Tire pressure sensor for motor vehicles

Details Tire pressure sensor for motor vehicles Tire pressure sensor for motor vehicles

1990-01-10

1991-07-30

Woodiel, Donald O.

Measuring and testing

Tire, tread or roadway

Tire inflation testing installation

73723, 200 6125, 340442, B60C 2302, G01L 900

Patent

active

050351370

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a tire pressure sensor for motor vehicles and which is to be secured at the wheel rim circumference and is actuatable by the tire pressure. The sensor comprises a reference pressure chamber and an electrically conducting diaphragm which separates the reference chamber from the tire and cooperates with a contact pin extending through the center of the base of the reference pressure chamber. In such a known pressure sensor (EP-A- 0 157 205), two pressure measuring elememts with different threshold values for monitoring the tire pressure are fastened next to one another in the circumferential direction at the wheel rim. In vehicles for which different tire pressures are provided at the front wheels and the rear wheels, the different threshold values make it possible to exchange the wheels between the front and rear axle at any time without the pressure measuring elements also having to be exchanged simultaneously. The two threshold values are adjusted to the different tire pressures, respectively.
An excess pressure in the tire, at which the driving comfort and possibly also the driving behavior of the vehicle is impaired due to the reduced contact of the tire with the road, can also be determined and indicated, if necessary, by such a sensor when tires with a lower required tire pressure are used. However, such monitoring of the excess tire pressure is not possible in the tires filled at higher pressure. Moreover, with the sensors of this type, the correct functioning of the tire pressure sensor can hardly be monitored after installation at the rim. Thus, for example, it is possible that the diaphragm of the tire pressure sensor or a protective cap thereof is pressed in when exchanging the tires, and the switching function of the diaphragm is accordingly blocked. In such cases, a sufficient air pressure in the tire is also indicated during the tire pressure monitoring while the air pressure lies below the threshold value of the tire pressure sensor.


SUMMARY OF THE INVENTION

The object of the invention is to provide the possibility of monitoring blocking of the diaphragm of the tire pressure sensor due to mechanical damage as well as the maintaining of the required air pressure in the tire between two threshold values in a simple manner.
The object of the invention is acheived by using at least one additional switching member for monitoring the tire pressure in the tire pressure sensor. The additional switching member is actuated jointly with the first switching member by the diaphragm of the tire pressure sensor at different values of the tire pressure. Accordingly, switching thresholds for different tire pressures at the front and rear wheels of the motor vehicle can be realized in a tire pressure sensor. But such a tire pressure sensor can also monitor the tire pressure with respect to different limits, e.g. to an upper limit and a lower limit, equally as well. Finally, with the tire pressure sensors according to the invention, it is also possible to determine blocking of the diaphragms due to mechanical damage in a simple manner after installation of the sensors at the rim, e.g. during the mounting of the tire. If the tire is filled to the prescribed air pressure, but the electronic tire pressure monitor indicates an excess pressure, it means both switching members of the tire pressure sensor are closed because of deformation of the diaphragm.
It is particularly advantageous to form the second switching member as an additional contact pin which is fastened with the first contact pin arranged in the center of the reference chamber, and which extends through the base of the reference pressure chamber and is insulated from it. This solution requires no additional work steps in the production of the tire pressure sensor, since the two contact pins are inserted jointly into the reference pressure chamber. Moreover, the contact arrangement is easier to form, if the second switching member comprises an annular contact body which is guided around the front

REFERENCES:
patent: 4701742 (1987-10-01), Ruchr

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