JP2009097925A - Heat radiation type flow sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat radiation type flow sensor which can control the drive voltage of a heater resistor with high precision and stably. <P>SOLUTION: The comparison result of a comparator 15 is input to a variable clock 16 and an updown counter 17. When the heater resistor 14 is heated, the updown counter 17 performs a countup operation in accordance with a clock signal with a first period tb output from the variable clock 16 and rapidly raises the output of a D/A convertor 18 to raise the drive voltage of the heater resistor 14. When stopping the heating of the heater resistor 14, the updown counter 17 performs a coundown operation in accordance with a clock signal with a second period ta, which is slower than the first period tb, thereby dropping the drive voltage of the heater resistor 14 gradually. The heater resistor 14 is thus drivingly controlled, performing control to allow the temperature difference between an indirectly-heated resistor 12 and an intake-air temperature measuring resistor 13 to be maintained constant. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat dissipation type flow rate sensor that performs heat dissipation using a heater resistor and detects the flow rate of a fluid flowing above the heater resistor.

  Conventionally, for example, Patent Document 1 proposes a flow sensor that detects a flow direction and a flow velocity of a fluid. Specifically, in Patent Document 1, a heating resistor (hereinafter referred to as a heater resistor) disposed in the center of a heat insulating substrate and a temperature measuring resistor installed at symmetrical positions on both sides of the heater resistor are provided. Proposed flow sensors have been proposed.

In this flow sensor, a heater resistance, a resistance temperature monitor for heating, a resistance for temperature measurement, and a resistance for fluid temperature compensation are installed in a flow path through which a fluid passes. Further, the fluid temperature compensation resistor and the heating resistor temperature monitor are connected to the other two resistors to form a bridge circuit. The output of this bridge circuit is differentially amplified by an amplifier (hereinafter referred to as an amplifier), the base potential of the switching transistor is controlled by the output of the amplifier, and the drive voltage applied to the heater resistor connected to the switching transistor is To be controlled.
Japanese Patent Publication No. 5-84867

  However, in the above-described conventional technique, the delay time of heat conduction from the heater resistance to the temperature measurement resistor, which is generated because the heater resistance and the temperature measurement resistor are arranged apart from each other, is not taken into consideration. For this reason, the amplifier that drives the switching transistor sometimes operates with positive feedback.

  That is, the heater resistance is heated to a specified temperature, and it is desired to stop the heating of the heater resistance. However, the amplifier continues to turn on the switching transistor due to the delay in the heat conduction, and after a while, the switching transistor is turned off to Stop heating the resistor. After that, the heater resistance is cooled, so that it is desired to start heating. However, the amplifier continues to turn off the switching transistor due to the delay of the heat conduction, and after a while, the switching transistor is turned on to resume heating of the heater resistance. According to this, the driving voltage of the heater resistor is like a triangular wave.

  In this way, the amplifier drives the switching transistor in accordance with the thermal conduction delay. For this reason, the drive voltage for driving the heater resistance becomes unstable, and the drive circuit for driving the heater resistance oscillates like a triangular wave, which deteriorates the accuracy of sensor flow rate detection.

  As a countermeasure, it is conceivable to increase the phase compensation capacitor of the amplifier. In this case, since the heat conduction delay is large, the capacitance of the capacitor is required to be 1000 pF or more. However, since a semiconductor sensor cannot incorporate a capacitor of 1000 pF or more, the capacitor must be externally attached to the sensor.

  An object of this invention is to provide the thermal radiation type flow sensor which can control the drive voltage of heater resistance accurately and stably in view of the said point.

  In order to achieve the above-mentioned object, the present invention has a side heat resistance (12) and a first resistance (11a) whose resistance value changes upon receiving heat from the heater resistance (14) and is connected in series to measure the temperature. The resistor (13) and the second resistor (11b) are connected in series to form a bridge circuit, and the potential at the connection point between the indirectly heated resistor (12) and the first resistor (11a) is set to the first potential (Va ) And the potential at the connection point between the temperature measurement resistor (13) and the second resistor (11b) is the second potential (Vb), the first potential (Va) and the second potential (Vb) The heater resistance driving transistor (19) is driven on the basis of the comparison result of the comparison means (15) for comparing the heat resistance of the heater resistance (14) connected to the heater resistance driving transistor (19). The temperature difference between the side heat resistance (12) and the temperature measurement resistance (13) The heat dissipation type flow sensor detects the flow rate of the fluid in a constant manner, and the comparison result of the comparison means (15) indicates that the second potential (Vb) is greater than the first potential (Va). A variable clock that outputs a clock signal having a first cycle and outputs a clock signal having a second cycle that is slower than the first cycle when the first potential (Va) is greater than the second potential (Vb). (16) and the clock signal of the first period input from the variable clock (16) when the comparison result of the comparison means (15) indicates that the second potential (Vb) is greater than the first potential (Va). Is counted up as an up-count value, and when the first potential (Va) is larger than the second potential (Vb), the second cycle clock signal input from the variable clock (16) is counted down as the down-count value. Updater to count And an output means (18) for driving the heater resistance driving transistor (19) by performing an output corresponding to the up count value or the down count value input from the up / down counter (17). It is characterized by.

  According to this, when heating the heater resistor (14), the output of the output means (18) corresponding to the clock signal of the first cycle is input to the heater resistance driving transistor (19). Thereby, the drive voltage of heater resistance (14) can be raised rapidly and heater resistance (14) can be heated quickly. On the other hand, when the heater resistance (14) becomes hot, the output of the output means (18) corresponding to the clock signal of the second period slower than the first period is input to the heater resistance driving transistor (19). Thereby, the time for applying a constant drive voltage to the heater resistor (14) can be extended as compared with the case where the drive voltage of the heater resistor (14) is controlled based on the clock signal of the first cycle. That is, a rapid temperature drop of the heater resistance (14) can be prevented. By repeating the control of the driving voltage of the heater resistor (14) as described above, the driving voltage of the heater resistor (14) can be stably controlled with high accuracy, and the heat generation of the heater resistor (14) is stabilized. be able to. Therefore, the accuracy of the heat dissipation type flow sensor can be improved.

  In this case, the second period can be a time constant of heat conduction from the heater resistance (14) to the indirectly heated resistance (12).

  Here, the time constant of heat conduction corresponds to the time taken for the resistance value of the heater resistor (14) to shift to a value corresponding to the external temperature when the external temperature changes.

  Further, when a power-on signal indicating that the power is turned on is inputted and a comparison result that the second potential (Vb) is larger than the first potential (Va) is inputted from the comparison means (15), the output means The output of (18) is set to the reference value, the clock signal of the first period is output to the variable clock (16), and the clock of the first period input from the variable clock (16) to the up / down counter (17) A power-on initial operation is performed in which the signal is counted down as a down-count value and the output means (18) outputs an amount corresponding to the down-count value input from the up-down counter (17). When the comparison result that the first potential (Va) is larger than the second potential (Vb) is input from the comparison means (15), the power-on for canceling the power-on initial operation It can comprise a period setting circuit (40).

  As a result, when the heat dissipation type flow sensor is activated, the heater resistance driving transistor (19) is driven in accordance with the clock signal of the first period so that the temperature of the heater resistance (14) reaches the control temperature at the fastest speed. it can. After the power-on initial setting circuit (40) cancels the power-on initial operation, the drive voltage of the heater resistor (14) can be controlled by the normal operation.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. The heat dissipation type flow sensor shown in the present embodiment is used for detecting the amount of intake air confined in the engine, for example. The detected intake air amount is used for controlling the fuel injection amount.

  FIG. 1 is a configuration diagram of a heat dissipation type flow sensor according to the first embodiment of the present invention. As shown in this figure, the heat-dissipating flow rate sensor includes a drive circuit unit 10 and a bridge circuit unit 20.

  The drive circuit unit 10 includes a first resistor 11a, a second resistor 11b, an indirectly heated resistor 12, an intake air temperature measuring resistor 13, a heater resistor 14, a comparator 15, a variable clock 16, an up / down counter 17, a D / A converter 18, and A heater resistance driving transistor 19 is provided. The drive circuit unit 10 is a circuit that controls the heater resistance 14 to generate heat according to the flow rate so that the temperature difference between the side heat resistance 12 and the intake air temperature measurement resistor 13 is constant.

  The indirectly heated resistor 12 is a resistor whose resistance value changes upon receiving heat from the heater resistor 14. The intake air temperature measurement resistor 13 is a resistor whose resistance value changes depending on the ambient temperature. The intake air temperature measurement resistor 13 corresponds to the temperature measurement resistor of the present invention. The heater resistor 14 is a resistor that generates heat when a current flows.

  The first resistor 11a and the indirectly heated resistor 12 are connected in series, and the second resistor 11b and the intake air temperature measuring resistor 13 are connected in series to form a bridge circuit. When the potential at the connection point between the indirectly heated resistor 12 and the first resistor 11a is Va and the potential at the connection point between the intake air temperature measurement resistor 13 and the second resistor 11b is Vb, the potential Va is the inversion of the comparator 15. The voltage Vb is input to the input terminal, and the potential Vb is input to the non-inverting input terminal of the comparator 15. Note that the potential Va corresponds to the first potential of the present invention, and the potential Vb corresponds to the second potential of the present invention.

  The comparator 15 compares the potential Va and the potential Vb and outputs the comparison result. The comparator corresponds to the comparison means of the present invention.

  The variable clock 16 outputs a clock signal having a first cycle or a second cycle having a different cycle according to the comparison result of the comparator 15. Specifically, the variable clock 16 outputs the first cycle clock signal when the comparison result of the comparator 15 is greater than the potential Va, and the first when the potential Va is greater than the potential Vb. A clock signal having a second period slower than the period is output. In the present embodiment, the second period is a time constant of heat conduction from the heater resistor 14 to the indirectly heated resistor 12.

  The up / down counter 17 counts up the first cycle clock signal input from the variable clock 16 as an up-count value when the comparison result of the comparator 15 indicates that the potential Vb is greater than the potential Va. When it is larger than Vb, the second cycle clock signal input from the variable clock 16 is down-counted as a down-count value.

  The D / A converter 18 outputs according to the up count value or the down count value input from the up / down counter 17. The D / A converter 18 corresponds to the output means of the present invention.

  The heater resistance driving transistor 19 is driven and controlled in accordance with the output of the D / A converter 18 and thereby plays a role of flowing a current from the power supply voltage Vcc to the heater resistance 14. The heater resistance driving transistor 19 passes a current having a magnitude corresponding to the output of the D / A converter 18. In other words, the heater resistor 14 generates heat in accordance with the magnitude of the current flowing through the heater resistor driving transistor 19.

  On the other hand, the bridge circuit unit 20 includes four resistors 21 to 24 and a differential amplifier 25 that constitute a bridge circuit. The resistance values of the resistors 21 to 24 are the same.

  Among the resistors 21 to 24, the resistor 21 and the resistor 22 are connected in series, the resistor 23 and the resistor 24 are connected in series, and these connected in series are connected in parallel to form a bridge circuit. Has been. One of the connection points of the bridge circuit is connected to the potential Vr for driving the bridge circuit, and the other is connected to the ground.

  When the potential at the connection point between the resistor 21 and the resistor 22 is Vc, and the potential at the connection point between the resistor 23 and the resistor 24 is Vd, the potential Vc is input to the non-inverting input terminal of the differential amplifier 25. Vd is input to the inverting input terminal of the differential amplifier 25.

  The heater resistor 14, the indirectly heated resistor 12, the intake air temperature measuring resistor 13, the first resistor 11a, and the second resistor 11b all have the same type of material and the same temperature coefficient (positive in this embodiment). . Further, when the resistance value of the intake air temperature measurement resistor 13 is Rk, the resistance value of the indirectly heated resistor 12 is Ri, the resistance value of the first resistor 11a is R1, and the resistance value of the second resistor 11b is R2, the same temperature (none In the energized state), Rk> Ri and R1 = R2 are designed.

  The differential amplifier 25 is an amplifier that outputs in proportion to the potential difference Vc−Vd between the potentials Vc and Vd input from the bridge circuit. The output of the differential amplifier 25 is output to the outside as the output Vout of the heat dissipation type flow rate sensor.

  In the above configuration, the resistors 21 to 24, the first resistor 11a, the second resistor 11b, the heater resistor 14, the indirectly heated resistor 12, and the intake air temperature measuring resistor 13 are built in one sensor chip. 2A is a plan view of the sensor chip 30, and FIG. 2B is a cross-sectional view taken along the line AA in FIG.

  As shown in FIG. 2A, a membrane 31 is formed on a part of the sensor chip 30. As shown in FIG. 2B, the membrane 31 is configured by thinning the sensor chip 30.

  A heater resistor 14 extending in the longitudinal direction of the sensor chip 30 is formed at the center of the membrane 31. In addition, an indirectly heated resistor 12 is formed so as to surround the heater resistor 14. Further, a resistance 24 and a resistance 21 are formed on the upstream side of the fluid from the indirectly heated resistor 12 in the membrane 31, and a resistor 23 and a resistor 22 are formed on the downstream side of the fluid from the indirectly heated resistor 12.

  An intake temperature measurement resistor 13 is formed in the sensor chip 30 on the upstream side of the fluid from the membrane 31. That is, the fluid flows from the intake temperature measurement resistor 13 to the membrane 31 side.

  On the other hand, a comparator 15, a variable clock 16, an up / down counter 17, a D / A converter 18, a heater resistor driving transistor 19, and a differential amplifier 25 are built in a circuit chip. The circuit chip and the sensor chip 30 shown in FIG. 2 are integrated into one component to constitute a heat dissipation type flow rate sensor. The above is the overall configuration of the heat dissipation type flow sensor.

  Next, the operation of the drive circuit unit 10 of the heat dissipation type flow sensor shown in FIG. 1 will be described with reference to FIG. FIG. 3 is a timing chart showing the operation of the drive circuit unit 10.

  First, when power is turned on, since Rk> Ri and R1 = R2 as described above, Va <Vb, and the comparator 15 outputs a comparison result indicating Va <Vb. In this case, the up / down counter 17 performs an up count operation each time a clock signal having a first period tb earlier than the second period ta is input from the variable clock 16. As a result, the output of the D / A converter 18 increases as the counter value increases, and the current flowing through the heater resistance driving transistor 19 also increases. Therefore, the driving voltage of the heater resistance 14 increases and the heater resistance 14 generates heat. To do.

  When the heat of the heater resistor 14 is conducted to the indirectly heated resistor 12, the resistance value Ri of the indirectly heated resistor 12 increases and the potential Va increases. When the potential Va rises and Va> Vb, the output of the comparator 15 is inverted. That is, the comparator 15 outputs a comparison result indicating Va> Vb. As a result, the up / down counter 17 performs a down-count operation every time a clock signal having the second period ta (> tb) is input from the variable clock 16. In this case, the cycle of the first clock is a time constant ta of heat conduction from the heater resistor 14 to the indirectly heated resistor 12. The period after the second clock is tb.

  Due to the countdown operation, the output of the D / A converter 18 decreases, the drive voltage of the heater resistor 14 decreases, and the temperature of the heater resistor 14 decreases. For this reason, the resistance value Ri of the indirectly heated resistor 12 decreases and the potential Va decreases. Unlike the above, since the second period ta is slower than the first period tb, the output of the D / A converter 18 decreases later than when Va <Vb.

  When the potential Va decreases and Va <Vb, the output of the comparator 15 is inverted again. Thereafter, the variable clock 16 and the up / down counter 17 operate in the same manner as described above. In this case, the cycle of the first clock after the output of the comparator 15 is inverted is the time constant (ta) of heat conduction from the heater resistor 14 to the side heat resistor 12. The period after the second clock is tb. Thereafter, Va = Vb can be realized stably and accurately by repeating the same operation.

  As described above, when the heater resistor 14 is controlled to be heated by the drive circuit unit 10, the resistors 21 to 24 of the bridge circuit unit 20 are heated. When the air does not flow, the resistance values of the four resistors 21 to 24 are the same. Therefore, the bridge circuit constituted by these resistors 21 to 24 is kept in equilibrium, while when the air flows, A temperature difference, that is, a difference in resistance value occurs between the formed resistors 21 and 24 and the resistors 22 and 23 formed on the downstream side, and the bridge circuit is in an unbalanced state. That is, the temperature distribution on the membrane 31 changes depending on the flow rate of the fluid, and the potential difference Vc−Vd increases as the flow rate increases, so that the flow rate is detected. Then, the potential difference Vc−Vd of the bridge circuit corresponding to the flow rate is amplified by the differential amplifier 25 and output to the outside as the output Vout.

  As described above, in the present embodiment, when the heater resistor 14 is heated using the variable clock 16 and the up / down counter 17, the drive voltage of the heater resistor 14 is quickly determined according to the clock signal of the first period tb. On the other hand, when the heating of the heater resistor 14 is stopped, the drive voltage of the heater resistor 14 is gradually lowered according to the clock signal of the second period ta.

  As a result, the drive voltage of the heater resistor 14 does not have a waveform like a triangular wave, and the drive circuit unit 10 becomes unstable and does not oscillate. Therefore, since the drive voltage of the heater resistor 14 can be stabilized and the heat generation of the heater resistor 14 can be stabilized, the accuracy of the heat dissipation type flow sensor can be improved.

  Further, since the drive voltage of the heater resistor 14 is controlled as described above, there is no need to attach a capacitor externally to the heat dissipation type flow rate sensor, and there is no problem of cost increase.

(Second Embodiment)
In the present embodiment, only different parts from the first embodiment will be described. The present embodiment is characterized in that the heater resistor 14 is quickly heated when the heat dissipation type flow sensor is started.

  FIG. 4 is a configuration diagram of the drive circuit unit 10 of the heat dissipation type flow sensor according to the present embodiment. FIG. 5 is a timing chart showing the operation of the drive circuit unit 10 shown in FIG. As shown in FIG. 4, the drive circuit unit 10 shown in FIG. 1 is provided with a power-on initial setting circuit 40. The power-on initial setting circuit 40 has a function of quickly heating the heater resistor 14 when the heat dissipation type flow sensor is turned on.

  Next, the power-on initial operation of the power-on initial setting circuit 40 will be described with reference to FIG. First, when a power supply voltage Vcc is input to the heat dissipation type flow sensor, the power-on initial setting circuit 40 inputs the power supply voltage Vcc as a power-on signal indicating that the power is turned on. When the comparison result of Va <Vb is input from the comparator 15, the power-on initial setting circuit 40 sets the output of the D / A converter 18 to the reference value, and supplies the variable clock 16 with the clock signal having the first period tb. Output.

  Here, in order to heat the heater resistor 14 quickly by passing a large current through the heater resistor driving transistor 19 and increasing the current flowing through the heater resistor 14, the reference value of the output of the D / A converter 18 is D The maximum output value of the / A converter 18 is preferable.

  Thereby, the up / down counter 17 counts down the clock signal of the first period tb input from the variable clock 16 as a down count value. Further, the D / A converter 18 outputs an amount corresponding to the down count value input from the up / down counter 17. That is, as shown in FIG. 5, the output of the D / A converter 18 gradually decreases from the time of power-on.

  The power-on initial setting circuit 40 cancels the power-on initial operation when the comparison result Va> Vb is input from the comparator 15. The release means that the variable clock 16, the up / down counter 17, and the D / A converter 18 perform the normal operation shown in the first embodiment. Thus, the power-on initial operation by the power-on initial setting circuit 40 is completed.

  As described above, by controlling the output of the D / A converter 18 from the maximum value by the power-on initial setting circuit 40 when the heat dissipation type flow sensor is started, the temperature of the heater resistor 14 is controlled at the highest speed. Can be reached.

(Other embodiments)
In each said embodiment, although the 2nd period is set to the time constant of the heat conduction from heater resistance 14 to side heat resistance 12, this shows an example. That is, the second period may be set later than the first period.

It is a block diagram of the thermal radiation type flow sensor which concerns on 1st Embodiment of this invention. (A) is a top view of a sensor chip, (b) is AA sectional drawing of (a). It is a timing chart showing the action | operation of a drive circuit part. It is a block diagram of the drive circuit part of the thermal radiation type flow sensor which concerns on 2nd Embodiment of this invention. 6 is a timing chart illustrating the operation of the drive circuit unit illustrated in FIG. 4.

Explanation of symbols

  11a ... 1st resistance, 11b ... 2nd resistance, 12 ... Side heat resistance, 13 ... Intake temperature measurement resistance, 14 ... Heater resistance, 15 ... Comparator, 16 ... Variable clock, 17 ... Up / down counter, 18 ... D / A Converter 19, heater resistor driving transistor 40, power-on initial setting circuit.

Claims (3)

The indirectly heated resistor (12) and the first resistor (11a) whose resistance value changes in response to the heat of the heater resistor (14) are connected in series, and the temperature measuring resistor (13) and the second resistor (11b). Are connected in series to form a bridge circuit,
A potential at a connection point between the indirectly heated resistor (12) and the first resistor (11a) is a first potential (Va), and a connection point between the temperature measurement resistor (13) and the second resistor (11b). Is the second potential (Vb),
Based on the comparison result of the comparison means (15) for comparing the first potential (Va) and the second potential (Vb), the heater resistance driving transistor (19) is driven, and the heater resistance driving transistor By controlling the heat generation of the heater resistor (14) connected to (19), the temperature difference between the indirectly heated resistor (12) and the temperature measuring resistor (13) is made constant so that the flow rate of the fluid A heat dissipation type flow sensor for detecting
When the comparison result of the comparison means (15) indicates that the second potential (Vb) is higher than the first potential (Va), a clock signal having a first period is output, and the first potential ( A variable clock (16) that outputs a clock signal having a second period slower than the first period when Va) is greater than the second potential (Vb);
The clock signal of the first period input from the variable clock (16) when the comparison result of the comparison means (15) is that the second potential (Vb) is larger than the first potential (Va). Is counted up as an up-count value, and when the first potential (Va) is larger than the second potential (Vb), the clock signal of the second period input from the variable clock (16) is reduced. An up / down counter (17) that counts down as a count value;
Output means (18) for driving the heater resistance driving transistor (19) by performing output according to the up-count value or the down-count value input from the up-down counter (17). A heat dissipation type flow sensor characterized by The heat dissipation type flow sensor according to claim 1, wherein the second period is a time constant of heat conduction from the heater resistor (14) to the side heat resistor (12). When a power-on signal indicating that the power is turned on is input and a comparison result that the second potential (Vb) is larger than the first potential (Va) is input from the comparison means (15), The output of the output means (18) is set to a reference value, the clock signal having the first period is output to the variable clock (16), and the variable clock (16) is input to the up / down counter (17). The power-on initial stage in which the clock signal of the first period is down-counted as a down-count value, and the output means (18) outputs an amount corresponding to the down-count value input from the up-down counter (17). A comparison result indicating that the first potential (Va) is larger than the second potential (Vb) from the comparison means (15). When a force, heat dissipation flow sensor according to claim 1 or 2, characterized in that it comprises a power-on initialization circuit for canceling the power-on initial operation (40).

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