Measuring and testing – Fluid pressure gauge – With protective separator
Patent
1992-03-03
1993-10-05
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
With protective separator
73115, 73727, 73756, 338 4, G01L 708, G01L 906
Patent
active
052494683
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a pressure sensor.
More particularly the present invention relates to a pressure sensor which has a housing and a sensor element composed of a piezoresistive material and arranged in the housing. In the case of such a pressure sensor, known from German Offenlegungsschrift 31 25 640.6, the piezoresistive measuring elements, such as for example thick-film resistors of cermet, contactive plastic or metal, are printed on a base. The resistor element and the base are arranged as close as possible to the pressure chamber in order to be able to determine the prevailing pressure. Furthermore, the measuring signal is passed with the aid of electric leads to an electronic evaluation circuit arranged outside the housing of the pressure sensor. As a result, the piezoresistive elements and the electronic components have to be elaborately connected to one another with the aid of sheathed leads. Since the piezoresistive measuring element is exposed directly to the pressure, it is also exposed to the high temperatures prevailing in the combustion chamber. The flames spread there at a temperature of about 2000.degree. C., whereby stresses can occur in the housing. As a result, the pressure signal is falsified by the high temperatures.
Furthermore, European Preliminary Published Specification 85 111 895.0 discloses a pressure sensor in which the thick-film resistor is arranged on the bottom of a base. However, this pressure sensor is intended only for determining the pressure in distributor pumps. The high temperatures prevailing in the combustion chamber would falsify the measuring signal in the case of this design as well.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a pressure sensor which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a pressure sensor in which between a diaphragm and a sensor element there is a punch which introduces a pressure to be determined onto said sensor element, and at least an end of the punch facing the piezoresistive sensor element is composed of a relatively soft material.
When the pressure sensor is designed in accordance with the present invention, it has the advantage that as uniform a force introduction as possible via the punch onto the piezoresistive measuring element is possible. It is possible to compensate for roughnesses occurring at the end of the punch. By the use of a relatively soft material for the punch, but in particular by the use of a soft material for the end of the punch facing the piezoresistive element, a uniform force introduction over the entire contact area is possible. If in this case the punch with a soft tip is pressed onto the glass layer surrounding the piezoresistive element under a pressure exceeding the pressure later to be determined, a virtually uninterrupted form fit is achieved between the end of the punch and the over-glazing of the piezoresistive element. A particularly homogeneous force introduction is possible as a result. Furthermore, the diameter of the end of the punch can be designed smaller than the resistor element. If, in particular, a hemispherical force-transferring element is used between the punch and the piezoresistive element, a homogeneous force introduction onto the piezoresistive element is achieved in a particularly simple way. Either the tip of the punch or the force-introducing part may consist of a relatively soft material. As a result, a multipart design of the punch can be avoided. This design is conceivable with and without impressing of the parts punch, force- introducing part and overglazing of the piezoresistive element, since a homogeneous force introduction onto the piezoresistive element is possible with the only approximately punctiform bearing of the force-introducing part on the punch.
By welding the diaphragm to the punch, measuring errors due to an undefined force
REFERENCES:
patent: 3204463 (1965-09-01), Taber
patent: 4567751 (1986-02-01), Ootsuka et al.
patent: 4839708 (1989-06-01), Kano et al.
patent: 4993266 (1991-02-01), Omura et al.
Benedikt Walter
Herden Werner
Konrad Johann
Kuesell Matthias
Schmidt Wolfgang
Robert & Bosch GmbH
Striker Michael J.
Woodiel Donald O.
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