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2012 Buick LaCrosse eAssist
Posted to Technical Theory Forum on 1/15/2012 10 Replies

Hi all. During the past week, I took the opportunity to attend training on the 115 volt GM eAssist system as currently fitted to 2012 Buick LaCrosse, which will also find its way into the Chevrolet Malibu for 2013 MY.

At a glance, we might consider this just another Belt Assisted System (BAS), but while there are obvious similarities there are a number of notable and subtle differences, besides the obvious higher voltage rating that separate this system from the earlier system.

We can expect to see more electric drive systems incorporated into a wider cross section of GM vehicles in the future, so taking a look at developments as they occur and sharing here, is worthwhile.

The previous BAS, while a mild hybrid, did serve a purpose in reduction of CO2 and other vehicle emissions during auto stop events and experiences have been drawn from that and other hybrids, as each step forward presents the opportunity to develop, or improve on certain technologies.

The eAssist is available on the LaCrosse in Canada, to models fitted with 2.4L LUK Ecotec engines and 6T40 automatic transaxles. There is no external or internal badging on the vehicle to identify that this is any form of hybrid, which may make for some interesting experiences where highway lanes and parking areas are available for use of hybrid vehicles. The main components of the system are a Hitachi liquid-cooled motor generator unit, similar in outward appearance, but larger than in previous BAS models and the controls which are all housed within the battery container, unlike previous systems of this general design.

Regarding the controls, wiring schematics will show a number of dotted lines that signify a part of a component is being displayed. In the case of the eAssist, there will be a a number of modules that are circuit board mounted and depicted by dotted line rectangles, within one or two more rectangles. Therefore, when programming is required, rather than HPCM, MCM and APM being available in a pick list, these components are incorporated into the (Starter)Geenerator Control Module. The Battery Energy Control Module is a separate silver box, mounted on the battery assembly, so expect to see BECM and GCM in SPS. I have not confirmed this, but that is how it was explained to be at this time.

There has been a shift from using the term "BAS" to "eAssist" for good reasons. There is more power available with the 15KW induction motor generator at 115 volts, for assistance when accelerating hard or negotiating steep hills. As in previous versions, the system incorporates auto stop and start capability, with deceleration fuel cut off and extended periods of lock up torque converter apply.

The motor spins the engine over during deceleration cut off, to provide regenerative braking. Other now familiar terms such as "torque smoothing" are used to describe the transitions from engine on to off and vice versa, during decel and auto start. With the belt removed, GDS2 can be used to spin the motor to ensure that it is free. While we can spin the motor by hand, using the scan tool might be useful if addressing a bearing noise concern. [2011 Buick LaCrosse CX, Photo] [2011 Buick LaCrosse CX, Photo]

A 115 volt Lithium ion battery pack is mounted in the same location between the rear wheels directly behind the rear seats inside the vehicle trunk. The battery and control system is air-cooled and air from the vehicle cabin is drawn through a grille in the rear "parcel" shelf through the battery and into the trunk. Here is the motor [2011 Buick LaCrosse CX, Photo] and the air intakes for each of the spiral wound Lithium ion battery packs. [2011 Buick LaCrosse CX, Photo]

Unlike the previous BAS system, there is no Starter Generator Control Module (SGCM) mounted up front in the engine compartment in a housing that resembles and performs inverter and various other functions. All controls are incorporated into the metal housing that contains two sixty volt Lithium ion batteries, along with now familiar hybrid control modules, pre-charge resistor, pre-charge contactor relay, Generator Control Module (GCM), Battery Energy Control Module (BECM) and much more.

Repair by technicians is anticipated, since we explore the innards of the battery energy storage system here in the photos as some preliminary procedures were performed.

From the manufacturers' names on the various modules and components, it can clearly be seen that this components are sourced from many manufacturers and locations around the globe by Hitachi. The whole assembly weighs in at approximately 65 lbs, so while it isn't particularly heavy, we need to be careful when removing the assembly from its mounting location.

Mounted directly to the battery housing is an electric motor, much like most fans used in motor vehicle HVAC systems. This system draws air through grille in the vehicle passenger rear compartment shelf, through ductwork and into the trunk. I can imagine a customer concern of "The tissue box on my rear parcel shelf empties itself!"

As with other hybrid applications that are rated as high voltage (>60v), following precautions by using required Personal Protective Equipment (PPE) is necessary is something that we all need to become more familiar with and practice until it becomes "second nature." apart from recognizable high voltage decals, systems with high voltage also carry the high voltage symbol, represented by a triangle with lightning bolt. [2011 Buick LaCrosse CX, Photo]

The vehicle components in the engine compartment, trunk and undercarriage all carry warning decals and instructions. Most notably, red warning labels indicate that high voltage is present at all times and orange labels identify that high voltage may be present. Unless the voltage has been measured and verified to be at safe levels for service outside the battery container, it is wise to always assume that high voltage is present. In the event that a contactor is stuck closed, this could be the case. The battery case contains two batteries that approximately ½ fill the container at the passenger (right side) of the vehicle the rest of the High Voltage Energy Storage system container is occupied by control modules, cables, contactors, current clamp and other aforementioned pieces.

Required tools for diagnosis and service, include Fluke 1587 or equivalent and is not considered to be an essential tool, but a necessary tool. In other words, GM isn't providing the tool to servicing dealers of eAssist or Volts. However, the cost should be borne by the servicing dealers, rather than the technicians.

The Fluke 1587 is required for Loss Of Isolation testing and GM does recommend wearing the high voltage electrical gloves when using the meter.

An aluminum conduit carries the three phase cables from the battery module, down through the trunk floor, under the vehicle and to the motor generator unit in the engine compartment. Being a belt assist system, there are some familiar but slightly different tensioning system components to the previous BAS systems. The same belt tensioner holding tool is used.

As in other hybrid systems, the hood latch plays an important role, especially so in the system, since the system does not charge the battery when the engine is running and the hood is open. This vehicle does incorporate "Jump Assist", which may be familiar to some of you who have worked on or learned the term from the GM 2 mode hybrid systems. However, in this application, there is no scan tool required to initiate jump assist, notably because this is a global vehicle platform for which the Tech 2 and Tech2Win, serve no useful purpose.

At this point, at least in Canada, batteries and/or components are serviced on an exchange basis only at this time. However, since training has technicians removing and opening up the battery storage system and the fact that part numbers are attached to many of the internal components, it is reasonable to assume that there will be a point where technicians will replace individual components.

Disabling the system is similar to other hybrid systems, where the key(s) must be removed to specified distance from the vehicle. Note that this system is apparently available in both key start and PEPS push button start versions. Disconnection of the 12 volt battery and waiting 5 minutes for capacitors to discharge is a typical routine in disabling systems, as is the used of "Live, Dead, Live" verification of confirming voltmeter functions and measurements at battery terminations in the trunk.

While the instructions use the term "manual disconnect lever", there is no actual "lever" involved. The purpose of removing, or positioning manual disconnect switches and levers is generally to separate battery packs into smaller units of lesser voltage and this application is no exception. To disconnect the batteries from one another, locate the greyish appearing sliding "switch" mounted to the front of the battery container, behind the right rear passenger seat back. Pull the small blue CPA tab out slightly. It will click into position. To the right side is a small grey button, referred to as "white". Depressing this button, will allow the switch to be slide sideways, opening the manual disconnect circuit and separating the two batteries. [2011 Buick LaCrosse CX, Photo]

In past, GM hybrid vehicle system High voltage Interlock Systems (HVICs) have been switches connected to a 5 volt series circuit. The purpose was and continues to be to shut down the system in the event of uneducated tampering or untrained attempts to diagnose the systems. The interlock in this particular system, contains a resistor, which I recall is approximately 3K Ω. So, rather than a simple switching circuit, it is now a sensing circuit, where information can be analyzed by the controls and an appropriate DTC set.

The Hitachi MGU differs from the BAS system, by way of being liquid-cooled, using a mix of DexCool and drinkable tap water. This is not a dedicated cooling system, rather it is a loop added to a conventional cooling system, with pumps added for coolant circulation and heater circuits.

Inside the battery case, voltage can be anywhere from 0 volts to 120 volts, depending on the condition of the components, level of charge and more. Once the manual disconnect process has been completed, the batteries should be isolated from each other, but may not be in the event of a stuck contactor as mentioned already. Regarding contactors, previous high voltage hybrids such as the 2 mode used three contactors, a pre-charge contactor, positive and a negative contactor. The 115 volt eAssist (sometimes referred to as BAS +) utilizes two contactors. One serves as the pre-charge relay and the second is the positive contactor. Engineers decided that a negative contactor is not necessary.

Inside view of the battery container lid, shows clear insulation material as bordered in red [2011 Buick LaCrosse CX, Photo]

Moving to view the components with the lid removed and PPE (1000volt gloves currently certified, physically inspects, safety glasses with side shields, CSA rated footwear, recommended non-flammable clothing, jewelry, watches, pens removed etc) [2011 Buick LaCrosse CX, Photo] What cannot be seen in the photos are the battery strap connections to the Generator Control Module (inside silver box) under the relay centre.

Replacement of batteries will require removal of battery cables from each battery terminal at each battery cable junction block , using insulated tools and step by step insulating each cable with 600v UL/CSA rated electrical tape and/or insulators as in the photograph [2011 Buick LaCrosse CX, Photo]

Here is a close up of the pre-charge resistor that measured approximately 3K Ω, current clamp, pre-charge contactor relay and positive contactor. There is no negative contactor. [2011 Buick LaCrosse CX, Photo]

Here is a close up of the fuse, manual disconnect, which is not actually a lever and the high Voltage Interlock Circuit (HVIC). [2011 Buick LaCrosse CX, Photo]

Here is a view of the battery cable junction blocks [2011 Buick LaCrosse CX, Photo]

With access to the Battery Energy Control Module (BECM) connectors X4 and X5, each battery pack can be tested using the test harness and the same tool El 48571 as previously used for 2 mode battery testing [2011 Buick LaCrosse CX, Photo] Connecting the X4 and X5 harnesses to the adaptor harness, allows each battery cell to be tested and voltage recorded. This will verify scan tool displayed values. [2011 Buick LaCrosse CX, Photo]

For a tour of the eAssist system, I recommend viewing videos posted to Youtube by John Kelly of Weber State University Automotive Department in Ogden, Utah.

You may John's other videos interesting. and is not from Weber, but is an animated overview of power flow relative to road speeds.


Martin from British Columbia

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