NVH Vehicle Speed Question

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NVH Vehicle Speed Question

Postby steevegt » Thu Jun 08, 2017 1:11 pm

Hi,

As far as I know, there are 3 options to read the engine speed: Square wave signal, OBDII and user manual input. What about vehicle speed?

I have a car (2008 model) that does not implement the vehicle speed PID (0D). What option do I have in this case?
This is a hard limitation, because without this there is no "easy" way of identifying tyre related frequencies.

In more generic terms, it looks like I can only have vibrations (custom or not) directly proportional to the Engine Speed, Vehicle Speed, Propshaft or a fixed frequency. Is this true?
In my opinion it will be very nice to have the same possibilities to create a "custom vibration" as I do have to create a math channel in the scope software. Better if I could also use a custom PID as an input, or the D channel signal.

Thanks
steevegt
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Re: NVH Vehicle Speed Question

Postby Steve Smith » Thu Jun 08, 2017 6:06 pm

Hello and thank you for the post.

With regards to vehicle speed, do you know if a Custom PID could be used to obtain Road speed via OBD?
If so (and you have the formula) you can create a Custom PID as described here: post49491.html#p49491

If not then no problem, you can use the "Calculate Road Speed" option.
Could you click on the Options Tab>Advanced options>and select "Calculate Road Speed"

CALCULATE ROAD SPEED.jpg
Calculate Road Speed


Here then you will be required to enter the transmission gear and differential ratio's under the Advanced Button found in under Vehicle Information

ENTER TRANSMISSION RATIOS.jpg
Enter transmission ratios


During your road-test the software will obtain engine speed via OBD and you will be required to enter the gear selected.

NVH GEAR SELECTION.jpg
Select relevant gear


With the relevant gear selected the software will calculate engine speed/frequency, divide this frequency by the gear ratio (selected by you) to obtain the transmission output shaft frequency/or propshaft frequency (RWD) and then divide again by the differential ratio to obtain wheel frequency. All of which will be identified by the software as E1, P1 and T1

NVH SPEEDS-FREQUECNY CALCULATION.jpg
Calculated frequencies


Moving onto Custom vibrations could you follow the procedure described here:
post62901.html#p62901

I hope this helps, take care.......Steve
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Re: NVH Vehicle Speed Question

Postby steevegt » Fri Jun 09, 2017 2:02 am

First, thank you Steve for your excellent post, as always...

My first move, as you suggested, was to to see if I had any road speed related PID available, but unfortunately I had not...

The "Calculate road speed" option should do the trick. That also answers another question that I had: I filled the data about the transmission and differential ratios, expecting that it will calculate the vehicle speed and shown the T type vibrations, but it did nothing, so I was wondering what is the purpose of that?!

IMHO, even if I have the ability in the software to use this calculated road speed based on the gear ratios, just using an extra scope channel connected to a wheel speed sensor could be a useful option.
steevegt
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Re: NVH Vehicle Speed Question

Postby Steve Smith » Tue Jun 27, 2017 5:28 pm

Hello and thank you for the feedback, sorry this is another late reply.

Rest assured I will add the wheel speed signal input to the New Feature Request List

Take care.....Steve
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