Abstract:
A needle valve assembly for providing fluid flow control includes a motor; an internally threaded valve body; and an externally threaded plunger threadably engaged with the internally threaded valve body and rotatably and reciprocally driven by the motor, wherein the valve body including a fluid inlet, a fluid outlet, and a flow chamber therebetween, the flow chamber including a flow chamber wall and a flow chamber outlet, the plunger including a flexible needle member reciprocating within the flow chamber outlet to provide variable flow control therethrough, the flexible needle member including a lip seal engageable with the flow chamber wall during reciprocation of the plunger and flexible needle member to provide a seal therebetween.

Description:
FIELD OF THE INVENTION 
     The field of this invention relates, in general, to needle valves for control of fluid flow and, in particular, to a needle valve for control of product flow in oxygen concentrators. 
     BACKGROUND OF THE INVENTION 
     Oxygen concentrators are commonly used in the home medical market to treat patients with chronic obstructive pulmonary diseases. Due to the wide availability of these oxygen concentrators on the market, the market for these devices is highly cost competitive and is expected to become even more competitive in the future. In order to remain competitive in this market, it is critical to reduce the manufacturing cost associated with every component in the oxygen concentrator system. The flow measurement and control system is one aspect of the overall concentrator system that may be cost-reduced; however, a less expensive flow system will only be viable if it provides sufficient accuracy and reliability. 
     Commercially available oxygen concentrators generally use one of two technologies to control the flow of product gas. The most common is a rotameter (flowmeter with a floating ball) combined with a manually controlled needle valve. Rotameters may be inexpensive, but in order to maintain accuracy, they are often coupled with a pressure regulator. Even combined with the regulator, due to pressure variations downstream of the rotameter, these needle valve/rotameter combinations provide an accuracy of about 10% which is sufficient for most home medical oxygen concentrators. Nonetheless, once combined with a regulator, this control method would not be considered inexpensive. 
     Another common technology is the use of an orifice plate in combination with a pressure regulator. The orifice plate usually contains 10 or more precision orifices, each providing an exact flow when an exact pressure is provided on the feed side. The regulator is used to provide a fixed pressure on the feed side. The orifice plate/regulator combination functions by allowing the user to adjust a dial to a specific orifice in order to provide a specific product flow. This method of flow control is generally more accurate than a rotameter; however, it is also more expensive and is also subject to inaccuracy due to downstream pressure fluctuations. 
     A need clearly exists for a low-cost, accurate flow control system for an oxygen concentrator. One method of achieving this goal makes use of the increasingly common use of acoustic systems to measure oxygen concentration in oxygen concentrators. For negligible additional cost, these acoustic systems can be modified to measure oxygen flow in addition to concentration Coupling the flow measurement with an inexpensive motorized valve would result in a low-cost, accurate flow control system. 
     SUMMARY OF THE INVENTION 
     To solve these problems and others, an aspect of present invention relates to a method of providing fluid flow control in a needle valve assembly. The method includes providing a needle valve assembly comprising a motor, an internally threaded valve body, and an externally threaded plunger threadably engaged with the internally threaded valve body and rotatably and reciprocally driven by the motor, the valve body including a fluid inlet, a fluid outlet, and a flow chamber therebetween, the flow chamber including a flow chamber wall and a flow chamber outlet, the plunger including a flexible needle member that reciprocates within the flow chamber outlet to provide variable flow control therethrough, the flexible needle member including a lip seal that engages the flow chamber wall during reciprocation of the plunger and flexible needle member to provide a seal therebetween; supplying fluid flow to the fluid inlet of the needle valve assembly; providing variable flow control in the needle valve assembly through reciprocation of the flexible needle member in the flow chamber outlet; and sealingy engaging the flow chamber wall with the lip seal of the flexible needle member to prevent fluid flow therebeween. 
     A further aspect of the invention involves a needle valve assembly for providing fluid flow control. The needle valve assembly includes a motor; an internally threaded valve body; and an externally threaded plunger threadably engaged with the internally threaded valve body and rotatably and reciprocally driven by the motor, wherein the valve body including a fluid inlet, a fluid outlet, and a flow chamber therebetween, the flow chamber including a flow chamber wall and a flow chamber outlet, the plunger including a flexible needle member reciprocating within the flow chamber outlet to provide variable flow control therethrough, the flexible needle member including a lip seal engageable with the flow chamber wall during reciprocation of the plunger and flexible needle member to provide a seal therebetween. 
     A further aspect of the invention relates to the flexible, elastomeric nature of the flexible needle member of the valve. The flexible characteristics of the material reduces the amount of torque required to seal the valve compared to the prior art and the amount of precision required in the valve components in order to insure a complete seal. 
     A further aspect of the invention involves the capability to adjust flow under varying downstream pressure effects. The invention coupled with control and measurement electronics enables the device to keep the flow at the set-point value regardless of upstream or downstream pressure effects. 
     A further aspect of the invention is the small number of parts required for the needle valve assembly. Fewer parts leads to the low manufacturing cost of the valve which is critical for the application. 
     Further objects and advantages will be apparent to those skilled in the art after a review of the drawings and the detailed description of the preferred embodiments set forth below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simple schematic of an embodiment of a gas separation device. 
         FIG. 2  is a perspective view of an embodiment of a needle valve assembly. 
         FIG. 3  is a partial cross-sectional view of the needle valve assembly of  FIG. 2 . 
         FIG. 4  is an enlarged cross-sectional view of a portion of the needle valve assembly of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a gas separation device  10  constructed in accordance with an embodiment of the invention will first be described before describing an embodiment of a needle valve assembly  100 . The gas separation device  10  may include a compressor  20 , a Pressure Swing Adsorption (PSA) Module or concentrator  30 , a measurement mechanism  40 , and a flow control mechanism  50 . In use, a feed fluid such as ambient air may be drawn into the compressor  20  and delivered under high pressure to the PSA Module  30 . The PSA module  30  separates a desired product fluid (e.g., oxygen) from the feed fluid (e.g., air) and expels exhaust fluid. Characteristics of the product fluid (e.g., flow/purity) may be measured by a measurement mechanism  40 . Delivery of the product fluid may be controlled with the flow control mechanism  50 . 
     With reference to  FIGS. 2–4 , an embodiment of a needle valve assembly  100  that is ideal for use in a flow control mechanism  50  of a gas separation device  10  will now be described. The needle valve assembly  100  includes a one-piece valve body  120  and a motor  130 . The motor  130  includes a motor mount  140  for mounting the motor  130  to motor mount bosses  150  of the valve body  120 . Threaded fasteners (not shown) may be used to secure the motor mount  140  to the motor mount bosses  150 . The valve body  120  may include additional mounting bosses  160  for mounting the needle valve assembly  100  to another component of the gas separation device  10 . Power and control may be supplied to the motor  130  through an electrical connector  170 . A motor gear  180  ( FIG. 3 ) is carried on a motor shaft  190 . The motor  130  is a stepper motor that rotates the motor shaft  190  and the motor gear  180  in a clockwise or counter-clockwise manner. In the embodiment shown, the motor  130  is a 48 step/rev stepper motor that provides roughly ¼ Liter per minute flow resolution with a feed pressure of 10 psig. In other embodiments, the motor  130  may have more or less than 48 steps/rev to provide either finer resolution with more steps/rev or faster response with less steps/rev. 
     A geared screw  200  of a reciprocating and rotating plunger  210  is operatively engaged with the motor gear  180 . In the embodiment shown, the gear ratio of the geared screw  200  to the motor gear  180  is 4:1. The gear ratio affects the torque and resolution of the needle valve assembly  100 . In an alternative embodiment, motor  130  could operate as a direct drive without motor gear  180  when the torque is sufficiently small. In another alternative embodiment, the gear ratio of the geared screw  200  to the motor gear  180  could be as high as necessary (e.g., 100:1) to provide the increased resolution and higher torque that might be required in large systems. The rotating plunger  210  includes a plunger shaft  212  with external threads  214  that are threadingly engaged with internal threads  216  of the valve body  120  and a bore  218 . An elastomeric, flexible, one-piece needle member  220  includes a shaft  230  received within the bore  218 , and a head  240 . In the preferred embodiment, the shaft  230  and bore  218  have non-circular (e.g., square) cross sections such that when the rotating plunger  210  is rotated, the flexible needle member  220  will also rotate. The head  240  of the needle member  220  includes a tip portion  250  and an integral lip seal  260 . In an alternative embodiment, the lip seal  260  may be a separate element from the needle member  220 . 
     With reference to  FIGS. 3 and 4 , the valve body  120  includes an inlet  270  having an inlet passage  280 , an outlet  290  having an outlet passage  300 , and a flow chamber  310  including flow chamber wall  312 . The tip potion  250  of the needle member  220  is disposed in the flow chamber  310 . Near an interface of the outlet passage  300  and the flow chamber  310 , the valve body  120  includes a flow chamber outlet port  320 . Outlet passage walls  330  terminate at one end at the outlet port  320 . 
     With reference to  FIGS. 2–4 , the needle valve assembly  100  will now be described in use. The motor  130  rotates the motor shaft  190  in a clockwise or counter-clockwise manner, causing motor gear  180  to rotate in a opposite manner. Rotation of motor gear  180  causes geared screw  200  and externally threaded plunger  210  to rotate. Rotation of the externally threaded plunger  210  within internally threaded valve body  120  causes the plunger  210  and, hence, the elastomeric needle member  220 , to reciprocate within the valve body  120 , depending on the direction of rotation of the motor  130 . Movement of the top portion into and out of the flow chamber outlet port  320  creates a variable orifice in the needle valve assembly  100 . Increased movement of the elastomeric needle member  220  towards the flow chamber outlet port  320  causes the tip portion  250  to further block the flow chamber outlet port  320 , further inhibiting or stopping fluid flow through the inlet passage  280 , flow chamber  310 , and outlet passage  300 . The flexible, elastomeric nature of the needle member  220  allows the tip portion  250  to flex and seal against the outlet passage walls  330  as the needle member  220  is moved towards the flow chamber outlet port  320 . The flexible, elastomeric needle member  220  relaxes concentricity requirements and minimizes the required torque by the motor  130  to reduce or stop flow through the needle valve assembly  100 . Increased movement of the elastomeric needle member  220  away from the flow chamber outlet port  320  causes the tip portion  250  to further withdraw and increase the opening at the flow chamber outlet port  320 , further increasing fluid flow through the inlet passage  280 , flow chamber  310 , and outlet passage  300 . Pressure on the lip seal  260  and the needle member  220  keeps the tip portion  250  engaged. Thus, by controlling reciprocating movement of the needle member  220 , fluid flow through the needle valve assembly  100  is controlled. While the elastomeric needle member  220  reciprocates in the valve body  120 , the flexible, elastomeric lip seal  260  sealingly engages the flow chamber walls  312 , preventing the escape of fluid flow through this part of the valve body  120 . This lip seal  260  is integrally formed with the elastomeric, one-piece needle member  220 . As mentioned above, in an alternative embodiment, the lip seal  260  may be separate from the elastomeric needle member  220 . The lip seal  260  eliminates the need for a gasket or o-ring for sealing within the valve body  120 . The lip seal  260  additionally allows the volume of the flow chamber  310  to be minimized, further reducing the size of the needle valve assembly  100 . Relative to other types of gaskets, the lip seal  260 , and specifically the small size and the small diameter of the lip seal  260 , functions to lower the torque required by the motor  130  to operate the needle valve assembly  100 . Use of integrated lip seal  260  eliminates the need for an o-ring or an external lip seal, which add additional complexity in the design. Thus, the main advantages to the lip seal  260  are reduced cost through a reduced number of parts and reduced torque required by the motor. 
     Utilizing a  48  step/rev stepper motor and a gear ratio of 4:1 for the geared screw  200  and the motor gear  180  provides about 120 steps between the closed and the full-flow positions. In alternative embodiments, a larger or smaller number of steps could be specified to provide either more precision or faster adjustment. Because resolution of the flow control in the needle valve assembly  100  is a function of the motor  130  and the gear ratio, the pressure differential resolution can be increased or decreased in the needle valve assembly  100  by adjusting these two variables. Utilizing a higher gear ratio between the geared screw  200  and the motor gear  180  allows a smaller motor  130  to be used and allows for precise movement of the needle member  220  for precise fluid flow control and improved flow control accuracy of less than about ¼ Liter per minute at 10 psig. However, this accuracy could be adjusted by changing the gear ratio and the stepper motor. 
     In an alternative embodiment, the head  240  of the elastomeric needle member  220 , the flow chamber  310 , and the outlet passage  300  may be longer and narrower, or shorter and wider than that shown in  FIGS. 1–3  to allow increased or decreased resolution of the flow control. 
     The needle valve assembly  100  consists of three main parts: 1) the stepper motor  130 , 2) the internally threaded valve body  120 , and 3) the externally threaded plunger  210  with needle member  220 . This simple construction of the needle valve assembly  100  allows the needle valve assembly  100  to be smaller, have less parts, be more precise (when coupled with closed-loop control electronics), and less expensive to manufacture than needle valve assemblies in the past, making the needle valve assembly  100  an economic means to provide flow control in a flow control mechanism  50  of a gas separation device  10 . 
     It will be readily apparent to those skilled in the art that still further changes and modifications in the actual concepts described herein can readily be made without departing from the spirit and scope of the invention as defined by the following claims.