3500 ENGINE CONTROL , ELECTRONIC UNIT INJECTION PART.2

ELECTRONIC CONTROL SYSTEM

This section of the presentation explains the 3500B Electronic Control
System including the following components:


- ECM
- Personality Module
- Electronic Unit Injector Solenoids
- Timing Wheel

Also covered are the following subsystems and related procedures:

- Timing control
- Fuel quantity control
- Speed control (governor)
- Cold modes
- Timing calibration.

ECM:

The Electronic Control Module (ECM) functions as the governor and fuel system computer. The ECM receives all the signals from the sensors and energizes the injector solenoids to control timing and engine speed.

The ECM is sealed except for access to the software which is contained in the Personality Module (next slide). This ECM is the second generation of Advanced Diesel Engine Management Systems and is often referred to as "ADEM II."
This ECM is used on all 3500B engines, including machine and industrial applications.

This ECM physically looks the same as the 3400 HEUI ECM. However, it is very different electrically in that the wave form (described later in the presentation) for the injectors has a different shape. Additionally, this ECM has no pump control valve output.

NOTE: The ECM has an excellent record of reliability. Therefore, any problems in the system are most likely to be in the connectors and wiring harness. In other words, the ECM should typically be the last item in troubleshooting.

Personality module contains software.

The Personality Module (shown here removed from the ECM) contains the software with all the fuel setting information (such as horsepower, torque rise and air/fuel ratio rates) which determines how the engine will perform. The Personality Module is installed on the lower face of the ECM, behind the access panel.

At this time, two methods can be used to update the software:

1. Remove and replace the Personality Module.
2. Flash Programming: Electronic reprogramming of the Personality Module.

NOTE: The ECM is sealed and needs no routine adjustment or maintenance. The Personality Module is mounted within the ECM.
Installation of the Personality Module is the only reason to enter the ECM. This operation would normally be performed during an ECM installation or a software update.

Fuel Injection

The 3500B EUI injector is very similar to the original 3500 EUI injector.
The injector is controlled electrically by the ECM. The signal from the ECM controls the opening and closing of the solenoid valve. The solenoid valve controls the flow of high pressure fuel to the cylinder. This system enables the ECM to control fuel volume and timing.

The 3500B injector now has bar and numerical codes marked on the tappet. The numerical code must be entered into the ECM using ET. Thepurpose of this code is to ensure that all injectors are matched as perfectly as possible in performance, both in timing and fuel quantity.

If an injector is replaced, moved to another position on the engine, or if two injectors are switched, then the injector codes must be reprogrammed.

The injector codes are programmed into the ECM using ET and the Calibrate Sensor Screen. Failure to enter the codes into a new ECM may result in unequal timing and fuel delivery between cylinders.

WARNING
The injector solenoids operate on 105 Volts direct current. Always remain clear of the injector area when the engine is running or electrical shock may occur.

Injector testing.

These tests can be used to determine which cylinder or injector is
malfunctioning:

INJECTOR SOLENOID TEST
This test is performed while the engine is stopped. The injector solenoids can be tested automatically with ET using the Injector Solenoid Test.
This function individually tests each solenoid in sequence and indicates if a short or an open circuit is present.

CYLINDER CUT-OUT (Manual test)
This test is performed while the engine is running at any speed.
The 105 Volt pulses can be individually cut out to aid in troubleshooting misfire problems in the injector and the cylinder.

AUTOMATIC CYLINDER CUT-OUT
This test is performed with ET while the engine is running at any speed.
The test makes a comparative evaluation of all injectors and numerically shows the results. The test enables an on-engine evaluation of the injectors. A satisfactory test of all injector solenoids without any diagnostic messages means that a problem is likely mechanical and in the cylinder.

(AUTOMATIC) MULTIPLE CYLINDER CUT-OUT
This test is performed with current engines and enables multiple cylinders to be cut-out simultaneously.

Fuel Injection Control System

This diagram shows the timing control logic within the ECM.
Engine speed and fuel quantity (which relates to load) inputs are received by the timing control. These combined inputs determine the start of fuel injection.

The timing control provides the optimum timing for all conditions. The benefits of a "smart" timing control are:

- Reduced particulates and lower emissions
- Improved fuel consumption while still maintaining performance
- Extended engine life
- Improved cold starting.

Fuel quantity control

Three inputs control fuel quantity:

1. Engine speed
2. Throttle position
3. Boost.

These signals are received by the electronic governor portion of the ECM.
The governor then sends the desired fuel signal to the fuel injection control. The electronic governor also receives signals from the fuel ratio control and torque control.

Two variables determine fuel quantity and timing:

- The start of injection determines engine timing.
- The injection duration determines the quantity of fuel to be injected.

Speed/timing sensor

The Speed/Timing Sensor serves three basic functions in the system:

1. Engine speed measurement
2. Engine timing measurement
3. Cylinder identification and TDC location.

The Speed/Timing Sensor is mounted on the rear housing below the timing wheel. This sensor is self-adjusting during installation and has zero clearance with the timing wheel.

The sensor head is extended prior to installation. The action of screwing in the sensor pushes the sensor head back into the body when the head contacts the timing wheel. This contact is momentary while the engine is starting. After initial start-up, the head runs with zero clearance.

Speed/timing sensor

The Speed/Timing Sensor (left rear of engine) measures engine speed for governing and crankshaft position for timing purposes and cylinder identification.

The ECM supplies 12.5 ± 1 Volts to the Speed/Timing Sensor. Connector pins A and B transmit the common power supply to the sensor.

The C connector pin transmits the signals from the sensor to the ECM.

NOTE: The Speed/Timing Sensor has a dedicated power supply. No other circuits should be spliced into this power supply.

Timing wheel and speed/timing sensor.

The Timing Wheel is indexed with a drilled hole which is mated to a dowel on the camshaft. This dowel locates the wheel in the correct position on the camshaft relative to the crankshaft.

As previously stated, the Timing Wheel has a total of 24 teeth. 21 teeth are large with small spaces between them (80/20 relative size). The other three teeth and spaces have equal dimensions (50/50 relative size). This configuration is used by the ECM as a reference point for determining the position of the engine for fuel timing.

The Speed/Timing Sensor can identify the equal size teeth because they create a different signal pattern than the other teeth.

NOTICE
The head of the sensor MUST NOT be positioned in the wide timing wheel slots during installation. Incorrect positioning will cause damage to the sensor head.

Sensor generates a PWM signal from timing wheel teeth

The Speed/Timing Sensor is positioned over the circumference of the teeth.

The teeth and sensor generate a Pulse Width Modulated (PWM) signal for the purpose of timing and a frequency modulated output for speed measurement..

Cranking

The Speed/Timing Sensor uses the timing wheel with the teeth arranged as shown to initially determine:

- Top Dead Center No. 1 (When found, the cylinders can be identified.)
- Engine speed

The sequence of signals shown in the second column (PWM duty cycle) is analyzed by the ECM. At this point, no fuel will be injected until certain conditions have been met.

After pattern recognition

During start-up, the sensor initially monitors the pulses created by the passing teeth and identifies the sequence as shown. After a complete rotation, the control can recognize the location of TDC from the pattern in the above illustration.

During initial cranking, no fuel is injected until:

* The Timing wheel has completed a revolution (the sensor has read the three 50/50 teeth).

* TDC for all cylinders is identified by the control.

* After the sensor has provided the necessary signals, the ECM is ready to start injection

NOTE: The reference points in the illustration are positions on the timing wheel from which the control measures the point of injection and TDC.

Normal operation

During normal operation, the ECM can determine timing (assumed TDC) from the cylinder reference point for each cylinder. The actual TDC is stored by the ECM after calibration is performed.

Injection timing is calibrated by connecting a TDC probe to the service access connector on the engine harness, and by activating the calibration sequence with the Caterpillar ET service tool. The ECM raises the engine speed to 800 rpm (to optimize measurement accuracy), compares the actual No. 1 TDC location to the assumed cylinder No. 1 TDC location, and saves the offset in the EEPROM (Electrically Erasable Programmable Read Only Memory).

NOTE: The calibration offset range is limited to ± 7 crankshaft degrees. If the range is exceeded, the offset is set to zero (no calibration) and a calibration diagnostic message is generated

Timing calibration sensor

The Timing Calibration Sensor (magnetic pickup) is installed in the flywheel housing during calibration. The connector is located above the ECM. (On some machines, i.e. D11 Tractor, the sensor is permanently installed.)

Using the Caterpillar ET service tool, timing calibration is accomplished automatically for both sensors when selected on the appropriate screen.

The desired engine speed is set to 800 rpm. This rpm setting is performed to avoid instability and ensure that no backlash is present in the timing gears during the calibration process. Also, the system has a repeatable point for improved calibration accuracy.

Timing calibration

As the Speed/Timing Sensor uses the timing wheel for a timing reference, timing calibration improves fuel injection accuracy by correcting for any slight tolerances between the crankshaft, timing gears and timing wheel.

During calibration, the offset is saved in the ECM EEPROM (Electrically Erasable Programmable Read Only Memory). The calibration offset range is limited to ± 7 crankshaft degrees. If the timing is out of range, calibration is aborted. The previous value will be retained and a diagnostic message will be logged.

The timing must be calibrated after performing the following procedures:

1. ECM replacement

2. Speed/timing sensor replacement

3. Timing wheel replacement

4. Camshaft, crankshaft or gear train replacement.

Unit injector current flow

This illustration shows how the current increases initially to pull in the injection coil and close the poppet valve. Then, by rapidly chopping (pulsing) the 105 Volts on and off, current flow is maintained. The end of injection occurs when the current supply is cut off and fuel pressure drops rapidly in the injector.

Cold modes

The EUI fuel system is designed to modify its operational characteristics during cold conditions. This modification is done to protect the environment and to improve the operational characteristics of the engine.

A feature which was introduced with the 3500B is the Cold Mode Cutout. This feature activates when the engine is at low speed, load and temperature. As each individual cylinder is cut out, the ECM looks at the fuel rate measurement. If the fuel rate does not increase, the ECM assumes that this cylinder is not firing.

To protect the dead cylinder from the effects of fuel washing down the piston and liner, the ECM leaves the cylinder in the cutout condition. The ECM now goes to the No. 2 cylinder and repeats the process. After the last cylinder is checked, the ECM goes to cylinder No. 1 and starts again.

The engine may appear to misfire during the process, but this condition is normal. Checking the active faults with the engine running will verify that no electrical faults are present.

This function is turned off when the throttle is opened more than 25%, coolant temperature is above 60°C or if the engine speed is above 1300 rpm.

Fuel system limits

Just as earlier engines had mechanical limits to determine maximum fuel delivery during full load, full torque and acceleration, the EUI system has electronic limits to protect the engine. These limits are:

- Maximum Horsepower
- Torque Limit (Determines torque rise characteristics)
- Fuel Ratio Control (Limits fuel until sufficient boost is available)
- Cold Mode Limit (Limits fuel with cold engine to control white smoke)
- Cranking Fuel Limit (Limits fuel during cranking)

An acceleration delay during start-up holds the engine at low idle for two seconds or until the oil pressure reaches 140 kPa (20 psi).

Off-highway Trucks have a system which increases engine horsepower in direct drive only. This system protects the drive line from excessive torque in the lower gears. The feature can be overridden with ET when dynamometer testing.

Off-highway Trucks also have a service tool programmable feature which is designed to lower shift points and the fuel limit to improve fuel consumption at the customer's request.

Fuel system derates

As the system limits fuel for every condition, derates are also built into the system for protection. These derates are individually covered later in the presentation, but are summarized here:

- Automatic Altitude Compensation (Altitude derate)
- Automatic Filter Compensation (Derates for air filter restriction if installed)
- Engine Warning Derate for the following conditions: Low oil pressure.
- High coolant temperature High exhaust temperature
- High and low boost.

If a loss of boost sensor output occurs, the ECM assumes zero boost pressure. Although not strictly a derate, power is reduced by approximately 50 to 60%.

FUEL SUPPLY SYSTEM
This portion of the presentation describes the operation of the EUI Fuel Supply System as used on the 3500B engines in machine applications.

Fuel Supply Circuit

The system illustrated is for a 3516B in the 793C truck. Other systems may vary according to the application.

Fuel is drawn from the tank through a fuel heater (if equipped) and through the primary fuel filter to the fuel transfer pump. Fuel from the transfer pump flows through the ECM for cooling purposes. From the ECM, the fuel flows through the secondary fuel filters.

Fuel from the fuel filter base flows to the fuel injectors in the cylinder heads. Return fuel from the injectors flows through the fuel pressure regulator and the fuel heater before returning to the fuel tank.

The fuel heater utilizes the hot return fuel from the engine to heat the incoming fuel passing through the filters. The heater prevents plugging of the filters in extremely cold conditions.

The Oil Renewal System is controlled by the engine ECM. A small amount of engine oil flows from the engine block to the oil renewal injector manifold. The oil flows from the oil renewal injector manifold into the return side of the fuel pressure regulator. The engine oil mixes with the fuel in the return line. It then flows to the tank. The combined oil and fuel mixture circulates back to the injectors to be burned with the fuel. It should be noted, however, that the ratio of oil to fuel is quite low.
This circuit is more fully described later under Application Specific Systems.
NOTICE
All current 3500 engines are equipped with two micron secondary filters. This requirement is common with most high pressure fuel systems. Failure to meet the two micron filter requirement will result in less than expected life for the injectors.

Fuel Supply Components

The fuel transfer pump (1) is driven by the front gear train.

The fuel transfer pump contains a bypass valve (2) to protect the fuel system components from excessive pressure. The bypass valve setting is higher than the setting of the fuel pressure regulator (next slide).

Fuel flows from the transfer pump through the ECM and the secondary fuel filters located on the left side of the engine.

Fuel system components

Fuel flows from the fuel filter base through the steel tubes (1) to the fuel injectors. Return fuel from the injectors flows through the Fuel Pressure Regulator (2) before returning to the fuel tank.

Fuel system pressure is controlled by the Fuel Pressure Regulator. This valve is set at 415 to 450 kPa (60 to 65 psi).

The valve is positioned downstream of the fluid manifold fuel passages and the injectors. Fuel which passes through the valve is returned to the fuel tank. The fuel lines from both fuel passages in the manifolds are joined at the regulating valve.

Fuel pressure can be checked at the Fuel Pressure Regulator Valve by removing a plug and connecting a gauge.

MUI and EUI installation differences

This slide shows the difference between the Mechanical Unit Injection (MUI) and current Electronic Unit Injection (EUI) installation in the cylinder head.

Notice the Helper Spring on the injector pushrod. This arrangement is designed to keep the follower in constant contact with the camshaft. The helper spring is required due to the increased injection pressures of
151 MPa (22,000 psi) and the steeper, high lift camshaft lobe profile.

Unit injector fuel supply
This view shows the injector and its fuel supply circuit. A larger volume of fuel passes through the injector than is required for injection. This extra flow is used to cool the injector, which is also surrounded by coolant.

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