NVH Tooling Case Study
Here is a case study using Pico NVH tool. The vehicle is a 2006 Hyundai Sonata 3.3L. Customer complaint is a road vibration. I test drove the car to verify the complaint. It experiences a vibration at about 45 mph and continues to vibrate up to at least 60mph maybe higher but I didn’t drive it any faster. This vibration would go away when you let off the throttle.
I didn’t need to use the NVH to fix this vehicle. I have felt this problem many times in the past. The reason I used the NVH here is for experience. This tool is not much different than a scope in the fact that you get better using it. Seeing what it looks like and getting familiar with the different views and how vibrations are displayed.
The NVH module is connected to the scope on the blue, red and green channels. These represent X, Y and Z axis. The yellow channel can be used for an RPM input or you can use a Jbox to pull RPM from the engine controller. The NVH module has a lead that you need to mount to the vehicle body. Typically the seat track. It has a strong magnet that hold it in position. This magnet mounted sensor has to be positioned with the X axis arrow facing forward. (You can mount it to a vertical plane if you unscrew the sensor and remount it on the side).
Using the software that comes with your Pico download you choose the NVH test. When you choose the test it will bring up a window that asks if you want to start a new test or load a saved one. After that it will bring you to a window to connect to a Jbox or use a separate input for RPM. I used the VCM2 this time. I like the VCM because it can be used wirelessly. I have used the MDI2 and the CardaqM in the past. All work well. I’m sure any Jbox would work fine. After you establish the link to the Jbox you need to build your vehicle. You will need to input the tire size and tell the software if it’s AWD, RWD, FWD etc. you can choose to use a static RPM. Your test results will not be as precise if you do that. You also have the option to do advanced settings. Under advanced you can tell the software what the gear ratio for each gear in the transmission is as well as the size of each accessory belt pulley.
After all the setup had been completed I performed my test drive and captured the data.
If you want the Pico file I can send them to you. The lower window shows the recording over time. The black is a representation of vibration. The red is vehicle speed and blue is engine RPM.
You will notice the vibration is roughly 12HZ and classified as a T1 vibration meaning it is something spinning at the same speed at the tires. The fact that it doesn’t vibrate if you let off the throttle points away from tire balance. This happened to be CV axle vibrations. The tires were also out of balance and were balanced. You will also notice the tires still showed vibrations after the repair but at a much lower measurement. It has been my experience that this amount is normal.
Post repair images:
Here are two video recordings:
Nice write up Justin. I have that NVH tool and use it quite frequently. The tool just plain rocks!
Thanks Albin, I remember sitting next to you in the class Matt Shanahan did on this at CAN a couple of years ago.
Looks great Justin! A great and under used tool. One question, how did you determine which side was causing the vibration?
I think both sides were worn. I did a visual inspection putting my hands on them. Both wobbled about the same. You can put the sensor in different locations and compare where the signal is stronger to help pinpoint the source.
Pretty slick, brother. I like how you make the valid point of using the tool when you already have the vehicle diagnosed. I can’t think of a better way to learn. When you know what “GOOD” looks like...”BAD” sticks out like a sore-thumb 👍👍
Justin very well done with a great explanation. We just covered NVH on a … Roundtable that helped open the eyes of many techs. The NVH took software designed by John Kelly is a great way for someone to get into NVH for $400.00. So for those that don't own a PICO scope check John Kelly's software out. John also wrote a good article on NVH about a month or two ago in Motor Age magazine. Once again Justin great job....it was good seeing you in Atlanta.
Thanks Justin! This was a nice write up. I appreciate you taking the time to put this together and share.
I've been interested in this. I have a question regarding application of this technology and technique to a real world issue that we face from time to time. Let's say that we test drive a front wheel drive vehicle with a vibration that is only present during acceleration. By the seat of our pants we are pretty confident that the vibration is caused by a worn CV joint. What are the chances that we will be able to pinpoint which axle is the cause by moving the magnetic mounted sensor in different locations?
I don’t have the answer to that question. My understanding is that you compare the amplitude of the signal from one location to the next. Kind of like the chassis ears tool, only on a scope measurement.
Brin, using the more advanced kits that have more than one sensor would allow you to analyze this. For instance, you could put one sensor on each strut tower to see what side the vibration was worse. This is common practice in finding bad tires, you identify that the vibration causing the complaint is tire related. Using more sensors you can find out which tire is to blame.