JP5029509B2 - Flow sensor - Google Patents

Description

  The present invention relates to a flow rate sensor used for measuring an intake air flow rate of an internal combustion engine, for example.

  Conventionally, as shown, for example, in Patent Document 1, an electric heater (heating resistor) and its resistance provided with its own temperature change provided on the downstream side and upstream side of the fluid with respect to the heating resistor, respectively. A flow sensor having two temperature-dependent resistors (resistance temperature detectors) whose values also change has been proposed.

When fluid flows from one direction, the temperature distribution generated by the heating resistor is deformed from one direction to the other. Thereby, the temperature of one resistance temperature detector falls, the temperature of the other resistance temperature detector becomes high, and a temperature difference arises between resistance temperature detectors. As described above, the resistance thermometer has the property that the resistance value of the resistance thermometer also changes with its own temperature change. There is also a difference in the voltage applied to the resistor. In Patent Document 1, a bridge circuit is formed by two resistance temperature detectors provided on the upstream side and the downstream side, a first reference resistor, and a second reference resistor, and provided on the first reference resistor and the downstream side. By measuring the potential difference between the first midpoint potential between the resistance temperature detectors and the second reference point and the second midpoint potential between the resistance temperature detectors provided on the upstream side, The flow direction is detected. The flow rate of the fluid is measured from the absolute value of the potential difference, and the flow direction of the fluid is detected from the positive / negative of the potential difference.
JP 56-57914 A

  By the way, in the flow sensor shown in Patent Document 1, the end portions on the ground side of the two resistance temperature detectors and the end portions on the ground side of the heating resistors are connected to the same ground wiring. For this reason, when the voltage drop of the heating resistor varies due to the change in the amount of current flowing into the heating resistor, the ground wiring itself has a resistance (wiring resistance), so the voltage drop of the ground wiring also varies. As a result, the potential at the end of the resistance temperature detector on the ground wiring side changes, and the voltage drop of the resistance temperature detector also changes. That is, the midpoint potential between the reference resistor and the resistance temperature detector also varies. As described above, the fluid flow rate is measured from the absolute value of the potential difference between the first midpoint potential and the second midpoint potential of the bridge circuit. Therefore, as the voltage drop of the heating resistor varies, the potential difference between the midpoint potentials also varies, which may reduce the flow rate detection reliability.

  Further, when the flow rate of the fluid is very small, the potential difference between the measured first midpoint potential and the second midpoint potential is also very small. For this reason, the positive / negative of the potential difference is reversed due to the fluctuation of the voltage drop of the heating resistor described above, and the flow direction of the fluid may be erroneously detected.

  In view of the above problems, an object of the present invention is to provide a flow sensor in which a decrease in detection reliability of the flow rate and the flow direction is suppressed.

In order to achieve the above-described object, the invention described in claim 1 includes a heating resistor that generates heat when a current is applied, and a sensor unit that includes a plurality of temperature measuring resistors whose resistance values change according to temperature. A circuit unit having an output unit for processing at least the output signal of the sensor unit and processing the output signal; a power supply terminal which is a power supply potential and electrically connected to the sensor unit and the circuit unit via wiring; A grounding terminal electrically connected to the sensor unit and the circuit unit via wiring, and an output terminal electrically connected to the circuit unit and outputting an output signal processed by the output unit to the outside. And a first ground terminal and a second ground terminal that are electrically independent of each other as a ground terminal, and a heating resistor and a first ground terminal. And electrically connect A first ground wiring, a second ground wire connecting the plurality of the temperature measuring resistor second ground terminal electrically, characterized in that are electrically independent.

Thus, according to the present invention, the first ground wiring that electrically connects the heating resistor and the ground terminal, and the second ground wiring that electrically connects the temperature measuring resistor and the ground terminal are electrically connected. Independent. The ground terminal (first ground terminal) to which the first ground wiring is connected and the ground terminal (second ground terminal) to which the second ground wiring is connected are electrically independent. That is, the voltage drop variation of the heating resistor does not affect the potential on the second ground wiring side in the temperature measurement resistor. Thereby, the fall of the detection reliability of a flow volume and a flow direction is suppressed.

In the first aspect of the present invention, as in the second aspect, the first power supply wiring for electrically connecting the heating resistor and the power supply terminal, and the temperature measuring resistor and the power supply terminal are electrically connected. It is preferable that the second power supply wiring connected to the terminal is electrically independent .

According to this, the current amount flowing through the second power supply wiring hardly changes with the change in the amount of current flowing through the heating resistor. Thereby, the fall of the detection reliability of a flow volume and a flow direction is suppressed.

According to a second aspect of the present invention, as in the third aspect of the present invention, the power supply terminal includes a first power supply terminal and a second power supply terminal that are provided electrically independent from each other, and the first power supply terminal Is preferably connected to the first power supply wiring and the second power supply terminal is connected to the second power supply wiring.

In the invention described in claim 2, as claimed in claim 4, the first power line and the second power supply wiring may have a structure connected to a common power supply terminal. According to this, the number of external connection terminals can be reduced.

  In addition, in invention of any one of Claims 1-4, as described in Claim 5, the heating resistance which comprises a sensor part, the resistance temperature detector as a several temperature measurement resistor, side The thermal resistor and the fluid temperature measuring resistor are provided on one surface of the same substrate, and the temperature measuring resistor is disposed upstream and downstream of the heating resistor symmetrically with respect to the heating resistor. A side resistance thermometer and a downstream resistance thermometer, and the indirectly heated resistor is disposed in the vicinity of the heating resistor and is controlled to be higher than the fluid temperature by a predetermined temperature. Is arranged at a position away from the heating resistor in order to measure the temperature of the fluid, and the circuit unit, together with the output unit, supplies a current to the heating resistor so as to keep the temperature of the indirectly heated resistor at a predetermined temperature. A current control unit for controlling the sensor, and is configured on a substrate different from the substrate on which the sensor unit is formed. It can be adapted to the flow rate sensor being.

  In the invention according to claim 5, as described in claim 6, the indirectly heated resistor has a substantially U-shape, and a pair of folded portions that are substantially parallel to each other, and one of the folded portions. It is preferable that a connecting portion for connecting the end portions is provided, and the pair of folded portions are symmetrically arranged with respect to the heating resistor. According to this, the heat of the heating resistor can be efficiently applied to the indirectly heated resistor, and the same amount of heat can be applied to the upstream temperature measuring resistor and the downstream temperature measuring resistor. it can.

  In the invention described in claim 5 or claim 6, as described in claim 7, the fluid temperature measuring resistor includes a first fluid temperature measuring resistor, a second fluid temperature measuring resistor, and A first fluid temperature measuring resistor arranged on the power supply terminal side and a second fluid temperature measuring resistor arranged on the ground terminal side having a third fluid temperature measuring resistor connected in series, and a power supply terminal The third fluid temperature measuring resistor arranged on the side and the indirectly heated resistor arranged on the ground terminal side are connected in series to form a first bridge circuit, and two middle points of the first bridge circuit A configuration in which the terminal is electrically connected to the current control unit may be employed.

  In the invention according to any one of claims 5 to 7, as described in claim 8, the upstream side resistance temperature detector includes a first resistance temperature detector and a second resistance temperature detector, and the downstream side. The resistance temperature detector has a third resistance temperature detector and a fourth resistance temperature detector, and the first resistance temperature detector and the fourth resistance temperature detector on the substrate with respect to the heating resistor. Are arranged symmetrically, the second RTD and the third RTD are arranged symmetrically, and the first RTD arranged on the power supply terminal side and the third RTD arranged on the ground terminal side are arranged. The second resistance circuit is connected in series with the fourth resistance temperature detector arranged on the power supply terminal side and the second resistance temperature detector arranged on the ground terminal side in series. A configuration in which the two midpoint terminals of the second bridge circuit are electrically connected to the output unit may be employed.

  In invention of any one of Claims 5-8, as described in Claim 9, a thin part is formed in a board | substrate, A resistance temperature detector, an indirectly heated resistor, and heat_generation | fever on this thin part formation area | region A configuration in which a resistor is formed and a fluid temperature measuring resistor is formed in a region other than the thin-walled portion forming region in the substrate is preferable. According to this, the temperature measuring resistor, the indirectly heated resistor, and the heating resistor can be thermally separated from the fluid temperature measuring resistor by the thin portion.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic perspective view illustrating a state after the Assy of the flow sensor according to the present embodiment. FIG. 2 is an enlarged plan view of the flow sensor in FIG. FIG. 3 is a plan view showing a schematic configuration of the sensor chip. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is a circuit diagram of the flow sensor. In FIG. 4, the resistors 13 to 22 are omitted for convenience. In the following, the flow direction of the fluid is simply referred to as the flow direction, and the direction perpendicular to the flow direction is simply referred to as the vertical direction.

  As shown in FIG. 1, the flow sensor 100 is arranged in the intake passage of the internal combustion engine so that the sensor chip 10 that measures the flow rate and flow direction of the fluid is exposed to the fluid. As shown in FIG. 2, the flow sensor 100 includes, as main parts, a sensor chip 10 that is exposed to a fluid, a circuit chip 30 that is electrically connected to the sensor chip 10, and a sensor chip via the circuit chip 30. 10, an external connection terminal 50 electrically connected to the sensor 10, and a support portion 70 on which the sensor chip 10 and the circuit chip 30 are mounted and formed integrally with the external connection terminal 50.

  The sensor chip 10 is made of, for example, a silicon substrate 11 (hereinafter simply referred to as the substrate 11). As shown in FIG. 3, an insulating film 12 is formed on one surface of the substrate 11, and a temperature measurement resistor 13 whose own resistance value changes according to its temperature on the insulating film 12. A heating resistor 14 is formed that generates heat when a current is applied. The temperature measurement resistor 13 includes an indirectly heated resistor 15 disposed in the vicinity of the heating resistor 14, temperature measuring resistors 16 to 19 disposed so as to be symmetric with respect to the heating resistor 14, and a resistor. 14 to 19 have fluid temperature measuring resistors 20 to 22 arranged at positions spaced from each other. These resistors 13 to 22 are, for example, wiring (electrical connection) on the substrate 11 (insulating film 12) by vacuum deposition or sputtering of platinum (Pt) or polysilicon (Poly-Si). (Not shown). A pad 23 is connected to the wiring, and the pad 23 is electrically connected to a pad 31 of a circuit chip 30 described later via a bonding wire 32. In the present embodiment, the wiring formed on the substrate 11 is formed such that the heating resistor 14 and the resistors 15 to 22 (temperature measuring resistor 13) are electrically independent. Therefore, on the substrate 11, the heating resistor 14 and the resistors 15 to 22 (temperature measuring resistor 13) are electrically independent. 3 and 4, the substrate 11 is formed with a membrane 24 (corresponding to a thin portion described in the claims) by etching from the back surface of the substrate 11. The resistors 14 to 19 are provided on the membrane 24, and the fluid temperature measuring resistors 20 to 22 are formed in a region other than the membrane 24. Thereby, the fluid temperature measuring resistors 20 to 22 are thermally separated from the resistors 14 to 19. The temperature of the fluid is determined based on the resistance values of the fluid temperature measuring resistors 20-22. Therefore, the temperature of the fluid can be detected in a state where the influence of heat by the heating resistor 14 is suppressed.

  The heating resistor 14 generates heat by applying a current. As shown in FIG. 3, the heating resistor 14 has a substantially rectangular plane shape, and is formed at the center of the substrate 11 in the flow direction so that its long side is substantially parallel to the vertical direction. ing. As will be described later, in the present embodiment, one end of the heating resistor 14 is connected to the power supply terminal 51 via the switching element 34, and the other end is connected to the first ground terminal 54. Therefore, when the switching element 34 is driven, the heating resistor 14 and the power supply terminal 51 (external power source) are connected, whereby a current is applied to the heating resistor 14 and the heating resistor 14 generates heat. ing.

  The side heat resistor 15 is controlled so as to be higher than the temperature of the fluid by a predetermined temperature. As shown in FIG. 3, the side heat resistor 15 has a substantially U-shape and a pair of folded portions 15a, which are substantially parallel to each other. 15b and a connecting portion 15c that connects the ends of the pair of folded portions 15a and 15b. The upstream folded portion 15 a disposed on the upstream side and the downstream folded portion 15 b disposed on the downstream side are provided so as to be symmetrical with respect to the heating resistor 14. In addition, the code | symbol 12a shown by FIG. 5 is the protective film 12a for protecting the resistors 13-22 and its wiring.

  Each of the resistance temperature detectors 16 to 19 has a substantially rectangular shape in the same plane, and each of the resistance temperature detectors 16 to 19 has a substrate whose longitudinal side is substantially parallel to the vertical direction. 11 is formed. Of the resistance temperature detectors 16 to 19, two resistance temperature detectors 16 and 17 are formed on the upstream side in the fluid flow direction, and the other two resistance temperature detectors 18 and 19 are formed on the downstream side. ing. As shown in FIGS. 3 and 5, the first resistance temperature detector 16 disposed on the upstream side and the fourth resistance temperature detector 19 disposed on the downstream side are symmetrical with respect to the heating resistor 14. Thus, the second resistance temperature detector 17 disposed on the upstream side and the third resistance temperature detector 18 disposed on the downstream side have a symmetrical relationship. The distance between the upstream folded portion 15a of the indirectly heated resistor 15 and the first resistance temperature detector 16 is equal to the distance between the downstream folded portion 15b and the fourth resistance temperature detector 19, and the upstream folded portion 15a The distance between the two resistance temperature detectors 17 is equal to the distance between the downstream folded portion 15 b and the third resistance temperature detector 18.

  In the present embodiment, as shown in FIG. 6, the first resistance temperature detector 16 and the fourth resistance temperature detector 19 are disposed on the power supply terminal 51 side, and the third resistance temperature detector 18 is disposed on the ground terminal 53 side. And the second resistance temperature detector 17 are arranged, the first resistance temperature detector 16 and the third resistance temperature detector 18 are connected in series, the fourth resistance temperature detector 19 and the second resistance temperature detector 17. Are connected in series to form a second bridge circuit 93. The two midpoint terminals of the second bridge circuit 93 are electrically connected to the second differential amplifier 36, respectively, so that the potential between the first resistance temperature detector 16 and the third resistance temperature detector 18 can be increased. V 3 and the potential V 4 between the fourth resistance temperature detector 19 and the second resistance temperature detector 17 are input to the second differential amplifier 36. The potential difference (V3-V4) is differentially amplified by the second differential amplifier 36 and output to an external ECU (not shown) via the output terminal 52. Thereby, the flow rate and the flow direction of the fluid are detected.

  Here, a mechanism for detecting the flow rate and flow direction of the fluid will be described. As shown in FIG. 5, a symmetrical temperature distribution T <b> 1 centering on the heating resistor 14 is formed in the no-wind state. Accordingly, in the no-wind state, the amount of heat transferred to the first resistance temperature detector 16 and the fourth resistance temperature detector 19 formed at positions symmetrical to the heating resistor 14 is substantially equal, and the second resistance temperature measurement. The amount of heat transmitted to the resistor 17 and the third resistance temperature detector 18 is substantially equal. Thereby, the resistance values of the first resistance temperature detector 16 and the fourth resistance temperature detector 19 are substantially equal to each other, and the resistance values of the second resistance temperature detector 17 and the third resistance temperature detector 18 are substantially equal to each other. Therefore, in the windless state, the potential V3 between the resistance temperature detectors 16 and 18 and the potential V4 between the resistance temperature detectors 19 and 17 are equal to each other, and the potential difference (V3-V4) is zero. However, for example, as shown in FIG. 5, when the fluid flows from the upstream side to the downstream side, the center position of the temperature distribution T1 moves from the center position of the heating resistor 14 to the downstream side. A new temperature distribution T2 shown in FIG. Therefore, the temperature of the resistance temperature detectors 16 and 17 disposed on the upstream side is lowered, and the temperature of the resistance temperature detectors 18 and 19 disposed on the downstream side is increased. Thereby, for example, the resistance value of the resistance temperature detectors 16 and 17 on the upstream side decreases, and the resistance value of the resistance temperature detectors 18 and 19 on the downstream side increases. The potential difference (V3-V4) is no longer zero, and in this case, the potential difference (V3-V4) takes a positive value. On the contrary, when the fluid flows from the downstream side to the upstream side, the center position of the temperature distribution T1 moves from the center position of the heating resistor 14 to the upstream side. The value increases, and the resistance value of the resistance temperature detectors 18 and 19 on the downstream side decreases. Therefore, in this case, the potential difference (V3−V4) takes a negative value. Thus, since the potential difference (V3−V4) has a positive / negative value with respect to the fluid flow direction, the fluid flow direction is detected by determining the positive / negative value. Further, when the flow rate of the fluid is large, the temperature distribution moves greatly, so that the resistance values of the resistance temperature detectors 16 to 19 also vary greatly, and the potential difference (V3-V4) also varies greatly. Thus, the flow rate of the fluid and the potential difference have a proportional relationship. Therefore, the flow rate of the fluid is detected by measuring the absolute value of the potential difference (V3-V4).

  The fluid temperature measuring resistors 20 to 22 measure the temperature of the fluid. In the present embodiment, the first fluid temperature measuring resistor 20 and the second fluid temperature measuring resistor 21 are arranged on the upstream side and the downstream side, respectively, so as to be symmetric with respect to the heating resistor 14. The third fluid temperature measuring resistor 22 is arranged on the upstream side. As will be described later, in the present embodiment, the first fluid temperature measuring resistor 20 and the third fluid temperature measuring resistor 22 are disposed on the power supply terminal 51 side, and the second fluid temperature is disposed on the ground terminal 53 side. The resistance temperature detector 21 and the above-mentioned indirectly heated resistor 15 are arranged, the first fluid temperature resistance resistor 20 and the second fluid temperature resistor 21 are connected in series, and the third fluid temperature resistance resistor 22 is connected. And the indirectly heated resistor 15 are connected in series to form a first bridge circuit 92. The potential difference between the potential V1 between the first fluid temperature measuring resistor 20 and the second fluid temperature measuring resistor 21 and the potential V2 between the third fluid temperature measuring resistor 22 and the indirectly heated resistor 15 ( By measuring V1-V2), the amount of current flowing through the heating resistor 14 is determined. Since the potential V1 is a potential between the fluid temperature measuring resistors 20 and 21, the potential V1 does not change and takes a constant value. However, since the potential V2 is a potential between the third fluid temperature measuring resistor 22 and the indirectly heated resistor 15, the potential V2 changes when the resistance value of the indirectly heated resistor 15 varies due to a temperature change. The potential difference (V1-V2) is set to be zero when the indirectly heated resistor 15 is at a predetermined temperature.

  As shown in FIG. 6, the circuit chip 30 has a potential difference (V1) between a potential V1 between the fluid temperature measuring resistors 20 and 21, and a potential V2 between the third fluid temperature measuring resistor 22 and the indirectly heated resistor 15. A current control unit 35 having a first differential amplifier 33 that amplifies -V2), a switching element 34 that controls the amount of current that flows through the heating resistor 14 based on the output signal of the first differential amplifier 33, and A second differential amplifier 36 for amplifying the potential difference (V3−V4) between the potential V3 between the temperature resistors 16 and 18 and the potential V4 between the temperature measuring resistors 19 and 17 (in the output section described in the claims) And a constant voltage circuit 37 for making the potential applied to one end of the first bridge circuit 92 and the second bridge circuit 93 (resistors 16, 19, 20, and 22 arranged on the power supply terminal 51 side) constant. , Are provided. In the present embodiment, a bipolar transistor is employed as the switching element 34. Note that a MOS transistor may be employed as the switching element 34.

  The external connection terminal 50 includes a power supply terminal 51 connected to an external power supply (not shown) and an external ECU that detects a flow rate and a flow direction of the fluid based on an output signal output from the second differential amplifier 36. And a ground terminal 53 for grounding one end of the heating resistor 14, the first bridge circuit 92, and the second bridge circuit 93. In the present embodiment, the ground terminal 53 includes a first ground terminal 54 that is electrically connected to the heating resistor 14 via the first ground wiring 90, and resistors 15 to 22 ( And a second ground terminal 55 electrically connected to the temperature measuring resistor 13). Note that the external connection terminal 50 according to the present embodiment is constituted by one lead frame, and the island 56 of the lead frame is integrated with the second ground terminal 55 as shown in FIG. .

  As shown in FIG. 2, the support unit 70 mounts the circuit chip 30 and bonds the pad 15 of the sensor chip 10 and the pad 31 of the circuit chip 30, and the pad 31 of the circuit chip 30 and the external connection terminal 50. After being electrically connected by the wire 32, the sensor chip 10 is mounted with a storage part 71 for storing a resin (not shown) for protecting the connection part and the circuit chip 30, and the sensor chip 10 is exposed to a fluid. And a tongue portion 72 for the purpose. One surface of the island 56 is exposed and fixed to the bottom of the storage portion 71, and the circuit chip 30 is mounted on the one surface of the island 56.

  Next, the characteristic part of the circuit configuration of the flow sensor 100 according to the present embodiment will be described. As shown in FIG. 6, the heating resistor 14 has one end connected to the power supply terminal 51 via the switching element 34 and the power supply wiring 94, and the other end connected to the first grounding terminal 54 via the first grounding wiring 90. It is connected. The first bridge circuit 92 and the second bridge circuit 93 have one end connected to the power supply terminal 51 via the constant voltage circuit 37 and the power supply wiring 94 and the other end electrically independent of the first ground wiring 90. The second ground terminal 55 is connected to the second ground terminal 55 via the second ground wiring 91. Therefore, the fluctuation of the voltage drop of the heating resistor 14 caused by the switching operation described later causes the potential on the second ground wiring 91 side of the first bridge circuit 92 and the second bridge circuit 93 (that is, the resistors 18, 17, 21, 15, the potential at the end of the 15 second ground wiring 91 side). In FIG. 6, reference numeral 95 indicates the wiring resistance 95 of the first ground wiring 90, and reference numeral 96 indicates the wiring resistance 96 of the second ground wiring 91.

  Next, the switching operation of the switching element 34 will be described. As shown in FIG. 6, the first bridge circuit 92 is configured by the three fluid temperature measuring resistors 20 to 22 and the indirectly heated resistor 15. The two midpoint terminals of the first bridge circuit 92 are electrically connected to the first differential amplifier 33 of the current control unit 35, respectively, and thereby, the potential V1 between the fluid temperature measuring resistors 20 and 21. The potential V2 between the third fluid temperature measuring resistor 22 and the indirectly heated resistor 15 is input to the first differential amplifier 33, and the potential difference (V1-V2) is differentially amplified by the first differential amplifier 33. And output to the base electrode of the switching element 34. When the indirectly heated resistor 15 has a predetermined temperature, the potential difference (V1−V2) is set to be zero, and in this case, the switching element 34 is not driven. However, when the indirectly heated resistor 15 becomes lower than the predetermined temperature, for example, the resistance value of the indirectly heated resistor 15 decreases and the potential V2 also decreases. That is, since the potential V2 is smaller than the potential V1, the potential difference (V1-V2) is a positive value. This positive potential difference (V 1 −V 2) is input to the first differential amplifier 33 and differentially amplified by the first differential amplifier 33. The amplified potential difference (V1-V2) is output to the base electrode of the switching element 34. As a result, the switching element 34 is driven, the heating resistor 14 and the power supply terminal 51 are connected, and a current flows through the heating resistor 14. As a result, the heating resistor 14 generates heat, and heat is applied to the indirectly heated resistor 15 and the temperature measuring resistors 16 to 19 disposed in the vicinity of the heating resistor 14. When the temperature of the indirectly heated resistor 15 is increased to a predetermined temperature, for example, the resistance value of the indirectly heated resistor 15 is also increased, and the potential V2 is increased to a value (V1) at the predetermined temperature. Thereby, the potential difference (V1-V2) becomes zero, the driving of the switching element 34 is stopped, and the current flowing through the heating resistor 14 is interrupted. In addition, when the indirectly heated resistor 14 becomes higher than a predetermined temperature, for example, the resistance value of the indirectly heated resistor 15 also increases, and the potential V2 becomes higher than V1. As a result, the potential difference (V1−V2) takes a negative value, and the negative potential difference differentially amplified by the first differential amplifier 33 is input to the base electrode of the switching element 34. In this case, the switching element 34 is not driven, so that no current flows through the heating resistor 14. Thus, feedback heating control is performed by the current control unit 35 so that the temperature of the indirectly heated resistor 15 becomes a predetermined value. The above is the switching operation of the switching element 34.

  Next, the effect of the flow sensor according to the present embodiment will be described. When the amount of current flowing through the heating resistor 14 changes due to the switching operation described above, the voltage drop of the heating resistor 14 also fluctuates accordingly. Then, since the ground wiring itself has a resistance (wiring resistance), the voltage drop of the ground wiring connected to the heating resistor 14 also varies. Therefore, when the heating resistor 14 is electrically connected to one end of the first bridge circuit 92 and the second bridge circuit 93 (one end of the resistors 18, 17, 21, 15) on the ground wiring side, for example. Since the voltage drop of the wiring resistance of the ground wiring varies (when the ground wiring is common), the potential applied to one end of the first bridge circuit 92 and the second bridge circuit 93 also varies. That is, the voltage applied to the first bridge circuit 92 and the second bridge circuit 93 varies. However, as described above, in the present embodiment, the first ground wiring 90 connected to the heating resistor 14 is connected to one end of the first bridge circuit 92 and the second bridge circuit 93 (resistors 18, 17, 21, 15). And the second ground wiring 91 connected to one end of the second electrical wiring. Accordingly, the potential on the second ground wiring 91 side of the first bridge circuit 92 and the second bridge circuit 93 (the potential at the end of the resistors 18, 17, 21, and 15 on the second ground wiring 91 side) is the heating resistor. 14 is not affected by fluctuations in the voltage drop. That is, the potentials V <b> 1 to V <b> 4 that are the midpoint potentials of the first bridge circuit 92 and the second bridge circuit 93 are not affected by fluctuations in the voltage drop of the heating resistor 14. Thereby, the fall of the detection reliability of a flow volume and a flow direction is suppressed.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the present embodiment, the ground terminal 53 has a first ground terminal 54 and a second ground terminal 55, the first ground terminal 54 and the first ground wiring 90 are connected, and the second ground terminal 55 and the second ground terminal 55 are connected. An example in which the ground wiring 91 is connected is shown. However, as shown in FIG. 7, the ground terminal 53 may have only one ground terminal 57, and the first ground wiring 90 and the second ground wiring 91 may be connected to the ground terminal 57. As a result, the number of external connection terminals 50 (ground terminals 53) can be reduced. FIG. 7 is a circuit diagram showing a modification of the flow sensor.

  In the present embodiment, one end of the heating resistor 14 is connected to the power supply wiring 94 via the switching element 34, and one end of the first bridge circuit 92 and the second bridge circuit 93 (the resistors 16, 19, 20, 22 is connected). An example in which one end) is connected to the power supply wiring 94 via the constant voltage circuit 37 is shown. That is, an example in which one end of the heating resistor 14 and one end of the first bridge circuit 92 and the second bridge circuit 93 are connected to the power supply wiring 94 is shown. However, as shown in FIG. 8, the power supply wiring 94 has a first power supply wiring 97 and a second power supply wiring 98 that are electrically independent from each other, and generates heat via the first power supply wiring 97 and the switching element 34. The resistor 14 may be connected, and the first bridge circuit 92 and the second bridge circuit 93 may be connected via the second power supply wiring 98 and the constant voltage circuit 37. As a result, the amount of current flowing through the resistors 15 to 22 (temperature measuring resistor 13) does not change with the change in the amount of current flowing through the heating resistor 14 by the switching operation. Therefore, the potential on the second power supply wiring 98 side of the first bridge circuit 92 and the second bridge circuit 93 (that is, the potential on the second power supply wiring 98 side of the resistors 16, 19, 20, 22) is the heating resistor 14. The configuration is not affected by fluctuations in voltage drop. That is, the potentials V <b> 1 to V <b> 4 that are the midpoint potentials of the first bridge circuit 92 and the second bridge circuit 93 are not affected by fluctuations in the voltage drop of the heating resistor 14. Thereby, the fall of the detection reliability of a flow volume and a flow direction is suppressed. Further, as shown in FIG. 9, the power supply terminal 51 is connected to the first power supply terminal 58 connected to the first power supply wiring 97 (heating resistor 14) and the second power supply wiring 98 (resistors 15 to 22). The second power supply terminal 59 may be used. However, in the case of this configuration, the number of power supply terminals 51 (external connection terminals 50) is increased, so that one power supply terminal 51 is preferable. 8 and 9 are circuit diagrams showing modifications of the flow sensor.

  6 to 9, one end of the first bridge circuit 92 and the second bridge circuit 93 on the power supply wiring 94 side (one end of the resistors 16, 19, 20, and 22 on the power supply wiring 94 side) is provided. A constant voltage circuit 37 is connected to make the potential applied to one end constant. Therefore, the change in potential applied to one end of the first bridge circuit 92 and the second bridge circuit 93 is suppressed by the constant voltage circuit 37 due to the change in the amount of current flowing through the heating resistor 14 by the switching operation. It has a configuration. However, if the amount of current supplied from the power supply terminal 51 changes due to the switching operation, the power supply voltage characteristic of the constant voltage circuit 37 also changes accordingly, and is applied to one end of the first bridge circuit 92 and the second bridge circuit 93. It is feared that the applied potential also changes and the potentials V1 to V4 also change. Therefore, as shown in FIGS. 8 and 9, the power supply wiring 94 preferably includes a first power supply wiring 97 and a second power supply wiring 98 which are electrically independent.

It is a schematic perspective view which shows the state after Assy of a flow sensor. It is the top view to which the flow sensor was expanded in FIG. It is a top view which shows schematic structure of a sensor chip. It is sectional drawing which follows the IV-IV line of FIG. It is sectional drawing which follows the VV line of FIG. It is a circuit diagram of a flow sensor. It is a circuit diagram which shows the modification of a flow sensor. It is a circuit diagram which shows the modification of a flow sensor. It is a circuit diagram which shows the modification of a flow sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Sensor chip 13 ... Temperature measuring resistor 14 ... Heating resistor 16-19 ... Resistance temperature detector 30 ... Circuit chip 36 ... 2nd differential amplifier 50 ... · External connection terminal 51 ··· Power terminal 52 ··· Output terminal 53 ··· Ground terminal 70 ··· Supporting portion 90 ··· First ground wire 91 ··· Second ground wire 100 ... Sensor

Claims (9)

A heat generating resistor that generates heat by applying a current, and a sensor unit having a plurality of temperature measuring resistors whose resistance values change according to temperature,
A circuit unit having an output unit for processing at least the output signal of the sensor unit and processing the output signal;
The power supply terminal is a power supply terminal electrically connected to the sensor unit and the circuit unit via wiring, and the ground potential is grounded and is electrically connected to the sensor unit and the circuit unit via wiring. A flow rate sensor comprising: a terminal; and an external connection terminal having an output terminal that is electrically connected to the circuit unit and outputs the output signal processed by the output unit to the outside,
As the ground terminal, a first ground terminal and a second ground terminal provided electrically independent from each other,
A first ground wiring electrically connecting the heating resistor and the first ground terminal; and a second ground wiring electrically connecting the plurality of temperature measuring resistors and the second ground terminal. A flow sensor characterized by being electrically independent. A first power supply wiring that electrically connects the heating resistor and the power supply terminal, and a second power supply wiring that electrically connects the temperature measurement resistor and the power supply terminal are electrically independent of each other. The flow sensor according to claim 1 , wherein: As the power supply terminal, having a first power supply terminal and a second power supply terminal provided electrically independent from each other,
The flow sensor according to claim 2 , wherein the first power supply terminal is connected to the first power supply wiring, and the second power supply terminal is connected to the second power supply wiring . The flow sensor according to claim 2 , wherein the first power supply wiring and the second power supply wiring are connected to the common power supply terminal. The heating resistor constituting the sensor unit, and the plurality of temperature measuring resistors, the side heat resistors, and the fluid temperature measuring resistors as the temperature measuring resistors are provided on one surface of the same substrate. ,
The resistance temperature detector has an upstream resistance temperature detector and a downstream resistance temperature detector arranged symmetrically with respect to the heating resistor upstream and downstream of the heating resistor,
The indirectly heated resistor is disposed in the vicinity of the heating resistor and is controlled to be a predetermined temperature higher than the fluid temperature.
The fluid temperature measuring resistor is arranged at a position away from the heating resistor to measure the temperature of the fluid,
The circuit unit has a current control unit that controls a current flowing through the heating resistor so as to keep the temperature of the indirectly heated resistor at a predetermined temperature together with the output unit, and is a substrate different from the substrate It is comprised by these, The flow sensor of any one of Claims 1-4 characterized by the above-mentioned. The indirectly heated resistor has a substantially U-shape and includes a pair of folded portions that are substantially parallel to each other and a connecting portion that connects between one end of the folded portions,
The flow sensor according to claim 5, wherein the pair of folded portions are symmetrically arranged with respect to the heating resistor. The fluid temperature measuring resistor has a first fluid temperature measuring resistor, a second fluid temperature measuring resistor, and a third fluid temperature measuring resistor,
The first fluid temperature measuring resistor arranged on the power supply terminal side and the second fluid temperature measuring resistor arranged on the ground terminal side are connected in series, and the first fluid temperature measuring resistor arranged on the power supply terminal side is connected. A three-fluid temperature measuring resistor and the indirectly heated resistor arranged on the ground terminal side are connected in series to form a first bridge circuit,
The flow rate sensor according to claim 5 or 6, wherein two middle point terminals of the first bridge circuit are electrically connected to the current control unit. The upstream resistance temperature detector has a first resistance temperature detector and a second resistance temperature detector, and the downstream resistance temperature detector has a third resistance temperature detector and a fourth resistance temperature detector. And
On the substrate, the first resistance temperature detector and the fourth resistance temperature detector are arranged symmetrically with respect to the heating resistor, and the second resistance temperature detector and the third resistance temperature detector are symmetrical. Has been placed,
The first resistance temperature detector arranged on the power supply terminal side and the third resistance temperature detector arranged on the ground terminal side are connected in series, and the fourth resistance temperature detector arranged on the power supply terminal side And the second resistance temperature detector arranged on the ground terminal side is connected in series to constitute a second bridge circuit,
The flow rate sensor according to any one of claims 5 to 7, wherein two midpoint terminals of the second bridge circuit are electrically connected to the output unit. A thin portion is formed on the substrate,
The resistance temperature detector, the indirectly heated resistor, and the heating resistor are formed on the thin wall forming region,
The flow sensor according to any one of claims 5 to 8, wherein the fluid temperature measuring resistor is formed in a region of the substrate excluding the thin portion forming region.

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