JP5425021B2 - Flow measuring device - Google Patents

Description

  The present invention relates to a flow rate measuring device including a sensor element that detects a flow rate of fluid in a sub-passage, and more particularly to a flow rate measuring device suitable for measuring an intake air amount in an intake pipe of an automobile engine.

  As a flow measurement device that measures the air flow rate, the heating resistor is heated and the flow rate is measured by the amount of heat released from the heating resistor, or the heating resistor is heated and the temperature sensitive resistor is placed near the heating resistor. What measures a flow volume by the temperature change of a body is known.

  And it is used as an apparatus which measures flow volume by arrange | positioning a heating resistor (henceforth a sensor element) in the subchannel | path arrange | positioned at the main channel | path. In general, in order to reduce the variation in air flow characteristics for the purpose of improving measurement accuracy, the wall of the passage facing the sensor element installed in the sub passage is gradually narrowed (constricted) from upstream to downstream. It is known to use a simple aperture shape. As a result, the flow velocity near the sensor element can be improved and the flow can be rectified.

  For example, Patent Document 1 discloses a technique in which a sensor element is disposed in a sub-passage and a flow shape is rectified by disposing a diaphragm shape on a wall surface facing the sensor element. According to this technique, when the level difference D of the sensor element detection unit, the width L of the sensor element, and the average gradient α of the diaphragm are set, the fluid (air) flowing through the sensor element within a range where the relational expression L> Dα is satisfied. The flow can be rectified, thereby suppressing variations due to mounting.

JP 2008-26172 A

  By the way, in recent measurement of the air flow rate, higher accuracy of measurement is required. Variations in the mounting of sensor elements in the manufacturing process can affect the characteristics.

  However, for example, in the case of the technology of Patent Document 1, as described above, the average gradient of the wall diaphragm facing the sensor element disposed in the sub-passage is α, the sensor element width L, the step difference D between the substrate and the sensor element, and However, when the position of the measuring unit is deviated within a tolerance range, for example, the flow velocity distribution changes due to this deviation ( The flow velocity fluctuates) and causes measurement errors.

  In order to reduce the influence of this variation, it is desirable to further improve the flow velocity. To improve the flow velocity, for example, the distance between the top of the projecting portion (the narrowest portion of the diaphragm) and the sensor element (the diaphragm) ) May be narrowed. However, if the interval (throttle) interval is too narrow, the pressure loss in the sub-passage increases, and the flow velocity in the vicinity of the sensor element becomes rather slow.

  In addition, when using a flow measurement device for measuring the intake air of an engine, foreign matter that has passed through the air cleaner filter may accumulate near the measurement unit. It is also assumed that

  The present invention has been made in view of the above points, and the present invention is a flow measuring device having a sensor element in a sub-passage in which a throttle shape is provided at a position facing the sensor element. Another object of the present invention is to provide a flow rate measuring device capable of satisfying both of the rectification effect by the improvement of the flow velocity and the countermeasure against contamination.

  In order to solve the above problems, a flowmeter side device according to the present invention includes a housing in which a sub-passage through which a part of the fluid flows in and passes along the flow direction of the fluid is formed in the main passage. The sensor element for detecting the flow rate of the fluid is mounted on the surface, and at least a plate-like substrate disposed in the sub-passage so that the surface is formed along the flow direction. Of the sub-passage wall surface of the housing forming the sub-passage, the opposing wall surface on the side facing the sensor element is adapted to approach the surface of the sensor element as it approaches the sensor element along the flow direction. A protruding portion having an inclined inclined surface is formed, and the inclined surface protrudes from the surface of the sensor element so as to restrict a flow of fluid flowing upstream of the sensor element by the inflowing fluid. It is characterized in that it is inclined so that a separation vortex is formed on this side.

  According to the present invention, the separation vortex is generated from the surface of the sensor element to the side of the protrusion, downstream from the terminal end (end near the sensor element) of the inclined surface of the protrusion. The flow of the fluid flowing through the fluid is restricted, and the passage area (passage cross-sectional area) of the fluid can be indirectly reduced.

  By using such a separation vortex, the flow rate of the rectified fluid flowing through the sensor element that is the measurement unit can be further improved, and stable measurement can be performed even if mounting deviation occurs in the measurement unit. be able to.

  Further, in order to increase the fluid flow rate in the vicinity of the sensor element, it is not necessary to further reduce the distance between the sensor element and the projecting portion. This can prevent clogging and prevent pollution.

1 is a schematic overall configuration diagram of a flow rate measuring device according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view of the flow rate measuring device shown in FIG. QQ arrow sectional drawing of the flow measuring device shown in FIG. The figure for demonstrating the rectification effect of the flow measuring device shown in FIG. It is the analysis result for confirming the rectification effect of the flow measuring device concerning a 1st embodiment, (a) is a figure showing the analysis result concerning the example of the 1st embodiment, and (b), The figure which showed the analysis result concerning a comparative example. It is the figure which showed the rectification | straightening effect of the flow measuring device shown in FIG. 1, and the figure which showed the graph of the relationship between angle (alpha) and a measurement error. The figure which shows a mode that the foreign material adhered in the protrusion part (throttle shape) of the flow measuring apparatus shown in FIG. The figure which showed the graph of the relationship between the angle (alpha) which considered foreign material adhesion, and the measurement error in the protrusion part (throttle shape) of the flow measuring device shown in FIG. Sectional drawing of the flow measuring device of 2nd Embodiment equivalent to PP sectional drawing of FIG. 1 of 1st Embodiment type | system | group. FIG. 10 is a partially enlarged view of the vicinity of the sensor element of the flow rate measuring device shown in FIG. 9. Sectional drawing of the flow measuring device of 2nd Embodiment corresponded in the QQ arrow sectional drawing of FIG. 1 of 1st Embodiment type | system | group.

  Below, with reference to FIGS. 1-11, the flow volume measuring apparatus which concerns on this invention is demonstrated by two embodiment.

[First Embodiment]
1-3 is a figure which shows the structure of the flow measuring device which concerns on 1st Embodiment of this invention, FIG. 1 is a typical whole block diagram of the flow measuring device which concerns on 1st Embodiment of this invention. 2 is a cross-sectional view taken along the line PP of the flow rate measuring device shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line QQ of the flow rate measuring device shown in FIG.

  4 is a diagram for explaining the rectifying effect of the flow rate measuring device shown in FIG. 1, and FIG. 5 is an analysis result for confirming the rectifying effect of the flow rate measuring device according to the first embodiment. These are the figures which showed the analysis result which concerns on the Example of 1st Embodiment, (b) is the figure which showed the analysis result which concerns on a comparative example.

  As shown in FIG. 2, the flow rate measuring apparatus 1 according to the present invention includes an assembly of a frame member 2 made of a resin molded product and a base member 3 covering the frame member as a housing 20. By forming the housing 20 as an assembly, a part of the fluid in the main passage 6 flows and a sub-passage 10 is formed for the passage. Such a housing 20 is inserted into the insertion hole 5 formed in the intake pipe 4 shown in FIG. 1 and is attached to the intake pipe 4 so that the lower portion is located in the main passage 6 of the intake pipe 4. Yes.

  The base member 3 is mounted with a circuit in which electronic components and wiring patterns are formed on a flat circuit board (plate board) 7 and a sensor element 8 which is a heating resistor on a silicon substrate. The frame member 2 is superposed on the frame member 2 and connected to a connector portion 9 having a power source, a signal output terminal 9a, and a guide 9b. Note that the sensor element 8 is a thermal sensor element for detecting the flow rate of air (fluid) in the main passage 6 by heat generation resistance, and the sensor element 8 itself is fluid (air) flowing in the sub-passage 10. FA is measured directly.

  By installing the above-described housing 20 in the main passage 6 of the fluid flowing through the intake pipe 4, the sub-passage 10 is formed at the position of the lower portion in the main passage 6. The sub-passage 10 is arranged along the flow direction F of the main passage 6 (the same direction as the main passage) so that a part of the fluid flowing through the main passage flows in and passes therethrough. A sensor element 8 for measuring a flow rate is positioned on the circuit board 7 in the sub passage 10.

  Thus, in the flow measuring device 1, the housing 20 is formed with the sub-passage 10 through which a part of the fluid flows in and passes through the main passage 6 along the flow direction F in which the fluid flows. The (plate-like substrate) 7 is mounted in the sub-passage so that the sensor element 8 for detecting the flow rate of the fluid is mounted along the surface and the surface of the plate-like substrate is formed along the flow direction F. Will be.

  In the present embodiment, there is a characteristic part in that a passage shape (aperture shape) as shown in FIG. 3 is further provided. Specifically, the sub passage 10 is formed by overlapping the frame member 2 and the base member 3 as shown in FIG. 2, and the circuit board 7 is mounted on the base member 3.

  A trapezoidal protruding portion 11 is formed on the opposing wall surface 10 d on the side facing the sensor element 8 of the auxiliary passage wall surface of the housing 20 (specifically, the frame member 2) forming the auxiliary passage 10. It is formed over the width direction. Further, an inclined surface 11 a is formed on the upstream side of the protruding portion 11, and is inclined so as to approach the surface of the sensor element 8 as it approaches the sensor element 8 along the flow direction F.

  Further, as shown in FIG. 4, the inclined surface 11 a is formed by the fluid flowing in the sub-passage 10 so that the fluid flow Fa flowing upstream of the sensor element 8 is narrowed from the surface 8 a of the sensor element 8. It is inclined so that a separation vortex Fc is formed on the side.

  Here, the projecting portion 11 has a trapezoidal diaphragm shape that is symmetric with respect to the center of the sensor element 8, but the shape is not limited to this shape as long as the separation vortex Fc is formed. Absent.

  Further, as described above, the circuit board 7 has a structure mounted on the base member 3. The sensor element 8 is disposed on the lower side of the circuit board 7 (see FIG. 1). In the flow measuring device 1, a part of the fluid Fa in the main passage 6 flows into the sub-passage, and the sensor element 8 The flow rate of the fluid flowing through the upper part is measured.

  Until now, the air flow cannot be rectified by simply flowing air through the sub-passage 10 and the flow velocity cannot be improved. Therefore, a throttle shape is formed on the side wall surface (frame member 2) opposite to the wall surface on which the sensor element 8 is mounted. It has been. However, this throttle shape is caused by narrowing the flow of fluid flowing upstream due to the throttle shape itself (for example, by narrowing so as to satisfy the relationship L> Dα described in Patent Document 1). The flow of the fluid is rectified on the surface of the sensor element 8, but this alone is not sufficient for improving the flow velocity, and is thus configured as in the present embodiment.

  With such a configuration, a separation vortex Fc is generated from the surface of the sensor element 8 to the side of the protruding portion 11 by the end portion (end portion close to the sensor element) 11d of the inclined surface 11a of the protruding portion 11. The fluid flow Fa flowing upstream of the sensor element 8 can be narrowed (the passage area of the fluid can be narrowed).

  By using such a separation vortex Fc, the flow velocity of the rectified fluid flowing through the sensor element 8 that is a measurement unit can be further improved, and stable measurement is possible even if mounting deviation occurs in the measurement unit. It can be.

  Furthermore, since it is not necessary to further reduce the distance L between the sensor element 8 and the protruding portion 11 in order to increase the fluid flow velocity in the vicinity of the sensor element 8, it is possible to sufficiently secure the distance between the throttles. It can prevent clogging of foreign substances in the air and can be a countermeasure against contamination.

  As long as the fluid flow Fa flowing upstream can be narrowed by such a separation vortex Fc, the detailed inclination and shape of the inclined surface are not particularly limited. Further, the inventors conducted analysis using a thermal fluid model using a general-purpose fluid analysis program STAR-CD (manufactured by CD-adapco-japan), and as shown in the example of FIG. It was confirmed that a separation vortex Fc that restricts the flow Fa of the fluid flowing upstream was formed, and this was also confirmed by experiments. Further, as shown in the comparative example of FIG. 5 (b), it is not possible to restrict the fluid flow Fa flowing upstream simply by providing a protrusion under the conditions shown in Patent Document 1 described above. confirmed. In addition, the same code | symbol as the structure corresponding to FIG. 4 is attached | subjected to each structure (part) of FIG. 5 (a) and (b).

  From the above analysis, a more preferable condition for deriving the fluid flow Fa flowing upstream from the separation vortex Fc was derived. Specifically, by optimizing the aperture angle α and the aperture interval L shown in FIG. 4, a shape that can be stably measured even when the mounting of the sensor element 8 varies analytically and experimentally. I found it. Here, the throttle angle α shown in FIG. 4 is an angle formed by the inclined surface 11a and a plane perpendicular to the flow direction F, and the throttle interval L is the top surface 11b of the protrusion 11 and the sensor element. This is the distance to the surface of 8.

  Specifically, first, the aperture interval L is preferably set to 2.0 mm or less from the viewpoint of rectifying the flow and performing stable measurement. If this exceeds 2.0 mm, even if a separation vortex is formed, a sufficient flow velocity (rectification effect) due to contraction and flow due to the separation vortex cannot be obtained, which greatly affects the measurement error of the air flow rate. It is to become.

  For the aperture distance L of 2.0 mm or less, the optimum aperture angle α for forming the separation vortex Fc is preferably 20 ° or less with respect to the flow vertical direction. In the embodiment shown in FIG. 5A, the aperture angle α is 20 ° or less and the aperture interval L is 2 mm or less. In the embodiment shown in FIG. 5B, the aperture angle α exceeds 20 °. The throttle interval L is 2 mm or less, and the flow velocity of the fluid measured in each is assumed to be 56 m / s. In addition, it analyzed in the range of the flow velocity of the fluid which flows through the intake pipe of an internal combustion engine, and confirmed that the rectification effect said by this embodiment was expressed.

  Then, through actual machine tests, a plurality of flow rate measuring devices selected for a plurality of aperture angles were prepared for each angle, and found from the relationship between a plurality of aperture angles and measurement errors for each aperture angle. . FIG. 6 is a diagram showing the rectification effect of the flow rate measuring device according to this embodiment, and is a diagram showing a graph of the relationship between the angle α and the measurement error.

  Here, the error X, which is a variation in mounting, is an error with respect to the actual air flow rate that occurs when the position of the sensor element is shifted from the position of the diaphragm. The error X is a value normalized with the error value at 20 ° being 1. As shown in FIG. 6, as can be seen from the analysis results, the variation error X is small when the aperture angle α is 20 ° or less. The cause of this is that a separation vortex Fc is generated at the end portion 11d of the convex portion (diaphragm), and a flow such as rectification Fb is caused to flow on the surface of the sensor element 8, and the flow velocity is further improved as compared with the conventional one. Because. This is considered to have been able to reduce the influence of variation due to mounting.

  This effect will be described below. The projecting portion 11 having a throttle shape has a shape having an inclined surface that is steeper than that of the conventional one, and a separation vortex Fc is generated at the terminal end portion 11d of the projecting portion (throttle) 11. Even if not, since the air cannot pass through the region where the separation vortex Fc exists, the substantial effective sectional area becomes small. As a result, the flow velocity flowing through the sensor element 8 is improved, so that even if the mounting position of the sensor element 8 varies somewhat, the degree of influence on measurement is reduced, and stable measurement is possible. That is, the smaller the throttle angle α, the more effective the rectification, and the flow rate measurement accuracy can be improved.

  By the way, when the vehicle is actually attached to the intake system and traveled, foreign objects such as carbon and dust cannot be avoided. FIG. 7 is a diagram showing a state in which foreign matter has adhered to the protruding portion (throttle shape) of the flow rate measuring device shown in FIG. 1, and when this foreign matter enters, the throttle angle α is suddenly (too small). It is assumed that the flow velocity in the vicinity of the measurement unit may change due to the foreign substance C accumulating on the aperture start unit 11c and changing its shape. Actually, the accumulation of the foreign substance C becomes a measurement error of the air flow rate, but this effect is minimized, and it was found by the following experiment that the range in which the measurement error is saturated is 10 ° or more.

  Specifically, a flow measuring device selected for a plurality of throttle angles was prepared, and a change (error) with respect to deterioration with time was obtained by an actual machine test.

  FIG. 8 is a diagram showing a graph of the relationship between the angle α taking account of foreign matter adhesion and the measurement error in the aperture shape of the invention, and the error X is normalized by setting the error value at 10 ° to 1. Value.

  From this result, the aperture angle where the influence of contamination is small is 10 ° or more, and it is optimal to use at this angle or more under actual vehicle conditions. When the aperture angle is optimized including the influence of characteristics due to contamination, it can be said that the aperture angle α is better in the range of 10 ° to 20 °.

[Second Embodiment]
The second embodiment is different from the first embodiment in that the sensor element 8 is exposed in the sub air passage and the sub passage is divided into two by the circuit board (plate-like substrate) 7. Therefore, this difference will be described with reference to the following drawings. The same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

  FIG. 9 is a cross-sectional view of the flow rate measuring device of the second embodiment corresponding to the cross-sectional view taken along the line P-P of FIG. 1 of the first embodiment. 10 is a partially enlarged view of the vicinity of the sensor element of the flow rate measuring device shown in FIG.

  FIG. 11 is a cross-sectional view of the flow rate measuring device according to the second embodiment corresponding to the cross-sectional view taken along the line QQ in FIG. 1 of the first embodiment.

  As described above, the flow rate measuring device 1 ′ shown in FIG. 9 is the frame member 2 made of a resin molded product and the housing 20 ′ of the base member 3 covering the frame member. The housing 20 ′ is the intake pipe shown in FIG. 4 and the lower part is located in the main passage 6. In the sub passage 10 ′, the base member 3 has a concave shape so that both surfaces of the circuit board 7 are exposed to the sub passage 10.

  As in the first embodiment, the base member 3 includes a circuit in which electronic components and wiring patterns are formed on a flat circuit board (plate-like board) 7, and a sensor element that is a heating resistor on the silicon substrate. 8 are mounted on the frame member 2 so as to be connected to a connector 9 having a power source, a signal output terminal 9a, and a guide 9b.

  As shown in FIG. 10, in the portion where the sub-passage 10 'is formed, the circuit board 7 is disposed at a position where the sub-passage 10' is divided in the sub-passage 10 '. That is, the circuit board 7 (plate-like board) divides the fluid flowing in the sub-passage 10 'into two flows.

  Further, as shown in FIG. 10, the circuit board 7 has a passage cross-sectional area S1 of the sub-passage 10A that flows on the surface 7a side of the circuit board 7 on which the sensor element 8 is mounted, of the two divided flows. The circuit board 7 on which the element 8 is not mounted is disposed so as to be smaller than the passage cross-sectional area S2 of the sub-passage 10B flowing on the back surface 7b side. That is, as shown in FIG. 11, the distance D1 on the sensor element measurement side / the distance D2 on the back side of the substrate is less than 1.

  Further, the sensor element 8 is disposed below the circuit board 7, and a part of the fluid Fa in the main passage 6 flows into the sub-passage 10 ′, and the flow rate of the fluid flowing over the sensor element 8 Measure. The frame member 2 is provided with a protruding portion (aperture shape) 11 as in the first embodiment.

  As described above, the circuit board 7 divides the sub passage into the sensor element measurement side and the back side of the substrate, whereby the fluid can easily flow into the sub passage 10B having a larger cross-sectional area than the cross-sectional area S1 of the sub passage 10A. A large amount of contaminated material that has entered the sub-passage 11 </ b> B flows to reduce dust and fouling substances contained in the fluid that passes through the sensor element 8. Thereby, it is possible to take measures against foreign matters and measure the stability of measurement accuracy.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed.

  For example, in the first and second embodiments, a method for manufacturing a thermal air flow meter has been presented. However, the air flow measuring element may be, for example, a pressure type flow measuring element, and is limited to a thermal type. For example, an air flow meter such as a pressure type or an ultrasonic type may be used.

1, 1 ': Flow rate measuring device 2: Frame member 3: Base member 4: Intake pipe 5: Insertion hole 6: Main passage 7: Circuit board (plate-like board)
8: Sensor element 9: Connector portion 10, 10 ′: Sub-passage 10A, 10B: Divided sub-passage 10a: Upstream opening 10b: Measurement passage 10c: Downstream opening 10d: Opposing wall 11: Projection ( Aperture shape)
11a: inclined surface 11b: top surface 11c: start portion 11d: end portion 20, 20 ': housing Fa: flow of fluid flowing upstream of the sensor element Fb: rectification Fc: separation vortex C: foreign matter F: flow direction α: restriction angle

Claims (4)

A housing in which a sub-passage through which a part of the fluid flows in and passes along the flow direction of the fluid is formed in the main passage, and a sensor element for detecting the flow rate of the fluid are mounted on the surface, A flow rate measuring device comprising at least a plate-like substrate disposed in the sub-passage so that a surface is formed along a flow direction,
Of the sub-passage wall surface of the housing forming the sub-passage, the opposing wall surface on the side facing the sensor element is adapted to approach the surface of the sensor element as it approaches the sensor element along the flow direction. A protruding portion having an inclined inclined surface is formed, and the inclined surface causes a separation vortex from the surface of the sensor element to the protruding portion so as to restrict a flow of fluid flowing upstream of the sensor element. A flow rate measuring device which is inclined so as to be formed.   The angle formed between the inclined surface and a plane perpendicular to the flow direction is 20 ° or less, and the distance between the top surface of the protrusion and the surface of the sensor element is 2 mm or less. The flow rate measuring device according to claim 1.   The flow rate measuring device according to claim 1 or 2, wherein an angle formed by the inclined surface and a plane perpendicular to the flow direction is 10 ° or more. The plate-like substrate divides the fluid flowing in the sub-passage into two flows; and
Of the two divided flows, the cross-sectional area of the sub-passage that flows on the surface side of the plate-like base material on which the sensor element is mounted is the back side of the plate-like base material on which the sensor element is not mounted. The flow rate measuring device according to claim 1, wherein the flow rate measuring device is disposed so as to be smaller than a cross-sectional area of the sub-passage flowing through the sub-passage.

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