Remote measurement of air pressure in a tire tube

Discussion in 'Automotive Electronics' started by Denesius, Dec 13, 2015.

  1. Denesius

    Thread Starter Member

    Feb 5, 2014
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    I'm hoping someone has a solution for a problem I need to solve: the issue is to find a means of measuring the pressure in a tire tube (it's equivalent to a 9-inch tire inner tube). It has to be remote, as the tube is in a high speed apparatus, and rapidly speeds up and slows down. The need is to confirm adeq pressure during the slow phase in order to minimize risk of failure during the high speed phase. I cannot use the common tire pressure transmitters that screw on the valve stem (because of balance & side load issues). I've thought of drilling another hole in the wheel for an automotive valve stem transmitter, but would they read pressure in a tube, and besides, how would I go about setting up a receiver? Any clever solutions or adaptations out there that would work for this application?
     
  2. BR-549

    Well-Known Member

    Sep 22, 2013
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    Is the high speed apparatus stationary, other than rotation?

    Is there any linear movement? With or against anything?
     
  3. DickCappels

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    Aug 21, 2008
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  4. Denesius

    Thread Starter Member

    Feb 5, 2014
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    Apparatus is stationary. The wheel assembly typically idles at 50-100RPM, but will periodically accelerate up to 2500-3000RPM. The wheel is dynamically balanced before testing, and the pressure in the tube should be maintained between 50-55PSI.
     
  5. Denesius

    Thread Starter Member

    Feb 5, 2014
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    That's great, but my other issue is the pressure measurement itself. The sensors used in auto wheels (at least the ones I looked at) have a port in the middle and measure air pressure directly. This is an inner tube setup. I was hoping there was an off the shelf system for inner tubes-probably using contact pressure rather than direct air pressure (that didn't screw on top of the valve stem).
     
  6. JohnInTX

    Moderator

    Jun 26, 2012
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    Some TPMS systems monitor the diameter/circumference of the wheel by measuring rotation speed and comparing it to vehicle speed (using the ABS sensors). If your innertube expands / contracts with pressure changes, that might be something to investigate. As pressure drops, you would see a corresponding decrease in circumference that could be compared to the rotation speed of the shaft. This assumes something in contact with the rotating tube so it may not be appropriate to your setup.
     
  7. BR-549

    Well-Known Member

    Sep 22, 2013
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    Why does pressure need to be measured at low speed and not before spin?
     
  8. BR-549

    Well-Known Member

    Sep 22, 2013
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    Is it the same size tire all the time? There are several ways to do this, DEPENDING on exactly what you are doing.
    If we don't know what you are doing..................then when a suggestion is made......................you add another condition.

    So....why and how are you doing?
     
  9. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    May be some but not all. GM does or did measure speed of all tire rotation against each other for tire pressure warning, had nothing to do with VSS. I was involved with building the test rig for the R&D.
     
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  10. JohnInTX

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    Jun 26, 2012
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    I think that's how Chrysler did it on the first 300s. I was told that the same rotation speed sensor (in the disk rotor) used in the ABS was also used by the tire pressure monitoring but I could have misunderstood.
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Yeah GM used the ABS reluctors to measure the speed of the wheels. Only real problem was if all four wheels are under inflated the same amount it doesn't show as low pressure.
     
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  12. Denesius

    Thread Starter Member

    Feb 5, 2014
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    The tire/tube setup is carefully measured before spinup, and the expansion is calculated based on a number of parameters. The test is a measure of friction between the wheel in question and the driven wheel, with observed changes in speed and friction due to centrifugal force. The reason for measuring the air pressure is for a basis for compensation for temp rise with use, to prevent apparatus failure due to excess air pressure, and to avoid bad data due to low pressure. Once started, the test runs for 48-96 hours, so stopping it for a pressure check is not practical. For obvious reason, calculation of pressure indirectly using speed is not practical.
     
  13. Denesius

    Thread Starter Member

    Feb 5, 2014
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    New vehicles use actual pressure monitors, although at the low end the wheel speed method may still be in use. The module is queried by the computer and returns a value. I've noticed that the aftermarket systems (the ones that screw on the valve stem) seem to use motion to activate the sensor and send the data to the display.
     
  14. BR-549

    Well-Known Member

    Sep 22, 2013
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    I would try 3 idlers, mounted 180 degrees from driven tire. One radial and 2 on the top and bottom walls. These idlers will give you the cross sectional area of the tire. The movement or pressure on idlers can be monitored by several methods.

    By making the idler jig rotatable, you should be able to map tire distortion under acceleration also.

    I don't know much about tires, but I would think this would give you warning of failure.

    I searched "9-inch tire inner tube" and still don't know what that means.

    Your rpm is high for auto tires. May I see a datasheet on that tire?
     
  15. Denesius

    Thread Starter Member

    Feb 5, 2014
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    The actual tire is a 9.00 x 6 multicord- it's similar to (if not actual) a small aircraft tire, with a high speed rating. It has to use a matching inner tube to maintain inflation, since the wheel is assembled as 2 halves.
    I'm getting the feeling that there's no such thing as a pressure monitor for an inner tube, without putting a dongle on the valve stem. I may have to look into how it's done on aircraft, but with most things aviation I'm guessing it will be cost prohibitive...
     
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