JP5288294B2 - Flow measuring device - Google Patents

Description

  The present invention particularly relates to a thermal flow rate measuring apparatus for measuring the flow rate of air flowing through an intake port communicating with a combustion chamber of an internal combustion engine.

2. Description of the Related Art Thermal type flow measurement devices that measure a flow rate by causing a flow rate sensor to generate heat and detecting the amount of heat released from the flow rate sensor to a fluid are known (see, for example, Patent Documents 1 to 5). However, the flow rate measuring devices described in the above-mentioned patent documents have the following problems.
In the apparatus described in Patent Document 1, since the measurement passage is curved, a drift occurs in the measurement passage, and the measurement result becomes unstable.

  Further, in the flow rate measuring device described in Patent Document 2, the obstacle member is formed in a cylindrical shape, and air in a narrow range in the axial direction of the obstacle member merges and flows into the sensor flow path. Since the merged air flows in, there is no drift in the sensor flow path, but since the range of the flowing air is narrow, the flow velocity of the flowing air is unlikely to correlate with the average flow velocity of the entire intake port. For this reason, a highly accurate measurement result cannot be obtained.

Moreover, since the inlet part is opening toward the upstream side, the hot-wire type air flow rate measuring device described in Patent Document 3 tends to allow dust to flow in. When dust flows in, it adheres to the flow sensor and the measurement result becomes unstable.
In the air flow meter described in FIG. 26 of Patent Document 4, since the deflector is smaller than the opening, the dust flowing from the upstream easily flows into the bypass flow path, and the measurement result becomes unstable.

Moreover, since the inlet part is opening toward the upstream, the air flowmeter of patent document 5 is easy to flow in dust. Therefore, the measurement result becomes unstable.
In addition, the thermal flow measuring device has a problem that detection accuracy is lowered due to heat loss due to heat escaping through a member supporting the flow sensor. In particular, when the flow rate of air flowing through the intake port is low, such as during idling, the rate of heat radiated to the air decreases, the rate of heat loss increases relatively, and the detection accuracy decreases greatly.

  The flow rate measuring devices described in Patent Documents 3 and 5 increase the flow velocity of the fluid flowing through the main passage by enlarging the central member (first flow path portion) and restricting the main passage, and the downstream core and the central member. The outlet portion of the bypass passage (first flow path) is throttled by the downstream portion, and the flow velocity of the fluid flowing through the bypass passage is increased by the negative pressure generated by the fluid flowing through the main passage. If the flow rate is increased, the rate of heat escaping to the air increases, so that the detection accuracy can be improved. However, the main passage of the flow rate measuring devices described in Patent Documents 3 and 5 forms a part of the intake port, and the outer wall surface of the central member approaches the inner wall surface of the intake port in order to restrict the main passage. The central member must be enlarged. That is, according to the flow rate measuring devices described in Patent Documents 3 and 5, there is a problem that the central member must be enlarged in order to improve detection accuracy.

JP 2004-53600 A JP 2003-214915 A Japanese Patent No. 3240782 US Pat. No. 4,709,581 JP-A-5-164585

The present invention has been created in view of the above-described problems, and an object of the present invention is to provide a flow measurement device that can stably obtain a highly accurate measurement result.
Another object of the present invention is to provide a flow rate measuring device that improves the detection accuracy without enlarging the flow path portion that forms the flow path in which the flow rate sensor is provided.

According to the first aspect of the present invention, since the outlet is throttled by the downstream member, the flow velocity around the outlet is increased and negative pressure is generated. Since the flow rate of the fluid flowing through the first flow path is increased by this negative pressure, the detection accuracy of the flow sensor is improved. According to the first aspect of the invention, since the first flow path portion and the downstream member are accommodated in the second flow path, the flow velocity around the outlet of the first flow path is stabilized over the entire circumference. Furthermore, by reducing the second flow path portion, the flow velocity of the fluid flowing through the flow path formed by the outer wall surface of the first flow path portion and the inner wall surface of the second flow path portion can be increased , and the main flow path can be reduced. Since the shape of the first channel portion and the second channel portion can be set independently without changing the shape of the third channel portion to be formed, the detection accuracy can be improved without increasing the size of the first channel portion. .

  According to the second aspect of the present invention, the first flow path is attached so as to extend linearly in the flow direction of the predetermined main flow path, specifically, for example, the flow direction of the intake port. Less detection accuracy is improved.

According to the third aspect of the present invention, the outlet of the first flow path portion is hidden by the downstream member, so that when the fluid flows backward through the intake port, the dust hardly flows into the first flow path. Thereby, the fall of the detection accuracy of a flow sensor by adhesion of the dust which flowed back can be prevented, and a measurement result becomes more stable.
According to the fourth aspect of the present invention, since the downstream end face of the first flow path portion is hidden by the downstream member, when the fluid flows backward through the intake port, the dust flows into the first flow path along the end face. hard. Thereby, the fall of the detection accuracy of a flow sensor by adhesion of the dust which flowed back can be prevented, and a measurement result becomes more stable.

  According to the fifth aspect of the present invention, the end surface on the downstream side of the first flow path portion is inclined so as to be inclined toward the upstream side of the second flow path as it approaches the inner wall of the second flow path portion. When the air flows back through the intake port, it is difficult for dust to flow into the first flow path. Thereby, the fall of the detection accuracy of a flow sensor by adhesion of the dust which flowed back can be prevented, and a measurement result becomes more stable.

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
1A is a perspective view showing a flow rate measuring device 10 according to the first embodiment of the present invention, FIG. 1B is a partial sectional view of the flow rate measuring device 10, and FIG. 2 is fixed to the intake port 11. It is sectional drawing of the flow direction of the flow measuring device 10 of a state. FIG. 3A is a front view of the flow rate measuring device 10 viewed from the upstream side, and FIG. 3B is a rear view of the flow rate measuring device 10 viewed from the downstream side. In FIG. 2, the arm portion 19 shown in FIG. 1 and the arm portion 12 and the arm portion 13 shown in FIG. 3 are omitted.

As shown in FIG. 2, the flow rate measuring device 10 includes a first flow path portion 15 (hereinafter referred to as “sensor flow path portion”) that forms a sensor flow path 14 as a first flow path, and a bypass as a second flow path. A second flow path portion 17 (hereinafter referred to as a “bypass flow path portion”) that forms the flow path 16, a flow straightening core 18 as a flow straightening member, a downstream core 22 as a downstream side member, a sensor portion 20, and a support portion 24 are provided. ing. The upstream side of the intake port 11 serving as the third flow path portion to which the flow rate measuring device 10 is attached is connected to an air cleaner, and the downstream side communicates with the combustion chamber of the internal combustion engine via a throttle valve.

The bypass channel portion 17 is formed in a substantially cylindrical shape.
The sensor flow path 15 is supported in the bypass flow path 16 by four arms 12 (see FIG. 3A) extending from the inner wall of the bypass flow path 17. The sensor flow path 15 is formed with a sensor flow path 14 penetrating from the upstream side toward the downstream side. The sensor flow path 14 is formed in a substantially pincushion in the cross section in the flow direction, and the area of the cross section perpendicular to the flow direction is the widest at the inlet 14a on the upstream side, and gradually decreases toward the downstream side. It gradually becomes wider as it goes downstream from the center. When the sensor flow path 15 is accommodated in the bypass flow path 17, the flow velocity around the outlet of the sensor flow path 14 is stabilized over the entire circumference.

  The outer wall of the sensor flow path part 15 is formed in a shape in which the outer diameter gradually increases from the upstream side toward the downstream side. The outer wall surface 15a and the inner wall surface 15b of the sensor flow path portion 15 are connected so as to intersect at an acute angle on the upstream side, and the air flowing through the bypass flow path 16 is in the sensor flow path 14 upstream of the sensor flow path portion 15. And air flowing outside the sensor flow path 14 are smoothly separated. The end surface 15c facing the downstream side of the sensor flow path portion 15 is formed in a conical surface shape whose outer diameter decreases toward the downstream side.

Further, as shown in the figure, the flow measuring device 10 is attached so that the bypass flow path 16 and the sensor flow path 14 extend linearly in the flow direction of the intake port 11, so that the air flowing through the intake port 11 There is no need to greatly change the direction when flowing into the sensor flow path 14. For this reason, there is little loss of the flow velocity of air.
The rectifying core 18 is supported upstream of the sensor flow path 14 by four arms 19 (see FIG. 1) that extend upstream from the sensor flow path portion 15. The rectifying core 18 is formed in a substantially spherical shape, and more specifically, the tip portion on the downstream side is formed in a shape extending conically toward the downstream side based on the spherical shape. As shown in FIG. 3A, the rectifying core 18 is formed in such a size that the inlet 14a of the sensor flow path 14 is hidden by the rectifying core 18 when viewed from the upstream side in the flow direction. Further, as shown in FIG. 2, the rectifying core 18 is provided so that the upstream side protrudes from the bypass flow path 16 to the upstream side. Further, as described above, the rectifying core 18 is supported by the sensor flow path portion 15. When the rectifying core 18 is supported by the sensor flow path unit 15, the positional accuracy of the rectification core 18 with respect to the sensor flow path unit 15 is improved, and as a result, the accuracy of the flow rate flowing into the sensor flow path 14 is improved. The accuracy is further improved. The shape of the rectifying core may be a spherical shape, or may be a streamlined type such as a rectifying core 40 shown in FIG. 4A or a rectifying core 41 shown in FIG. Further, the entire rectifying core 18 may be accommodated in the bypass channel 16 without protruding the upstream side of the rectifying core 18 from the bypass channel 16.

  The sensor unit 20 includes a flow velocity measuring resistor 21 as a flow sensor, a temperature compensation resistor (not shown), and a control circuit (not shown). The flow velocity measuring resistor 21 is provided in the sensor flow path 14 and is heated at a constant temperature relative to the air temperature by the control circuit. The control circuit outputs the amount of heat released from the flow velocity measuring resistor 21 to the air flowing around the flow velocity measuring resistor 21 as an electric signal. Based on this electric signal, a flow rate and a flow velocity are specified by a predetermined control computer.

  The downstream core 22 is supported in the vicinity of the outlet of the sensor flow path 14 by four arm portions 13 (see FIG. 3B) extending from the inner wall of the bypass flow path portion 17. A surface 22a facing the upstream side of the downstream core 22 is formed as a concave surface, and a surface 22b facing the downstream side of the downstream core 22 is formed as a convex surface protruding from the outer periphery of the concave surface 22a toward the downstream side. The downstream core 22 is supported downstream of the sensor flow path 15 with a predetermined space between the downstream core 22 and the sensor flow path 15. The downstream sensor flow that inclines so as to incline toward the upstream side of the bypass channel 16 and expands in an annular shape as it approaches the inner wall 17a of the bypass channel unit 17 by the conical surface 15c of the sensor channel unit 15 and the concave surface 22a of the downstream core 22. A path 23 is formed. In addition, the outer diameter of the downstream core 22 is larger than the outlet of the sensor flow path 14 and smaller than the outer diameter of the sensor flow path portion 15. Therefore, as shown in FIG. 3B, when viewed from the downstream side, the outlet of the sensor flow path 14 is hidden by the downstream core 22, and the outer peripheral side of the conical surface 15c is visible. Further, as shown in FIG. 2, the downstream core 22 is provided so that the downstream side protrudes from the bypass channel 16.

  The support portion 24 includes a cylindrical portion 24a and a flange portion 24b, and is formed integrally with the bypass flow path portion 17. A cable for connecting the control computer and the control circuit is disposed inside the cylindrical portion 24a. As shown in FIG. 1A, a bolt hole 24c for fastening and fixing the flow rate measuring device 10 to the inner wall of the intake port 11 is formed in the flange portion 24b.

Next, the drift and pulsation generated in the intake port 11 will be described.
FIG. 5 is a schematic diagram showing an outline of the drift that occurs in the intake port 11. FIG. 5 schematically shows an example of the drift generated in the intake port 11 of the curved pipe, and detailed portions are omitted, and the inside of the flow rate measuring device 10 is also omitted. When the intake port 11 is bent, there is a difference in flow velocity between the inner side 61 and the outer side 62 as shown in the bent portion, thereby causing a drift in the downstream side of the bent portion. Here, the intake port 11 with a bend has been described as an example, but drift occurs even with a straight pipe intake port without a bend. For example, if the filter element of the air cleaner connected to the upstream side of the intake port is clogged, there will be a part where the air easily flows and a part where it is difficult for the filter element to flow. Arise. Since the area of the flow velocity measuring resistor 21 is smaller than the flow passage area of the sensor flow channel 14, if a drift occurs, the flow velocity of the air flowing around the flow velocity measuring resistor 21 is not stable, and the measurement result is unstable. Become.

  FIG. 6 is a schematic diagram showing the influence of pulsating flow when uneven flow occurs. FIG. 6 shows the distribution of the flow velocity of the air flowing through the intake port 11, and shows that the flow velocity is higher in the region surrounded by the inner line. FIG. 6 shows the measurement of the flow velocity at a position where a non-flowing air flows through the intake port 11 of the curved pipe, and the position of the downstream side of the bent portion, specifically the position A shown in FIG. A pulsating flow is generated in the air in the intake port 11 corresponding to the combustion cycle of the internal combustion engine. When the pulsating flow is generated, the generation of the uneven flow is periodically changed corresponding to the pulsating flow, and thereby the flow velocity of the air flowing around the flow velocity measuring resistor 21 is periodically changed. The measurement result becomes more unstable.

Next, the operation of the rectifying core 18 will be described.
First, an operation in which the rectifying core 18 causes air to flow into the inlet 14a of the sensor flow path 14 from the entire circumference will be described.
FIG. 7 is a schematic diagram showing the flow of air. When the air flowing in the vicinity of the center of the intake port 11 flows up to the rectifying core 18, it flows along the upstream surface of the rectifying core 18, so that it expands 360 ° outward in the radial direction when viewed from the upstream side. Escaped. Part of the escaped air flows along the downstream surface of the rectifying core 18, merges and is made uniform on the downstream side of the rectifying core 18, and flows into the sensor flow path 14 from the inlet 14 a. When the uniformed air is caused to flow into the sensor flow path 14, the drift of air in the sensor flow path 14 can be almost eliminated. When the drift is eliminated, the flow velocity of the air flowing around the flow velocity measuring resistor 21 is stabilized, and the influence of the pulsating flow is reduced by eliminating the drift, so that the measurement result is stabilized.

  When a part of the escaped air flows along the downstream surface of the rectifying core 18, a part of the escaped air flows from the entire circumference of the rectifying core 18. When air flows from the entire circumference of the rectifying core 18, the air uniformly flows into the sensor flow path 14 from a wide range along the entire circumference of the rectifying core 18. When air uniformly flows into the sensor flow path 14 from a wide range, the flow speed of the air flowing through the sensor flow path 14 correlates with the average flow speed of the air flowing into the bypass flow path 16. As a result, the correlation with the average flow velocity of the entire intake port 11 is also increased. Thereby, a highly accurate measurement result can be obtained.

Next, the operation in which the rectifying core 18 removes dust will be described.
In general, the dust 27 smaller than about 100 μm passes through the filter element of the air cleaner and flows from the upstream side of the intake port 11 as shown in FIG. When the dust 27 contained in the air flowing near the center of the intake port 11 flows to the rectifying core 18, it is repelled radially outward by the rectifying core 18. At this time, as described above, the inlet 14a of the sensor flow path 14 is hidden by the rectifying core 18, so that a large amount of dust 27 does not flow into the sensor flow path 14 and directly flows outside the sensor flow path 14 toward the downstream. Washed away. Thereby, the dust 27 flowing into the sensor flow path 14 can be reduced, and the deterioration of the detection accuracy of the flow velocity measuring resistor 21 due to the adhesion of the dust 27 can be reduced.

Next, the operation of the downstream core 22 will be described.
First, an operation for increasing the flow velocity of the air flowing through the sensor flow path 14 by the downstream core 22 will be described.
As shown in FIG. 7, the air flowing through the sensor flow path 14 flows through the downstream sensor flow path 23 formed by the sensor flow path portion 15 and the downstream core 22 and flows out. By providing the downstream core 22, the outlet of the sensor flow path 14 is throttled, so that the flow rate at the outlet is increased and negative pressure is generated. The air in the sensor flow path 14 is drawn out by this negative pressure, and the flow velocity of the air flowing in the sensor flow path 14 is increased, so that the rate of heat loss is reduced and the detection accuracy can be improved.

  Further, in order to improve the detection accuracy, the flow rate measuring device 10 includes the bypass flow path portion 17, so that the outer wall surface 15 a of the sensor flow path portion 15 and the bypass flow path portion can be reduced by reducing the bypass flow path portion 17. The flow path formed by the 17 inner wall surfaces 17a can be narrowed. When the flow path is narrowed, the flow rate of air flowing through the flow path is increased, so that the negative pressure is increased and the flow speed of air flowing through the sensor flow path 14 is further increased. This further improves the detection accuracy. That is, according to the flow rate measuring device 10, the detection accuracy can be improved without increasing the sensor flow path portion 15.

Next, the operation | movement which prevents inflow of the dust which the downstream core 22 flowed back is demonstrated.
FIG. 8 is a graph showing temporal changes in the flow rate. In the graph, a line 30 indicates a temporal change in the flow rate when the throttle valve is relatively closed, and a line 31 indicates a temporal change in the flow rate when the throttle valve is relatively open. As described above, a pulsating flow is generated in the air in the intake port 11, and a part of the air flows backward through the intake port 11 when the opening degree of the throttle valve exceeds a certain level. In FIG. 8, a region 32 indicated by parallel oblique lines indicates a period during which air flows backward and a flow rate at which the air flows backward.

  FIG. 9 is a schematic diagram showing the flow of air that flows backward. As described above, since the outlet of the sensor flow path 14 is hidden by the downstream core 22, the dust 27 repelled radially outward by the downstream core 22 does not easily flow into the sensor flow path 14. Further, as described above, the downstream end face 15 c of the sensor flow path portion 15 is inclined so as to be inclined toward the upstream side of the bypass flow path 16 as it approaches the inner wall surface 17 a of the bypass flow path portion 17. If the downstream end face of the sensor flow path portion 15 is inclined so as to be inclined to the downstream side of the bypass flow path 16 as it approaches the inner wall surface 17a of the bypass flow path section 17, when the air flows backward, the dust 27 is generated. It will be guide | induced in the sensor flow path 14 along the downstream end surface. On the other hand, since the flow measuring device 10 is inclined so that the downstream end face 15c is inclined to the upstream side, the dust 27 is difficult to flow into the sensor flow path 14. Thereby, it can reduce that dust 27 flows backward and adheres to resistor 21 for flow velocity measurement.

Next, an experimental result in which the characteristic change of the flow measuring device 10 is compared with the comparative example will be described. Here, the characteristic change S is expressed by the following equation.
S = (flow velocity when there is drift-flow velocity when there is no drift) / flow velocity when there is no drift The flow velocity when there is drift is the flow of air without drift to the intake port 11 of the curved pipe. The flow velocity is measured at the position where the downstream drift occurs, specifically at the position A shown in FIG. The flow rate when there is no drift is measured by flowing air without drift through the intake port of the straight pipe. When there is no drift, the flow velocity substantially matches the average flow velocity of the air flowing through the entire intake port. Since the same flow rate of air flows through the bent pipe intake port 11 and the straight pipe intake port, if the characteristic change is close to 0%, the flow rate measuring device 10 causes the average flow velocity of the air flowing through the entire bent pipe intake port 11. Can be measured accurately. That is, a highly accurate measurement result in which the influence of drift is eliminated is obtained.

  FIG. 10 is a graph showing experimental results comparing the characteristic change of the flow rate measuring device 10 with a comparative example. Here, the flow rate measuring device described in Patent Document 2 is used as a comparative example. In the experiment, characteristic changes were obtained for the flow rate measuring device 10 and the comparative example while gradually increasing the flow rate. As shown in the graph, the characteristic change of the flow rate measuring device 10 is around 0% at any flow rate. On the other hand, in the comparative example, the characteristic change is biased in the negative direction at any flow rate. As is clear from this, the flow rate measuring device 10 can accurately measure the average flow velocity of the air flowing through the entire intake port 11 despite the drift in the intake port 11. That is, according to the flow measurement device 10, a highly accurate measurement result can be obtained.

  According to the flow rate measuring device 10 according to the first embodiment described above, air can be introduced into the sensor flow path 14 from a wide range along the entire circumference of the rectifying core 18. Since air flows in from a wide range, the correlation between the flow velocity of the air flowing in and the average flow velocity of the air flowing through the entire intake port is increased, and a more accurate measurement result can be obtained. In addition, since air flowing from the entire circumference merges and flows in the downstream of the rectifying core 18, the sensor channel 14 does not drift and the measurement result is stabilized. Moreover, since the inlet 14a of the sensor flow path 14 is hidden by the rectifying core 18 when viewed from the upstream side, the dust 27 hardly flows into the sensor flow path 14. Therefore, the measurement result is more stable. Therefore, according to the flow measuring device 10, a highly accurate measurement result can be obtained stably.

(Second embodiment)
FIG. 11 is a cross-sectional view of the flow rate measuring device 50 according to the second embodiment. As shown in the drawing, the downstream core 51 is formed in such a size that the downstream end face 15a of the sensor flow path portion 15 is hidden when viewed from the downstream side. For this reason, when air flows backward through the intake port 11, the dust 27 that has flowed back hardly flows into the downstream sensor flow path 52 along the end face 15a. Thereby, the measurement result is stabilized.

  In the second embodiment, the case where the downstream end face 15a of the sensor flow path 15 is inclined so as to be inclined toward the upstream side of the bypass flow path 16 as approaching the inner wall 17a of the bypass flow path section 17 will be described as an example. However, you may incline so that it may incline to the downstream of the bypass flow path 16 as it approaches the inner wall wall 17a of the bypass flow path part 17. FIG. Also in this case, by concealing the downstream end face 15a with the downstream core 51, it is possible to prevent a decrease in detection accuracy of the flow velocity measuring resistor 21 due to the adhering dust 27 flowing backward.

(A) is a perspective view showing a flow measurement device according to an embodiment of the present invention, (B) is a partial cross-sectional view of the flow measurement device Sectional drawing of the flow direction of the flow volume measuring apparatus which concerns on one Embodiment of this invention. (A) is a front view of the flow measuring device concerning one embodiment of the present invention, and (B) is a rear view. (A) And (B) is sectional drawing of the baffle member which concerns on one Embodiment of this invention. The schematic diagram which shows an example of the drift which has arisen in the main flow path. The schematic diagram which shows the pulsating flow which has arisen in the main flow path. The schematic diagram which shows the flow of the air of the flow volume measuring apparatus which concerns on one Embodiment of this invention. The graph which shows the time change of the flow volume which flows through the main flow path. The schematic diagram which shows the flow of the air of the flow volume measuring apparatus which concerns on one Embodiment of this invention. The graph which shows the characteristic change of the flow measuring device concerning one embodiment of the present invention. Sectional drawing of the flow direction of the flow volume measuring apparatus which concerns on one Embodiment of this invention.

  DESCRIPTION OF SYMBOLS 10 Flow measurement apparatus, 11 Intake port (main flow path), 14 Sensor flow path (1st flow path), 14a Inlet, 15 Sensor flow path part (1st flow path part), 16 Bypass flow path (2nd flow path) , 17 Bypass channel part (second channel part), 18 Rectification core (rectification member), 21 Flow velocity measuring resistor (flow sensor), 22 Downstream core (downstream member), 23 Downstream sensor channel, 24 Support section, 40 rectifying core (rectifying member), 41 rectifying core (rectifying member), 50 flow rate measuring device, 51 downstream core (downstream member), 52 downstream sensor flow path

Claims (5)

A first flow path portion forming a first flow path through which a fluid flows;
A flow sensor provided in the first flow path;
Forming a second flow path for accommodating the first flow path portion, and a second flow path portion accommodated in a third flow path portion forming a main flow path;
A downstream member that is provided in the vicinity of the outlet of the first flow path and throttles the outlet;
A flow rate measuring device comprising: The first flow path is formed in a straight line;
And characterized in that a support portion for mounting the flow measuring device on an inner wall of the main channel, further comprising a support portion to which the first flow path is mounted in a posture extending straight in the flow direction of the primary flow passage The flow rate measuring device according to claim 1.   The flow rate measuring device according to claim 1, wherein the outlet of the first flow path is hidden by the downstream member when viewed from the downstream side.   The flow rate measuring device according to claim 3, wherein when viewed from the downstream side, an end face on the downstream side of the first flow path portion is hidden by the downstream side member.   5. The downstream end face of the first flow path portion is inclined so as to be inclined toward the upstream side of the second flow path as it approaches the inner wall of the second flow path portion. The flow measurement device according to any one of the above.

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