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Hydraulically Actuated Electronic Unit Injector (HEUI) Systems Introduction The goal to build diesel engines achieving outstanding fuel economy and high torque output from relatively small engine displacements while lowering engine emissions produced an innovative injection technology appearing in the early 1990’s. The use of hydraulic force to pressurize fuel for injection was groundbreaking technology to advance the use of cleaner, more powerful and efficient diesels engines.
Hydraulically
actuated Electronic Unit Injection (HEUI) fuel systems utilize highly pressurized engine lubrication oil to drive plungers pressurizing fuel for injection. Until the development of HEUI technology, pressurization of fuel and injection timing events were controlled mechanically and limited limited by the fixed geometry geometry of camshaft profiles. profiles. HEUI systems however were the first truly modern injection system having the capability to pressurize fuel independently of engine speed. Electronic engine control also permits enormous flexibility for engine software to optimally adjust injection pressure, fuel delivery rates and timing of the injection event for each engine speed and load condition.
The HEUI advantage One of the first largest evolutionary steps of high pressure diesel injection technology is the Hydraulically actuated Electronic U nit Injection (HEUI) system. In the 1980’s when manufacturers began exploring technical solutions for upcoming emission standards, they realized that mechanically governed fuel systems had several handicaps. The primary disadvantage is mechanical systems pressurized fuel by either an engine or an injection pump driven camshaft. These systems could not vary injection timing or change fuel delivery rates with the flexibility necessary for emission reductions. Engine operating conditions such as load, coolant and air inlet temperatures, inlet boost pressures, vehicle speed, atmospheric pressure and other factors require unique injection timing and rate control to obtain optimum performance, fuel economy and emission reduction. More critically, these mechanically actuated fuel systems could not adequately pressurize fuel at low engine speeds to obtain best possible atomization and distribution of fuel in the combustion chamber. Since fuel plunger velocities in camshaft actuated engines are dependent on engine speed, at low rpm, plunger speeds are proportionally slow, preventing high pressurization. What is necessary is a system ca pable of pressurizing fuel independent of engine speed. The HEUI system is intended to do just that; to develop peak injection pressure independent of engine speed. This means that maximum spray-in pressure is available whether the engine is operating at maximum or minimum rpm. Therefore, during hard acceleration or sudden load changes at low speeds, the system can instantly adjust fuel pressurization to meet requirements for outstanding performance while minimizing emissions. emissions. Electronic control of injection timing and fuel rate means these events are adjustable, taking into account vehicle and engine operating conditions for lowest emissions and peak performance.
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Conventional fuel systems depend on camshaft rotational speed and geometric shape to control operating parameters such as injection pressure and rate.
HEUI fuel systems can develop injection pressures independently of en ine s eed.
Conventional mechanically actuated fuel injection systems cannot develop the high pressure, control injection rate and timing with the flexibility of HEUI systems.
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HEUI fuel systems can achieve lower emissions, improved fuel economy and power output because of its superior ability to highly pressurize fuel at almost any engine speed. Higher pressurization leads to better atomization for more complete and faster combustion
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Conventional fuel systems depend on camshaft rotational speed and geometric shape to control operating parameters such as injection pressure and rate.
HEUI fuel systems can develop injection pressures independently of en ine s eed.
Conventional mechanically actuated fuel injection systems cannot develop the high pressure, control injection rate and timing with the flexibility of HEUI systems.
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HEUI fuel systems can achieve lower emissions, improved fuel economy and power output because of its superior ability to highly pressurize fuel at almost any engine speed. Higher pressurization leads to better atomization for more complete and faster combustion
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Hydraulic pressurization of fuel HEUI systems replace the mechanical camshaft with highly pressurized lubrication oil which is used instead of cam lobes to actuate plungers pressurizing fuel for injection. Since the functions of pressurization, metering, timing and atomization are all incorporated into the injector, HEUI injectors are classified classified as unit injectors. These uniquely designed injectors are supplied not only with fuel but highly pressurized lube oil. an engine driven high pressure pressure oil pump supplies fuel to the injectors injectors at pressures close to 4,000 psi. Inside the injector, hydraulic force is further amplified to give HEUI’s the capability to achieve injection pressures of up to 28,500 psi from the latest injectors. Since oil can be pressurized to very high pressures independently of engine speed, high injection pressure is available at low engine RPM. The high pressure injection capabilities combined with electronic control of timing and injection rate ensures the finest atomization of fuel, low emissions, superior performance and fuel economy. This pressure is available at almost any engine speed and load condition which permits the HEUI system to operate in any diesel engine application by simply changing software programming. This feature by definition distinguishes the HEUI system as a type of common rail fuel system. Consecutive developments in HEUI technology have allowed for improved ability to shape the rate of fuel injection which further reduces combustion noise and emissions for quieter cleaner engine operation. HEUI injectors are easily replaced by technicians with almost no adjustment or special engine maintenance required except to change engine oil at regular scheduled intervals. Quieter engine operation Beginning with some 1996 models, first generation HEUI injectors used split-shot injection. This is a type of rate shaped injection which delivers a small quantity of fuel 810-degrees before the main injection. Caterpillar refers to this same feature as PRIME metering. The use of a pilot injection shortens the ignition delay period which reduces combustion noise. Through shortening the ignition delay period injection timing can be retarded which can reduce formation of N0x emissions. Gen II HEUI injectors used in the 6.0L/VT365 and VT-275 V-6 have full rate shaping capabilities. Techtip Many HEUI injectors are identical in shape and size s ize but are not no t interchangeable. For example, the injectors will have different injection volumes and fueling characteristics. HEUI injectors should never be interchanged from one engine model to another. The technician should ensure the injector replacements are chosen correctly by manufacturer, engine model and engine serial number.
329 HEUI injectors are capable of changing the rate at which fuel is injected during the injection cycle. While limited in comparison to the most recently developed fuel injection systems, the HEUI system is referred to as having rate shaping capabilities. In this graph of injection pressure from a HEUI B injector, a pilot injection also known as a split shot or PRIME metering is depicted.
Beginning with HEUI injectors built from 1996 and onwards, the main injection is preceded with a pilot injection. The pre-injection, increases the cylinder temperatures before the main injection which shortens the ignition delay period. Combustion noise is subsequently reduced and the shortened combustion period permits retarding of injection timing for lower N0x emissions.
Electro-hydraulic valve operation (cam-less diesel engines) HEUI technology has also enabled the integration of valve-train operation into this high pressure actuation system. Currently, International DT series truck engines use an internal compression release brake operated using the same high pressure oil supply used for the injectors. Anticipated soon is the release of the cam-less diesel by International Truck and Engine Company which integrates electro-hydraulic operation of intake and exhaust valves with HEUI oil system supply. These engines have demonstrated the tremendous advantages of variable valve timing, valve lift, and duration which provides for ultimate control of engine operation. Engine breathing is optimized for each engine load and speed condition allowing the engine to produce the lowest emissions and best
330 performance characteristics without the constraints of a mechanical, fixed geometry camshaft. Hydraulic actuation of valves also permits the use of compression-less starts allowing the use of smaller starting motors and fewer batteries. An engine can be easily cranked with exhaust valves slightly open allowing high initial cranking RPM with minimum power required. Subsequently closing the valves in one or all cylinders at the correct time will allow the engine to start. These engines are also capable of displacement on demand (DOD) which means cylinders can be cut-out with minimal parasitic loss of power until they are needed. Hydraulically actuated valve operation also enables the use of engine based compression release braking systems without additional components required of conventional compression release brakes.
This combustion chamber module integrates both the fuel injector and valves into a common unit which are actuated by hydraulic oil pressure.
The concept of using eliminating the camshaft is simple – use hydraulic pressure to open and close the valve.
Applications Collaboration between International Truck & Engine Corporation and Caterpillar lead to the HEUI system production in 1993. HEUI engines continue to be produced by these manufacturers. The most popular HEUI application of this joint venture are the 7.3L (DIT) Powerstroke branded T-444 for International used between 1993.5MY and 2003.5 MY for Ford. More than 2.5 million of these engines have been manufactured since the early nineties. In fact, two out of every three Ford F-250 and larger trucks are equipped
331 with this engine. Evidence of its reliability and durability is reflected in a recent survey indicating over 98% of these engines are still in service. International also uses HEUI for its DT series of engines, the DT-466 and the DT 570. International has also used HEUI technology for its T-444E, DT-466–570, Max Force 5, 7, 9, 10, Max Force DT and VT365 engines. Caterpillar has used HEUI in the 3116 and 3126 engines found in GMC Topkicks, Ford, Sterling and Freightliner truck chassis. Caterpillar also uses HEUI for some large off-road engines. The Daimler-Detroit Diesel branded Series 40 engine is also supplied by International which uses an HEUI fuel system.
The Ford Powerstroke made by International Engine Company also is badged as a T-444-E in International brand vehicles. More than 2.5 million of these HEUI equipped engines were produced between 1993 and 2003.
This 4.5L 275 CID V-6 engine with a 90 degree bank arrangement is referred to as a VT-275. It is fabricated by removing 2 cylinders from the VT-365 –Ford 6.0L Powerstroke and adding a balance shaft.
Caterpillar uses the HEUI system for its popular 3116, 3126, C7 ACERT and C9 ACERT engines. These engines can be found both on-highway medium-duty truck and RV and in off-road applications. Freightliner, Sterling, GMC Top-kick and medium duty Ford vehicles have used the Caterpillar engines. Other larger industrial applications of the HEUI are included in Caterpillar line-up of engine offerings. Second generation HEUI termed, GEN II or G2 is a more recent refinement of HEUI technology. A partnership between Siemens AG, International Truck and Engine Company, and Sturman Industries has produced what is termed digital valve technology. The 6.0L Powerstroke engine or, VT-365 used in International brand trucks uses this new injector design. A 275 cid 4.5L V-6 version of the 6.0L/VT-365 V-8 engine is also in production and used in military vehicles and in medium duty, class 4-5, cab-over CF series chassis.
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HEUI System Components The HEUI system has four major subsections. These include the HEUI Injectors Low-pressure oil system High-pressure oil system Electronic control system • • • •
A low-pressure supply system provides fuel to the injectors at the correct pressure, free of water, air, and contamination. Fuel supply pressure is regulated to between 30 and 80-psi on most systems. (See chapter on low pressure transfer systems)
This pictorial schematic of Caterpillar’s HEUI system for a large V-8 engine shows the major components of the HEUI fuel system.
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Insert figure 12 Two types of low pressure fuel supply systems are used on Powerstroke diesels and T-444E engines. One uses a mechanical pump which returns fuel back to the tank and another using an electric pump which does not return fuel to the tank.
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HEUI Injectors Types HEUI injectors use highly pressurized engine oil to provide injection force. Three basic variations of these injectors exist. The early systems from 1993-1995 International/Ford used a “A” type injector. Caterpillar also manufactured their own distinct injector design on the 3116 and 3126A engines that used a side mounted solenoid and high pressure jumper tubes supplying oil. Beginning in 1996 California and subsequent model years for other engines, International/Ford and Caterpillar used the split shot or, PRIME injector. This HEUI B injector is distinguished by the white coloured solenoid. Caterpillar’s injector, while appearing similar to the Ford and International application has a larger plunger bore and greater fuel delivery volume capabilities.
Split-shot injectors are used in: 1996 and later California 7.3L DIT 1997 and later 7.3L DIT Econoline 1999 and later 7.3L DIT F-Series truck 3126B Caterpillar engines. DT-466 and 530’s • • • • •
This HEUI A injector is identified by black coloured solenoid and does not have split-shot capabilities.
This HEUI B injector is identified by a white coloured solenoid and is capable of a single pilot injection used to reduce combustion noise and emissions .
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This early HEUI injector used in Caterpillar engines had the solenoid mounted on the side of the injector. High pressure oil entered through the top of the injector through a high-pressure steel line. Subsequent engines used oil passageways drilled through the block to supply pressurized oil .
Generation II or digital valve injectors developed through a partnership between Siemens and International are used in the 6.0L VT-365 engines. These injectors appeared for the 2002 MY at International and 2003.5 at Ford. The more compact design allows the use of 4 valves per cylinder engine design. These injectors use less energy, are faster responding, and have rate shaping capabilities covering a full range of engine speed and load conditions.
This 6.0L injector is a second generation HEUI (G2 or Gen-II). The two electromagnetic coils and other design features give it full injection rate shaping capabilities. This means it is able to precisely control the quantity and pressure of fuel injected over all engine speed and load conditions.
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HEUI Construction A type and split shot The HEUI injector has two grooves on the outside of body for receiving fuel and high pressure oil from rails drilled in the cylinder head. Sealing the grooves to maintain pressure around the injector are replaceable sets of O-rings. The top set which seals oil pressure consists of two rings: a steel back-up ring, a square cushion seal. One middle, round O-ring separates fuel and oil pressure. A bottom round O-ring seals fuel below the groove where fuel is delivered to the injector. Finally, a copper sealing washer around the injector tip seals combustion gases in the cylinder. Two hold-down bolts are used to position and clamp the injector. Only one bolt requires removal to extract the injector for service. This cylinder head cut-way depicts the low-pressure fuel and high pressure oil passageways separated by sealing “O”-rings. Note the lowest “O” ring is missing in this picture.
Techtip High pressure oil, in excess of 2,000 psi is separated from the fuel circulating in the cylinder head by an “O”-ring. Deteriorated or leaking injector “O”rings can result in high engine oil consumption evidenced by oil in the fuel tank.
Both type A and B-split shot injectors have four major components that operate together for precise metering, timing and rate control. The components are: •
High voltage electric solenoid. This device controls poppet valve operation. The solenoid requires approximetely 115 v D/C and 7-15 amps of current to actuate.
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Poppet valve - This device controls oil flow into the injector. When the poppet valve is closed, oil pressure is dead-headed or completely stopped preventing oil from entering the injector. Intensifier piston and plunger. The intensifier piston, also termed amplifier piston, magnifies the lube oil pressure which operates between 480 – 3,000 psi of pressure. Depending on the manufacturer the intensifier piston is seven or eight times larger in surface area than the plunger diameter which has high pressure oil acting upon it. This results in a multiplication of hydraulic pressure of fuel beneath the plunger which increases injection pressure. Nozzle assembly. The nozzle is a multi-orifice design operating to atomizes and distribute fuel into the combustion chamber. Nozzle opening pressure is in the vicinity of 2,700-psi on early injectors to over 5,500-psi on later injectors
Components of a typical HEUI injector
338 Stages of Injection: Type A injector HEUI injection can be understood by examining the three stages of injection. The three stages of injection are: Fill cycle Injection End of injection • • •
Pressurization of oil supplied to the injector supplies the force to pressurize the fuel inside the injector. The operation of this system is covered in another section of this chapter. Fill cycle During this part of the injection cycle, the poppet valve is blocking high-pressure oil from entering the injector. Internal components are shown in accompanying diagram in their relaxed, spring-loaded positions. The plunger and intensifier have returned to the top of the barrel. Fuel pressurized to between 30-80 psi by the low-pressure transfer system enters the injector through a passage way located just above the bottom groove of the injector. A fuel-fill check valve unseats and allows fuel to fill the plunger cavity. Insert Figure 21 HEUI Fill cycle. Poppet valve is closed, fuel inlet check valve is open fuel outlet check valve to nozzle tip may be either open or closed. No electrical current is applied to the injector solenoid. Injection During the injection cycle, current will energize the solenoid and the corresponding magnetic field overcomes spring tension that previously held the poppet on its seat. A piece of connecting linkage or armature between the poppet valve and solenoid lifts the valve from its seat. When the poppet lifts, the oil drain path at the upper poppet valve seat is closed. The result is high-pressure oil pushes past the poppet to the top of the intensifier piston. High-pressure oil over the piston pressurizes the fuel in the cavity beneath the plunger. Pressurized fuel travels to the nozzle valve causing the valve to lift beginning at approximately between 2,700-psi and 5,500-psi. Injection pressures may be as high as 23,000 psi depending on the operating conditions. Caterpillar systems operate at higher pressures.
Note the passageways around the upper and lower poppet seat. When no current is applied to the solenoid, oil can drain from above the amplifier piston through the upper poppet valve seat. High pressure oil is prevented from entering the injector by the lower poppet valve seat.
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Injection cycle Current is applied to the solenoid lifting the armature and poppet valve. The poppet valve is lifted off its seat allowing high pressure oil into the chamber above the amplifier piston. The drain path around the upper poppet valve seat leading out the top of the injector is closed. The amplifier piston pushes fuel below the plunger out the nozzle tip. Note the fuel inlet check valve is closed and the outlet check to the nozzle tip is opened.
When current is applied to the solenoid, oil cannot drain from the injector through the upper poppet valve seat but high pressure oil can now enter the injector through the lower poppet valve seat.
End of injection The injection cycle ends when the solenoid is de-energized. The magnetic field collapses that held the poppet valve open and spring tension forces the poppet valve against its seat. High-pressure oil can no longer enter the injector and oil now spills out the oil drain path beneath the solenoid around the upper poppet valve seat. The sudden oil pressure drop above the intensifier piston combined with spring tension and fuel pressure beneath the plunger, force the plunger upwards in its bore. The fuel-delivery check valve remains closed to maintain residual fuel pressure in the injector body.
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End of injection cycle. The position of internal components is identical to the first diagram of the injection cycle except that the amplifier piston is moving upwards expelling fuel out the upper poppet relief.
Metering Injection quantity is determined by the amount of plunger travel. Two factors determine how far the plunger will travel. 1. Injector solenoid on time. The longer the solenoid is energized, the more time is available to push the amplifier piston and injector plunger down the injector bore. 2. Oil pressure. The higher the oil pressure applied to the amplifier piston the faster the plunger will travel for a given amount of time. Longer on-time for the solenoid and higher oil pressure will result in greater quantities of fuel injected into the combustion chamber. Similarly, the same injection quantity could be metered into the cylinder by either increasing oil pressure and decreasing solenoid ontime or conversely, decrease oil pressure and increase solenoid on-time. Varying injection timing is accomplished by changing the point of beginning and end of solenoid actuation. Techtip To prevent damage to HEUI injectors after replacement the Association of Diesel Specialist (ADS) recommends priming the high-pressure oil galleries with oil before attempting to start the engine. This is accomplished by disconnecting the cam position sensor and cranking the engine over for two consecutive starting cycles. Internal damage to the injectors is avoided when injectors are primed with oil before attempting to fire the injectors.
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Tech tip When replacing or servicing HEUI injectors, oil and fuel must be drained from the cylinder heads first or it will drain into the cylinder when the injector is removed. A hydrostatic lock will occur in the engine after an injector is reinstalled if these procedures are not followed
Injection timing The beginning and end of injection are entirely variable and dependent on the electrical signal applied to the injector solenoid. Fuel timing maps and algorithms incorporated into the ECM software determine these events to obtain lowest emissions and best performance for any given engine operating condition load and speed.
Rate control Injection rate refers to the quantity of fuel injected per degree of crank angel rotation. Rate control is the ability of the fuel system to adjust the quantity of fuel injected during the injection sequence. Engine designers have discovered that if injection rates can be varied for a given engine load, speed or operating condition the engine can deliver improvements to emissions, fuel economy, power and noise levels.
Engine performance and emissions are optimized by using different injection rates. The square shaped edges of the fueling profiles represent a sharp beginning of injection with a maximum quantity of fuel injected through-out the injection event. The sloped edged injection rates represent a gradual build-up of injection quantity and consequently a gentler rise in cylinder pressure. Pilot injection permits retrded timing and shorter ignition delay time for quieter engine operation and low NOx.
342 HEUI injection systems have the unique capability to change the rate of fuel delivery. Since oil pressure to the injector is can be electronically controlled by the ECM, changing oil pressure will change injection rate without any requirement to change the on-time of the injector solenoid. For example, at high oil pressure compared to low pressure, the rate of fuel delivery is at higher. The reason for this is high oil pressure applied to the intensifier piston will drive the plunger farther and faster per degree of crank rotation. Pressurization is also independent of engine speed. Whether at idle or maximum engine speed, the output pressure of the high pressure oil pump can instantly change though the modifying the electrical signal applied to the injection oil pressure regulator. Typically at idle, actuation pressure is low to minimize combustion noise causes by ignition delay. When the driver demands more fuel such as during hard acceleration, the actuation pressure will instantly and sharply increase to adequately pressurize, atomized and distribute the larger injection quantities. Techtip Oil quality is critical to effective HEUI operation. Antifoaming additives are needed to HEUI engines to prevent air bubbles from forming and staying in the oil. If oil does contain air created as oil is thrown off the crankshaft and other moving parts injection pressurization and timing are affected. Poor fuel economy, low power and stalling are typical operator complaints.
HEUI-B Split-Shot - PRIME Injectors Advantages These injectors have special capability to inject a small quantity of fuel to the combustion chamber 8-10 degrees before the main injection. This pilot injection also known as splitshot or PRIME (an acronym formed from the term pre-injection metering) will begin to burn before the main injection arrives. The result is the chamber to be much hotter and have greater pressure when the main injection occurs. This injection strategy shortens the ignition delay period and operates to provide the following benefits: Lower combustion chamber noise. This is especially evident at idle when prolonged delay causes the diesel engine characteristic knocking sound. The hotter chamber will shorten the amount of time required for ignition of the main injection. Lower N0x emissions. The shortened ignition delay time allows for the use of retarded injection timing. Since the main injection delivery quantity will ignite faster, the beginning of injection can be delayed longer. The result is a less intense pressure spike after TDC in the cylinder that reduces N0x formation. Lower particulate emissions. Increased pre-ignition heat and temperature in the cylinder will assist a more complete combustion of fuel. The result is a more efficient burn evidenced by cleaner emissions and improved fuel economy.
343 Split-shot injector operation By 1999MY and newer, all Powerstroke, Caterpillar, and International brand vehicles used HUEI injectors with this updated design feature. The injector incorporates only slight change in the plunger and barrel to accomplish this fueling strategy. First, the injector barrel includes a new relief port that allowed injection pressure to bleed back to fuel supply pressure. The plunger has a groove cut through the bottom that allows injection pressure to travel up channels cut into the outer edge of the plunger. When the channels around plunger aligns with the spill port in the barrel, a momentary drop in pressure beneath the plunger occurs. This effectively stops injection. As the plunger continues to move downward in its stroke, pressure redevelops when the relief port is covered. The main injection will then take place subsequent to the plunger channel moving past the barrels spill port.
A split shot injector can mechanically separate the injection event into two parts using a uniquely shaped plunger design. Stage 1 Fill stage. Fuel pressure fills the plunger cavity with fuel supplied by the fuel rail in the cylinder head.
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Stage 2 First Injection. When the lower edge of the plunger covers the spill port in the barrel, plunger movement increases fuel pressure unseating the delivery check valve. Fuel delivery begins.
Stage 3 End of First Injection. When the plungers relief groove moves past the spill port in the barrel, pressure is released into the fuel supply system and fuel delivery is stopped.
Step 4 Second Injection - When relief groove in the plunger passes the spill port in the barrel pressurization of fuel resumes. The plunger continues to move downwards delivering fuel until the end of injection.
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Environmental tip High injection pressures improve mixture preparation and combustion quality which in turn: • Enable higher engine operating speed since smaller droplets ignite and burn faster. Improves fuel economy due to more complete combustion of smaller well mixed fuel droplets. • Minimizes particulate formation caused by incompletely burned carbon.. • Increase combustions ability to tolerate retarded injection timing • Increases combustion tolerance for the use of re-circulated exhaust gas (EGR) used to reduce N0x emissions. • Improves smoke limited power output
Injection Oil Systems Low-pressure oil system Caterpillar and International 7.3L HEUI engines use conventional lubrication oil systems with the addition of oil capacity and a separate high-pressure oil system for actuating the injectors. A supplemental circuit connects the engine lubrication system to a reservoir for supplying the high-pressure oil pump with oil. Because this circuit does not pass through a filter but instead connects the main oil gallery to the reservoir, it is called a shortcircuit. This ensures a rapid filling of the reservoir subsequent to an oil change or when the engine is cold. Without it, prolonged cranking would be necessary. A one-way check-ball prevents oil draining from draining back to the crankcase when the engine is not operated. 6.0L engines also use a reservoir but oil passes through the oil cooler and filters before being stored in a reservoir. This ensures only filtered oil free of debris and dirt reaches the injector. Caterpillar uses an accumulator to store oil for its high-pressure pump. These reservoirs hold approximately 0.95L of oil.
The short circuit of the high pressure oil system ensures sufficient oil flow to the injectors during starting and after oil changes.
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Layout of the oil system of a 7.3L Powerstroke diesel.
High-pressure circuit The high-pressure oil system delivers engine oil under high pressure to actuate the fuel injectors. Another name for the circuit is the injection control circuit. To increase the lube oil to pressures usable by the injectors, a high-pressure oil pump connected to the reservoir. These pumps are commonly gear driven, fixed displacement, swash plate or axial piston pumps. Lines or tubes will connect the pump output to oil galleries or manifolds delivering oil to the injectors.
This accumulator is located on top of the high-pressure pump for 3116, 3126, and C-7 Caterpillar engines.
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Injection control pressure regulator (ICPR) Oil pressure is regulated using a pulse width modulated pressure regulator. This device is an electrically operated spool valve that moves in response to the strength of a magnetic field. By changing the current flow through a coil surrounding the spool valve, the oil pressure for injection actuation is adjusted. When not building pressure the spool valve will direct oil back to the oil sump. To build pressure the spool valve will close the passage to the sump and direct oil to the common oil rail. International and Ford refer to this as the ICPR. Caterpillar’s term for the same device is injection actuation pressure control valve (IAPCV). To provide feedback to the ECM regarding injection control pressure, a sensor is located in the high-pressure oil circuit. THE injection control pressure sensor (ICP) will provide closed loop feedback to the ECM about whether the oil pressure is too low or high. The ECM can change the amount of current to the injection control pressure regulator (ICPR) coil and adjust oil pressure. A minimum of 325-500-psi pressure is usually required to start the engine. When running, the oil pressure will vary depending on the engine calibration and model. However, operating should remain relatively stable for any given operating condition. During hard acceleration and under full load conditions, injection control pressure will reach maximum pressures. Lowest pressures are encountered during warm idle. The injection control pressure regulator uses a PWM signal to adjust oil pressure to the injectors. Pressure is usually low at idle and increases with engine speed and load conditions.
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The injection control pressure sensor is a variable capacitance type sensor which measures injection actuation oil pressure. A feedback loop is formed between this sensor, the pressure regulator and the ECM. Loss of this sensor signal will usually cause the injection oil pressure to operate at a factory default value based on the PWM signal to the regulator.
The feedback loop to adjust injection actuation pressure is formed between the ICP ICPR and ECM. This ICPR regulator for a 6.0L Powerstroke regulates injection actuation pressure by returning oil pressure back to an oil sump.
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HEUI Diagnostics Injection control pressure problems The high-pressure oil pumps on HEUI have finite delivery volume. This means the output volume of the pump matches the quantity required by the injectors when they are operating at their maximum output. Some extra delivery volume is designed into the system however on many engines this volume is not adequate if there are leaks in the high-pressure oil systems. Thus, if there is a leak in the injector control system, engine performance is significantly affected. For example, system leaks can occur when oil leaks past leaking injector O-Rings, through defective or leaking poppet valves internal to the injectors or from a worn pump. These leaks will cause rough running, low-power, high fuel consumption and even no start conditions. Symptoms of high pressure oil leakage include: Large difference between starting times hot and cold, particularly a quick cold start and long hot starting. Loss of power when hot, Low power High fuel consumption Oil consumption Blue exhaust smoke, especially on startup. •
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The high pressure oil pump is located beneath the fuel conditioning module between the cylinder banks on a 7.3L Powerstroke. The ICPR is located on the pump. High pressure oil lines from the pump direct oil to the oil galleries located in each cylinder bank.
Oil quality Since the HEUI fuel injectors are electronically controlled and use high-pressure lube oil for actuation, understanding the operation of the oil system is necessary to diagnose possible performance complaints. Oil quality is critical for the same reason. The correct viscosity and grade of oil are important to proper HEUI operation. For example, oil that has little or no antifoaming additive will cause aeration of oil. Aerated oil will not
350 properly transmit pressure and motion, which leads to drivability complaints such as stalling and low power. Tech tip Diesel engine oil used in HEUI engines must have the proper level of antifoaming additive. This additives causes air bubbles to quickly release from oil. Antifoaming additive package contained in diesel engine oil depletes with distance traveled and is affected by chemicals action such as from silicon from RTV gaskets material. On engines having repairs done such as resealing the oil pan using RTV, an additional antifoaming additive package is recommended
Oil contaminated with water, fuel, dirt or particulate will lead to premature wear and malfunctioning injectors. For example, an improperly installed or incorrect air filter will cause dirt contamination of oil leading to rapid and premature injector failure. HEUI oil systems are divided into two sections, the low-pressure supply, and the high pressure system. The low-pressure system supplies the high pressure and problems in either system will effect engine operation. Diagnostic test to detect system leakage include: Measuring the duty cycle of the injection control pressure regulator. An unusually high duty cycle indicates the ECM is compensating for oil leakage by increasing the on-time for the pressure regulator. Longer on time or, duty cycle means less oil returns to the sump and more oil is delivered to the high-pressure circuit. •
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Pressurizing the high-pressure circuit and checking for leak-down of oil. High pressure circuits when highly pressurized with oil should be able to retain pressure for hours with no significant drop. A hand operated or electrically operated oil pump can be used to verify the sealing capabilities of the high pressure circuit. Oil contamination of fuel should also be visually checked to determine if oil is bypassing injector O-rings and entering the fuel. If the middle O-ring has failed on the early generation of HEUI engines, oil will push its way into the lower pressure fuel circuit. A diagnostic test to determine whether oil is aerating is performed by monitoring the injection control pressure while operating the engine at hi-idle for three minutes. If oil begins to aerate, the duty cycle of the injection control pressure regulator will increase. This happens since as the control system compensates for a loss in pressure caused by aeration of oil.
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Generation II HEUI Systems Generation II HEUI Injector Features The discontinuation of the 7.3L and introduction of the 6.0L for the 2002 MY and brought with it a revolutionary new injector design. The second generation or G2 or Gen II injector uses what is termed digital control valve technology. It is not the ones and zero type of digitization but refers to the position of the control valve which operates like the poppet valve in earlier injectors – the control valve is either open or closed. The injector uses two electromagnetic, coils and a spool valve. Four external electrical pins supply the coils current to operate at 48-volts and 20-amps per coil, which is lower voltage than other HEUI injectors. However, the time current is applied to the coils is only 800 microseconds. That is 800 millionths not thousandths of a second. This contrasts with type A and B HEUI injectors require at least 500 milliseconds before they build-up adequate magnetic filed strength to close the poppet valve. This dramatically shorter pulse time means the coils can operate cooler. Most importantly, the coil and spool valve design enable the electrical signals, rapidly control the quantity of fuel injected throughout the entire injection cycle. This capability known as rate shaping is critical to obtaining low emissions without sacrificing performance and fuel economy. The new control valve design provides for a smaller compact injector allowing the use of four valves per cylinder – two intake and exhaust. The 6.0l Powerstroke or VT-365 uses an new generation of HEUI injectors referred to as GEN-II or G2 injectors
352 What is also so unique about the digital valve is dependence on residual magnetism to operate and it uses no springs to center or return the spool valve. Instead, residual magnetism from electric current which is applied only momentarily to the coil will indefinitely hold the spool valve in an open or closed or position. When a second pulse of electric current is applied to the opposing coil, the valve will move in the opposite direction. Pressurized lube oil supplies the force needed to physically open and close valves. By using residual magnetic energy as the triggering force and hydraulics as the driving force, the valve operates more quickly, using less energy and generates less heat than its predecessors. This digital valve overcomes the technological barriers of switching very high-pressure fluid at extreme speeds with reduced coil response time. The high-pressure oil circuit of the 6.0l supplies oil to injectors through a manifold above the injectors.
This G2 injector uses sealing washers similar to other HEUI injectors except there is no oil circulating around the injector.
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The O-ring in the top of the injector seals highpressure oil from leaking out of the oil manifold and injector. This O-ring is not serviceable.
O-rings and AWA oil rail High-pressure oil is supplied to the injector through a high-pressure oil manifold or rail externally attached to the top of the injectors. The rail incorporates dampening devices called Acoustic Wave Attenuation (AWA) to minimize hydraulic noise and pressure waves. Early model engines used a straight rail. Later models introduced a wavy high pressure oil rail with higher oil capacity and dual AWA fittings fin each rail. A replaceable O-ring seals the oil rail to the injector. Fuel to the injector is supplied through drilled passageways in the cylinder head and sealed with two O-rings around the injector body. A copper sealing washer at the injector tip prevents combustion gases in the cylinder from leaking from the chamber into the area around the injector body. Removal of the injector from its bore is accomplished by removing a single hold-down clamp bolt.
The G2 injectors used in the 6.0l Powerstroke, VT-365 and VT-275 receive fuel through a rail passing through the cylinder head. High pressure oil is delivered through a manifold attached to the top of the injectors.
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The high pressure oil pump and reservoir are located between the cylinder banks at the rear of the engine on a 6.0l Powerstroke diesel
Injector coil and spool valve Inside the injector, the digital control valve consists of two coils, an open and closed coil. A spool valve moves from side to side controlled only by magnetic forces. Total movement of the valve is only 0.017” The valve has only two positions. When open, it allows oil to flow from the high-pressure oil rail into the injector, pushing the intensifier piston and plunger downwards. In the closed position, it allows oil to drain out of the injector. A cross sectional view of the G2 injector coils and spool valve and plunger. The spool valve operates similarly to the poppet valve of HEUI A and B injectors. Oil is admitted and released from the injector through the spool valve. Oil pressure acts on the plunger to pressurize fuel for injection.
355 Intensifier piston, barrel, and plunger Similar to the earlier HEUI injectors the intensifier piston multiplies fuel pressure below the fuel plunger. The intensifier has a surface area of 7.1 times greater compared to the plunger diameter. A mechanical pressure relief valve in the system opens at 4000 psi. This limits oil pressure in the event of a malfunctioning injection pressure regulator. These systems theoretically can operate at up to 28,500-psi injection pressure. The plunger and barrel assembly develop injection pressure. Earlier injectors used a coating of tungsten carbide on the plunger to reduce the possibility of scuffing from poor fuel quality, water contamination and the effects of ultra low sulphur diesel (ULSD)fuel. 2004 MY and later use a silicon carbide or Diamond Like Carbon (DLC) coating. A new clevis over the fuel plunger has eliminated failures encountered with earlier injectors. Injection Cycle The injector has three main events during an injection cycle: Fill Main injection End of main injection Fill cycle This event begins with the spool valve in the closed position preventing oil from entering the injector. Low-pressure fuel regulated to 45-50 psi enters the injector through fuel rails in the cylinder head. After entering the injector through the fuel inlet located in a groove around the injector body, fuel fills the cavity below the plunger.
Main injection A pulse width modulated signal energizes the open coil moving the spool valve to the open position. This allows high-pressure oil to begin forcing the intensifier piston and plunger downward. A fuel inlet check-ball closes causing pressurization of fuel below the plunger. The pressurized fuel begins to lift the nozzle valve at approximately 3,100psi. End of injection After the correct amount of fuel is delivered based on time the injector digital valve has been left open, the close coil is pulsed with 800 microseconds of current. This moves the spool valve from an open to a closed position. High-pressure oil is blocked from entering the cavity above the intensifier piston. Oil above the intensifier piston leaves the injector
356 through an exhaust port. Pressure from the plunger return spring returns the intensifier to its initial position. The nozzle valve simultaneously closes and injection abruptly ends after delivering fuel. Insert figure 53 Main injection step two ends with the spool valve moved to the closed position and injection stops. Oil vents from injector through spool valve and out the injector.
Metering, timing and rate control Similar to previous HEUI injectors the Gen II plunger travel determines injection quantity. Plunger travel however is determined not by the amount of time the open or close coils are energized but by the length of time the digital valve is left open. The coil needs only pulsing once to remain in its position. The opposite coil requires energizing to change the poison of the spool valve. Varying injection timing is accomplished by changing the specific time during crankshaft rotation to cycle the open and close coils. To change the rate of fuel delivery, the oil pressure to the injector is can be electronically varied by the ECM. At higher pressure, the rate of fuel delivery is proportionally greater since the force acting on the plunger is increased. The plunger will then displace more fuel per degree of crankshaft rotation at high pressure than during low pressure operation. Pressurization is independent of engine speed so high pressures are available at low engine speed operation. Rate control or shaping is performed through more than just varying the oil pressure. The additional rate shaping feature of the G2 injector is its capability to rapidly open and close the spool valve many times during the course of one injection sequence. This pulsing is accomplished electronically and not just mechanically like HEUI B injectors. Software instructions contained in the ECM can send several pulses to the digital valve
357 control coils within one injection cycle. This enables execution of several injection sequences within one injection cycle.
Electronic Management System Information processing on these engines is similar to other electronically governed diesels. Input device send signals or information to the electronic control module (ECM). The ECM processes the information and generates outputs based on control algorithms, memory containing tables of look-up information and software instructions to devices such as the injectors and pressure regulating valves.
On board Diagnostics II (OBD-II) & HEUI On Board Diagnostic (OBD-II) strategies legislated for all vehicles with GVW of 14,000 lbs or less are programmed into the ECM. In California, the legislation applies to all diesel engine vehicles up to 14,000 lbs. GVWR starting in the 1997 MY. Starting in the 2004 MY, jurisdictions using Federal emission standards will start phasing in OBD-II for vehicles over 8,500 lbs. OBD-II strategies are used to manage faults within the subsystems and allow the engine to operate at the highest efficiency level possible and prevent excessive emissions. If the engine defect exceeds certified emission levels by more than 10%, the MIL will illuminate.
HEUI & OBD-II system monitoring relevant to combustion includes: 1. Engine misfires Misfire for diesels is defined as a loss of compression. The amount of compression loss in a cylinder that misfire monitor will detect is referenced as a 3/16" or larger hole in a cylinder or valve train component. 2. Glow-plugs 3. Injection control pressure 4. EGR operation 5. Comprehensive component monitoring of engine inputs, Manifold absolute pressure (MAP), Barometric pressure (BARO), Engine oil temperature (EOT), Exhaust pressure (EP), Intake air temperature (IAT), Injection control pressure (ICP), Mass air flow (MAF), Accelerator pedal poison (AP), Crank poison sensor (CKP), Cam position sensor (CMP), Dual alternators, Electronic variable response turbocharger (EVRT), 6. Injection control circuits
A number of electronic systems operate to manag e the fueling of the HEUI engine. Common electronic engine input devices consist of: Camshaft position (CMP) sensor Engine coolant temperature (ECT) sensor Manifold absolute pressure (MAP) sensor
358 Intake air temperature (IAT) sensor Accelerator pedal position (APP) sensor Engine oil temperature (EOT) sensor Engine oil pressure (EOP) sensor Barometric pressure (BARO) sensor Crankshaft position (CKP) sensor Mass airflow (MAF) sensor Idle validation switch (IVS) Manifold air temperature (MAT) sensor Injection control pressure (ICP) sensor
Common outputs devices associated with HEUI fuel systems include: Injection control pressure regulator (IPR or IAPCV - Caterpillar) HEUI injectors Malfunction indicator lamps (MIL) Processing These modules are devices which make-up the information processing or engine control devices: Electronic Control Module (ECM) or Powertrain control module (PCM) Injector Driver Module (IDM). Fuel injector control module (FICM)
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Common sensor locations for a 7.3L Powerstroke
Input device functions Accelerator pedal position (APP) sensor or Throttle position senor (TPS) The Accelerator Pedal (AP) position sensor or throttle position sensor (TPS) is a threewire potentiometer, connected to the accelerator pedal. The AP/TPS sensor measures pedal position demanded by the operator. The analog voltage signal is a variable used to calculate injection fuel quantity, injector timing, and injection control pressure in order to regulate engine speed. The Idle Validation Switch (IVS) This device is a three-wire SPDT switch used by Ford and International to verify throttle pedal position. At idle one of the switch thorws is open and the other closed. Off idle the switch status changes. The IVS will detect out of range failure of the AP/TPS sensor. If the ECM measures a discrepancy between IVS and AP/TPS sensor, the engine will operate only at idle. This input device can prevent sudden unintended engine acceleration.
360 Each track of this three track pedal posiyion sensor is used to validate the data from the other tracks. The design eliminates the requirement for an idle validation switch. An error in pedal data, such as caused by a worn or resistive pathway in one track, allows information from another track to be used to operate the vehicle thus increasing vehicle reliability.
Engine Oil Temperature (EOT) Sensor The engine oil temperature (EOT) sensor is a NTC thermister that sends an analog signal to the ECM to proportional to engine oil temperature. EOT is used by the ECM to calculate injection quantity and injection timing. The sensor can also help the ECM compensate for changes to oil viscosity due to temperature. This ensures adequate power and torque are available under all operating conditions. The EOT is monitored by the ECM to determine glow plug on time. Manifold Air Temperature (MAT) sensor This sensor is a NTC thermister, located in the charge air cooler housing, measures intake air temperature exiting the charge air cooler. Data from the MAT with MAF data is used to calculate air density. The ECM will adjust injection quantity and injection timing based on air density and temperature.
361 Manifold Absolute Pressure (MAP) sensor The Manifold Absolute Pressure (MAP) sensor is used to measure intake manifold pressure. The sensor may be either a digital or an analogue type. The analogue type sends a varying voltage whereas the digital type sends a varying frequency signal. Information supplied by the MAP sensor is used by the ECM to calculate injection quantity and timing. For example, to minimize particulate emissions MAP sensor data will control the delivery quantities of fuel until adequate air or boost pressure to support combustion is available. The MAP sensor also measures engine load. Under heavy load conditions, boost pressure is proportional load. Injection timing is retarded under this condition. The Barometric Pressure (BARO) sensor This is a variable capacitance sensor producing an analog signal proportional to atmospheric pressure. The ECM uses the BARO sensor to adjust fuel timing and delivery quantities of fuel based on altitude. At high altitudes, the delivery quantities of fuel may be reduced to prevent excessive emissions. The BARO sensor is also used to control the glow plug subsystem. Higher altitudes will increase glow plug preheat time. Intake Air Temperature (IAT) sensor This device is a thermister, mounted usually in the air cleaner providing ambient air temperature data to the ECM. IAT sensor data is used by the ECM to employ operating strategies that compensate for cold ambient temperature. On 6.0L engines, this sensor is located within the MAF sensor to calculate air density. Camshaft position (CMP) sensor The Camshaft Position (CMP) sensor is a three-wire Hall-effect sensor on 7.3L Ford/Navistar engines and a two-wire variable reluctance sensor on Caterpillar engines. This sensor provides information about engine speed and position. Position information is required by the ECM to determine which cylinder is on compression stroke to properly inject fuel into the appropriate cylinder at the correct time. The sensor is located in the front of the engine on the timing gear cover on Ford/Navistar 7.3L engines and in the rear of the cover on Caterpillar engines. The Hall Effect CMP on 7.3L engines generates a varying frequency signal as vanes of a trigger wheel on the cam gear pass through a magnetic field.
The number of the vanes passing by the sensor per second indicates engine speed. The number of vanes passing the sensor provides information about the number of degrees of engine rotation. A narrow vane on the trigger wheel indicates the position of cylinder number one at TDC. Cylinder number four cylinder is indicated by a wide vane on the trigger wheel. This information is used by the PCM to generate the cylinder identification (CID) signal for the injector drive or fuel injection control module. Engine speed and camshaft position information is a critical variable to control injection pressure, timing, and delivery quantity. The loss of data from this sensor will cause the engine to stop operating.
362 On 6.0L engines, the CMP is a two-wire variable reluctance sensor located on the left front side of the block. It responds to a peg pressed into the camshaft and provides an engine position or cylinder identification signal.
The cam position sensor provides critical information regarding cylinder identification, engine position and speed used to calculate injection events. Since an engine rotates twice to fire all cylinders the cam poison sensor helps identify which cylinder is near TDC at the end of compression stroke or end of exhaust stroke. Crankshaft position (CKP) sensor The CKP sensor is a two-wire variable reluctance sensor located on the right front side of 6.0L engines. This sensor generates a signal from a target wheel located on the crankshaft. The wheel is 60 teeth minus two teeth design. This means a wide gap is created in one spot from two teeth missing on the wheel. The missing teeth will correspond to the CMP signal every two-crankshaft revolutions. A synchronization of the CKP and CMP signal is used to calculate engine speed and position to control firing order, injection timing, and quantity. The other teeth provide data regarding engine speed and degrees of crankshaft rotation. OBD-II diagnostic strategies will use the data from both the CKP and CMP sensor to identify cylinder misfires. Changes in rotational speed caused by compression and power strokes will identify misfiring cylinders which can cause excessive emissions. Crankshaft position data is a more accurate strategy to calculate engine position than a cam sensor since data since it does not contain error due to crank/cam gear backlash.
363 Engine coolant temperature (ECT) sensor The engine coolant sensor is a two-wire thermister providing data for coolant temperature. This data is used for calculation of injection timing, quantity, glow plug on time and fan operation.
Mass airflow (MAF) sensor The mass airflow sensor provides data measurements for the mass of air entering the engine. It uses a hot wire-sensing element maintained at 392F 200C to provide a fixed voltage drop across the element. When air passes over the element, it cools and causes the current flow through the wire to increase in order to maintain its temperature. Therefore, the current flow through the wire will be proportional to the mass of air entering the engine. The MAF is used on 6.0L engines to calculate the quantity of EGR flow into the engine. OBD-II requires the MAF to perform diagnostics checks on EGR functions. When the EGR is enabled, the amount of airflow into the engine should decrease proportional to the increase in EGR flow. Figure 57 The Mass air flow senor for a 6.0L Powerstroke incorporating an intake air sensor. The MAF is used by the OBD system to verify correct operation and diagnose problems associated with the intake air and EGR system Injection control pressure (ICP) sensor This is also termed the Injection actuation pressure (IAP) sensor by Caterpillar and is a three-wire variable capacitance device measuring oil pressure to the injectors. The ECM monitors this sensor to achieve an ideal control pressure determined by engine operating factors such as load, throttle position, speed, and oil temperature. If the oil pressure is outside its desired range, the ECM will attempt to adjust pressure by changing the signal to the injection control pressure regulator (IPR). Data from this sensor is critical to adjustments to injection timing and volume.
Output devices Injection control pressure regulator (ICPR) The most significant output device for engine fueling control is the Injection control pressure regulator (IPR). Caterpillar refers to this valve as the Injection actuation control valve (IAPCV). This device is a pulse width modulated (PWM), variable position spool valve located on the high-pressure oil circuit. It is used to modulate or chan ge oil pressure within the system when commanded by the ECM. When no signal is applied to the control coil around the spool valve, oil flow from the high-pressure pump is redirected to the oil sump. Increasing the amount of time current is applied to the coil gradually closes the valve and increases oil pressure supplied to the injectors. As the time current is applied increases, the IPR duty cycle expressed in percentage increases proportionally. This means the higher the duty cycle, the greater the oil pressure or a greater amount of the pump output is used to build pressure. Values for the duty-cycle are between 0 and 65%. An increase in injector control pressure results in an increase in fuel injection quantity if accompanied with little or no change in injector pulse width.
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Together the ICP and the IPR form a closed loop system. This means the ECM monitors the ICP sensor and adjustments are made to the IPR duty cycle based on this feedback. Injector drive modules (IDM) Fuel Injection control module (FICM) Since the HEUI injectors require substantial amounts of current 115-volts 8 amps for 7.3L engines and 48 volts 20 amps for Gen-II, the ECM is not able to supply these high current demands. Instead, a separate module capable of switching injectors and monitoring injector performance is used. The Injector Driver Module (IDM) or Fuel injector control module (FICM) receives data from the ECM and uses it to calculate injection timing and duration. In the 7.3L engines, the IDM receives two control signals from the ECM: the Fuel Delivery Control Signal (FDCS) and the Cylinder Identification (CID) signal. The FDCS indicates ECM commanded engine rpm and is used by the IDM to establish injection timing and injection duration. The CID signal indicates engine position and is used to establish the beginning of firing sequence. Since the firing order sequence is built into the IDM, it can begin the injection sequence after learning when a particular cylinder is at TDC. An Electronic Feedback (EF) signal is used to send diagnostic trouble codes (DTC) information about the IDM and injectors to the ECM. Cat engines do not require a separate IDM module. All engine functions are integrated into the Advanced Diesel Engine control Module (ADEM) or ECM.
The ECM communicates information regarding timing, injection quantity and engine position with the injector drive module (IDM) Using this information the IDM calculates the appropriate pulse width for the injectors and delivers high voltage electrical signals to the correct cylinder at the correct time. Injector circuit diagnostics are performed by the IDM and diagnostic information is communicated across data lines connecting the two modules.
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Caterpillar HI300B HEUI Injector
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