Abstract:
Disclosed herein is a wobble diaphragm pump having a housing with an open neck. A wobble piston can be passed through the open neck and fit onto the pump motor shaft. A separate support ring is fastened to the housing to close the open neck and provide a circumferential support surface for the diaphragm. The support ring also includes locking projections that mate with recessed features in the housing and a valve head to properly align and unite these components during assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention pertains to pumps and in particular to wobble diaphragm pumps. 
     Wobble diaphragm pumps, such as those used in air compressors, typically have one or more pistons mounted on a rotatable shaft that is eccentrically driven by a suitable motor to reciprocate each piston in a compression chamber. One type of diaphragm pump has a compliant seal member or diaphragm fixed to the housing at its periphery and attached to the flange of the piston. As the piston reciprocates the diaphragm flexes in and out. Using an appropriate valve assembly, having intake and exhaust valves (such as flapper valves) which alternately open and close during the suction and pump strokes, respectively, the reciprocating motion moves air into and out of the compression chamber. 
     One problem with ordinary wobble diaphragm pumps is that they can be difficult to assemble. Specifically, the shell of the electric motor unit is often press-fit onto the housing to which the rotor is journaled. Thus, the pistons must be mounted on the shaft by inserting the piston connecting rod down through a hole in the bottom of the compression chamber and angling it as needed to fit a bore in the connecting rod over the shaft. A bearing and an eccentric element must also be mounted onto the shaft and within the connecting rod. This makes it difficult to properly position the connecting rod on the shaft. Failure to properly mount the piston can cause misalignment leading to pump start-up problems, such as motor stall, diaphragm “slap”, higher than normal amp draw and shortened operating life. 
     For conventional piston pumps without diaphragms, piston assembly is made easier by using a housing having an open neck. This allows the assembler to insert the shaft into the housing from the end of the housing and slide the connecting rod through the open neck and onto the shaft until it is seated at the appropriate position on the shaft. Once properly mounted, the open neck can be closed by an end cap fastened to the housing. 
     While this is suitable for conventional piston pumps, the diaphragm in wobble diaphragm pumps must be held down along its entire circumference to form a seal and create proper pressure differentials. As such, an open necked cylinder would ordinarily leave the diaphragm unsupported at the gap in the neck, and therefore, could not be used in a such a pump. 
     Accordingly, there is a need for a wobble diaphragm pump that allows for simpler and more accurate assembly. 
     SUMMARY OF THE INVENTION 
     The present invention solves the problems of the prior art by providing a diaphragm pump with a housing with an open-neck and a separate support ring that closes the open neck and supports the diaphragm about its entire circumference. 
     In particular, the present invention provides a diaphragm pump having a wobble piston eccentrically mounted to a rotatable shaft at one end and having a compliant sealing member attached at an opposite end. The pump also includes a housing and a support ring. The housing defines a crankcase extending axially beyond the shaft to an open access end and a neck extending perpendicularly to the axis of the shaft. The neck has an open throat which extends to the access end of the crankcase. The open throat allows the piston to be moved axially with respect to the shaft through the throat and onto the shaft. The support ring is mounted to the housing over the throat so as to span the throat and provide a circumferential support surface to which is mounted the circumference of the sealing member. 
     In a preferred form, the housing and support ring have complimentary locking features for aligning the support ring to the housing. Additionally, the pump includes a valve head mounted to the support ring opposite the sealing member. The support ring and valve head also have complimentary locking features for aligning the valve head to the support ring. The support ring has a stop-gap section that fits within the throat of the housing neck. The stop-gap section is of increased dimension relative to the rest of the support ring and has a convex bottom surface that matches the curvature of the end of the housing. This is provided so that cooling air flow through the housing cannot escape too easily through the throat. The housing also preferably includes a raised wall surrounding a portion of the support ring circumference. 
     The present invention also provides a method of assembling the diaphragm pump described above. Specifically, the pump is assembled by supporting the shaft inside of the housing crankcase and inserting the piston axially with respect to the shaft through the open throat onto the shaft so that the piston is substantially centered in the neck of the housing. The support ring is mounted on to the housing over the neck so as to span the throat. The sealing member is supported from below about its circumference by the support ring and captured between the support ring and the valve head assembly. 
     Thus, the present invention provides a diaphragm pump that can be accurately assembled in a simple, cost effective manner. This is accomplished by using an open-neck housing which allows the piston to be slid through the crankcase onto the motor shaft in the proper position. The support ring fills the gap of the throat and provides a circumferential support surface for the sealing member. The accurate piston positioning afforded prevents the occurrence of the aforementioned problems of difficult assembly. 
     The foregoing and other objects and advantages of the invention will appear from the following description. In this description reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a dual-cylinder air compressor having two identical open-neck housings, one at each end, and separate support rings which close the gap of the open neck, the housing being shown without end caps over the access ends of the housings; 
     FIG. 2 is an exploded view of one end of the pump of FIG. 1; and 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a diaphragm pump preferably used to provide forced air movement in air compressors of various sizes and capacities, however, the present invention could be used for other pumping applications and media. Referring to FIG. 1, a dual-cylinder air compressor  10  includes a motor  12 , such as an AC electric motor, driving a pair of identical diaphragm pump units  14 . It should be noted that the air compressor could be a single-cylinder compressor in which case an AC or DC motor could be used. 
     Referring to FIGS. 1 and 2, each pump unit  14  includes a housing  16  containing a wobble piston  18  mounted to a shaft  20  which is rotated by the motor  12 . Although the compressor  10  of FIG. 1 includes two pump units  14 , for simplicity, only one of the pump units  14  will be described in detail. 
     Referring to FIG. 2, each housing  16  has a motor end  24  and an open access end  26  covered by an end cap (not shown) suitably mounted to the housing  16 . The housing  16  defines a generally cylindrical crankcase  28  concentric with the shaft  20  and separated from the motor end  24  by a partition  23  having an opening for receiving a bearing  25  through which the shaft  20  is disposed so that it is journaled to the housing  16  (as shown in FIG.  3 ). Preferably, the motor rotor  27  is fixed to the shaft  20  and the stator shell  13  is press-fit onto the motor end  24  of the housing  16 . 
     The housing  16  also defines a generally cylindrical neck  30  extending upwardly perpendicular to the crankcase  28  between the ends  24  and  26 . The neck  30  has an axially open throat  32  in common with the access end  26  of the housing  16 . The neck  30  has a raised wall  34  and a flat ledge  36  around much of its outer circumference other than at the open throat  32 . The ledge  36  provides a flat surface for supporting a diaphragm support ring  38 , which fits within the raised wall  34 . 
     The diaphragm support ring  38  has a stop-gap  40  of increased dimension that extends downwardly and is sized to fit closely within the throat  32  of the neck  30 . The stop-gap  40  has a convex lower surface  42  of substantially the same radius as the chamber  28  so that when the diaphragm support ring  38  is mounted to the housing  16 , there is a generally circular opening at the access end  26  so that a substantially circular end cap can be use to close the access end  26 . A fan (not shown) may be mounted on the end of the shaft  20  adjacent the access end  26  and ventilation slots formed in the end cap for drawing cooling air into the housing  16 . Closing off substantially all of the throat  32  prevents an excessive amount of cooling air from escaping out through it. 
     The diaphragm support ring  38  has a pair of bosses  44  projecting downwardly on each side of the stop-gap  40  that fit within recesses  46  in the housing  16  for aligning the diaphragm support ring  38  with the neck  30  and holding it in place prior to fastening. The diaphragm support ring  38  also includes bores  48  aligned with threaded recesses  50  in the housing  16  for securing the diaphragm support ring  38  to the housing  16  via suitable fasteners  90  extending down through the plate  72 , head  70  and ring  38  (shown in FIG.  3 ). 
     The diaphragm support ring  38  has a top surface defining a circular ledge  52  for supporting an annular elastomeric diaphragm sealing member  54  about is entire circumference. The sealing member  54  is attached to a connecting rod  58  of the wobble piston  18 . The connecting rod  58  has a circular flange  60  that fits within an inverted recess  62  which is formed in the sealing member  54 . A backing plate  64  at the top surface of the inverted recess  62  is fastened to the connecting rod  58  via a suitable fastener  92  disposed through its center, which is threaded into a central boss  56  of the connecting rod  58 , thereby securing the sealing member  54  to the connecting rod  58 . The connecting rod  58  has an insert-molded bearing  65  opposite the flange  60  for receiving an eccentric element  66  that mounts onto the shaft  20  by a suitable means, such as a set screw connection. The eccentric element  66  has an axial bore  79  that is eccentric to its outer diameter so that the piston  18  reciprocates and wobbles within the neck  30  when the shaft  20  rotates. The eccentric element  66  also has an axially-projecting nib  67  (see FIG. 3) sized to contact the shaft bearing  23  so as to properly position the piston  18 . This nib  67  has a small contact surface which rides on the inner race of the shaft bearing  25  to provide a positive stop for positioning the piston  18 . 
     The outer circumference of the sealing member  54  is sandwiched between the diaphragm support ring ledge  52  and a valve head assembly  68 . The valve head assembly  68  includes a valve head  70  having inlet and exhaust flapper valves (not shown) which move in response to air pressure, as known in the art, and which are in communication with inlet  80  and exhaust  82  chambers in the valve head  70 . The inlet  80  and exhaust  82  chambers are each in fluid communication with three inlet  84  and exhaust  86  ports having fittings for attaching air lines (not shown). The valve chambers  80  and  82  of the valve head  70  are covered by a head plate  72  fastened to the valve head  70  by the threaded fasteners  90  that extend through bores  75 , valve head bores  74  and diaphragm support ring bores  48  and threaded into threaded recesses  50  of the housing  16 . Preferably, a suitable sealing ring or gasket  94  is disposed between the valve head  70  and the head plate  72  to prevent air leakage. 
     In a preferred form, the housing  16  and diaphragm support ring  38  are preferably made of aluminum alloy or a glass-filled nylon. The piston connecting rod  58  and backing plate  64  are preferably made of aluminum alloy or a polyphthalamide. The sealing member  54  is preferably a reinforced EPDM. The eccentric element  66  is a powdered metal and the valve head  70  and head plate  72  are aluminum. 
     As the motor  12  is operated the shaft  20  rotates and the eccentric element  66  causes the piston  18  to reciprocate back and forth with a wobble motion. The sealing member  54  and the reciprocating connecting rod  58  of the piston  18  draw air in through the inlet valve into the compression chamber  30  on the downstroke and force air out the exhaust valve to the valve head assembly  68  on the upstroke. The valves of the valve head  70  alternately open and close in response to the reciprocating piston  18  to allow outside air to be drawn through the inlet ports  84  and compressed air to be discharged through the exhaust ports  86 , as known in the art. 
     Referring again to FIGS. 2 and 3, each pump  14  is assembled by journaling the shaft  20  to the housing  16  and press-fitting the shell onto the motor end  24  of the pump. Then, the piston  18  is assembled by fastening the backing plate  64  and the sealing member  54  to the connecting rod  58 . The connecting rod  58  of the assembled piston is then inserted into the opening of the diaphragm support ring  38 . The connecting rod  58  is then slid through the open throat  32  into the crankcase  28  onto the shaft  20  by inserting the shaft  20  through the bearing  65 . The eccentric element  66  is then fit onto the shaft  20  and into the connecting rod bearing  65  in a light press fit. The eccentric element  66  is slid on the shaft  20  until the nib  67  contacts the shaft bearing  23  and can slide no more. In that position, the piston  18  is properly centered in the compression chamber  30 . The connecting rod  58  is secured in place by fastening the eccentric element  66  to the shaft  20 . The diaphragm support ring  38  is then mounted to the housing  16  over the neck  30  so as to close the open throat  32 , aligning the bosses  44  with the housing recesses  46 , so that the sealing member  54  is supported about its entire circumference by the diaphragm support ring  38 . The circumference of the sealing member  54  is then sandwiched between the diaphragm support ring  38  and the valve head assembly  68  which is secured to the housing  16  by the threaded fasteners  90 . The access end  26  is covered by an end cap (not shown) fastened to the housing  16 . 
     Thus, the present invention provides easy to assemble diaphragm pumps that afford facile and accurate positioning. This reduces or eliminates the problems associated with assembly. 
     An illustrative embodiment of the invention has been described in detail for the purpose of disclosing a practical, operative structure whereby the invention may be practiced advantageously. The novel characteristics of the invention, however, may be incorporated in other structural forms without departing from the scope of the invention. Accordingly, in order to apprise the public of the full scope of the present invention, reference should be made to the following claims.