Communications: electrical – Land vehicle alarms or indicators – Internal alarm or indicator responsive to a condition of the...
Reexamination Certificate
2000-05-19
2001-04-10
Wu, Daniel J. (Department: 2736)
Communications: electrical
Land vehicle alarms or indicators
Internal alarm or indicator responsive to a condition of the...
C340S442000, C073S146400, C073S146500
Reexamination Certificate
active
06215393
ABSTRACT:
BACKGROUND OF THE INVENTION
A system for monitoring the pressure of a tire of a vehicle wheel serves to indicate incorrect pressure to the on-board computer of the vehicle in order for it to alert the driver promptly.
A system of this type, attached to the valve inside the tire is thus inaccessible and power must be drawn in moderation from the battery which supplies it. To this end, the pressure-value radio transmissions are discontinuous, with, for example, a cycle of six minutes when the vehicle is moving and one hour when stationary. It is thus necessary to ensure that the result of each measurement is well received in order for the cycle of information not to be extended undesirably.
To this end, each measurement is transmitted with redundancy in the form of a series of a number of bursts of bits of information relating to the pressure. For example, in a standard manner, three bursts of 50 ms are transmitted with a spacing of about looms. Each wheel thus transmits its data in a random manner with respect to the others, and possible collisions in the transmissions of two wheels do not generally affect the totality of the bursts of a series. The redundancy, ie. the number of repetitions of transmission of each measurement, is thus determined according to the random risk of such radio collisions.
The Applicant has noted, however, that above a certain vehicle speed, the correct reception of the bursts was no longer assured, this means that a number of bits of each burst were erroneous and this caused the total loss of each burst. The redundancy lost all effectiveness. It is even possible to speak in terms of fading of the transmission data.
The Applicant has thus observed, especially at high speeds, that upon each rotation of the wheel, the pressure-monitoring system temporarily lost radio contact with the on-board computer over a specific angular sector linked to the presence of metal masses of the chassis and of the wheel, forming a screen. This was therefore not a question of random events, which explained the ineffectiveness of the redundancy.
Thus the Applicant proposes the following solution to the problem of transmission of remote readings from a tire of a wheel.
SUMMARY OF THE INVENTION
The invention thus relates to a safeguarded system for monitoring the pressure of a tire of a vehicle wheel comprising
a pressure sensor,
a transmitter of series of identical bursts of pressure data,
a processor for controlling the transmission of the bursts of data, arranged in order that, at least at wheel rotation speeds higher than a threshold, at least one burst of a series is transmitted in its entirety upon one wheel rotation.
Thus, for each burst, the probability is good that its transmission will take place outside a period in which the transmitter-receiver connection is cut and the redundancy linked to the transmission of a number of bursts increases the overall probability that at least one of the bursts is transmitted correctly to the on-board computer for utilising these bursts.
Since the invention relates to the transmission of data, it is conceived that the system can transmit data other than those relating to pressure, such as, for example, temperature and wheel identification.
The transmitter is advantageously of the frequency modulation type.
The computer for utilising this data thus receives a signal in which the information linked to the frequency is independent of the signal level received. This avoids any necessity for monitoring the gain of the demodulated signal which, in amplitude modulation, is difficult to achieve by reason of the fact that the radio level received varies continuously and with large dynamics by reason of the presence of the metal masses, and that it is thus impossible to determine an average reference level.
REFERENCES:
patent: 3835451 (1974-09-01), Church
patent: 4734674 (1988-03-01), Thomas et al.
patent: 5231391 (1993-07-01), Rigaux
patent: 5497657 (1996-03-01), taguchi et al.
patent: 5837891 (1998-11-01), Bridge
Sagem SA
Vorys Sater Seymour and Pease LLP
Wu Daniel J.
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