JP2008039704A - Wind velocity sensor, mass airflow sensor, and fuel battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wind velocity sensor capable of improving responsiveness using a simple circuit while reducing costs; to provide a mass airflow sensor using such a wind velocity sensor; and to provide a fuel battery system using such a mass airflow sensor. <P>SOLUTION: The fuel battery system comprises: diodes D1, D2 arranged in a gas for detecting wind velocity; resistors R1, R2 for supplying a forward current to the diodes D1, D2; a zener diode ZD1 for heating the diode D2; and a differential amplification circuit 531 for outputting a differential signal S1 for indicating the difference between a forward voltage Vd1 generated in the diode D1 and a forward voltage Vd2 generated in the diode D2 as a signal for indicating wind velocity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermal wind speed sensor that utilizes a heat dissipation phenomenon caused by a flowing gas, an air volume sensor that measures an air volume using the wind speed sensor, and a fuel cell system that uses the air volume sensor.

  When supplying air as an oxidizer to the air electrode of a fuel cell, or when sending air to a combustion boiler for combustion assistance, it is necessary to control the amount of air to be blown and the wind speed. An air volume / air speed sensor is used. As this air volume air speed sensor, a thermal sensor utilizing the heat dissipation phenomenon of a heating element is generally used. When air is applied to the generated platinum wire, the temperature of the platinum wire changes according to the wind speed, and the resistance of the platinum wire is changed. What measures a wind speed using the change of a value is known.

  However, since platinum wires are expensive, it is known to measure the wind speed by using an inexpensive diode instead of platinum wire and utilizing the fact that the forward voltage of the diode changes according to the temperature of the diode. (For example, refer to Patent Document 1).

  FIG. 9 is a schematic circuit diagram showing a configuration of a wind speed sensor using a diode according to the background art. A wind speed sensor 101 shown in FIG. 9 includes a diode 102, constant current circuits 103 and 104, and a switch 105. The constant current circuit 103 is a constant current circuit that supplies a forward current for detecting a forward voltage to the diode 102. The constant current circuit 103 constantly supplies a minute current that does not cause a problem of self-heating of the diode 102. The constant current circuit 104 is a constant current circuit that supplies a large current for causing the diode 102 to self-heat. The switch 105 is a switch that turns on and off the current output from the constant current circuit 104 to the diode 102.

  In addition, a control circuit 106 configured using, for example, a CPU (Central Processing Unit), an AD converter, or the like is provided outside the wind speed sensor 101. The cathode voltage of the diode 102, that is, the forward voltage of the diode 102 is provided. Vf is AD-converted by the control circuit 106, and data indicating the wind speed is acquired.

  A gas 107 whose wind speed is to be measured hits the diode 102.

  FIG. 10 is an explanatory diagram for explaining the operation of the wind speed sensor 101 shown in FIG. FIG. 10A shows the forward voltage Vf of the diode 102. FIG. 10B shows the on / off operation of the switch 105. As shown in FIG. 10, since a small current is constantly supplied to the diode 102 by the constant current circuit 103 with the switch 105 turned off, the forward voltage Vf of the diode 102 is 0.6V to 0V. The voltage V1 is about 7V.

  Next, the switch 105 is turned on by the control circuit 106, for example. Then, a large current flows through the diode 102 by the constant current circuit 104, and the forward voltage Vf rises to the voltage V2. The temperature of the diode 102 gradually increases due to self-heating of the diode 102. Then, since the forward voltage Vf of the diode 102 has a negative temperature characteristic, the forward voltage Vf gradually decreases as the temperature of the diode 102 gradually increases.

  Here, if the wind speed of the gas 107 is small, the heat dissipation of the diode 102 is also small, so that the temperature rise rate of the diode 102 is fast and the rate of decrease of the forward voltage Vf is fast. Since the heat radiation of 102 is also large, the temperature rise rate of the diode 102 becomes slow, and the rate of decrease of the forward voltage Vf becomes slow. Therefore, the wind speed of the gas 107 can be obtained by measuring the forward voltage Vf after a predetermined time has elapsed after the switch 105 is turned on by the control circuit 106.

  When the diode 102 is self-heated in this way, the silicon chip itself of the diode that generates the forward voltage Vf generates heat. Therefore, if the temperature of the diode 102 rises to a steady state, the difference in wind speed. As a result, it becomes difficult to measure the wind speed using the temperature characteristic of the forward voltage Vf. Therefore, the wind speed of the gas 107 is obtained from the forward voltage Vf by measuring the forward voltage Vf after the switch 105 is turned on and heat is generated and before the temperature reaches a steady state.

Further, if the wind speed sensor 101 is arranged in a pipe having a predetermined opening cross-sectional area, the wind speed and the amount of gas flowing through the pipe are in a proportional relationship, and therefore the wind speed measured by the wind speed sensor 101 flows through the pipe. It shows the air volume of gas. Therefore, the wind speed sensor 101 can be used as an air volume sensor for measuring the air volume of the gas flowing through the pipe. Such an air volume sensor is used as a sensor for detecting the amount of air supplied, for example, for controlling the amount of air supplied to the fuel cell.
JP 2004-309202 A

  However, since the wind speed sensor 101 configured as described above requires a sequence operation in which the switch 105 is turned on and the forward voltage Vf is measured after a certain time, the control circuit 106 is complicated. It was. Further, such a wind speed sensor 101 has a disadvantage in that the responsiveness is poor because the forward voltage Vf indicating the wind speed cannot be obtained unless a certain time elapses after the switch 105 is turned on. Further, in the wind speed sensor 101, it is necessary to cause a forward current to flow through the diode 102 to generate heat. The amount of heat generated by the diode 102 is obtained by the product of the forward current and the forward voltage. Since the diode is a non-linear element and the amount of increase in the forward voltage relative to the amount of increase in the forward current is small, the diode 102 To generate heat, a large current must be passed. For this reason, it is necessary to use a circuit having a large current capacity as the constant current circuit 104, and there is a disadvantage that the cost increases.

  The present invention has been made in view of such circumstances, and a wind speed sensor capable of improving responsiveness using a simple circuit while reducing cost, and an air volume sensor using such a wind speed sensor And it aims at providing the fuel cell system which uses such an air volume sensor.

  A wind speed sensor according to the present invention includes a first diode and a second diode arranged in a gas whose wind speed is to be detected, and a current supply unit that supplies a preset forward current to the first and second diodes. And a heating unit for heating the second diode, and a difference signal indicating a difference between a forward voltage generated in the first diode and a forward voltage generated in the second diode as a signal indicating the wind speed. And a signal output unit.

  According to this configuration, the first and second diodes are arranged in the gas for detecting the wind speed, and the second diode is heated by the heating unit. And since the 1st diode is not heated, it is ambient temperature, ie, the same temperature as gas, and even if the flowing gas hits the 1st diode, the temperature of the 1st diode hardly changes. On the other hand, since the second diode is heated by the heating unit, the heat radiation amount of the second diode increases and the temperature difference from the first diode decreases as the wind speed hitting the second diode increases. When the same forward current set in advance from the current supply unit is supplied to the first and second diodes having such a temperature, a forward voltage corresponding to the temperature of the gas is generated in the first diode, In the two diodes, a forward voltage corresponding to the gas temperature and the wind speed is generated. When the difference signal output unit outputs the difference between the forward voltage generated in the first diode and the forward voltage generated in the second diode as a difference signal, the difference signal is a voltage generated according to the gas temperature. As a result of removing the components and leaving the voltage component obtained according to the wind speed, the wind speed is indicated.

  In this case, since the wind speed can be measured using the temperature characteristic of the forward voltage of an inexpensive diode, the cost can be reduced as compared with the case where expensive platinum is used. In addition, since the second diode is heated by the heating unit without causing self-heating, the wind speed can be measured using the forward voltage when the temperature of the second diode reaches a steady state, and the diode self-heating is reduced. A sequence operation of measuring the forward voltage after a certain time from the start is not required, and the circuit can be simplified. And since there is no need to wait for a certain period of time from the start of self-heating of the diode until the forward voltage is measured, the responsiveness of wind speed measurement can be improved. Further, since the second diode is heated using the heating unit, it is not necessary to flow a large forward current to cause the second diode to self-heat, and a current drive circuit having a large rating is provided for self-heating of the diode. As a result, the increase in cost can be reduced.

  The heating unit preferably includes a Zener diode thermally coupled to the second diode, and a Zener current supply unit that supplies a reverse current to the Zener diode.

  According to this configuration, the amount of heat generated by the Zener diode is obtained by the product of the reverse current supplied from the Zener current supply unit and the Zener voltage. The second diode is heated by the heat generated by the Zener diode. Generally, a heater marketed as a general-purpose product in major countries such as Japan and Europe and America has a large external dimension, and when such a heater is used as a heating unit, it is not easy to reduce the size of the heating unit. On the other hand, Zener diodes, which are sealed in a small package, are widely marketed as general-purpose products in Japan, Europe, and the United States, so the wind speed sensor can be downsized by using Zener diodes as heating elements. Easy to do.

  Further, as in the case of the wind speed sensor according to the background art, the amount of heat generated when a forward current flows through the diode to generate heat is the product of the current flowing through the diode and the forward voltage generated in the diode. In such a case, the forward voltage of the diode cannot be set freely like the Zener voltage of the Zener diode, and since it becomes a small voltage value, the forward current of the diode is set to ensure a necessary amount of heat generation. There is a need to increase it. On the other hand, according to the wind speed sensor of the present invention, a reverse current is passed through the Zener diode to generate heat. As a result, the Zener voltage can be appropriately set to a large value. The reverse current supplied from the supply unit can be reduced. Then, the Zener current supply unit can be configured with a circuit having a small current capacity, and the cost can be easily reduced.

  The second diode and the Zener diode are disposed adjacent to the same printed wiring board and connected to the same copper foil pattern formed on the printed wiring board for conducting heat. It is preferable that they are thermally coupled.

  According to this configuration, since the heat generated in the Zener diode can be conducted to the second diode by the copper foil pattern having high thermal conductivity, the second diode and the Zener diode can be efficiently thermally coupled. . Moreover, since a copper foil pattern can be formed in the manufacturing process of a printed wiring board, the member for carrying out heat conduction separately is not required, and the increase in cost can be suppressed.

  The copper foil pattern is preferably a wiring pattern for supplying the forward current to the second diode and supplying the reverse current to the Zener diode.

  According to this configuration, since the copper foil pattern is a wiring pattern electrically connected to the second diode and the Zener diode, the electrode portion and the copper foil pattern, which are portions having high thermal conductivity in the second diode, And between the electrode portion and the copper foil pattern, which are parts having high thermal conductivity in the Zener diode, are soldered for electrical connection, respectively, between the second diode and the copper foil pattern, and The thermal resistance between the Zener diode and the copper foil pattern is reduced, and the second diode and the Zener diode can be easily thermally coupled.

  The first diode is connected to the wiring pattern, the current supply unit supplies the forward current to the first diode through the wiring pattern, and the wiring pattern includes the Zener diode and the In a portion where heat is conducted between the second diode, the width in the direction perpendicular to the direction in which heat is conducted is the width of the portion where the forward current supplied from the current supply unit to the first diode flows. It is preferable to make it thicker.

  According to this configuration, the first diode is connected to the second diode and the Zener diode via the copper foil pattern. And the copper foil pattern of the location where the forward current supplied from a current supply part to a 1st diode flows rather than the width | variety of a perpendicular | vertical direction with respect to the direction where the heat | fever of the copper foil pattern from a Zener diode to a 1st diode conducts Therefore, the heat generated in the Zener diode is reduced from being conducted to the first diode through the copper foil pattern.

  In addition, it is preferable that a distance between the Zener diode and the first diode is longer than a distance between the Zener diode and the second diode.

  According to this configuration, the path length in the case where the heat generated in the Zener diode is transmitted to the first diode by thermal conduction of the printed wiring board, and the distance until the radiant heat of the Zener diode is transmitted to the first diode are The distance between the second diode and the second diode is longer, and heating of the first diode by the Zener diode is reduced.

  Moreover, it is preferable that a hole penetrating the printed wiring board is provided so as to cross between the first diode, the second diode, and the Zener diode.

  According to this configuration, the heat generated in the Zener diode is reduced from being transmitted to the first diode by the heat conduction of the printed wiring board by the hole penetrating the printed wiring board.

  Moreover, it is preferable that the first diode, the second diode, and the Zener diode are arranged in a line in this order from the windward side.

  According to this configuration, since the first diode, the second diode, and the Zener diode are arranged in a line along the air flow in this order from the windward, the disturbance of the air flow is reduced. As a result, the measurement accuracy of the wind speed is improved. In addition, since the Zener diode, which is a heating element, is disposed on the leeward side from the first and second diodes, the temperature of the first and second diodes is not changed by the air warmed by the Zener diode, and the wind speed The occurrence of the measurement error is suppressed.

  An air volume sensor according to the present invention includes the above-described wind speed sensor, a pipe having a predetermined opening cross-sectional area and guiding the gas, and the wind speed sensor is disposed inside the pipe, and the differential signal The output unit outputs the difference signal as a signal indicating the amount of air flowing through the pipe.

  According to this configuration, the differential signal indicates the wind speed of the gas flowing through the pipe having a predetermined opening cross-sectional area, that is, the amount of air flowing through the pipe, so that the responsiveness is improved while reducing the cost using a simple circuit. An air velocity sensor that can be used to measure the amount of air flowing through the tube.

  In addition, the fuel cell system according to the present invention includes the above-described air volume sensor, the fuel cell, a blower that supplies air to the fuel cell via a pipe in the air volume sensor, and the fuel cell by the blower. And a controller that adjusts the amount of air to be supplied according to the difference signal.

  According to this configuration, the amount of air supplied to the fuel cell by the blower is detected by the air volume sensor and output as a difference signal. The control unit adjusts the amount of air to be supplied to the fuel cell by the blower in accordance with the difference signal output from the air flow sensor, so feedback control based on the amount of air actually supplied to the fuel cell. As a result of being able to adjust the amount of air supplied from the blower to the fuel cell, using a wind speed sensor that can improve the responsiveness while reducing the cost using a simple circuit, from the blower to the fuel cell The adjustment accuracy of the air supply amount can be improved.

  Since the wind speed sensor having such a configuration can measure the wind speed using the temperature characteristic of the forward voltage of an inexpensive diode, the cost can be reduced as compared with the case of using expensive platinum. In addition, since the second diode is heated by the heating unit without causing self-heating, the wind speed can be measured using the forward voltage when the temperature of the second diode reaches a steady state, and the diode self-heating is reduced. A sequence operation of measuring the forward voltage after a certain time from the start is not required, and the circuit can be simplified. And since there is no need to wait for a certain period of time from the start of self-heating of the diode until the forward voltage is measured, the responsiveness of wind speed measurement can be improved. Further, since the second diode is heated using the heating unit, it is not necessary to flow a large forward current to cause the second diode to self-heat, and a current drive circuit having a large rating is provided for self-heating of the diode. As a result, the increase in cost can be reduced.

  Moreover, the air volume sensor of such a structure can measure the air volume which flows through a pipe | tube using the wind speed sensor which can improve responsiveness, reducing cost using a simple circuit.

  In the fuel cell system having such a configuration, the amount of air supplied to the fuel cell is adjusted by the blower according to the difference signal output from the air flow sensor, so that the amount of air actually supplied to the fuel cell is adjusted. As a result of being able to adjust the amount of air supplied from the blower to the fuel cell by feedback control based on the amount, using a wind speed sensor that can improve responsiveness while reducing cost using a simple circuit, The adjustment accuracy of the air supply amount from the blower to the fuel cell can be improved.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted. FIG. 1 is a schematic configuration diagram showing an example of a configuration of a fuel cell system using an air volume sensor according to an embodiment of the present invention. A fuel cell system 1 shown in FIG. 1 includes, for example, a fuel cell stack 2 in which fuel cells are stacked, a fan 3 (blower device) that supplies air to the fuel cell stack 2, and air blown from the fan 3 as fuel. A duct 4 (tube) that leads to the battery stack 2, a wind speed sensor 5 disposed inside the duct 4, and an amount of air that is supplied to the fuel cell stack 2 by the fan 3 according to an output signal of the wind speed sensor 5. And a control unit 6 for controlling.

  The fuel cell stack 2 includes a cathode (not shown) and an anode (not shown), and generates power by supplying fuel to the anode and supplying air to the cathode. The fan 3 supplies air to the cathode of the fuel cell stack 2 through the duct 4. The wind speed sensor 5 measures the wind speed of the air flowing through the duct 4, and outputs a signal S 1 indicating the wind speed to the control unit 6. In this case, since the opening cross-sectional area of the duct 4 is known, the signal S1 indicates the wind speed of the air flowing through the duct 4 and at the same time the air volume of the air flowing through the duct 4. That is, the wind speed sensor 5 is disposed inside the duct 4 and functions as the air volume sensor 7.

  The control unit 6 includes, for example, a CPU that executes predetermined arithmetic processing, a ROM (Read Only Memory) that stores a predetermined control program, a RAM (Random Access Memory) that temporarily stores data, and a signal S1. An AD converter for converting to a digital signal and these peripheral circuits are provided. And the control part 6 controls the rotation speed of the fan 3 according to signal S1 by executing the control program memorize | stored in ROM, for example, and the air supplied from the fan 3 to the fuel cell stack 2 is controlled. The amount is adjusted appropriately.

  Here, when power generation is performed in the fuel cell stack 2, water generated along with the power generation adheres to the cathode air flow path. As a result, the air flow path becomes narrow and the airflow resistance increases, making it difficult for the air to flow. Therefore, if the rotational speed of the fan 3 is kept constant, the fuel cell stack 2 generates power from the fan 3 as the fuel cell stack 2 generates power. As a result, the amount of air supplied to 2 is reduced, resulting in a shortage of air at the cathode and a decrease in generated power.

  On the other hand, if the amount of air supplied from the fan 3 to the fuel cell stack 2 is too large, the cathode electrode dries out and the generated power decreases. Some fuel cells collect and recycle the water produced at the cathode, but the amount of air supplied from the fan 3 to the fuel cell stack 2 is too large to be produced at the cathode. If the water evaporates and is discharged to the outside, the recovered amount of water for reuse is insufficient.

  Accordingly, it is necessary to appropriately adjust the amount of air supplied from the fan 3 to the fuel cell stack 2. However, as described above, even if the rotational speed of the fan 3 is constant, the ventilation resistance in the air flow path of the cathode. The amount of air supply will change due to the fluctuations. Therefore, in the fuel cell system 1, an appropriate amount from the fan 3 to the fuel cell stack 2 is controlled by controlling the rotational speed of the fan 3 based on the air supply amount detected by the air volume sensor 7 using the control unit 6. It is designed to supply air.

  FIG. 2 is an explanatory diagram showing an example of the configuration of the air volume sensor 7. An air volume sensor 7 shown in FIG. 2 includes a duct 4 and a wind speed sensor 5. The wind speed sensor 5 includes a sensor element portion 51 disposed inside the duct 4, a wiring portion 52 that draws a signal from the sensor element portion 51 to the outside of the duct 4, and a wind speed based on a signal drawn by the wiring portion 52. And a detection circuit 53 that generates a signal S1 to be output to the control unit 6. Note that the detection circuit 53 may be disposed inside the duct 4.

  The opening cross section of the duct 4 has a substantially square shape with, for example, one side of about 1 cm. The diodes D1 and D2 and the Zener diode ZD1 are sealed in a substantially cubic package having a side of about 1 mm, for example.

  FIG. 3 is a circuit diagram showing an example of the configuration of the wind speed sensor 5. The wind speed sensor 5 shown in FIG. 3 includes a diode D1 (first diode), a diode D2 (second diode), a Zener diode ZD1, resistors R1, R2, and R3, and a differential amplifier circuit 531. In the sensor element portion 51, diodes D1 and D2 and a Zener diode ZD1 are attached in approximately one row in this order. Furthermore, the sensor element unit 51 is disposed inside the duct 4 in such a direction that the diode D1 is on the fan 3 side, that is, the windward side.

  Resistors R 1, R 2, R 3 and a differential amplifier circuit 531 are attached to the detection circuit 53, and the sensor element portion 51 and the detection circuit 53 are connected by a wiring portion 52. The power supply voltage is applied to the anode of the diode D1 through the resistor R1, and the cathode of the diode D1 is connected to the ground through the wirings 511 and 513. The power supply voltage is applied to the anode of the diode D2 via the resistor R2, and the cathode of the diode D2 is connected to the ground via the wirings 512 and 513. The power supply voltage is applied to the cathode of the Zener diode ZD1 through the resistor R3, and the anode of the Zener diode ZD1 is connected to the ground through the wirings 512 and 513.

  The resistors R1 and R2 are current supply units for supplying a preset forward current, for example, 1 mA, for generating the forward voltages Vd1 and Vd2 corresponding to the temperatures of the diodes D1 and D2. For example, if the power supply voltage is 10 V, the resistors R1 and R2 are set to 10 kΩ.

  The Zener diode ZD1 is used as a heating element, and the Zener voltage is set to about 4V to 6V, for example. The resistor R3 is for causing a current for causing the zener diode ZD1 to generate heat, for example, 20 mA to flow in the reverse direction from the cathode of the zener diode ZD1 to the anode. The resistance is used. In this case, the resistor R3 and the Zener diode ZD1 correspond to an example of a heating unit, and the resistor R3 corresponds to an example of a Zener current supply unit.

  Here, when a power supply voltage is applied to the wind speed sensor 5, a forward current of about 1 mA flows through the diodes D1 and D2 by the resistors R1 and R2, respectively. Due to such a small current, the diodes D1 and D2 hardly self-heat.

  Further, when a power supply voltage, for example, 10V is applied to the Zener diode ZD1, the Zener diode ZD1 is repeatedly turned on and off, whereby the voltage across the Zener diode ZD1 is set to a Zener voltage, for example, 6V, and to 20 mA by the resistor R3. The limited current flows through the Zener diode ZD1 in the reverse direction. In this case, the amount of heat generated by the Zener diode ZD1 is obtained as the product of the Zener voltage and the current, so that 6V × 20 mA = 120 mW.

  On the other hand, when the diode self-heats like the wind speed sensor 101 according to the background art shown in FIG. 9, for example, the heat generation amount is obtained as a product of the forward voltage and current of the diode. Since the forward voltage of the diode is about 0.6 V to 0.7 V, a current of 120 mW / 0.6 V = 200 mA is necessary to obtain a heat generation amount of 120 mW, and a current 10 times larger than that in the case of the wind speed sensor 5 is passed. Therefore, it is necessary to use a circuit having a current capacity 10 times larger as the constant current circuit 104.

  That is, since the wind speed sensor 5 can obtain a sufficient amount of heat generation with a current smaller than that of the wind speed sensor 101 according to the background art, the Zener diode ZD1 has a Zener diode ZD1 more than the constant current circuit 104 used for the wind speed sensor 101. As a result of being able to reduce the current (power) rating of the Zener current supply section, for example, the resistor R3, through which current flows, the cost can be reduced.

  In addition, a heater using a resistor such as a heating wire or a thermistor may be used as the heating unit. However, a heater that is generally marketed as a general-purpose product in major countries such as Japan and Europe and the United States has a large outer dimension, When the opening cross section is only about 1 cm × 1 cm as in the duct 4 used in the battery system 1, it is possible to obtain a general-purpose heater that can be disposed in the duct 4 without obstructing the air flow. Have difficulty. Therefore, when a heater using a resistor such as a heating wire or a thermistor is used as a heating element, it is necessary to make a heater of a size that can be disposed in the duct 4 without obstructing the air flow. As a result, the cost increases.

  On the other hand, as the Zener diode ZD1, for example, a chip part sealed in a substantially cubic package with a side of about 1 mm is widely available as a general-purpose product in major countries such as Japan and Europe and America. By using the diode ZD1 as a heating element, the cost of the air volume sensor 7 can be reduced.

  The difference between the anode voltage of the diode D1, that is, the forward voltage Vd1 generated at the diode D1, and the voltage of the anode of the diode D2, that is, the forward voltage Vd2 generated at the diode D2, is amplified by the differential amplifier circuit 531 and then the duct 4 Is output to the control unit 6 as a signal S1 indicating the internal air speed, that is, the amount of air flowing through the duct 4.

  The wind speed sensor 5 is configured using, for example, a flexible substrate, and is wired by a copper foil pattern formed on the flexible substrate. The wind speed sensor 5 is not limited to an example configured by a flexible substrate, and for example, the sensor element unit 51 and the detection circuit 53 may be configured by a glass epoxy substrate or the like, and an electric wire may be used as the wiring unit 52. .

  FIG. 4 is a circuit diagram showing an example of a detailed configuration of the differential amplifier circuit 531. The differential amplifier circuit 531 illustrated in FIG. 4 includes, for example, operational amplifiers 532, 533, and 534 and resistors R4, R5, R6, and R7. The non-inverting input terminal of the operational amplifier 532 is connected to the anode of the diode D2 and applied with the forward voltage Vd2, and the output terminal and the inverting input terminal of the operational amplifier 532 are connected. The output terminal of the operational amplifier 532 is connected to the inverting input terminal of the operational amplifier 534 via the resistor R4.

  The anode of the diode D1 is connected to the non-inverting input terminal of the operational amplifier 533 and the forward voltage Vd1 is applied, and the output terminal and the inverting input terminal of the operational amplifier 533 are connected. The output terminal of the operational amplifier 533 is connected to the non-inverting input terminal of the operational amplifier 534 via the resistor R5.

  The output terminal of the operational amplifier 534 is connected to the inverting input terminal via the resistor R6, and the non-inverting input terminal of the operational amplifier 534 is connected to the ground via the resistor R7. The output signal of the operational amplifier 534 is output to the control unit 6 as the signal S1. For example, the resistors R4 and R5 are set to 10 kΩ, and the resistors R6 and R7 are set to 1 MΩ. Accordingly, the differential amplifier circuit 531 operates as a differential signal output unit that amplifies and outputs the difference between the forward voltage Vd1 and the forward voltage Vd2 by 100 times. Further, the operational amplifiers 532 and 533 increase the input impedance of the differential amplifier circuit 531, thereby improving the detection accuracy of the forward voltages Vd1 and Vd2.

  FIG. 5 is an external view for explaining the details of the sensor element unit 51. The sensor element unit 51 shown in FIG. 5 includes, for example, diodes D1 and D2 and a Zener diode ZD1 arranged in a line in this order from the windward side on the surface of a flexible board 515 (printed wiring board).

  The Zener diode ZD1 and the diode D2 are disposed close to each other, and the distance L1 between the Zener diode ZD1 and the diode D1 is longer than the distance L2 between the Zener diode ZD1 and the diode D2. Thereby, the path length when the heat generated in the Zener diode ZD1 is transmitted to the diode D1 by the heat conduction of the flexible substrate 515 and the distance until the radiant heat of the Zener diode ZD1 is transmitted to the diode D1 are the Zener diode ZD1 and the diode D2. Longer than the distance between and the diode D1 is reduced from being heated by the Zener diode ZD1.

  In addition, the cathode of the diode D2 and the anode of the Zener diode ZD1 are thermally coupled by being connected to a wiring 512 formed of a copper foil pattern having a wide thermal conductivity. The diode D2 and the Zener diode ZD1 are not necessarily limited to those that are thermally coupled by the wiring 512. For example, an electrically insulated copper foil pattern different from the wiring is formed below the diode D2 and the Zener diode ZD1. It may be formed and adhered, or may be thermally coupled by connecting the diode D2 and the Zener diode ZD1 with a member having high thermal conductivity. However, the wiring 512 is a wiring pattern for supplying a forward current to the diode D2 and a reverse current to the Zener diode ZD1, and is soldered to the cathode electrode of the diode D2 and the anode electrode of the Zener diode ZD1. Therefore, by soldering for electrical wiring connection, the electrode portion, which is a portion with high thermal conductivity in the diode D2 and the Zener diode ZD1, and the wiring 512 can be closely thermally coupled, and as a result, the diode D2 and It becomes easy to thermally couple the Zener diode ZD1 closely.

  Further, since the cathode of the diode D1 is connected to the ground in the same manner as the cathode of the diode D2 and the anode of the Zener diode ZD1, the wiring 511 connected to the cathode of the diode D1 is a wiring connected to the anode of the Zener diode ZD1. 512 is electrically connected. Then, a heat conduction path is formed from the Zener diode ZD1 to the diode D1 via the wiring 512 and the wiring 511 which are copper foil patterns. The width W1 of the wiring 511 is larger than the width W2 of the wiring 512. Since it is narrowed, the heat generated in the Zener diode ZD1 is reduced from being conducted to the diode D1 through the wiring 511.

  A slit 516 (hole) that penetrates the flexible substrate 515 is provided between the diode D1 and the diode D2. This reduces the heat generated in the Zener diode ZD1 from being transmitted to the diode D1 due to the heat conduction of the flexible substrate 515.

  The diode D2 and the Zener diode ZD1 are not limited to the example of being disposed on one surface of the substrate such as the flexible substrate 515, and may be disposed on the front and back of the substrate, for example. In this case, the copper foil pattern connected to the diode D2 on one surface of the substrate and the copper foil pattern connected to the Zener diode ZD1 on the other surface of the substrate are connected by a through hole having a copper foil pattern formed on the inner wall. By doing so, the diode D2 and the Zener diode ZD1 may be thermally coupled by thermal conduction of the copper foil pattern.

  Next, the operation of the fuel cell system 1 using the air volume sensor 7 configured as described above will be described. First, referring to FIG. 3, when a power supply voltage is applied to the wind speed sensor 5, forward currents of about 1 mA flow through the diodes D1 and D2 by the resistors R1 and R2, respectively. In this case, the same amount of forward current flows through the diodes D1 and D2, and if the temperature is the same, the forward voltage Vd1 and the forward voltage Vd2 are equal. Then, the forward voltages Vd1 and Vd2 are, for example, 125 mV.

  For example, the terminal voltage of the Zener diode ZD1 is 4.7 V, and the flowing current is 21 mA. Then, the Zener diode ZD1 consumes 4.7 V × 21 mA = 100 mW and generates heat.

  The Zener current supply unit is not limited to a fixed resistor such as the resistor R3 as long as it can stably supply a current to the Zener diode ZD1, and various circuits such as a constant current circuit can be used.

  Further, when the current flowing through the Zener diode ZD1 is limited by the resistor R3, power is consumed by the resistor R3. For example, the supply of the power supply voltage to the resistor R3 and the Zener diode ZD1 is pulsed using a switching element. Power consumption may be reduced by turning on and off.

  The heat dissipation coefficient of the Zener diode ZD1 is 400 ° C./W, for example, and the temperature rises by 40 degrees due to heat generation of 100 mW. Now, if the ambient temperature is 25 degrees, the Zener diode ZD1 becomes 65 ° C.

  Then, the heat generated in the Zener diode ZD1 is transmitted to the diode D2 by heat conduction or heat radiation through the wiring 512, and the diode D2 is heated, for example, the temperature of the diode D2 rises by 30 degrees to 55 degrees. Since the forward voltages Vd1 and Vd2 of the diodes D1 and D2 have a temperature characteristic of −2 mV / ° C., the forward voltage Vd2 changes by −2 mV / ° C. × 30 ° C. = − 60 mV with a temperature increase of 30 degrees. 125 mV-60 mV = 65 mV.

  On the other hand, the distance between the diode D1 and the Zener diode ZD1 is longer than that of the diode D2, the heat conduction from the Zener diode ZD1 to the diode D1 by the flexible substrate 515 is blocked by the slit 516, and the width of the wiring 511 is narrow. As a result, the heat conduction by the wiring 511 is reduced, so that the diode D1 is not heated by the Zener diode ZD1. Therefore, as a result of maintaining the temperature of the diode D1 at 25 degrees which is the same as the ambient temperature, the forward voltage Vd1 is maintained at 125 mV.

  Next, the difference between the forward voltage Vd1 and the forward voltage Vd2 is amplified 100 times by the differential amplifier circuit 531, and the signal S1 indicating the wind speed in the duct 4, that is, the amount of air flowing through the duct 4, is sent to the control unit 6. Is output. In this case, the signal S1 indicates zero wind speed, and S1 = (Vd1−Vd2) × 100 = (125 mV−65 mV) × 100 = 6V.

  Next, the fan 3 is driven in accordance with a control signal from the control unit 6, and air is supplied to the fuel cell stack 2 through the duct 4. Then, the diode D2 is cooled by the air flowing through the duct 4, and the forward voltage Vd2 increases. On the other hand, since the diode D1 has the same ambient temperature, that is, the temperature of air, even if air flows through the duct 4, the temperature of the diode D1 does not change.

  Then, the difference between the forward voltage Vd1 and the forward voltage Vd2 is reduced, and the signal level of the signal S1 is reduced. That is, the signal S1 decreases as the wind speed and air volume of the air flowing through the duct 4 increases, and increases as the wind speed and air volume decrease.

  Further, since the differential amplifier circuit 531 generates the signal S1 based on the difference (Vd1−Vd2) between the forward voltage Vd1 and the forward voltage Vd2, the voltage component depending on the ambient temperature is canceled in the signal S1. As a result, the signal S1 is generated based on the signal component indicating the wind speed and the air volume of the air flowing through the duct 4, so that the measurement accuracy of the wind speed and the air volume is improved.

  In this case, for example, if parts such as the diodes D1 and D2 and the Zener diode ZD1 are arranged in a direction crossing the air flow, Karman vortices are generated between the parts or on the leeward side to disturb the air flow, The wind speed and volume cannot be measured correctly. However, in the air volume sensor 7, the diodes D1 and D2 and the Zener diode ZD1 are arranged in a line along the air flow in this order from the windward, so that the disturbance of the air flow is reduced. As a result, the measurement accuracy of the wind speed and volume is improved.

  Further, since the Zener diode ZD1 which is a heating element is disposed on the leeward side from the diodes D1 and D2, the temperature of the diodes D1 and D2 is not changed by the air heated by the Zener diode ZD1, and the wind speed, The occurrence of air flow measurement errors is suppressed.

  FIG. 6 shows the flow rate (L / min) of air flowing through the duct 4 using the air volume sensor 7, the forward voltages Vd1 and Vd2, and the difference between the forward voltage Vd1 and the forward voltage Vd2 (Vd1−Vd2). It is a graph which shows the data which calculated | required the relationship experimentally. Each of the forward voltages Vd1 and Vd2 is measured twice, and (Vd1−Vd2) is also shown in the graph twice correspondingly.

  As shown in FIG. 6, the forward voltage Vd1 hardly changes even when the air flow rate increases. On the other hand, the forward voltage Vd2 increases as the air flow rate increases. Therefore, the difference (Vd1−Vd2) between the forward voltage Vd1 and the forward voltage Vd2 decreases as the air flow rate increases.

  Next, the speed of the fan 3 is controlled by the control unit 6 in accordance with the signal S1, that is, the measured value of the air volume that actually flows through the duct 4 and is supplied to the fuel cell stack 2, so that the fuel from the fan 3 is controlled. An appropriate amount of air is supplied to the battery stack 2. As a result, a predetermined amount of air can be supplied from the fan 3 to the fuel cell stack 2 regardless of the change in the air flow resistance of the air flow path at the cathode of the fuel cell stack 2, so that the amount of air supply is inappropriate. Therefore, the generated power is reduced, or the amount of air supplied is excessive, so that the water generated at the cathode evaporates and is discharged to the outside, and there is not enough water to be reused. It is possible to reduce the amount of

  Meanwhile, the air volume sensor 7 measures the wind speed and air volume based on the forward voltages Vd1 and Vd2 obtained according to the temperatures of the diodes D1 and D2, and the forward voltages Vd1 and Vd2 are diodes D1 and D2. Therefore, the fluctuations of the currents I1 and I2 appear as fluctuations of the forward voltages Vd1 and Vd2, that is, fluctuations of the signal S1, and become a measurement error of the wind speed and the air volume. Here, when the currents I1 and I2 are supplied to the diodes D1 and D2 using the resistors R1 and R2, the fluctuation of the power supply voltage appears as it is as a measurement error of the wind speed and the air volume.

  Therefore, instead of using the resistors R1 and R2 as a current supply unit for supplying a constant forward current to the diodes D1 and D2, for example, as shown in FIG. 7, a constant current circuit is used to provide a constant current to the diodes D1 and D2. You may make it comprise the electric current supply part which sends forward current.

  The current supply unit shown in FIG. 7 is supplied from the current mirror circuit CS1 to the diodes D1 and D2 by the current mirror circuit CS1 that supplies the same current to the diode D1 and the diode D2, and the constant voltage obtained by the Zener diode ZD1. And a current mirror circuit CS2 for setting a current value. In this case, the current value supplied to the diodes D1 and D2 is set according to the constant voltage value obtained by the Zener diode ZD1 regardless of the fluctuation of the power supply voltage. Therefore, the currents I1 and I2 supplied to the diodes D1 and D2 are maintained at a constant value regardless of fluctuations in the power supply voltage, so that measurement errors due to power supply voltage fluctuations can be reduced.

  Further, as shown in FIG. 8, an air pump 8 may be used instead of the fan 3. For example, in a small fuel cell system of about 10 W used for a portable personal computer, the air pump 8 can be suitably used as a blower.

  In addition, although the example which uses the air volume sensor 7 comprised using the wind speed sensor 5 for the measurement of the supply_amount | feed_rate of the air in the fuel cell system 1 was shown, the use of the wind speed sensor 5 and the air volume sensor 7 is restricted to a fuel cell system. Instead, it can be used in various applications for measuring the wind speed and volume of gas. The wind speed sensor 5 is not limited to the example disposed in the duct 4 and may be used for measuring the wind speed in an open space. The gas may not be air.

  Since the wind speed sensor and the air volume sensor according to the present invention can measure the wind speed and the air volume of gas with a simple configuration, for example, in a fuel cell system, for controlling the amount of air supplied to the air electrode of the fuel cell. It is useful as a sensor.

It is a schematic block diagram which shows an example of a structure of the fuel cell system using the air volume sensor which concerns on one Embodiment of this invention. It is explanatory drawing which shows an example of a structure of the air volume sensor shown in FIG. It is a circuit diagram which shows an example of a structure of the wind speed sensor shown in FIG. FIG. 4 is a circuit diagram showing an example of a detailed configuration of the differential amplifier circuit shown in FIG. 3. It is an external view for demonstrating the detail of the sensor element part shown in FIG. Using the air volume sensor shown in FIG. 2, the relationship between the flow rate of air flowing through the duct and the forward voltages Vd1 and Vd2 and the difference between the forward voltage Vd1 and the forward voltage Vd2 (Vd1−Vd2) is experimentally determined. It is a graph which shows the calculated | required data. It is a circuit diagram which shows an example of the constant current circuit used as a current supply part. It is a schematic block diagram which shows another example of a fuel cell system. It is a schematic circuit diagram which shows the structure of the wind speed sensor which concerns on background art. It is explanatory drawing for demonstrating operation | movement of the wind speed sensor shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell stack 3 Fan 4 Duct 5 Air speed sensor 6 Control part 7 Air volume sensor 8 Air pump 511,512 Wiring 515 Flexible board 516 Slit 531 Differential amplifier circuit D1, D2 Diode ZD1 Zener diode R1-R7 Resistance S1 Signal Vd1, Vd2 Forward voltage

Claims (10)

First and second diodes disposed in a gas to detect wind speed;
A current supply unit configured to supply a predetermined forward current to the first and second diodes;
A heating unit for heating the second diode;
A wind speed sensor comprising: a differential signal output unit that outputs a differential signal indicating a difference between a forward voltage generated in the first diode and a forward voltage generated in the second diode as a signal indicating the wind speed. . The heating unit is
A Zener diode thermally coupled to the second diode;
The wind speed sensor according to claim 1, further comprising: a Zener current supply unit that supplies a reverse current to the Zener diode. The second diode and the Zener diode are disposed adjacent to the same printed wiring board and connected to the same copper foil pattern formed on the printed wiring board for conducting heat. The wind speed sensor according to claim 2, wherein the wind speed sensor is thermally coupled. The wind speed sensor according to claim 3, wherein the copper foil pattern is a wiring pattern for supplying the forward current to the second diode and supplying the reverse current to the Zener diode. The first diode is connected to the wiring pattern;
The current supply unit supplies the forward current to the first diode through the wiring pattern,
In the wiring pattern, the width in the direction perpendicular to the direction in which heat is conducted is supplied from the current supply unit to the first diode at a portion where heat is conducted between the Zener diode and the second diode. The wind speed sensor according to claim 4, wherein the wind speed sensor is thicker than a width of a portion where the forward current flows. The wind speed according to any one of claims 2 to 5, wherein a distance between the Zener diode and the first diode is longer than a distance between the Zener diode and the second diode. Sensor. The hole which penetrates the said printed wiring board is provided so that it may cross between the said 1st diode, the said 2nd diode, and the said Zener diode, The any one of Claims 3-6 characterized by these. The described wind speed sensor. The wind speed sensor according to any one of claims 2 to 7, wherein the first diode, the second diode, and the Zener diode are arranged in a line in this order from the windward side. The wind speed sensor according to any one of claims 1 to 8,
A pipe having a predetermined opening cross-sectional area and guiding the gas,
The wind speed sensor is disposed inside the pipe,
The difference signal output unit outputs the difference signal as a signal indicating the amount of air flowing through the pipe. The air volume sensor according to claim 9,
A fuel cell;
A blower for supplying air to the fuel cell via a pipe in the air flow sensor;
A fuel cell system comprising: a control unit that adjusts an amount of air to be supplied to the fuel cell by the blower according to the difference signal.

Images