Apparatus for measuring flow characteristics

A flow detection device for detecting a flow characteristic of a fluid within a pipe is disclosed. The flow detection device includes a first channel portion that defines a first channel with an upstream aperture. The fluid can flow into the first channel through the upstream aperture. The device also includes a flow sensor disposed in the first channel, and the flow sensor detects the flow characteristic of the fluid. Furthermore, the device includes a flow straightening member that is provided upstream of the first channel. The upstream aperture is hidden by the flow straightening member as viewed looking downstream along an axis of the first channel portion. Also, the fluid flows from substantially the entire circumference of the flow straightening member into the first channel.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2005-157136 filed on May 30, 2005, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an apparatus for measuring flow characteristics such as the amount of air flowing through an intake port connected to the combustion chamber of an internal combustion engine.

BACKGROUND OF THE INVENTION

Several devices have been provided for measuring flow characteristics of a fluid. For instance, thermal apparatuses for measuring flow amounts have been designed. In these devices, a flow sensor generates heat, and the amount of heat radiated from the flow sensor to fluid is detected to thereby measure the flow amount. (See, e.g., U.S. Pat. No. 6,973,823 (claiming priority to Japanese Patent Publication No. 2004-53600), U.S. Pat. No. 6,938,473 (claiming priority to Japanese Patent Publication No. 2003-214915), U.S. Pat. No. 5,485,746 (claiming priority to Japanese Patent 3240782), U.S. Pat. No. 4,709,581, and U.S. Pat. Nos. 5,571,964 and 5,581,026 (claiming priority to Japanese Patent Publication No. Hei 5(1993)-164585). However, these and other related prior art devices have certain disadvantages.

For instance, in the device of U.S. Pat. No. 6,973,823, the axis of the measurement passage is curved. As such, the flow of the fluid may become uneven, making measurement inaccurate.

The apparatus described in U.S. Pat. No. 6,938,473 includes an obstruction member formed in a columnar shape, and air within a narrow area of the pipe flows into a sensor channel. As such, the flow velocity within the sensor channel is less likely to correlate with the flow velocity in the main portion of the intake port. For this reason, the flow measurements may be inaccurate.

Furthermore, the apparatus described in U.S. Pat. No. 5,485,746 has an inlet portion open toward the upstream side. As such, dust may flow in and stick to the flow sensor, and this makes measurement results unstable.

Moreover, the air flow meter illustrated inFIG. 26of U.S. Pat. No. 4,709,581 includes a deflector that is smaller than the inlet opening. This allows dust to flow into a bypass channel, and this makes measurement results unstable.

Also, the devices described in U.S. Pat. No. 5,571,964 and U.S. Pat. No. 5,581,026 each include an inlet portion open toward the upstream side. As such, dust may flow in and measurement results may be unreliable.

In addition, flow sensing devices with thermal sensors (e.g., hot wire type mass air flow sensors) can be inaccurate. For instance, these devices often include one or more support members to which the thermal sensor is coupled. However, heat may be lost to the support member instead of the fluid. This may be especially true when the flow velocity of the fluid is relatively low (e.g., when an engine is idling). As such, the ratio of heat radiated to the fluid is reduced, and the ratio of heat loss is relatively increased. This significantly degrades the detection accuracy.

The devices in U.S. Pat. Nos., 5,485,746, 4,709,581, 5,571,964 and 5,581,026 include a central member (i.e., a first channel portion) and a main passage. The central member is enlarged to obstruct size of the main passage. The flow velocity of fluid flowing through the main passage is thereby increased. Also, the outlet portion of a bypass passage (i.e., a first channel) is obstructed by a downstream member or the downstream portion of the central member. Thus, the flow velocity of fluid flowing through the bypass passage is increased by the negative pressure produced by fluid flowing through the main passage. When the flow velocity is increased, the ratio of heat escaping to air is enhanced; therefore, the detection accuracy can be enhanced. However, the main passages respectively form part of an intake port. Thus, to obstruct the main passage, the central member is enlarged so that the outer wall surface of the central member is adjacent the inner wall surface of the intake port. That is, to enhance the detection accuracy of these devices, the central members are enlarged.

SUMMARY OF THE INVENTION

Accordingly, a flow detection device for detecting a flow characteristic of a fluid within a pipe is disclosed. The flow detection device includes a first channel portion that defines a first channel with an upstream aperture. The fluid can flow into the first channel through the upstream aperture. The device also includes a flow sensor disposed in the first channel, and the flow sensor detects the flow characteristic of the fluid. Furthermore, the device includes a flow straightening member that is provided upstream of the first channel. The upstream aperture is hidden by the flow straightening member as viewed looking downstream along an axis of the first channel portion. Also, the fluid flows from substantially the entire circumference of the flow straightening member into the first channel.

Also, another flow detection device for detecting a flow characteristic of a fluid within a pipe is disclosed. The flow detection device includes a first channel portion that defines a first channel through which the fluid can flow. The first channel has an upstream aperture and a downstream aperture such that the fluid can enter the first channel through the upstream aperture and exit the first channel through the downstream aperture. The device also includes a flow sensor disposed in the first channel, and the flow sensor can detect the flow characteristic of the fluid. Furthermore, the device includes a second channel portion that defines a second channel. The first channel portion is coupled to the second channel portion and is disposed within the second channel. Additionally, a downstream member is disposed downstream of the downstream aperture so as to obstruct flow out of the downstream aperture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, description will be given to multiple embodiments of the invention with reference to drawings.

First Embodiment

Initially referring toFIGS. 1A-3B, one embodiment of a flow detection device10is illustrated. As shown inFIG. 2, the flow detection device10can be disposed within a pipe11, such as an air intake port of an engine. In one embodiment, an air cleaner (i.e., filter) is included upstream of the flow detection device10. Downstream of the detection device10is a combustion chamber of an internal combustion engine.

As shown, the flow detection device10includes a first channel portion15that defines a first channel14extending therethrough. The first channel14includes an upstream aperture14aand a downstream aperture29. The flow detection device10also includes a second channel portion17that defines a second channel16extending therethrough. The second channel16includes an upstream aperture25and a downstream aperture26. The device10further includes a flow straightening member18and a downstream member22, each of which will be described. Furthermore, the device10includes a sensor portion20and a support portion24.

The sensor portion20includes a flow sensor21that is disposed in the first channel14. As will be described below, as fluid flows through the pipe11, the flow sensor21detects at least one flow characteristic (e.g., flow amount, mass flow rate, flow velocity, etc.) of the fluid. It will be appreciated that the flow detection device10can be used for detecting any suitable flow characteristic for any suitable fluid.

In the embodiment shown, the second channel portion17has a substantially cylindrical shape. The first channel portion15is coupled to the second channel portion17and is supported in the second channel16by a plurality of arm portions12(FIG. 3A). The arm portions12extend from the inner wall of the second channel portion17.

The axis of the first channel14is substantially straight and is disposed approximately parallel to the direction of fluid flow. In the embodiment shown inFIG. 2, the first channel portion15includes an inner surface15b, which defines the first channel14. The inner surface15bis shaped such that sections of the first channel14taken along the direction of flow are approximately bobbin-shaped. In other words, an upstream end of the first channel14has a width perpendicular to the flow direction; moving downstream from the upstream end, the width of the first channel14gradually decreases; then, moving further downstream, the width of the first channel14gradually increases. Also, in the embodiment shown, the first channel14is widest at the upstream end. As such, the flow velocity in proximity to the downstream end of the first channel14is stabilized over the circumference thereof.

The first channel portion15also includes a first outer surface15aand an end face15c, which is disposed downstream of the first outer surface15a. The width of the first outer surface15agradually increases moving from an upstream end toward a downstream end. Also, the first outer surface15aand the inner surface15bintersect at an acute angle on the upstream side of the first channel portion15. As such, the fluid flowing into the second channel16is smoothly separated to flow either into the first channel14or to continue through the second channel16.

The end face15cis frustoconical in shape. The width of the end face15cdecreases as observed moving downstream, such that the width of the end face15cis smallest at the downstream end.

In the embodiment illustrated, the axis of the first channel14and the axis of the second channel16are substantially straight, and these axes are substantially parallel to the axis of the pipe11. As such, the direction of the fluid flowing through the pipe11changes insignificantly when flowing through the flow detection device10. For this reason, flow velocity losses of the fluid are reduced.

The flow straightening member18is disposed upstream from the first channel14. In the embodiment shown, the device10includes a plurality of arm portions19that each extend upstream from the first channel portion15and are coupled to the flow straightening member18(FIG. 1B). As such, the flow straightening member18is coupled to the first channel portion15. Thus, the position of the flow straightening member18relative to the first channel portion15can be accurately controlled, thereby enhancing the accuracy of the flow measurements.

In the embodiment shown, the flow straightening member18projects at least partially from the upstream aperture25of the second channel portion17. In another embodiment, the entire flow straightening member18is disposed within the second channel portion17.

It will be appreciated that the flow straightening member18can be of any suitable shape. For instance, in the embodiment shown, the flow straightening member18includes an upstream side that is substantially hemispherical. Also, the flow straightening member18includes a downstream side that is conic in shape such that the width of the flow straightening member18decreases as observed moving downstream. In another embodiment shown inFIG. 4A, the flow straightening member18is streamlined so as to include an upstream side that has a gradually increasing width as observed moving downstream, and the flow straightening member18also includes a downstream side that is hemispherical in shape. In still another embodiment shown inFIG. 4B, the flow straightening member is streamlined so as to include an upstream side that has a gradually increasing width as observed moving downstream and a downstream side that has a gradually decreasing width as observed moving downstream.

As illustrated inFIG. 3A, the size of the flow straightening member18is such that the upstream aperture14aof the first channel14is hidden behind the flow straightening member18as viewed looking downstream along the axis of the first channel14.

The flow sensor portion20includes flow sensor21for detecting the flow characteristic (e.g., flow velocity). It will be appreciated that the flow sensor21could be of any suitable type for detecting the flow characteristic by any suitable means. In one embodiment, the flow sensor portion20includes a temperature compensating resistance element (not shown) and a control circuit (not shown). The flow sensor21is heated to a certain temperature relative to the temperature of air by the control circuit. The control circuit outputs as an electrical signal the amount of heat radiated from the flow sensor21to the fluid flowing around the flow sensor21. Based on this electrical signal, a flow amount or a flow velocity is determined by predetermined computer logic.

The downstream member22is disposed downstream of and adjacent the downstream aperture29of the first channel portion15. A plurality of arm portions13(FIG. 3B) extend from an inner surface17aof the second channel portion17and are coupled to the downstream member22such that the downstream member22is coupled to the second channel portion17.

The downstream member22includes a face22a, which faces upstream, and a face22b, which faces downstream. In the embodiment shown, the face22ais concave in shape, and the face22bis convex in shape. The downstream member22is supported downstream of the first channel portion15such that a predetermined gap exists between the downstream member22and the first channel portion15. Thus, a downstream-side first channel23is formed by the circular conical end face15cand the concave face22a. The downstream-side first channel23is inclined relative to the axis of the device10. As such, the path of flow through downstream-side first channel23extends toward the inner surface17aof the second channel portion17and toward the upstream aperture25of the second channel portion17. Also, in the embodiment shown, the downstream-side first channel23is annularly widened.

As shown inFIG. 2, the width of the downstream member22greater than the width of the downstream aperture29of the first channel14and less than the width of the first channel portion15. As viewed looking upstream (FIG. 3B), the downstream aperture29of the first channel14is hidden behind the downstream member22, and yet a portion of the end face15cof the first channel portion15is still visible. Furthermore, the downstream member22is disposed such that the downstream face22bextends out of the second channel16through the downstream aperture26.

The support portion24is constructed of a cylindrical portion24aand a flange portion24b, and is formed integrally with the second channel portion17. A cable for connecting the computer for control and the control circuit is disposed in the cylindrical portion24a. As illustrated inFIG. 1A, fastener apertures24care provided in the flange portion24bfor coupling the device to the pipe11.

Referring now toFIG. 5, the flow of the fluid through the pipe11will now be discussed. As shown, asymmetric flow (i.e., drift) can occur in the pipe11, especially if the pipe11includes a bend. When the intake port11is bent, a difference in flow velocity is produced at the bent area between the inside61and the outside62, as illustrated in the drawing. As a result, asymmetric flow occurs downstream from the bent area. It will be appreciated that asymmetric flow could occur in a pipe11of any type, including a pipe11without a bend. For instance, if a filter element connected at an upstream end11of the pipe is partially clogged, air will flow more easily through certain areas of the filter and will flow less easily through other areas of the filter. Therefore, asymmetrical flow is likely to occur.

FIG. 6is a schematic diagram illustrating the influence of a pulsating flow observed when asymmetric flow and swirl occurs. The distribution of the flow velocity in the pipe indicates that the flow velocity is higher in an area encircled with a line positioned further inside. Specifically,FIG. 6shows the result of measurement carried out by passing symmetrically flowing fluid through a pipe11with a bend. Then, the flow velocity of the fluid was measured in a position downstream from the bent area where drift is occurring (e.g., position A shown inFIG. 5). Then, a pulsating flow was produced in the pipe11in correspondence with the combustion cycle of an internal combustion engine. Thus, asymmetrical flow and swirl varies cyclically in correspondence with the pulsating flow, as illustrated inFIG. 6. Accordingly, the flow velocity of the air flowing around the flow sensor21for flow velocity measurement is cyclically varied, and it can be difficult to accurately detect flow characteristics, such as flow velocity.

Despite the flow patterns shown inFIGS. 5 and 6, the flow detection device10is able to more accurately detect flow characteristics of the fluid. For instance, the flow straightening member18causes air to flow from the entire circumference into the upstream aperture14aof the first channel14.

As shown inFIG. 7, fluid flowing in approximately the center of the pipe11eventually interacts with the flow straightening member18. Specifically, the fluid flows along the upstream side of the flow straightening member18and is directed outward radially in 360° as viewed looking downstream. Some of the fluid then flows along the downstream side of the flow straightening member18, and that fluid converges and is made uniform downstream of the flow straightening member18. Then, the fluid flows into the first channel14through the upstream aperture14a. In this manner, asymmetrical flow of the fluid is substantially reduced. As such, the flow velocity of the air flowing around the flow sensor21becomes stable. Further, by reducing asymmetrical flow, the influence of pulsating flow is reduced, and this makes measurement results more accurate.

It will be appreciated that as the fluid flows along the downstream side of the flow straightening member18, the fluid flows along the entire circumference of the flow straightening member18. As such, the air flows along a relatively large area along the entire circumference of the flow straightening member18for more even flow into the first channel14. Thus, the flow velocity of the fluid flowing through the first channel14is more likely to correspond with the average flow velocity of the fluid flowing through the second channel16and the rest of the pipe11. As a result, more accurate measurement results can be obtained.

Furthermore, the flow straightening member18can reduce the amount of foreign particles that contact the flow sensor21as shown inFIG. 7. In general, foreign particles may be contained in the fluid. For instance, dust27of a small size (e.g., smaller than approximately 100 μm) is likely to pass through a filter element of an air cleaner and flow in the pipe11. As the dust27approaches the flow straightening member18, the dust27is directed outwardly in the radial direction by the flow straightening member18. As mentioned above, the upstream aperture14aof the first channel14is hidden behind the flow straightening member18. Therefore, a significant amount of the dust27is directed away from the first channel14and is caused to flow through the second channel16. Thus, dust27is less likely to flow into the first channel14, and the detection accuracy of the flow sensor21is less likely to be impaired by dust27sticking to the flow sensor21.

The downstream member22also improves the detection accuracy of the flow sensor21. First, the downstream member22improves accuracy by increasing the flow velocity of the fluid in the first channel14. Specifically, as illustrated inFIG. 7, the fluid flowing through the first channel14flows through the downstream-side first channel23formed by the first channel portion15and the downstream member22. Thus, the downstream member22obstructs the outlet of the first channel14. As a result, the flow velocity increases adjacent the downstream aperture29of the first channel14, and negative pressure is produced. The negative pressure draws the fluid out of the first channel14, and the flow velocity of the fluid in the first channel14is increased. Therefore, a ratio of thermal loss is reduced, and the detection accuracy of the flow sensor21is enhanced.

Furthermore, flow between the surface15aof the first channel portion15and the inner surface17aof the second channel portion17can be changed by making the second channel portion17smaller. When the channel is narrowed, the flow velocity between the surface15aand the inner surface17ais increased. As a result, the negative pressure becomes higher, and the flow velocity of the fluid flowing through the first channel14is further increased. Thus, the detection accuracy is further enhanced. In other words, the detection accuracy can be enhanced without enlarging the first channel portion15.

In addition, the downstream member22reduces the amount of dust moving upstream from flowing back into the first channel14.FIG. 8is a graph showing temporal change in flow amount. In the graph, Line30shows temporal change in flow amount observed when the throttle valve is relatively closed, and Line31shows temporal change in flow amount observed when the throttle valve is relatively open. Thus, when a pulsating flow is produced in the fluid in the pipe11and the opening of the throttle valve becomes equal to a certain value or higher, part of the air flows upstream in the pipe11. The hatched areas32inFIG. 8represent the periods during which fluid flows upstream.

This type of flow is represented inFIG. 9. As mentioned above, the outlet aperture29of the first channel14is hidden behind the downstream member22. Therefore, dust27flowing upstream is directed outward in the radial direction by the downstream member22and is less likely to flow into the first channel14. Furthermore, the end face15cof the first channel portion15is shaped conically so as to direct the dust27away from the first channel14. As a result, dust27is unlikely to flow upstream and stick to the flow sensor21, and the accuracy of the flow sensor21can be maintained.

Description will now be given to the result of an experiment conducted to compare change in the characteristics of the apparatus10for measuring flow amounts with a comparative example. Change in characteristics (S) is expressed by the following expression:
S=(FVA−FVS)/FVS
FVArepresents flow velocity with asymmetric flow and is obtained by passing air with symmetric flow through a bent pipe and measuring flow velocity downstream from the bent area where asymmetric flow is occurring (e.g., Position A inFIG. 5). FVSrepresents flow velocity with symmetric flow and is obtained by passing air with symmetric flow through an straight pipe. The flow velocity with symmetric flow substantially correlates with the average flow velocity of the air flowing through the entire pipe. The same amount of air is passed through the bent pipe and the straight pipe. Therefore, when change in characteristics (S) approaches 0%, the flow detection device10is more accurately measuring the average flow velocity of the air flowing through the pipe11with a bend. That is, an accurate measurement is taken despite the presence of asymmetrical flow.

FIG. 10is a graph showing the result of an experiment conducted to compare change in the characteristics (S) using the device10and a comparative example. Here, the device disclosed in U.S. Pat. No. 6,938,473 is used as the comparative example.

In the experiment, the flow amount was gradually increased, and change in characteristics were determined with respect to the flow detection device10and the comparative example. As shown in the graph ofFIG. 10, the change in the characteristics of the device10is close to 0% with each flow amount. Meanwhile, change in the characteristics of the comparative example is biased in the negative direction with any flow amount. Thus, the flow detection device10is capable of more accurately measuring the average flow velocity of the fluid flowing through the entire pipe11even though there is asymmetrical flow in the pipe11. In other words, the device10allows more accurate measurement results to be obtained.

Second Embodiment

Referring now toFIG. 11, another embodiment of the flow detection device50for detecting a flow characteristic is shown. The device50includes a downstream member51that is disposed downstream of a first channel portion15. A downstream-side first channel52is defined between the downstream member51and the first channel portion15. In the embodiment shown, the downstream member51is formed in such a size that a downstream-side end face15aof the first channel portion15is hidden behind the downstream member51as viewed looking upstream along the axis of the device50. In other words, the width (perpendicular to the axis of the device50) of the downstream member51is equal to or greater than that of the end face15a. For this reason, when fluid flows upstream in the pipe11, dust27is less likely to flow along the end face15ainto the downstream-side first channel52. Thus, measurement results become more stable.

Also, in the embodiment shown, the end face15ais inclined such that the first channel portion15reduces in width moving downstream along the axis of the first channel portion15. In other words, the end face15ais inclined so that it is inclined upstream relative to the second channel16when moving along the end face15atoward the inner wall17aof the second channel portion17.

In another embodiment, the end face15ais inclined in an opposite direction, such that the end face15ais inclined downstream relative to the second channel16when moving along the end face15atoward the inner wall17aof the second channel portion17. Also, in this embodiment, the end face15ais hidden behind the downstream member51when viewed looking upstream along the axis of the device50. Thus, the detection accuracy of the flow sensor21is unlikely to be impaired by dust27flowing back and sticking to the flow sensor21.

While only the selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.