Abstract:
A pump includes a housing, a shaft supported by the housing, a piston assembly, a fan blade, and a fan guard. The piston assembly includes a piston cylinder and is operably coupled to the shaft. The fan blade is operable to generate cooling flow. The fan guard is mounted to the housing and includes a channel configured to direct at least a first portion of the cooling flow to the piston cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The invention relates generally to the field of pumps, such as compressors and vacuum pumps, and more particularly, to a compressor having a fan guard with a channel to direct cooling air to a piston cylinder.  
         [0004]     Reciprocating piston or diaphragm pumps typically have a metal housing, for example, a cast aluminum alloy, in which bearings are mounted which journal the shaft which drives the pump. A metal housing is needed, particularly for larger pumps, to withstand the forces of driving the piston or diaphragm and containing the pressure exerted in the compression chamber of the pump.  
         [0005]     A rotary electric motor is usually used to drive these pumps and the motor requires cooling. In one such pump, the motor is provided between two housings, each of which is separate from the other and houses one compression chamber. The shaft of the motor is a through shaft so that each end of the shaft mounts one of the pistons or diaphragms that work to vary the volume of the compression chamber in the housing at the corresponding end of the shaft. Further out from where the piston or diaphragm is mounted, a rotary fan blade is mounted to each end of the shaft to draw a flow of cooling air into the housing at that end and blow it onto the rotor and stator coils of the motor.  
         [0006]     For cooling efficiency, it is desirable to make the part of the housing in which the rotary fan blade is mounted circular and just slightly larger than the diameter of the fan blade. The clearance between the tips of the fan blades and the interior housing surface should be as small as possible because, if not, the air drawn into the housing by the fan blades will simply blow back out past the tips of the blade, and not be directed over the coils of the motor. For applications in which the pump is contained inside of a separate enclosure, it may be permissible to leave open the end of the housing at which the fan blade is mounted. However, if the pump is going to be exposed or sold as a stand-alone product, the end of the housing must be closed with a cover that permits air to be drawn into the housing, but prevents the insertion of larger objects or fingers. This cover, typically called a fan guard, should not deleteriously affect the operation of the fan nor add to the lateral size or detract from the appearance of the fan.  
         [0007]     The effectiveness of the cooling system in reducing the stator temperature of the motor affects the range of applications in which the pump may be employed. The voltage at which the motor is driven and the output pressure of the pump affect the amount of heat that is generated in the motor. More effective cooling expands the range of applications suitable for a given pump and motor.  
         [0008]     The motor is not the only temperature-sensitive component in a pump. Wobble pistons are sometimes used in oil-less air compressors and vacuum pumps. A wobble piston includes a peripheral seal on the piston head that engages the cylinder bore. The piston head and its connecting rod are fixed to each other, and the connecting rod is mounted on an eccentric on a shaft. As the eccentric is turned by the shaft, the wobble piston is moved in and out and “wobbles” from side to side. Wobble pistons typically employ a Teflon® or other similar material disc or cup which serves both as a guide for the wobble piston and as a pneumatic seal between the piston and the wall of the cylinder in which it moves. The working surface of the cylinder has a hardened polished surface, providing a smooth surface for cooperating with the Teflon® seal of the piston. The service life of the Teflon® material depends in part on the temperature of the cylinder with which the seal interfaces. A higher temperature typically corresponds to a shorter service life due to increased friction between the cup and the cylinder wall.  
         [0009]     The bearings used to support the motor shaft also have a service life determined at least in part by temperature. Generally, a higher bearing temperature equates to a shorter bearing service life.  
         [0010]     Hence, cooling efficiency not only affects the range of applications for a particular pump, but also the service life of temperature-sensitive components in the pump. The present invention addresses these problems.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     The present invention is directed generally to a fan guard that directs cooling air flow to a piston cylinder.  
         [0012]     One aspect of the invention is seen in a pump including a housing, a shaft supported by the housing, a piston assembly, a fan blade, and a fan guard. The piston assembly includes a piston cylinder and is operably coupled to the shaft. The fan blade is operable to generate cooling flow. The fan guard is mounted to the housing and includes a channel configured to direct at least a first portion of the cooling flow to the piston cylinder.  
         [0013]     Another aspect of the present invention is seen in a fan guard. The fan guard includes a front surface defining a cooling flow opening and sidewalls defining a channel having a first end proximate the cooling flow opening. A baffle is positioned proximate a second end of the channel.  
         [0014]     Other objects, advantages and features of the present invention will become apparent from the following specification when taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0015]     The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements and in which:  
         [0016]      FIG. 1  is an isometric view of a pump in accordance with one embodiment of the present invention;  
         [0017]      FIG. 2  is a partial cross section view of the pump of  FIG. 1 ;  
         [0018]      FIG. 3  is an end view of the pump of  FIG. 1  with the fan guard removed; and  
         [0019]      FIG. 4  is an isometric back view of a fan guard employed in the pump of  FIG. 1 . 
     
    
       [0020]     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     While the present invention may be embodied in any of several different forms, the present invention is described here with the understanding that the present disclosure is to be considered as setting forth an exemplification of the present invention that is not intended to limit the invention to the specific embodiment(s) illustrated. Nothing in this application is considered critical or essential to the present invention unless explicitly indicated as being “critical” or “essential.” 
         [0022]      FIG. 1  illustrates a pump  10  of the invention having a motor  12  with a housing  14  at one end and a housing  16  at the other. The housings  14 ,  16  are cast of aluminum alloy and are essentially identical. A head assembly  18 , which includes head members  20 ,  22  and connecting tubes  24 ,  26 , is bolted to the housings  14 ,  16  above respective compression chamber portions  28 ,  30  of the housings  14 ,  16  to help hold the housings  14 ,  16  together and maintain their angular position with respect to each other. The pump  10  also includes fan guards  32 , one at each end, which are essentially identical to one another. The pump  10  of the present invention may be employed in a variety of applications, including but not limited to cable drying, sewage aeration, tire inflation, etc.  
         [0023]     Referring to  FIGS. 2 and 3 , a partial cross section view of the pump  10  and an end view of the pump  10  with the fan guard  32  removed are shown, respectively. The motor  12  has a shaft  34  which extends through it and into both housings  14 ,  16 , nearly to the end of each respective housing  14 ,  16 . As both housings  14 ,  16  are essentially identical, only the housing  14  is shown in  FIG. 2 . Each end of the shaft  34  mounts a rotary fan blade  36  which is rotated by the shaft  34  within a fan cavity  37  defined by the housing  14  in a direction so as to draw air into each respective housing  14 ,  16  and direct it over the coils of the motor  12  (i.e., an axial component of the cooling flow). In one embodiment, the rotary fan blade  36  is secured to the shaft  34  using a spring clip  38 .  
         [0024]     The housings  14 ,  16  are provided with ventilation slots  39  to allow the exhausting of cooling air. The housings  14 ,  16  mount bearings  40  which journal the shaft  34 . The housings  14 ,  16  also have openings (not shown) in them which provide for the axial through-flow of air so that air moved by the fan blade  36  reaches the coils of the motor  12 .  
         [0025]     The pump  10  includes a piston assembly  42  including a piston cylinder  44  and a piston head  46  operating within the piston cylinder  44  to compress the operating fluid (e.g., air) to provide the pumping action. The piston head  46  is coupled by a connecting rod  48  to an eccentric  50  fixed to the shaft  34 . In operation, the shaft  34  and attached eccentric  50  rotates causing the connecting rod  48  and piston head  46  to move within the piston cylinder  44 . A flapper valve (not shown) mounted to the valve plate  52  allows the air to enter the piston cylinder  44  on the downstroke of the piston cycle and seals to prevent air passage on the upstroke. The piston head  46  also includes a piston cup  54  constructed of Teflon® or other similar material that provides a sliding seal between the piston head  46  and the piston cylinder  44 . The piston cup  54  has a service life that may vary based on the temperature of the piston cylinder  44 , with a higher cylinder temperature resulting in a shorter service life.  
         [0026]     Besides allowing axial cooling air flow to dissipate heat that is transferred from the motor  12  to the housings  14 ,  16  to the bearings  40 , the fan guard  32  also directs cooling flow over the piston cylinder  44  to dissipate heat generated during the compression process. The housings  14 ,  16  includes openings  56  (shown in  FIG. 1 ) to allow the exhaust of cooling air directed over the piston cylinder  44 .  
         [0027]     Turning now to  FIG. 4  an isometric back view of the fan guard  32  is provided. The front surface of the fan guard  32  is visible in  FIG. 1 . The fan guard  32  defines a cooling flow opening  57  in its front surface to provide for the passage of cooling flow past the fan guard  32 . The fan guard includes rib members  58  spanning the cooling flow opening  57  and support members  60  running perpendicular to the rib members  58 . The spacing and arrangement of the rib and support members  58 ,  60  may vary depending on the particular implementation. In general, the rib and support members  58 ,  60  are arranged to allow the passage of cooling flow, but to prevent foreign objects from entering the area proximate the moving rotary fan blade  36 . In the illustrated embodiment, the fan guard  32  is made of a resilient plastic resin, such as a polyester polymer. The fan guard  32  includes a tab  62  that interfaces with a corresponding notch  64  (shown in  FIG. 2 ) in the housing  14  to secure the bottom portion of the fan guard  32  to the housing  16 . Mounting holes  66  are defined in the fan guard  32  to allow the passage of screws for securing the fan guard  32  to the housing  14  via corresponding holes  68  (shown in  FIG. 3 ) in the housing  14 . Any means may be used to secure the fan guard  32  to the housing  14 .  
         [0028]     The fan guard  32  includes sidewalls  70  that define a channel  72 . The channel  72  terminates in a baffle  74  that changes the direction of radial cooling flow generated by the rotary fan blade  36  to impinge on the piston cylinder  44 , as indicated by the arrow  76  shown in  FIG. 2 . The sidewalls  70  also define a flared portion  78  that collects the radial air flow and directs the flow into the channel  72 .  
         [0029]     Returning to  FIG. 2 , the rotary fan blade  36  includes an extended hub  80  that abuts the eccentric  50  to positively locate the rotary fan blade  36  along the shaft  34  within the fan cavity  37 . The rotary fan blade  36  is positioned to optimize the cooling provided to the piston cylinder  44  by the cooling flow redirected by the fan guard  32 . The optimal shaft position may be determined empirically and may vary depending on the particular geometry of the pump  10 . In the illustrated embodiment, the rotary fan blade  36  extends axially beyond the fan cavity  37  defined by the housing  14  into the space bounded by the fan guard  32 . This position has been found to increase the effectiveness of the fan guard  32  in redirecting the radial air flow to cool the piston cylinder  44 .  
         [0030]     Redirecting cooling flow over the piston cylinder  44 , as described herein, reduces the operating temperature of the piston assembly  42 . The combination of the rotary fan blade  36  and fan guard  32  also reduces the temperature of the bearings  40  and the motor  12 . Such temperature reductions increase the operating lives of the piston cup  54  and the bearings  40  for a given set of operating conditions. The improved heat dissipation characteristics may also be employed to extend the operating range of the pump  10  to allow operation at higher pressures, different voltages, and/or lower frequency voltage inputs.  
         [0031]     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.