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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.


Martin from British Columbia

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