Recent NVH test on an eight cylinder diesel.

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carspector
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Recent NVH test on an eight cylinder diesel.

Post by carspector » Tue Apr 02, 2019 12:32 pm

Hello,

I recently did an NVH test on a 2015 Ford F-250 (4WD) with a 6.7 liter diesel engine. The NVH tool detected first order tire and fourth order engine vibrations. Since the vehicle has an eight cylinder engine I was expecting to see an E4 vibration to some extent. At times the E4 vibration would go over 32mg. The higher (E4) readings were when the engine speed was between 1600 and 1700 RPM and the actual vehicle speed was around 66-70mph, with the transmission in 6th gear. Unfortunately I did not have a comparison vehicle.

Have you all had a chance to look at any eight cylinder (Ford) diesel trucks? Any thoughts on the attached files?

Any information would be greatly appreciated.
Attachments
190402_VibrationAnalysiser_0012.pddata
(692.72 KiB) Downloaded 18 times
190402_VibrationAnalysiser_001.pddata
(704.39 KiB) Downloaded 14 times

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

Re: Recent NVH test on an eight cylinder diesel.

Post by Steve Smith » Thu Apr 04, 2019 4:28 pm

Hello and thank you for the post, sorry I have only just seen your request.

Looking at 001 capture E4 is predominantly high as would be expected on a V8 given we have 4 combustion events disturbing the crankshaft every revolution
001 Capture.png
Typical E4
The following forum post will help describe these orders post86961.html#p86961

A 6.7 litre V8 Diesel is some engine for sure and the characteristic E4 disturbances will most certainly be present with NVH.

Please don’t be alarmed by E4 exceeding the customer complaint which I believe to be T1?

A good exercise if you have time, is to drive over various road inclines/declines and monitor E4.

Low road speed, high gear, low rpm is a classic scenario in which E4 (or any engine combustion related vibration order) will go over-range.

Think of hill climbing in the wrong gear (too higher gear)
As the load increases on the engine, the engine rpm falls and the vibration in the cabin intensifies. (Often the cabin booms) This is where you would typically downshift to obtain the relevant torque with an increase in engine rpm. At this point cabin vibration and boom reduces dramatically, this is your E4

We see this very often with auto transmissions where the vehicle manufacturer has you in 6th gear at 28 mph! This great for emissions and fuel economy due to low rpm but torque suffers as a consequence. To downshift often requires the gas pedal pushing down by ¾ before downshift is permitted, whilst in the interim, the cabin is booming due to E4.

This can be exaggerated further by customers who are towing heavy machinery etc.

Try comparing hill climb E4 levels in different gears, then when you level out at cruise, and then finally notice what happens to E4 when you take your foot off the gas pedal, E4 disappears as we have Fuel Cut Off and no combustion.

Again looking at 001 capture your T1 is in a lateral direction, was your accelerometer mounted as per the Wizard Set up? Have you resolved the customer compliant and was this tyre related?

I have also noticed there is no signal present on the Y axis of your accelerometer measurement (Channel B red) Was this a connection issue?

I hope this helps, take care……Steve

carspector
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Posts: 2
Joined: Wed Jan 27, 2016 3:09 am

Re: Recent NVH test on an eight cylinder diesel.

Post by carspector » Mon Apr 15, 2019 1:29 am

Hey Steve,

Thank you so much for getting back to me. Sorry for the delay. I will have to go back and look at the data. I looked at this truck for a friend. I am waiting to hear if the issue has been resolved.

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