Source: http://www.google.com/patents/US5404753?ie=ISO-8859-1
Timestamp: 2014-03-13 17:34:04
Document Index: 238154892

Matched Legal Cases: ['art 24', 'art 25', 'art 25', 'art 25', 'art 24', 'art 25', 'art 25', 'art 25', 'art 24', 'art 25', 'art 25']

Patent US5404753 - Mass flow sensor - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA mass flow sensor detects the intensity of a media flow. The mass flow sensor includes a measurement chip, with a dielectric membrane and a frame of monocrystalline silicon. At least one heater is arranged on the membrane. The measurement chip is installed in the in-flow channel of a housing. By means...http://www.google.com/patents/US5404753?utm_source=gb-gplus-sharePatent US5404753 - Mass flow sensorAdvanced Patent SearchPublication numberUS5404753 APublication typeGrantApplication numberUS 08/069,888Publication dateApr 11, 1995Filing dateJun 1, 1993Priority dateJun 13, 1992Fee statusPaidAlso published asDE4219454A1, DE4219454C2Publication number069888, 08069888, US 5404753 A, US 5404753A, US-A-5404753, US5404753 A, US5404753AInventorsHans Hecht, Wolfgang Kienzle, Eckart Reihlen, Rudolf Sauer, Kurt WeiblenOriginal AssigneeRobert Bosch GmbhExport CitationBiBTeX, EndNote, RefManPatent Citations (15), Referenced by (35), Classifications (12), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetMass flow sensorUS 5404753 AAbstract A mass flow sensor detects the intensity of a media flow. The mass flow sensor includes a measurement chip, with a dielectric membrane and a frame of monocrystalline silicon. At least one heater is arranged on the membrane. The measurement chip is installed in the in-flow channel of a housing. By means of the structure of the housing, contamination of the measurement chip is reduced, thermal equalization with the media flow is improved, the resistance of the sensor to sudden pressure variations is increased, and the dielectric contacts are improved.
What is claimed is: 1. A mass flow sensor comprising:a housing having a flow channel and a sealing lip, an interior side of the sealing lip defining a first side of the flow channel; a measuring chip including a semiconductive frame bonded to the housing; the sealing lip connected to a central portion of the frame for sealing the flow channel; a first portion of the frame being on the interior side of the sealing lip and a second portion of the frame being on a posterior side of the sealing lip; a surface of the first portion of the frame being flush with a wall of the flow channel thereby forming a smooth flow channel; a closed dielectric membrane disposed on the surface of the first portion of the frame and adjacent to the flow channel, the membrane being suspended from the frame on all sides; a heating element coupled to the membrane for heating the membrane; at least one bonding wire coupled to at least one bond pad on the second portion of the frame, the at least one bond pad coupled to at least one track in the semiconductive frame, the at least one track coupled to the heating element. 2. The mass flow sensor according to claim 1, wherein the frame is made of monocrystalline silicon.
3. The mass flow sensor according to claim 1, wherein a geometry of the flow channel accelerates the mass flow.
4. The mass flow sensor according to claim 1, wherein a cross-section of the flow channel narrows in a direction of flow.
5. The mass flow sensor according to claim 1, wherein the flow channel tapers in a direction of flow, the tapering of the flow channel accelerating the mass flow, a smallest cross-section of the flow channel being after the measuring chip in the direction of flow.
6. The mass flow sensor according to claim 1, wherein the housing further has a vent for venting a bottom side of the membrane.
7. The mass flow sensor according to claim 1, further comprising an adhesive for connecting the sealing lip to the frame.
8. The mass flow sensor according to claim 1, wherein the measuring chip further includes monolithically integrated circuits adjacent to the bond pad.
9. The mass flow sensor according to claim 1, wherein the housing further has a heat sink including a plurality of cooling ribs.
10. The mass flow sensor according to claim 1, wherein the measuring chip further includes a temperature sensor coupled to the membrane.
FIELD OF THE INVENTION The present invention relates to sensors and in particular to a mass flow sensor.
BACKGROUND INFORMATION A mass flow sensor is described in International Application No. WO 89/05963, in which a dielectric membrane is arranged in a frame of monocrystalline silicon. Heating elements and temperature measurement elements are arranged on the membrane. Other temperature measurement elements are arranged on the silicon frame.
SUMMARY OF THE INVENTION The mass flow sensor according to the present invention includes a measuring chip installed in an in-flow channel of a housing. The measuring chip includes a dielectric membrane disposed on a surface of a silicon frame, adjacent to the in-flow channel. A heating element is used to heat the membrane.
An advantage of the mass flow sensor according to the present invention is that precisely defined and easily reproducible flow conditions on the surface of the measurement chip are achieved by the installation of the measurement chip in the in-flow channel of a housing. Another advantage is that better protection of the measurement chip against mechanical stress and particles conducted in the media flow can be achieved by the installation of the measurement chip in the in-flow channel.
By an acceleration of the mass flow in the in-flow channel, the deposit of dirt particles on the measurement chip is reduced. Furthermore, the release of vortexes, which result in greater noise, is suppressed and, thus, the measurement is improved. This acceleration is achieved in a particularly simple manner by narrowing the cross-section of the in-flow channel in the flow direction. In a particularly advantageous embodiment, the smallest cross-section in the flow direction lies after the measurement chip, because, in this way, it can be ensured that the air is accelerated also above the sensor.
By installing the measurement chip flush in a wall of the in-flow channel, edges in the flow channel, which lead to especially severe dirt deposits, are avoided. By connecting the frame flush,a good thermal contact with the housing is ensured. Mechanical torsion stresses in the membrane are reduced if the surface is glued down on only one side of the membrane. Adaptation of the housing temperature to the temperature of the media flow is improved with a cooling element.
To protect the dielectric membrane against a sudden pressure increase of the media flow and thermal expansion of the gas enclosed between the measurement chip and the housing, the housing has a vent hole. In order to prevent flow on the bottom of the membrane in this connection, the cross-section of the vent hole should be less than the length of the vent hole.
Particularly well-sealed installation of the measurement chip in the housing is achieved by using a sealing lip. If the sealing lip rests on the frame, the assembly of the measurement chip and the housing is particularly simple. The mechanical stress on the measurement chip is reduced in that the sealing lip has a slight gap towards the frame, and this gap is closed off with adhesive. By means of the arrangement of the membrane and the bond pads on different sides of the sealing lip, a clear separation of the measurement region from the electrical connection region is achieved. This separation particularly allows the use of circuits or other sensitive elements in the immediate vicinity of the membrane, without any influence on these elements by the media flow.
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1a and 1b show cross-sectional and top views, respectively, of a measurement chip.
FIGS. 2, 3 and 4 show top, longitudinal cross-sectional (along line I--I in FIG. 2) and cross-sectional (along line II--II in FIG. 2) views, respectively, of a first embodiment of the mass flow sensor according to the present invention.
FIG. 5 shows a cross-sectional view of a second embodiment of the mass flow sensor according to the present invention.
DETAILED DESCRIPTION FIG. 1a shows a measurement chip 2 in cross-section, and FIG. 1b shows the measurement chip 2 in a top view. A dielectric membrane in a frame 4 of monocrystalline silicon is designated by the reference numeral 3. At least one heater 5 and at least one temperature sensor 6 are arranged on the membrane 3. Another reference temperature sensor 20 is arranged on the frame 4. The heater 5, the temperature sensor 6 and the reference temperature sensor 20 are connected to bond pads 8 by means of tracks (printed conductors) 7. An electrical contact between the heater 5, the temperature sensor 6, the reference temperature sensor 20 and the outside world is produced by means of the tracks 7. By bonding wires to the bond pads 8, an electrical connection to external circuits (not shown) can be produced.
The dielectric membrane 3 is composed of, for example, silicon nitride and/or silicon oxide. These materials have low thermal conductivities and can be produced on the surface of a silicon wafer in a particularly simple manner. The self-contained membrane 3 is formed by etching the surface of a silicon wafer coated with a dielectric material. The corresponding etching methods are familiar to a person skilled in the art.
The heater 5 includes a resistor element, which generates heat on the membrane by means of a current flow sent through the tracks 7. The resistor element can be composed of a metal, for example, or of suitably doped silicon. The temperature sensor 6 and the reference temperature sensor 20 can include a resistor element, for example, the conductivity of which is dependent upon temperature. Suitable materials for this resistor element are metals or suitably doped silicon. An element which utilizes the temperature difference between the membrane and the frame via the Seebeck effect can also be used for the temperature sensor 6.
With this measurement chip 2, the value of a mass flow can be determined, where the flow direction is parallel to the surface of the measurement chip 2. The membrane 3 is kept at a temperature which is greater than the temperature of the mass flow, by means of the heater 5. The amount of heat conducted away from the membrane 3 by the mass flow is dependent upon the intensity of the mass flow. By measuring the temperature of the membrane 3, the intensity of the mass flow can be determined in this way. The membrane temperature can be measured by means of the temperature sensor 6, or by measuring the resistance of the heater 5. The reference temperature sensor 20 is used to eliminate the influence of the temperature of the medium that is flowing past the membrane 3. In this connection, it is assumed that the frame 4 is at the temperature of the flowing medium. Experience has shown that such a measurement chip is very sensitive to contamination of the surface, which can be caused by dirt particles, for example.
FIG. 2 shows a top view of the mass flow sensor according to the present invention. The measurement chip 2 is installed in the in-flow channel 9 of the housing 1. The direction of the flow through the in-flow channel is indicated by the arrow. For the sake of simplicity, the representation of the temperature sensor 6 and the reference temperature sensor 20 are eliminated in the representation of the measurement chip 2. The heater 5, arranged on the membrane 3, is connected to the bond pads 8 by means of tracks 7. An electrical contact to circuits (not shown) is produced by means of the bond wires 21. Circuits arranged directly on the measurement chip are schematically represented as 14. With these circuits 14, processing of the signals of the temperature sensor 6 and the reference temperature sensor 20, i.e. control of the heater 5, can be carried out. By means of the monolithic integration of the circuits with the measurement chip, the latter becomes more sensitive, the resistance to disruptions is increased, and the costs are potentially reduced.
The cross-section of the in-flow channel 9 decreases along the flow direction. The smallest cross-section is located after the measurement chip, in the flow direction. As such, the deposit of dirt particles on the measurement chip 2 is reduced. Furthermore, the release of vortexes on the surface of the chip is suppressed, and the resulting lower noise improves the measurability of the sensor signal.
FIG. 3 shows a longitudinal cross-section through the mass flow sensor of FIG. 2, along line I--I. The measurement chip 2 is installed in the housing 1 in such a way that the membrane 3 and the frame 4 are flush with a wall 10 of the in-flow channel 9. The frame 4 is glued to an area of the housing 1 by means of adhesive 22. The cross-section of the in-flow channel 9 narrows such that the smallest cross-section is after the measurement element 2, in the flow direction. Furthermore, the housing 1 has a cooling element (heat sink) in the form of cooling ribs 11. The cooling ribs 11 are oriented parallel to the media flow (see arrow) with the longitudinal side.
Because of the flush installation of the measurement chip 2, edges are avoided in the in-flow channel 9; these are known to cause many dirt particles to collect. Because dirt particles, particularly in the vicinity of the membrane 3, change the characteristic of the measurement chip, the flush installation improves the long-term stability of the output signal of the mass flow sensor. In order to reduce the influence of the temperature of the media flow, the reference temperature sensor 20 must have approximately the temperature of the media flow. For this purpose, the measurement chip 2 is glued to the housing with a large part of its surface. As such, good thermal contact between the measurement chip 2 and the housing 1 is ensured. Furthermore, the cooling element 11 must give off a sufficient amount of heat to the media flow, in order to balance out the heating of the frame 4 caused by the heater 5. In addition, the temperature adjustment of the frame should take place quickly in case of a temperature change in the medium. The housing 1 and the cooling element 11 therefore have a low mass and are made from materials having a low specific heat capacity. By means of a large surface-to-volume ratio of the cooling element, for example by structuring the cooling element as cooling ribs, a large transfer of heat to the medium and a rapid adjustment to a change in temperature are guaranteed.
FIG. 4 shows a cross-section through the mass flow sensor, along line II--II of FIG. 2. The housing 1 includes an upper part 24 and a lower part 25. The measurement chip 2 is installed in a recess 26 of the lower part 25 of the housing 1. The frame 4 is glued flush with the lower part 25 of the housing 1 by means of adhesive 22. The measurement chip 2 further has circuits 14 and a bond pad 8. The measurement chip 2 is connected to other circuits by means of a bond wire 21. Furthermore, the lower part of the housing has cooling ribs 11. The bottom of the membrane 3 is vented by means of a vent hole 12. The upper housing part 24 has a sealing lip 13, which is connected to the measurement chip 2 by means of adhesive 23.
By means of the vent hole 12, a pressure difference between the top and bottom of the membrane 3 is avoided. Since the membrane 3 is very thin, in order to keep the thermal conductivity of the membrane low, there is a risk that the membrane will be destroyed if there are pressure differences. However, it is undesirable for flow to occur in the cavity formed by the membrane 3, the frame 4 and the lower housing part 25, since dirt particles can be deposited in this case. The cross-section of the vent hole 12 should therefore be less than its length.
The top of the measurement chip 2 is divided into regions by the sealing lip 13. The membrane 3 and the in-flow channel 9 are located in one region. The circuits 14, the bond pads 8 and the bond wires 21 are located on the other side of the sealing lip 13. This division ensures that the circuits 14, the bond pads 8 and the bond wires 21 will be protected against disruptive influences of the media flow. A hermetic separation between these two regions is achieved by setting the sealing lip 13 onto the frame 4 or by using an adhesive layer 23 between the sealing lip 13 and the frame 4.
FIG. 5 shows another embodiment of the mass flow sensor according to the present invention, in which the measurement chip 2 is glued to the lower housing part 25 only on one side of the membrane 3, and the recess 26 of the lower housing part 25 for the measurement chip 2 is slightly larger than the measurement chip 2. The result achieved is that the measurement chip 2 can expand if it heats up, without creating any distortion relative to the housing 1. The sealing lip 13, which is formed out of the upper housing part 24 and separates the membrane 3 and the bond wires 21, is elastic and set onto the measurement chip 2 without gluing. The seal can again be improved by gluing. In this embodiment of the mass flow sensor according to the present invention, the lower housing part 25 does not have a vent hole, because pressure equalization between the top and bottom of the membrane can take place by means of the vent hole formed by the measurement chip 2 and the lower housing part 25.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4403506 *Oct 13, 1981Sep 13, 1983Robert Bosch GmbhApparatus for the measurement of the mass of a flowing mediumUS4548078 *Jul 25, 1984Oct 22, 1985Honeywell Inc.Integral flow sensor and channel assemblyUS4587844 *Mar 19, 1985May 13, 1986Robert Bosch GmbhFlow rate meterUS4685331 *Apr 10, 1985Aug 11, 1987InnovusThermal mass flowmeter and controllerUS4829818 *Dec 27, 1983May 16, 1989Honeywell Inc.Flow sensor housingUS4870860 *Feb 25, 1988Oct 3, 1989Nippon Soken, Inc.Direct-heated flow measuring apparatus having improved response characteristicsUS4884443 *Dec 23, 1987Dec 5, 1989Siemens-Bendix Automotive Electronics L. P.Control and detection circuitry for mass airflow sensorsUS4976145 *Sep 6, 1989Dec 11, 1990Robert Bosch GmbhFlow rate meterUS5167147 *Jun 8, 1990Dec 1, 1992Robert Bosch GmbhAir-measuring deviceDE2900220A1 *Jan 4, 1979Jul 17, 1980Bosch Gmbh RobertVorrichtung zur messung der masse eines stroemenden mediumsDE3844354A1 *Dec 30, 1988Jul 5, 1990Bosch Gmbh RobertMessvorrichtung zur messung der masse eines stroemenden mediumsEP0094497A1 *Mar 26, 1983Nov 23, 1983Honeywell Inc.Gas flow sensing apparatusJPS61194317A * Title not availableWO1989005963A1 *Dec 16, 1988Jun 29, 1989Siemens Bendix Automotive ElecSilicon-based mass airflow sensorWO1989005967A1 *Dec 16, 1988Jun 29, 1989Siemens Bendix Automotive ElecControl and detection circuitry for mass airflow sensors* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS5723784 *Jul 8, 1996Mar 3, 1998Robert Bosch GmbhFlow rate meterUS5841032 *Jan 24, 1997Nov 24, 1998The United States Of America As Represented By The Administrator National Aeronautics And Space AdministrationVariable and fixed frequency pulsed phase locked loopUS6089103 *May 6, 1998Jul 18, 2000Radi Medical Systems AbMethod of flow measurementsUS6106486 *Dec 22, 1997Aug 22, 2000Radi Medical Systems AbGuide wireUS6343514Jan 30, 1997Feb 5, 2002Radi Medical Systems AbCombined flow, pressure and temperature sensorUS6474154Jan 5, 2001Nov 5, 2002Ngk Spark Plug Co., Ltd.Flow measurement device for measuring flow rate and flow velocityUS6553829 *Jun 30, 2000Apr 29, 2003Hitachi, Ltd.Air flow sensor having grooved sensor elementUS6571623 *Feb 26, 1999Jun 3, 2003Pierburg GmbhMeasuring instrument with rectangular flow channel and sensors for measuring the mass of a flowing mediumUS6591674 *Dec 21, 2000Jul 15, 2003Honeywell International Inc.System for sensing the motion or pressure of a fluid, the system having dimensions less than 1.5 inches, a metal lead frame with a coefficient of thermal expansion that is less than that of the body, or two rtds and a heat sourceUS6615667Dec 20, 2001Sep 9, 2003Radi Medical Systems AbCombined flow, pressure and temperature sensorUS6655207Feb 16, 2000Dec 2, 2003Honeywell International Inc.Flow rate module and integrated flow restrictorUS6694811Mar 6, 2003Feb 24, 2004Denso CorporationFlow meter having airflow sensorUS6729181Aug 16, 2001May 4, 2004Sensiron AgFlow sensor in a housingUS6768291Mar 28, 2002Jul 27, 2004Denso CorporationFluid flow sensor and method of fabricating the sameUS6779395Nov 20, 2003Aug 24, 2004Sensirion AgDevice for measuring the flow of a gas or a liquid in a bypassUS6845660Mar 13, 2002Jan 25, 2005Robert Bosch GmbhSensor chip with additional heating element, method for preventing a sensor chip from being soiled, and use of an additional heating element on a sensor chipUS6854325Apr 17, 2002Feb 15, 2005Robert Bosch GmbhSensor chip having potential surfaces for avoiding contaminantUS6920786Aug 21, 2003Jul 26, 2005Sensirion AgFlow detector with lead-throughs and method for its productionUS7201046Feb 21, 2001Apr 10, 2007Hitachi, Ltd.Flowmeter with resistor heaterUS7757553Mar 20, 2009Jul 20, 2010Sensirion AgFlow detector with a housingUS7905140Jan 21, 2008Mar 15, 2011Sensirion AgDevice with flow sensor for handling fluidsUS8156815Feb 24, 2010Apr 17, 2012Sensirion AgSensor in a moulded package and a method for manufacturing the sameUS8356514Jan 13, 2011Jan 22, 2013Honeywell International Inc.Sensor with improved thermal stabilityUS8397586Mar 22, 2010Mar 19, 2013Honeywell International Inc.Flow sensor assembly with porous insertUS8408050Aug 25, 2009Apr 2, 2013Sensirion AgMethod for measuring a fluid composition parameter by means of a flow sensorUS8418549Jan 31, 2011Apr 16, 2013Honeywell International Inc.Flow sensor assembly with integral bypass channelUS8485031Jan 30, 2012Jul 16, 2013Honeywell International Inc.Sensor assembly with hydrophobic filterUS20110252882 *Apr 19, 2010Oct 20, 2011Honeywell International Inc.Robust sensor with top capUS20120001273 *Jul 2, 2010Jan 5, 2012Siargo Ltd.Micro-package for Micromachining Liquid Flow Sensor ChipUS20120161256 *Mar 10, 2010Jun 28, 2012Oleg GrudinFlow sensing device and packaging thereofUSRE39863 *Jan 30, 1997Oct 2, 2007Radi Medical Systems AbCombined flow, pressure and temperature sensorEP1024350A1 *Oct 14, 1998Aug 2, 2000Mitsui Mining &amp; Smelting Co., LtdFlow rate sensor, flow meter, and discharge rate control apparatus for liquid discharge machinesEP1363109A1 *Feb 21, 2001Nov 19, 2003Hitachi Car Engineering Co., Ltd.Flowmeter with resistor heaterEP1760437A1 *Sep 6, 2005Mar 7, 2007Sensirion AGA method for manufacturing detector devicesWO2002008699A1 *Jul 20, 2001Jan 31, 2002Bosch Gmbh RobertAirtight sealed sensor* Cited by examinerClassifications U.S. Classification73/204.22International ClassificationG01F1/684, G01F1/688, G01F1/692, G01F1/68Cooperative ClassificationH01L2224/73265, G01F1/6842, G01F1/684, G01F1/6845European ClassificationG01F1/684C, G01F1/684M, G01F1/684Legal EventsDateCodeEventDescriptionOct 10, 2006FPAYFee paymentYear of fee payment: 12Sep 17, 2002FPAYFee paymentYear of fee payment: 8Sep 30, 1998FPAYFee paymentYear of fee payment: 4Jun 1, 1993ASAssignmentOwner name: ROBERT BOSCH GMBH, GERMANYFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HECHT, HANS;KIENZLE, WOLFGANG;SAUER, RUDOLF;AND OTHERS;REEL/FRAME:006574/0268;SIGNING DATES FROM 19930422 TO 19930517RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google