Air flow meter

Abstract

The present disclosure provides an air flow meter with which it is possible to highly accurately measure the flow rate of air in a main passage even in an environment in which there is increased pulsation of air in the main passage. The air flow meter is provided with a flow rate extraction element, a computation unit 121, a signal extraction unit 122, a first correction unit 123, and a combining unit 124c. The flow rate detection element is installed on an auxiliary passage for intaking air from the main passage and returning the air to the main passage, and outputs a detection signal DS corresponding to the flow rate of air flowing through the auxiliary passage. The computation unit 121 generates, on the basis of the detection signal DS, a detection flow rate Qo serving as an output signal corresponding to the flow rate of air flowing through the main passage. The signal extraction unit 122 extracts an AC component Qhpf of the detection flow rate Qo that is the output signal. The first correction unit 123 outputs a first corrective amount Q1 that corresponds to half-wave rectified waves of the AC component Qhpf and increases in correspondence with an increase in the pulsation amplitude rate of the AC component Qhpf. The combining unit 124c subtracts a corrective amount CA based on the first corrective amount Q1 from the detection flow rate Qo serving as the output signal.

Description

[Technical field]

[0001] The present disclosure relates to air flow meters. [Background technology]

[0002] Devices for measuring the flow rate of a fluid such as air have been known for some time. The flow rate measurement device described in Patent Document 1 below has a detection element that outputs a nonlinear signal according to the flow rate. This flow rate measurement device includes a first signal processing system, a second signal processing system, an amplifier, and a correction unit (Abstract, Claim 1, paragraphs 0015 to 0019, etc.).

[0003] The first signal processing system filters the nonlinear source signal of the detection element, then adjusts the sensitivity to obtain a first signal. The second signal processing system linearizes the source signal, filters it, adjusts the sensitivity, and makes it nonlinear again to obtain a second signal. An amplifier amplifies a difference signal between the first signal and the second signal. A correction unit uses the amplified difference signal to correct the source signal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-205916 A Summary of the Invention [Problem to be solved by the invention]

[0005] For example, an air flow meter is installed in the intake passage of an internal combustion engine vehicle to measure the flow rate of air flowing through the intake passage. For internal combustion engine vehicles, development of high-performance systems is underway through downsizing to reduce the number of cylinders, increasing the capacity of exhaust gas recirculation (EGR), and adopting the Atkinson cycle.

[0006] As a result, there is a tendency for air pulsation in the intake passage to increase due to the expansion of the area where air backflow occurs due to the EGR valve and the expansion of valve overlap due to the reduced number of cylinders.Even in such an environment where air pulsation is increasing, there is a demand for an air flow meter to measure the air flow rate with high accuracy.

[0007] The present disclosure provides an air flow meter that is capable of measuring the air flow rate with high accuracy even in an environment where air pulsation is increasing. [Means for solving the problem]

[0008] One aspect of the present disclosure is an air flow meter that measures the flow rate of air flowing through a main passage, the air flow meter comprising: a flow detection element that is installed in a secondary passage that takes in air from the main passage and returns it to the main passage and outputs a detection signal corresponding to the flow rate of air flowing through the secondary passage; a calculation unit that generates an output signal corresponding to the flow rate of air flowing through the main passage based on the detection signal; a signal extraction unit that extracts an AC component of the output signal; a first correction unit that corresponds to a half-wave rectified wave of the AC component and outputs a first correction amount that increases according to an increase in the pulsation amplitude rate of air flowing through the main passage; and a combination unit that subtracts the correction amount based on the first correction amount from the output signal. Effect of the Invention

[0009] According to the above aspect of the present disclosure, it is possible to provide an air flow meter that is capable of measuring the air flow rate with high accuracy even in an environment where air pulsation is increasing. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a first embodiment of an air flow meter according to the present disclosure. [Diagram 2] 2 is a rear view of the physical quantity detection device shown in FIG. 1 with the cover removed. [Diagram 3] 3 is an enlarged cross-sectional view of the air flow meter of the physical quantity detection device of FIG. 2 taken along line III-III. [Figure 4] 4 is a graph showing the relationship between the output signal of the air flow meter of FIG. 3 and the true flow rate. [Diagram 5] 4 is a graph showing an error between the output signal of the air flow meter of FIG. 3 and a true flow rate. [Figure 6] 4 is a graph showing an error between the output signal of the air flow meter of FIG. 3 and a true flow rate. [Figure 7] 3 is a graph illustrating the flow of air in a sub-passage of the physical quantity detection device of FIG. 2. [Figure 8] FIG. 4 is a block diagram of a signal processing unit of the air flow meter of FIG. 3. [Figure 9] 9 is a graph illustrating signal processing by the signal processing unit in FIG. 8. [Figure 10] 9 is a graph showing an example of a change in the amount of correction by the signal processing unit in FIG. 8. [Figure 11] 9 is a graph showing an error between a corrected flow rate by the signal processing unit in FIG. 8 and a true flow rate. [Figure 12] FIG. 6 is a block diagram of a signal processing unit of an air flow meter according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of an air flow meter according to the present disclosure will be described with reference to the drawings.

[0012] [Embodiment 1] Fig. 1 is a schematic cross-sectional view of an internal combustion engine control system 1 which is a first embodiment of an air flow meter according to the present disclosure. An air flow meter 100 (see Fig. 2) of this embodiment constitutes, for example, a part of a physical quantity detection device 20 included in the internal combustion engine control system 1. Below, the configurations of the internal combustion engine control system 1, the physical quantity detection device 20, and each part of the air flow meter 100 of this embodiment will be described.

[0013] In the internal combustion engine control system 1, for example, intake air is drawn in through an air cleaner 21 based on the operation of an internal combustion engine 10 having an engine cylinder 11 and an engine piston 12. The intake air is guided to the combustion chamber of the engine cylinder 11 through an intake body which is a main passage 22, a throttle body 23, and an intake manifold 24.

[0014] The physical quantity detection device 20 installed in the main passage 22 measures the physical quantity of the intake air. That is, the measured gas 2 of the physical quantity detection device 20 is, for example, the intake air flowing through the main passage 22. Furthermore, based on the physical quantity of the intake air measured by the physical quantity detection device 20, fuel is supplied from the fuel injector 14 and is introduced into the combustion chamber in a mixed state together with the intake air.

[0015] The fuel injection valve 14 is provided, for example, in an intake port of the internal combustion engine 10, and injects fuel into the intake port to mix with intake air, thereby leading the mixture of fuel and intake air to a combustion chamber via an intake valve 15. The mixture led to the combustion chamber is combusted explosively by spark ignition from an ignition plug 13, generating mechanical energy.

[0016] The physical quantity detection device 20 measures physical quantities such as the flow rate, temperature, humidity, and pressure of intake air as the measurement target gas 2 that is taken in through the air cleaner 21 and flows through the main passage 22. The physical quantity detection device 20 outputs an electric signal according to the physical quantity of the intake air. The output signal of the physical quantity detection device 20 is input to the control device 4.

[0017] In addition, the output of a throttle angle sensor 26 that measures the opening degree of a throttle valve 25 is input to the control device 4. In addition, the output of a rotation angle sensor 17 is input to the control device 4 in order to measure the positions and states of the engine piston 12, intake valve 15, and exhaust valve 16 of the internal combustion engine 10, as well as the rotation speed of the internal combustion engine 10. In addition, the output of an oxygen sensor 28 is input to the control device 4 in order to measure the mixture ratio state of the fuel amount and the air amount from the state of the exhaust gas 3.

[0018] The control device 4 calculates the fuel injection amount and ignition timing based on the physical quantity of the intake air, which is the output of the physical quantity detection device 20, and the rotation speed of the internal combustion engine 10 obtained from the output of the rotation angle sensor 17. Based on these calculation results, the amount of fuel supplied from the fuel injection valve 14 and the ignition timing by the spark plug 13 are controlled. Furthermore, the fuel supply amount and the ignition timing are finely controlled based on the temperature measured by the physical quantity detection device 20, as well as the change in the throttle angle, the change in the engine rotation speed, the air-fuel ratio measured by the oxygen sensor 28, and the like.

[0019] The control device 4 further controls the amount of air bypassing the throttle valve 25 by an idle air control valve 27 when the internal combustion engine 10 is in an idle operating state, thereby controlling the rotation speed of the internal combustion engine 10 in an idle operating state. The amount of fuel supply and ignition timing, which are the main control amounts of the internal combustion engine 10, are both calculated using the output of the physical quantity detection device 20 as a main parameter. Therefore, improving the accuracy of the physical quantity detection device 20, suppressing changes over time, and improving its reliability are important for improving the control accuracy of the vehicle and ensuring its reliability.

[0020] In particular, in recent years, there has been a very strong demand for fuel efficiency in vehicles and for exhaust gas purification. In order to meet these demands, it is extremely important to improve the measurement accuracy of the physical quantity of the intake air as the measurement target gas 2 measured by the physical quantity detection device 20. It is also important that the physical quantity detection device 20 maintains high reliability.

[0021] Furthermore, in recent years, the development of high-performance systems has been promoted by downsizing internal combustion engine vehicles to reduce the number of cylinders, increasing the capacity of exhaust gas recirculation (EGR), adopting the Atkinson cycle, etc. As a result, there is a tendency for air pulsation in the intake passage to increase due to an expansion of the backflow generation area caused by the blowback from the EGR valve and an expansion of valve overlap caused by the reduction in the number of cylinders of the internal combustion engine 10. Thus, even in an environment where air pulsation is increasing, the air flow meter constituting the physical quantity detection device 20 is required to measure the air flow rate with high accuracy.

[0022] Fig. 2 is a rear view of the physical quantity detection device 20 shown in Fig. 1 with its cover removed. The physical quantity detection device 20 includes a housing 201 and a cover (not shown) attached to the housing 201. The cover is made of a plate-like member made of a conductive material such as an aluminum alloy or an injection-molded synthetic resin material, and is formed in the shape of a thin plate having a wide, flat cooling surface.

[0023] The housing 201 is made of, for example, an injection-molded synthetic resin material, and includes a flange 201f, a connector 201c, and a measuring portion 201m.

[0024] The flange 201f is fixed to the intake body, which is the main passage 22. The flange 201f has, for example, a substantially rectangular plate shape in a plan view and has through holes at the corners. The flange 201f is fixed to the main passage 22, for example, by inserting fixing screws into the through holes at the corners and screwing them into screw holes in the main passage 22.

[0025] The connector 201c protrudes from the flange 201f and is exposed to the outside from the intake body for electrical connection with an external device. The connector 201c is provided with, for example, four external terminals and a correction terminal inside. The external terminals are terminals for outputting physical quantities such as flow rate and temperature that are measurement results of the physical quantity detection device 20, and power supply terminals for supplying DC power for operating the physical quantity detection device 20. The correction terminals are terminals used for measuring the manufactured physical quantity detection devices 20, determining correction values ​​for each physical quantity detection device 20, and storing the correction values ​​in a memory inside the physical quantity detection device 20.

[0026] The measurement section 201m extends from the flange 201f so as to protrude toward the center of the main passage 22. The measurement section 201m has a thin, long plate-like shape extending from the flange 201f toward the center of the main passage 22, and has a wide front and back surface, and a pair of narrow side surfaces, an upstream end surface 223 and a downstream end surface 224. Note that Figs. 1 and 2 show a three-dimensional Cartesian coordinate system including an X-axis parallel to the central axis 22a of the main passage 22 and the short direction of the measurement section 201m, a Y-axis parallel to the thickness direction of the measurement section 201m, and a Z-axis parallel to the longitudinal direction of the measurement section 201m.

[0027] With the physical quantity detection device 20 attached to the main passage 22, the measuring section 201m protrudes from the inner wall of the main passage 22 toward the central axis 22a of the main passage 22, and its front and back surfaces are arranged parallel to the central axis 22a of the main passage 22. Of the narrow upstream end face 223 and downstream end face 224, the measuring section 201m is arranged such that the upstream end face 223 on one side in the short direction of the measuring section 201m faces the upstream side of the main passage 22, and the downstream end face 224 on the other side in the short direction of the measuring section 201m faces the downstream side of the main passage 22.

[0028] The measuring section 201m is provided with an inlet 231 for taking in a part of the measurement target gas 2 such as intake air into a bypass passage 234 in the measuring section 201m on an upstream end face 223 of the tip end portion 201t opposite to the flange 201f provided at the base end portion. The measuring section 201m is provided with a first outlet 232 and a second outlet 233 for returning the measurement target gas 2 taken in the bypass passage 234 in the measuring section 201m to the main passage 22 on a downstream end face 224 opposite to the upstream end face 223 of the tip end portion 201t.

[0029] In the physical quantity detection device 20, the inlet 231 of the sub-passage 234 is provided at the tip 201t of the measurement section 201m extending from the flange 201f toward the center of the main passage 22. Therefore, the physical quantity detection device 20 can take in, into the sub-passage, gas in a portion close to the center away from the inner wall surface, rather than gas in the vicinity of the inner wall surface of the main passage 22. This allows the physical quantity detection device 20 to measure the flow rate of gas in a portion away from the inner wall surface of the main passage 22, and can suppress deterioration of accuracy due to the influence of heat, etc.

[0030] The measurement section 201m is provided with a bypass passage groove 250 for forming the bypass passage 234, and a circuit chamber 235 for accommodating the circuit board 207. The circuit chamber 235 and the bypass passage groove 250 are provided in a concave shape on one surface of the measurement section 201m in the thickness direction of the plate-like measurement section 201m.

[0031] The circuit chamber 235 is disposed at a position upstream of the main passage 22 in the flow direction of the measurement target gas 2, and the bypass passage 234 is disposed at a position downstream of the circuit chamber 235 in the flow direction of the measurement target gas 2 in the main passage 22. The bypass passage groove 250 forms the bypass passage 234 together with the cover. The bypass passage groove 250 has a first bypass passage groove 251 and a second bypass passage groove 252 branching off from the first bypass passage groove 251 midway.

[0032] The first sub-passage groove 251 is formed to extend along the short side direction of the measuring section 201m between the inlet 231 opening on the upstream end face 223 of the measuring section 201m and the first outlet 232 opening on the downstream end face 224 of the measuring section 201m. Between the first sub-passage groove 251 and the cover, a first sub-passage 234a is formed, which extends from the inlet 231 along the central axis 22a of the main passage 22 to the first outlet 232. The first sub-passage 234a takes in the measurement target gas 2 flowing in the main passage 22 from the inlet 231 and returns the taken-in measurement target gas 2 to the main passage 22 from the first outlet 232. The first sub-passage 234a has a branch between the inlet 231 and the first outlet 232.

[0033] Between the second sub-passage groove 252 and the cover, a second sub-passage 234b is formed, which branches from the first sub-passage 234a toward the flange 201f and reaches the second outlet 233. The second outlet 233 is opened to face the downstream side in the flow direction of the measurement target gas 2 in the main passage 22. The second outlet 233 has an opening area larger than that of the first outlet 232, and is formed closer to the base end side in the longitudinal direction of the measurement section 201m than the first outlet 232. The second sub-passage 234b has, for example, a linear upstream section 237, an arc-shaped or U-shaped curved section 238, and a linear downstream section 239, and has a path that travels back and forth along the longitudinal direction of the measurement section 201m.

[0034] More specifically, the second bypass passage groove 252 forming the second bypass passage 234b branches from the first bypass passage groove 251 toward the flange 201f in the longitudinal direction of the measurement section 201m and extends in a direction generally perpendicular to the central axis 22a of the main passage 22. The second bypass passage groove 252 is curved in a U-shape or arc shape toward the tip 201t in the vicinity of the flange 201f of the measurement section 201m and turns back, and extends in the longitudinal direction of the measurement section 201m, i.e., in a direction perpendicular to the central axis 22a of the main passage 22. The second bypass passage groove 252 is bent, for example, in an arc shape toward the downstream end face 224 of the measurement section 201m and connected to the second outlet 233.

[0035] 1 is taken into the first sub-passage 234a from the inlet 231 in the forward flow, and flows through the first sub-passage 234a toward the first outlet 232. The measurement gas 2 flowing through the first sub-passage 234a flows into the second sub-passage 234b from the branching portion of the first sub-passage 234a in the forward flow. The measurement gas 2 branching from the first sub-passage 234a and flowing into the second sub-passage 234b passes through the second sub-passage 234b and returns to the main passage 22 from the second outlet 233.

[0036] The physical quantity detection device 20 includes, as a detection element for detecting a physical quantity, for example, an air flow meter 100 arranged in the upstream portion 237 of the second sub-passage 234b. More specifically, in the upstream portion 237 of the second sub-passage 234b, the air flow meter 100 is arranged between the first sub-passage 234a and the curved portion 238. By having the above-mentioned curved shape, the second sub-passage 234b can ensure a longer passage length, and when pulsation occurs in the measurement target gas 2 in the main passage 22, the effect on the air flow meter 100 can be reduced. Details of the air flow meter 100 of this embodiment will be described later.

[0037] The circuit board 207 is housed in a circuit chamber 235 provided on one side of the short side of the measuring section 201m. The circuit board 207 has a generally L-shaped configuration that extends, for example, along the longitudinal direction of the measuring section 201m and also extends along the short side of the measuring section 201m at the end of the measuring section 201m on the flange 201f side.

[0038] An intake air temperature sensor 203, a pressure sensor 204, a humidity sensor 206, and a chip package 110 constituting the air flow meter 100 are mounted on the surface of the circuit board 207. That is, the physical quantity detection device 20 includes the intake air temperature sensor 203, the pressure sensor 204, the air flow meter 100, and the humidity sensor 206 as elements for detecting the physical quantities of the measurement target gas 2, namely, the temperature, pressure, flow rate, and humidity.

[0039] Fig. 3 is an enlarged cross-sectional view of air flow meter 100 constituting physical quantity detection device 20, taken along line III-III shown in Fig. 2. Chip package 110 constituting air flow meter 100 has flow detection element 111 that outputs a detection signal corresponding to the flow rate of air flowing through sub-passage 234. Flow detection element 111 is, for example, a thermal flow sensor, and has semiconductor substrate 111a and diaphragm 111d formed on the front surface side of semiconductor substrate 111a.

[0040] Although not shown, the diaphragm 111d includes, for example, a pair of temperature sensors arranged on the upstream and downstream sides of the flow direction of the measurement target gas 2, and a heater arranged between the pair of temperature sensors. The flow rate detection element 111 measures the flow rate of the measurement target gas 2 by detecting, for example, a temperature difference generated in the pair of temperature sensors by the flow of the measurement target gas 2 along the diaphragm 111d.

[0041] The flow rate detection element 111 measures the flow rate of the measurement target gas 2 flowing through a measurement flow path 110d formed between, for example, the circuit board 207 and the recessed groove 110c of the chip package 110. As shown in FIG. 2, the measurement flow path 110d is formed between a curved portion 238 and an upstream portion 237 of a second sub-passage 234b constituting the sub-passage 234.

[0042] The chip package 110 has, for example, an electronic component 112, a lead frame 113, and a resin sealing portion 114. The electronic component 112 is mounted on the lead frame 113 together with a flow rate detection element 111. The electronic component 112 is, for example, an LSI, and is connected to the flow rate detection element 111 via a bonding wire to drive the flow rate detection element 111.

[0043] Resin sealing portion 114 is integrally molded by, for example, transfer molding of a thermosetting resin, and seals a part of flow rate detection element 111, electronic component 112, and a part of lead frame 113. Diaphragm 111d of flow rate detection element 111 and a part of lead frame 113 are exposed from resin sealing portion 114. The outer lead of lead frame 113 exposed from resin sealing portion 114 is connected to a terminal on the surface of circuit board 207 as shown in FIG.

[0044] Fig. 4 is a graph showing an example of the relationship between the detected flow rate Qo, which is the output signal of the air flow meter 100, and the true flow rate when air flowing through the main passage 22 of the internal combustion engine control system 1 is pulsating. In the graph of Fig. 4, the vertical axis is the flow rate Q, and the horizontal axis is time t. In Fig. 4, the true flow rate Qt of the air flowing through the main passage 22 is represented by a two-dot chain line, and the detected flow rate Qo, which is the output signal of the air flow meter 100 installed in the sub-passage 234 of the physical quantity detection device 20, is represented by a solid line.

[0045] 4, the true flow rate Qt of air flowing through the main passage 22 of the internal combustion engine control system 1 regularly alternates between a forward flow where the flow rate Q is positive and a reverse flow where the flow rate Q is negative, generating pulsation in the air flowing through the main passage 22. In contrast, the detected flow rate Qo of the air flow meter 100 has a more attenuated amplitude than the true flow rate Qt and lags in phase with respect to the true flow rate Qt.

[0046] Here, the ratio of the pulsation amplitude PA to the average value Qta of the true flow rate Qt of the air flowing through the main passage 22 when the air flowing through the main passage 22 pulsates is defined as the pulsation amplitude ratio PAR. That is, the pulsation amplitude ratio PAR of the air flowing through the main passage 22 can be calculated, for example, by using the pulsation amplitude PA and average value Qta of the true flow rate Qt of the air flowing through the main passage 22, according to the following formula (1).

[0047] PAR[%]=(PA / Qta)×100 (1)

[0048] The difference between the average value Qoa of the detected flow rate Qo of the air flow meter 100 and the average value Qta of the true flow rate Qt is defined as the error E of the detected flow rate Qo of the air flow meter 100. Here, the ratio of the error E to the average value Qta of the true air flow rate Qt when the air flowing through the main passage 22 is pulsating is defined as the pulsation error PAE. That is, the pulsation error PAE can be calculated, for example, by using the error E and the average value Qta of the true air flow rate Qt of the air flowing through the main passage 22, according to the following formula (2).

[0049] PAE[%] = (E / Qta) × 100 (2)

[0050] Figures 5 and 6 are graphs showing an example of an error E of the detected flow rate Qo, which is the output signal of the air flow meter 100, relative to the true flow rate Qt of air flowing through the main passage 22. In Figure 5, the true air flow rate Qt and the detected flow rate Qo of the air flow meter 100 when the pulsation amplitude rate PAR is 150% are shown by a two-dot chain line and a solid line, respectively. Also, in Figure 6, the true air flow rate Qt and the detected flow rate Qo of the air flow meter 100 when the pulsation amplitude rate PAR is 100% are shown by a two-dot chain line and a solid line, respectively.

[0051] As shown in Fig. 5, when the pulsation amplitude rate PAR is 150%, the detected flow rate Qo of the air flow meter 100 tracks the true flow rate Qt relatively well. As a result, the error E of the average value Qoa of the detected flow rate Qo of the air flow meter 100 with respect to the average value Qta of the true air flow rate Qt is almost zero. For example, when the pulsation amplitude rate PAR exceeds 100%, the error E approaches zero.

[0052] On the other hand, as shown in Fig. 6, when the pulsation amplitude rate PAR is 100%, the closer the detected flow rate Qo of the air flow meter 100 approaches the maximum value, the larger the positive error of the detected flow rate Qo from the true flow rate Qt. As a result, the error E of the average value Qoa of the detected flow rate Qo of the air flow meter 100 from the average value Qta of the true air flow rate Qt when the pulsation amplitude rate PAR is 100% is larger than when the pulsation amplitude rate PAR is 150%.

[0053] In this way, the positive error of the detected flow rate Qo of the air flow meter 100 relative to the true flow rate Qt tends to be larger, for example, in the low pulsation amplitude region where the pulsation amplitude ratio PAR is 100% or less than in the high pulsation amplitude region where the pulsation amplitude ratio PAR exceeds 100%.

[0054] The reason why the positive error of the detected flow rate Qo of the air flow meter 100 with respect to the true flow rate Qt increases in the low pulsation amplitude region where the pulsation amplitude ratio PAR of the air flowing through the main passage 22 is 100% or less will be described below with reference to Fig. 7. Fig. 7 is a graph illustrating the transition from laminar flow to turbulent flow of air flowing through the secondary passage 234 of the physical quantity detection device 20 of Fig. 2.

[0055] 7, the horizontal axis represents the flow rate q of the air flowing through the second sub-passage 234b of the physical quantity detection device 20, and the vertical axis represents the pressure difference ΔP between the inlet 231 and the second outlet 233 of the physical quantity detection device 20. In addition, in the graph of Fig. 7, the condition under which the air flowing through the second sub-passage 234b becomes a laminar flow LF is indicated by a solid line, and the condition under which the air flowing through the second sub-passage 234b becomes a turbulent flow TF is indicated by a dashed line.

[0056] As shown in Fig. 1, when air as the measurement gas 2 flows through the main passage 22 of the internal combustion engine control system 1, a differential pressure ΔP is generated between the inlet 231 and the first outlet 232 and second outlet 233 of the physical quantity detection device 20 shown in Fig. 2. As a result, air flows at a flow rate q according to the differential pressure ΔP through the second sub-passage 234b between the inlet 231 and the second outlet 233 of the physical quantity detection device 20.

[0057] When the air flowing through the main passage 22 is a steady flow SF, the flow rate q of the air flowing through the second sub passage 234b increases continuously with an increase in the differential pressure ΔP, and the air flow transitions from a laminar flow LF to a turbulent flow TF, as shown by the dashed-dotted arrow in Fig. 7. On the other hand, when the air flowing through the main passage 22 is an accelerating flow AF, the flow rate q at which the air flowing through the second sub passage 234b transitions from a laminar flow LF to a turbulent flow TF increases compared to the steady flow SF shown by the dashed-dotted line, as shown by the dashed-dotted arrow in Fig. 7.

[0058] Moreover, in the case of the above-mentioned accelerating flow AF, when the differential pressure ΔP further increases, the differential pressure ΔP increases without an increase in the flow rate q of the air flowing through the second sub passage 234b, and the air flowing through the second sub passage 234b transitions from the laminar flow LF to the turbulent flow TF. Therefore, even if the differential pressure ΔP is the same, the flow rate q2 of the air flowing through the second sub passage 234b when the air flowing through the main passage 22 is the accelerating flow AF is greater than the flow rate q1 of the air flowing through the second sub passage 234b when the air flowing through the main passage 22 is the steady flow SF.

[0059] As shown in Fig. 6, for example, in a low pulsation amplitude region where the pulsation amplitude ratio PAR of the true flow rate Qt of air flowing through the main passage 22 is 100% or less, an accelerated flow AF is likely to occur in the main passage 22. On the other hand, as shown in Fig. 5, for example, in a high pulsation amplitude region where the pulsation amplitude ratio PAR of the true flow rate Qt of air flowing through the main passage 22 exceeds 100%, an accelerated flow AF is unlikely to occur in the main passage 22.

[0060] As a result, in the low pulsation amplitude region, the flow rate q of air flowing through the sub-passage 234 increases more than in the high pulsation amplitude region, making it easier for a positive error to occur between the true flow rate Qt and the detected flow rate Qo of the air flow meter 100. Therefore, in the air flow meter 100, it is important to reduce the positive error that occurs between the true flow rate Qt and the detected flow rate Qo of the air flow meter 100 in the low pulsation amplitude region of air flowing through the main passage 22.

[0061] 8 is a block diagram of the signal processing unit 120 of the air flow meter 100 of this embodiment. The signal processing unit 120 can be configured by, for example, electronic components 112 of a chip package 110, a program stored in a memory, a central processing unit (CPU) mounted on a circuit board 207 of the physical quantity detection device 20, and other electronic components.

[0062] The signal processing unit 120 includes, for example, a calculation unit 121, a signal extraction unit 122, a first correction unit 123, and combination units 124a, 124b, and 124c. In this embodiment, the signal processing unit 120 further includes, for example, a second correction unit 125.

[0063] As described above, the flow rate detection element 111 of the air flow meter 100 outputs a detection signal DS corresponding to the flow rate of air flowing through the secondary passage 234 of the physical quantity detection device 20. The detection signal DS output from the flow rate detection element 111 is input to the calculation unit 121. The calculation unit 121 outputs a detected flow rate Qo, which is an output signal corresponding to the flow rate of air flowing through the main passage 22, based on the input detection signal DS.

[0064] The calculation unit 121 calculates the detected flow rate Qo as an output signal from the detection signal DS using, for example, an inverse function model IFM. The inverse function model IFM is a calculation model for performing a known inverse function correction, for example, as described in JP 2018-205134 A. The calculation unit 121 outputs the detected flow rate Qo as the generated output signal.

[0065] The signal extraction unit 122 receives the detected flow rate Qo as an output signal output from the calculation unit 121. The signal extraction unit 122 extracts an AC component Qhpf of the input detected flow rate Qo. The signal extraction unit 122 is configured with, for example, a high-pass filter (HPF). The signal extraction unit 122 outputs the extracted AC component Qhpf to the first correction unit 123.

[0066] Fig. 9 is a graph for explaining signal processing by the signal processing unit 120 of Fig. 8. The horizontal axis of each graph in Fig. 9 is time t. The top graph in Fig. 9 is the AC component Qhpf extracted by the signal extraction unit 122 from the detected flow rate Qo, which is the output signal of the flow detection element 111. In Fig. 9, the dashed line and solid line respectively indicate the cases where the pulsation amplitude rate PAR of the air flowing through the main passage 22 is 150% and 100%, respectively.

[0067] 9 shows the first correction amount Q1 output from the first correction unit 123. The first correction unit 123 receives the AC component Qhpf of the detected flow rate Qo output from the signal extraction unit 122. The first correction unit 123 is configured with, for example, a half-wave rectifier, and generates a half-wave rectified wave of the AC component Qhpf input from the signal extraction unit 122.

[0068] Furthermore, the first correction unit 123 outputs a first correction amount Q1 that corresponds to a half-wave rectified wave of the AC component Qhpf and increases in accordance with an increase in the pulsation amplitude ratio PAR of the air flowing through the main passage 22. More specifically, the first correction unit 123 outputs the first correction amount Q1 that increases in accordance with an increase in the pulsation amplitude ratio PAR of the AC component Qhpf until the pulsation amplitude ratio PAR of the AC component Qhpf exceeds a first threshold value th1, for example.

[0069] Furthermore, for example, when the pulsation amplitude rate PAR of the air flowing through the main passage 22 exceeds the first threshold value th1, the first correction unit 123 limits the first correction amount Q1 to the first correction amount Q1 when the pulsation amplitude rate PAR of the AC component Qhpf is the first threshold value th1. The first threshold value th1 can be set, for example, to the maximum value of the first correction amount Q1 corresponding to an arbitrary pulsation amplitude rate PAR in the low pulsation amplitude range where the positive error of the detected flow rate Qo increases and the pulsation error PAE becomes maximum.

[0070] More specifically, the first threshold th1 can be set to, for example, a first correction amount Q1 of an arbitrary pulsation amplitude ratio PAR of 100% or less at which the pulsation error PAE is maximized. As a result, as shown in the second graph from the top in Fig. 9, a saturation process is performed in which the first correction amount Q1 when the pulsation amplitude ratio PAR is 150% is limited to the first correction amount Q1 of the pulsation amplitude ratio PAR at which the pulsation error PAE is maximized.

[0071] The bottom graph in Fig. 9 shows the second correction amount Q2 output from the second correction unit 125. As shown in Fig. 8, the AC component Qhpf of the detected flow rate Qo output from the signal extraction unit 122 is input to the first combination unit 124a. The first combination unit 124a outputs, for example, a difference obtained by subtracting the maximum value of the first correction amount Q1 corresponding to the first threshold value th1 from the AC component Qhpf of the detected flow rate Qo.

[0072] The second correction unit 125 receives, for example, the difference output from the coupling unit 124a. The second correction unit 125 outputs, for example, a second correction amount Q2 that corresponds to a half-wave rectified wave of the AC component Qhpf and increases with an increase in the ripple amplitude ratio PAR. The second correction unit 125 outputs the second correction amount Q2 until, for example, the ripple amplitude ratio PAR exceeds the first threshold value th1 and reaches the second threshold value th2.

[0073] Furthermore, for example, when the pulsation amplitude ratio PAR exceeds the second threshold th2, the second correction unit 125 limits the second correction amount Q2 to the second correction amount Q2 when the pulsation amplitude ratio PAR is the second threshold th2. More specifically, when the pulsation amplitude ratio PAR in the low pulsation amplitude range is 100% or less, the second threshold th2 can be set to the maximum value of the second correction amount Q2 for a pulsation amplitude ratio PAR of 100%, which is the upper limit of the low pulsation amplitude range where the pulsation error PAE increases.

[0074] The second combining unit 124b receives the first correction amount Q1 output from the first corrector 123 and the second correction amount Q2 output from the second corrector 125. The second combining unit 124b outputs a difference obtained by subtracting the second correction amount Q2 from the first correction amount Q1. The third combining unit 124c receives the difference between the first correction amount Q1 and the second correction amount Q2 output from the second combining unit 124b and the detected flow rate Qo, which is an output signal output from the calculation unit 121.

[0075] The combining unit 124c subtracts a correction amount CA based on the first correction amount Q1 from the detected flow rate Qo, which is an output signal. More specifically, the combining unit 124c subtracts the correction amount CA, which is obtained by subtracting the second correction amount Q2 from the first correction amount Q1, from the detected flow rate Qo, and outputs the result as a corrected flow rate Qc, which is the detected flow rate Qo after correction.

[0076] Fig. 10 is a graph showing an example of a change in the correction amount CA by the signal processing unit 120 of Fig. 8. As shown by the two-dot chain line in Fig. 10, the first correction amount Q1 increases at a constant rate until the pulsation amplitude ratio PAR reaches the first threshold th1, and is limited to a predetermined value when the pulsation amplitude ratio PAR exceeds the first threshold th1. On the other hand, as shown by the one-dot chain line in Fig. 10, the second correction amount Q2 increases at a constant rate until the pulsation amplitude ratio PAR reaches the second threshold th2 when the pulsation amplitude ratio PAR exceeds the first threshold th1, and is limited to a predetermined value when the pulsation amplitude ratio PAR exceeds the second threshold th2.

[0077] As a result, as shown by the solid line in Fig. 10, the absolute value of the correction amount CA increases with an increase in the pulsation amplitude ratio PAR until the pulsation amplitude ratio PAR reaches the first threshold th1. Furthermore, the absolute value of the correction amount CA decreases with an increase in the pulsation amplitude ratio PAR until the pulsation amplitude ratio PAR exceeds the first threshold th1 and reaches the second threshold th2. Furthermore, when the pulsation amplitude ratio PAR exceeds the second threshold th2, the absolute value of the correction amount CA becomes a minimum, for example, zero.

[0078] Fig. 11 is a graph showing the error between the corrected flow rate Qc by the signal processing unit 120 in Fig. 8 and the true flow rate Qt. In the air flow meter 100 of this embodiment, the signal processing unit 120 executes a process of adding the negative correction amount CA shown in Fig. 10 to the detected flow rate Qo, which is the output signal of the calculation unit 121, that is, a process of subtracting the correction amount CA from the detected flow rate Qo. As a result, the detected flow rate Qo in the low pulsation amplitude region in which the positive error from the true flow rate Qt increases as shown in Fig. 6 can be corrected to a corrected flow rate Qc that accurately follows the true flow rate Qt as shown in Fig. 11.

[0079] As described above, the air flow meter 100 of this embodiment is an air flow meter 100 that measures the flow rate of air as the measurement target gas 2 flowing through the main passage 22. As described above, the air flow meter 100 includes the flow rate detection element 111, the calculation unit 121, the signal extraction unit 122, the first correction unit 123, and the coupling unit 124c. The flow rate detection element 111 is installed in the sub-passage 234 that takes in air from the main passage 22 and returns it to the main passage 22, and outputs a detection signal DS according to the flow rate of air flowing through the sub-passage 234. The calculation unit 121 generates a detected flow rate Qo as an output signal according to the flow rate of air flowing through the main passage 22 based on the detection signal DS. The signal extraction unit 122 extracts an AC component Qhpf of the detected flow rate Qo as an output signal. The first correction unit 123 outputs a first correction amount Q1 that corresponds to a half-wave rectified wave of the AC component Qhpf and increases according to an increase in the pulsation amplitude rate PAR of the air flowing through the main passage 22. The combining unit 124c subtracts a corrected flow rate Qc based on the first correction amount Q1 from the detected flow rate Qo as an output signal.

[0080] With this configuration, the detected flow rate Qo of the air flow meter 100 is corrected with respect to the true flow rate Qt, thereby reducing the pulsation error PAE. More specifically, for example, a first threshold value th1 of the pulsation amplitude ratio PAR shown in Fig. 10 is set to an arbitrary pulsation amplitude ratio PAR in the low pulsation amplitude range where the pulsation error PAE is maximized. In this case, the correction amount CA corresponds to the half-wave rectified wave of the AC component Qhpf, and is a first correction amount Q1 that increases with an increase in the pulsation amplitude ratio PAR of the air flowing through the main passage 22.

[0081] This correction amount CA is subtracted from the detected flow rate Qo, which is the output signal of the calculation unit 121 of the air flow meter 100, in a range in which the pulsation amplitude rate PAR shown in Fig. 10 is equal to or less than the first threshold value th1. This makes it possible to reduce the pulsation error PAE of the corrected flow rate Qc of the air flow meter 100 in the pulsation amplitude rate PAR in the low pulsation amplitude range in which the pulsation error PAE increases. Therefore, according to this embodiment, it is possible to provide an air flow meter 100 that can measure the air flow rate with high accuracy even in an environment in which the pulsation of the air flowing through the main passage 22 is increasing.

[0082] Furthermore, in air flow meter 100 of this embodiment, first correction unit 123 outputs a first correction amount Q1 that increases with an increase in pulsation amplitude rate PAR until the pulsation amplitude rate PAR exceeds a first threshold value th1, for example, as shown in Fig. 10. Furthermore, when the pulsation amplitude rate PAR exceeds the first threshold value th1, first correction unit 123 limits the first correction amount Q1 to the first correction amount Q1 when the pulsation amplitude rate PAR is the first threshold value th1, for example.

[0083] With this configuration, the air flow meter 100 of this embodiment can correct the detected flow rate Qo, which is the output signal of the air flow meter 100, by limiting the pulsation amplitude ratio PAR in the low pulsation amplitude region where the pulsation error PAE increases. That is, at the pulsation amplitude ratio PAR in the high pulsation amplitude region, the pulsation error PAE of the detected flow rate Qo of the air flow meter 100 decreases more than the pulsation error PAE at the pulsation amplitude ratio PAR in the low pulsation amplitude region. Therefore, the first threshold value th1 is set to, for example, an arbitrary pulsation amplitude ratio PAR in the low pulsation amplitude region where the pulsation error PAE is maximized. As a result, at the pulsation amplitude ratio PAR in the high pulsation amplitude region where the pulsation error PAE decreases, the correction amount CA based on the first correction amount Q1 can be limited, and the error of the corrected flow rate Qc can be reduced by limiting it to the low pulsation amplitude region.

[0084] The air flow meter 100 of this embodiment further includes a second correction unit 125 that outputs a second correction amount Q2 that corresponds to a half-wave rectified wave of the AC component Qhpf of the detected flow rate Qo and increases with an increase in the pulsation amplitude rate PAR. The second correction unit 125 outputs the second correction amount Q2 that increases with an increase in the pulsation amplitude rate PAR until the pulsation amplitude rate PAR exceeds the first threshold value th1 and reaches the second threshold value th2. When the pulsation amplitude rate PAR exceeds the second threshold value th2, the second correction unit 125 limits the second correction amount Q2 to the second correction amount Q2 when the pulsation amplitude rate PAR is the second threshold value th2. The coupling unit 124c then subtracts the correction amount CA, which is obtained by subtracting the second correction amount Q2 from the first correction amount Q1, from the detected flow rate Qo as an output signal.

[0085] With this configuration, the air flow meter 100 of this embodiment can correct the detected flow rate Qo, which is the output signal of the air flow meter 100, by limiting the pulsation amplitude ratio PAR in the low pulsation amplitude region where the pulsation error PAE increases. That is, at the pulsation amplitude ratio PAR in the high pulsation amplitude region, the pulsation error PAE of the detected flow rate Qo of the air flow meter 100 is reduced more than the pulsation error PAE at the pulsation amplitude ratio PAR in the low pulsation amplitude region. Therefore, the first threshold th1 is set, for example, to an arbitrary pulsation amplitude ratio PAR in the low pulsation amplitude region where the pulsation error PAE is maximum, and the second threshold th2 is set, for example, to the upper limit value of the low pulsation amplitude region. As a result, at the pulsation amplitude ratio PAR in the high pulsation amplitude region where the pulsation amplitude ratio PAR is higher than the second threshold th2, the correction amount CA based on the first correction amount Q1 is offset and reduced by the second correction amount Q2, and the error of the corrected flow rate Qc can be reduced by limiting it to the low pulsation amplitude region.

[0086] Furthermore, in air flow meter 100 of this embodiment, calculation unit 121 uses inverse function model IFM to calculate detected flow rate Qo as an output signal from detection signal DS of flow detection element 111. With this configuration, air flow meter 100 of this embodiment can suppress variation in detected flow rate Qo caused by variation in detection signal DS of flow detection element 111.

[0087] As described above, according to this embodiment, it is possible to provide an air flow meter 100 that can measure the flow rate of air in the main passage 22 with high accuracy even in an environment where the air pulsation in the main passage 22 is increasing.

[0088] [Embodiment 2] Next, a second embodiment of the air flow meter according to the present disclosure will be described with reference to Fig. 12, with reference to Figs. 1 to 7 and Figs. 9 to 11 of the first embodiment described above. Fig. 2 is a block diagram of a signal processing unit 120 of the second embodiment of the air flow meter according to the present disclosure.

[0089] 12, the signal processing section 120 of the air flow meter 100 of this embodiment differs from that of the air flow meter 100 of the above-described first embodiment in that it further includes an average value output section 126, a first threshold value output section 127, and a second threshold value output section 128. The other configuration of the air flow meter 100 of this embodiment is similar to that of the air flow meter 100 of the above-described first embodiment, so similar parts are denoted by the same reference numerals and description thereof will be omitted.

[0090] The average value output unit 126 receives the detected flow rate Qo as an output signal output from the calculation unit 121. The average value output unit 126 is, for example, configured with a low pass filter (LPF), and outputs an average value Qlpf of the detected flow rate Qo as an output signal. The first threshold value output unit 127 receives the average value Qlpf of the detected flow rate Qo output from the average value output unit 126. The first threshold value output unit 127 multiplies the average value Qlpf of the detected flow rate Qo by a gain k1, for example, and outputs a first threshold value th1 proportional to the average value Qlpf.

[0091] The second threshold output unit 128 receives the average value Qlpf of the detected flow rate Qo output from the average value output unit 126. The second threshold output unit 128 outputs a second threshold th2 that increases according to the average value Qlpf of the detected flow rate Qo. More specifically, the second threshold output unit 128 includes, for example, a second threshold calculation unit 128a and a gain multiplication unit 128b.

[0092] The second threshold calculation unit 128a outputs a correction value that increases according to the average value Qlpf until the average value Qlpf reaches a predetermined threshold value th4, for example. When the average value Qlpf exceeds the predetermined threshold value th4, the second threshold calculation unit 128a outputs a correction value when the average value Qlpf is the predetermined threshold value th4. The gain multiplication unit 128b receives the correction value output from the second threshold calculation unit 128a. The gain multiplication unit 128b outputs a second threshold value th2 obtained by multiplying the input correction value by a gain k2.

[0093] As described above, the air flow meter 100 of this embodiment further includes an average value output unit 126, a first threshold value output unit 127, and a second threshold value output unit 128 in addition to the configuration of the air flow meter 100 of the above-mentioned embodiment 1. The average value output unit 126 outputs the average value Qlpf of the detected flow rate Qo, which is the output signal of the calculation unit 121. The first threshold value output unit 127 outputs a first threshold value th1 proportional to the average value Qlpf. The second threshold value output unit 128 outputs a second threshold value th2 that increases as the average value Qlpf increases.

[0094] With this configuration, air flow meter 100 of the present embodiment can change the first threshold value th1 and the second threshold value th2 of the pulsation amplitude rate PAR according to the average value Qlpf of the detected flow rate Qo output from the calculation unit 121. Therefore, air flow meter 100 of the present embodiment can not only achieve the same effects as air flow meter 100 of the above-described first embodiment, but also determine appropriate first threshold value th1 and second threshold value th2 according to the average value Qlpf of the detected flow rate Qo.

[0095] Although an embodiment of the air flow meter according to the present disclosure has been described in detail above using the drawings, the specific configuration is not limited to this embodiment, and even if there are design changes and the like within the scope that does not deviate from the gist of the present disclosure, they are included in the present disclosure. [Explanation of symbols]

[0096] 2. Gas to be measured (air) 22 Main aisle 100 Air Flow Meter 111 Flow detection element 121 Arithmetic section 122 Signal Extraction Unit 123 First Correction Section 124a Joint 125 Second Correction Section 126 Average value output section 127 First threshold output unit 128 Second Threshold Output Unit 234 Sub-aisle CA correction amount DS detection signal IFM Inverse Function Model PAR pulsation amplitude rate Q1 1st correction amount Q2 2nd correction amount Qhpf AC component Qlpf average value Qo Detected flow rate (output signal) th1 First threshold th2 Second threshold

Claims

1. An air flow meter for measuring a flow rate of air flowing through a main passage, a flow rate detection element that is installed in a sub-passage that takes in the air from the main passage and returns the air to the main passage, and outputs a detection signal corresponding to a flow rate of the air flowing through the sub-passage; a calculation unit that generates an output signal corresponding to a flow rate of air flowing through the main passage based on the detection signal; A signal extraction unit that extracts an AC component of the output signal; a first correction unit that outputs a first correction amount that corresponds to a half-wave rectified wave of the AC component and increases in accordance with an increase in a pulsation amplitude rate of air flowing through the main passage; a coupling unit that subtracts a correction amount based on the first correction amount from the output signal.

2. The first correction unit is outputting the first correction amount until the pulsation amplitude ratio exceeds a first threshold value; 2. The air flow meter according to claim 1, wherein when the pulsation amplitude rate exceeds the first threshold value, the first correction amount is limited to the first correction amount when the pulsation amplitude rate is the first threshold value.

3. A second correction unit that outputs a second correction amount that corresponds to a half-wave rectified wave of the AC component and increases according to an increase in the pulsation amplitude rate, The second correction unit is outputting the second correction amount until the pulsation amplitude ratio exceeds the first threshold value and reaches a second threshold value; When the pulsation amplitude ratio exceeds the second threshold value, the second correction amount is limited to the second correction amount when the pulsation amplitude ratio is the second threshold value, 3. The air flow meter according to claim 2, wherein the combining unit subtracts the second correction amount from the first correction amount from the output signal.

4. an average value output unit that outputs an average value of the output signal of the calculation unit; a first threshold output unit that outputs the first threshold value that is proportional to the average value; The air flow meter according to claim 3 , further comprising: a second threshold output unit that outputs the second threshold value that increases in accordance with an increase in the average value.

5. 2. The air flow meter according to claim 1, wherein the calculation unit calculates the output signal from the detection signal using an inverse function model.

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