795F AC Off-Highway Truck Electric Drivetrain Control System: General Information

795F AC Off Highway Truck

The 795F AC Off Highway Truck is equipped with an electric drive train system that takes the place of a mechanical transmission and rear differential. This manual covers the system operation, the testing, and adjusting and the troubleshooting for electronic control of the electric drive train system.
The electric drive train system includes the following main components:

The Drivetrain ECM
The Motor 1 ECM
The Motor 2 ECM
The Generator
The Generator Excitation Field Regulator
The Inverter Cabinet
Two electric traction motors
The retarding grid resister assembly

The main electric drive train system components.

(1) Inverter Cabinet - houses all of the traction motor control components, system input status devices, and the Retarding Grid Blower Inverter.

(2) Retarding Grid Assembly. Contains the load resistor elements that are used for loading during dynamic braking and the Grid Blower Motor that is used to cool the resistors.

(3) Electric Drive Cooling Fan (not visible). Located under the chassis. The hydraulic fan is used to provide cooling airflow for the components in the Inverter Cabinet, the Generator, and the traction motors.

(4) Generator. When the Engine is operating, the Generator supplies 3 phase AC voltage to the Inverter Cabinet.

(5) Traction Motor 1. Contained inside of the rear axle housing (not shown) and controlled by the Motor 1 ECM.(6) Traction Motor 2. Contained inside of the rear axle housing (not shown) and controlled by the Motor 2 ECM.

Isolation and Grounding

DANGER: The Power Train Electric Drive System will contain hazardous voltage levels during machine operation and for a short period of time after engine shutdown.
Do not remove any covers that will expose energized high voltage electrical components while the engine is operating.
Any type of maintenance on the following components can only be performed after the Power Train Electrical System Service Shutdown procedure has been followed:

High voltage compartments in the inverter cabinet
The rear axle housing that contains the electric drive traction motors
The generator
The retarding resistor grid, the grid blower motor and the grid system cabling
The excitation field regulator
The high voltage cables and connection enclosures

Failure to follow these instructions could result in personal injury or death.

DANGER: In order to avoid the buildup of hazardous live voltages on the exposed surfaces, all grounding wires and grounding straps must be properly connected at all times during engine operation.
Any disconnected grounding wires, including the grounding wires for all high voltage components and the grounding strap for the inverter cabinet must be properly reconnected before the engine is started.Failure to follow these instructions could result in personal injury or death.

The electric drive train system operates at high AC voltage levels and at high DC voltage levels. The system is designed to keep these voltages isolated from the truck frame and isolated in protected areas where any accidental contact cannot occur.

The system electrical components and the electrical system voltages are electrically isolated from the machine frame ground. Each of the system component enclosures and housings is grounded to the machine frame ground by a ground strap. The ground straps must remain connected at all times during the operation of the machine.

The electrical system components that are inside of the component housings are electrically isolated from the housing. A ground fault is a "leakage" of electrical current or a short circuit to the machine frame. If a ground fault occurs, the isolation of the system components from frame ground ensures that there is not a path for current flow back to the voltage source.

Detection systems are in place that monitor the AC voltage system and the DC voltage system. Very small amounts of current leakage to frame ground can be detected. A small amount of this leakage is normal in a high voltage power system.

If an amount of current leakage to the frame ground reference is detected that could damage system components, a system control module will activate a ground fault Event. The Event will be activated at a level that will indicate the severity of the problem to the operator and to the technician.

Safety is your responsibility. The best designs for a safe system can be defeated by a lack of a basic understanding of how the system works. Following the recommended practices and procedures that are required when working on the truck or around the truck.

Before performing maintenance procedures or troubleshooting procedures on the electric drive train system, be familiar with the components and the operation of the system.

Refer to the Systems Operation, "Electric Power Generation" section of this manual in order to become familiar with the control and operation of the Generator.

Refer to the Systems Operation, "Electric Drive System" section of this manual in order to become familiar with the control and operation of the electric drive train system.

After you are familiar with the drive train system components, refer to the electrical system shutdown procedures and practices that are provided in this manual. The procedures must be performed before any maintenance procedures or troubleshooting procedures are done on any of the high voltage systems or subsystems.

These procedures are located in the Troubleshooting, "Electrical Shutdown and Voltage Discharge" section of this manual. This section of the manual contains the procedures that must be followed before performing maintenance procedures on the machine high voltage electrical system.

Note: If information for a particular system or component is needed and the location of this information is not indicated in the table of contents, refer to the Index in the back of this manual. The Index provides a more detailed listing of the subsystems and components that are covered under the main section titles.

Electronic Control Modules

Electronic control of the electric drive train system is provided by three Electronic Control Modules (ECM). The three electronic control modules are the Drivetrain ECM, the Motor 1 ECM and the Motor 2 ECM. The Drivetrain ECM is located in the cab front ECM compartment. The two motor control modules are located in the Inverter Cabinet.

The electrical sections of this manual deal with the Systems Operations, the Troubleshooting and the Testing And Adjusting of the machine systems that are controlled by these three control modules.

The main control assignments for the three control modules are:

Drivetrain ECM - Exercises primary control of the system. Controls the Generator output based on operator input and the demands of the system. Enables operation of the drive train system and the motor control modules. The ECM sends torque commands to the motor control modules that are used for traction motor control. The Drivetrain ECM also controls the operation of the hydraulic Electric Drive Cooling Fan.

Motor 1 ECM - Based on the torque commands received from the Drivetrain ECM, the Motor 1 ECM controls the operation of the power transistors in the Inverter Cabinet that are used to control the left-hand side Motor 1 ECM. During operation, the module monitors the output current and the operating temperature of the traction motor. In addition, the Motor 1 ECM controls the operation of the Chopper Module. This module is used to control the voltage level of the DC Power Bus and the Retarding Contactors that are used for retarding.

Motor 2 ECM - Based on the torque commands received from the Machine ECM, the Motor 2 ECM controls the operation of the power transistors in the Inverter Cabinet that are used to control the right-hand side Traction Motor 2. During operation, the module monitors the output current and the operating temperature of the traction motor. In addition, the Motor 2 ECM controls the operation of the Crowbar which is used for immediate discharge the DC Power Bus during system shutdown or if a problem occurs that requires an immediate discharge of the DC Power Bus.

All of the diagnostic codes will be activated by an ECM in a "MID - CID - FMI" format. All event codes will be activated in an "EID - Level 1, 2 or 3" format. This information will be displayed on the Advisor. The active and logged codes can be viewed using the Caterpillar Electronic Technician (Cat ET) software on a laptop computer.

For a list of all of the possible diagnostic codes that can be activated by each of the three control modules, refer to the Troubleshooting, "Diagnostic Code List" section of this manual. A troubleshooting procedure for each diagnostic code can be found in the "Troubleshooting" section of this manual.

See You Soon!!!

MARYGAR