Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
1999-09-20
2001-11-20
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06318170
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to improvements in a measurement device for measuring the mass of a flowing medium.
BACKGROUND OF THE INVENTION
A measurement device has already been disclosed by German Patent Publication 195 24 634 A1, which includes a plate-shaped sensor element with a dielectric membrane that is inserted into a recess of a sensor support. The sensor element is made of a semiconductor material, e.g. silicon, and is manufactured in a micromechanical construction. The membrane is comprised of a dielectric material, for example silicon nitride or silicon oxide. A measurement resistor and a heating resistor are disposed on the dielectric membrane, which are to a large extent thermally insulated from a silicon frame that encompasses the membrane due to the thin embodiment of the membrane and the low heat conductivity of the dielectric membrane. Between the dielectric membrane and the sensor support, there is a hollow space in the plate-shaped sensor element, which extends from a bottom face adjoining the sensor support to the dielectric membrane and is manufactured, for example, by means of an etching process. The sensor element is fixed in the recess of the sensor support by means of a glue. Since the relatively thin membrane must be protected from excess pressure peaks, a ventilation of the hollow space provided underneath the membrane cannot be omitted. The ventilation of the recess in the measurement sensor or the rear of the membrane, however, must take place so that a flow of the medium is kept away from the rear of the membrane in order to prevent the rear flow from contributing to the measurement signal. In order to prevent the penetration of glue into the hollow space adjoining the membrane, the gluing region does not extend over the entire sensor element, but the sensor element is glued into the recess of the sensor support on only half of its surface and the region of the sensor element which has the electric membrane is disposed freely in the recess. In order to prevent underflow of the membrane, i.e. a flow of the medium to the hollow space embodied underneath the membrane, or to at least counteract this, a flow conduit is provided, which is embodied in the sensor support as a channel-shaped recess and extends around the sensor element. At the same time, the provision is made that the recess embodied in the sensor support is matched to the dimensions of the sensor element so that only a small gap respectively remains between the lateral boundary of the sensor element and the lateral boundary of the recess in the sensor support, which permits only a throttled flow of the medium to the hollow space disposed underneath the dielectric membrane.
However, it is disadvantageous in this embodiment that the sensor element must be aligned with high precision in regard to the recess of the sensor support during mounting in order to produce the extremely narrow gap. But this task cannot always be reliably fulfilled for tolerance reasons and due to manufacturing variations so that not insignificant losses in efficiency occur during manufacture.
A measurement device can be inferred from German Patent Publication 42 19 454 A1, in which a sensor element with a dielectric membrane is inserted into the recess of a cooling body. The cooling body has a ventilation bore between the cooling ribs in order to assure the ventilation of the rear of the membrane.
OBJECTS AND SUMMARY OF THE INVENTION
A principal object of the measurement device according to the invention is to provide the advantage over the prior art that in the manufacturing, a relatively low tolerance must be maintained in the positioning of the sensor element in relation to the recess of the sensor support. As a result, the manufacturing efficiency is increased and the manufacturing costs are reduced. Furthermore, the manufacturing speed can be increased. In another object of the invention the ventilation of the rear of the membrane remote from the flowing medium is reliably assured with a sufficient opening cross section so that a destruction of the sensor element due to pressure peaks is prevented. The glue seam is used simultaneously for tolerance compensation between the sensor element and the sensor support as well as for compensation of different coefficients of thermal expansion.
Yet another object of the invention provides that the glue seam extends into a region beneath the connecting elements for connection to the connecting wires or that an additional glue seam is provided in this region in order to assure a reliable fixing of the sensor element in the vicinity of the connecting elements and to counteract the danger of breakage when the connecting wire is attached, e.g. by means of bonding.
Still another object of the invention is to embody a recess in the sensor support, which communicates with the hollow chamber of the sensor element and is not completely covered by the sensor element. This recess of the sensor support can, for example, be produced by means of embossing. The recess of the sensor support reliably assures the ventilation of the rear of the membrane.
Still a further object of the invention provides that on a support face disposed opposite from the bottom face of the sensor element, spacers can be provided, which are produced, for example, by means of embossing, which set the distance between the sensor support and the bottom face of the sensor element to a precisely defined dimension. Furthermore, it is advantageous if the sensor support has at least one glue displacement chamber into which excess glue that is used to produce the glue seam can be displaced upon insertion of the sensor element into the recess of the sensor support. In this manner, an accumulation of glue at unfavorable locations is avoided, particularly in the hollow space of the sensor element that is formed underneath the membrane. The mechanical stress of the sensor element is minimized through the use of an elastic silicon glue, even when there are differences in thermal expansion coefficients between the material of the sensor element and the material of the sensor support.
REFERENCES:
patent: 4129042 (1978-12-01), Rosvold
patent: 4220852 (1980-09-01), Seidel
patent: 5723784 (1998-03-01), Lembke et al.
patent: 5834755 (1998-11-01), Haghiri-Tehrani et al.
Hecht Hans
Hueftle Gerhard
Kallabis Matthias
Konzelmann Uwe
Marberg Henning
Fuller Benjamin R.
Greigg Ronald E.
Mack Corey D.
Robert & Bosch GmbH
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