Circuit for the coding of the value of two variables measured in a tire, and device for monitoring tires employing such a circuit

• US 4,703,650 A
• Filed: 06/24/1986
• Issued: 11/03/1987
• Est. Priority Date: 07/03/1985
• Status: Expired due to Term

• Current Assignee: Compagnie générale des établissements Michelin
• Original Assignee: Compagnie générale des établissements Michelin
• Inventors: Myatt, David, Dosjoub, Andre
• Primary Examiner(s): Woodiel, Donald O.
• Application Number:
  US06/877,844
• Time in Patent Office: 497 Days
• Field of Search: 73/146.5, 73/152, 73/766, 73/726, 73/727, 73/753, 73/714, 374/143
• US Class Current: 73/146.5
• CPC Class Codes: B60C 23/0427 Near field transmission with inductive or capacitive coupling means

Abstract

A coding circuit comprises an astable multivibrator which transforms the measurement of the variables in question, for instance pressure and temperature, into a time measurement. The astable multivibrator delivers a pulse signal whose pulse width is a function of the temperature and the cyclic ratio of which is a function of the pressure.

Claims

1. A circuit for coding the value of two variables measured in a tire, which permits the transmission of the values to the chassis bearing the tire without galvanic contact, characterized by the fact that the circuit comprises:

(a) a first unit the transfer function of which is a function of the first of the variables measured;

(b) means for alternately connecting to the input of the first unit either a reference voltage or a voltage which is a function of the second of the variables measured to provide an output signal representing either said first variable or said second variable, respectively; and

(c) a second unit controlled by the output signal of the first unit and delivering a pulse signal having parameters representing the values of the measured variables,

said connecting means being actuated in response to said pulse signal.

2. A circuit according to claim 1, characterized by the fact that the first unit comprises essentially an integrator and by the fact that the time constant of the first unit is a function of the first measured variable.

3. A circuit according to claim 1 or 2, characterized by the fact that the second unit comprises essentially means permitting the referencing of two thresholds for the output signal of the first unit.

4. A circuit according to claim 3, characterized by the fact that the means permitting the referencing comprise two comparators and a flipflop.

5. A circuit according to claim 3, characterized by the fact that the means permitting the referencing comprise a single comparator provided with a feedback loop.

6. A circuit according to claim 1 or 2, characterized by the fact that the voltage which is a function of the second of the variables measured is applied to the input of the first unit via an operational amplifier receiving a voltage delivered by a detector responsive to the second variable.

7. A circuit according to claim 6, characterized by the fact that said second variable is the pressure prevailing in the tire and by the fact that the detector is a piezoresistive gauge.

8. A circuit according to claim 1 or 2, characterized by the fact that the connecting means are formed of a transistor mounted as a common emitter the base of which is controlled by the output of the second unit and the collector of which is joined to the input of the first unit.

9. A circuit according to claim 1 or 2, characterized by the fact that it is essentially in the form of a hybrid circuit or integrated circuit.

10. A circuit according to claim 2, characterized by the fact that the integrator is formed of a connection which comprises at least one operational amplifier, a resistor being connected to the inverting input and a condenser being inserted in the feedback circuit, a voltage being applied to the non-inverting input of the operational amplifier by a resistance divider bridge permitting calibration of the the circuit relative to the second measured variable.

11. A circuit according to claim 10, characterized by the fact that the first variable is the temperature prevailing in the tire and by the fact that a temperature detector is used in the form of a silicon resistor mounted in the feedback loop of an additional operational amplifier, the output of which acts on said one operational amplifier in the integrator.

12. A circuit according to claim 10, characterized by the fact that the first variable is the temperature prevailing in the tire and by the fact that a temperature detector is used in the form of a silicon resistor mounted at the output of said one operational amplifier in the integrator.