Data processing: measuring – calibrating – or testing – Measurement system – Pressure
Patent
1998-05-11
2000-08-29
Hoff, Marc S.
Data processing: measuring, calibrating, or testing
Measurement system
Pressure
731465, 731463, 340447, B01C 2302
Patent
active
061121657
DESCRIPTION:
BRIEF SUMMARY
The invention proceeds from a method having the features indicated in the preamble of claim 1. A method of this kind is known from DE 43 03 583 A1. This document discloses a device having means, arranged in a valve of the pneumatic tire, for generating a wirelessly transmittable pressure decrease indication signal with a battery as power source; having a preferably semiconducting piezoresistive pressure sensor; having an analog/digital converter for digitising the pressure signal obtained from the pressure sensor; having a memory for storing the pressure signal; having a comparator which compares the pressure signal with a previously stored comparison pressure signal; having a transmitter; and having a timing switch which activates the device from time to time and otherwise keeps it deactivated for purpose of power conservation. The analog/digital converter, memory, comparator, and timing switch are preferably realised in a module with a microprocessor which compares the pressure signal supplied by the pressure sensor with the previously stored comparison pressure signal, generates a signal if the deviation of the pressure signal from the comparison pressure exceeds a threshold, and then activates the transmitter, which thereupon transmits a datum regarding the detected deviation to a receiver arranged in the vehicle, in particular in the region of the dashboard, which processes the datum and indicates to the driver the pneumatic tire in which the air pressure is deviating significantly from the comparison pressure. The nominal pressure of the pneumatic tire is stored permanently, as the comparison pressure, each time the air pressure is checked, at a filling station, by means of an external gauge and set to its nominal value by means of a compressed air source.
The practical applicability of such a device to the monitoring of tire pressure depends on the fact that the device uses so little power that it is capable of operating for several years without a battery change. The transmitter has the greatest power consumption. With the known device, it is activated only if the deviation of the measured tire pressure from the nominal value exceeds a defined threshold. In addition, the pressure is measured not continuously, but instead only at regular intervals, for example every four seconds, and compared with the nominal value. The nominal value is an absolute value. It is stored each time air is added to the tire. For this purpose, the movement of the valve plunger is automatically monitored, for example by means of a magnet attached to the valve plunger, which actuates a magnetic switch when the valve plunger moves. When the device recognises a movement of the valve plunger, the tire pressure measured thereafter is stored as the comparison pressure.
Despite its power-saving operation, the known device has many disadvantages:
The tire pressure changes not only as a result of leakage, but also because of differences in vehicle loading and in response to tire temperature, which depends on driving conditions. If the tire is filled at low temperature, the pressure then rises as the outside temperature rises, but also as a result of tire flexing during driving. If, on the other hand, the tire is filled after having been driven, or on a hot day, the pressure then decreases with decreasing temperature, or if the vehicle is stationary or is driven slowly. This means that with a low threshold value, the transmitter is activated more often than necessary simply due to changes in tire temperature, resulting in unnecessary power consumption which reduces battery service life. This could be counteracted by raising the threshold value, but that degrades the reliability of the tire pressure monitoring system. Another possibility, disclosed in DE 43 03 583 A1, is to additionally arrange a temperature sensor in the valve of the pneumatic tire, and by means of said sensor to compensate by calculation, taking into account the known temperature dependence of air pressure, for the change in tire pressure caused by changes in tempe
REFERENCES:
patent: 5109213 (1992-04-01), Williams
patent: 5656993 (1997-08-01), Coulthard
patent: 5965808 (1999-10-01), Normann et al.
Kessler Ralf
Normann Norbert
Schulze Gunter Lothar
Uhl Gunter
Doduco GmbH
Hoff Marc S.
Vo Hien
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