with initial reference to fig1 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 fig1 , 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 fig2 , 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 fig3 ) 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 fig3 , 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 fig3 , 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 fig4 - 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 ( fig3 ). 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 fig4 - 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 ( fig5 ) 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 fig5 , 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 ( fig6 ) 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 fig6 , 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 .
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 .