Abstract:
A compact pump has a uni-body, or alternately a two-part, housing of self-skinning foam construction for superior noise and vibration reduction, such as needed for medical nebulizer applications. The uni-body foam housing is formed by molding the housing around a pump assembly having special features designed to shield and space apart moving or sensitive internal components of the pump assembly from the foam during the insert molding process. The alternate two-part foam housing is assembled using a union ring having multiple barbed pins that fit into openings in mating faces of the two housing sections.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims benefit to U.S. Provisional Patent Application No. 60/583,424, filed on Jun. 28, 2004. 
     
    
     STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates to pumps and compressors and in particular to pumps and compressors with low noise characteristics, especially suited for use in medical nebulizer applications.  
         [0004]     Nebulizers are commonly used to deliver medication to persons with respiratory ailments. For example, bronchodialators, which are used to open airway passages, are commonly administered with nebulizers. A nebulizer changes liquid medication into a fine, atomized mist or vapor. The medicinal vapor is inhaled through a mouthpiece or mask and the atomized medication is able to penetrate deeply into one&#39;s airways because of its fine particle size. The liquid medicine is atomized by mixing it with compressed air or oxygen.  
         [0005]     Typical nebulizers include a small compressor with a piston that reciprocates rapidly within a cylinder to pressurize the air. U.S. Pat. No. 6,135,144, assigned to the assignee of the present invention and hereby incorporated by reference as though fully set forth herein, discloses a compressor with a wobble piston. The piston is connected by a connecting rod to an eccentric mounted to a rotating shaft so that its head pivots as it slides within the cylinder. The pressurized air is forced out of the cylinder through a valve head and exhaust chamber to a hose leading to a mixing chamber. Internal conduit is usually necessary to direct the pressurized air leaving the valve head to the outlet port of the housing. After leaving the compressor, the pressurized air passes over an orifice leading from the liquid medicine to aspirate and atomize the medicine, which is then ordinarily mixed with ambient air, oxygen or oxygen enriched air for inhalation.  
         [0006]     Persons with significant respiratory problems often require multiple nebulizer treatments every day, each taking several minutes to administer. It is also not uncommon for such persons to receive nebulizer treatments in hospitals, at work or other public places. It is thus important for the nebulizer compressors to operate discreetly. Quiet operation of the compressor can be obtained by insulating the housing, however, this adds bulk and can cause cooling problems. Mufflers can be added at the compressor exhaust, however, this adds hardware and cost.  
         [0007]     Conventional metal housings are prone to vibrate in response to the reciprocating components during operation of the pump at an audible frequency that may be too loud for suitable for hospital and home use. To avoid this, various vibration damping spring arrangements have been devised. For example, spring arrangements can be provided to isolate the moving components from the housing to dampen vibration and noise. However, this adds parts and complicates assembly, thereby increasing unit costs.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a pump, particularly designed for use with a medical nebulizer having improved noise, vibration and manufacturing characteristics.  
         [0009]     Specifically, the present invention provides a piston pump having a cylinder and piston disposed along a piston axis and a valve head having an intake port and an exhaust port in communication with the cylinder and respective inlet and outlet ports of a housing. The housing, forming an internal chamber containing the cylinder, piston and valve head, is of molded foam construction. In an especially preferred form, the foam is self-skinning so that the foam has a smooth, generally non-porous outer surface.  
         [0010]     In one preferred form, the housing is of uni-body construction. The pump is formed by inserting a pre-assembled pump assembly, including the cylinder and piston arrangement and valve head into a mold die and then molding a uni-body foam housing around this assembly. The pump assembly has special components designed to encapsulate and protect internal components during the insert molding process and provide the internal air space necessary for the drive components to reciprocate after the housing is formed. Preferably, the foam is allowed to cure and develop on its own a skin layer. Inlet and outlet passages are also molded into the housing in communication with the respective intake and exhaust ports of the valve head as are vent passages and a unitary carrying handle. Assembly is completed by attaching a power switch and lead to the actuator, which may be an electromagnet wire coil moving an armature linearly or a motor rotatably driving the piston to reciprocate.  
         [0011]     Another preferred form of the pump has a split housing with two similar housing sections that are coupled together by a double sided plastic union ring mated to peripheral faces of the two housing sections by a pin and slot connection. Preferably, the union ring has two sets of tapered barbed pins extending from opposite sides that fit into two sets of openings in the peripheral faces of the two housing sections. The union ring in part defines the inlet of the housing as well as a handle opening aligned with handle openings defined by the housing sections.  
         [0012]     The present invention thus provides a compact piston pump having a foam housing providing very low operating vibration and noise such that it is particularly suitable for use in a medical nebulizer device. The pump can have a uni-body construction in which the pump components are pre-assembled and insert molded with the foam forming the housing. Or, the pump can have a split housing in which the parts are assembled with a special ring providing a simple pin and socket connection. Further, the reciprocating drive components of the pump assembly can be suspended in the housing by individual springs or spring stacks to further isolate the housing from vibration caused by the reciprocating elements of the assembly, and thereby reduce noise. The integral air inlet and outlet ports simplify assembly and cost by eliminating the need for separate air lines or tubing.  
         [0013]     These and other advantages of the invention will be apparent from the detailed description and the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a perspective view of a pump having a foam housing according to the present invention;  
         [0015]      FIG. 2  is side plan view thereof;  
         [0016]      FIG. 3  is an end plan view thereof;  
         [0017]      FIG. 4  is an opposite end plan view thereof;  
         [0018]      FIG. 5  is a perspective view thereof with the housing shown exploded;  
         [0019]      FIG. 6  is another perspective view thereof with the housing shown exploded;  
         [0020]      FIG. 7  is a fully exploded perspective view thereof;  
         [0021]      FIG. 8  is a side cross-sectional view taken along line  8 - 8  of  FIG. 4 ;  
         [0022]      FIG. 9  is a top cross-sectional view taken along line  9 - 9  of  FIG. 2 ;  
         [0023]      FIG. 10  is another top cross-sectional view taken along line  10 - 10  of  FIG. 2 ;  
         [0024]      FIG. 11  is an end cross-sectional view taken along line  11 - 11  of  FIG. 8 ;  
         [0025]      FIG. 12  is perspective view of alternate embodiment of the pump according to the present invention having a one-piece or uni-body foam housing;  
         [0026]      FIG. 13  is a side plan view thereof;  
         [0027]      FIG. 14  is a perspective view thereof with the pump assembly shown exploded from the uni-body housing;  
         [0028]      FIG. 15  is a fully exploded perspective view thereof;  
         [0029]      FIG. 16  is a side cross-sectional view taken along line  16 - 16  of  FIG. 19 ;  
         [0030]      FIG. 17  is a bottom cross-sectional view taken along line  17 - 17  of  FIG. 16 ;  
         [0031]      FIG. 18  is an end view cross-sectional view taken along line  18 - 18  of  FIG. 13 ; and  
         [0032]      FIG. 19  is another end cross-sectional view taken along line  19 - 19  of  FIG. 13 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     The present invention provides a pump with a foam housing construction providing quiet operation such that the pump is suitably used in a medical nebulizer application. The foam housing gives the pump improved noise and vibration dampening characteristics in a compact, preferably hand-held, package. These characteristics of the foam housing reduce dependency on other vibration dampening components, such as suspension spring assemblies disposed between the reciprocating components and the housing or isolation springs supporting the fixed components in the housing.  
         [0034]     The pump of the present invention will be described herein in two different embodiments. A first embodiment, shown in  FIGS. 1-11 , has a two-piece foam housing in which the two parts are joined by union ring with multiple pin elements that engage the housing parts. A second embodiment, shown in  FIGS. 12-19 , has a uni-body foam housing formed around the components of the pump assembly, preferably by an insert molding process. The pump is shown and described herein as an axial (or linear) piston pump. However, other types of pump arrangements are included within the scope of the invention, including rotary driven piston pumps such as wobble type piston pumps.  
         [0035]     Referring to  FIGS. 1-7 , the pump  10  has a compact, generally oblong foam housing  12 . The foam can be any moldable or thermoformable foam material, however, the foam is preferably an expanded polyurethane self-skinning foam in which a smooth “skin” forms at the exterior surface of the pump housing  12  as the foam cures so that it is generally non-porous. The foam material is lightweight but strong so as to resist damage or cracking. Importantly, the foam has very good sound insulating and vibration dampening properties.  
         [0036]     The foam housing  12  has two shell parts  14  and  16 . The shells  14  and  16  are generally the same, each has a peripheral wall  18  with openings  20  spaced there along. Each has two feet  22  and forms a handle opening  24  and vent passages  26 . When joined, the shells  14  and  16  define a handle  28  at the top of the housing  12  adjacent the opening  24  and also define an inner cavity  30 , an intake passageway  32  and an opening  34  for a power switch  35 . Shell  14  is formed with a side opening  36  for an exhaust nipple  38 , as discussed below.  
         [0037]     The housing shells  14  and  16  are joined by a union ring  40  having a wall  42  disposed between the peripheral walls  18  with a number of barbed pin elements  44  projected toward opposite sides thereof to fit into the openings  20  in the shells  14  and  16 , thereby providing a mechanical, pin and socket connection of the two shells  14  and  16 . The pins  44  can be formed as a unitary part of the union ring  40  or than can be separate components that fit into associated openings of the union ring  40 . A flange  46  extends around the wall  42  to overlap the edges of the shells  14  and  16 . The union ring  40  is also formed with an interior wall  48  defining a handle opening  50  aligned with the handle openings  24  in the shells  14  and  16  as well as a port  52  disposed in the intake passageway  32  and an opening  54  disposed in the switch opening  34 . The union ring  40  is preferably made of a suitable moldable plastic, such as nylon, ABS, or polystyrene, having sufficient resiliency so that the wall  42  and flange  46  seal against the shells  14  and  16  and form an air tight connection.  
         [0038]     Referring now to  FIGS. 5, 6  and  8 , a pump assembly  56  is contained within the inner cavity  30  of the housing  12 . The pump assembly  56  generally includes an electromagnet  58 , a piston  60 , a cylinder  62  and a valve head  64 , all aligned concentrically about a piston axis  66 .  
         [0039]     Working from left to right in  FIG. 8  and right to left in  FIGS. 7, 9  and  10 , a tail piece  68  having an enlarged trailing end mounts to an axially extending hub  70  of an armature  72 . The armature  72  has a series of axial bores  74  (see  FIG. 11 ) therethrough spaced about the axis  66 . The armature  72  slides in and out of an annular cavity  76  of a stator  78  which holds a bobbin  80  about which is wound a wire coil  82 , thereby comprising the electromagnet  58  when energized by an input current. A diode  83  (shown in  FIG. 9 ) is electrically coupled to the coil  82  to rectify the alternating current input signal so that it drives the armature  72  in only one direction, preferably toward the stator  78 .  
         [0040]     The armature hub  70  has a bore receiving a narrowed threaded end of a connecting rod  84  to which the tail piece  68  threads to clamp the armature  72  between the tail piece  68  and the connecting rod  84 . Clamped between the armature hub  70  and the tail piece  68  is a center portion of one or more leaf springs  86  having their outer peripheries held fixed with respect to the housing  12  by being clamped between a retainer ring  88  and a spacer  90 . The connecting rod  84  extends along the piston axis  66  through the center of the armature  72  and the stator  78  to another narrowed threaded end that threads into a bore in a stem of the piston  60 , which has an enlarged head  92  to which a piston seal or cup  94  is clamped by a cup retainer  96 . The piston cup  94  creates a sliding seal against the inner diameter of the cylinder  62  which is mounted between the valve head  64  and another spacer  98 . The spacer  98  is fixedly mounted in the housing  12  to clamp the outer periphery of another one or more leaf springs  100  between it and another retainer ring  102 , which is notched to abut and capture the outer edge of the stator  78 . The center of the spring(s)  100  are clamped between the connecting rod  84  and the piston stem. The cup retainer  96  is secured by a screw threaded into the connecting rod  84  through the bore of the piston stem. The leaf springs  86  and  100  preferably are configured with a pair of concentric circular rings joined by three spokes. The outer ring preferably includes hair pin elements disposed between the spokes.  
         [0041]     The valve head  64  is clamped against one open end of the cylinder  62 . The valve head  64  includes a valve plate  103 , a chamber housing  104  and a cover  106 . The valve plate  103  includes intake  108  and exhaust  110  ports over which are mounted flapper valves (not shown) to control flow through the ports. The intake flapper valve is mounted to the valve plate  103  at the interior of the cylinder  62  and the exhaust flapper valve is mounted at the opposite side of the valve plate  102 . The chamber housing  104  is clamped between the valve plate  103  and the cover  106 , with a seal  107  therebetween, to define intake  112  and exhaust  114  chambers isolated from each other by a partition wall  116 . The exhaust chamber  114  is communication with the exhaust nipple  38  through an opening in the side of the chamber housing  104 . The intake chamber  112  is in communication with an intake port  118  in the cover  106  and the intake passageway  32  in the housing  12  leading to ambient via port  52 . Suitable o-rings or other gaskets, like seal  107 , can be disposed between the components of the valve head  64  and/or between the ends of the cylinder  62  and the mating components as necessary to ensure an air tight seal.  
         [0042]     During operation, energizing the coil  82  creates a magnetic flux that drives the armature  72  toward the stator  78 , which in turn drives the piston  60  to reciprocate within the cylinder  62 . In one preferred version of the pump  10 , the piston stroke length is approximately 9 mm (4.5 mm in each direction) and is positioned approximately 1 mm from the top of the cylinder  62  when at top dead center (furthest right in  FIG. 9 ). The piston  60  and the armature  72  reciprocate (along with the tail piece  68  and the connecting rod  84 ) against the internal spring forces of the springs  86  and  100  arising from the centers of the springs reciprocating with the piston  60  and armature  72 .  
         [0043]     The reciprocating piston  60  and armature  72  causes the assembly inside the housing  12  to vibrate. The associated noise and movement is dampened by the spring  86  and  100 . The number and size of leaf springs is primarily a function of the mass of the piston and the power input frequency. The springs are selected so that in combination (between the two sets) they result in a resonant frequency of the piston and springs (i.e., the spring-mass system) approximately equal to the input frequency, that is 50 or 60 Hertz. For example, in one preferred embodiment there is one spring (or possibly two) at this location and a stack of two springs (or possibly three) at the piston in a 115 v/60 Hz application. A stack of two springs are preferably at each location for a 230 v/50 Hz application. Operating at the resonant frequency improves efficiency and reduces vibration, and thereby reduces noise.  
         [0044]      FIGS. 12-19  show an alternate embodiment of the pump in which the foam housing has a uni-body construction. Components of this embodiment that are similar to the above-described embodiment are referred to with similar reference numerals albeit with the suffix “A”.  
         [0045]     Referring to  FIGS. 12-14 , the pump  10 A has a compact, generally oblong foam housing  12 A. Like in the preceding embodiment, the foam is preferably an expanded polyurethane self-skinning foam in which a smooth, non-porous “skin” forms at the exterior surface. Here, the housing  12 A has a uni-body construction such that the components of the pump assembly need to be pre-assembled and inserted into the mold before the housing  12 A is formed. The housing  12 A is formed with a handle  28 A at the top and four feet  22 A at the bottom. Vent passages  26 A are also formed into the side of the housing  12 A as are intake passageway  32 A, an opening  34 A for an on/off switch  35 A and an opening  36 A for an exhaust nipple  38 A. The vent passages  26 A, intake passageway  32 A, switch opening  34 A and exhaust opening  38 A can be formed during the molding process or by a machining operation thereafter.  
         [0046]     Referring now to  FIGS. 14 and 15 , a pump assembly  56 A is contained within the inside of the housing  12 A and generally includes an electromagnet  58 A, a piston  60 A, a cylinder  62 A and a valve head  64 A, all aligned concentrically about a piston axis  66 A.  
         [0047]     With reference to  FIGS. 15-19  and working from left to right in  FIG. 15  and right to left in  FIGS. 16 and 17 , the pump assembly  56 A includes a dome-shaped end cap  202  defining an interior space for movement of the piston  60 A and an armature  72 A. The end cap  202  has openings in communication with associated vent openings  26 A allowing ambient conditions to exist therein and prevent back pressure piston. This piece is necessary here because of the uni-body construction of this embodiment and the fact that the pump assembly  56 A is inserted molded within the housing  12 A, without it the foam would adhere to, or at least form tightly around, the pump assembly  56 A so as to prevent reciprocation of the otherwise movable components. The end cap  202  has a section defining an open cavity  203  for the power switch  35 A. The end cap  202  has an annular flange at its periphery that is notched to receive the periphery of an annular spacer  90 A between which is clamped one or more leaf springs  86 A (one shown). The spacer  90 A abuts the periphery of a stator  78 A, which defines a cavity  76 A (see  FIG. 16 ) in which is disposed a bobbin  80 A about which is wound a wire coil  82 A, thereby providing the electromagnet  58 A when energized by an input current. As before, a diode  83 A, shown in  FIG. 17 , is electrically coupled to the coil  82 A to rectify the alternating current input signal so that it drives the armature  72 A in only one direction, preferably toward the stator  78 A. Also as before, the armature  72 A has a series of axial bores  74 A therethrough and slides in and out of part of the annular cavity  76 A of the stator  78 A.  
         [0048]     The armature  72 A has a central hub  70 A with a bore through which extends a bolt  204  passing through a connecting rod  84 A and threading into the stem of the piston  60 A. Clamped between the armature hub  70 A and a head of the bolt  204  is a center portion of the one or more leaf springs  86 A (one shown in  FIG. 15 ), configured as described above, which have their outer peripheries held fixed with respect to the housing  12 A. The connecting rod  84 A extends along the piston axis  66 A through the center of the stator  78 A and abuts the stem of the piston  60 A, which as before has an enlarged head  92 A to which a piston seal or cup  94 A is clamped by a cup retainer  96 A. Clamped between the piston  60 A and the connecting rod  84 A are the center portions of one or more leaf springs  100 A (two shown in  FIG. 15 ), which have their outer peripheries clamped between a retainer ring  102 A and an annular electromagnet cup or housing  206 , which surrounds the stator  78 A and armature  72 A and has a recess at one end in which one end of the cylinder  62 A is disposed. The other end of the cylinder  62 A fits into a groove in a valve plate  103 A, which in this case takes a cup shape having an annular wall  208  spaced from and surrounding the cylinder  62 A and abutting the electromagnet cup  206 .  
         [0049]     The valve plate  103 A and the electromagnet cup  206  have the cup-like configuration to enclose the components therein to shield and space them from the foam during the molding of the housing, as is the purpose of the end cap  202 . Both the valve plate  103 A and the electromagnet cup  206  also have openings that are communication with the housing vents  26 A to allow cooling air flow therethrough as well as to allow these non-compression or vacuum areas of the pump assembly to operate at ambient pressure.  
         [0050]     The valve head  64 A includes the valve plate  103 A, a chamber housing  104 A and a cover  106 A. The valve plate  103 A includes intake  108 A and exhaust  110 A ports over which are mounted flapper valves (not shown) to control flow through the ports. The intake flapper valve is mounted to the valve plate  103 A at the interior of the cylinder  62 A and the exhaust flapper valve is mounted at the opposite side of the valve plate  103 A. The chamber housing  104 A is clamped between the valve plate  103   a  and the cover  106 A to define intake  112 A and exhaust  114 A chambers isolated from each other by a partition wall  116 A. The exhaust chamber  114 A is communication with the exhaust nipple  38 A through an opening in the side of the chamber section  104 A. The intake chamber  112 A is in communication with an intake port  118 A in the cover  106 A and the intake passageway  32 A in the housing  12 A leading to ambient air. Like above suitable o-rings or other gaskets can be disposed between the components of the valve head  64 A and/or between the ends of the cylinder  62 A and the mating components as necessary to ensure an air tight seal.  
         [0051]     As mentioned, given the uni-body construction of this embodiment of the pump, a special insert molded assembly method is utilized. In particular, the aforementioned components of the pump assembly  56 A are pre-assembled and inserted into a mold die. The foam resin is then, preferably injected, into the die to form the housing  12 A around the pump assembly  56 A. A non-porous skin forms at the exterior of the foam as it cools, preferably while the housing  12 A is still inside the mold. As mentioned, preferably the vent and intake and exhaust openings are formed by the molding process to be in communication with the respective intake and exhaust ports of the valve head  64 A. Similarly, the vent passages and handle are also preferably so formed. The power on/off switch  35 A, with leads (not shown) connecting it to the electromagnet wire coil, is mounted to the housing  12 A at the switch opening  200 . The switch opening  200  is located to allow access to the coil  82 A for coupling the electrical leads thereto.  
         [0052]     The present invention thus provides a compact axial piston pump having a foam housing providing very low operating vibration and noise such that is particularly suitable for use in a medical nebulizer device. The pump can have a uni-body construction in which the pump components are pre-assembled inserted molded with the foam forming the housing. Or, the pump can have a split housing in which the parts are assembled with a special ring providing a simple pin and socket connection. Further, the drive assembly can be suspended in the housing by spring stacks to further isolate the housing from vibration caused by the reciprocating elements of the assembly, and thereby reduce noise. The integral air inlet and outlet ports simplifies assembly and cost by eliminating the need for separate air lines or tubing.  
         [0053]     Illustrative embodiments of the present invention have been described above in detail. However, the invention should not be limited to the described embodiments. For example, it is within the scope of the invention to substitute other spring members for the leaf springs described above, such as compression springs or other energy absorbing members made of suitably resilient materials, such as rubber or foam. To ascertain the full scope of the invention, the following claims should be referenced.