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Tire air pressure measuring device

  • US 5,837,891 A
  • Filed: 11/18/1996
  • Issued: 11/17/1998
  • Est. Priority Date: 11/18/1996
  • Status: Expired due to Fees
First Claim
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1. A tire air pressure measuring device for detecting the release of air from a tire and notifying a driver of such an occurrence comprising, in combination:

  • a plurality of transmitters each coupled to an associated tire, each transmitter including;

    a water proof housing having an internally threaded open first end for engaging a valve of a tire, the housing having a cylindrical configuration, the housing having a length of 4 cm, a diameter of 2 cm, and a thickness of 1 mm, wherein each housing has a weight of less than 50 grams;

    a valve pressure indicator means secured within the housing, the valve pressure indicator having a needle extending outwardly therefrom to engage a contact point of the valve of the tire, the valve pressure indicator means adapted to determine the amount of pressure within the tire and further generate a specific pressure value of the tire, wherein the valve pressure indicator means comprises a silicon piezoresistive pressure sensor adapted to measure between 0 to 100 PSI and provide a linear voltage output directly proportional to the specific pressure value;

    analog circuit means including amplification means for amplifying the linear voltage output by a magnitude of forty, filter means for attenuating undesired voltage spikes, biasing means for clipping the linear voltage output above 3 volts and below 0 volts;

    a temperature sensor means secured within the housing for determining a current temperature of a surrounding area, wherein an output voltage of the temperature sensor means is a function of the temperature of the surrounding area;

    a transmitter means secured within the housing and connected to the temperature sensor means and valve pressure indicator means, the transmitter means adapted to transmit a compensated specific pressure value consecutively for 30 seconds only upon the triggering thereof, the compensated specific pressure value being a function of both the current temperature of a surrounding area and the specific pressure value of the tire, the compensated specific pressure value being transmitted with six pre-amble bits followed by a start bit, address byte, pressure data byte, five cyclic redundancy check bits, and two stop bits at a bit rate of about 30-100 kbits per second, wherein the transmission means transmits the compensated specific pressure value at under 50 mV/m;

    an antenna connected to the transmission means with a length of less than 1.94 cm;

    microcontroller means connected to the valve pressure indicator means, analog circuit means, and transmitter means, the microcontroller means adapted to trigger the transmitter means once every 20 minutes and further if the specific pressure value is less than a specific pressure value;

    an 8 bit switch situated on the housing to send with each transmission of the specific pressure value a unique identification address;

    a 3 volt lithium battery electrically coupled to the valve pressure indicator means, the temperature sensor means, analog circuit means, microcontroller means and the transmitter means, wherein the transmission means is adapted to provide an indication upon the detection of power delivered by the battery falling below a predetermined amount;

    a receiver secured within an interior of a rectangular housing, the housing having a flashing light mechanism secured within a front wall thereof, a speaker secured within the front wall thereof adjacent to the flashing light mechanism, the receiver being in communication with the transmitter means, the receiver having wiring extending to electrically couple with the flashing light mechanism, the speaker, and display, the receiver adapted to depict on the display the compensated specific pressure value of one tire at a time with an associated source tire number corresponding to the identification address for several seconds and then switch to a next one, the receiver means further adapted to immediately display the compensated specific pressure value of a tire that has experienced a major change, the receiver means and further adapted to actuate the flashing light mechanism and the speaker upon a change in the compensated specific pressure value of one of the tires which is greater than a predetermined amount.

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