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 current limit relay, 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, vent fan, vent fan relay, current limit relay, and HV contactor relays are located within the hybrid battery assembly.

State of Charge

The battery energy control module (BECM) uses a complex calculation method based on varying conditions over a range of operation to determine and update the state of charge (SOC) of the hybrid battery. The hybrid battery parameters used by the BECM include current, voltage, and temperature. These inputs are monitored by several sensors within the hybrid battery assembly.

Operating Functions

The battery energy control module (BECM) is also referred to as the drive motor generator 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 contactor relays at the request of the hybrid powertrain control module (HPCM). The BECM is located within the hybrid battery assembly.

Communication and Hosted Diagnostics

The HPCM is the host controller for diagnostic trouble code (DTC) information for the following control modules:

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 HPCM through the Hybrid LAN communication circuit.

In the event a hosted module communicates a fault condition, the HPCM will determine if hybrid operation is affected and notify the vehicle operator by requesting the MIL illuminate and/or by displaying a hybrid service required message. In addition, the HPCM 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 HPCM.

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, and sums up these values to generate a calculated voltage value. The BECM also measures high voltage when the contactors are closed by monitoring the total bus voltage from the harness on the output side of the high voltage positive and negative contactor relays, this is the terminal voltage measurement.

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. A reading of 2.5 volts is 0 amps.

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 certain 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 HV contactor relay, the negative main HV contactor relay and the current limit relay, also called the precharge 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 HPCM. Either the BECM or the HPCM 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 HV contactor relay is closed.
2. The current limit relay is closed. The precharge high voltage circuit contains an in-line current limit resistor. With both the negative main HV contactor relay and the current limit 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 BECM reads 95 percent of available buss voltage at the HV terminals, the BECM will close the HV positive contactor relay.
4. The positive main HV contactor relay is closed. The positive main HV contactor relay bypasses the current limit relay and resistor in the precharge circuit and allows high current flow in and out of the hybrid batteries to occur.
5. The current limit relay is opened once the system is at operating voltage.

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 HPCM must ensure the system is in a low current flow condition prior to allowing the BECM to open the HV contactor relays. The HPCM will command that all high voltage components like the APM and the air conditioning compressor stop drawing current. Also, the HPCM 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.

The hybrid drive motor generator battery contains 40 individual batteries. The hybrid drive motor generator 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 at the rear of the hybrid drive motor generator battery through a single hose and is vented through the floor panel of the vehicle.

Each of the 40 hybrid batteries has a vent for electrolyte gas that is located on the top of each battery. The hybrid batteries vent system connects all of the 40 hybrid battery vents to a rubber manifold. The vent exits the hybrid drive motor generator battery through a single hose in the rear and is vented through the floor panel of the vehicle. These vents are mechanical and will only open when a predetermined amount of internal battery pressure is reached.

The battery energy control module (BECM) communicates the amount of power available from the drive motor generator battery for use by the hybrid system and also the amount of charge power allowed back to the drive motor generator battery from the hybrid system. This information is sent over on the GMLAN communications network to the hybrid powertrain control module (HPCM).

The BECM can adjust these power limits either based on hybrid battery temperature, hybrid battery voltage or DTC information.

The HPCM compares the BECM power limit capability to a similar value calculated in the HPCM and uses the lower of the 2 values to control the power.

Under normal operation the BECM will communicate both the available charge power and available discharge power limits according to the following power limit table based upon the maximum hybrid battery temperature.