JP2019066253A - Flow rate measuring device - Google Patents

Abstract

To provide a flow rate measuring device with which it is possible to realize the increased accuracy of a flow rate signal by correcting a temperature characteristics attributable to the manufacturing variation of a flow rate detection element.SOLUTION: A flow rate measuring device comprises: a flow rate detection element 1, provided in a sub-passage, for outputting a signal that corresponds to the flow rate of a fluid; and a flow rate computation unit 47 for computing a flow rate signal on the basis of the output signal output by the flow rate detection element 1. The flow rate detection element 1 includes a heat generating resistor and temperature detection elements 4, 5 for detecting the temperature upstream and the temperature downstream of the heat generating resistor, outputting signals that correspond to the temperature changes of the temperature detection elements 4,5 as output signals. The flow rate measuring device further includes a temperature measuring element 15 for measuring the temperatures of the temperature detection elements 4, 5, and a correction amount computation unit for computing, on the basis of the temperatures of the temperature detection elements 4, 5 measured using the temperature measuring element 15, a correction amount for correcting a flow rate signal error based on the temperature characteristics of the temperature detection elements 4, 5.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a flow rate measuring device, and more particularly to a flow rate measuring device which is installed in an intake system of an automobile engine and is suitable for detecting an intake air amount of the engine.

  In recent years, there has been a demand for higher precision combustion control in an internal combustion engine of a vehicle to reduce environmental load, and in response to this, it is desired to improve the precision of a flow rate measuring device for measuring the amount of intake air to the internal combustion engine. There is. Above all, since the ambient temperature of an internal combustion engine of a car fluctuates largely due to various factors, in a flow rate measuring device which is often installed near the internal combustion engine, a technique for reducing measurement error due to temperature is an important technique It is.

  For example, as a flow rate measuring device mounted on an internal combustion engine, a thermal fluid measuring device (hereinafter referred to as a thermal flow meter) described in JP-A-2014-169948 (Patent Document 1) is known. In the thermal flow meter of Patent Document 1, the heating resistor heats a portion of the air taken into the internal combustion engine, and the temperature difference due to the difference between the heat release upstream of the heating resistor and the heat release downstream of the heating resistor. Is detected as a flow rate signal. Since many of the flow rate signals include errors due to temperature, temperature correction is performed in consideration of the influence of temperature and is output to the engine control unit. In order to perform this temperature correction, in the thermal flowmeter of Patent Document 1, the temperature of the air taken in is detected by a first temperature sensor constituted by a thermistor and a fixed resistor, and it is constituted by a thermistor and a fixed resistor. The temperature of the sensor module is detected by the second temperature sensor, and the intake air temperature and the sensor module temperature are input to the correction unit to correct the flow rate signal.

JP, 2014-169948, A

  On the other hand, in recent years, further downsizing and low idling of internal combustion engines have progressed, and highly accurate flow rate measurement is required even in an extremely low flow rate region. As a result of studies by the present inventors, in an extremely low flow rate region, an intake air temperature sensor (the first temperature sensor of Patent Document 1) that measures the temperature of intake air and a module temperature that measures the module temperature provided in the circuit chamber By correcting the temperature characteristic due to the manufacturing variation of the flow rate detection element as opposed to the temperature correction with the sensor (the second temperature sensor of Patent Document 1), the measurement error is further reduced to realize the high accuracy of the flow rate signal It turned out that it was possible.

  An object of the present invention is to provide a flow rate measuring device capable of realizing an increase in the accuracy of a flow rate signal by correcting a temperature characteristic caused by manufacturing variations of the flow rate detection element.

In order to solve the above-mentioned subject, the thermal type flow meter of the present invention,
An auxiliary passage for taking in part of the fluid flowing in the main passage, a flow rate detection element provided in the auxiliary passage and outputting a signal according to the flow rate of the fluid taken in the auxiliary passage, and the flow rate detection element A flow rate calculating unit that calculates a flow rate signal based on the output signal to be
The flow rate detection element includes a heat generation resistor, and a plurality of temperature detection elements for detecting the temperature on the upstream side and the temperature on the downstream side with respect to the heat generation resistor in the fluid flow direction,
In a flow rate measuring device which calculates the flow rate signal by using a signal corresponding to a temperature change of the temperature detection element as the output signal,
The error of the flow rate signal based on the temperature characteristic of the temperature detection element is corrected based on the temperature measurement element for measuring the temperature of the temperature detection element and the temperature of the temperature detection element measured using the temperature measurement element A correction amount calculation unit that calculates a correction amount to be
The detected flow rate is corrected based on the correction amount.

  According to the present invention, a highly accurate flow rate measuring device can be provided. Problems, configurations, and effects other than those described above will be apparent from the description of the embodiments below.

FIG. 6 is a schematic view of a flow rate measuring element provided with a heating resistor and a temperature detection element in a membrane part. It is a conceptual diagram which shows the change of the temperature distribution of the membrane part according to the flow rate. It is a figure which shows the example of the flow volume detection error by the temperature characteristic dispersion | variation of a temperature detection element. It is a figure which shows the temperature distribution image at the time of heating resistor heating in the membrane part cross section (near the temperature sensitive resistor) of a flow rate detection element. It is a schematic diagram which shows the temperature characteristic dispersion | variation of a temperature sensitive resistor. It is a bridge circuit diagram of the thermosensitive resistor for detecting the deviation of the temperature distribution of a membrane part. It is a figure which shows the temperature of a temperature sensitive resistor, and the temperature characteristic of a bridge circuit output. FIG. 2 is a view showing a configuration of a bridge circuit of the flow rate measuring apparatus according to the first embodiment. It is a figure which shows the temperature of a thermosensitive resistor, and the relationship of Vs voltage (bridge voltage). FIG. 5 is a block diagram showing the configuration of a temperature characteristic correction processing unit according to the first embodiment. It is a block diagram which shows the structure of a temperature characteristic correction process part at the time of providing a detection resistance in a signal processing circuit. It is a figure which shows the example of the flow measurement error of the thermal type flow meter after temperature characteristic correction. It is a figure which shows the temperature distribution image at the time of heating resistor heating in the membrane part cross section of the flow volume detection element at the time of using a thermocouple as a temperature detection element. It is a thermocouple circuit diagram for detecting the deviation of the temperature distribution of a membrane part. It is a schematic diagram which shows the temperature characteristic variation of a thermocouple. It is a figure which shows the temperature characteristic of the temperature of a thermocouple, and a thermoelectromotive force difference. FIG. 7 is a block diagram showing a configuration of a temperature characteristic correction processing unit according to a second embodiment. It is a figure showing an example of a flow rate measuring device incorporating a flow rate detection element.

  Hereinafter, embodiments for carrying out the present invention will be described using the drawings.

Example 1
A first embodiment will be described using FIGS. 1 to 12.

  FIG. 1 is a schematic view of a flow rate detecting element provided with a heating resistor and a temperature detecting element in a membrane part. As shown in FIG. 1, the flow rate detection element 1 includes a membrane portion (thin film structure portion, diaphragm) 2 which is a thin film structure, and the membrane portion 2 includes a heating resistor 3 and at least two temperature detection elements 4 and 5.

  The downstream side temperature detection element 5 is provided on the downstream side of the heating resistor 3 in the direction in which the fluid (air in this embodiment) flows normally. The upstream temperature detection element 4 is provided on the upstream side of the heating resistor 3 in the direction in which the fluid (air in this embodiment) flows normally. That is, in the present embodiment, the membrane portion 2 is provided with the heating resistor 3 and the plurality of temperature detecting elements 4 and 5, and at least one temperature detecting element as the downstream side temperature detecting element 5 downstream of the heating resistor 3. At least one temperature detection element is provided upstream of the heating resistor 3 as the upstream temperature detection element 4.

  In the present embodiment, the fluid flow rate is detected using the change in temperature distribution due to the heat generated by the heating resistor 3. For this reason, the flow rate measuring device is constituted by a thermal flow meter 45 (see FIG. 18). Hereinafter, the flow rate measuring device may be referred to as a thermal flow meter 45 and may be described.

  FIG. 2 is a conceptual view showing a change in temperature distribution of the membrane part according to the flow rate. The temperature distribution of the membrane unit 2 changes as shown in FIG. 2 in accordance with the flow of fluid on the flow rate detecting element 1. The flow rate measuring element 1 changes the temperature distribution of the membrane unit 2 by the upstream temperature The flow rate is detected by the deviation (temperature difference) between the temperature distribution on the upstream side and the downstream side, which is measured by the detection element 4 and the downstream temperature detection element 5.

  In FIG. 2, the temperature distribution 6 shows the temperature distribution in the absence of fluid flow, and the temperature at the position of the upstream temperature detection element 4 and the temperature at the position of the downstream temperature detection element 5 are equal. There is no temperature difference at the positions of the detection elements 4 and 5. On the other hand, the temperature distribution 7 shows the temperature distribution in the state where the fluid flow (flow indicated by the arrow Flow) is generated, and the temperature at the position of the upstream temperature detection element 4 and the position of the downstream temperature detection element 5 There is a temperature difference with the temperature at. When the flow of fluid is generated, the temperature at the position of the downstream temperature detection element 5 becomes higher than the temperature at the position of the upstream temperature detection element 4.

  FIG. 3 is a diagram showing an example of the flow rate detection error due to the temperature characteristic variation of the temperature detection element. The upstream temperature detection element 4 and the downstream temperature detection element 5 respectively have variations in temperature characteristics, and even if the deviation of the temperature distribution between the upstream side and the downstream side is constant, A change in temperature may indicate an erroneous detection result that is different from the deviation of the actual temperature distribution. Due to this erroneous detection result, as shown in FIG. 3, a flow rate detection error 8 of the flow rate detection element 1 occurs.

  The flow rate detection error 8 increases as the flow rate Q decreases, and causes a large error in an extremely low flow rate region. Therefore, a circuit is configured to measure the temperature of the temperature detection elements 4 and 5, and the erroneous detection result is corrected based on the temperatures of the temperature detection elements 4 and 5 to realize the flow rate detection element 1 with high accuracy. Do.

FIG. 18 is a diagram showing an example of a flow rate measuring device incorporating a flow rate detecting element.
As shown in FIG. 18, the flow rate detection element 1 is supported by the lead frame 35, molded with a thermosetting resin 37, and configured in a chip package 36. The flow rate detection element 1 constitutes a sensing unit (sensor) of the thermal flow meter 45 and is electrically connected to the LSI 32. In the present embodiment, the temperature detection elements 4 and 5 are formed of temperature sensitive resistors, and the resistance values of the temperature detection elements 4 and 5 detected by the flow amount detection element 1 The flow rate based on the temperature difference is determined. The calculation (calculation) of the flow rate is executed by the LSI 32. Further, the LSI 32 performs correction processing of the calculated flow rate value. The flow rate value determined by the LSI 32 is output as a flow rate signal in the intake pipe passage 42 detected by the thermal flow meter 45 via the input / output terminal 38 and the connector terminal 43.

  A method of reducing the flow rate detection error 8 when a temperature sensitive resistor is used as the temperature detection elements 4 and 5 will be described.

  FIG. 4 is a view showing a temperature distribution image at the time of heating the heating resistor in the cross section of the membrane portion (in the vicinity of the temperature sensitive resistor) of the flow rate detecting element. If the temperature rise of the membrane 2 is controlled not to depend on the environmental temperature Ta by the heating control of the heating resistor 3, the temperature distribution of the membrane part 2 at each environmental temperature T1, T0, T2 is offset according to the environmental temperature It becomes distribution. As shown in FIG. 4, as the environmental temperature Ta is higher, the temperature distribution of the membrane portion 2 is offset to a higher temperature range.

  FIG. 5 is a schematic view showing the temperature characteristic variation of the temperature sensitive resistor. In FIG. 5, the temperature characteristic in the case where the temperature coefficient of resistance is positive is shown as an example.

  The resistance value of the temperature sensitive resistors 4 and 5 increases as the environmental temperature rises. Due to manufacturing variations of the temperature sensitive resistors 4 and 5, the resistance value and the temperature coefficient of resistance also vary. When the resistance value of the upstream temperature detection element 4 is large and the resistance temperature coefficient varies in a small direction, while the resistance value of the downstream temperature detection element 5 is small and the resistance temperature coefficient varies in a large direction, the upstream temperature The temperature characteristic of the resistance value of the detection element 4 is the temperature characteristic variation 9, and the temperature characteristic of the resistance value of the downstream side temperature detection element 5 is the temperature characteristic variation 10.

  In this case, even if no fluid flow occurs, RT1 − between the resistance value of the upstream temperature sensitive resistor 4 and the resistance value of the downstream temperature sensitive resistor 5 at the environmental temperature Ta = T1. A resistance difference of RT1 ′ occurs, and a resistance difference of RT0−RT0 ′ occurs between the resistance value of the upstream temperature sensitive resistor 4 and the resistance value of the downstream temperature sensitive resistor 5 at the environmental temperature Ta = T0. At the environmental temperature Ta = T2, a resistance difference of RT2-RT2 'occurs between the resistance value of the upstream temperature sensitive resistor 4 and the resistance value of the downstream temperature sensitive resistor 5. For this reason, the detection error of the flow rate according to each resistance difference arises.

  Silicon, platinum, tungsten, molybdenum, tantalum, titanium or the like is used as the temperature sensitive resistor material, and a material having a large temperature coefficient of resistance is useful because the sensitivity of the resistance value change with respect to temperature can be increased.

  FIG. 6 is a bridge circuit diagram of a temperature-sensitive resistor for detecting deviation of temperature distribution in a membrane part. The temperature sensitive resistors 4 and 5 are configured as a bridge circuit as shown in FIG. 6 in order to measure the deviation of the temperature distribution of the membrane 2 with high accuracy.

  The bridge circuit is provided with two temperature-sensitive resistor pairs in which the upstream temperature-sensitive resistor 4 and the downstream temperature-sensitive resistor 5 are connected in series. The upstream temperature sensitive resistor 4 is connected to the GND potential (ground potential) side, and the downstream temperature sensitive resistor 5 is connected to the Vref potential (reference potential, reference potential) side. Another temperature sensitive resistor pair 12 is configured such that the downstream temperature sensitive resistor 5 is connected to the GND potential (ground potential) side and the upstream temperature sensitive resistor 4 is connected to the Vref potential (reference potential, reference potential) side It has become. That is, in the present embodiment, the upstream temperature sensitive resistor 4 is constituted by two temperature sensitive resistors, and the downstream temperature sensitive resistor 5 is constituted by two temperature sensitive resistors. In the temperature sensitive resistor pair 11 and the temperature sensitive resistor pair 12, the connection between the upstream temperature sensitive resistor 4 and the downstream temperature sensitive resistor 5 with respect to the GND potential and the Vref potential is reversed.

  FIG. 7 is a diagram showing the temperature characteristics of the temperature sensitive resistor and the temperature characteristics of the bridge circuit output. When the upstream temperature sensitive resistor 4 and the downstream temperature sensitive resistor 5 are ideal temperature sensitive resistors (when the resistance value and the resistance temperature coefficient do not vary), the output voltage of the bridge circuit is as shown in FIG. Thus, the characteristic 13 has no temperature characteristic.

  In an actual temperature sensitive resistor, for example, due to the variation as shown in FIG. 5, the bridge circuit output has a characteristic that changes in accordance with the temperature T as in the temperature characteristic 14 of FIG. The temperature characteristic 14 becomes remarkable in a very low flow rate region as a flow rate detection error of the flow rate detection element 1 and becomes a flow rate detection error 8 as shown in FIG.

  FIG. 8 is a diagram showing a configuration of a bridge circuit of the flow rate measuring apparatus according to the first embodiment. In the thermal flowmeter 45 of this embodiment, as shown in FIG. 8, detection is performed in series with the bridge circuit so that the average temperature of the temperature sensitive resistors 4 and 5 constituting the bridge circuit as shown in FIG. The resistance (reference resistance) 15 is provided, and the detection result of the flow rate detection element 1 is corrected by the temperature of the temperature sensitive resistors 4 and 5. Thereby, the flow rate detection error 8 depending on the temperature due to the variation of the temperature detection element 1 can be reduced as shown by the flow rate detection error 21 when the temperature characteristic due to the variation of the temperature detection elements 4 and 5 is corrected. . In particular, the effect of error reduction in a very low flow rate area is large. Thereby, a highly accurate thermal flowmeter 45 can be provided.

  The detection resistance (reference resistance) 15 is used to measure the combined resistance of the bridge circuit. The temperature of the temperature detection elements 4 and 5 is detected from the combined resistance of the bridge circuit detected by the detection resistor 15. That is, the detection resistor 15 is provided in series with the bridge circuit to generate a Vs voltage in which a predetermined voltage drop corresponding to the temperature is generated from Vref, and the temperature of the temperature sensitive resistors 4 and 5 is detected by the Vs voltage. It will be possible to That is, the detection resistor 15 constitutes a temperature measurement element for measuring the temperature of the temperature sensitive resistors 4 and 5. In this embodiment, one of the temperature sensitive resistors 4 and 5 may be referred to as a first temperature detection element, and the other may be referred to as a second temperature detection element. Therefore, the detection resistor (element for temperature measurement) 15 may be referred to as a third temperature detection element, and may be described separately from the first temperature detection element and the second temperature detection element.

  The temperature of the temperature-sensitive resistor can be measured by configuring a circuit as shown in FIG. 8 and measuring the voltage Vs (bridge voltage: potential difference generated in the temperature-sensitive resistor pair 11, 12).

  FIG. 9 is a diagram showing the relationship between the temperature of the temperature sensitive resistor and the Vs voltage (bridge voltage). Although it is desirable that the detection temperature coefficient of the detection resistor 15 is zero, if the temperature coefficient of resistance is different between the temperature sensitive resistors 4 and 5 and the detection resistor 15, the temperature Tr of the temperature sensitive resistor as shown in FIG. The amount of correction can be calculated by examining and storing the relationship with the Vs voltage in advance.

  FIG. 10 is a block diagram of the configuration of the temperature characteristic correction processing unit according to the first embodiment. In the present embodiment, the detection resistor 15 is provided on the same substrate as the flow rate detection element 1.

  Since the flow rate detection element 1 is a bridge circuit formed by the temperature sensitive resistors 4 and 5, the first intermediate voltage of the temperature sensitive resistor pair 11 (the GND side potential of the temperature sensitive resistor 5, Vref of the temperature sensitive resistor 4 Side potential), the second intermediate voltage of the temperature sensitive resistor pair 12 (the GND side potential of the temperature sensitive resistor 4, the Vref side potential of the temperature sensitive resistor 5), and the Vs voltage (the GND side potential of the detection resistor 15) The temperature sensitive resistor pair 11 and the Vref side potential of the temperature sensitive resistor pair 12 are output. The voltage difference (potential difference) between the first intermediate voltage and the second intermediate voltage changes in accordance with the flow rate of the fluid, and the flow rate can be detected from this potential difference. The configurations of the heat generating resistor 3, the temperature sensitive resistors 4 and 5, and the bridge circuit can use various configurations conventionally known.

  Since the detection resistor 15 is provided on the same substrate as the flow rate detection element 1, the Vs voltage changes in accordance with the temperature of the flow rate detection element 1 (that is, the temperature sensitive resistors 4 and 5).

  The first intermediate voltage, the second intermediate voltage, and the Vs voltage are input to the AD conversion circuit 19, and the analog value is converted to a digital value. The first intermediate voltage, the second intermediate voltage, and the Vs voltage converted into digital values are input to the flow rate calculation unit 47, and based on the voltage difference between the first intermediate voltage and the second intermediate voltage and the Vs voltage. The fluid flow rate (flow rate signal) is calculated. Various methods conventionally known can be used to calculate the fluid flow rate.

  The Vs voltage output from the flow rate detection element 1 is input to the AD conversion circuit 18, and the analog value is converted to a digital value. The Vs voltage converted into the digital value is input to a temperature characteristic correction constant calculation circuit (temperature characteristic correction constant calculation processing unit) 20. Based on the measurement result of Vs voltage (that is, the temperature of the flow rate detection element 1), the correction amount is calculated by the polynomial function or map type temperature characteristic correction constant calculation circuit 20, and the detection result of the flow rate detection element 1 (flow rate signal) Offset correction.

  The temperature characteristic correction constant calculation circuit 20 may be simply referred to as a correction amount calculation unit.

  FIG. 11 is a block diagram showing the configuration of the temperature characteristic correction processing unit when the detection resistor is provided in the signal processing circuit. FIG. 11 shows the case where the detection resistor 15 is provided on a signal processing circuit board different from the substrate of the flow rate detection element 1.

  The signal processing circuit board is a board on which the AD conversion circuit 18, the AD conversion circuit 19, the temperature characteristic correction constant calculation circuit 20, and the flow rate calculation unit 47 are provided. Further, this substrate may be a substrate constituting the LSI 32, or may be a substrate on which the LSI 32 and other electronic components are mounted.

  The temperature of the signal processing circuit board provided with the detection resistor 15 is measured, and as shown in FIG. 11, the temperature characteristic correction constant calculation of the polynomial function or the map system according to the temperature of the signal processing circuit board according to the measurement result of Vs voltage The correction amount is calculated by the circuit (temperature characteristic correction constant calculation processing unit) 20, and the detection result of the flow rate detection element 1 is offset corrected.

  In FIG. 11, the temperature of the signal processing circuit board provided with the detection resistor 15 may be different from the temperature of the bridge circuit, that is, the temperature of the flow rate detection element 1 provided with the temperature sensitive resistors 4 and 5. So, in FIG. 11, the temperature detection circuit 17 which detects the temperature of the detection resistance 15 is provided. The temperature detection circuit 17 has a function of converting the voltage (analog value) of the detection resistor 15 into a digital value.

In the present embodiment, the output signal of the temperature detection circuit 17 (that is, the temperature of the signal processing circuit board) and the Vs voltage are input to the temperature characteristic correction constant calculation circuit 20 to calculate the correction amount. In this case, the temperature of the flow detection element 1 (that is, the temperature of the temperature sensitive resistors 4 and 5) can be detected from the relationship (voltage division ratio) between the voltage of the detection resistor 15 and the Vs voltage. It is a figure which shows the example of the flow measurement error of the thermal type flow meter after correction | amendment. The flow rate detection error of the thermal flowmeter 45 can be reduced by correcting the detection result of the flow rate detection element 1 according to the temperature of the temperature sensitive resistors 4 and 5, that is, the change of the environmental temperature. In particular, the flow rate detection error in the extremely low flow rate area of the thermal flow meter 45 can be reduced, and the high-precision thermal flow meter 45 can be provided.

Example 2
A second embodiment will be described with reference to FIGS. The configuration of the second embodiment will be described in the case where a thermocouple is used as the temperature detection elements 4 and 5 instead of the temperature sensitive resistor of the first embodiment. About the contents which overlap with Example 1, the same numerals as Example 1 are attached, and explanation is omitted.

  FIG. 13 is a view showing a temperature distribution image at the time of heating the heating resistor in a cross section of the membrane part of the flow rate detection element when a thermocouple is used as the temperature detection element. FIG. 14 is a thermocouple circuit diagram for detecting deviation of temperature distribution in the membrane part. Although the temperature distribution of the membrane part 2 is the same as that of Example 1, in the case of a thermocouple, the method of temperature detection is different.

  The thermocouples 24 and 25 measure the temperature difference between the cold junction and the hot junction by the magnitude of the thermoelectromotive force generated according to the temperature difference between the cold junction and the hot junction. The contact at a position close to the heating resistor 3 is a hot contact 22, and the contact (contact away from the heating resistor 3) near the end of the membrane portion 2 in the fluid flow direction is a cold contact 23. A contact is placed at a position where the temperature difference is to be measured to perform measurement, and the hot contact 22 and the cold contact 23 are serially connected in series to form a thermal contact. The sum of the power (temperature difference) can be measured. That is, V is obtained as the thermoelectromotive force of the thermocouple 24, and V ′ is obtained as the thermoelectromotive force of the thermocouple 25.

  In the present embodiment, the flow rate calculating unit (flow rate calculating circuit) 48 calculates the fluid flow rate (flow rate signal) based on the difference between the thermoelectromotive force V of the thermocouple 24 and the thermoelectromotive force V 'of the thermocouple 25. .

  In FIG. 13, in the thermocouple 24, when the environmental temperature Ta = T 1, a temperature difference of dT 1 a occurs between the hot contact 22 and the cold contact 23, and when the environmental temperature Ta = T 0, the hot contact 22 and the cold contact 23 In the case of environmental temperature Ta = T2, a temperature difference of dT2a occurs between the hot junction 22 and the cold junction 23. Then, a thermoelectromotive force corresponding to the temperature difference dT1a is generated in the thermocouple 24 when the environmental temperature Ta = T1, and a thermoelectromotive power corresponding to the temperature difference dT0a is generated when the environmental temperature Ta = T0. When Ta = T2, a thermoelectromotive force corresponding to the temperature difference dT2a is generated. On the other hand, in the thermocouple 25, when the environmental temperature Ta = T1, a temperature difference of dT1b occurs between the hot junction 22 and the cold junction 23, and when the environmental temperature Ta = T0, the hot junction 22 and the cold junction 23 In the case of environmental temperature Ta = T2, a temperature difference of dT2b occurs between the warm junction 22 and the cold junction 23 when the ambient temperature Ta = T2. Then, a thermoelectromotive force corresponding to the temperature difference dT1b is generated in the thermocouple 25 when the environmental temperature Ta = T1, and a thermoelectromotive power corresponding to the temperature difference dT0b is generated when the environmental temperature Ta = T0. When Ta = T2, a thermoelectromotive force corresponding to the temperature difference dT2b is generated.

  For example, polysilicon and aluminum thermocouples are often used as the thermocouples 24 and 25. Although the magnitude of the thermoelectromotive force with respect to temperature is determined by the physical properties of the materials to be combined, the magnitude of the thermoelectromotive force changes depending on, for example, the type and concentration of the impurity of polysilicon. Even if the temperature difference between the cold junction 23 and the hot junction 22 does not change with the ambient temperature, if the temperature sensitivity of the thermocouples 24 and 25 varies, the magnitude (temperature sensitivity) of the thermoelectromotive force changes. It will

  FIG. 15 is a schematic view showing temperature characteristic variation of the thermocouple. FIG. 15 shows the temperature characteristic when the temperature difference between the cold junction 23 and the hot junction 22 is constant and the environmental temperature changes.

  For example, when the temperature sensitivity of the upstream thermocouple 24 disposed upstream of the heating resistor 3 is high and the temperature sensitivity of the downstream thermocouple 25 disposed downstream of the other is low, the temperature of the upstream thermocouple 24 is low. The thermoelectromotive force has a temperature characteristic such as 27 and the thermoelectromotive force of the downstream thermocouple 24 has a temperature characteristic 28 such as 28.

  In this case, even if no fluid flow occurs, VT1-VT1 'between the thermoelectromotive force of the upstream thermocouple 24 and the thermoelectromotive force of the downstream thermocouple 25 at the environmental temperature Ta = T1. An electromotive force difference of VT0-VT0 'occurs between the thermoelectromotive force of the upstream thermocouple 24 and the thermoelectromotive force of the downstream thermocouple 25 when the environmental temperature Ta = T0. At Ta = T2, an electromotive force difference of VT2-VT2 'occurs between the thermoelectromotive force of the upstream side thermocouple 24 and the thermoelectromotive force of the downstream side thermocouple 25. For this reason, the detection error of the flow rate according to each electromotive force difference 29 arises.

  FIG. 16 is a graph showing the temperature characteristics of the temperature of the thermocouple and the thermoelectromotive force difference. When the environmental temperature becomes high, the cold junction temperature Tc shown in FIG. 16 becomes high, and the difference in thermal electromotive force (V−V ′) becomes large. Therefore, the detection error of the flow rate becomes larger as the environmental temperature becomes higher.

  In the thermal flow meter of the present embodiment, the temperature characteristic (temperature characteristic) of the thermoelectromotive force due to the variation of the thermocouple as shown in FIG. 15 is corrected by measuring the temperature of the cold junction 23 to obtain high accuracy thermal power. A flow meter 45 is provided.

  As shown in FIG. 16, the relationship 30 between the temperature of the cold junction 23 and the thermoelectromotive force difference is checked in advance, and based on the relationship 30, the temperature characteristic due to the variation of the thermocouples 24 and 25 is corrected.

  FIG. 17 is a block diagram of the configuration of the temperature characteristic correction processing unit according to the second embodiment. As shown in FIG. 17, the temperature detection circuit 31 receives a detection signal of the temperature measuring element 46 for measuring the temperature of the cold junction 23 to detect the temperature of the cold junction 23. Further, the temperature characteristic correction constant calculation circuit (temperature characteristic correction constant calculation processing unit) 20 calculates the correction amount of the temperature characteristic from the output of the temperature detection circuit 31 and offsets the detection result of the flow rate detection element 1 according to the correction amount. Do. The measurement error of the thermal flowmeter 45 after correction can be reduced as in FIG.

  The temperature measuring element 46 can detect the temperature of the flow rate detecting element 1 (that is, the temperature of the thermocouples 24 and 25) by being provided in one of the thermocouple 24 and the thermocouple 25. The temperature measuring element 46 may be provided on both the thermocouple 24 and the thermocouple 25.

  The temperature measuring element 46 can use various detection elements capable of detecting temperature, in addition to a temperature element using a temperature sensitive resistor or a diode.

  In the present embodiment, one of the thermocouples 24 and 25 constitutes a first temperature detection element, and the other constitutes a second temperature detection element. The temperature measurement element 46 constitutes a third temperature detection element.

  Also in the present embodiment, as in the first embodiment, by correcting the detection result of the flow rate detecting element 1, it is possible to reduce the flow rate error in the extremely low flow rate region of the thermal flowmeter 45, and high accuracy thermal A flow meter can be provided.

  In each of the above-described embodiments, the flow rate operation unit 47 is disposed at the next stage of the AD conversion circuit, but the flow rate operation unit 47 outputs the output signal of the temperature characteristic correction constant operation circuit 20 and the output signal of the AD conversion circuit 19 The flow rate signal may be calculated by offsetting the temperature error by the flow rate calculation unit 47.

  The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the embodiments described above are described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, with respect to a part of the configuration of each embodiment, it is possible to add, delete, and replace other configurations.

1 flow rate detection element 2 membrane 3 heating resistor 4 upstream temperature detection element (first temperature detection element or second temperature detection element)
5 downstream temperature detection element (second temperature detection element or first temperature detection element)
6 Temperature distribution at time of Zero Flow 7 Temperature distribution at the time of flow flow generation 8 Example of flow detection error depending on temperature due to dispersion of temperature detection element 9 Temperature characteristic example of upstream temperature-sensitive resistor with dispersion 10 Dispersion Temperature characteristic example of the downstream side temperature-sensitive resistor 11 having temperature-sensitive resistor pair 12 temperature-sensitive resistor pair 13 output temperature characteristic of bridge circuit in ideal temperature-sensitive resistor 14 temperature-sensitive resistance with realistic variation Output Temperature Characteristic of Bridge Circuit in Body 15 Detection Resistance for Measuring Temperature of Temperature-Sensitive Resistor (3rd Temperature Detection Element)
16 Detection Characteristic of Temperature-Sensitive Resistor Temperature by Detection Resistance 17 Detection Resistance Temperature Detection Circuit 18 AD Conversion Circuit for Temperature Detection of Temperature-Sensitive Resistor 19 AD Conversion Circuit for Air Flow Rate Signal 20 Temperature Characteristic Correction Constant Arithmetic Circuit (Correction Amount Operation Unit )
21 Flow rate detection error 22 when temperature characteristics are corrected due to variations in temperature detection element 22 hot junction of thermocouple 23 cold junction 24 of thermocouple upstream thermocouple 25 downstream thermocouple 26 temperature detection element 27 of cold junction with variation Example of temperature characteristics of upstream thermocouples 28 Example of temperature characteristics of downstream thermocouples having variations Example 29: Thermoelectric power difference between upstream thermocouples and downstream thermocouples 30: Thermoelectricity of thermocouples having realistic variations Temperature characteristic of power difference 31 Temperature detection circuit of cold junction 32 LSI
33: Intake temperature detection temperature sensing resistor 34: Chip capacitor 35: Lead frame 36: Chip package 37: Thermosetting resin 38: I / O terminal 39: Circuit chamber 40: Housing 41: Subpassage 42: Intake passage 43: Connector terminal 44: Connector 45: Thermal flowmeter 46 Temperature detection element (third temperature detection element)
47 Flow rate calculation unit (flow rate calculation circuit)
48 Flow rate calculation unit (flow rate calculation circuit)

Claims (5)

An auxiliary passage for taking in part of the fluid flowing in the main passage, a flow rate detection element provided in the auxiliary passage and outputting a signal according to the flow rate of the fluid taken in the auxiliary passage, and the flow rate detection element A flow rate calculating unit that calculates a flow rate signal based on the output signal to be
The flow rate detection element includes a heat generation resistor, and a plurality of temperature detection elements for detecting the temperature on the upstream side and the temperature on the downstream side with respect to the heat generation resistor in the fluid flow direction,
In a flow rate measuring device which calculates the flow rate signal by using a signal corresponding to a temperature change of the temperature detection element as the output signal,
The error of the flow rate signal based on the temperature characteristic of the temperature detection element is corrected based on the temperature measurement element for measuring the temperature of the temperature detection element and the temperature of the temperature detection element measured using the temperature measurement element A correction amount calculation unit that calculates a correction amount to be
A flow rate measuring apparatus characterized by correcting a flow rate detected based on the correction amount. In the flow rate measuring device according to claim 1,
The temperature detection element is disposed downstream of the heat-generating resistor with respect to the first temperature-sensitive resistor, which is disposed upstream of the heat-generating resistor in the fluid flow direction, and in the fluid flow direction. And a second temperature sensitive resistor.
A bridge circuit configured of the first temperature sensitive resistor and the second temperature sensitive resistor; and a reference resistor connected in series to the bridge circuit as the temperature measurement element;
The correction amount calculation unit detects the temperature of the first temperature sensitive resistor and the second temperature sensitive resistor based on the combined resistance of the bridge circuit, and the first temperature sensitive resistor and the second temperature sensitive device. A flow rate measuring device characterized by correcting a flow rate detected by offsetting the flow rate signal according to a temperature of a resistor. In the flow rate measuring device according to claim 2,
A flow rate measuring device comprising the temperature measuring element provided on the flow rate detecting element. The flow rate measuring device according to any one of claims 2 to
A signal processing circuit board provided with the correction amount calculation unit;
The temperature measurement element is provided on the signal processing circuit board,
The flow rate measuring device, wherein the correction amount calculation unit calculates the correction amount based on the temperature of the signal processing circuit board and the temperature of the temperature detection element, and offsets the flow rate signal by the correction amount. In the flow rate measuring device according to claim 1,
The temperature detection element includes a first thermocouple disposed upstream with respect to the heating resistor in the fluid flow direction, and a second thermocouple disposed downstream with respect to the heating resistor in the fluid flow direction. Comprising a thermocouple,
The flow rate calculating unit calculates the flow rate signal based on a difference between an electromotive force of the first thermocouple and an electromotive force of the second thermocouple,
The temperature measurement element is provided to measure a temperature of a cold junction of at least one of the first thermocouple and the second thermocouple.
The said correction amount calculating part correct | amends the flow detected by offsetting the said flow signal according to the temperature of the said cold junction measured by the element for temperature measurement.

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