The engine’s electronic system consists of the Engine Control Module (ECM), the engine sensors and the vehicle interface. The ECM is the computer. The personality module is the software for the computer. The personality module contains the operating maps. The operating maps define the following characteristics of the engine:
• Torque curves
• Other characteristics
The Electronic Controls on the engine serves as the engine governor.
The Electronic Controls determine the timing and the amount of fuel that is delivered to the cylinders.
These decisions are based on the actual conditions and the desired conditions at any given time.
The governor uses the accelerator pedal position sensor to determine the desired engine speed. The governor compares the desired engine speed to the actual engine speed. The actual engine speed is determined through the primary engine speed/timing sensor. If the desired engine speed is greater than the actual engine speed, the governor injects more fuel in order to increase engine speed.
The desired engine speed is typically determined by one of the following conditions:
• The position of the accelerator pedal
• The desired vehicle speed in cruise control
• The desired engine rpm in PTO control
Once the governor has determined the amount of fuel that is required, the governor must determine the timing of the fuel injection. Fuel injection timing is determined by the ECM after considering input from the following components:
• Coolant Temperature Sensor
• Intake Manifold Air Temperature Sensor
• Atmospheric Pressure Sensor
• Boost Pressure Sensor
At start-up, the ECM determines the top center position of the number 1 cylinder from the signal from the secondary engine speed/timing sensor. After start-up, the ECM determines the top center position of the number 1 cylinder from the primary engine speed/timing sensor. The ECM decides when fuel injection should occur relative to the top center position and the ECM provides the signal to the injector at the desired time. The ECM adjusts timing for the best engine performance, the best fuel economy and the best control of white smoke. Actual timing cannot be viewed with the Caterpillar Electronic Technician (Cat ET), and desired timing cannot be viewed with Cat ET.
The ECM controls the amount of fuel that is injected by varying the signals to the injectors. The injectors will pump fuel only if the injector solenoid is energized. The ECM sends a high voltage signal to the solenoid. This high voltage signal energizes the solenoid. By controlling the timing and the duration of the high voltage signal, the ECM can control injection timing and the ECM can control the amount of fuel that is injected.
The personality module inside the ECM sets certain limits on the amount of fuel that can be injected. The FRC Limit (Fuel) is based on the boost pressure. The FRC Limit (Fuel) is used to control the air/fuel ratio for control of emissions. When the ECM senses a higher boost pressure, the ECM increases the FRC Limit (Fuel). A higher boost pressure indicates that there is more air in the cylinder. The ECM allows more fuel into the cylinder when the ECM increases the FRC Limit (Fuel).
The Rated Fuel Limit is a limit that is based on the power rating of the engine and engine rpm. The Rated Fuel Limit is similar to the rack stops and the torque spring on a mechanically governed engine. The Rated Fuel Limit provides the power curves and the torque curves for a specific engine family and a specific engine rating. All of these limits are determined at the factory. These limits are in the Personality Module and these limits cannot be changed.
The ECM will set cold mode when the coolant temperature is below 18 °C (64 °F).
Cold mode is activated five seconds after the start of the engine. During cold mode, low idle speed will be increased to 800 rpm. After 60 seconds, the engine speed is reduced to 600 rpm. Engine power will be limited until cold mode is deactivated. Cold mode will be deactivated when the coolant temperature reaches 18 °C (64 °F).
Customer Parameters And Engine Speed Governing
A unique feature with electronic engines is customer specified parameters. These parameters allow the vehicle owner to fine tune the ECM for engine operation. Fine tuning the ECM for engine operation allows the vehicle owner to accommodate the typical usage of the vehicle and the power train of the vehicle.
Many of the customer parameters provide additional restrictions on the actions that will be performed by the ECM in response to the driver’s input. For example, the “PTO Top Engine Limit” is an engine rpm limit. The “PTO Top Engine Limit” is an engine rpm limit that is used by the ECM as a cutoff for the fuel. The ECM will not fuel the injectors above this rpm.
Some parameters are intended to notify the driver of potential engine damage (“Engine Monitoring Parameters”). Some parameters enhance fuel economy (“Vehicle Speed Parameters”, “Cruise Control Parameters”, “Engine/Gear Parameters” and “Smart Idle Parameters”). Other parameters are used to enhance the engine installation into the vehicle. Other parameters are also used to provide engine operating information to the truck engine owner.