NVH Diagnostic

Ask questions relating specifically to the PicoDiagnostics NVH equipment and software here.
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mbrown1073
Newbie
Posts: 8
Joined: Fri Nov 11, 2022 4:40 am

NVH Diagnostic

Post by mbrown1073 »

Hi,

Was looking for some guidance with diagnosing a vibration complaint on a 2022 Kenworth W990 with a Cummins X15, 18 speed Eaton Endurant transmission. The complaint is just vibration all the time. Have had several test drives, with no vibration felt. We purchased the NVH kit to help diagnose this complaint and I am currently trying to learn how to use it. I have a capture for your viewing pleasure. Any help would be appreciated.

Thank you,
Matt Brown
Attachments
231102_VibrationAnalyser_Hummer.pddata
Base line drive
(15.3 MiB) Downloaded 66 times

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1567
Joined: Sun Aug 25, 2013 7:22 am

Re: NVH Diagnostic

Post by Steve Smith »

Hello Matt and thank you for the post

One concern I have is that the customer complaint is a vibration all the time but we cannot feel the vibration.

Can we road test this vehicle with the customer and ask him/her to point out when they can feel the vibration.
Another pointer is where can they feel the vibration? I.e., is it the driver and can they feel the vibration in their feet, seat, fingers or even hear the vibration

I know hearing a vibration sounds “wrong” but remember sound and vibration are one and the same, we experience lower frequencies as vibration rather than sound and we all interpret such lower frequencies differently.

Is there a fixed speed where the vibration occurs or is this load related?

We also need to sperate engine vibrations from road speed vibrations
i.e., if this occurs at 70 mph @ 1367 rpm, what happens if we select neutral and allow the engine to idle whilst we maintain 70 mph?

If our vibration remains present, this is road speed related

Looking at your capture below we do have a lateral T1 vibration both at 65 and 70 mph
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I will assume your accelerometer was mounted vertically with the screw thread facing forward in the cabin?

If so, we can focus on a lateral T1 vibration (A component rotating at the same frequency as wheel and tyres)

Below I also notice a continual P1 vibration (A component rotating at the same frequency as the Propshaft)

I have added an annotation that describes the sporadic activity we see around T1 & E0.5 which is quite normal when the vehicle hits a pot hole, drain grid or uneven road surface. This can also be seen in the spikey nature of the black data from the accelerometer recorded in the signal history
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As ever, before we dive in, back-to-back comparison would help and qualifying the customer complaint against the objective data we simultaneously capture

With regards to NVH Help, there is a large amount of Help within the NVH software and in the links below:

Our YouTube channel has several NVH videos (Search for NVH)
https://www.youtube.com/@PicoScopeAutom ... ?query=NVH
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We also have tutorials and customer case studies in our NVH section on the forum here:
https://www.picoauto.com/support/forum481.html

We also have a number of NVH topics which you can link to directly here
https://www.picoauto.com/support/topic15231.html

I hope this helps, take care…..Steve

mbrown1073
Newbie
Posts: 8
Joined: Fri Nov 11, 2022 4:40 am

Re: NVH Diagnostic

Post by mbrown1073 »

Steve,

Thank you for the reply. I will try to get more information form the customer and update the case when available. As well as get a capture of a truck without any vibrations for comparison. Give me a few days to get this lined up.

Thank you,
Matt Brown

mbrown1073
Newbie
Posts: 8
Joined: Fri Nov 11, 2022 4:40 am

Re: NVH Diagnostic

Post by mbrown1073 »

Steve,

Was able to get the customer to come drive the unit while I had the NVH sensor attached to the inner driver's seat rail screw hole facing forward.

Customer stated that the vibration would come and go but was most noticeable at speed 68 mph and above. I rode with the customer and could feel a slight vibration at these speeds, but the tool would show the vibrations when the customer would say there it is. Which was around 70mph and above.

I then started moving the extra sensor around to narrow down where the issue might be. I believe that I have 2 different issues with this unit. I have attached all the driving data for review. Let me know what you think.

Thank you,
Matt Brown
Attachments
Left hand rear drive axle wheel end LAT1.pddata
(15.6 MiB) Downloaded 64 times
Left hand front drive axle VER1.pddata
(11.51 MiB) Downloaded 61 times
Right hand front drive axle wheel end LAT.pddata
(7.35 MiB) Downloaded 62 times
Right hand rear drive axle wheel end LAT.pddata
(11.44 MiB) Downloaded 58 times
Customer driving unit.pddata
(9.92 MiB) Downloaded 66 times

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1567
Joined: Sun Aug 25, 2013 7:22 am

Re: NVH Diagnostic

Post by Steve Smith »

Hello and thank you for the feedback, sorry for the late reply

Below I have used the “right-click” Channel in view option to focus on cabin vibration first

We have a strong T1 lateral vibration in the cabin (This is strong enough to be felt by the occupants)
Note also P1 is there too
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If we now bring back channel D and use the “right-click” auto scale feature we can see the 2nd accelerometer also captures this same vibration at a much larger intensity (431 mg)
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Could you confirm the accelerometer connected to channel D (mounted at the “rear drive l/h wheel”) was measuring the lateral axis of vibration and mounted vertically with the screw thread facing forward?

Notice in the file below how the data appears “clipped” in the signal history due to an over-range condition
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This will be caused by channel D location setting at “Passenger compartment” instead of “Engine compartment”

With that said, channel D indicates a T1 again at 394 mg

Below we have T1 at 217 mg at the “Right hand front drive wheel end”
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Below is interesting as at 77 mph we have a continual P1 (First order propshaft vibration)
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Finally, we have the customer driving unit which confirms what we have discussed in these posts (T1 lateral and P1 vertical)
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Based on the above we can summarize below assuming channel D accelerometer is mounted virtually with the screw thread facing forward and measuring the desired axis:

• We have a component (rotating at wheel and tyre speed/frequency) exhibiting a first order (T1) lateral vibration at road speeds from approx. 70 to 79 mph
• We also have a component (rotating at propshaft speed/frequency) exhibiting a first order (P1) vertical vibration at a road speed of approx. 79 mph
• The largest T1 vibration was detected at the “rear drive l/h wheel” (see image 2 above)

I hope this helps move the diagnosis along, take care……Steve

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