NVH Vibrations, tyre X-axis

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Joined: Fri Mar 20, 2020 9:00 am

NVH Vibrations, tyre X-axis

Post by Peter24 » Fri Mar 20, 2020 9:10 am

Hello everyone,

I am just starting my journey with picoscope measurement, previously had some propshaft balanced with great results.

Right now I am facing vibration complaint that according to the measurement is T1 (mostly on X-axis).
Wheels were balanced on Hunter to <50N.

Well as it's T1 it can be everything that is rotating with wheel speed but I was wondering if the high value mostly on X-axis can lead to something?

Do you have any tips like what could cause only X axis vibrations?

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Steve Smith
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Re: NVH Vibrations, tyre X-axis

Post by Steve Smith » Fri Mar 20, 2020 10:19 am

Hello and thank you for the post, rest assured you can count on our support throughout this journey

At first glance this does indeed look like a first order Tyre Frequency related vibration (T1)
More information on orders and harmonics can be found here

However we may have other issues which I will come to in a moment

Sticking with T1, your RFV of <50 Newtons is great, and so we can assume rim and tyre run out, deviation etc. are ok (The following video from Hunter explains RFV perfectly

If wheels and tyres are OK, then we need to focus on "zoning" into the vibration by re-positioning your accelerometer. If you have 2 accelerometers keep the X Axis attached to the drivers seat and measure the X Axis at each corner of the vehicle as we have here in this video

Moving on, click on "Add Vibration" and select Engine Speed Vibration 0.5 Order.

You can see below that a 0.5 order engine vibration also coincides with your T1 frequency and this could be responsible for your vibration

Please click on the E0.5 label in the Frequency view to read more about E0.5 vibration orders where the largest offender is often a misfire (combustion anomaly) A V8 will carry/disguise a misfire quite well

The image below will help
Image 1
I hope this helps, take care......Steve

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