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Air pressure indicator for a vehicle tyre

  • US 6,553,820 B1
  • Filed: 06/09/2000
  • Issued: 04/29/2003
  • Est. Priority Date: 10/15/1998
  • Status: Expired due to Fees
First Claim
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1. A device for indicating safety limits of air pressure in tires of at least two wheel assemblies of a vehicle, the device including for each of the at least two wheel assemblies of the vehicle a first conductive surface, a second conductive surface, a third conductive surface and a fourth conductive surface, a first pair of conductive surfaces including said first and second conductive surfaces, said first pair of conductive surfaces being mounted onto an insulated base fixed onto a rotating portion of each wheel assembly, and a second pair of conductive surfaces including said third and fourth conductive surfaces, said second pair of conductive surfaces being mounted onto an insulated base fixed onto a nonrotating shaft of each wheel assembly, a pair of air capacitors being formed between said first pair and said second pair of conductive surfaces, an electronic circuit which includes a high frequency oscillator, an amplifier, a magnitude and phase comparator, a sequential circuit, two diodes, and a bridge circuit with three resistors and four capacitors which are connected with said nonrotating conductive surfaces for each of said at least one pair of wheels, a detection circuit that also includes a pulse generator, a comparator, RLC sinusoidal wave transformer, and a signal display and a tire pressure sensor including means for converting air pressure variations in the tires into displacement of a semiconductor membrane to thereby operate as an ON-OFF switch which shorts out said first with second conductive surfaces with a metallic frame of the wheel assembly when in an ON position when air pressure in a tire is abnormal, said pair of air capacitors being adapted to operate as a variable capacitor in said electronic circuit wherein a first frequency range is produced by said pair of air capacitors when the ON-OFF switch is in an OFF position, and a second frequency range is produced by said pair of air capacitors when the ON-OFF switch is in the ON position which results in said electronic circuit activating the signal display to thereby reflect a tire with abnormal air pressure.

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