Fuel System C7 and C9 - Caterpillar Electronic Engine

Fuel System C7 and C9 Industrial Engine




(1) Oil pump
(2) Hydraulic electronic unit injectors
(3) Oil filter
(4) Oil cooler
(5) High-pressure oil
(6) Fuel
(7) Connector for the Injection Actuation Pressure Control Valve (IAPCV)
(8) Unit injector hydraulic pump
(9) Sensor for the Injection Actuation Pressure (IAP)
(10) Fuel filter
(11) Primary fuel filter and water separator
(12) Fuel tank
(13) Camshaft gear
(14) Speed/Timing sensors
(15) Electronic Control Module (ECM)
(16) Battery
(17) Fuel pressure regulator
(18) Boost pressure sensor
(19) Oil pressure sensor
(20) Coolant temperature sensor
(21) Throttle position sensor
(22) Inlet air temperature sensor
(23) Atmospheric pressure sensor
(24) Air inlet heater

Introduction
The operation of the Hydraulic Electronic Unit Injector fuel system is different from any other fuel system that is actuated mechanically. The HEUI fuel system is free of adjustment. Adjustments to the components that are mechanical cannot be made. Changes in performance are made by installing different software in the Electronic Control Module (ECM). This fuel system consists of four basic components:
-Hydraulic Electronic Unit Injector (HEUI)
-Electronic Control Module (ECM)
-Unit injector hydraulic pump
-Fuel transfer pump

Component Description
Hydraulic Electronic Unit Injector (HEUI)

-The fuel system utilizes a hydraulically actuated electronically controlled unit injector.
-All fuel systems for diesel engines use a plunger and barrel in order to pump fuel under high pressure into the combustion chamber.
-The HEUI uses engine oil under high pressure in order to power the plunger. The HEUI uses engine lubrication oil that is pressurized from 6 MPa (870 psi) to 28 MPa (4061 psi) in order to pump fuel from the injector. The high-pressure oil is called the injection actuation pressure. The HEUI operates in the same way as a hydraulic cylinder in order to multiply the force of the high-pressure oil. This multiplication of pressure is achieved by applying the force of the high-pressure oil to a piston. The piston is larger than the plunger by approximately six times. The piston that is powered by engine lubrication oil under high pressure pushes the plunger. The actuation pressure of the oil generates the injection pressure that is delivered by the unit injector. Injection pressure is greater than actuation pressure of the oil by approximately six times.
-Low actuation pressure of the oil results in low injection pressure of the fuel. High actuation pressure of the oil results in high injection pressure of the fuel.

Electronic Control Module (ECM)
-The ECM is located on the left side of the engine. The ECM is a powerful computer that provides total electronic control of engine performance. The ECM uses data from engine performance that is gathered by several sensors. The ECM uses this data in order to adjust the fuel delivery, injection pressure, and injection timing. The ECM contains programmed performance maps (software) in order to define horsepower, torque curves, and rpm.
-The ECM logs faults of engine performance. The ECM is also capable of running several diagnostic tests automatically when the ECM and Caterpillar Electronic Technician (ET) are used together.

Unit Injector Hydraulic Pump

-The unit injector hydraulic pump is a variable delivery piston pump. The unit injector hydraulic pump uses a portion of the engine lubrication oil. The unit injector hydraulic pump pressurizes the engine lubrication oil to the injection actuation pressure that is required in order to power the HEUI injectors.

Fuel Transfer Pump
The fuel transfer pump is mounted on the back of the unit injector hydraulic pump. The fuel transfer pump is the only serviceable part of the unit injector hydraulic pump. The fuel transfer pump is used in order to draw fuel from the fuel tank . Also, the fuel transfer pump is used in order to pressurize the fuel to 450 kPa (65 psi). The fuel transfer pump has an internal relief valve in order to protect the system. The pressurized fuel is supplied to the injectors.

Injection Actuation Pressure Sensor (IAP)
The IAP Sensor monitors injection actuation pressure. The IAP Sensor sends a continuous voltage signal back to the ECM . The ECM interprets the signal. The ECM is aware of the injection actuation pressure at all times. The ECM analyzes the voltage from the sensor. The ECM then adjusts the current to the solenoid.

HEUI Fuel System
Low Pressure Fuel System


(2) Hydraulic electronic unit injector
(8) Unit injector hydraulic pump
(11) Secondary fuel filter
(12) Fuel tank
(17) Fuel pressure regulator
(25) Fuel transfer pump
(24) Primary fuel filter and water separator

The low-pressure fuel system serves two functions. The low-pressure fuel system supplies fuel for
combustion to injectors. The low-pressure fuel system also supplies excess fuel flow in order to remove air from the system. The low-pressure fuel system consists of five basic components:
-Fuel tank
-Primary fuel filter/water separator
-Two micron secondary fuel filters
-Fuel transfer pump
-Fuel pressure regulator

Fuel is drawn from the fuel tank and flows through a 13 micron primary fuel filter/water separator. The primary fuel filter/water separator removes large debris from the fuel. The primary filter element also separates water from the fuel. The water is collected in the bowl at the bottom of the primary fuel filter/water separator.

Fuel flows from the primary fuel filter/water separator to the inlet side of fuel transfer pump. Fuel flows from the inlet port in the pump to the outlet port. Pressurized fuel flows from the outlet port of the pump to the 2 micron secondary fuel filter. A two micron secondary fuel filter is standard on all Caterpillar engines. These fuel filters are high efficiency. This filter removes small abrasive contaminants from the fuel. The primary fuel filter/water separator will not trap these small contaminants. Small abrasive particles in the fuel cause abrasive deterioration of the unit injectors. The secondary fuel filter removes particles in the size of 2 microns in size or particles that are greater than 2 microns in size. The use and regular maintenance of this 2 micron filter will provide a significant improvement in injector life.

Fuel flows from the 2 micron secondary filter to the fuel supply passage in the cylinder head. The fuel supply passage is a drilled hole which begins at the front of the cylinder head. The fuel supply passage extends to the back of the cylinder head. This passage connects with each unit injector bore in order to supply fuel to unit injectors. The excess fuel flows out of the back of the cylinder head. The fuel flows into the fuel pressure regulator.

The fuel pressure regulator consists of an orifice and a check valve that is spring loaded. The orifice is a flow restriction that pressurizes the supply fuel. The check valve that is spring loaded will open at 35 kPa (5 psi) in order to allow the fuel that has flowed through the orifice to return to the fuel tank. When the engine is off, there is no fuel pressure that is acting on the check valve. With no fuel pressure on the check valve, the check valve will close. The check valve will close in order to prevent the fuel that is in the cylinder head from draining back to the fuel tank.

Injection Actuation System
Actuation Oil Flow

(1) Engine oil pump
(3) Oil filter
(4) Oil cooler
(5) High-pressure oil
(8) Unit injector hydraulic pump

The injection actuation system serves two functions. The injection actuation system supplies high-pressure oil in order to power the injectors. Also, the injection actuation system regulates the injection pressure that is produced by the unit injectors by changing the actuation pressure of the oil.
The injection actuation system consists of four basic components:
-Engine oil pump
-Engine oil filter
-Unit injector hydraulic pump
-Injection actuation pressure sensor (IAP Sensor)

Oil that is drawn from the sump is pressurized to the lubrication system oil pressure by the engine oil pump. Oil flows from the engine oil pump through the engine oil cooler, through the engine oil filter, and then to the main oil gallery. A separate circuit from the main oil gallery directs a portion of the lubrication oil in order to supply the unit injector hydraulic pump. A steel tube on the left side of the engine connects the main oil gallery with the inlet port of the unit injector hydraulic pump. The connection point is the top port of the manifold on the engine side cover.

Oil flows into the inlet port of the unit injector hydraulic pump and the oil fills the pump reservoir. The pump reservoir provides oil to the unit injector hydraulic pump during start-up. Also, the pump reservoir provides oil to the unit injector hydraulic pump until the engine oil pump can increase pressure.

Oil from the pump reservoir is pressurized in the unit injector hydraulic pump. Then the oil is pushed out of the outlet port of the pump under high pressure. Oil then flows from the outlet port of the unit injector hydraulic pump to the high-pressure oil passage in the cylinder head.

Actuation oil that is under high-pressure flows from the unit injector hydraulic pump through the cylinder head to all of the injectors. Oil is contained in the high-pressure oil passage until the oil is used by the unit injectors. Oil that has been exhausted by the unit injectors is expelled under the valve covers. This oil returns to the crankcase through oil drain holes in the cylinder head.

Actuation Oil Pressure Control


(27) Control valve solenoid
(28) Poppet valve
(29) Armature
(30) Actuator spring
(31) Sliding sleeve
(32) Actuator piston
(33) Eccentric drive plate
(34) Idler
(35) Spill port
(36) Pump outlet ports
(37) Drive gear
(38) Check valve
(39) Piston

The unit injector hydraulic pump is a variable delivery piston pump. The variable piston pump uses an angled drive plate which rotates. The pistons do not rotate. The pistons move in relation to the angled drive plate. The pistons move in the sliding sleeves.

The unit injector hydraulic pump is driven by the gear train on the front of the engine. The drive gear on the front of the pump turns the common shaft. The angled drive plate is mounted on the common shaft. The rotation of the angled drive plate causes the pump piston to move in and out within the sliding sleeves.

As the pistons move out of the sliding sleeves, oil is drawn into the inside of the pistons through the passage in the drive plate. Oil is forced out of the piston when the piston is pushed back into the sliding sleeve and the ports are exposed.

Changing the relative position of the sliding sleeve to the spill port changes the volume of oil in the piston. The location of the sliding sleeve is continuously changing. The location of the sliding sleeve is determined by the ECM. Changing the location of the sliding sleeves changes the flow of the pump. The result is the amount of oil that can be pressurized.

The pressure of the injection actuation system is controlled by matching pump outlet flow and pressure demand for the injection actuation system. The position of the sliding sleeves is changed in order to control the pump outlet flow. Moving the sleeves to the left covers the spill port for a longer distance. This increases effective pumping stroke and pump outlet flow. Moving the sleeves to the right covers the spill ports for a shorter distance which reduces the effective pumping stroke. This movement also reduces the pump outlet flow.

The sliding sleeves are connected by an idler. One sleeve is connected to an actuator piston. Moving the actuator piston right or left causes the idler and sleeves to move the same distance to the right or to the left.

Control pressure is determined by the amount of current from the ECM to the solenoid. A small amount of pump outlet flow goes through a small passage in the actuator piston. This small amount goes out of an orifice and into the control pressure cavity. The pressure in this cavity is limited by a small poppet valve. The opening of the poppet valve allows a portion of the oil in the cavity to flow to drain. A force holds the poppet valve closed. This force on the poppet valve is created by a magnetic field that acts on an armature. The strength of the magnetic field determines the required pressure in order to overcome the force of the actuator spring.

An increase of current to the solenoid causes an increase to the following items:
-The strength of the magnetic field
-The force on the armature and poppet valve
-The control pressure which causes the actuator piston to move to a position that results in more flow
A reduction of current to the solenoid causes a reduction to the following items:
-The strength of the magnetic field
-The force on the armature and poppet valve
-The control pressure which causes the actuator piston to move to a position that results in less flow

The ECM monitors actuation pressure. The ECM constantly changes current to the pump control valve in order to control actuation pressure. Three components work together in a closed loop circuit in order to control actuation pressure:
-ECM
-Sensor for the Injection Actuation Pressure (IAP)
-Pump control valve
The closed loop circuit works in the following manner:
-The ECM determines a desired actuation pressure by gathering information from sensor inputs and
software maps.
-The ECM monitors actual actuation pressure through a constant signal voltage from the IAP sensor.
-The ECM constantly changes control current to the pump control valve. This changes the pump outlet flow.

There are two types of actuation pressure:
-Desired actuation pressure
Desired actuation pressure is the injection actuation pressure that is required by the system for optimum engine performance. The desired actuation pressure is established by the performance maps in the ECM. The ECM selects the desired actuation pressure. The selection is based on the signal inputs from many sensors. The ECM is getting signal inputs from some of the following sensors: throttle position sensor, boost pressure sensor, speed-timing sensors and coolant temperature sensor . The desired actuation pressure is constantly changing. The change is based on various signal inputs. The changing engine speed and engine load also cause the desired actuation pressure to change. The desired actuation pressure is only constant under steady state conditions (steady engine speed and load).
-Actual actuation pressure
Actual actuation pressure is the actual system pressure of the actuation oil that is powering the injectors. The ECM and the pump pressure regulator are constantly changing the amount of pump outlet flow. This constant changing makes the actual actuation pressure equal to the desired actuation pressure.

Pump Control Valve Operation
The pump control valve has the following three stages:
-Valve operation (engine off)
When the engine is off, there is no pump outlet pressure and no current to the control valve solenoid. The actuator spring pushes the actuator piston completely to the left. The idler which is not shown and the sliding sleeves are moved to the left also, the pump is in the position of maximum output.
-Valve operation (cranking the engine)
During engine start-up, approximately 6 MPa (870 psi) of injection actuation pressure is required in order to activate the unit injector. This low injection actuation pressure generates a low fuel injection pressure of about 35 MPa (5000 psi). This low fuel injection pressure aids cold starting.
In order to start the engine quickly, the injection actuation pressure must rise quickly. Because the unit injector hydraulic pump is being turned at engine cranking speed, pump flow is low. The ECM sends a strong current to the control valve solenoid in order to keep the poppet valve closed. With the poppet valve in the closed position, all of the flow to the drain is blocked. The hydraulic forces that act on each side of the actuator piston are equal. The actuator spring holds the actuator to the left. The pump produces maximum flow until the 6 MPa (870 psi) desired pressure is reached. Now, the ECM reduces the current to the pressure regulator solenoid in order to reduce control pressure. The reduced control pressure allows the actuator piston to move to the right. This movement reduces pump outlet flow in order to maintain the 6 MPa (870 psi) desired pressure.

Note: If the engine is already warm, the pressure that is required to start the engine may be higher than 6 MPa (870 psi). The values for the desired actuation pressures are stored in the performance maps of the ECM. The values for desired actuation pressures vary with engine temperature.
Once the unit injectors begin to operate, the ECM controls the current to the control valve. The ECM and the control valve solenoid will maintain the actuation pressure at 6 MPa (870 psi) until the engine starts. The ECM monitors the actual actuation pressure through the IAP Sensor that is located in the high-pressure oil manifold. The ECM establishes desired actuation pressure by monitoring several electrical input signals and the ECM sends a predetermined current to the control valve solenoid. The ECM also compares the desired actuation pressure to the actual actuation pressure in the high-pressure oil passage. The ECM adjusts the current levels to the control valve solenoid in order to make the actual actuation pressure equal to the desired actuation pressure.

-Valve operation (running engine)
Once the engine starts, the ECM controls the current to the pump control valve in order to maintain the desired actuation pressure. The IAP Sensor monitors the actual actuation pressure in the high-pressure oil passage in the cylinder head. The ECM compares the actual actuation pressure to the desired actuation pressure 67 times per second. The ECM adjusts the current levels to the pump control valve when the actual actuation pressure and the desired actuation pressure do not match. These adjustments make the actual injection actuation pressure equal to the desired injection actuation pressure.
-Oil Flow (engine running)
A small amount of pump outlet flow flows through the actuator piston and into the control pressure cavity. Control pressure increases and the increased pressure unseats the poppet valve. The open poppet valve allows flow to the drain. The ECM changes control pressure by increasing or reducing the current to the control valve solenoid and resultant force on the poppet.

The following items create a closed loop system:
-ECM
-IAP
-Pressure Regulator

This closed loop system provides infinitely variable control of pump outlet pressure. This pump outlet pressure has a range from 6 MPa (870 psi) to 28 MPa (4061 psi).



Read More:
Hydraulic Electronic Unit Injector (HEUI) Components
Fuel System C15, C16, and C18 - Caterpillar Electronic Engine 
Unit Injector C11 and C13 - Caterpillar Electronic Engine
Fuel System C11 and C13 - Caterpillar Electronic Engine





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