Pressure sensor

Details Pressure sensor Pressure sensor

1987-03-03

1988-09-06

Woodiel, Donald O.

Measuring and testing

Tire, tread or roadway

Tire inflation testing installation

73720, 338 4, 340 58, B60C 7304, G01L 708, G01L 904

Patent

active

047683759

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention is directed to a pressure sensor for detecting the air pressure of a tubeless tire mounted on the rim of a wheel of a motor vehicle.


BACKGROUND OF THE INVENTION

A pressure sensor of this type is used to detect the air pressure in the interior of so-called tubeless tires in motor vehicles. The air pressure in such tires is highly important for both vehicle road holding quality and tire life. In the context of the measurement of important vehicle data, it would appear desirable for this tire pressure also to be detected and monitored as accurately as possible.
The problem in obtaining these measured values is that during vehicle operation, as when the tires are mounted or removed, tires undergo considerable mechanical strain, which can cause sensor damage, particularly with sensitive sensors, which are inherently desirable. There is also the problem that the centrifugal forces involved can falsify the measurements made by the pressure sensors.
From U.S. Pat. No. 4,237,728, an apparatus is known which enables an indirect, rough ascertainment of the tire pressure by means of an elastically deformable feeler protruding radially outward from the drum-like central rim portion; the feeler is deflected whenever the tire cross section varies, for instance, when because of a pressure drop, the inside wall of the tire comes to rest on the feeler. The feeler is connected to a piezoelectric crystal, and the resultant compression of the piezoelectric crystal generates a voltage, from which the measurement signal is derived. This previously known measuring system is accordingly relatively insensitive and is substantially suitable only for detecting highly abnormal conditions. Because of the insensitivity of the feeler provided in the prior art, falsification of the measured results is less serious.


SUMMARY OF THE INVENTION

Starting from the above, the object of the invention is to provide a pressure sensor of the above type such that simple and operationally reliable mounting of the entire pressure sensor on the rim is made possible; the individual sensor elements of the pressure sensor should be disposed therein in a strain-free manner, protected from damage, and subjected to the pressure and temperature of the air in the tires.
The fastening technique provided by the invention enables absolutely pressure-tight installation, even with high centrifugal forces, and enables mounting in the rim from the outside with only slight protrusions inside the tire, as well as enabling a mechanically sturdy embodiment.
An advantage of the pressure sensor of the invention is that a falsification of measured values by centrifugal force is largely precluded, and furthermore, shocks or other mechanical strains at right angles to the pressure-sensitive surfaces of the pressure sensor are avoided.
Another advantage of the pressure sensor of the invention is that it is particularly simple to mount the sensor in the rim from outside, as desired. No sensitive fastening parts of any kind come to rest on the inside of the rim, that is, toward the inside of the tire, and so even when the tire is mounted or removed, damage to the retaining and fixation devices of the pressure sensor by the machines and tools used for this purpose need not be feared.
A sealing ring for sealing off the interior of the tire with respect to the ambient assures hermetic sealing, so that pressure losses due to the inserted pressure sensor need not be feared.
Still another advantage of the pressure sensor of the invention is that on the one hand it makes mutually independent pressure measurements by independent sensor elements possible, which substantially increases the operational reliability. On the other hand, because the sensor elements are disposed in a region completely free of fastening strains, such strains are precluded from impairing the measurements.
A particularly strain-free fastening of the substrate of the sensor elements is attained by potting, because the epoxy resin, for example, used for this purpose hardens

REFERENCES:
patent: 4085620 (1984-08-01), Tanaka
patent: 4467641 (1984-08-01), Abraham
patent: 4562874 (1986-01-01), Scheller

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