The invention relates to systems in which a bend is defined in a fluid-handling conduit or passage that otherwise extends between a first region of relatively-higher pressure to a second region of relatively-lower pressure, as may be found in the bypass passage of a thermal-type or “hot-wire” mass fluid flow sensor.
The prior art teaches that the importance of measuring air intake into an internal combustion engine for purposes of improving engine control. One type of mass fluid flow sensor includes a housing that projects into the main air intake tube of the engine and defines a bypass passage into which a small sample of intake air is diverted, for example, by a converging inlet section of the passage that is placed in opposition with the primary direction of airflow in the tube. A hot-wire resistive element disposed within the passage is used to generate a signal representative of instantaneous mass fluid flow through the passage, from which a controller calculates instantaneous mass airflow into the engine, as taught in co-pending U.S. patent application Ser. No. 10/126,810 tiled Apr. 19, 2002, now published as U.S. patent application No. 2003/0196486A1, and assigned to the assignee of the invention, the disclosure of which is hereby incorporated by reference.
The sensor housing is preferably provided with an exterior surface contour that cooperates with the relative location of the outlet section of the passage to create a low pressure area which draws air out of the bypass passage. The resulting “push-pull” configuration enhances the flow of fluid through the passage to thereby increase the sensor's signal-to-noise ratio. By way of example, in U.S. Pat. No. 5,556,340, the exterior surface contour is a wedge-shaped air deflector on the housing's leading edge immediately upstream of the outlet section of the passage.
The prior art further recognizes the importance of limiting the effect of back flow through the bypass passage on the airflow measurement. Thus, for example, the '340 patent teaches use of a U-shaped bypass passage that positions the inlet and outlet sections of the bypass passage relatively close to one another in the primary direction of air flow, to thereby reduce back flow by creating a similar pressure at the inlet and outlet sections of the passage under reverse flow conditions.
Unfortunately, the conduit turns or bends inherent to the U-shaped design generate fluidic losses as the diverted flow impinges against the outer wall of each passage bend, as well as due to turbulent flow induced along the inner wall of each passage bend, which disrupts the velocity profile of the diverted flow as it passes the hot-wire element, notwithstanding the use of a “push-pull” passage configuration. These effects, in turn, limit the signal-to-noise ratio and dynamic range that may be achieved with such sensors.
Under the invention, a mass fluid flow sensor, for example, for measuring airflow in a primary direction through an air intake system of a motor vehicle, includes a housing adapted to be inserted into the airflow. The housing includes an internal passage having an inlet that is placed in opposition to the primary direction of airflow, and an outlet disposed at a predetermined angle with respect to the primary direction of airflow such that a minimum pressure drop is developed at the outlet relative to the inlet as fluid flow in the primary direction passes over the housing. A sensing element, such as a hot-wire element, is disposed within the passage to detect fluid flow through the passage.
In accordance with an aspect of the invention, the passage includes, in series, a first section converging along a first axis to define an annular nozzle having a nozzle diameter, and a generally-right-cylindrical second section adjacent to the first section and extending along the first axis, wherein the second section has a nominal diameter that is greater than the nozzle diameter, such that a radial step is defined immediately downstream of the nozzle. The sensing element is preferably disposed in the passage proximate to the nozzle exit.
The passage also includes a third section adjacent to the second section that defines a generally-semi-spherical chamber centered on the first axis in opposition to the radial step, with the chamber having an effective radius substantially equal to one half of the diameter of the second section. The passage further includes a fourth section adjacent to at least one of the second and third sections, with the fourth section converging along a second axis to a minimum diameter. The second axis is disposed at a first, nonzero angle with respect to the first axis and, in a preferred embodiment, is disposed at roughly a ninety degree angle with respect to the first axis.
In accordance with another aspect of the invention, the sensing element is preferably disposed in the passage proximate to the radial step, whereby the sensing element is exposed to a diverted flow that is accelerated by the first section for increased sensor dynamic range, and which is provided a more uniform velocity profile by virtue of passage's several sections.
In accordance with yet another aspect of the invention, the minimum diameter of the fourth section is not less than the diameter of the second section and, most preferably, is substantially equal to the diameter of the second section, such that the velocity profile of the airflow at the minimum diameter portion of the fourth passage section is roughly the same as the velocity profile of the airflow within the downstream portion of the second passage section.
In accordance with a further aspect of the invention, the passage also includes a substantially-constant-diameter fifth section immediately adjacent to the fourth section, in which the diameter of the fifth section is substantially equal to the minimum diameter of the fourth section. Preferably, the fifth section includes an arcuate bend characterized by a substantially-constant cross-sectional area through the bend, and the fifth section terminates along an outlet axis that is substantially parallel to the first axis of the first section, whereby the passage is provided a nominal “U-shaped” configuration and the passage outlet is placed in close proximity to the passage inlet.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.
Referring to
As best seen in
The second section 38 of the passage 22, immediately adjacent to the first section 30, is a radially-expanded section of generally-right-cylindrical configuration that is coaxial with the first axis 32. The nominal diameter D2 of the expanded second section 38 is significantly greater than the minimum diameter D1 of the first passage section 30 (at the nozzle exit 36). As seen in
The third section 44 of the passage 22, immediately adjacent to the downstream portion 42 of the second section 38, defines a generally-semi-spherical chamber 46 centered on the first axis 32 in opposition to the radial step 40, with the third chamber 46 having an effective radius R3 substantially equal to one half of the diameter D2 of the second section 38.
The fourth section 48 of the passage 22, adjacent to at least one of the second and third sections 38, 44, converges along a second axis 50 to a minimum diameter D4 that is substantially equal to the diameter D2 of the second section 38, such that the velocity profile of the airflow at the minimum diameter portion 52 of the fourth passage section 48 is roughly the same as the velocity profile of the airflow within the downstream portion 42 of the second passage section 38. While the invention contemplates that the second axis 50 may be disposed at a range of nonzero angles with respect to the first axis 32, as seen in
Lastly, the passage 22 includes a substantially-constant-diameter fifth section 58 immediately adjacent to the fourth section 48, whose diameter D5 is substantially equal to the minimum diameter D4 of the fourth section 48. As seen in
Referring again to
In operation, as air is drawn into the air intake system 12 by the engine, a portion of the air is diverted into the sensor's bypass passage 22 by the converging first section 30 of the passage 22. The first passage section serves to accelerate the diverted airflow through the nozzle while reducing local turbulence and “conditioning” the airflow for a streamline approach to the hot wire element 66, thereby improving measurement sensitivity, stability, and accuracy. As the diverted airflow exits the nozzle, the airflow expands into the radially-larger, coaxial, second passage section 38. Turbulence generated at the radial step 40 defined between the first and second passage sections 30, 38 acts in the manner of a diffuser section to thereby provide an improved velocity profile, both in the critical area 34 proximate to the nozzle exit 36 and in the downstream portion 42 of the second section 38. The semispherical third section 44 and converging fourth section 48 cooperate to reduce pressure losses as the diverted airflow is redirected through the fifth passage section 58 to the passage outlet 26 with a substantially uniform velocity profile. And the relative proximity of the passage's inlet and outlet 24, 26 helps to reduce back flow through the passage 22 by creating similar air pressures at both the inlet 24 and the outlet 26.
While the above description constitutes the preferred embodiment, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the subjoined claims. For example, while the exemplary sensor 10 is described in connection with the measuring the amount of air inducted into an internal combustion engine, the invention may be used in connection with the measurement of air flow through other conduits, and of other fluid flows generally, as well as for the design of low-loss ducts and passages. Further, as employed in the context of the airflow sensor illustrated in the Drawings, the fifth section of the illustrated airflow sensor passage features a gradual, constant diameter bend 60 so as to provide a nominal outlet axis 62 that is parallel to the nominal inlet axis 32 of the passage 22; however, it will be appreciated that the invention contemplates other relative outlet axis angles that are other than ninety degrees off the second axis 50, or that lie in a different plane from the inlet axis 32.
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