G3600 A4 Engines System Overview Caterpillar

System Overview

Ambient Based Rating

The ambient based rating feature provides flexibility for Separate Circuit Aftercooler (SCAC) temperature, so the engine is NOT shutdown for reaching temperatures exceeding the purchased rating. The air/fuel ratio and load factor are automatically adjusted based on the SCAC temperature.

Ambient based rating feature:

  • Load calculation, load limiting, and fuel correction factor are a function of the Intake Manifold Air Temperature (IMAT).

  • Ambient based rating is enabled by default on all 32C and 43C software and cannot be disabled in Cat® Electronic Technician (ET).

Control System

The following components are included in the control system:

  • An Electronic Control Module (ECM) and an emergency stop button in an engine-mounted junction box

  • Optional remote control panel with either an Operator Control Panel (OCP) or Human Machine Interface (HMI)

  • Integrated Sensing Module (ISM)

  • Fuel metering valve

  • Gas Shutoff Valve (GSOV)

  • Ignition system that is controlled by the ECM

  • Detonation sensor for each two cylinders

  • A system for prelube or postlube that includes a solenoid and prelube pump

  • Actuators that are hydraulically actuated and electronically controlled for the air choke and the exhaust bypass (wastegate)

  • A system for cranking that includes the solenoid and starting motor

  • Air/Fuel pressure module (G3616)

The ECM controls most of the functions of the engine. The module is an environmentally sealed unit that is in an engine-mounted junction box. The ECM monitors various inputs from sensors to activate relays, solenoids, and so on, at the appropriate levels. The ECM supports the following five primary functions:

  • Governing of the engine

  • Control of ignition

  • Air/fuel ratio control

  • Start/stop control

  • Monitoring of engine operation

The ECM does not have a removable personality module. The software and maps are changed by using the Cat ET to flash program a file.

Governing of the Engine RPM

Desired engine speed is determined by these factors: status of the idle/rated switch, status of the desired speed input (analog voltage, 4 mA to 20 mA, or CAN) and of parameters that are programmed into the software. Actual engine speed is detected via a signal from the engine speed/timing sensor. Parameters such as idle speed and governor gain can be programmed with Cat ET, but the governor gain should not be programmed.

The ECM monitors the actual engine speed. The ECM calculates the difference between the actual engine speed and the desired engine speed. The ECM controls the fuel metering valve to maintain the desired engine speed. The fuel metering valve is located in the gas line after the GSOV.

If actual engine speed is less than desired engine speed, the ECM commands the fuel metering valve to move toward the open position to increase the fuel flow. The increase of fuel accelerates the engine speed.

The speed governor gain adjustments Proportional (P) and Integral (I) are available in Cat ET. The speed governor gain adjustment Derivative (D) does not exist in the software.

The air/fuel ratio control gains adjustment is not available in Cat ET for Adem 4 (A4) controlled engines.

G3606, G3608, and G3612

The fuel flow is controlled by the desired air/fuel ratio until 500 rpm.

  • The airflow is calculated using the engine speed, IMAT, and Intake Manifold Air Pressure (IMAP).

  • The desired fuel flow is calculated based on the airflow and desired air/fuel ratio.

The speed governor turns on at 500 RPM.

  • The speed difference drives change to the desired fuel flow.


The fuel metering valve is in a fixed position until 250 RPM.

The speed governor turns on at 250 RPM.

  • The speed difference between the actual speed and the desired speed drives the change in the fuel metering valve position.

Control of Ignition

Each cylinder has an ignition transformer. To initiate combustion, the ECM sends a pulse of approximately 108 V to the primary coil of each ignition transformer. The pulse is sent at the appropriate time and for the appropriate duration. The transformer increases the voltage which creates a spark across the spark plug electrode.

The ECM provides variable ignition timing that is sensitive to load, speed, and detonation. Detonation sensors monitor the engine for excessive detonation. The engine has one detonation sensor for each two adjacent cylinders. The sensors generate data on vibration that is processed by the ECM to determine detonation levels. If detonation reaches an unacceptable level, the ECM retards the ignition timing of the whole engine. If retarding the timing does not limit detonation to an acceptable level, the ECM shuts down the engine.

Levels of detonation can be displayed by the OCP or HMI on the optional control panel. Alternatively, the "Cylinder X Detonation Level" screen of Cat ET can also be used. The "X" represents the cylinder number.

An Ignition Multi-Strike feature is an option that is programmable. The Ignition Multi-Strike feature must be activated by a AVSpare dealer.

The ECM provides extensive diagnostics for the ignition system.

Air/Fuel Ratio Control

The ECM provides control of the air/fuel mixture for performance and for efficiency at low emission levels. The system includes the following components: maps in the ECM, output drivers in the ECM, fuel metering valve, air choke actuator, exhaust bypass actuator (wastegate), and ISM. Illustrations 1 and 2 are diagrams of the system main components and of the system lines of communication.

Illustration 1g03789900
G3606 and G3608

Illustration 2g03795220
G3612 and G3616

The desired air/fuel ratio is based on maps that are stored in the ECM. The maps are specific for different applications, for engine speeds, and for engine loads.

The engine load is calculated from the fuel flow. The load calculation starts at 500 rpm and the load reads zero below 500 rpm.

Note: The calculated engine load varies. Several variables affect the calculated engine load, including timing, settings for emissions, fuel quality, and specific gravity of the fuel.

G3606, G3608, and G3612

The volume of fuel that is consumed by combustion is calculated by the TecJet measuring the following conditions:

  • Fuel inlet pressure

  • Fuel temperature

  • TecJet differential pressure


The volume of fuel that is consumed by combustion is calculated by measuring the following conditions:

  • Pressure differential between the fuel manifold and the inlet air manifold

  • Temperature of the fuel to the cylinder

  • Engine rpm

The system has three modes of operation for the air/fuel ratio:

  • Start-up mode (fixed actuator positions)

  • NOx feedback disabled mode (open loop and prechamber calibration operates in this mode)

  • NOx feedback enabled mode (closed loop NOx control)

The relationship of the modes of operation to the speed and load and the transitions between the modes are represented in Illustrations 3 and 4.

The modes of operation are explained in more detail below.

Illustration 3g03807798
G3606, G3608, and G3612

Illustration 4g03808256

  • The NOx feedback enabled mode and air system initialization thresholds have high and low speed (and high/low load for NOx feedback) values. If the high threshold is crossed, they remain active even if speed drops below the high threshold, until the low threshold is crossed. The area between the low and high thresholds is called the hysteresis band, and it prevents the controls from switching on and off rapidly during small engine speed/load fluctuations. The hysteresis band on the A4 has a wider range than on the A3.

  • The air system becomes active at 500 rpm for the G3606, G3608, and G3612, and the air system becomes active at 700 rpm for the G3616.

  • The green region in Illustration 3 shows the NOx feedback/No feedback hysteresis band on the G3606, G3608, and G3612. The brown region in Illustration 4 hysteresis band for all 3 modes on G3616.

  • The upper left hashed region is based on the recommended 30 percent maximum startup load.

  • In the "Start-up" mode, the choke and wastegate actuator positions are fixed. The choke position is set to value in Cat ET and the wastegate position is fixed by the software. The start-up wastegate position cannot be changed like in the A3 software.

  • In the NOx feedback disabled mode (open loop), air/fuel ratio is controlled to desired value in map. This is a function of the IMAT, speed, and load.

  • In the NOx feedback enabled mode, air/fuel ratio is trimmed until the NOx sensor reading matches the set point in Cat ET via the fuel correction factor.

  • If the engine enters the hysteresis band below 40 percent load, the desired NOx target is scaled up by 10 ppm per 10 percent load. For example, if the Cat ET set point is 50 ppm, at 30 percent load the controller will target 60 ppm.

Combustion burn time - The combustion burn time is measured in each cylinder. Each cylinder has a combustion sensor. The pulse of the ignition starts a timer in the ISM. The flame travels in the cylinder from the spark plug to the combustion sensor. The ISM monitors the voltage across the combustion sensor. When the flame reaches the combustion sensor, the ionization that surrounds the sensor changes the voltage. When the ISM detects the change of the sensor voltage, the ISM stops the timer. The combustion burn time is a method of measuring the air/fuel ratio. A rich air/fuel mixture provides a faster combustion burn time. A lean air/fuel mixture provides a slower combustion burn time.

Prechamber calibration mode - This mode can be activated with Cat ET. This mode can be activated during operation at any load. The mode is used for adjustment of the precombustion chamber needle valves to balance the cylinders. In the prechamber calibration mode, the fuel correction factor is maintained at 100 percent. After an exit from this mode, the fuel correction factor is adjusted to achieve the desired NOx emissions.

Crankcase pressure calibration - The crankcase pressure calibration procedure is used to set the high crankcase pressure trip point within the programmable monitoring system. While the calibration is running, the engine ECM is sampling local current atmospheric and crankcase pressure. After the calibration procedure is complete, the ECM will have determined the average baseline crankcase pressure reading. The engine software will then add an extra 0.5 kPa (0.073 psi) to the baseline number to achieve the trip point for high crankcase pressure within the programmable monitoring system.

Start/Stop Control

The ECM contains the logic and the outputs for control of engine prelubrication, of starting, of shutdown, and of postlube. The customer programmable logic responds to signals from the following components: engine control switch, emergency stop switch, remote start switch, data link, and other inputs.

To control the engine at the appropriate times, the ECM provides +Battery voltage to the solenoids that control these components: prelube pump, starting motor and the gas shutoff valve.

When the programmable logic determines that the prelubrication function is necessary, the ECM supplies +Battery voltage to the solenoid for the prelube pump. The prelubrication must develop sufficient engine oil pressure before the engine will crank. The engine has a pressure switch for the prelube. When the engine oil pressure is sufficient, the pressure switch closes. The engine will crank after the maintaining oil pressure for the programmed delay period.

When the programmable logic determines the necessity to crank the engine, the ECM supplies +Battery voltage to the solenoid for the starting motor. Rotation of the crankshaft also operates the pump for the electrohydraulic actuators. The pump develops hydraulic oil pressure for operation of the air choke actuator and the wastegate actuator.

The engine has an energize-to-run type of Gas Shutoff Valve (GSOV). When the programmable logic determines that fuel is required to start the engine, the ECM supplies +Battery voltage to the valve solenoid.

At one second after the GSOV is energized, the pressure differential between the fuel and the air is monitored. The pressure is monitored to ensure that no fuel is entering the fuel manifold before the ECM issues a command to the fuel metering valve. If the differential pressure for fuel to air is less than 0.5 kPa (0.073 psi), the ECM supplies a command signal to open the fuel metering valve.

The ECM controls the fuel metering valve by sending a PWM signal to control flow through the valve. During start-up, the combustion chambers are normally filled with excessive combustion air. The ECM operates the fuel metering valve in order to supply sufficient fuel for a combustible air/fuel mixture.

The ECM removes the voltage from the starting motor solenoid when the programmable crank terminate speed is reached. The ECM also removes the voltage when a programmable cycle crank time has expired. The starter motor pinion disengages from the flywheel ring gear.

The ECM removes +Battery voltage from the GSOV and commands the fuel metering valve closed. The fuel is shut off.

The prelube system is programmed to perform a postlube cycle during engine shutdown. This supplies the turbocharger with adequate lubrication during shutdown. The post lube time is configurable in Cat ET.

Engine Monitoring and Protection

The ECM monitors both the engine operation and the electronic system.

Problems with engine operation cause the ECM to generate an event code. The ECM can issue a warning or a shutdown for events. The issuance depends on the severity of the condition.

For example, a high-pressure pump provides hydraulic pressure with oil for the electrohydraulic system. The oil supply is separate from the engine oil. The high-pressure oil supply is monitored by a pressure sensor. If the pressure drops below an acceptable level, the ECM generates an event code and the ECM shuts down the engine.

For more information on monitoring of the engine, refer to Systems Operation, "Electronic Control System Parameters".

The ISM monitors the combustion sensors and the thermocouples for the cylinders and for the turbocharger. The ISM sends signals regarding the parameters to the ECM over the CAN Data Link. If any parameter exceeds the acceptable range, the ECM can initiate a warning or a shutdown.

For more information, refer to Troubleshooting, "Event Codes".

Problems with the electronic system such as an open circuit produce a diagnostic code. For more information, refer to Troubleshooting, "Diagnostic Trouble Codes".

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