795F AC Off-Highway Truck Electric: Chassis Components and Operation ( Electric Drive System):

Chassis Components

Retarding Grid

Upper photo - the Retarding Grid Assembly mounted on the truck. Lower photo - one of the four grid resistor elements

Retarding Grid Assembly connections

The Retarding Grid Assembly consists of the grid blower motor, the fan, and two separate sets of resistor elements. One set of elements is Contactor Grid and the other set of elements is Chopper Grid.

The maximum rated power load for the grid is 4.7 megawatt (6303 HP).

The resistor elements provide the resistive load that is used during dynamic retarding. The resistor elements are also used for the discharging of the DC Power Bus voltage during shutdowns or severe fault conditions.

Each set of elements consists of four curved segments. Each of the four segments contains a grid 1 resistor and a grid 2 resistor. The resistors are electrically isolated from each other.

When the four segments are mounted in the grid housing, the segments form two separate electrically isolated circles.

The contactor grid resistors are mounted closer to the fan. These resistors will be used to dissipate the most energy when the retarding contactors close during dynamic retarding.

The chopper grid resistors are placed further from the fan. The chopper grid 1 resistors are used to dissipate energy when the Chopper Module is in operation or when the Crowbar is activated. The Motor 1 ECM will limit Chopper Module operation when the fan is not in operation in order to limit the heat that is created.

When mounted, the segments must be placed in the correct position as each segment has different electrical resistance values. The resistance of each resistor element and the complete sets are listed.

Individual untapped grid elements 1, 3, 4 resistance at 25° C (77° F):

• Between contacts 1 and 2 - 0.66 ohms to 0.69 ohms.
• Between contacts 3 and 4 - 0.53 ohms to 0.59 ohms.

Individual tapped grid element 2 resistance at 25° C (77° F):

• Between contacts 1 and 2 - 0.71 ohms to 0.75 ohms.
• Between contacts 3 and 4 - 0.53 ohms to 0.59 ohms.

Chopper Grid resistance with cables disconnected from supply cables:

• Between contacts CHN and CHP - 2.2 ohms to 2.3 ohms.
• Between contacts 3 and 4 - 0.53 ohms to 0.59 ohms.

Contactor Grid resistance with cables disconnected from supply cables:

• Between contacts CNN and CNP - 2.7 ohms to 2.8 ohms.
• Between tapped contacts IN and IP - 0.71 ohms to 0.75 ohms.

Electric Drive Cooling Fan System

Electric Drive Cooling Fan System (79) Main duct that directs the intake air flow from the Inverter Cabinet to the fan housing (80) Flexible inlet duct that supplies air flow through the cabinet pressurization filter to the cabinet interior (81) Ducts that are used to circulate the cooling air flow into the Generator (82) Ducts that are used to circulate the cooling air flow into the rear axle housing in order to cool the traction motors (83) Hydraulic Motor for the Electric Drive Cooling Fan(84) Two oil coolers for the final drives and brake cooling oil

Hydraulic Motor for the Electric Drive Cooling Fan (85) Electric Drive Cooling Fan Speed Sensor(86) Electric Drive Cooling Fan Solenoid

The Drivetrain ECM controls and monitors the operation of the Electric Drive Cooling Fan. A hydraulic motor is used to power the fan.

The Drivetrain ECM will send current to the proportional Electric Drive Cooling Fan Solenoid in order to control the rotational speed of the hydraulic fan motor.

The ECM will control the speed of the fan in relation to the speed of the Engine. At low idle Engine speed, the Drivetrain ECM will operate the fan at approximately 1800 rpm. As the Engine speed is increased, the speed of the fan is increased proportionately. When the speed of the Engine reaches 1300 rpm and higher, the ECM will proportionally reduce current to the solenoid in order to provide a greater amount of cooling air flow to all system components. Maximum fan speed is approximately 3400 rpm.

The Drivetrain ECM will use the Electric Drive Cooling Fan Speed Sensor to monitor the speed of the hydraulic motor and the fan.

Intake vent sand filter removal

The cooling system intake vents are located on the front of the Inverter Cabinet. Every compartment that houses a phase module and the Chopper Module has an intake vent. Each vent is covered by a removable sand filter that will stop large particles from entering the intake vent.

The sand filters should be checked regularly for obstructions that could cause a reduction of air flow.

Heat exchangers on top of each phase module and the Chopper Module are lined up with the air intake vents. Seals on the heat exchangers prevent the lightly filtered intake air from entering the interior of the cabinet. The cooling fan draws the air in through the phase module heat exchangers in order to provide cooling for the power transistors in each phase module.

After passing through the phase module heat exchangers, the cooling air is directed out through the back of the Inverter Cabinet into the main duct that will direct the air flow through the hydraulic fan housing. The fan forces most of the air flow on to the Generator and the traction motors for cooling.

Two circular ducts route a portion of the airflow into the Generator housing. The air circulates through the Generator in order to cool the windings. The air is then exhausted out of the rear of the Generator.

Most of the air is then directed into the rear axle housing. A smaller amount is of air flow is exhausted out of the system through two oil coolers that are used to cool the final drive and brake oil.

The air flow that is directed into the axle housing is circulated through the open ended traction motor stators in order to cool the motor windings. The air flows back through the motors. The air is then exhausted out of the axle housing through the vented access cover on the rear of the housing.

Louvers on the cover direct the exhaust air flow upward to avoid creating more dust at the rear of the truck.

Inverter Cabinet Pressurization Filter

A circular flexible duct branches off on the main duct behind the fan housing and connects to an inlet fitting on the rear left-hand side of the Inverter Cabinet. This duct directs air flow through the Pressurization Filter in the front cabinet compartment. This filter enables clean air to be forced into the cabinet interior. This air flow will cause a positive air pressure to be maintained in the cabinet interior. The positive air pressure in the cabinet prevents outside contamination from entering the cabinet. The pressurized air in the cabinet is naturally exhausted out of the cabinet at a slow rate.

The Pressurization Filter must be checked and cleaned at regular intervals in order to ensure that adequate air flow is entering the cabinet. Consult the Operation and Maintenance Manual for the recommended cleaning interval.

Seals on every cabinet compartment cover provide the means to maintain the positive air pressure in the Inverter Cabinet. Always ensure that the cover seals are in good condition before the cover is installed. Ensure that the compartment covers are completely and securely fastened in place before operating the truck.

The Drivetrain ECM monitors the circuits for the Electric Drive Cooling Fan Speed Sensor and the Electric Drive Cooling Fan Solenoid for diagnostics. The ECM will activate a diagnostic code for either circuit if an abnormal circuit condition is detected.

Each motor control ECM monitors the circuits of the temperature sensors in the respective phase modules and Chopper Module. Each ECM will activate a diagnostic code for the involved circuit if an abnormal condition is detected.

If a over temperature condition is detected in a phase module or the chopper module, the motor control ECM will activate either a level 2 Event or a level 3 event. The level of the activated event will indicate the severity of the problem.

Traction Motors

Traction motor - drive-end

Two identical three phase AC induction traction motors are mounted in the rear axle housing.

The electric drive train system is designed around the need for precise control of the operation of the two electric traction motors.

Traction Motor 1 provides the power to turn the left hand set of rear wheels. Traction Motor 1 is controlled by the Motor 1 ECM.

Traction Motor 2 provides the power to turn the right hand set of rear wheels. Traction Motor 2 is controlled by the Motor 2 ECM.

The specifications for each traction motor are:

• The three phase windings are connected in a wye configuration.
• Maximum rotational speed - 3180 rpm.
• Full load travel mode voltage - 1960 VAC.
• Full load retarding mode voltage - 2060 VAC.
• Maximum stall current - 1300 amps.
• Maximum torque output - 35,523 N-m (26,200 lbf-ft).
• Nominal power in travel mode - 1206 kilowatts
• Nominal power in retarding mode - 2430 kilowatts
• Weight (each) - 4100 kg (9,039 lbs)

Each traction motor has a "drive-end" which is the rotor shaft end that connects to the final drive. Each traction motor has a "non-drive end" which can be seen from the access opening at the rear of the axle housing.

During operation, the motors are air cooled. The two traction motors have an open frame design. In order to cool the motor windings, the air flow that is directed into the axle housing by the Electric Drive Cooling Fan circulates through the motor toward the drive-end. Then, the air flows back through the motor and is exhausted out through the vented cover on the axle housing access opening.

Three 777 MCM gauge high voltage power cables from the Inverter Cabinet are connected to lugs on the non-drive end of each motor.

In order to control and monitor the electrical current in each of the three phases for each traction motor, the controlling motor control ECM will use the input signals from a current sensor or CT that is located in the Inverter Cabinet.

For more information on the operation of the motor current sensors, refer to "Current Sensors" in the "Inverter Cabinet Components" section.

The PWM voltage pulses from the phase modules are seen by the traction motors as AC sine wave signals. The three phases of AC voltage create a rotating magnetic field in the stator of the motor. The magnetic field will force the rotation of the rotor.

For each motor phase, when the motor control ECM modulates the output PWM pulses to increase the time that the pulse width is high, the AC voltage of each phase will increase.

For each motor phase, when the motor control ECM increases the transistor switching frequency, the current for each phase will increase. Higher frequency and current results in greater motor speed and greater torque output.

When a request to change the direction of machine travel is received from the Drivetrain ECM, each motor control ECM will electronically switch two of the three phase outputs for each traction motor. This phase switch will result in the motors reversing direction of rotation.

For more information on how the traction motors are controlled, refer to the "System Operation Overview" section at the beginning of this procedure and the "Phase Modules" operation section.

The rotor shaft of each motor is connected to the mechanical final drive system in each axle. In order to multiply the torque that is delivered by the motors, the final drives are designed to provide a 36:1 gear reduction ratio.

Non-drive end of each traction motor as viewed from the rear axle housing opening (87) Three phase high voltage cable connections from the Inverter Cabinet (88) One of two speed sensors for each motor(89) Enclosure that contains the terminal connections for the motor winding temperature sensors and the bearing temperature sensors

Note: The two traction motors are identical. When mounted, the location of the components on the non-drive end are reversed when looking at one motor as compared to the other motor.

Each motor control ECM monitors the motor speed and the operating temperature of the motor that is under control.

In addition, the Drivetrain ECM receives an input from one of two speed sensors that are mounted on the non-drive end of each motor.

Traction Motor 1 speed sensors (view: inside the rear axle housing looking at the non-drive end of Drive Motor 1) (1) Drive Motor Speed Sensor 1 Signal 1(2) Drive Motor Speed Sensor 1 Signal 2

Traction Motor 1 speed sensor connections and Traction Motor 2 speed sensor connections

Note: The speed sensor 1 circuit numbers change when passing through the Inverter Cabinet through wall connector CN1 / CX-C3. The speed sensor 2 power supply circuit numbers change passing through the MC-C20 / CX-C6 connector that comes out of the cab. Use the connection diagram in this procedure or the system schematics in the back of this manual in order to insure that the correct circuits are followed when passing through these connectors.

The speed sensors are the Motor Speed Sensor 1 Signal 1 (Motor 1 Speed Sensor 1) and the Drive Motor Speed Sensor 1 Signal 1 (Motor 1 Speed Sensor 2).

For both of the traction motors, the speed sensor 1 is monitored by the controlling motor control ECM for control of the traction motors.

The Drivetrain ECM monitors the speed sensor 2 for both motors. The speed sensor enables the Drivetrain ECM to determine the speed of each traction motor and the wheel speed for control purposes instantly.

Each speed sensor provides two signal inputs to the ECM. The two inputs allow the ECM to determine the direction of motor rotation in addition to the motor speed.

Each ECM monitors the circuits of the monitored speed sensors for diagnostics. If an abnormal condition is detected in a speed sensor circuit, the ECM will activate a diagnostic code for the involved circuit.

A test procedure is available that will help to determine if a motor speed sensor has failed. Refer to the Testing and Adjusting, "Motor speed Sensor - Test" section in this manual for the test procedure.

For more information on the traction motor speed sensors and the speed sensor signals that are sent to each ECM, refer to the Systems Operations, "Electrical Input Components" section in this manual.

Traction Motor 1 temperature sensor connections

Traction Motor 2 temperature sensor connections

Note: The traction motor temperature sensor circuit numbers change when passing through the Inverter Cabinet through wall connector CN1 / CX-C3. Use the connection diagram in this procedure or the system schematics in this manual in order to insure that the correct circuits are followed when the circuits pass through this connector.

Using a small flat blade screwdriver to release or install the winding temperature sensor or bearing temperature sensor wires in the terminals

Each of the two electric drive traction motors has internal temperature sensors for the drive-end bearing and the non-drive end bearing. Each temperature sensor is a 100 ohm (at 0.0° C (32.0° F) Resistive Temperature Device (RTD).

Bearing 1 temperature sensor is the monitoring the drive-end bearing and bearing 2 temperature sensor is monitoring the non-drive end bearing.

The range of resistance of the sensor that the ECM considers acceptable is 80 ohms to 180 ohms.

Each temperature sensor provides a passive analog (resistive) signal to the motor control ECM that is controlling the operation of the drive motor. The ECM will use an internal capacitance circuit in order to determine the resistance of the circuit. The ECM will use this information to determine the operating temperature of the traction motor bearings.

Two redundant return circuits are used for each sensor positive signal circuit.

The bearing temperature sensors are not serviceable. A backup temperature sensor is available for each of the original bearing temperature sensors. If a temperature sensor has failed, the harness circuit wires will be reconnected to the backup temperature sensor circuits at the terminal block in the enclosure.

In order to determine the operating temperature of the traction motors, each controlling motor control ECM will monitor two temperature sensors that are embedded in two of the motor stator windings.

The winding temperature sensors are of the same type of RTD sensor that is used to monitor the bearing temperatures.

The winding 1 and winding 2 temperature sensor designations refer to the ECM circuits, not a specific motor winding.

Like the bearing sensors, the winding temperature sensors are not serviceable. A backup temperature sensor is available for each of the original winding temperature sensors. If a winding temperature sensor has failed, the harness circuit wires will be reconnected to the backup temperature sensor circuits at the enclosure terminal block.

If a high temperature condition for the bearings or the windings is detected by the controlling motor control ECM, one or more of the following high temperature Events will be activated by either ECM. The ECM that activates the Event determines the traction motor that is involved.

• E0720 - High Drive Motor Bearing 1 Temperature Sensor (level 2 or level 3).
• E0721 - High Drive Motor Bearing 2 Temperature Sensor (level 2 or level 3).
• E1067 - High Drive Motor Winding 1 Temperature Sensor (level 2 or level 3).
• E1068 - High Drive Motor Winding 2 Temperature Sensor (level 2 or level 3).

If the controlling motor control ECM detects an abnormal condition in one of the bearing temperature sensor circuits or a winding temperature sensor circuit, the ECM will activate one of the following diagnostic codes for the involved circuits:

• CID 3004 - Drive Motor Winding 1 Temperature Sensor.
• CID 3005 - Drive Motor Winding 1 Temperature Sensor.
• CID 3006 - Drive Motor Bearing 1 Temperature Sensor.
• CID 3007 - Drive Motor Bearing 2 Temperature Sensor.

Limp Home Mode

The "Limp Home Mode" enables the operator or technician to use the Advisor or Cat ET to disable the operation of one of the traction motors. Limited travel of the truck with only one traction motor operating can be enabled under certain conditions.

The truck must be unloaded before attempting to activate the Limp Home Mode.

The Limp Home Mode can be enabled when any of the following conditions are active on the truck:

• A level 3 event or diagnostic code is activated by ONE motor control ECM for components that are under the ECM control.
• A mechanical problem is present in ONE of the traction motors or in ONE of the final drive assemblies.

Certain mechanical conditions may require the disassembly of traction motor or final drive components before the Limp Home Mode can be activated. Refer to the Operation and Maintenance Manual, SEBU8349, "Disabled Machine Recovery" for more information.

The Limp Home Mode cannot be enabled when any of the following conditions are active on the truck:

• If a level 3 event or diagnostic code has been activated by BOTH of the motor control ECMs.
• If a level 3 event or diagnostic code for the Generator is active.
• If a diagnostic code for the EFR is active.
• If a level 3 event or diagnostic code for a DC Power Bus component or condition is active.

1. When using Cat ET to activate the Limp Home Mode:
   
   
   1. Under the Drivetrain ECM configurations, select "Configuration Group 1"
   
   
   2. Highlight the "Power Inverter Disable Configuration" line.
   
   
   3. Select "Change".
   
   
   4. A "Change Parameter Value" menu will appear that will allow the user to highlight either "#1" for motor 1 (left), "#2" for motor 2 (right) or "None". Select the motor that is to be disabled or select "None".
   
   
   5. Select "OK".

When activating the Limp Home Mode using the Advisor, similar menus are provided under the "Settings" menu.

The Drivetrain ECM will enforce the following logic when the Limp Home Mode is active:

• The truck must be in "PARK" to attempt to activate the Limp Home Mode.
• If Traction Motor 1 is disabled. The Drivetrain ECM will activate an informational E1182 Event for "Drive Motor 1 Manually Disabled".
• If Traction Motor 2 is disabled. The Drivetrain ECM will activate an informational E1183 Event for "Drive Motor 2 Manually Disabled".
• The Drivetrain ECM will disable Limp Home Mode operation if any level 3 event or diagnostic codes are activated for the traction motor or controls that are active.
• The retarding function will be disabled when the mode is active. Service brakes must be used to slow or stop travel. The service brake pedal or the retarder lever will activate the service brakes.
• When the mode is active, travel speed will be limited to 11.2 km/h (7.0 mph)
• Traction control (slip control) will be active when in the Limp Home Mode.
• The Limp Home Mode will be disabled when the key start switch is cycled.

See You Soon!!!

MARYGAR

795F AC Off-Highway Truck Electric: Chassis Components and Operation ( Electric Drive System): 2012-12-01T07:57:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown