Drive Motor Battery System Description
Drive Motor Battery System Description
Overview
The drive motor generator battery is also referred to as the hybrid battery. The drive motor generator battery contains 40 individual battery modules. Each battery module is rated at 7.2 volts direct current (DC) and all the modules are connected together in series. The combined output voltage of all the modules is about 288 volts DC. The DC high voltage (HV) connects to the drive motor/generator power inverter module (PIM) through HV DC cables that route underneath the vehicle. The HV battery positive and negative cable assembly (300v) is always colored orange to denote the potential for high voltage. The PIM converts the DC voltage to alternating current (AC) voltage to enable the electrical portion of the powertrain hybrid functions. The drive motor / generator battery has few moving parts. The moving parts are the 2 HV contactor relays, the HV pre-charge relays, the battery vent fan relay and a battery vent fan. The vent fan is used to help cool the batteries. The battery energy control module (BECM) controls these devices and monitors current, voltage and temperature by using several sensors within the hybrid battery assembly. The BECM will set diagnostic trouble codes based on these inputs.
Location
The hybrid drive motor/generator battery is located beneath the middle row seat on sport utility models and beneath the rear seat on crew cab pickup truck models. The BECM is located within the hybrid battery assembly.
Battery Energy Control Module (BECM)
Operating Functions
The battery energy control module (BECM) is also referred to as the drive motor battery control module. In order to maintain proper state of charge levels and operate efficiently, the hybrid drive motor generator battery has several systems that need to be monitored and controlled. These systems include hybrid battery voltage measurement, hybrid battery current measurement, hybrid battery cooling and the high voltage interlock loop system. Additionally, the BECM operates the high voltage relays (contactors) at the request of the hybrid control module (HCM). The BECM is located within the hybrid battery assembly.
Communication and Hosted Diagnostics
The HCM is the host controller for diagnostic trouble code (DTC) information for the following control modules:
* Accessory DC power converter module (APM)
* Battery energy control module (BECM)
* Motor control module (MCM) 1
* Motor control module (MCM) 2
* Auxiliary transmission fluid pump (ATFP) control module
The BECM will diagnose its own systems and determine when a fault condition is present. Diagnostics and system status is communicated from the BECM to the HCM through the GM Hi-speed, Hybrid LAN communication circuit.
In the event a hosted module communicates a fault condition, the HCM will determine if hybrid operation is effected and notify the vehicle operator by requesting the MIL illuminate and/or by displaying a hybrid service required message. In addition, the HCM will store the associated DTC information for retrieval by a scan tool. Some hosted modules may require an ignition cycle to clear certain DTCs from the HCM.
Input Circuits - Voltage Measurement
The BECM monitors the voltage values of the hybrid batteries using two different methods. The BECM monitors the sum of the voltage at 20 battery locations (calculated voltage) and the total bus voltage from the harness before the positive and negative relays (sensed voltage).
Input Circuits - Hybrid Battery Current Measurement
The BECM monitors current through the hybrid battery current sensor. The hybrid battery current sensor is mounted on the positive cable side internal to the hybrid drive motor generator battery assembly. The current sensor detects the amperage that flows in and out of the hybrid batteries. The current sensor inputs a voltage between 0-5 volts in proportion to the amperage.
Input Circuits - Hybrid Battery Temperature
The hybrid drive motor battery is an air cooled component. The hybrid drive motor battery vent fan and relay are located inside the hybrid drive motor battery assembly and controlled by the BECM. The BECM monitors four hybrid battery temperature sensors, one air inlet temperature sensor, and one air outlet temperature sensor. These six temperature sensors are internal to the hybrid drive motor generator battery assembly. The four hybrid battery temperature sensors are located on the top of the hybrid batteries. The resistances of these temperature sensors increase with temperature. The BECM can adjust the vent fan speed based on vehicle speed and temperature.
Input Circuits - High Voltage Interlock Circuit (HVIC)
The vehicle is equipped with a high voltage interlock circuit (HVIC) feature. The purpose of the HVIC is to detect attempted access to HV components when HV is present. The BECM sources and monitors current on a 2 wire circuit that runs through the HV components and their access points. The BECM will take action based on the results of the measured current at both the input and output circuits. Additionally, the drive motor generator PIM monitors the HVIC and will also take action based upon the measured current. Refer to High Voltage Monitoring Systems Description.
Output Circuits - High Voltage Contactor Relays
There are three high voltage contactor relays, the positive main contactor relay, the negative main contactor relay and the pre-charge contactor relay. The HV contactor relays, sometimes called contactors, open the high voltage battery negative and positive circuits and isolate the hybrid battery voltage from the rest of the vehicle. The BECM will close the HV contactor relays only at the request of the HCM. Either the BECM or the HCM can command that the HV contactor relays be opened in the event a system fault is detected. The contactors must be opened and closed under tightly controlled conditions in order to prevent damage to either the PIM or the HV contactor relays themselves.
In order to prevent damage to the PIM capacitors, the HV contactor relays are always closed in the following sequence:
1. The negative main contactor relay is closed.
2. The pre-charge contactor relay is closed. The pre-charge high voltage circuit contains an in-line resistor. With both the negative main contactor relay and the pre-charge contactor relay closed, the high voltage is slowly brought to operating voltage. Slowly bringing the high voltage to operating level prevents surge damage of the PIM capacitors.
3. Once the TPIM reads 95 percent of available buss voltage it sends a contactor command signal to the BECM to close the HV positive contactor relay.
4. The positive main contactor relay is closed. The positive main contactor relay bypasses the pre-charge resistance and allows high current flow in and out of the hybrid batteries to occur.
5. The pre-charge contactor relay is opened. Once at operating voltage, the pre-charge resistance is no longer required.
In order to prevent damage to the HV relays, current flow through the relay switch contacts must be minimized prior to any attempt at opening them. The HCM must ensure the system is in a low current flow condition prior to allowing the BECM to open the HV contactor relays. The HCM will command that all high voltage components like the APM and the air conditioning compressor stop drawing current. Also, the HCM will ensure that the motor/generators have stopped rotating and that they are neither consuming nor generating electrical current.
Output Circuits - Hybrid Drive Motor Battery Vent Fan
The hybrid drive motor battery is an air cooled component. The hybrid drive motor battery vent fan and relay are located inside the hybrid drive motor battery assembly and controlled by the BECM. The BECM monitors hybrid battery temperature air inlet and air outlet temperatures. The BECM can adjust the vent fan speed based on vehicle speed and temperature. The BECM grounds the primary side of the vent fan relay to supply voltage to the vent fan. The BECM controls the vent fan speed through a separate wire with a pulse width modulated signal (PWM). The vent fan assembly internal circuitry converts the PWM signal into fan speed.
Drive Motor Generator Battery Venting System
The hybrid drive motor battery contains 40 individual batteries. The hybrid drive motor battery has two venting systems. One is for battery air cooling. The other is for venting of possible electrolyte gases from the 40 hybrid batteries. The hybrid batteries vent system connects all the battery vents to a rubber manifold that exits the hybrid drive motor battery through a single hose and is vented through the floor panel of the vehicle. For more information, refer to Drive Motor Generator Battery Venting and Cooling Description.