referring now in detail to the drawings , the covered litter box assembly 10 is comprised of a generally rectangular open litter tray 12 for containing a supply of cat litter ( not shown ), an upstanding rear cover 14 , a retractable hood 16 , and a filter element 18 carried by a supporting grate 20 disposed in the upper surface of cover 14 . the litter tray 12 , cover 14 and retractable hood 16 are all preferably molded of a polypropylene or other suitable plastic material . while the litter box assembly 10 is particularly designed for use with a clumping cat litter which typically requires more frequent access for removal of the soiled litter than conventional cat litter , any type of cat litter can be employed with the litter box assembly of the present invention . tray 12 which contains the cat litter defines a front wall 22 , rear wall 24 and side walls 26 which are all inclined slightly outwardly so that a plurality of boxes 12 can be compactly nested together for shipping . the walls of tray 12 also define smoothly radiused corners and outwardly flared upper edge portions 22 &# 39 ;, 24 &# 39 ; and 26 &# 39 ; extending about the upper perimeter of tray 12 . the front wall 22 of litter tray 12 additionally defines an elongated step down portion 28 for reducing the height of the cat access opening as will be described later herein . as seen in fig1 and 10 , a pair of resilient snap - on locking clips 30 are provided on the upper edge 28 &# 39 ; of the step down portion 28 of tray 12 for securing a water - proof litter liner 32 within the box ( see fig1 and 15 ). as shown in fig1 , edge 28 &# 39 ; is provided with grooves 34 which receive ribs 36 on clips 30 to secure clips 30 in place and firmly hold portions of the litter liner 32 between clips 30 and the upper forward edge of litter tray 12 . this securement of the liner prevents the liner from coming loose and being pulled into the box by the cat &# 39 ; s digging . when this occurs , cats will often playfully shred the liner , which is of course undesirable . the side walls of 26 of tray 12 each define a resilient upstanding locking tab 38 for securing the rear cover 14 in place on tray 12 as shown in fig1 . the rear cover 14 is comprised of slightly inclined and oppositely disposed upstanding side walls 40 , a slightly inclined rear wall 42 , and a top wall 44 and defines an open front end 46 bordered by a forward edge 48 . integrally formed with side walls 40 and rear wall 42 at the lower ends thereof is a continuous mounting channel 50 extending about the perimeter of the lower end of the cover which is adapted to receive upper edge portions of the side and rear walls of litter tray 12 as shown in fig1 . as seen in fig3 channel 50 is defined by a horizontal wall portion 52 which abuts the upper edge portions of litter tray 12 , an interior depending flange 54 extending downwardly from side and rear walls 40 and 42 so as to form a splash guard to prevent cat urine from passing between the cover 16 and upper end of tray 12 , and an exterior outwardly depending flange 56 which abuts and mates with the outer inclined portions 24 &# 34 ; and 26 &# 34 ; of litter tray &# 39 ; s upper edges 24 &# 39 ; and 26 &# 39 ;. elongated slots 58 are formed in the horizontal wall portions 52 of channel 50 adjacent the side walls of cover 16 to accommodate the resilient locking tabs 36 on tray 12 as seen for example in fig3 . mounted in the top wall 44 of the rear cover 14 is a filter element 18 for neutralizing the cat waste odors in the litter box assembly 10 . filter element 18 is preferably formed of 275 per cent grade , high density , activated carbon for effective odor neutralization . filter element 18 is held between a slightly elevated and perforated portion 60 of top wall 44 of cover 14 and a supporting grate 20 affixed to the underside of cover top wall 44 and spaced slightly below perforated portion 60 to accommodate filter element 18 therebetween . cover 14 forms an elongated transverse opening 62 at the rear upper end thereof which communicates with the area between perforated portion 60 and grate 20 such that filter element 18 can be slidably inserted and removed therethrough ( see fig4 and 15 ). to minimize any occlusion of filter element 18 by grate 20 , upstanding support ribs 64 are provided at spaced intervals on grate 20 as shown in fig1 to provide a slightly elevated and spaced apart support surface for the filter element 18 and thus allow air flow over the grate fingers 66 disposed between ribs 64 to maximize access of the air flow and vapors within the litter box to the filter element 18 . the grate fingers 66 , which do not carry a filter element , support rib 64 thereon protecting the filter element 18 from being attacked or eaten by the cat . the perforated portion 60 of cover top wall 44 is provided with a particular aperture configuration comprising oppositely oriented rows of apertures 67 of increasing diameter to minimize and equally distribute the resistance to air flow therethrough while providing the necessary support for the filter element 18 . the retractable hood 16 defines a pair of oppositely disposed side walls 70 depending from and merging into an arcuate upper wall 72 . side walls 70 are inclined slightly such that when hood 16 is retracted within cover 14 , the side walls 70 will move parallel to and substantially adjacent to the side walls 40 of the rear cover 16 . the curvature of upper wall 72 is defined by a segment of a constant radius circle to allow pivotal movement of the hood 16 within cover 14 without occluding the access to the litter tray 12 or litter contained therein as will be hereinafter described . integrally formed on the side walls 70 of hood 16 are a pair of outwardly projecting pivot members 74 which extend through aligned apertures 76 in the side walls 40 of rear cover 14 adjacent the forward lower ends thereof . pivot members 74 and aligned apertures 76 each define projecting wing portions 74 &# 39 ; and 76 &# 39 ; so as to provide a keyed fitment therebetween and thereby a simple and readily detachable pivotal mounting of hood 16 on cover 14 . the perimeter surfaces of the retractable hood 16 defines a trailing edge 78 extending along the rearward ends of the side and upper walls 70 and 72 of the hood and a pair of forwardly disposed supporting surfaces 80 adapted to abut the upper edges 26 &# 39 ; of the forwardly disposed ends of side walls 26 of the litter tray 12 when the hood 16 is in the extended position shown in fig2 . hood 16 additionally defines at its forwardly projecting end an elongated u - shape edge portion 82 which extends between supporting surfaces 80 and is outwardly and upwardly inclined such that when the hood 16 is in the extended position as seen in fig2 and 6 for example , edge portion 82 is disposed above and forwardly of the upper edge 22 &# 39 ; of the front wall 22 of tray 12 and cooperates therewith to define an elongated cat entry area 84 which extends virtually along the entire length of the widest portion of the cat litter tray 12 . the large size of the elongated entry area 84 defined by hood 16 and the forward wall 22 of litter tray 12 renders access to the litter box assembly 10 quite easy even for older and larger cats . in the preferred embodiment of the invention , the dimensions of which will be set forth in more detail later herein , the side and rear walls of litter tray 12 defines a height of about seven inches and the step down portion 28 in the front wall defines an elevation of about six inches and thereby forms both an adequate barrier to prevent litter being kicked from the box by the cat and yet is of an elevation which can be easily negotiated by most all cats , given the length and size of entry area 84 . the straight line distance between the upper edge of the step down portion of litter tray 12 and the edge 82 defining area is six inches and edge 82 is disposed about ten inches above the ground . while this dimension could , of course , be increased by raising the elevation of the hood , such an entry size is adequate for most all cats and minimizes the vertical space required to locate the litter box assembly . the retractable hood 16 is configured relative to rear cover 14 and litter box 12 such that when the hood is in the extended position , the trailing edge portion 78 is disposed proximate the forward perimeter edge 48 of cover 16 and the forward edge 82 is disposed forwardly of and above the upper forward edge 22 &# 39 ; of litter tray 12 to provide the cat access area 84 above - described . the forward support surface 80 which projects forwardly and rearwardly from the forward edge 22 &# 39 ; of the litter tray and abuts the forwardmost upper edge portions of the litter tray side walls 26 and thus supports the hood 16 in its extended position . in addition , depending flanges 86 are provided on the forward hood supporting surfaces 80 which , when the hood is in its extended position , are in axial alignment with and extend forwardly from the forward ends of depending cover flange 54 . like flange 54 , flange 86 projects downwardly below the inner upper edge of the litter box side walls and thus forms an extension of the urine splash guard defined by flange 54 . support surface 80 also defines an outwardly extending depending flange 88 which projects over and extends forwardly of the tapered upper surface of the forward most portions of the side walls of litter box 12 . the extension of the forward edge 82 defined by hood 16 above and beyond the front wall 22 of litter box 12 in combination with the curvature of the upper wall 72 of hood 16 directs upwardly flowing air and fumes within the cat litter box assembly 10 to the filter element 18 where they are trapped and neutralized . to prevent breezes and side drafts from passing closely by the cat entry area 84 and drawing fumes from assembly 10 into the surrounding room , the hood support surfaces 80 are extended forwardly of the forward wall 22 of litter box as above - described in a horizontal disposition , as seen for example in fig6 and thus extend the lower forward extensions of the side walls of the hood so as to define projecting skirt portions 90 which effectively block the sides of access area 84 and deflect any such breezes or drafts to prevent any fumes from being drawn outwardly of the litter box assembly . to prevent fumes from leaking from the assembly between the cover and retractable hood , sealing beads 92 and 94 are provided proximate the trailing edge portion 78 of the hood 16 and the forward perimeter edge 48 of cover 14 . with hood 16 in the extended position , the sealing beads are in abutment and prevent fluid passage therethrough thereby providing a totally odor free cat litter box assembly . in the retracted position illustrated in fig1 the trailing edge 78 of the hood 16 is disposed substantially adjacent the lower perimeter edges of side walls 40 and rear walls 42 of rear cover 14 as seen in fig1 and 4 whereby any intrusion of the retractable hood into the interior of litter tray 12 in the retracted position is avoided to provide a completely unobstructed view of and access to the entire area of tray 12 and the cat litter contained therein . as seen in fig4 however , the hood 16 is preferably spaced slightly away from the cover 14 so that if a cat sprays the lower end of the cover when the hood is in the extended position , the hood will not be contaminated when pushed to the retracted position . to move the hood 16 from the retracted position shown in fig1 to the extended position shown in fig2 it is merely necessary to grasp the leading edge of the hood and rotate the hood forwardly to its extended position . the hood 16 is preferably provided with a raised button 96 proximate the trailing edge 78 of upper wall 72 which , in the extended position , projects through a circular opening 100 formed adjacent the perimeter edge 48 in top wall 44 of the cover . the protrusion of button 98 into opening 100 forms a push - button lock which secures the hood in its extended position and renders the assembly 10 more resistant to litter tampering by children and curious dogs . to move the hood to its retracted position , one must merely depress the button and pivot the hood rearwardly . to this purpose , a u - shape cut 102 is provided in hood 16 about button 98 as seen in fig1 whereby the button can be readily depressed without having to force the entire hood downwardly to effect disengagement between the hood and cover . when the hood 16 is in the extended position , it is important that the side walls 40 of the rear cover 14 and side walls 70 of hood 16 project upwardly from the upper edges of the litter tray 12 a distance so as to dispose the top wall 44 of cover 14 and the proximate rearward portions of upper wall 72 of hood 16 sufficiently above litter box to provide ample interior space and headroom for a cat thereunder . in an embodiment of the invention configured to provide such space and an adequate cat entry opening for most all cats while minimizing room space , the top wall 44 of the rear cover is disposed approximately 10 to 10 . 25 inches above the upper edge of the side wall of the litter tray 12 . the radius of curvature defined by hood 16 is about 9 . 5 inches as measured from the center of the pivot members 74 . the litter box 12 is approximately 14 inches deep and 19 . 3 inches across and the elevation of the side walls of tray 12 and access opening 84 are as above described . further , the perimeter edge 48 of cover 14 is preferably angled slightly rearwardly to allow the hood to retract slightly further within the cover and thereby improve visibility and access to the interior of the tray 12 and the litter therein . to prevent damage to the litter box assembly 10 during shipping and to reduce the cost of the shipping , the litter box 12 , cover 14 and hood 16 are configured so as to be nested in a compact array within a shipping carton as illustrated in fig1 . as seen therein , six litter boxes 12 are nested together at the bottom of the array . to effect uniform stacking , each of the boxes 12 is provided with a pair of nesting spacers 106 at locations on the opposite side walls 26 thereof proximate the front and rear walls 22 and 24 . nested within the cavity of the uppermost litter box 12 in the stacked array are six of the rear covers 14 . as seen therein , the rear covers are placed in alternate opposite alignment and each side of the covers is also provided with a pair of nesting spacers 108 at the lower ends of side walls 40 adjacent the upper surface of horizontal wall 52 . finally , six of the hoods 16 are nested together and placed within the open cavity formed by nested covers 14 . a nesting spacer 110 is provided adjacent the lower ends of the side walls 70 of hood 16 for such purpose . by slightly tapering the side and rear walls of the cover 14 and the side walls of hood 16 as shown in the drawings , the functional objects of the assembled litter box assembly can be obtained as well as the nesting of the disassembled components described above . various changes and modifications may be made in carrying out the present invention without departing from the scope thereof . insofar as these modifications are within the purview of the appended claims , they are to be considered as part of the present invention .
a cat litter box assembly comprises a rectangular litter box tray , an upstanding cover removably securable on the walls of the tray so as to extend over and about a portion of the tray rearwardly of the front wall thereof , and a removable hood pivotally mountable on the cover between an extended position and a retracted position . the hood defines an elongated forward edge portion which , when the hood is in the extended position is disposed forwardly of and above the front wall of the tray and cooperates therewith to define an elongated cat entry area therebetween extending substantially the length of the front wall of the litter tray . the front and rear litter tray walls are longer than the side walls , maximizing the width of the cat entry area for the size of the tray . in the retracted position the hood is disposed interiorally of the cover and in substantial juxtaposition therewith so as to provide unobstructed access to the interior of the litter box tray for viewing and litter cleaning . a filter element is mounted in the upper end of the cover . the cover and the hood are provided with mating sealing members which are in sealing engagement when the hood is in its extended position , preventing odors from escaping therebetween . air deflectors are defined by the hood adjacent the ends of the cat entry area to prevent cross drafts from drawing odors outwardly therethrough and rendering the assembly virtually odor free .