) Engine speed (rpm) | |
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| Illustration 3 | g00912708 |
Electronic governor (A) Fuel injection control (B) Electronic governor (C) Fuel ratio control maps (D) Torque maps (E) Coolant temperature sensor (F) Crankshaft position sensor (G) Engine speed signal interpreter (H) Boost pressure sensor (1) Signals to unit injectors (2) Fuel position (3) Desired engine speed (rpm) (4) FRC fuel position (5) Rated fuel position (6) Coolant temperature (7) Top center for number one cylinder (8) Engine speed (rpm) (9) Boost pressure (10) Wastegate solenoid | |
The injection pump, the fuel lines, and the nozzles that are used in the traditional Caterpillar diesel engines have been replaced with a mechanically actuated electronically controlled unit injector in each cylinder. A solenoid on each injector controls the amount of fuel that is delivered by the injector. An engine control module (ECM) sends a signal to each injector solenoid in order to provide complete control of the engine.
Electronic Controls
The electronic control system consists of two main components:
- Engine 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
- Engine speed (rpm)
- Other characteristics
The ECM determines a desired rpm that is based on the following criteria:
- Accelerator pedal position
- Diagnostic codes
- Status of the PTO switch
- Vehicle speed
The vehicle must be in a CRUISE/PTO mode in order to use the last two criteria.
The ECM maintains the desired engine speed (rpm) by sensing the actual engine rpm. The ECM calculates the amount of fuel that needs to be injected in order to achieve the desired rpm.
Fuel Injection
This engine uses a dual injection pattern. A pilot injection takes place in order to start the combustion process. Thenormal injection process takes place after the pilot injection. This requires a new camshaft with a modified injector lobe.
The ECM controls the amount of the fuel that is injected by varying the signals to the electronic unit injectors. The electronic unit injectors will inject fuel ONLY if the electronic unit injector solenoid is energized. The ECM sends 120 VDC to the solenoid in order to energize the solenoid. By controlling the timing of the 120 volt signal, the ECM can control injection timing. By controlling the duration of the 120 volt signal, the ECM can control the injected fuel amount.
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 air/fuel 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 horsepower rating. The limits are programmed by the factory into the Personality Module.
Injection timing depends on three factors: the engine speed (rpm), the engine load and other engine data. The ECM determines the top center position of cylinder number 1 from the signal that is provided by the crankshaft position sensor. The ECM determines when the fuel injection should occur relative to the top center position. The ECM then provides the signal to the electronic unit injector at the correct time.
Electronic Unit Injector Mechanism
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| Illustration 4 | g00291269 |
Electronic unit injector mechanism (1) Electronic unit injector (2) Adjusting nut (3) Rocker arm assembly (4) Camshaft | |
The electronic unit injector mechanism provides the downward force that is required to pressurize the fuel in the unit injector. Electronic unit injector (1) injects fuel in the combustion chamber at the correct time. The camshaft gear is driven by two idler gears and a cluster gear that is driven off the crankshaft gear. The timing marks on the crankshaft gear, on the cluster gear, and on the housing of the timing cover are aligned in order to provide the correct relationship between the piston and the valve movement. The camshaft has three lobes for each cylinder. Two lobes operate the inlet valves and the exhaust valves, and one lobe operates the electronic unit injector mechanism. Force is transmitted from the lobe on camshaft (4) to the top of electronic unit injector (1) through rocker arm assembly (3). Adjusting nut (2) allows the injector lash to be set. For the proper setting of the injector lash, refer to the topic on adjustment of the electronic unit injector in Testing and Adjusting, "Electronic Unit Injector - Adjust".
Electronic Unit Injector
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| Illustration 5 | g00984466 |
Electronic unit injector (1) Spring (2) Solenoid connection to the ECM (3) Solenoid valve assembly (4) Plunger assembly (5) Barrel (6) Seal (7) Seal (8) Spring (9) Spacer (10) Body (11) Check valve | |
Fuel at low pressure from the fuel supply manifold enters the electronic unit injector at the fill port through drilled passages in the cylinder head.
As the electronic unit injector mechanism transfers the force to the top of the electronic unit injector, spring (1) is compressed and plunger (4) is driven downward. This action displaces fuel through the valve in solenoid valve assembly (3), and into the return manifold to the fuel tank. The passage in barrel (5) is closed by the outside diameter of the plunger. The passages within body (10) and along check valve (11) 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 (3) is energized from a signal across solenoid connection (2), the valve closes and pressure is elevated in the injector tip. Injection starts at 34500 ± 1900 kPa (5000 ± 275 psi) as the force of spring (8) above spacer (9) is overcome. The check valve starts moving off the valve seat. The pressure continues to rise as the plunger cycles through a full stroke. After the correct amount of fuel has been discharged into the cylinder, the electronic control module signals across solenoid connection (2). The solenoid valve assembly is de-energized and the valve in solenoid valve assembly (3) 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.
The duration of injection meters the fuel that is consumed during the fuel injection process. Injection duration is controlled by the governor logic that is programmed into the electronic control module.
As the camshaft lobe rotates past the point of maximum lobe lift, the force on top of the electronic unit injector is removed and spring (1) expands. The plunger returns to the 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 flows out of the spill port. This continues until solenoid valve assembly (3) is again re-energized.