Hydraulic-Driven Electronically Controlled Individual Injector (HEUI) Technology Lecture

Hydraulic-Driven Electronically Controlled Individual Injector (HEUI) Technology Lecture (Lecture 2)

History of HEUI Injectors

HEUI injectors use high-pressure engine oil to provide injection pressure, and there are three different models. Early HEUI systems, used between 1993 and 1995, were referred to as "Type A" injectors by International and Ford. Caterpillar also independently designed and manufactured a HEUI injector with a control valve on the side of the injector and high-pressure oil supplied via a high-pressure steel pipe, which was installed on the 3116 and 3126A engines.

From 1996 onwards, International, Ford, and Caterpillar began using injectors with pre-injection functionality, called HEUI "Type B" injectors. This HEUI-B injector can be identified by its white solenoid coil housing. Caterpillar injectors look similar to International or Ford injectors, but have a larger plunger diameter and greater fuel delivery capacity.

Medium-pressure common rail injectors with pre-injection capability are used in the following engines:

· 1996 and later Californian 7.3L DIT

· 1997 and later 7.3L DITEconoline

· 1999 and later 7.3L DIT F-Series trucks

· 3126B Caterpillar engine

· DT-466 and D-530 series

The second-generation HEUI injector, also known as the digital control valve HEUI injector, was jointly developed by Siemens and IGC. This injector was subsequently used in the 6.0L VT-365 engine.

Its sophisticated injector design allows it to be used in four-valve engines, using less drive energy, offering faster response times, and the ability to control the fuel injection curve under all operating conditions.

HEUI-A Type Injector

This HEUI injector model has two external annular grooves to receive the supplied diesel fuel and high-pressure engine oil. Replaceable sealing rings are used to seal these grooves.

The upper set of sealing rings seals against any potential leakage of high-pressure engine oil. It consists of two sealing rings, a metal support ring, and a rubber sealing ring. The middle set of sealing rings isolates the high-pressure engine oil from the diesel fuel. The lower sealing ring seals against the diesel fuel. A copper gasket below seals against the high-pressure exhaust gases in the combustion chamber. Two bolts secure the injector. To remove the injector for inspection, simply loosen one of the bolts.

Note:

The high-pressure engine oil driving the injectors, typically reaching hundreds of kilograms, can cause oil leaks or even enter the diesel fuel tank if the sealing rings fail or are not installed correctly.

Both Type A and subsequent Type B two-stage injectors have four main components for fuel metering, timing, and injection profile control:

* **High-voltage solenoid coil:** This coil controls the movement of the control valve. The control voltage is 115 volts, and the current is 7-15 amps.

* **Oil control valve:** This valve controls the flow of high-pressure engine oil into the injector. When the valve is closed, high-pressure engine oil cannot enter the injector. Only when the valve is open can high-pressure engine oil enter the injector and push the pressure amplification piston to compress the diesel fuel.

* **Pressure amplification piston and plunger:** The pressure amplification piston amplifies the 33-200 kg oil pressure supplied to the injector. The top surface area of the pressure amplification piston is 7-8 times the bottom surface area. The hydraulic pressure of the high-pressure engine oil forces the diesel plunger downwards, compressing the diesel fuel and ultimately producing diesel fuel with a pressure amplified by 7-8 times.

• Nozzle Assembly: This nozzle is a non-electronic diesel injector. When the pressure exceeds its opening pressure, the needle valve is opened by hydraulic pressure and fuel injection begins. The nozzle opening pressure varies depending on the injector type.

Fuel injection steps for Type A injectors:

Filling process:

During this process, the oil control valve is not energized, and high-pressure oil cannot enter the injector. All internal components are in their static positions, with the plunger and pressure amplification piston at the top. The low-pressure fuel supply system supplies 2-5.5 kg of diesel fuel to the injector's inlet. At this time, the inlet check valve is raised, allowing fuel to enter the plunger chamber inside the injector. The internal pressure of the injector is equal to the diesel fuel inlet pressure, and the nozzle does not inject fuel.

Injection process:

During the injection process, current is applied to the corresponding solenoid coil. The corresponding oil control valve moves upward under the action of the armature, eventually opening the oil passage and simultaneously sealing the upper oil drain passage. This causes the high-pressure oil continuously entering the upper chamber of the piston, pushing the lower piston downward. The piston drives the diesel compression plunger downward, rapidly increasing the diesel pressure inside the plunger chamber and sealing the inlet check valve. Subsequently, as the pressure continues to rise, the high-pressure diesel fuel will open the needle valve and begin injection once it reaches the nozzle opening pressure, with peak diesel injection pressure reaching as high as 1600 kg. The Caterpillar system will have even higher injection pressures.

End of Injection Process:

With the removal of the driving current, the injector will cease injection. The electromagnetic force will no longer exist, and the oil control valve will return to its static position under the action of the return spring. At this point, the high-pressure oil supply to the injector will be cut off, while the upper oil drain passage will open. Oil in the injector's internal oil chamber will leak to the outside of the injector through the upper gap. The pressure amplification piston will return to its upper static position under the action of the return spring. The diesel plunger will also move upwards, and the negative pressure formed in the plunger chamber will open the diesel check valve. Under the action of the diesel inlet pressure, diesel will refill the plunger chamber, preparing for the next injection.

Determination of Injection Quantity:

The injection quantity is determined by the downward stroke of the diesel plunger. The following two variables will affect the plunger's downward stroke and thus the injector's fuel quantity:

· Injector solenoid coil energization time: The longer the energization time, the longer the downward stroke of the pressure amplification piston will be, pushing the diesel plunger a greater distance.

• Oil Pressure: The greater the hydraulic pressure applied to the pressure amplification piston, the longer the piston's downward stroke will be in the same amount of time, thus increasing the final fuel injection quantity.

Therefore, a longer coil energizing time and higher oil pressure will increase the fuel injection quantity. Similarly, decreasing oil pressure or shortening the coil energizing time will decrease the fuel injection quantity.

Note:

To avoid damaging the new injector after replacing it with a HEUI injector, the injector must be filled with oil before actuating it. This can be done by disconnecting the camshaft position sensor, starting the engine, and rotating it two revolutions.

Injection Timing:

The start and end times of fuel injection are controlled by the current applied to the solenoid coil. Injection timing is integrated into the ECU based on various engine operating conditions to determine engine performance and emissions.

Injection Rate Control:

Injection rate refers to how much fuel is injected into the cylinder per camshaft rotation.

Fuel injection rate control refers to the ability of a fuel system to adjust the injection rate during the injection process. Engine experts have found that adjusting the injection rate during injection can effectively improve emissions, fuel economy, power, and noise levels.

HEUI injectors have a unique advantage: the ability to easily change the fuel injection rate.

Because the pressure of the high-pressure oil can be controlled by the ECU, changing the oil pressure will change the injection rate. For example, higher oil pressure results in a faster injection rate compared to lower oil pressure. This is because higher oil pressure drives the pressure amplification piston downwards more quickly, increasing the amount of fuel injected per camshaft rotation.

Oil pressure and diesel pressure are also independent of engine speed. Whether at idle or engine speed, the output pressure of the high-pressure oil pump can be quickly changed by adjusting the oil pressure control valve.

Especially at idle, to reduce engine noise, the driving oil pressure will be lower. When the driver suddenly presses the accelerator pedal deeply, the high-pressure oil pressure will immediately be increased to the required higher pressure to provide a greater fuel injection quantity.

Note:

Engine oil quality is crucial for the effective operation of HEUI. An anti-foaming agent needs to be added to the engine oil used in HEUI systems to prevent foam formation. If there is air foam in the lubricating oil, it will affect injection pressure and injection timing, reducing fuel economy and causing engine power loss or difficulty starting.

HEUI-B Type

Advantages:

This type of HEUI injector is capable of injecting a smaller amount of fuel 8 to 10 degrees before the main injection. This advance injection is also called pre-injection. Due to pre-injection, the combustion chamber is preheated and pressurized before the main injection. This injection strategy reduces ignition delay and brings the following benefits:

Lower engine noise. Extensive evidence shows that longer ignition delays lead to increased engine noise, especially at idle. The high-temperature, high-pressure combustion chamber effectively reduces the time delay of fuel ignition after the main injection, thereby reducing engine vibration and noise.

Lower nitrogen oxide emissions. A shorter main injection ignition delay time postpones the start of main injection. As the main injection time is delayed, the peak combustion chamber pressure at the piston's pointing position is reduced, resulting in lower nitrogen oxide emissions.

Lower particulate emissions. Higher cylinder temperatures before the main injection fuel ignites ensure more complete combustion. This effectively reduces particulate emissions and improves fuel economy.

The working principle of the two-stage HEUI injector:

In mid-1999, Powerstroke, Caterpillar, and International vehicles all used the improved HEUI injector. The injector features design improvements in the plunger head and plunger sleeve inner wall to achieve this pre-injection control strategy.

First, a new oil passage was designed into the plunger sleeve inner wall to release the oil pressure inside the plunger chamber. The plunger has an annular groove with oil channels leading to the bottom of the plunger. As the plunger descends, when the plunger ring groove connects with the pressure relief passage on the plunger wall, the oil pressure inside the plunger cavity is instantly released. This causes the fuel injection to stop immediately. As the plunger continues to descend, when the ring groove on the plunger slides past the pressure relief port, the oil pressure inside the plunger cavity will be rebuilt, and fuel injection will resume.

Features:

The revolutionary new HEUI injector was used in the Powerstroke 7.3L and 6.0L engines launched in mid-2002. This new injector, called the G2 or Gen II medium-pressure common rail injector, features digital control valve technology.

This injector has two solenoid coils and one spool valve. Four pins provide each solenoid coil with a control current of 48 ft, 20 amps. This voltage is lower than other medium-pressure common rail injectors, yet the pulse width of the driving current for these two solenoid coils is only 800µs. Previous Type A and Type B medium-pressure common rail injectors required at least 500ms for the solenoid coils to generate sufficient electromagnetic force to close the control valve.

This significantly reduces the solenoid coil energizing time and allows the solenoid coils to operate at lower temperatures. More importantly, the design of the solenoid coils and spool valve allows for faster and more precise control of the injection quantity via electrical signals throughout the injection process.

This ability to edit the injection profile effectively reduces emissions without compromising engine performance and fuel economy. The new control valve design allows for a more compact injector design, enabling the use of a four-valve configuration in the engine.