Abstract:
A variable orifice fluid flow sensor is provided that includes a fluid flow passage therethrough formed with a first port portion adjacent to one end of said passage and a second port portion adjacent to the other end of said passage. A bending member is mounted in the fluid flow passage between the first and second port portions and having a fluid flow limiting flapper extending across the fluid flow passage for creating a fluid flow opening in the passage, the size of the opening being variable responsive to fluid flow in said fluid flow passage. A biasing member is also mounted between the first and second port portions and includes at least one biasing element extending away from the biasing member into contact with the bending member to exert a contact force on the bending member.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to flow sensors, and more particularly, to variable orifice fluid flow sensors. 
     Orifice flow sensors are used to measure the flow rates of fluids, which include liquids and gases. A typical orifice flow sensor comprises a fixed orifice through which a fluid is made to flow. A pressure difference is established between the fluid that is present upstream from the orifice and the fluid that is flowing through the orifice. This pressure difference can be used to measure the flow rate of the fluid. For this purpose, a pressure transducer measures the pressure difference that is established across the orifice, and is calibrated such that the flow rate of the fluid is calculated from this pressure difference. 
     Variable orifice flow sensors provide sufficient pressure difference for measurement purposes across a broad range of flow rates. This is achieved by introducing a bending member into the fluid flow passage. The bending member is mounted to the housing for the fluid flow passage and includes a flapper that is positioned across the fluid flow passage and bends or flexes in the direction of the fluid flow as a result of contact with the fluid flow, and hence creates a variable orifice within the fluid flow passage. The measurement of flow rates in a variable orifice flow sensor is similar to the measurement of flow rates in fixed orifice flow sensors. That is, a pressure transducer measures the pressure difference across the variable orifice and calculates the flow rate of the fluid from the pressure difference. 
     U.S. Pat. Nos. 4,989,456; 5,033,312; 5,038,621; 6,722,211 and 7,270,143 show variable orifice flow sensors. 
     The performance of the sensor can be directly influenced by the connection of the bending member including the flapper to the housing that defines the fluid flow passage. In situations where the bending member is rigidly secured to the housing, this tight engagement with the housing can distort the movement of the flapper to negatively affect its operation. Further, in situations where the bending member is too loosely secured to the housing, it is possible for fluid to flow around the bending member through leaks located between the housing and the bending member. 
     In either situation, the movement and operation of the flapper is affected by the connection of the bending member to the housing, and hence the measured pressure difference across the variable orifice defined by the flapper becomes altered, such as by poor low flow resolution and non-linear movement of the flapper. This, in turn, leads to inaccurate measurements of the flow rate of the fluid. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In the present invention a variable orifice fluid flow sensor is provided having two port portions engaged with one another that form a fluid flow passage through the sensor. A variable orifice device with a bending member including a fluid flow limiting flapper is provided between the two port portions. The variable orifice device also includes a biasing member that is disposed between the two port portions and that engages the bending member around the gas flow passage. The biasing member includes a number of biasing elements that extend outwardly from the biasing member into contact with the bending member. The engagement of the biasing elements with the bending member provides a constant contact and/or biasing force against the bending member to hold the bending member relative to the two port portions in a manner that does not negatively affect the operation of the flapper in determining a fluid flow pressure differential and measuring the corresponding fluid flow rate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a variable orifice fluid flow sensor in accordance with an exemplary embodiment of the invention. 
         FIG. 2  is an exploded isometric view of a variable orifice fluid flow sensor in accordance with another exemplary embodiment of the invention. 
         FIG. 3  is an isometric view of a biasing member and a bending member of a variable orifice fluid flow sensor in accordance with an exemplary embodiment of the invention. 
         FIG. 4  is a cross sectional view of a variable orifice fluid flow sensor in accordance with yet another exemplary embodiment of the invention. 
         FIG. 5  is a partially broken away cross sectional view of a variable orifice fluid flow sensor in accordance with yet another exemplary embodiment of the invention. 
         FIG. 6  is a partially broken away cross sectional view of a variable orifice fluid flow sensor in accordance with yet another exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an isometric view of a variable orifice fluid flow sensor  100  in accordance with one embodiment of the present invention. Variable orifice fluid flow sensor  100  develops pressure differences that are used to measure flow rates of fluids, such as gases, flowing through the flow sensor  100 . Therefore, variable orifice fluid flow sensor  100  can also be referred to as a differential pressure variable orifice gas flow sensor. Variable orifice gas flow sensor  100  has a generally cylindrical configuration. However, variable orifice gas flow sensor  100  may be formed in a variety of shapes and sizes and still lie within the scope of this invention. 
       FIGS. 2-4  illustrate variable orifice gas flow sensor  100  comprising a housing  102  that includes a first port portion  104  and a second port portion  106  that are connected to one another to define a gas flow passage  108  therein through which a gas flows. A sealing member  110  is disposed and engaged between the first port portion  104  and the second port portion  106  to prevent gas flowing through the gas flow passage  108  from exiting the passage  108  between the first port portion  104  and second port portion  106 . When variable orifice gas flow sensor  100  is used for measuring gas flow rates in a breathing apparatus, a flow sensor  100  is inserted at one or more desired locations in a breathing circuit. 
     Variable orifice gas flow sensor  100  includes a bending member  112  intermediate to first port portion  104  and second port portion  106 . Bending member  112  is generally complementary in shape to the shape of the gas flow passage  108 , and includes an outer peripheral member  114  that a diameter larger than the diameter of the gas flow passage  108 , such that a portion of the outer peripheral member  114  is disposed within a gap  116  defined between first port portion  104  and second port portion  106  when engaged with one another. The gap  116  can be formed to have the desired with, but hi an exemplary embodiment is formed to be approximately 0.005 inches in width. 
     To maintain the position of the outer peripheral member  114  and bending member  112  relative to the first port portion  104  and second port portion  106 , outer peripheral member  114  includes a number of apertures  118  formed therein that are alignable and positionable on mounting projections  120  formed on first port portion  104  and/or second port portion  106 . The mounting projections  120  operate to properly locate the bending member  112  with respect to the first port portion  104  and second port portion  106  an to prevent rotation of the bending member  112  with respect to the first port portion  104  and second port portion  106 . Alternatively, in another exemplary embodiment, the apertures  118  and the projections  120  can be omitted entirely or substituted therefor by another suitable structure. 
     The bending member  112  also includes a fluid or gas flow limiting flapper  122  that is connected at one end to the outer peripheral member  114  and extends inwardly into and across the gas flow passage  108  to separates first port portion  104  and second port portion  106 . Because gas flow limiting flapper  122  is attached at one end to the outer peripheral member  114 , as gas flows along the gas flow passage  108  through variable orifice gas flow sensor  100 , gas flow limiting flapper  122  bends or flexes in the direction of the flow of the gas. For this purpose, gas flow limiting flapper  122 , and outer peripheral member  114  when formed integrally with flapper  122 , is made from a resilient material. For example, gas flow limiting flapper  122  can be made from resilient plastic or a metal. The bending of gas flow limiting flapper  122  leads to the formation of an increased fluid or gas flow opening  123  in the gas flow passage  108 . This gas flow opening  123  defined between the outer peripheral member  114  and the flapper  122  varies with the bending of gas flow limiting flapper  122  due to the flow rate of the gas within the passage  108 . A pressure difference is established across gas flow limiting flapper  122 . This pressure difference is measured by means of a conventional pressure transducer (not shown in  FIGS. 2-4 ). Gas pressures are provided to the pressure transducer through pressure measurement ports  124  and  126 , which open into the gas flow passage upstream and downstream of flapper  122  on first port portion  104  and second port portion  106 , respectively. The pressure transducer is calibrated such that the flow rate of the gas through variable orifice gas flow sensor  100  is obtained from the pressure difference across gas flow limiting flapper  122 . 
       FIGS. 2-5  illustrate a biasing member  128  that is positioned between first port portion  104  and second port portion  106  within the gap  116 . The biasing member  128  is formed with any suitable shape and of any suitable resilient material, such as a resilient plastic or a metal. In the illustrated exemplary embodiment, the biasing member  128  is formed as ring  130  that defines a central opening  132  therein. The ring  130  is positioned within the gap  116  with the central opening  132  disposed around gas flow passage  108  so as not to obstruct gas flow through the passage  108  or the movement of the flapper  122 . The ring  130  also includes a pair of apertures  134  that are formed similarly to apertures  118  in outer peripheral member  114  of bending member  112 , though any number of apertures  134  can be utilized, or the apertures  134  can be omitted entirely. The apertures  134  are positioned over the mounting projections  120  to locate the ring  130  properly with respect to the bending member  112  as well as first port portion  104  and second port portion  106 , and to prevent rotation of ring  130 . 
     Biasing member  128  also comprises a number of biasing elements  136  disposed on the ring  130  that extend inwardly from the ring  130  into the central opening  132 . The biasing elements  136  can extend from the inner edge of the ring  130 , or can be separated from the ring  130  by slots  138  disposed on each side of the biasing element  136  that extend into the ring  130 . The biasing elements  136  contact the outer peripheral member  114  of the bending member  112  to act on the bending member  112  in a manner that holds the bending member  112  in position between first port portion  104  and second port portion  106  with the desired amount of force to enable proper operation of the flapper  122  on the bending member  112 . In the exemplary embodiment in the drawing figures, the biasing elements  136  take the form of tabs  140  that are at least partially bent at an angle with respect to the plane of the ring  130 , forming biasing member  128  as a spring washer. The tabs  140  provide localized points of force on the bending member  112 , thereby providing a constant biasing force on the outer peripheral member  114  to hold the bending member  112  in the desired position. The size, number and angle of the tabs  140  can be varied from the configuration shown in the exemplary embodiment of the invention showing equidistant tabs  140 , along with the material from which the biasing member  128  is formed, to provide the desired amount of force from the tabs  140  on the bending member  112  and enable the flapper  122  to operate correctly, but without distorting the flapper  122  or allowing leaks to form around the bending member  112  in the gas flow passage  108 . Further, the use of the biasing member  128  secures the bending member  112  within the gas flow passage  108  with looser assembly tolerances between first port portion  104  and second port portion  106  and without the need for any direct securing of the bending member  112  and/or biasing member  128  to the housing  102 , including any additional securing means or members, such as adhesives, fasteners or threaded components on first port portion  104  and second port portion  106 . It is also contemplated that the only structure holding the bending member  112  in position in the sensor  100  is the biasing member  128 , such that the bending member  112  may float within the gap formed between the first port portion  104  and second port portion  106  under the bias of the biasing member  128 . 
       FIG. 6  illustrates another exemplary embodiment of the invention in which the biasing elements  136  contact the outer peripheral member  114  of the bending member  112  within holes  142  formed in the outer peripheral member  112 . In this configuration, the tabs  140  apply a force at an angle to the axis of the bending member  112  when the tabs  140  engage an edge or surface  144  of the hole  142  in the bending member  112 . This further assists in holding the bending member  112  in position between first port portion  104  and second port portion  106  with the desired amount of force to enable proper operation of the flapper  122  on the bending member  112 . 
     Variable orifice gas flow sensor  100  may be of the single use, disposable type or of the multiple use, reusable type. The former will typically be manufactured from inexpensive plastic material. The latter will usually be manufactured from autoclavable materials, such as metal or high temperature resistant plastic(s). 
     Variable orifice gas flow sensor  100  may also optionally include one or more fixed orifices (not shown) and a flow-limiting member (not shown). The fixed orifice ensures that gas flows having a velocity that is insufficient to cause bending of gas flow limiting flapper  122  can pass through variable orifice gas flow sensor  100 . This can be achieved by shaping gas flow limiting flapper  122  such that there is space for the gas flow to pass through. A flow limiting member restricts the bending of gas flow limiting flapper  122  to provide an appropriate pressure difference across the flapper for high flow rates. 
     The various embodiments of the invention provide a variable orifice gas flow sensor  100  that is capable of reproducibly measure a broad range of flow rates by attaching the bending member  112  to the housing  102  for the variable orifice fluid flow sensor  100  in a manner that minimizes the effect of the attachment on the operation of the bending member  112 . 
     The written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.