Torsion Resonant Frequency (TPMS)

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Mark Dalton
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Torsion Resonant Frequency (TPMS)

Post by Mark Dalton »

Upfront, I don't have a waveform for this car. I only came across information after the vehicle was returned to the customer.
The customer concern is for the Tyre Pressure Monitoring message appearing in the cluster. The system doesn't provide any actual readings, just an indication that one or more tyres may be under inflated. The TPMS system is an indirect system i.e. there are no in-tyre sensors, tyre pressure is infered via an algorithm.
My original understanding was that the system infers low tyre pressure because the tyre with lower tyre pressure has a smaller diameter and rotates faster. After a drive at constant speed on the Motorway for as long as I possibly could, I could see no more than 1 Km/Hr difference from all 4 wheels in the scan tool data. After being unable to reproduce the customers concern, I have returned the vehicle to the customer for the time being.
Later I came across a second method for infering tyre pressure from wheel speed sensor data called, Torsion Resonant Frequency. Up to this point the diagram below is the best explanation of this method I have come across without having to pay for an academic paper.
Has anyone had any experience with this method of TPMS and trying to scope the wheel speed sensors and extract the resonant frequency. No doubt there is some next level maths involved.
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Screenshot 2022-07-04 230120.jpg

Steve Smith
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Re: Torsion Resonant Frequency (TPMS)

Post by Steve Smith »

Hi Mark, I hope you are well?

Thank you for this and now you have set wheels in motion as I was not aware of this additional Resonance Frequency method

I did start to have a look yesterday and started to go down numerous rabbit holes

I will devote some time to this in the future and see what we can come up with

Don’t you just love this profession Mark?

Just when you think you know something, real-life pulls you back and lets you know you know very little indeed

Thank you again, take care……Steve

victor2k
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Re: Torsion Resonant Frequency (TPMS)

Post by victor2k »

Hello,
Due to the elastic properties of a tire, while driving, the rim speed v1 will be different from the speed of the outer part of the tire v2.
The magnitude of the difference is determined (among others) by a torque constant k which is proportional to the tire pressure.While driving, the irregularities on the road surface create a resonance between the speeds of the rim v1 and the tire v2.The resonant frequency is proportional to the elastic constant k and thus to the tire pressure.
Changes in tire pressure can be detected by monitoring the resonant frequency. Wheel speed sensors provide information about this resonant frequency.Systems that use the resonant frequency method also use the relative wheel speed difference method.In practice, for pressures of 1.6-2.5 bar the resonant frequency will be 40-50 Hz.
Best regards

Steve Smith
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Re: Torsion Resonant Frequency (TPMS)

Post by Steve Smith »

Hello and THANK YOU Victor

This is awesome information and I am intrigued to see how we can measure this resonance captured by the wheel speed sensor

Would you have further literature you can share Victor on this subject?

I would like to carry out a number of tests and experiments that demonstrate the theory in practice

Take care......Steve

victor2k
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Re: Torsion Resonant Frequency (TPMS)

Post by victor2k »

Hello,
I can't find anything new except an article(saemobilus.sae.org/content/2016-01-0459) from which I can read only the beginning,but for the estimation of resonant frequency,the vibration noise in wheel speed must be analyzed in frequency domain.
update:On Mazda6 2014- I found this system,please see the attached file,on 2018- Mazda 6 use tyre sensors for pressure,temperature.
Best regards
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mazda6 tmps.pdf
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Last edited by victor2k on Sun Jul 31, 2022 6:36 am, edited 2 times in total.

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Mark Dalton
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Re: Torsion Resonant Frequency (TPMS)

Post by Mark Dalton »

Thanks Viktor and Steve,
As you say Steve just when you think you're getting to grips with the complexities of cars, along comes something new to boggle your mind. The things the engineers come up with, blows my mind....
Would be very cool to be able to see that frequency in the wheel speed traces, it would be just one more thing that proves just how powerfull the Pico can be.

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