Vibration during acceleration

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Vibration during acceleration

Post by Willow »

Hello all, I have hit a bit of a mental dead end with this vehicle. I'm working on a 2015 Porsche 911 Turbo S that has a vibration under heavy load around 1500 to 2000 RPM. This vibration seems to be shaking the entire vehicle but is most notable to the driver in the steering wheel at appx 38Hz. I have attached my baseline run with the accelerometers on the drivers set and front/rear subframes as well as one with the sensor on the steering wheel. The vibration maintains 36 - 40 Hz regardless of vehicle speed but does require load at 1500 to 2000 RPM. It seems to loosely follow the E1.5 order. The dual mass flywheel was replaced appx 300 mi ago. Aside from this vibration the vehicle is in near perfect condition. There are no misfires or abnormal engine roughness readings noted, the fuel quality is good, the relative compression is perfect. I am new to the Pico and NVH, so hopefully I am missing something obvious.

Thanks in advance for any help you can offer.
333733 steering wheel baseline.pddata
(13.17 MiB) Downloaded 105 times
333733 baseline.pddata
(13.3 MiB) Downloaded 93 times

car diagnose
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Re: Vibration during acceleration

Post by car diagnose »

Hi, hast du es versucht mit andere Rädern zu fahren? Die vorhandene Rädern ausgewuchtet? Grüße

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

Re: Vibration during acceleration

Post by Steve Smith »

Good morning, thank you for the post, sorry for the late reply

Just looking at each capture, they are like chalk and cheese when it comes to peak vibration levels around E1.5

Below, I have called this the BAD capture where I have highlighted several areas to consider
Based on the image above we have our car progressively accelerating under load (5th gear 1530 rpm @ 43 mph)

This is where I found the highest peak clearly from the accelerometer connected to channel B (LF seat frame bolt) Is this the correct location or is this the steering wheel?

The offending vibration captured is at 36.4 Hz (36.4*60 = 2184 rpm) with a peak of 72.5mg

I agree, it does loosely follow E1.5 but I am not convinced they are related given E1.5 passes by the offending peak vibration on numerous occasions

Looking now at the GOOD capture below, at near identical road and engine speeds (and therefore load) the vibration levels are worlds apart (chalk & cheese)
At 36.6 Hz, the peak vibration levels are near equal from all connected accelerometers @ 8.84 mg

I have a number of questions and suggestions below:

1. Could I ask if all accelerometers were connected to the same axis (E.g., Y Axis and mounted vertically)
2. Could I confirm you are using the TA259 3 output NVH interfaces or the TA366 interface
3. If using the TA366 interface (found only in VAS NVH kits) were you using the SUM output
4. Regarding the “333733 Steering wheel” capture (BAD) could you confirm if accelerometer B was connected to the steering wheel
5. Would it be possible to repeat this measurement on a similar vehicle (not always possible I know)
6. When did our customer first notice this vibration? Has it always been present or has it appeared during ownership?

Moving onto further measurements:

Assuming our BAD capture has channel B connected to the steering wheel, we have successfully zoned in on the area of concern.

Could we mount a single 3 axis accelerometer vertically with the screw thread facing forward (XYZ to ABC respectively on the scope) in and around the steering column area?

The big clue we are trying to acquire is “what is our offending axis” within the steering gear.

This information does not always yield a result but it is another clue

For example, we know the steering wheel “responds” to a vibrating force at approx. 36.4 Hz (which could be from a component rotating at 2184 rpm. Can we look through the drive train at these given road and engine speeds and calculate what component is rotating at such a speed/frequency.

Knowing the axis (e.g., Z, lateral) would be another clue. E.g., What is rotating at 2184 rpm in and around the steering gear that could offend these components from side-to-side

Road test

I can see in the road test data that load is required to produce the vibration, with that said (and I think I know what will happen) rather than take the foot off the gas pedal in 5th gear when the peak vibration is present, can neutral be selected and then coast down?

It would be another clue as to whether we can feel this vibration with the engine speed low but road speed high. (if this is load related then I believe the vibration will disappear) but once again it is another pointer/clue

I hope this helps, take care……..Steve

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