795F AC Off-Highway Truck :Resistive Input Sensors

Generator Temperature Sensors

Drive end (DE) Generator Bearing 1 Temperature Sensor

During machine operation, the Drivetrain ECM monitors the operating temperature of two of the generator stator windings and monitors the operating temperature of the two generator shaft bearings.

Each of the two Generator shaft bearings has a probe type temperature sensor inserted in the Generator housing to monitor the operating temperature of the bearing.

The engine side drive-end (DE) bearing sensor is the Generator Bearing 1 Temperature Sensor. The non-drive end (NDE) bearing sensor is the Generator Bearing 2 Temperature Sensor.

The Drivetrain ECM will monitor the temperature sensor circuits using an internal capacitance circuit that will determine the resistance of the circuit. The resistance of the circuits will indicate the bearing temperature to the ECM.

The temperature sensors are base rated 100 ohm (at 0° C (32.0° F)) Resistance Temperature Detectors (RTD).

The sensor is a three wire sensor. The red wire is the positive circuit. The two white wires are redundant parallel return circuits.

The bearing temperature sensors are serviceable. When a bearing temperature sensor has failed, the sensor can be removed from the Generator and replaced.

To determine if the RTD has failed, the expected resistance of a 100 ohm base rated RTD temperature sensor can be calculated for a known bearing temperature. Use the following calculations:

The coefficient is .392 ohms per each Celsius degree of temperature
The formula is: .392 ohms x temperature + 100 ohms = sensor resistance (ohms)
For a temperature of 60°C, the calculation would be .392 ohms x 60 = 23.52 ohms + 100 ohms = 123.52 ohms.
For a temperature of -10°C, the calculation would be .392 ohms x -10 = -3.92 ohms + 100 ohms = 96.08 ohms.

The resistance calculation for the temperature sensor resistance will only be useful if the approximate bearing temperature is known. If the resistance of the RTD circuits between the signal wire and the return wire is known, the temperature of the bearing can be figured. Use the following calculation:

The formula is: sensor circuit resistance (ohms) - 100/.392 = degrees Celsius
For a circuit resistance 131.5 ohms, the calculation to find temperature would be 131.5 ohms -100 = 31.5 ohms divided by .392 = 80.5° C (177° F).

The Drivetrain ECM will activate a level 2 Event if a bearing reaches a temperature of 85° C (185° F) for 10 seconds or longer. The ECM will activate a level 3 Event if a bearing reaches a temperature of 95° C (203° F) for 10 seconds or longer.

The specific EIDs for the temperature sensor circuits are E0724 for Bearing 1 and E0725 for Bearing 2.

If the Drivetrain ECM detects that there is a problem in a bearing sensor circuit, the ECM will activate a diagnostic code for the involved circuit (CID 3015 for Bearing 1, CID 3016 for Bearing 2).

Each of the three Generator stator windings has two temperature sensors imbedded in the winding.

The sensors are the same type of sensor that is used for the Generator bearings. The temperature sensors are base rated 100 ohm (at 0° C (32.0° F)) Resistance Temperature Detectors (RTD).

The sensor is a three wire sensor. The red wire is the positive circuit. The two white wires are parallel return circuits. Two return circuits help to eliminate wire resistance effects from the measurements.

Refer to the calculations listed for the bearing sensors in order to calculate the resistance of the winding sensor circuits or the winding temperatures.

The Drivetrain ECM will use two temperature sensors at any one time to determine the operating temperature of the stator windings. The two temperature sensors are referred to as the Generator Winding 1 Temperature Sensor and the Generator Winding 2 Temperature Sensor. These names are used to differentiate the two separate sensor circuits. The names do not refer to specific temperature sensors.

The stator winding temperature sensors are not serviceable. If a temperature sensor has failed, one of the remaining four spare temperature sensors should be connected. Connect the spare sensor at the terminal block in the auxiliary connection enclosure on the left-hand side of the Generator.

If the Drivetrain ECM detects that the temperature of a winding is above the acceptable limits, the ECM will activate a level 2 Event if a winding reaches a temperature of 155° C (311.0° F) for 10 seconds or longer. The ECM will activate a level 3 Event if a winding reaches a temperature of 165° C (329.0° F) for 10 seconds or longer.

The specific EIDs for the temperature sensor circuits are E0738 for the sensor that is connected to the winding 1 circuit and E0739 for the sensor that is connected to the winding 2 circuit.

If the Drivetrain ECM detects that there is a problem in a winding sensor circuit, the ECM will activate a diagnostic code for the involved circuit (CID 2780 for the winding 1 circuit, CID 2781 for the winding 2 circuit).

High Speed PWM Communication Inputs

High Speed PWM Communication circuit connections

Note: The PWM communication circuit numbers change when passing through the Inverter Cabinet through wall connector CN2 / CX-C4. Use the connection diagram in this procedure or the system schematics in the back of this manual to insure that the correct circuits are followed when passing through these connectors.

To control the DC Power Bus voltage, the Drivetrain ECM must be able to determine the DC bus voltage at all times. Each motor ECM will use sinking driver circuits to create a PWM signal that will provide "real time" voltage status to the Drivetrain ECM.

The circuits are connected to Drivetrain ECM switch to ground type input circuits. When the motor ECM turns on the sinking driver, the circuits are pulled low. The length of time that the driver circuit is ON determines the duty cycle of the PWM signal.

If one motor ECM is indicating a voltage that is higher or lower than the other motor ECM is indicating, the Drivetrain ECM will use the higher value for control purposes.

If the voltage status from one motor ECM differs by 200 VDC from what the other motor ECM is indicating, the Drivetrain ECM will activate a level 2 E1126 Event (DC Power Bus Voltage Mismatch).

Requested Gear Command Input


Requested Gear Command signal circuit connections between the Drivetrain ECM, the Chassis ECM, and the Shift Control Lever Position Sensor

The position of the shift control lever is monitored by the Chassis ECM. For system control purposes, the Drivetrain ECM must know when the operator moves the lever and what position the lever is in.

The Chassis ECM provides this information to the Drivetrain ECM on a separate circuit that is connected between the controls.

The circuit contact at the Drivetrain ECM has an internal pull up voltage that holds the circuit high. The Chassis ECM will switch a sinking driver circuit ON and OFF in order to create the PWM duty cycle that will indicate the direction lever status to the Drivetrain ECM.

The following table lists the PWM duty cycle percentages that the Chassis ECM will send to the Drivetrain ECM on the requested gear command circuit in order to indicate the position of the Shift Control Lever.