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Smartphone-based NVH diagnostics

Friday, June 1, 2018 - 07:00
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Have you ever had a problem vehicle with a vibration that just seemed to be impossible to fix? Have you performed repair work or installed parts, in an attempt to correct a vibration and it ended up being a complete waste of your time and the customer’s money? I have, and I know that I am not alone. 

As you may already know, correcting a vibration concern has been much easier than diagnosing the source of a vibration. Correcting a vibration concern can be as easy as balancing a tire or as difficult as correcting a backlash variation problem on a ring and pinion gear set. You cannot correct a vibration concern without first diagnosing the source. 

There have been many vibration diagnostic tools over the years, some mechanical and some electronic. Most of them are bulky and time consuming to setup. To make things worse, almost all of them are difficult to understand without hours of technical training because there were no definitive results. You had to decide what was wrong with the vehicle based upon the measurements displayed on the tools.

Previous generations of vibration diagnostic tools

Today I suspect that almost all of you have a smartphone within an arm’s reach at this very minute. That smartphone (with its amazing internal sensors) along with a unique smartphone app, can turn your smartphone (and some tablets) into an easy-to-use-and-understand vibration diagnostic tool. The smartphone app I am referring to is called “NVH” on the Apple App Store, and “NVH for Android” on the Google Play store. Since both apps have slightly different names, we will just refer to them as “the App” in this article. By the way, NVH is an industry standard term for Noise, Vibration and Harshness. The App currently measures vibration and harshness; noise measurements may come in the future.

The next generation in vibration diagnostic tools: The “NVH” app (Apple) and the “NVH for Android” app (Google).

This is a very sophisticated professional diagnostic app. This App incorporates all of the vibration diagnostic experience, knowledge and expertise I have accumulated over the last 27 years teaching vibration correction at Weber State University.  

The App can help you diagnose the source of a vibration on almost any car, light truck or commercial truck. It can automatically tell you the exact type of vibration the vehicle is experiencing (there are at least 10 different types of vibrations on a typical vehicle) and will lead you to find the exact cause of the vibration by following step-by-step diagnostic and repair procedures. I have identified at least 276 different causes of vibrations on a typical vehicle. 

I have had many people laugh at me in disbelief when I tell them we have identified 276 causes of vibrations. I ask them “What are you going to do when the typical repairs (balancing the tires and driveshaft) have already been performed and the vibration is still there?” At that point you typically have a several options: 1. Search the internet for help; 2. Start replacing or swapping parts; 3. Admit defeat and send the customer to someone else; 4. Try to get some help. This App is an excellent source of professional help; it is as close to having me in the shop helping you as you are going to get (unless you are one of my current students).  

Warning: Educational content!  

Before discussing the automatic diagnostic capabilities of the App, we need to define three boring, but helpful-to-understand, technical terms: 

Frequency: The number of times per second or number of times per minute a vibration is detected. The App uses Hertz (Hz) as the default unit of measure, but can be changed to cycles per minute (CPM) or RPM in the app settings. Any part on the vehicle that rotates can cause a vibration. Each of these parts has its own unique rotational speed. The App uses the vibration’s frequency to identify the type of vibration.  

Amplitude: A measurement of how hard or harsh a vibration is. The unit of measure is g-force (the force of gravity). Low amplitude vibrations usually cannot be felt or heard, while high amplitude vibrations can be heard, felt or both depending on the frequency of the vibration. Decreasing the amplitude of a vibration is the primary objective of any vibration repair procedure. The App uses amplitude to identify the harshness of the vibration. 

Order: The number of disturbances or shakes in one revolution of a rotating part. Each order of vibration can only be caused by certain failures. For example: Anything that is out of balance will only cause a first order vibration. In other words, balancing a tire with a second order vibration is a waste of time. Understanding this concept can be very helpful when diagnosing the source of a vibration. Each rotating part on the vehicle can have many different orders of vibrations. Obviously, there are many rotating parts. The App uses the order to identify the type of vibration and to guide you to the correct repair procedures contained in the help file. 

Four easy diagnostic steps 
Now that we understand the technical terms, let’s get back to the App. Using the App requires four easy steps.  

Step 1: Identify your vehicle. First, the App needs to know some technical information about your vehicle. The App uses that information to determine which vibrations to pay attention to and which to ignore. For example, we would not want to confuse evenly spaced joints in the road with a tire speed-related vibration. Determining which vibrations to pay attention to on each vehicle is a complicated process. Depending on the vehicle, the app will use up to 31 different pieces of vehicle data while performing vibration analysis.  

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