Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1999-11-10
2001-09-04
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C307S009100
Reexamination Certificate
active
06282966
ABSTRACT:
The invention relates to a Pressure Sensor Unit, specifically for automotive engineering, with characteristics according to the preamble of Patent Claim
1
.
Pressure Sensor units are known in a variety of designs and are used, for example, in automotive engineering as sensor elements for monitoring the oil pressure of engines or the brake pressure.
Such pressure sensor units comprise, as a rule, a housing with a supply opening for the pressure medium, whose pressure must be monitored, whereby the pressure medium is transported via the supply opening to a pressure measuring cell fitted in the housing. The housing of the pressure sensor unit may have, for example, in an anterior region, an exterior thread, which serves for screwing the pressure sensor unit into a corresponding inner thread of the system that is to be monitored.
Since specifically in automotive engineering high long-term stability is a requirement, combined with simultaneous resistance against aggressive media and rough environmental conditions, specifically so-called media-separated pressure sensor units are being employed here, in which the pressure medium, whose pressure is to be monitored, does not come in contact with the sensor element itself which is arranged in the pressure measuring cell fitted in the housing of the pressure sensor unit.
A separation membrane is employed for media separation, which membrane hermetically seals an admission opening of the pressure measuring cell, and which is acted upon by the to be monitored pressure medium. The pressure acting upon the separation membrane is transmitted via a pressure transmission medium to the pressure sensor itself contained in the pressure measuring cell. In the known pressure measuring cells or pressure sensor units a silicon oil is used as pressure transmission medium. The separation membrane is mostly designed in form of a thin specialty steel foil, which is welded together, such as laser-welded, with the housing of the pressure measuring cell. Following the welding, the interior of the pressure measuring cell, in which is arranged the pressure sensor proper, is filled with the silicon oil by means of a small filling tube.
Such type of pressure measuring cell, which is known for example from “SENSORMAGAZIN April 1989, pages 16 to 10” has, however, a complicated construction as a result of the welding process for the separation membrane and the filling process via the small filling tube, which results in commensurately high manufacturing costs. The complicated construction requires, as a rule, that such pressure measuring cells must be installed by an OEM manufacturer as finished, functioning elements, and the end user, for instance a motor vehicle manufacturer, can have no influence with regard to the constructive design of such measuring cells.
Moreover, from “SENSORREPORT May 1994, pages 22 to 24” a media-separated pressure measuring cell is known, where the membrane may consist of elastomers, such as EPDM, Viton or FVMO. For this pressure measuring cell, the membrane has a pot-like shape, whereby the bottom of the pot serves as separation membrane itself and the membrane is clamped at the upper, outwardly curved edge of the pot wall between two housing parts of the pressure measuring cell. The interior of the pressure measuring cell is again filled with silicon oil as pressure transmission medium.
With this type of pressuring measuring design, the relatively complicated design of the housing of the measuring cell is, however, a drawback with respect to installation and fastening of the separation membrane, which, likewise, has a relatively complicated design. This construction also requires that such type of pressure measuring cell is to be supplied fully functional by the manufacturer.
Proceeding from this state of the art, the object of the present invention is based on creating a pressure sensor unit, specifically for automotive engineering, which has a simple design and which, consequently, can be realized at low manufacturing costs.
The invention solves this object with the characteristics of Patent Claim
1
. The invention proceeds from the knowledge that a very simple and cost effective design of the pressure sensor unit can be realized by means of simply clamping the separation membrane between the outer surfaces of the pressure measuring cell housing and the cooperating inner surfaces of the housing proper of the pressure sensor unit. The previously travelled path is no longer being travelled, according to which the pressure measuring cell itself is first completely manufactured to functional condition, and only afterwards mounted in the housing of an appropriately designed pressure sensor unit with a supply opening for the pressure medium and connection contacts for the sensor proper.
In the preferred specific embodiment of the invention, the measuring cell housing is equipped with a perforation, whose one opening represents the admission opening, which is to be sealed by the separation membrane, and whose other opening serves for installation of a support with a pressure sensor arranged thereon. The support may, for example, be designed as TO-housing with connection pins, onto which the sensor proper is mounted. The sensor may be designed in customary fashion, for instance as silicon membrane with integrated piezo-resistive semiconductor resistances. In the preferred specific embodiment of the invention, the separation membrane consists of synthetic material, preferably of a polyamide.
In the non-mounted state of the sensor unit, the separation membrane is preferably arranged as level foil. This results in the benefit of extremely low cost for the manufacture of the separation membrane.
In the preferred specific embodiment of the invention, the cooperating exterior surfaces of the separation membrane for clamping of the measuring cell housing and the interior surfaces of the pressure sensor unit are basically designed plane. This results in the benefit that into the corresponding recess of the housing of the pressure sensor unit, which is also connected with the supply opening for the pressure medium, only the separation membrane, preferably designed in form of a level foil, needs to be inserted and the pressure measuring cell subsequently introduced. For clamping of the membrane between the level surfaces, the housing of the pressure measuring cell is being stressed with a suitable press-on force.
For sealing of both the admission opening of the pressure measuring cell as well as the interior of the housing of the pressure sensor unit against the supply opening, one or several grooves may be provided in the respectively cooperating surfaces of the measuring cell housing or the housing of the pressure sensor unit, for acceptance of sealing elements, preferably O-rings. In non-mounted state, said sealing elements slightly project above the respective surface and effect simple and secure sealing by means of corresponding compression during installation.
In the preferred specific embodiment of the invention, in place of the former customary silicon oil as pressure transmission medium, a gel-like or jelly-type pressure transmission medium is employed. This produces the benefit of less complicated sealing of the pressure sensor unit, since such type of pressure medium does not have any creeping properties. The viscosity of a gel-like pressure transmission medium is preferably chosen in such manner that in essence there would not take place any gravity-produced flow-off of the gel from the recess of the measuring cell housing, or if there were any flow-off, it would be at an acceptably slow rate.
If the viscosity of the pressure transmission medium is reduced to the extent that a jelly-like consistency results, then any flow-off is totally prevented. In this respect one needs, however, to take into consideration that the hardness/elasticity of the jelly must be chosen in such manner that its function as a pressure transmission medium is maintained.
As a result of utilizing a jelly-like or gel-type pressure transmission medium, there is pr
Probst Uwe
Skofljanec Robert
Aw-Musse Abdullahi
Fay Sharpe Fagan Minnich & McKee LLP
Fuller Benjamin R.
TRW Automotive Electronics & Components GmbH & Co. KG
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