Abstract:
A dishwasher includes a drain pump assembly having a chopper assembly coupled to an impeller and driven by a synchronous motor. The chopper assembly includes an impeller housing that includes a central hub portion for pivotally supporting a plurality of rotatable chopper blades. An apertured plate is secured to the impeller housing and maintained in a spaced relationship from the chopper blades. The chopper assembly is coupled to the impeller through an axially sliding drive mechanism that facilitates assembly of the chopper assembly into the impeller housing. The synchronous motor drives the chopper blade in a first direction until encountering a hard soil particle whereupon the chopper blades can pivot so that the chopper assembly can continue to operate or, if the chopper blade becomes jammed, the synchronous motor can oscillate to hammer the hard soil particle until it becomes small enough to pass through the apertured plate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of dishwashers and, more particularly, to a drain pump assembly employed in a dishwasher, preferably a drawer-type dishwasher. 
     2. Discussion of the Prior Art 
     In a typical dishwasher, washing fluid is pumped from a sump into upper and lower wash arms such that kitchenware, retained on vertically spaced racks within a tub of the dishwasher, will be sprayed with the washing fluid for cleaning purposes. The washing fluid is heated, filtered and recirculated through operation of a wash pump. Prior to recirculating the washing fluid, some or all of the fluid is directed through one or more filters to remove soil from the fluid, with the soil being collected in one or more chambers. Periodically, the system will be purged in order to drain the collection chamber(s) of the soil, as well as the washing fluid from the overall dishwasher. 
     In many dishwashers, the wash pump is provided with a chopper blade that is rotated about an apertured chopper plate to macerate soil particles entrained in the washing fluid. The wash pump can either be designed to macerate the food particles prior to recirculation or, upon draining the washing fluid from the washing chamber, macerate the soil particles during a drain operation. Regardless of the particular configuration, it has been found that incorporating the chopper blade into the wash pump increases noise output by the dishwasher. As the demand for quiet appliances is on the rise, this configuration requires re-design. 
     One proposed solution is to add a second or drain pump to the dishwasher. The drain pump can be fitted with the chopper blade so that soil particles are macerated only during operation of the drain pump. Due to the fact that the drain pump is operated less frequently than the wash pump, the overall noise produced by the dishwasher can be reduced. However, in addition to noise considerations, size, and particularly vertical height, is also a consideration when designing a dishwasher. Thus, adding a second pump to the dishwasher presents a different set of design considerations. Fortunately, in contrast to recirculating fluid within the dishwasher where high pressure is required, drain pumps do not have a corresponding high pressure requirement. Instead, a drain pump need only overcome a pressure head maintained in a siphon loop of a drain hose. Therefore, a relatively small pump can be used to drain washing fluid and soil from the dishwasher. 
     While smaller pumps can generate sufficient pressure to perform a drain operation, the smaller pumps typically employ a synchronous motor and produce less torque. That is, when operating a chopper mechanism, the smaller pump cannot rotate a chopper blade with as much torque as a larger pump. If the chopper blade encounters a hard or large soil particle, the pump could stall or jam. When a stall condition occurs, the synchronous motor must restart, causing the chopper blade to repeatedly impact the large/hard soil particle. That is, when the synchronous motor restarts, the chopper blade oscillates back and forth “hammering” the soil particle until the particle becomes small enough to pass through the apertured plate. While effective, it may take some time to fully break up the soil particle as the smaller pump cannot impart a high degree of inertia to rotate the chopper blade. Also, while the synchronous motor is stalled, draining is postponed until the particle can pass through the apertured plate. Obviously, this interaction can create a substantial amount of noise, as well as lengthen an overall wash operation. 
     Another consideration when constructing a drain pump is the overall construction and assembly of the pump. Minimizing potential leakage points is critical. Therefore, the drain pump should be constructed so as to reduce the number of openings or joints that could act as potential leakage points. Ideally, the drain pump would be formed from a one piece housing into which all the components are installed. However, when positioning components in a one piece housing, it can be difficult to locate the chopper blade relative to the chopper plate and to connect the pump with a pump motor. Too large a gap between the chopper blade and the chopper plate will allow soil particles to become trapped or stuck in openings that are arrayed about the apertured plate. Too small a gap and the chopper blade can become jammed or could come in contact with and abrade the chopper plate, resulting in damage to either one or both components. 
     Based on the above, there still exists a need for an enhanced drain pump for a dishwasher, preferably a low profile drain pump that operates a chopper blade to macerate soil particles in a washing fluid. In addition, there exists a need for a drain pump that includes an alignment device that assures proper positioning of the chopper blade relative to an apertured chopper plate. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a dishwasher including a tub having integral top, bottom, rear and opposing side walls that collectively define a washing chamber. The dishwasher also includes a wash pump for delivering a washing fluid to at least one wash arm in the washing chamber and a drain pump for expelling at least a portion of the washing fluid during purging and/or draining operations. The drain pump includes a pump housing having both an inlet portion and an outlet portion. An impeller, having a central recess portion and a plurality of vanes, is rotatably driven by a synchronous motor secured to the pump housing. More specifically, the plurality of vanes extend radially outward from the central recess portion so that, upon rotation of the impeller, a flow of washing fluid is established. In addition, the drain pump includes a chopper assembly including at least one blade member and an apertured plate mounted between the intake portion of the housing and the impeller. During a drain or purge operation, the chopper assembly macerates soil particles entrained in the washing fluid. 
     In accordance with a preferred embodiment of the present invention, the drain pump includes a central hub positioned at the inlet portion of the pump housing. The central hub includes a bearing surface that is adapted to support, at least partially, the chopper assembly. More specifically, the chopper assembly is drivingly connected to the impeller through an axially sliding drive mechanism. The drive mechanism includes a first end mounted within the central recess of the impeller that extends through the central hub to a second end that is connected to the chopper assembly. With this arrangement, a proper alignment or spacing can be achieved between the blade member and the apertured plate. 
     In further accordance with the preferred embodiment of the present invention, the at least one blade member is pivotal about an axis extending substantially perpendicular to the apertured plate. With this arrangement, in the event the blade member contacts a large or hard soil particle, the blade member will pivot or deflect around the soil particle so that the motor does not stall. However, continued rotation of the chopper blade will eventually reduce the soil particle to a size small enough to pass through openings in the apertured plate. However, in the event the large particle does cause the motor to stall, the motor is oscillated so that the blade member repeatedly impacts, or hammers, the soil particle from two directions. 
     Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of a preferred embodiment when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an upper right perspective view of a drawer-type dishwasher having a drain pump assembly constructed in accordance with the present invention; 
         FIG. 2  is an upper perspective view of a wash tub of the dishwasher of  FIG. 1 ; 
         FIG. 3  is a lower perspective view of the tub of  FIG. 2 ; 
         FIG. 4  is an exploded, partial cut-away view of a portion of a drain pump assembly constructed in accordance with the present invention; 
         FIG. 5  is an enlarged, partial cut-away view of an impeller housing and chopper assembly of the drain pump assembly of  FIG. 4 ; and 
         FIG. 6  is an exploded, partial cut-away view of the impeller housing and chopper assembly of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With initial reference to  FIGS. 1 and 2 , a dishwasher constructed in accordance with the present invention is generally indicated at  2 . As shown, dishwasher  2  includes a support frame  4  arranged below a kitchen countertop  6 . Also below kitchen countertop  6  is shown cabinetry  8  including a plurality of drawers  9 - 12 , as well as cabinet doors  13  and  14 . Although the actual dishwasher into which the present invention may be incorporated can vary, the invention is shown in connection with dishwasher  2  depicted as a dual cavity dishwasher having an upper washing unit  16  and a lower washing unit  18 . As best illustrated in  FIG. 1 , upper washing unit  16  takes the form of a slide-out drawer unit having a small or medium capacity so as to be used for cleaning glassware and the like, while lower cavity  18  is illustrated as a larger capacity drawer for washing items such as dinnerware, cookware and other large sized objects. 
     In accordance the invention, upper washing unit or drawer  16  is shown to include a front wall  20 , a rear wall  21 , a bottom wall  22  and opposing side walls  23  and  24  that collectively define an upper washing chamber or tub  28 . In a manner known in the art, upper washing tub  28  is provided with a dish rack  30  for supporting various objects, such as glassware, and the like, to be exposed to a washing operation. In a manner also known in the art, upper washing unit  16  is slidingly supported within support frame  4  through a pair of extensible drawer support guides, one of which is indicated at  33 . 
     As best shown in  FIG. 2 , a main filter housing  38  is provided along bottom wall  22  within washing tub  28 . Main filter housing  38  is actually positioned within a central, generally U-shaped, intake ring  40  (see  FIG. 3 ) formed in bottom wall  22 . In any event, main filter housing  38  includes a coarse or first radial strainer  42 , a fine or second radial strainer  43  and a cover  44 . Actually, second radial strainer  43  is part of a fine particle filter chamber (not shown) including a fine mesh filter screen (not separately illustrated) provided within each of a plurality of large radial spaced openings  45  arranged about cover  44 . A hub member  47  extends through cover  44  and serves as a support for a wash arm  49 . As will be discussed more fully below, wash arm  49  directs a flow of washing fluid onto kitchenware placed within washing tub  28  on rack  30 . 
     With particular reference to  FIG. 3 , washing tub  28  includes a sump  64  having a plurality of fluid conduits  67 - 69  formed along bottom wall  22  of washing tub  28 . In accordance with one form of the invention, fluid conduit  67  constitutes a wash fluid supply conduit, fluid conduit  68  constitutes a wash fluid recirculation conduit, and fluid conduit  69  constitutes a wash fluid drain conduit so that each of fluid conduits  67 - 69  provide washing fluid flow management during various portions of a washing operation. Preferably, fluid conduits  67  and  69  are spaced from and arranged substantially parallel to one another across bottom wall  22 , while extending from a central portion  71  of intake ring  40  to an outer edge portion  74  of washing tub  28 . On the other hand, fluid conduit  68  extends across intake ring  40  between fluid conduits  67  and  69 . More specifically, supply conduit  67  includes a first end  78  which is fluidly connected to wash arm  49  and leads to a second end  79 . Second end  79  is provided with an attachment or mounting flange  80 . Likewise, recirculation conduit  68  extends from a first portion  81 , which is positioned at a front edge of intake ring  40 , to a second end  82 . Recirculation conduit  68  is provided with an inlet (not shown) that receives a flow of washing fluid from wash tub  28 . In a manner similar to that described with respect to supply conduit  67 , recirculation conduit  68  is provided with a corresponding attachment or mounting flange  83 . Finally, drain conduit  69  extends from a first end  85 , which is in fluid communication with main filter housing  38 , to a second end  86 , which is also provided with an attachment or mounting flange  88 . 
     In addition to managing the flow of washing fluid in dishwasher  2 , sump  64  serves as a mounting platform for a plurality of wash system components. As best shown in  FIG. 3 , a wash pump  110  and a drain pump  111  are mounted to washing tub  28  along outer edge portion  74 . More specifically, wash pump  110  and drain pump  111  are connected to mounting flanges  80 ,  83  and  88  respectively. Preferably, wash pump  110  includes a wash motor housing  115  and a wash pump housing  116 . In the embodiment shown, wash pump housing  116  includes a fresh water inlet  118 , a supply outlet  119  and a recirculation inlet  120 . Supply outlet  119  directs washing fluid to wash arm  49 , while recirculation inlet  120  conducts washing fluid back from washing tub  28  into wash pump housing  116 . Toward that end, wash pump housing  116  is generally F-shaped, with supply outlet  119  and recirculation outlet  120  terminating in mounting flanges  80  and  83  respectively. With this overall construction, a substantially closed loop recirculation system is formed within washing tub  28 . In accordance with one aspect of the invention, a heating element  90  is mounted within recirculation conduit  68 . In accordance with the embodiment shown, washing fluid flowing from washing tub  28  through recirculation conduit  68  can be heated by selectively activating heating element  90 . In any event, a more detailed description of sump  64  can be found in commonly assigned U.S. patent application Ser. No. entitled “Multi-Use Sump for a Drawer-Type Dishwasher” which is filed on even date herewith and incorporated herein by reference. The present invention is directed to the particular design, construction and operation of drain pump  111 . 
     As best seen in  FIGS. 4-6 , drain pump  111  includes a pump housing  150  and a motor base  155 . In accordance with a preferred form of the invention, pump housing  150  includes an inlet portion  160  extending to an outlet portion  161  through a tapered segment  162 . Inlet portion  160  is adapted to be inserted into mounting flange  88  of drain conduit  69 . In the embodiment shown, outlet portion  161  extends from tapered segment  162  to a sealing edge portion  167  adapted to abut motor base  155 . As will be detailed more fully below, sealing surface  167  is secured to motor base  155  through a pair of mounting ears  169  and  170 . In addition, outlet portion  161  is provided with a discharge conduit  173  including an outlet passage  174  that, in the embodiment shown, extends generally perpendicularly from an interior region  176  of outlet portion  161  and leads to a drain through a drain hose (not shown). 
     In further accordance with the embodiment shown, motor base  155  includes an outer edge portion  190  that defines a sealing surface  193  adapted to abut with sealing edge portion  167  of pump housing  150 . Sealing surface  193  is provided with a central opening  196  about which is arranged a locating ring  200 . In order to secure motor base  155  to pump housing  150 , a plurality of preferably L-shaped mounting lugs, two of which are indicated at  204  and  205 , project generally perpendicularly from sealing surface  193 . L-shaped mounting lugs  204  and  205  are formed so as to receive mounting ears  169  and  170  in a twist-lock fashion so as to removably secure motor base  155  to pump housing  150  while, at the same time, providing a snug fit to prevent washing fluid from escaping out of pump housing  150 . Of course, pump housing  150  could be sealed to motor base  155  using a silicone gasket material or through sonic welding or other more permanent means so as to ensure a leak-tight fit. In the embodiment shown, motor base  155  is also adapted to support a motor assembly  206  ( FIG. 3 ). That is, a synchronous motor  209  including a permanent magnet rotor  211  is secured to motor base  155  so as to drive drain pump  111 . Furthermore, arranged about permanent magnet rotor  211  are a pair of motor coils, one of which is indicated at  214 , that provide the impetus to rotate rotor  211 . 
     As best illustrated in  FIGS. 4-6 , drain pump  111  also includes a chopper assembly  220  arranged within interior region  176  of pump housing  150 . In accordance with the preferred embodiment shown, chopper assembly  220  includes an impeller housing  225  having an outer surface  226  and an inner surface  227  that collectively define an impeller chamber  228 . Arranged within impeller chamber  228  is an impeller  229  having a plurality of vanes  230  that extend from a central hub  231 . In accordance with one aspect of the invention, vanes  230  are interconnected by a flange  232  that bifurcates impeller  229 . More specifically, flange  232  divides impeller  229  into an intake portion and a discharge portion (not separately labeled). Impeller  229  is drivenly connected to rotor  211  of motor assembly  206  through a drive shaft (not shown) that extends through central opening  196  in motor base  155 . In any event, impeller housing  225  includes a first end  233  which defines an overall intake opening  234  and leads to a second end  235  adapted to receive and seat about locating ring  200  so as to position and support impeller housing  225  within pump housing  150 . 
     In the embodiment shown, first end  233  includes a first lip portion  236  ( FIG. 5 ) that extends inward to a first segment  238 . First segment  238  leads to a second segment that defines a first land  240 . First land  240  merges to a third segment  241  that leads to a second lip portion  242 . As further shown in  FIG. 5 , second lip portion  242  extends through a fourth segment  243  to a second land, illustrated at  244 , which ultimately leads to a tapered portion  245 . Tapered portion  245  leads to outer surface  226  of intake housing  225  and ultimately terminates at second end  235 . In addition, impeller housing  225  includes an annular rib  248  formed on inner surface  227 . Rib  248  protrudes, as near as reasonably possible, toward vanes  230  to reduce circulation losses from a peripheral portion (not separately labeled) of intake opening  234 . 
     First end  233  includes a hub portion  260  ( FIG. 6 ) that is supported within intake opening  231  by a plurality of flow straightening fins, one of which is indicated at  264 . Flow straightening fins  264  are provided to straighten a flow of washing fluid entering intake opening  234  and flowing into impeller chamber  228 . The rotation of chopper assembly  220  imparts a rotation to the washing liquid entering intake opening  234 . Without flow straightening fins  264 , the washing fluid could cavitate, thereby causing an increase in noise output and a decrease in pump efficiency. In further accordance with the embodiment shown, hub portion  260  includes a bearing surface  268  having a central passage  270 . Bearing surface  268  provides a gliding and support surface for chopper assembly  220  as will be discussed further below. 
     As best shown in  FIG. 6 , chopper assembly  220  includes a guide bearing  300  having an inner surface  302  adapted to rotate against bearing surface  268  of hub portion  260 , an outer surface  303  and a central hub  305 . Central hub  305  preferably includes a first portion  310  that extends perpendicularly beyond outer surface  303 , and a second portion  311  that extends beyond inner surface  302  and is adapted to extend within central passage  270  of hub  260 . Outer surface  303  is also provided with a pair of opposing spindles  320  and  321 . In accordance with the most preferred form of the invention, spindles  320  and  321  pivotally support respective blade members  324  and  325 . Each blade member  324  and  325  includes a respective cutting end portion  329  and  330 , as well as a pivoting portion  332  and  333  having a respective opening  335  and  336 . Openings  335  and  336  are sized so as to be positioned over spindles  320  and  321  so that blades  324  and  325  can pivot relative to guide bushing  300 . Chopper assembly  220  further includes a mounting plate  345  adapted to retain blade members  324  and  325 . Toward that end, mounting plate  345  includes a pair of opposing outer openings  348  and  349  sized to slide over and engage spindles  320  and  321 , and a central opening  350  adapted to engage over central hub  305  of guide bearing  300 . Thereafter, mounting plate  345  is fixed in place relative to guide bushing  300 , such as by welding or other means known in the art. 
     During draining and/or purging portions of a washing operation, blade members  324  and  325  are rotated about an apertured plate  366  to macerate food particles that are contained within the washing fluid. Apertured plate  366  includes an outer edge portion  370  having an L-shaped lip  372  adapted to snap-fittingly engage onto first lip portion  236  of impeller housing  225 . Outer edge portion  370  leads to a cutting plate portion  375  having a plurality of openings or apertures, one of which is indicated at  380 , and a central opening  383 . With this arrangement, chopper assembly  220  can be assembled and mounted within hub  260  before apertured plate  366  is mounted to impeller housing  225 . In accordance with the most preferred form of the invention, once chopper assembly  220  is arranged within hub  260 , blade members  324  and  325  can be deflected about spindles  320  and  321  so as to pass through central opening  383  of apertured plate  366 . In this manner, a preferred spacing can be maintained between each blade members  324 , 325  and apertured plate  366  so as to adequately chop or macerate food particles without having food particles become trapped between blade members  324  and  325  and apertured plate  366 . 
     Given that blade members  324  and  325  pivot about spindles  320  and  321 , in the event that a large or hard food particle becomes lodged against apertured plate  366 , blade members  324  and  325 , upon impacting the hard food particle, can pivot or deflect, thus enabling chopper assembly  220  to continue rotating without becoming jammed. Actually, with this particular arrangement, blade members  324  and  325  will hammer against a food particle that is too large to pass through apertures  350  until, eventually, the food particle crumbles and passes through one of openings  380  in apertured plate  366 . 
     In further accordance with the most preferred form of the invention, in the event that chopper assembly  220  does become jammed, synchronous motor  209  can be oscillated or operated in reverse a short distance, e.g., through 90° of rotation, so as to allow blade members  324  and  325  to become dislodged and then rotated in a forward direction to macerate the food particle. The fact that blade members  324  and  325  pivot also provides another advantage. As most drain motors have a low torque rating, allowing blade members  324  and  325  to pivot enables motor  209  to achieve a desired speed without having to initially overcome the inertia of blade members  324  and  325 . Pivoting blade members  324  and  325  therefore require less initial inertia when rotated. As motor  209  reaches the desired speed, blade members  324  and  325  become fully extended and rotate about cutting plate portion  375 . 
     In order to further ensure a proper spacing between blade members  324  and  325  during assembly of pump housing  150 , chopper assembly  220  is drivenly connected to impeller  229  through an axially sliding drive mechanism  400 . In still further accordance with the most preferred form of the invention, axially sliding drive mechanism  400  includes an impeller guide bushing  412  having an outer surface  414  provided with a key element  415 . Guide bushing  412  is also provided with an inner bore  417  having an inner keyway  418 . Guide bushing  412  is adapted to seat or nest within a central recess portion  421  of impeller  229  that includes a corresponding keyway  422  so as to receive key element  415 . Extending through guide bushing  412  and interconnecting with guide bearing  300  is a drive pin  433 . In the embodiment shown, drive pin  433  includes a first end  435  having a cap member  436  adapted to nest within central recess portion  421  of impeller  229 , a key element  437  adapted to extend into inner keyway  418  of guide bushing  412 , a second end portion  440  and an intermediate portion  441 . Second end  440  is adapted to extend through hub  305  of guide bearing  300  and either be secured through an interference type fit or through use of a rivet, pin or other mechanical attachment. In order to minimize friction between guide bushing  412  and hub member  268  of impeller housing  225 , a bearing or washer  448  is provided therebetween. As shown, bearing  448  includes a central opening  449  having a keyway  450  adapted to receive key element  437  of drive pin  433  and a pair of opposing bearing surfaces  452  and  453 . Bearing surface  452  is adapted to ride against a rear bearing surface  457  of hub  260  in order to prevent wear and extend the overall operation and life of chopper assembly  220 . 
     With the above description, it should be readily apparent that drain pump  111  can be assembled with minimal potential leakage points while, at the same time, enabling ease of assembly, providing toleranced clearance for cutting blade members to rotate about an apertured plate, and preventing the chopper from becoming jammed so as to provide a smaller dishwasher, preferably a drawer-type dishwasher, with many of the advantageous features found in larger dishwasher models. Although described with reference to a preferred embodiment of the present invention, it should be readily apparent to one of ordinary skill in the art that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For instance, the particular shape and number of blade members  324  and  325  could vary without departing from the spirit of the present invention. In addition, while the axially sliding drive mechanism is described as being keyed to the impeller, splines are also acceptable. In general, the invention is only intended to be limited by the scope of the following claims.