Hybrid Drive Systems: Description and Operation

Starter Generator Control Module Cooling System Description and Operation

Generator Control Module

The generator control module, also referred to as the starter generator control module, is a serviceable GMLAN device located under the hood, toward the front of the vehicle on the drivers side. It is connected to the vehicles 12 and 36-volt DC power circuits, and it is also joined to the starter-generator by 3-phase AC cables. The generator control module is cooled by engine coolant, which is circulated through a cold plate. A separate, electrically driven pump is used to ensure adequate coolant flow, and individual coolant inlet and outlet hoses connect the cold plate to the cooling system. The generator control module performs 3 main functions:

1. As the power inverter for the starter-generator, the generator control module converts 36-volt DC power into 3-phase AC power to drive the starter-generator as a motor. The power inverter also rectifies 36-volt AC output power from the starter-generator into the 36-volt DC power used to charge the 36-volt generator battery.
2. An auxiliary power module contained within the generator control module converts 36 volt DC power into the 12-volt DC power which is used for 12-volt vehicle loads and to charge the underhood 12-volt battery. A serviceable 175-Amp Fuse (GM P/N 15305191) located beneath the generator control module DC cable terminal box cover protects the vehicles 12-volt electrical system from excessive current.
3. The generator control module contains a Renesas M32 processor, and it directly controls the starter-generator, transmission auxiliary oil pump, hill-hold solenoids, auxiliary coolant pump and the generator control module coolant pump. The pumps and solenoids are driven by 12-volt pulse width modulated (PWM) power through vehicle wiring harnesses.

Starter Generator

The starter generator, sometimes referred to as the motor generator unit (MGU), is a serviceable 16-pole, permanent magnet, enhanced Lundell AC machine. This device not only serves as a 36-volt AC generator, it is also used to provide engine power assist and to start the engine following hybrid "autostops". 36-volt AC power flows between the starter generator and the generator control module through a 3-phase cable assembly.

As a generator, the starter-generator provides up to 3 KW of AC power to the generator control module power inverter. Field current is provided by the generator control module through a 7-pin connector, and starter generator RPM feedback is transmitted back to the controller through the same connector. Starter generator temperature data is provided to the generator control module through a separate 3-pin connector.

As a motor, the machine provides up to 65 Nm of torque for power assist and engine starting. The motor receives 3-phase AC power from the power inverter within the generator control module.

Generator Control Module Coolant Pump

The generator control module coolant pump is a serviceable component which is connected to the vehicle cooling system and the module cold plate using separate, serviceable hoses. The pump augments the engine driven water pump to ensure adequate coolant flow to the cold plate.

Three Phase Cable Assembly

Three cables carry 36-volt AC power between the generator control module and the starter generator. The cables are serviceable as an assembly which includes the generator control module AC terminal box. The cables are shrouded in a blue conduit to alert the technician to the presence of intermediate voltage electrical energy.

Generator Battery (Carrier Assembly)

The generator battery carrier assembly contains several individually serviceable components: the generator battery, generator battery vent fan, generator battery temperature sensors, generator battery temperature sensor wiring harness, generator battery fuse/fuse nut, generator battery disconnect control module and the generator battery disconnect control module cover.

Generator Battery

A serviceable 36-volt nickel metal hydride battery is located behind the rear seat, beneath the load floor. The battery contains 3 separate 12-volt cassettes which are wired together in series. The cassettes are serviceable and weigh approximately 10 pounds each. The cassettes will not be serviced individually, they will be replaced as a set of 3. Each cassette contains 2 non-serviceable, 12-volt, 8.5 amp-hr modules which are connected in parallel using bus bars.

Generator Battery Vent Fan

The generator battery vent fan is a serviceable component attached to the rear of the generator battery carrier assembly. This variable speed fan is controlled and powered by the generator battery disconnect control module. The fan draws cooling air through the bottom of the generator battery carrier assembly, exhausting it into the spare tire tub. Fan speed is varied, as required, to ensure that generator battery temperature remains within desired limits.

Generator Battery Temperature Sensors

Each battery module has a separate temperature sensor, or thermistor. These sensors are serviced as a pair (one pair for each battery cassette). The battery cassette must be removed from the vehicle in order to access the thermistors. These sensors receive power and provide a battery temperature feedback signal to the generator battery disconnect control module through the generator battery temperature sensor wiring harness.

Generator Battery Temperature Sensor Wiring Harness

The generator battery temperature sensor wiring harness is a serviceable component contained within the generator battery carrier assembly. It serves as a conduit for the battery temperature and voltage feedback signals which are processed by the generator battery disconnect control module. The harness features individual voltage terminals for each battery cassette as well as separate connectors for each of the 3 generator battery temperature sensor assemblies. The connector on the opposing end of the harness mates with the generator battery disconnect control module.

Generator Battery Fuse

The vehicles 36-volt electrical system is protected from excessive current by a 200-amp fuse located at the negative terminal of the generator battery. This fuse features an indicator window which should be oriented toward the top of the generator battery. The fuse is applied outboard of the negative 36-volt battery cable and is held in place by a serviceable, non-conductive generator battery fuse nut.

Generator Battery Disconnect Control Module

The generator battery disconnect control module, sometimes referred to as the battery disconnect unit (BDU) or battery energy control module (BECM), is a serviceable GMLAN device which is mounted to the rear of the generator battery carrier assembly. This controller also includes several non-serviceable sub-components, including a current sensor, service disconnect switch and the 36-volt system contactor. The generator battery disconnect control module controls the generator battery vent fan and monitors temperature, voltage and current levels within the generator battery. The service disconnect switch attached to the controller is a plunger type switch used to open the 36-volt system contactor during service activities. The switches plunger rests against the generator battery disconnect control module cover, and it closes when the cover is closed and opens when the cover is opened. The 36-volt system contactor will open and close in conjunction with the service disconnect switch. When the contactor is in an open position, the generator battery will be electrically isolated from the vehicle, although intermediate voltage potential will still be present within the generator battery carrier assembly and the generator battery disconnect control module.

Generator Battery Disconnect Control Module Cover

The generator battery disconnect control module cover, sometimes referred to as the battery disconnect unit cover (or BDU cover), is a serviceable, hinged panel attached to the rear of the generator battery carrier assembly. This cover shields personnel from intermediate voltage potential when properly secured in a closed position. The service disconnect switch plunger rests against the generator battery disconnect control module cover such that the switch will open with the cover in an open position, and it will close when the cover is in a closed position. The cover is securely fastened to the generator battery carrier assembly by an M6 bolt with a 10 mm hex head.