Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1999-11-01
2001-05-08
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06227055
ABSTRACT:
TECHNICAL FIELD
This invention relates to apparatus for detecting the pressure of a fluid, and more particularly to a sensor assembly in which the pressure to be sensed is directly applied to the back-side of a pressure sensor element.
BACKGROUND OF THE INVENTION
In automotive control applications, it is frequently desired to measure the pressure of certain fluids, such as engine crankcase oil, brake fluid, engine fuel, etc. In general, the best results have been achieved with so-called “backside-sensing” designs in which the fluid to be sensed enters a sealed cavity terminated by the back (inboard) face of the sensor element. The remainder of the cavity is defined by the interior walls of a pressure port which attaches to a wall of the fluid container by a threaded fitting, or the like. The electrical terminals of the sensor element are formed on its front (outboard) face, and may be conveniently coupled to suitable interface circuitry by wire-bonding, for example. In high pressure applications, the sensor element and port are typically formed of stainless steel, and the sensor is welded to the pressure port, forming a hermetic and leak-proof seal between the fluid and the sensor housing. In lower pressure applications, a lower cost silicon sensor may be used; in this case the pressure port may also be formed with a lower cost material, and the sensor can be bonded to the pressure port with a suitable adhesive, which also seals the fluid from the sensor housing.
Clearly, the silicon approach enables significant cost savings compared to the stainless steel approach due to lower cost materials and processing. However, there is some concern about the long term integrity of the seal provided by the adhesive joint between the sensor and pressure port, since the sensed fluid pressure applies tension to the joint. Accordingly, what is needed is a low cost back-side sensor assembly having a durable and high integrity seal between the sensor and pressure port.
SUMMARY OF THE INVENTION
The present invention is directed to an improved, low-cost, back-side sensing pressure sensor assembly having a high integrity seal between the sensor element and the pressure port. The pressure port has a stud portion at an inboard end for attachment to a pressure vessel wall, and a cup portion at an outboard end for housing the sensor and interface circuitry. A central well extends inward from an inboard face of the cup portion, and a central axial bore in the stud portion opens into the well. A planar carrier disc carrying the sensor element closes the outboard end of the well. The sensor element comprises a silicon diaphragm formed on the outboard end of a glass pedestal that passes through a complementary opening formed in the carrier disc, and the inboard end of the pedestal includes an integral radially extending rim or shoulder that seats on the inboard face of the carrier disc about the opening. A suitable adhesive is used to bond the pedestal rim to the disc, and in operation, the fluid pressure in the vessel places the adhesive joint in compression to provide a long term, high integrity, seal between the well and the remainder of the cup portion. In a first embodiment, the interface circuitry and conductor traces and pads that interconnect the sensor terminals are formed on the outboard face of the carrier disc, whereas in a second embodiment, the circuitry and conductor traces and pads are formed on a flexible circuit glued to the outboard face of the carrier disc.
REFERENCES:
patent: 5257547 (1993-11-01), Boyer
patent: 5648615 (1997-07-01), Jeske et al.
patent: 5706372 (1998-01-01), Viduya
patent: 5939637 (1999-08-01), Pitzer et al.
Delphi Technologies Inc.
Funke Jimmy L.
Oen William
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