System for monitoring the tires of a vehicle, comprising a device for automatic location of wheel transmitters

1. A system for monitoring the tires of a vehicle having two axles, each axle having a tire-wheel assembly and the two tire-wheel assemblies defining an axis D 1 , said system comprising:

a wheel unit disposed in each tire-wheel assembly comprising a radio transmitter capable of transmitting waves of a frequency F of more than 300 MHz in short pulses,

a central unit for processing data transmitted by the radio transmitter

a device for automatically locating the position on the vehicle of the radio transmitters, wherein the automatic locating device comprises:

a first radio reception channel having a first aerial;

a second radio reception channel having a second aerial, the first and second aerials defining an axis that is substantially parallel to D 1 , said first and second aerials being separated by a distance d, wherein d satisfies the following equation:

(2 n +1)λ/4−λ/8 ≦d ≦(2 n+ 1)λ/4+λ/8,

n being an integer greater than or equal to 0, wherein λ is the wavelength of the frequency F of the radio transmissions of the transmitters;

a first means of comparison of the phases of a radio signal received by the first and second aerials in order to determine whether the radio signal received by the first aerial is ahead of phase, behind phase or has an identical phase relative to the radio signal received by the second aerial; and

a means of processing the results transmitted by the first means of comparison to indicate the position of the radio transmitter relative to the said aerials.

2. The system according to claim 1 , in which d is substantially equal to λ/4.

3. A system for monitoring the tires of a vehicle having two axles, each axle having two tire-wheel assemblies, and the four tire-wheel assemblies defining two diagonal axes D 1 and D 2 , said system comprising:

a wheel unit disposed in each tire-wheel assembly comprising a radio transmitter capable of transmitting waves of a frequency F of more than 300 MHz in short pulses,

a central unit for processing the data transmitted by the radio transmitters,

and a device for automatically locating the position on the vehicle of the radio transmitters wherein the automatic locating device comprises:

a first radio reception channel having a first aerial;

a second radio reception channel having a second aerial, the first and second aerials defining an axis that is intended to be substantially parallel to D 1 , said first and second aerials being separated by a distance d, wherein d satisfies the following equation:

(2 n+ 1)λ/4 −λ/8 ≦d ≦(2 n+ 1)λ/4+λ/8,

n being an integer greater than or equal to 0; wherein λ is the wavelength of the frequency F of the radio transmissions of the transmitters;

a first means of comparison of the phases of a radio signal received by the first and second aerials in order to determine whether the radio signal received by the first aerial is ahead of phase, behind phase or has an identical phase relative to the radio signal received by the second aerial;

a third radio reception channel having a third aerial;

a fourth radio reception channel having a fourth aerial, the third and fourth aerials defining an axis intended to be disposed substantially parallel to D 2 , said third and fourth aerial being separated by a distance d′ such that, λ being the wavelength of the frequency F of the radio transmissions of the transmitters, d′ satisfies the following equation:

(2 n +1)λ/4−λ/8 ≦d ′≦(2 n +1)λ/4+λ/8,

n being an integer greater than or equal to 0;

a second means of comparing the phases of a radio signal received by the third and fourth aerials in order to determine whether the radio signal received by the third aerial is ahead of phase, behind phase or has an identical phase relative to the radio signal received by the fourth aerial;

a means of processing the results originating from the first and second means of comparison intended to indicate the position of the radio transmitter of the signal relative to the said aerials.

4. The system according to claim 3 , wherein the third and first channels are shared.

5. The system according to claim 3 , wherein the distances d and d′ are substantially equal to λ/4.

6. The system according to claim 2 , wherein:

when the first means of comparison determine that the radio signal received by the first aerial is ahead of phase relative to the radio signal received by the second aerial, the processing means indicate that the radio transmitter is disposed on the side of the first aerial relative to the axis D 1 ; and

when the first means of comparison determine that the radio signal received by the first aerial is behind phase relative to the radio signal received by the second aerial, the processing means indicate that the radio transmitter is disposed on the side of the second aerial relative to the axis D 1 .

7. The system according to claim 6 , wherein when the first means of comparison determine that the radio signal received by the first and second aerials are substantially in phase, the processing means indicate that the radio transmitter is disposed substantially at an equal distance from the first and second aerial.

8. The system according to claim 5 , wherein:

when the second means of comparison determine that the radio signal received by the third aerial is ahead of phase relative to the radio signal received by the fourth aerial, the processing means indicate that the radio transmitter is disposed on the side of the third aerial relative to the axis D 2 ; and

when the second means of comparison determine that the radio signal received by the third aerial is behind phase relative to the radio signal received by the fourth aerial, the processing means indicate that the radio transmitter is disposed on the side of the fourth aerial relative to the axis D 2 .

9. The system according to claim 8 , wherein when the second means of comparison determine that the radio signals received by the third and fourth aerials are substantially in phase, the processing means indicate that the radio transmitter is disposed substantially at an equal distance from the third and fourth aerials.

10. The system according to claim 5 , wherein the processing means indicate that the radio transmitter is disposed, relative to an axis D 1 or D 2 respectively, on the side of a given aerial only if the second, or first, means of comparison record that the signals received by the corresponding pair of aerials have substantially the same phase shift.

11. The system according to claim 5 , wherein the processing means indicate “zero signal” when the first and second means of comparison both record that the signals received by the corresponding pairs of aerials are substantially in phase.

12. The system according to claim 1 , wherein the aerials comprise a helical winding such that the unwound length of the wire of the winding is substantially equal to λ/4.

13. The system according to claim 12 , wherein the windings of the aerials have their axes intended to be disposed perpendicular to the axes D 1 and D 2 .

14. The system according to claim 1 , wherein each reception channel comprises a limiting amplifier.

15. The system according to claim 1 , wherein each reception channel further comprises a frequency mixer connected to a local oscillator of frequency F 2 , which oscillator is common to all reception channels of the radio signal.

16. The system according to claim 1 , wherein one of the reception channels of the radio signal of the locating device is used to receive and decode the data originating from the wheel unit transmitting to the central processing unit.

17. The system according to claim 1 , wherein a complementary reception channel receives and decodes the data from the wheel unit transmitting to the central processing unit.

18. The system according to claim 1 , wherein the locating device is disposed in the central part of the ceiling of the passenger compartment.