Measuring and testing – Tire – tread or roadway – Tire inflation testing installation
Patent
1987-07-23
1988-11-15
Woodiel, Donald O.
Measuring and testing
Tire, tread or roadway
Tire inflation testing installation
200 83N, 340 58, B60C 2304, G01L 708, G01L 900
Patent
active
047839937
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates a tire pressure sensor for motor vehicles. It is known from DE-OS 28 32 447 to screw in a tire pressure sensor at the circumference of a wheel rim, which tire pressure sensor comprises a pressure switch for monitoring the air pressure in the tire and is actuated by the tire pressure. The pressure switch includes, on the one hand, an electrically conducting diaphragm, which closes a reference pressure chamber in the direction of the tire, and, on the other hand, a contact pin which is sealed in a glass bushing so as to be electrically insulated and is contacted by the middle area of the diaphragm when there is sufficient air pressure in the tire in order to close an electric circuit. The reference pressure chamber is filled to a desired reference pressure with air or nitrogen via a duct and is then closed so as to be pressure-sealed. The reference pressure is selected in such a way that the diaphragm contacts the end of the contact pin when there is sufficient air pressure in the tire. On the other hand, if the air pressure in the tire falls below a minimum pressure which is predetermined by means of the reference pressure, the diaphragm rises off the contact pin and opens an oscillating circuit, which comprises a coil and a capacitor, which is arranged in the tire pressure sensor. By means of a high-frequency oscillation of the evaluating circuit, which is arranged so as to be fixed in the vehicle, it can be determined whether or not the pressure switch is closed with a signal receiver arranged in the proximity of the tire when passing the tire pressure sensor with each revolution of the wheel.
In the known constructions of such a tire pressure sensor, it is a disadvantage that a pressure compensation occurs in the reference pressure chamber when there is a leak in the reference pressure chamber, e.g., at the clamping point of the diaphragm, wherein the electric circuit remains closed by the diaphragm so that the information "tire pressure normal" is transmitted by the tire pressure sensor even when the air pressure is too low. A corresponding indication error also occurs if a leak occurs in the reference pressure chamber at the filling duct or at the bushing of the contact pin.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved tire pressure sensor.
The present solution attempts to transmit a signal to the evaluating circuit when a leak occurs in the reference pressure chamber using simple means.
The tire pressure sensor, according to the invention, has the advantage that the diaphragm rises off the contact pin already when there is a pressure compensation between pressure in the reference chamber and the tire pressure and accordingly transmits an alarm signal to the evaluating circuit, i,e, the contact is open in the state of the absence of differential pressure. If the pressure compensation occurs because of a leak, insufficient pressure will be signalized again after a short time when refilling the tire (because of pressure compensation). This does not happen when there is inadequate tire pressure and during refilling.
It is another advantage of this invention that such a leak indication can be used for testing the tightness of the reference pressure chamber already during the production of the tire pressure sensor or before it is shipped or during assembly in a workshop by means of the slight application of compressed air. It is particularly advantageous to fasten the reference pressure chamber in a housing of the reference pressure sensor in such a way that it is completely surrounded by the air pressure in the tire, the housing being screwed into the wheel rim and closed outwardly. In this case, leaks at the filling duct, at the bushing of the contact pin, or in other areas of the reference pressure chamber lead to a pressure compensation with the compressed air in the tire and, accordingly, to an alarm signal. Since the coil and the capacitor of the tire pressure sensor are arranged in an oscillating circuit
REFERENCES:
patent: 4071724 (1978-01-01), LeJeune
patent: 4701742 (1987-10-01), Ruehr
Gerhard Hettich
Hans-Dieter Schmid
Lothar Haas
Robert & Bosch GmbH
Striker Michael J.
Woodiel Donald O.
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