On-board tire pressure indicating system performing temperature-compensated pressure measurement, and pressure measurement circuitry thereof

Claim 2

In a vehicle comprising at least one wheel and a chassis to which said at least one wheel is rotatably attached, a system for communicating temperature-compensated tire pressure from said at least one wheel to said chassis, said system comprising: first energy transmitting means (9), mounted on said chassis, for transmitting first energy of a first predetermined frequency; first energy receiving means (10), mounted on said at least one wheel, for receiving said first energy; tire pressure signal generating means (1,2), mounted on said at least one wheel and responsive to pressure of a tire mounted on said at least one wheel, for generating a tire pressure signal; constant current applying means (A1) for applying a constant current to said tire pressure signal generating means; voltage polarity reversing means (A2, A3) for reversing polarity of voltage applied to said tire pressure signal generating means; wherein said tire pressure signal generating means comprises a piezoresistive bridge, said constant current applying means and said voltage polarity reversing means enabling compensation for temperature drift, to produce a temperature-compensated tire pressure signal; and wherein said temperature-compensated tire pressure signal is transmitted by said first energy receiving means to said first energy transmitting means, and alters operation of said first energy transmitting means, so as to communicate said signal from said at least one wheel to said chassis; said system further comprising indicating means (5) for processing said temperature-compensated tire pressure signal to provide information indicative of said temperature-compensated tire pressure within said vehicle.

Claim 3

A system as claimed in claim 1, wherein said voltage polarity reversing means comprises an integrator including a first operational amplifier (A2) and a capacitor (C1) connected in negative feedback manner, and Schmitt trigger means (A3, R2, R3), and wherein said constant current source applying means comprises a second operational amplifier (A1) connected to said Schmitt trigger means, wherein said piezoresistive bridge is connected in a feedback circuit with said voltage polarity reversing means.

Claim 4

A system as claimed in claim 1, wherein said voltage polarity reversing means comprises a plurality of N-channel and P-channel enhancement MOSFETs.

Claim 5

A system as claimed in claim 1, further comprising storage means for storing a plurality of said temperature-compensated tire pressure signal at spaced intervals, to provide a tire pressure history.

Claim 6

A system as claimed in claim 1, wherein said voltage polarity reversing means comprises an integrator including a first operational amplifier (A2) and a capacitor (C1) connected in negative feedback manner, Schmitt trigger means (A3, R2, R3), and inverting means (I₅, I₆, I₇) connected between an output of said constant current source applying means and said piezoresistive bridge, for providing a constant voltage to said piezoresistive bridge, and wherein said constant current source applying means comprises a second operational amplifier (A1) connected to said Schmitt trigger means, wherein said piezoresistive bridge is connected in a feedback circuit with said voltage polarity reversing means.

Claim 7

In a vehicle comprising at least one wheel and a chassis to which said at least one wheel is rotatably attached, a tire-pressure sensor for monitoring pressure of a tire mounted on said at least one wheel and for outputting a temperature-compensated tire pressure signal from said at least one wheel to said chassis, said sensor comprising: first energy transmitting means (9), mounted on said chassis, for transmitting first energy of a first predetermined frequency; first energy receiving means (10), mounted on said at least one wheel, for receiving said first energy; tire pressure signal generating means (1,2), mounted on said at least one wheel and responsive to pressure of a tire mounted on said at least one wheel, for generating a tire pressure signal; voltage polarity reversing means (A2, A3) for reversing polarity of voltage applied to said tire pressure signal generating means, wherein said voltage polarity reversing means comprises an integrator including a first operational amplifier (A2) and a capacitor (C1) connected in negative feedback manner, and Schmitt trigger means (A3, R2, R3); constant current applying means (A1) for applying a constant current to said tire pressure signal generating means, wherein said constant current source applying means comprises a second operational amplifier (A1) connected to said Schmitt trigger means; wherein said tire pressure signal generating means comprises a piezoresistive bridge, said piezoresistive bridge being connected in a feedback circuit with said voltage polarity reversing means, said constant current applying means and said voltage polarity reversing means enabling compensation for temperature drift, to produce a temperature-compensated tire pressure signal; and wherein said temperature-compensated tire pressure signal is transmitted by said first energy receiving means to said first energy transmitting means, and alters operation of said first energy transmitting means, so as to communicate said signal from said at least one wheel to said chassis.

Claim 8

In a vehicle comprising at least one wheel and a chassis to which said at least one wheel is rotatably attached, a tire-pressure sensor for monitoring pressure of a tire mounted on said at least one wheel and for outputting a temperature-compensated tire pressure signal from said at least one wheel to said chassis, said sensor comprising: first energy transmitting means (9), mounted on said chassis, for transmitting first energy of a first predetermined frequency; first energy receiving means (10), mounted on said at least one wheel, for receiving said first energy; tire pressure signal generating means (1,2), mounted on said at least one wheel and responsive to pressure of a tire mounted on said at least one wheel, for generating a tire pressure signal; voltage polarity reversing means (A2, A3) for reversing polarity of voltage applied to said tire pressure signal generating means, wherein said voltage polarity reversing means comprises an integrator including a first operational amplifier (A2) and a capacitor (C1) connected in negative feedback manner, and Schmitt trigger means (A3, R2, R3); constant current applying means (A1) for applying a constant current to said tire pressure signal generating means, wherein said constant current source applying means comprises a second operational amplifier (A1) connected to said Schmitt trigger means; wherein said tire pressure signal generating means comprises a piezoresistive bridge, said piezoresistive bridge being connected in a feedback circuit with said voltage polarity reversing means, said constant current applying means and said voltage polarity reversing means enabling compensation for temperature drift, to produce a temperature-compensated tire pressure signal; and wherein said temperature-compensated tire pressure signal is transmitted by said first energy receiving means to said first energy transmitting means, and alters operation of said first energy transmitting means, so as to communicate said signal from said at least one wheel to said chassis.

Claim 9

A sensor as claimed in claim 1 or claim 6, wherein said vehicle comprises a plurality of wheels including a spare, and said first energy receiving means, said tire pressure signal generating means, said constant current applying means, and said voltage polarity reversing means are mounted on each of said wheels, each of said first energy receiving means transmitting a respective said temperature-compensated tire pressure signal to said chassis for communication to a central location on said chassis.

Claim 10

A system as claimed in claim 1 or claim 6, wherein said first energy transmitting means comprises a primary coil, and said first energy receiving means comprises a tuned circuit, including a secondary coil (10b) and a capacitor (10a) connected across said secondary coil, and wherein said primary coil is excited at said predetermined frequency in response to connection of an ignition switch.

Claim 11

A system as claimed in claim 8, further comprising switching means (TR2) for alternately opening and closing said secondary coil to alter operation of said primary coil.

Claim 12

A system as claimed in claim 8, further comprising secondary coil short circuiting means for short circuiting said secondary coil to alter operation of said primary coil.

Claim 13

A system as claimed in claim 8, further comprising secondary coil open circuiting means (TR S , D S ) for open circuiting said secondary coil to alter operation of said primary coil.

Claim 14

A system as claimed in claim 11, wherein said secondary coil open circuiting means comprises a transistor connected to one end of said secondary coil and a diode connected across a collector and an emitter of said transistor, a base of said transistor being connected to an output of said Schmitt trigger means.

Claim 15

A system as claimed in claim 1 or claim 6, wherein said constant current source applying means comprises a current mirror circuit (TR3, TR4).

Claim 16

A system as claimed in claim 2 or claim 6, wherein said voltage polarity reversing means further comprises inverting means (I₅, I₆, I₇) connected between an output of said constant current source applying means and said piezoresistive bridge, for providing a constant voltage to said piezoresistive bridge.

Claim 17

A system as claimed in claim 1 or claim 6, wherein said constant current source applying means, said voltage polarity reversing means, and said piezoresistive bridge are integrated in a monolithic IC chip.

Claim 18

In a vehicle comprising at least one wheel and a chassis to which said at least one wheel is rotatably attached, a tire-pressure sensor for monitoring pressure of a tire mounted on said at least one wheel and for outputting a temperature-compensated tire pressure signal from said at least one wheel to said chassis, said sensor comprising; first energy transmitting means (9), mounted on said chassis, for transmitting first energy of a first predetermined frequency; first energy receiving means (10), mounted on said at least one wheel, for receiving said first energy; tire pressure signal generating means (1,2), mounted on said at least one wheel and responsive to pressure of a tire mounted on said at least one wheel, for generating a tire pressure signal, said tire pressure signal generating means comprising a piezoresistive bridge; voltage polarity reversing means (A2, A3) for reversing polarity of voltage applied to said tire pressure signal generating means, wherein said voltage polarity reversing means comprises an integrator including a first operational amplifier (A2) and a capacitor (C1) connected in negative feedback manner, and Schmitt trigger means (A3, R2, R3); constant current applying means (A1) for applying a constant current to said tire pressure signal generating means, wherein said constant current source applying means comprises a second operational amplifier (A1) connected to said Schmitt trigger means, wherein said voltage polarity reversing means further comprises inverting means (I₅, I₆, I₇) connected between an output of said constant current source applying means and said piezoresistive bridge, for providing a constant voltage to said piezoresistive bridge; wherein said piezoresistive bridge is connected in a feedback circuit with said voltage polarity reversing means, said constant current applying means and said voltage polarity reversing means enabling compensation for temperature drift, to produce a temperature-compensated tire pressure signal; and wherein said temperature-compensated tire pressure signal is transmitted by said first energy receiving means to said first energy transmitting means, and alters operation of said first energy transmitting means, so as to communicate said signal from said at least one wheel to said chassis.

Claim 19

In a vehicle comprising at least one wheel and a chassis to which said at least one wheel is rotatably attached, a tire-pressure sensor for monitoring pressure of a tire mounted on said at least one wheel and for outputting a temperature-compensated tire pressure signal from said at least one wheel to said chassis, said sensor comprising; first energy transmitting means (9), mounted on said chassis, for transmitting first energy of a first predetermined frequency; first energy receiving means (10), mounted on said at least one wheel, for receiving said first energy; tire pressure signal generating means (1,2), mounted on said at least one wheel and responsive to pressure of a tire mounted on said at least one wheel, for generating a tire pressure signal, said tire pressure signal generating means comprising a piezoresistive bridge; voltage polarity reversing means (A2, A3) for reversing polarity of voltage applied to said tire pressure signal generating means, wherein said voltage polarity reversing means comprises an integrator including a first operational amplifier (A2) and a capacitor (C1) connected in negative feedback manner, and Schmitt trigger means (A3, R2, R3); constant current applying means (A1) for applying a constant current to said tire pressure signal generating means, wherein said constant current source applying means comprises a second operational amplifier (A1) connected to said Schmitt trigger means, wherein said voltage polarity reversing means further comprises inverting means (I₅, I₆, I₇) connected between an output of said constant current source applying means and said piezoresistive bridge, for providing a constant voltage to said piezoresistive bridge; wherein said piezoresistive bridge is connected in a feedback circuit with said voltage polarity reversing means, said constant current applying means and said voltage polarity reversing means enabling compensation for temperature drift, to produce a temperature-compensated tire pressure signal; and wherein said temperature-compensated tire pressure signal is transmitted by said first energy receiving means to said first energy transmitting means, and alters operation of said first energy transmitting means, so as to communicate said signal from said at least one wheel to said chassis.