Hydraulically Actuated Electronic Unit Injector (HEUI) Systems PDF

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326 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 ...

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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 by the fixed geometry of camshaft 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 Unit 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 capable 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. 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 engine speed.

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 as unit injectors. These uniquely designed injectors are supplied not only with fuel but highly pressurized lube oil. an engine driven high pressure oil pump supplies fuel to the 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 but are not 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 highpressure 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 highpressure 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.

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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.

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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...