JP2010197322A - Air flow rate measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air flow rate measuring device 1 improving measurement detection accuracy of an air flow rate by suppressing deposition of intake dust on the upstream/downstream ends of a chip support member, concerning a thermal air flow rate measuring device having a chip sensor structure. <P>SOLUTION: A bypass flow is formed by taking a part of air flowing along the main channel 6 of an intake pipe 2 into a bypass channel 7 of a sensor body 3, and besides a sub-bypass flow is formed by taking a part of the bypass flow into a sub-bypass channel 8 deflected approximately rectangularly. A flow rate measuring element 40 having a chip sensor structure of a flow rate sensor 4 is disposed in a direction orthogonal to the sub-bypass flow. The upstream end 44 of the support member 43 of the flow rate sensor 4 is arranged slantingly with respect to the sub-bypass flow. Hereby, a split flow to a tilt direction of the flow is generated, and generation of a stagnation of the flow is suppressed, to thereby suppress deposition of intake dust. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an air flow rate measuring device that is disposed inside an intake passage and measures the flow rate of air.

[Conventional technology]
2. Description of the Related Art Conventionally, a thermal flow rate measuring device that measures an air flow rate based on a heat release amount of a heating resistor is known, and is employed as an air flow meter that measures a flow rate of intake air of an internal combustion engine for an automobile (for example, , See Patent Document 1).

  This air flow meter (air flow measuring device) has a sensor body disposed in an intake passage of an internal combustion engine, and a bypass passage that takes in part of the air flowing through the intake passage into the sensor body, and the bypass passage A flow rate sensor for measuring the amount of intake air is disposed inside. The flow sensor has a chip sensor structure of a heating element and a temperature sensing element made of a thin film resistor formed on the surface of a semiconductor substrate, and the chip sensor is embedded in the sensor support member and bypassed in the bypass flow path. It arrange | positions so that it may be orthogonal to the streamline of a flow.

  Then, a circuit for controlling the chip sensor is configured, and the resistance value difference between the upstream and downstream temperature sensing elements that transfer heat from the heating element that generates heat at a constant temperature according to the ambient temperature is output as an electrical signal (for example, a voltage signal). To do. This detection signal is input to the ECU, and the air flow rate is calculated by the ECU.

  Here, as shown in FIG. 5, the arrangement of the chip sensor 101 and the chip support member 102 in the conventional air flow measuring device 100 is such that part of the air (main flow) flowing through the intake passage 103 is not deflected. Directly on the inlet side of the bypass flow path 104 that flows in, orthogonal to the bypass flow and parallel to the streamline direction so that the bypass flow is along the front and back surfaces of the chip sensor 101 and the chip support member 102. The

  Further, as shown in FIG. 5 (b), the tip support member 102 has a chamfered or arcuate chamfered upstream end portion 105 and downstream end portion 106 that are orthogonal to the bypass flow. The flow is not disturbed or separated. Therefore, the bypass flow draws a smooth streamline perpendicular to the chip sensor 101 and flows out downstream through the two U-turn configuration. At this time, the air flow rate is detected by the chip sensor 101 exposed to the bypass flow.

[Problems with conventional technology]
However, in the air flow measuring device of this structure, the bypass flow is directly introduced into the bypass flow path without being deflected, and the chip sensor is orthogonal to the flow line of the bypass flow. Even relatively large and heavy objects may accumulate in the stagnation part that occurs perpendicular to the flow.

  As shown in FIG. 6B, the intake dust accumulates irregularly on the tapered or arcuate portion of the upstream end portion 105 of the sensor support member 102, so that the flow line of the bypass flow changes. If the generated vortex or the like just overlaps the chip sensor position, the detection characteristics of the chip sensor change. FIG. 6 (c) is a graph showing the change in detection characteristics after the dust test in the actual air flow measurement device with respect to the actual flow rate. According to this, the detection characteristic becomes negative in the region where the flow rate is small. It turns out that it changes greatly. That is, there is a problem that the detection error becomes large in a small flow rate region.

JP 2005-156570 A

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to suppress the accumulation of intake dust on the upstream and downstream ends of the chip support member in the thermal air flow measurement device having the chip sensor structure. Thus, an object of the present invention is to provide an air flow rate measuring device capable of improving the accuracy of measurement and detection of air flow rate.

[Means of Claim 1]
According to the first aspect of the present invention, the bypass passage that takes in part of the air flowing through the air passage, and the bypass passage, the passage cross-sectional area gradually decreases toward the outlet of the bypass passage. An inlet is provided on one side of a predetermined radial direction of the bypass passage, which is provided on the upstream side of the throttle portion and branched from the bypass passage and orthogonal to the flow direction of the air flowing through the bypass passage. In an air flow rate measuring device having a sub-bypass channel that takes in part of the air flowing through the channel, and a flow rate sensor that is disposed in the sub-bypass channel and measures the flow rate of air flowing through the sub-bypass channel, The flow sensor has a pair of thermal flow measurement elements made of a thin film resistor formed on the surface of a semiconductor substrate, and the thermal flow measurement element is a flat support member whose longitudinal direction is coaxial with the semiconductor substrate. To support The thermal flow rate measuring element is orthogonal to the flow direction of the air flowing through the sub-bypass channel, and the upstream end of the support member is inclined to the flow direction of the air flowing through the sub-bypass channel. It is characterized by that.

  Thereby, the flow along the inclined surface is always generated at the upstream end portion of the support member, the generation of the stagnation portion of the flow is eliminated, and the intake dust floats without adhering and flows away with the flow. Therefore, dust accumulation at the upstream end can be suppressed, and the measurement and detection accuracy of the air flow rate can be improved.

[Means of claim 2]
According to the second aspect of the present invention, the downstream end of the support member is disposed so as to be inclined in the direction opposite to the flow direction of the air flowing through the sub-bypass channel.

  As a result, even when a transient backflow due to engine pulsation occurs in the intake flow path, dust accumulation on the downstream end of the support member of the intake dust due to the backflow can be suppressed, and the backflowing air The measurement and detection accuracy of the flow rate can be improved.

[Means of claim 3]
According to the means described in claim 3, the inclination angle formed by the upstream end portion and the downstream end portion of the support member and the flow direction of the air flowing through the sub-bypass channel is 20 to 40 degrees. It is said.
Accordingly, it can be said that the setting range of the inclination angle is preferably 20 to 40 degrees from the trade-off relationship between the deterioration characteristic amount due to dust accumulation due to the inclination angle and the output characteristic change amount. Within this inclination angle range, it is possible to prevent the accumulation of dust and suppress the deterioration characteristic amount to the minimum value without causing a decrease in the output characteristics of the flow rate measuring element.

(Example 1) which is a fragmentary sectional view of an air flow measuring device. The flow sensor of the principal part of an air flow measuring device is shown, (a) is a top view, (b) is a flow characteristic view (Example 1). (Example 1) which is the characteristic diagram which described the deterioration characteristic amount by dust accumulation, and the output characteristic change amount with respect to inclination-angle (theta) of the supporting member of the flow sensor of an air flow measuring device. The structure of an air flow rate measuring apparatus is shown, (a) is a fragmentary sectional view, (b) is an expansion detailed top view of the flow sensor of the principal part (Example 2). The structure of an air flow measuring device is shown, (a) is a fragmentary sectional view, (b) is a XX sectional view, (c) is a ZZ sectional view (conventional example). The operation and characteristics of the flow sensor of the air flow measuring device are shown, (a) is the initial air flow, (b) is the air flow during dust accumulation, and (c) is the detection after the dust test. It is a characteristic view which showed the characteristic change (conventional example).

  The best mode of the present invention will be described together with Example 1 shown in the drawings.

[Configuration of Example 1]
1 to 3 show a first embodiment of the present invention, and FIG. 1 is a partial cross-sectional view showing a configuration of an air flow rate measuring apparatus. FIG. 2 shows a flow sensor of the main part of the air flow rate measuring device shown in FIG. 1, (a) is a plan view, and (b) is a flow characteristic diagram. FIG. 3 is a characteristic diagram in which the deterioration characteristic amount due to dust accumulation and the output characteristic change amount are shown together with the inclination angle θ of the support member of the flow rate sensor of the air flow rate measuring device.

  An air flow rate measuring apparatus 1 shown in this embodiment measures, for example, an intake air (intake) amount of an internal combustion engine (hereinafter referred to as an engine) for an automobile. As shown in FIG. Is detachably attached to the intake pipe 2 that forms an air passage to be connected by a plug-in method.

  The air flow rate measuring device 1 includes a sensor body 3, a flow rate sensor 4, a circuit module 5, and the like. The sensor body 3 is inserted into the intake pipe 2 through an attachment hole formed in the pipe wall of the intake pipe 2 that forms the main flow path 6. The sensor body 3 includes a cylindrical cylindrical body 3a and a rectangular parallelepiped box body 3b provided integrally with the cylindrical body 3a. The cylindrical body 3a has a bypass passage 7 for taking in a part of air (hereinafter referred to as main flow) flowing from the left side to the right side of the intake pipe 2 in the drawing, and the box-type body 3b has this bypass. A sub-bypass channel 8 that takes in a part of the air flowing through the channel 7 (hereinafter referred to as bypass flow) is formed.

  The bypass channel 7 has an inlet 9 that opens at the center of the front end of the cylindrical body 3a and an outlet 10 that opens at the center of the rear end of the cylindrical body 3a, and is formed linearly from the inlet 9 to the outlet 10. Has been. Further, on the outlet side of the bypass channel 7, a tapered throttle portion 14 is provided that gradually decreases the channel cross-sectional area of the bypass channel 7 toward the outlet 10.

  The sub-bypass channel 8 has an inlet 12 branched from the bypass channel 7 on the upstream side of the narrowed portion 14 of the bypass channel 7 and an outlet 13 formed in an annular shape around the outlet 10 of the bypass channel 7. A U-turn portion is provided between the inlet 12 and the outlet 13 so that the air flow direction changes 180 degrees (U-turn).

  The flow sensor 4 measures the flow rate of the air flowing through the sub-bypass channel 8 and outputs it as an electrical signal (for example, a voltage signal). For example, the heating element is formed on the surface of the semiconductor substrate with a thin film resistor. And a flow rate measuring element having a chip sensor structure composed of a temperature sensitive element, and these elements are connected to a circuit board (not shown) built in the circuit module 5.

  The flow sensor 4 is disposed at a predetermined position downstream of the inlet 12 of the sub bypass flow path 8. In this embodiment, the sub-bypass passage 8 is disposed at the approximate center of the U-turn portion, but may be disposed in a straight pipe portion upstream from the U-turn portion and downstream from the inlet 12.

  Further, the circuit module 5 is integrally provided on the other end side of the sensor body 3 and is disposed outside the attachment hole of the intake pipe 2. The circuit module 5 controls the temperature of the heat generating element and the output detected by the temperature sensitive element.

  Here, in this embodiment, the flow sensor 4 of the present invention is characterized in that the upstream end portion of the support member that supports the flow rate measuring element of the chip sensor structure is provided with an inclination to suppress the accumulation of intake dust due to the flow. It is said. Below, it demonstrates in detail based on FIG.

  As shown in FIG. 2A, the temperature sensor 4 of the present invention includes one heating element 41 and two temperature sensing elements 42 formed on the surface of a semiconductor substrate with thin film resistors on the upstream and downstream sides, respectively. A pair of flow rate measuring elements 40 arranged close to each other in parallel and a flat plate-like support member 43 that supports the flow rate measuring elements 40 in a predetermined position and direction. In the present embodiment, since the longitudinal direction of the flow rate measuring element 40 is arranged so as to coincide with the longitudinal direction of the support member 43, the pair of heating elements 41 and the temperature sensitive element 42 are arranged in sub-bypass flows orthogonal to each other. The front and back surfaces will be exposed. Here, the reason why each of the pair of heating elements 41 and the temperature sensitive elements 42 is orthogonal to the flow is to increase the detection sensitivity of each element.

  Further, the upstream end 44 of the support member 43 is chamfered in a taper shape or an arc shape so that the collision flow is not disturbed or separated, and has an end structure that is inclined with respect to the flow. Yes. This inclination is formed so that when a flow collides with this inclination, a part of the flow (divided flow) flows smoothly from the upstream side to the downstream side along the ridgeline of the inclination. That is, a positive (positive) inclination angle θ (upstream inclination angle θ) is formed from a virtual plane orthogonal to the sub-bypass flow toward the downstream side of the flow. Thereby, unlike the case of being arranged orthogonal to the flow (corresponding to the inclination angle θ = 0), the generation of the stagnation part due to the flow is suppressed.

  Therefore, the relatively large and heavy intake dust floating in the air is collected at the throttle portion 14 of the bypass flow path 7 due to the inertial effect of the flow. Then, only a relatively small and light minute dust remains in the sub-bypass flow that flows through the sub-bypass flow path branched at a substantially right angle from the bypass flow path 7. Even if the minute dust collides with the upstream end 44 of the support member 43, no stagnation is generated, so that the dust is caused to flow downstream without being attached. Therefore, accumulation of intake dust is suppressed (see FIG. 2B).

Here, a preferable setting range of the predetermined upstream inclination angle θ will be described.
The purpose of inclining the upstream end 44 with respect to the flow is to prevent the accumulation of stagnation due to the flow and to prevent dust accumulation derived from the stagnation by causing the flow to be diverted in the direction of inclination of the flow. . Therefore, if the inclination angle θ is increased, the diversion increases, and the generation of the stagnation part is completely eliminated by the large diversion, and the intake dust does not mix and flow out to the downstream side and accumulate.

  FIG. 3 is a plot of the characteristic results against the upstream inclination angle θ when the inventor conducted a dust test using an actual air flow measuring device, and the characteristic values are degradation during dust accumulation relative to the initial time. This is indicated by the characteristic quantity. According to FIG. 3, the deterioration characteristic amount is greatest when there is no inclination angle θ, is a characteristic that decreases sharply as the inclination angle θ increases, and stabilizes to a minimum value when the inclination angle θ is 20 degrees or more.

  Therefore, in order to prevent dust accumulation and reduce the deterioration characteristic amount, it can be said that the inclination angle θ with respect to the flow is preferably set to a large inclination of 20 degrees or more. However, when the inclination angle θ is increased, the flow diversion also increases. As a result, the flow rate (velocity) flowing toward the flow rate measuring element 40 decreases, and the intersection between the flow rate measuring element 40 and the streamline is shifted from an orthogonal state. It becomes like this. Then, the decrease in the flow rate flowing toward the flow rate measuring element 40 and the deviation of the stream line will decrease the detection sensitivity of the flow rate measuring element 40.

  Therefore, the inventor further plots the change in the detection sensitivity of the flow rate measuring element 40 when the dust test is performed using the same test apparatus with respect to the upstream inclination angle θ as the amount of change in the output characteristic and also writes it in FIG. Yes. According to this, the output characteristic change amount is the smallest when the inclination angle θ is zero, and stably changes to a substantially minimum value as the inclination angle θ increases, but the output characteristic change amount when the inclination angle θ exceeds 40 degrees. Increases to the minus side. That is, in order to keep the output characteristic change amount small, it is preferable to keep the inclination angle θ to 40 degrees or less.

  Therefore, the above-described two characteristic change amounts are in a trade-off relationship, and it is preferable that the inclination angle θ is 20 to 40 degrees based on a predetermined allowable width of each characteristic change amount (within hatching in the figure). I can say that. Within this range of the inclination angle θ, it is possible to reliably prevent dust accumulation and suppress the deterioration characteristic amount to the minimum value without causing a decrease in the output characteristics of the flow rate measuring element 40.

[Operation of Example 1]
When an air flow (main flow) is generated inside the intake pipe 2 by starting the engine, a part of the main flow is taken into the bypass flow path 7 of the sensor body 3 to become a bypass flow, and a part of the bypass flow Is taken into the sub-bypass channel 8. At this time, in the flow sensor 4 arranged in the sub-bypass flow path 8, when the flow speed of the sub-bypass flow increases, the heat transfer of the heating element 41 decreases to the upstream side, increases to the downstream side, and the upstream / downstream feeling. The resistance value difference of the temperature element 42 is increased.

  On the other hand, when the flow speed of the sub-bypass flow is reduced, the heat dissipation amount of the heat generating element 41 is reduced, so that the heat transfer of the heat generating element 41 tends to be uniform in the upstream and downstream, so the resistance value difference between the upstream and downstream temperature sensitive elements 42 Becomes smaller. An electrical signal (for example, a voltage signal) corresponding to the resistance value difference is output from the circuit module 5 to an external ECU (electronic control unit), and the intake air amount is measured by the ECU.

  At this time, since the upstream end 44 of the flow rate sensor 4 is inclined with respect to the flow by a predetermined inclination angle θ, dust accumulation on the upstream end 44 is suppressed, and the flow rate reaches from a small amount to a large amount. In the range, the electric signal is output without lowering the detection accuracy of the flow rate.

[Effect of Example 1]
In the present embodiment, a part of the air flowing through the main flow path 6 is taken into the bypass flow path 7 of the sensor body 3 to become a bypass flow, and further, a part of the bypass flow is changed to a sub-bypass flow path 8 that is deflected substantially at right angles. It is taken in and becomes a sub-bypass flow. A flow rate measuring element 40 having a chip sensor structure of the flow rate sensor 4 is arranged in a direction orthogonal to the sub-bypass flow. The upstream end portion 44 of the support member 43 of the flow sensor 4 is arranged to be inclined by a predetermined inclination angle θ with respect to the sub-bypass flow.

  As a result, the intake dust floating in the air is collected in the bypass flow path 7 by the relatively large and heavy one due to the inertial effect of the flow. Then, only a relatively small and light minute dust remains in the sub-bypass flow that flows through the sub-bypass flow path 8 branched from the bypass flow path 7 at a substantially right angle. And even if this minute dust collides with the upstream end 44 of the support member 43, a stagnation part is not generated, so that it will flow to the downstream side along with the diversion without adhering. Therefore, accumulation of intake dust is suppressed, and the detection accuracy of the flow sensor 4 is improved.

[Configuration of Example 2]
A second embodiment of the present invention is shown in FIG. 4A and 4B show the configuration of the air flow rate measuring device, where FIG. 4A is a partial cross-sectional view, and FIG. 4B is an enlarged detailed plan view of a main part flow sensor. Components that are substantially the same as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the first embodiment, a part of the air flowing through the main flow path 6 is taken into the bypass flow path 7 of the sensor body 3 to become a bypass flow, and further, a part of the bypass flow is changed to a sub-bypass flow path 8 that is deflected substantially at right angles. It is taken in and becomes a sub-bypass flow. A flow rate measuring element 40 having a chip sensor structure of the flow rate sensor 4 is arranged in a direction orthogonal to the sub-bypass flow. The upstream end 44 of the support member 43 of the flow rate sensor 4 is arranged to be inclined with respect to the flow by a predetermined inclination angle θ.

  The present embodiment is further characterized in that the downstream end 45 of the support member 43 has an end structure that is inclined with respect to the flow similarly to the upstream end 44. As shown in FIG. 4, the flow sensor 4 of the present invention has one heating element 41 and two temperature sensing elements 42 formed of a thin film resistor on the surface of a semiconductor substrate, close to the upstream and downstream sides, respectively. A pair of flow rate measuring elements 40 arranged in parallel and a flat plate-like support member 43 that supports the flow rate measuring elements 40 in a predetermined position and direction (see FIG. 4B).

  In the present embodiment, the flow measuring element 40 is arranged so that the longitudinal direction of the flow measuring element 40 coincides with the longitudinal direction of the support member 43, and the pair of flow measuring elements 40 are respectively exposed orthogonally to the flow. The flow of air flowing through the intake pipe 2 during engine operation shows a fluctuation behavior of a waveform that periodically increases and decreases in conjunction with the engine pulsation, but intermittent backflow may occur depending on the magnitude of the engine pulsation. . Here, the reverse flow refers to a flow from the downstream side to the upstream side in contrast to the forward flow that flows from the intake pipe (upstream side) of the engine into the cylinder (downstream side).

  The pair of flow rate measuring elements 40 can be applied to the measurement of the intake air amount of an engine having a large pulsation, and can determine the flow direction, that is, the forward flow and the reverse flow as well as the flow rate measurement. Therefore, since the reverse flow rate is measured as a negative flow rate, the net intake air amount is measured by a calculation obtained by subtracting the reverse flow rate from the forward flow rate.

  Also in this case, it is important that the backflow measurement can be detected accurately and accurately. For this reason, the downstream end 45 of the support member 43 is also chamfered in a taper shape or an arc shape so that the colliding flow is not disturbed or peeled off, similarly to the upstream end 44. It has an end structure which is inclined with respect to it. At this time, this inclination is formed so that a part of the reverse flow (divided flow) flows smoothly along the ridgeline of the inclination when the reverse flow collides with the inclination. ) Is formed. This is to form a negative (negative) inclination angle φ toward the flow direction of the sub-bypass flow that is the forward flow, that is, to be inclined in the direction opposite to the flow direction of the air flowing through the sub-bypass channel. It is what is done.

Thereby, unlike the case where it arrange | positions orthogonally to a backflow, the production | generation of a stagnation part is suppressed.
Therefore, even if the intake dust mixed in the reverse flow collides with the downstream side end portion 45 of the support member 43, the stagnation portion is not generated, so that it flows along with the diversion. Therefore, even when a backflow occurs, the accumulation of intake dust is suppressed, and the backflow detection accuracy of the flow sensor 4 is improved.

DESCRIPTION OF SYMBOLS 1 Air flow measuring device 4 Flow sensor 5 Circuit module 6 Main flow path (air passage)
7 Bypass channel 8 Sub-bypass channel 40 Flow rate measuring element (chip sensor, thermal flow rate measuring element)
41 Heating element (thin film resistor)
42 Temperature sensing element (thin film resistor)
43 Support Member 44 Upstream End 45 Downstream End θ Upstream Inclination Angle (Inclination Angle)

Claims (3)

A bypass flow path for taking in part of the air flowing through the air passage;
A throttling portion provided in the bypass channel and gradually reducing the channel cross-sectional area toward the outlet direction of the bypass channel;
An inlet is provided on one side of a predetermined radial direction of the bypass flow path that is branched from the bypass flow path on the upstream side of the throttle portion, and orthogonal to the flow direction of the air flowing through the bypass flow path, A sub-bypass channel that takes in part of the air flowing through the bypass channel;
In the air flow rate measuring device having a flow rate sensor that is disposed in the sub-bypass channel and measures the flow rate of the air flowing through the sub-bypass channel,
The flow sensor has a pair of thermal flow measuring elements made of a thin film resistor formed on the surface of a semiconductor substrate,
The thermal flow rate measuring element is supported by a flat plate-like support member having the longitudinal direction of the semiconductor substrate as the same axis,
The thermal flow rate measuring element is orthogonal to the flow direction of air flowing through the sub-bypass channel,
The air flow rate measuring apparatus according to claim 1, wherein the upstream end portion of the support member is disposed to be inclined in a flow direction of air flowing through the sub-bypass channel. The air flow rate measuring device according to claim 1,
The downstream end portion of the support member is disposed to be inclined in the direction opposite to the flow direction of the air flowing through the sub-bypass channel. In the air flow rate measuring device according to claim 1 or 2,
An air flow rate measuring apparatus, wherein an inclination angle formed by the upstream end portion and the downstream end portion of the support member and a flow direction of air flowing through the sub-bypass channel is 20 to 40 degrees.

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