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.
http://www.youtube.com/watch?v=ByAQvuzcTq8 and http://www.youtube.com/watch?v=n2NQ_dO3lMU
http://www.youtube.com/watch?v=7JvHT23ubHs&feature=related is not from Weber, but is an animated
overview of power flow relative to road speeds.
Regards,
Martin from British Columbia