Aspen 4WD V8-5.7L Hybrid (2009)
CONTACTORS
The 12-Volt system, connects and disconnects the HV battery from the remainder of the HV system through heavy-duty relays called contactors. There is
a positive and negative contactor connected to the positive and negative side of the battery.
These contactors are normally open and must have reliable 12-Volt power to keep them closed. If the 12-Volt supply to the HV battery is intermittent,
this may cause the contactors to open momentarily and then close. This can cause an arc across the contactor surfaces that can weld closed the contactor.
If this happens, the 12-Volt system cannot control the HV system and the HV system remains energized. Contactor failures set a DTC and illuminates the
HEV Service Lamp.
PRE-CHARGE COMPONENTS
Pre-charge components control voltage and current applied to the HV system. The initial application of current or in-rush of current, could damage the
HV system if not controlled. To control the current application, a large resister is used when the HV system is initially powered up.
The pre-charge components consist of the pre-charge resister, a pre-charge contactor and the required wiring to connect the components. The negative
contactor is used during the pre-charge routine.
To perform the pre-charge routine, the BPCM commands the pre-charge contactor and the negative contactor to close. The pre-charge resistor is in series
on the circuit with the pre-charge contactor so this controls the power applied to the HV system.
After the pre-charge and negative contactors close and apply partial voltage to the HV system, the BPCM commands the positive contactor to close. This
creates a circuit with very little resistance compared to the pre-charge circuit. After the positive contactor has closed, the BPCM opens the pre-charge
contactor. The HV system is now fully enabled and ready for operation.
HIGH VOLTAGE BATTERY COOLING FAN
As the HV system charges and discharges the HV battery, significant heat is created. To control the temperature of the battery, a 12-Volt fan located on
the passenger side of the battery pack, pulls air across the battery components. The battery modules have spaces between them to allow airflow. Airflow
also cools the contactors, BPCM and pre-charge resister on the driver side of the battery case.
The cooling air passes around the carpeted beauty cover over the battery case and then enters the battery through an intake grate on the passenger side of
the case. All airflow from the battery case is blown out of the case through an exhaust vent and exits under the vehicle.
The intake grate for the cooling air is in a protected position under the battery cover. This area must be kept clear so that air can enter the battery with no
restriction.
The fan speed can be commanded though the scan tool under the BPCM miscellaneous function menu. This is an easy way to confirm operation of the
fan.
The BPCM controls the fan under direction from the HCP. The BPCM modulates the fan speed in response to battery temperature. The BPCM activates
the fan:
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Under 25°C (77°F), the cooling fan is not needed.
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25°C (77°F) to 50°C (122°F), the fan runs up to the maximum RPM allowed by the HCP.
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Over 50°C (122°F), the fan runs at maximum RPM.
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Over 60°C (140°F), the BPCM requests HV battery shut down from the HCP.
The HCP limits the speed of the fan according to vehicle speed, HVAC blower speeds and engine RPM, to reduce Noise Vibration and Harshness
(NVH) concerns. If the battery temperature exceeds 50°C (122°F), the fan runs at maximum speed.
The fan does not run if the air inlet temperature is higher than the battery cell temperatures, to prevent hot air from entering the battery case. This may be
the case if the vehicle sits for a long time in direct sunlight. The BPCM runs the fan intermittently and rechecks the temperature readings after circulating
air.
The fan is Pulse Width Modulated (PWM) on the ground side of the fan motor circuit.
Any time the battery cooling fan is running, the fan removes air from the interior of the vehicle. As a result, air flows through the HVAC vents if all
windows are closed. This is normal and the recirculation door in the HVAC system is designed with adequate fresh air access under all conditions.
THERMISTORS
There are six thermistors used to read temperature throughout the battery pack. Four are in the battery modules, to give a sample of battery cell
temperatures. Two sensors read air inlet and air outlet temperatures. These readings are inputs to the BPCM and are used to determine desired fan speed.
