General Motors eAssist Electric System

Figure 1 - This is the eAssist system on the 2012 Buick LaCrosse.
Figure 1 - This is the eAssist system on the 2012 Buick LaCrosse.

Another version of electric-assist vehicle technology is showing up in collision repair facilities. General Motors in 2012 introduced what it refers to as "light electrification" technology on select models. This system is called eAssist, and is available on some 2012 Buick LaCrosse, Regal, and 2013 Chevrolet Malibu models (see Figure 1).

The eAssist system is a similar configuration to the Belt Alternator Starter (BAS) system that was available on some recent model year GM vehicles. The BAS system was discontinued as of the 2010 model year.

System Features

The eAssist system uses a starter/generator, which may also be referred to as the drive motor. This unit serves as an AC generator, a power assist to the engine in certain driving situations, and for starting the engine when it is in the auto-stop mode.

The drive motor is mounted to the front of the engine in place of the alternator. The drive motor is connected to the crankshaft pulley using a specially designed serpentine belt and belt tensioner.

Vehicles with the eAssist system also have regenerative braking, electronically controlled shutters in the lower grille, and a system that shuts down fuel delivery to the engine in certain deceleration conditions. The grille shutters open or close based on engine coolant temperature and vehicle speed.

High Voltage (HV) Battery Pack

12390Figure 2 - The eAssist system high voltage battery is located in the trunk of the vehicle as shown on this 2012 Buick Regal.Unlike the BAS system, which used a 36-volt nickel-metal hydride battery, a 115-volt lithium-ion battery powers the eAssist system. The eAssist system high voltage (HV) battery pack is located in the trunk of the vehicle, directly behind the rear passenger seat (see Figure 2).

The battery pack contains two battery sections connected in series that together provide 115-volts DC. The battery pack also contains some of the control modules and parts used by the eAssist system.

The battery pack has a metal tray that is fixed to the vehicle floor, which provides a mounting location for the HV parts. A cover is secured over the parts to prevent access without first disabling the HV system.

The HV battery sections are air-cooled. Each battery section case has an air inlet and an air outlet vent tube. An electric fan draws air through a vent located behind the rear seat through the battery case to cool the individual cells. In the event of a damaged or ruptured battery, any gases are vented to the outside of the vehicle.

High Voltage Safety

1120Figure 3 - Always wear Class 0 electrically insulating rubber gloves with protective leather outer gloves when working on or near high voltage parts.When working on or around vehicles with high voltage systems, always follow the appropriate safety precautions. Read and follow the recommended service procedures for high voltage systems and parts.

Be sure to wear the appropriate personal protective equipment, which includes Class 0 insulated rubber gloves with leather outer gloves (see Figure 3). Always inspect the insulated gloves for any defects that might prevent the insulating properties, and do not wear them if they are damaged.

More information on high voltage safety can be found in the Emergency Response Guides for the Buick LaCrosse, Regal, and Chevrolet Malibu eAssist equipped vehicles. These documents can be accessed for free at the www.gmstc.com website.

Damage Analysis and Repairs

GM service information states to not remove the battery pack cover when inspecting for damage. Inspect the battery pack assembly, cooling fan, air ducts, drive motor, and HV cables. Verify there are no cracks or dents, pinched, cut, or frayed cables, or other physical damage.

For repairs, some parts of the high voltage system are serviceable. For example, the two lithium-ion battery sections are diagnosed and serviced as a single battery assembly. The individual battery sections are not serviced separately. The drive motor has two internal sensors that are not serviceable, the drive motor position sensor and the drive motor temperature sensor.

Refer to the service information for the proper procedures. Always refer to the service information for the appropriate disabling and safety procedures when working on any HV system parts.

High Voltage Disabling

12393Figure 4 - Shown here is a display cutaway of the eAssist system high voltage battery and drive motor.GM service information recommends waiting five minutes after turning the ignition OFF, to allow the HV capacitors to discharge before working on or around the HV system or parts (see Figure 4).

The HV battery pack, and the starter/generator each have an interlock switch located on the service access covers. The interlock will disable the high voltage when the starter/generator control module identifies that an high voltage area has been accessed. When either cover is removed, the interlock loop is opened. The starter/generator control module will open the contactors to prevent contact with high voltage.

The HV battery pack has a manual disconnect lever to allow disconnecting high voltage from the eAssist system when performing service on the system (see Figure 5). The high voltage manual disconnect lever and generator battery fuse are located in the battery energy control module wiring junction block assembly. This assembly is in a plastic tray that is secured to the top of the starter/generator control module.

High Voltage Enabling

12403Figure 5 - The location of the manual disconnect switch on this eAssist system high voltage battery prop is shown here.

When enabling the eAssist HV system, be sure that the manual disconnect lever, and the interconnect switch are in the closed position. Refer to the appropriate service information for the recommended procedures.

All fasteners for the HV parts must be tightened to the specified torque. Insufficient or excessive torque may result in malfunctions or damage to the parts or the system.

Conclusion

GM is introducing another version of electric-assist vehicle technology called eAssist beginning on some 2012 models. This system uses 115 volts to operate. It is important that anyone working on or around the high voltage parts follows the appropriate safety precautions, and refers to the appropriate service information. Doing so will help to ensure a high level of safety when inspecting damage or making repairs on these vehicles.

This article first appeared in the October 11, 2012 edition of the I-CAR Advantage Online.