PicoScope 7 Automotive
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2021 MERCEDES SPRINTER VAN NVH DIAGNOSING HELP
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CShackelford
- Newbie
- Posts: 1
- Joined: Tue Feb 01, 2022 9:41 pm
2021 MERCEDES SPRINTER VAN NVH DIAGNOSING HELP
Hello. Can somebody help me understand what I am looking at when viewing vibration indices on the NVH during this test run. From what I can tell, its picking up mostly first-order propeller vibrations in this test run. The vibration occurs under hard acceleration on initial pickup. Additionally, at around 75mph there is a noticeable howl.
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- FLETCHER JONES 2021 SPRINTER NVH.pddata
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Steve Smith
- Pico Staff Member
- Posts: 1594
- Joined: Sun Aug 25, 2013 7:22 am
Re: 2021 MERCEDES SPRINTER VAN NVH DIAGNOSING HELP
Hello and thankyou for the post, sorry for the late reply
Looking at the capture I can see we have 2 areas of concern which include P1 (Propshaft frequency 1st order vibration) during acceleration and deceleration
Below I have captured P1 on deceleration @ 57 mph
This suggest a road speed related vibration that is not influenced by load
Looking at the spikey nature of the signal history, could you confirm if the road surface was uneven during the road test?
If not, I suspect this may be “bouncing” of an unladen vehicle which can present other issues such as the momentary appearance of T2 and T3 due to tyre bounce and flex
With that said, below the T3 vibration is exceptional high for a sustained period of time during acceleration suggesting this is load related and could be linked to 3 disturbances per rotation of the road wheel (Possibly Tripod joint of a drive shaft)
Ideally, we need to repeat the road test on a favorable road surface or add vehicle load (i.e., Weight)
Try to sustain the vibration for longer periods by finding the sweet spot which includes load, road speed and engine speed.
If possible, select neutral and allow the vehicle to coast or remove foot off the gas pedal to introduce “fuel cut” and also driven load. You may find you can create and cure the vibration simply by adding and removing gas
If you have an additional Accelerometer/Microphone, add the mic to the cabin to narrate your road test and another accelerometer at an alternative location on the vehicle (Measuring the offending vertical axis (Keep the Accelerometer mounted vertically)
Please note this vehicle may be exhibiting 2 different offending vibrations
I hope this helps, take care……Steve
Looking at the capture I can see we have 2 areas of concern which include P1 (Propshaft frequency 1st order vibration) during acceleration and deceleration
Below I have captured P1 on deceleration @ 57 mph
- Image 1
Looking at the spikey nature of the signal history, could you confirm if the road surface was uneven during the road test?
If not, I suspect this may be “bouncing” of an unladen vehicle which can present other issues such as the momentary appearance of T2 and T3 due to tyre bounce and flex
With that said, below the T3 vibration is exceptional high for a sustained period of time during acceleration suggesting this is load related and could be linked to 3 disturbances per rotation of the road wheel (Possibly Tripod joint of a drive shaft)
- Image 2
Try to sustain the vibration for longer periods by finding the sweet spot which includes load, road speed and engine speed.
If possible, select neutral and allow the vehicle to coast or remove foot off the gas pedal to introduce “fuel cut” and also driven load. You may find you can create and cure the vibration simply by adding and removing gas
If you have an additional Accelerometer/Microphone, add the mic to the cabin to narrate your road test and another accelerometer at an alternative location on the vehicle (Measuring the offending vertical axis (Keep the Accelerometer mounted vertically)
Please note this vehicle may be exhibiting 2 different offending vibrations
I hope this helps, take care……Steve