Vibration Diagnosis Technology
Posted to Technical Tips Forum on 4/25/2016
17 Replies
Some active dialog is taking place in a current Industry
Issues thread, as posted by iATN's resident poster of "All
Things doom and Gloom" Ozdjan Hassan, who manages to dig up
and air the "dirty laundry" in the automotive industry. Hmm,
do they build cars in Cyprus? VBG.
The fact of the matter, on the trucks in question is that
not all trucks of the exact same build exhibit the same or
any concerns and the main contributing factors that are most
common, appear to be an extremely stiff chassis and body
assembly reacting to tires of questionable quality.
Understanding the dynamics of resonant frequencies, source
(transponder), transfer path and responder (seat/controls)
allows technicians some opportunity to effect improvements.
However, some natural resonant frequencies are inherent to
various vehicle components and it can require significant
re-engineering to eliminate or engineer a resonant frequency
out of the objectionable range.
GM and tire engineers in their attempts to diagnose some
problem trucks have gone through several tires before
identifying a set that is truly acceptable quality. Many
times that is still the issue, but a slight degradation of
tire could cause the same concern at any time. Vehicles do
perhaps need to accommodate and tolerate the less than
perfect environment and adapt for wear on components a
little better in some cases.
So, knowing that no vehicle will have perfect tires for all
of it's lifetime, even beyond the first tire rotation in
some cases, improved isolation, mass dampening and mount
stiffness may be just a few ways to address transfer path
issues, if the source (mostly tires and wheels) cannot be
made "110%" perfect.
For those discussing such issues of vibration without
knowledge of current vibration diagnosis technology
available, they might just as well pack up and go home,
since it can be extremely challenging even with the most
current technology available to technicians. All GM
dealerships must now use the PicoScope with NVH kit for
vibration diagnosis.
Many technicians have attended training to date and benefit
from this tooling, over it's predecessor, the EVA, before
that, VAL, sirometers, reed tachometers etc. I've used them
all and the difference between the old and new technologies
is the level of G force that can be measured and identified
to be typical of components or assemblies. The EVA was
okayish, but cannot measure down to the milli Gs or micro G
forces that are creating concerns with current technology
vehicles.
Since the introduction of the PicoScope with NVH kit which
I've had for well over a year now, the scope itself has been
updated to the latest and greatest and the introduction of
the 3 axis sensor is the biggest improvement over the single
axis sensor. The sensor when mounted properly will
accurately display the XYZ axis (direction) of the dominant
frequency in bar graph. At the push of a button, to the
default setting, the consolidated value is displayed,
similar to the single axis sensor of a year ago.
Here are some screen shots of an induced vibration from a
couple of weeks ago, but more importantly, I encourage those
of you who not familiar with the tool to look at what is
being displayed. In other words take a look at E1 and E2,
P1, P2, T1, T2, T3 etc, to get an idea of what is being
displayed.
Take a look at various methods of displaying the data,
frequency, 3D frequency, bar graph, RPM order, road speed,
etc. Think of this as having the same characteristics as
John Kelly's Vibrate Software, because it does.
This screen shows the option to "Add a Vibration" that is
not in the default display, such as an Active Fuel
Management order[2006 Pontiac Solstice, Engine/Propulsion
Scan Data].
In the 3D frequency mode, I have manipulated (stretched out)
the graph for improved viewing)[2006 Pontiac Solstice,
Engine/Propulsion Scan Data]
This view shows the 3 axis sensor being used in consolidated
(default) mode, looking the same as a single axis sensor bar
graph.[2006 Pontiac Solstice, Engine/Propulsion Scan
Data]
Here we are viewing in RPM order mode. Look at the 3 axis
"XYZ" sensor plots (red, blue and green) and sympathetic
frequencies [2006 Pontiac Solstice, Engine/Propulsion
Scan Data]
Of course, my old reed tachometer and the EVA will do that
too, but those tools are not suitable as a primary
diagnostic tool on current technology vehicles.
A comment was made in regards to Active Fuel Management
effects, which can be monitored by selecting the "Add a
Vibration" option which opens a menu and selecting the
appropriate value that would correlate to an engine in AFM
mode.
This really is the best viewing technology readily and
economically available to technicians, especially when
compared to some very expensive engineering level
alternatives.
By the way, in the set up menu, instead of choosing the MDI
2 as I did, if working on a non-GM vehicle, a generic low
cost "ELM 327" interface can be selected.
Regards,
Martin from British Columbia