NVH Vehicle Speed Question

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steevegt
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NVH Vehicle Speed Question

Post by steevegt » Thu Jun 08, 2017 11:11 am

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

Steve Smith
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Re: NVH Vehicle Speed Question

Post by Steve Smith » Thu Jun 08, 2017 4:06 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

steevegt
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Re: NVH Vehicle Speed Question

Post by steevegt » Fri Jun 09, 2017 12:02 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.

Steve Smith
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Re: NVH Vehicle Speed Question

Post by Steve Smith » Tue Jun 27, 2017 3:28 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

steevegt
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Re: NVH Vehicle Speed Question

Post by steevegt » Fri Sep 07, 2018 10:52 am

Hi again Steve!

The timing many not be ideal, but because I have something to add about this I'm replying here.

I follow the option you gave me for this car (with no PID for road speed), to have the road speed calculated based on gear ratios, gear, and engine rpm.
The thing is that, after setting everything up I was unable to select the gear. The Up and Down buttons simply were not there.
I tried to find a pattern, and based on what I had tested I believe this is a software bug/limitation.

I believe that the software has the rule to show the Up and Down buttons, if and only if you had the option to calculate road speed and if you are not using OBD as input. I'm saying this because if I change the RPM input to be calculated from a channel or if I insert a fixed RPM the buttons appear as expected, and I can select the gear I want.

I believe that the software was programmed with the idea that the RPM and road speed, when using OBD, are inseparable and a car that has one should have the other.
The thing is that in this case I want to use the RPM from OBD, and the road speed to be calculated. It makes total sense in this car, since I only do not have a PID for road speed. My option in here is to drive a wire to the engine compartment and use the crank sensor...
I'm also unable to remove from the list the PID that corresponds to road speed. Not direct reason to be able do this, but that was something I experiment, trying to workaround this issue.

This should be easy to replicate, but if you need more information please say.

Thanks
Steeve

Steve Smith
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Re: NVH Vehicle Speed Question

Post by Steve Smith » Mon Sep 10, 2018 3:48 pm

Hi Steeve and sorry once again for the late follow up with this one.

You are most certainly correct as I have reproduced the issue here.

The software does not make allowances for RPM only via OBD and as a result "Calculate Road Speed" is not valid when selected in this scenario!

It does make perfect sense to allow for RPM only via OBD for vehicles where only this PID is available and yet still allow users to "Calculate Road Speed"

I will pass this through as a bug rather than a New Feature Request (NFR) and include the suggestion to allow for the removal of the Road Speed PID. My feeling here is this can remain locked (Road Speed PID) if we allow for "Calculate Road Speed" where only RPM is present via OBD

Thank you again and rest assured all NFR's and Bugs are filed for the software team to review and prioritise.

Take care.......Steve

steevegt
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Re: NVH Vehicle Speed Question

Post by steevegt » Thu Sep 13, 2018 8:47 am

Hi Steve!
Thank you once again for your reply.

I do agree with you, the Road Speed PID can remain locked, nothing against that.
The only thing I would change is that when "Calculated Road Speed" is on, this PID should be ignored and you should be able to select the gear. At least that's how I see it...

Thanks
Steeve

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