NVH fails to connect to EV's via OBD
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NVH fails to connect to EV's via OBD
There have been a number of Help Desk inquiries and forum posts highlighting the fact that NVH cannot connect to EV’s to obtain data such as VIN, Vehicle speed and RPM
Here is one such example viewtopic.php?p=103793#p103793
This is because EV's no longer have to provide standardized emission data at the OBD socket; the typical method by which NVH obtains VIN, Vehicle speed & RPM!
Add into the mix the fact that several EV’s utilise the “Unified Diagnostic Services” protocol (UDS SAE J1979-2 / ISO 14229) to permit diagnostic access rather than standardized OBD (SAE J1979 / ISO 15031-5) we certainly have our work cut out.
Not only do we have to contend with a protocol change, a number of EV’s do not respond to standard OBD requests via the UDS protocol! In this scenario, bespoke addressing of the relevant ECU is required, which of course means a bespoke response requiring decoding
Rest assured we are working on a solution but the huge number of variables and options will take time to overcome.
In the interim, we have a number of options to calculate electric motor or vehicle speed should you find yourself with an EV NVH complaint…….
In a scenario where electric motor or road speed cannot be obtained via the OBD connector, we can use channel D as a speed input from an optical sensor or an on-board speed sensor (e.g., ABS) to generate an RPM speed signal
Below is the NVH set-up configuration required to obtain a speed pulse from any rotating component using our BNC+ optical sensor https://www.picoauto.com/products/nvh-a ... sensor-kit to generate an RPM signal
Let’s assume we have an EV with a noise or vibration complaint.
Below we aim the optical sensor at a drive shaft to obtain and graph the frequency of the drive shaft/road wheel in the signal history
Note above how the displayed RPM in the signal history (blue line graph) is the RPM of the driveshaft/roadwheel and not the engine! This means the displayed default vibration orders E, P & T etc. are not applicable in the Frequency view and so require deselected by clicking on “Add Vibration”
With the “Add Vibration” dialog box open, click on the “Add” button to create a “Custom vibration” order relative to your speed signal from the optical sensor aimed at the driveshaft/road wheel. You can find more on adding custom vibrations here post62901.html#p62901
In the example above, NVH believes the speed signal from our optical sensor to be engine RPM (E1) our “Source”. If we add a “Correction factor” (multiplication factor) of 1.00 and give this a Display & Short name (I have chosen T1 Custom / T1C) “T1C” will represent our first order tyre vibration frequency in the Frequency View (The frequency of our road wheel)
Once we know T1 (called T1C) we can then use the same method to find our electric motor speed using the total ratio of the transmission.
Our source is now "T1C" X Correction factor 9.580 (total transmission ratio) to find the frequency of our Front Electric Motor (called MF)
For Dual Motor vehicles, apply the same technique above using T1C as the source X the total transmission ratio of the rear transmission
E.g., T1C x 11.880 to find the frequency of our Rear Electric Motor (called MR)
Remember, once you know frequency (Hz), multiply this value by 60 to find RPM
A tip here, once you have identified the frequencies of MF & MR, multiplying these by 3 will give you phase frequency of these 3 phase motors
E.g., Source MF X Correction factor of 3.00 = Motor Front Phase frequency (MFP)
Any peaks in our Frequency view attributed to phase frequencies will be clearly identified with the initials MFP if the Front Electric Motor Phase Frequency is our offender
The above technique can be made easier if we connect channel D of the scope to the E-Motor speed signal wire (Output from the motor speed/position sensor) Depending on style of output
Let’s assume the output of the E-motor speed sensor has 6 pulses per revolution of the E-motor
We enter 6 pulses as below
This will enable NVH to graph the electric motor RPM within the signal history rather than the driveshaft /road wheel frequency (using the optical sensor)
To now display our driveshaft / road wheel frequency enter the total transmission ratio of our EV to derive T1 ( See below for a FWD)
Next, we need to select “Calculate Road Speed” as below
Upon road test, select Gear 1 (see below) and you will be graphing E-Motor and Road speed as normal in the signal history. You can also use the default Tyre vibration orders and retain E1, knowing that E1 is the frequency of your Electric Motor rather than “Engine”
The final option is to use a Static rpm speed input.
Given the OBD connector is free, use serial data with a 3rd party scan tool to capture the E-Motor speed when the NVH complaint occurs (let’s assume 4900 rpm)
Enter 4900 rpm into our static rpm field and ensure the vehicle is held at this E-Motor speed throughout the customer
complaint of noise/vibration
Once again, ensure “Calculate Road Speed”, Total transmission ratio and Gear 1 are entered / selected as described above and your road speed (along with associated “orders”) will be displayed as normal when the E-Motor speed is held 4900 rpm (displayed by scan tool)
I hope this helps