Abstract:
The present invention is a unitary piece block formed of polymers (such as polystyrene or other high strength polymer) by a single injection molding step which are assembled into a recreational vehicle leveler. The invention ramp provides four sets of four connectors at a top of a floor plate, which are adapted to interlock in cavity structures formed within a cavity on the underside of the block. Two adjacent blocks are secured together by applying to their top surfaces the securing cavity structure of an underside of a third such block. Such blocks can be stacked in an interlocking manner to reduce storage space.

Description:
FIELD OF THE INVENTION 
   The present invention relates to devices used to level recreational vehicles and travel trailers. More specifically, the present invention relates to plastic interlocking blocks used to level recreational vehicles and travel trailers. 
   BACKGROUND OF THE INVENTION 
   The prior art describes several forms of interlocking pieces connected so that trucks and recreational vehicles can drive on to them and be leveled at an uneven site. 
   US Patent D426,933 shows one of a set of at least three interlocking blocks that are set up with two side by side and the third placed on top of halves of the bottom two to lock the three together. It has been found that this form of interlocking block suffers from substantial (over 20%) breakage in actual use with loaded trucks and recreational vehicles. The breakage is due to the particular strains placed on the blocks. A tire must be able to drive up a stepped ramp formed by the blocks and then come to rest preferably at the top of the third or top block or at any place on the stepped ramp. The strain that this makes on plastic pieces has been found to be unique in engineering of plastic parts. 
   U.S. Pat. No. 5,458,315 attempts to solve this breakage problem by using a heavily reinforced skeleton of brace plates. While in some ways preferable over the device of US Patent D426,933, the polygonal form of the raised part to interlock with a cavity in another block allows substantial lateral twisting that is not allowed with the square raised part shown in US Patent D426,933. 
   U.S. Pat. No. 7,040,603 shows that, for an interlocking type of ramp piece, from a floor plane level four square upward extensions are formed with four “key recesses” cavities formed therein. The underside of the each piece is formed to receive and interlock with the upward extensions. 
   There is a need for a device that would combine the non-rotation form of a leveling block with an improved non-breakable form. 
   SUMMARY OF THE INVENTION 
   The present invention is a set of at least three interlocking blocks where two of the blocks are set adjacent on a ground surface and are connected at their top surfaces by a particular configuration of the underside of the third block. Other blocks are capable being set adjacent to the ones on the ground surface and interlocked by stacking additional blocks between them to form a leveling device for recreational vehicles. 
   The present invention is formed of individual unitary interlocking blocks formed of polymers (such as polyethylene, polypropylene, polystyrene or other high strength polymer) by a single injection molding step. Each block comprises a square floor plate whose from periphery extends uniformly downward to a first height an outer sidewall, thereby forming a underside cavity and whereby a lower rim of the outer sidewall defines a ground plane level. Extending down from an underside of the floor plate to the ground plane in a central portion of the square floor plate are four central support sidewalls forming a central support square and defining a central underside cavity where each vertex of central support square is directed at an inner midpoint of one of the outer sidewalls. The underside cavity is further divided by a paired sets of support flanges which extend from said midpoints to vertices of said central support square, further thereby defining four equal sized and generally square receiving cavities. Each paired set of support flanges extends from an underside of the floor plate to the ground plane level and is bisected by a square cross-section side peripheral support extending down from the floor plate to the ground plane. Two opposite vertices of each side peripheral support are connected with one of the support flanges. 
   Sixteen octagonal flat-topped connectors extend up from the floor plate and each define a central pin bore extending from a top opening to a closed end at the floor plate. Said connectors collectively define eight top peripheral square receiving cavities and one top central square receiving cavity. The sixteen connectors are divided into four connector sets, each connector set having four octagonal connectors linked by low projections from the floor plate, each set being generally square and arranged at one of four corner portions of the top of the floor plate. Opposing and center facing sides of the octagonal connectors are parallel, thereby defining in a central part of the connector set a square corner peripheral receiving cavity. A square opening is defined in the floor plate at a bottom of each corner peripheral receiving cavity from which extends down to the ground plane four walls which end in a bottom plate, the combination of the four walls and bottom plate thereby forming square cross-section corner peripheral support. 
   Opposing and center facing sides of the four central-most connectors of the four connector sets are parallel and define a square central receiving cavity. The opposing sides of the four central-most connectors of the four connector sets are parallel and define a square central receiving cavity. 
   Opposing and center facing sides of the four connectors of two adjacent connector sets are parallel and define a square side peripheral receiving cavity. Opposing sides of the four connectors of the four connector sets are parallel and define a square central receiving cavity. A square opening is defined in the floor plate at a bottom of each side peripheral receiving cavity from which extends down to the ground plane four walls which end in a bottom plate, the combination of the four walls and bottom plate thereby forming the square cross-section side peripheral support. 
   Each connector defines a central cylindrical bore extending from a top opening to the floor plate. From the underside of the floor plate of said bore&#39;s floor plate extends a cylinder to the ground plane, said cylinder having a diameter less than the diameter of said central cylindrical bore. 
   The underside cavity beneath the floor plate comprises bridge flanges connecting sides of all the downward extensions from the floor plate. Said bridge flanges extend from the underside of the floor plate to a depth of one half or less of the distance from the underside of the floor plate to the ground plane. 
   Relative to any edge of a first block, in a horizontal direction across the floor plate and normal to said edge, first, second and third rows of four connectors each are adapted, respectively, to engage and interlock a first, second or third row of cavities underneath a second block. A user is thereby capable to forming a steeper or less steep effective ramp grade when said blocks are connected in an assembly of three or more blocks for use in leveling a recreational vehicle. 
   In using an assembly of three said blocks, weight of a single wheel portion of a supported vehicle is transmitted onto a top surface of a topmost block, which in turn transmits that force downward in two directions. A first quantity of the downward force is transmitted across the top platform surface to the outer sidewalls of the blocks. A second quantity of the force is transmitted directly downward onto a underlying set of supports. These supports join the sidewalls by way of the underside flanges so that downward force from the top platform surface urges the supports apart, creating a tensioned structure which resists fracture of the floor plate. There is no similar structure to accomplish this effect in prior art leveling ramps. 
   The force distribution of the present invention ramp is so efficient that the plates of the bridge flanges do not descend all the way from the underside of the floor plate surface to the ground plane. Surprisingly, the overall structure is sufficiently strong to support even the heaviest of recreational vehicles without sagging, cracking or breaking. It is this unique construction that permits the invention ramps to be stacked, using about half the storage volume of a comparable ramp by way of prior art construction. 
   It is an object of the invention to provide square, relatively low profile, leveler blocks where a first, second or third row of connectors can be engaged, respectively, a first, second or third row of connector cavities which are adapted to interlock by way of square and cylindrical extensions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top perspective view of the invention block. 
       FIG. 2  is a bottom perspective view of the invention block. 
       FIG. 3  is a top view of the invention block. 
       FIG. 4  is a bottom view of the invention block. 
       FIG. 5  is a side view of the invention ramp. 
       FIG. 6  is a cross section  125  of  FIG. 4 . 
       FIG. 7  is a cross section  124  of  FIG. 4 . 
       FIG. 8  shows three blocks as shown in  FIG. 5  in a stacked configuration. 
       FIG. 9  shows three blocks as shown in  FIG. 6  in a stacked configuration. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention is now discussed with reference to the figures. 
     FIG. 1  shows a block  100  having sixteen octagonal flat-topped connectors  105  that extend up from the floor plate  102  and comprise a top surface  110  and vertical sidewalls  113 . Each connector  105  a central pin bore having cylinder walls  111  and a closed end  112  at the level of floor plate  102 . Said connectors  105  collectively define eight top peripheral square receiving cavities  104  and  107  and one top central square receiving cavity  108 . The sixteen connectors  105  are divided into four connector sets  106  (shown in broken lines), each connector set  106  having four octagonal connectors linked by low projections  109  from the floor plate  102 , each set being generally square and arranged at one of four corner portions of the top of the floor plate  102 . Opposing and center facing sidewalls  113  of the octagonal connectors  105  are parallel, thereby defining in a central part of the connector set a square corner peripheral receiving cavity  104 . A square opening is defined in the floor plate at a bottom of each corner peripheral receiving cavity from which extends down to the ground plane four walls  121  which end in a bottom plate  120  (not shown), the combination of the four walls and bottom plate thereby forming square cross-section side peripheral support  114 . 
   Opposing and center facing sidewalls  113  of the four central-most connectors  105  of the four connector sets  106  are parallel and define a square central receiving cavity  108  (shown in broken lines). 
   Opposing and center facing sides of the four connectors of two adjacent connector sets  106  are parallel and define a square side peripheral receiving cavity  107 . A square opening is defined in the floor plate at a bottom of each side peripheral receiving cavity  107  from which extends down to the ground plane four walls which end in a bottom plate (not shown), the combination of the four walls and bottom plate thereby forming square cross-section side peripheral support  114   a , which has dimensions identical to those of corner peripheral support  114 . 
   Each connector  105  defines a central cylindrical bore extending from a top opening to the level of the floor plate  102  at closed end  112 . From the underside of the closed end  112  and referring now to  FIG. 2  extends to the ground plane, a pin cylinder having cylindrical sidewalls  122  and a bore  123  open at a lower end. Cylindrical sidewalls  122  have an outside diameter less than a diameter of said central cylindrical bore of the sidewalls  111  of connectors  105  (as in  FIG. 1 ). 
     FIG. 2  shows that block  100  comprises a square floor plate  102  whose from periphery extends uniformly downward to a first height an outer sidewall  101  (having optional support notches  103 ), thereby forming a underside cavity and whereby a lower rim of the outer sidewall defines a ground plane level. Extending down from an underside of the floor plate  102  to the ground plane in a central portion of the square floor plate are four central support sidewalls  118  open at the bottom forming a central support square  119 , which define a central underside cavity where each vertex of central support square  119  is directed at an inner midpoint of one of the outer sidewalls  101 . The underside cavity is further divided by a paired sets of support flanges  117  which extend from said midpoints to vertices of said central support square  119 , further thereby defining four equal sized and generally square receiving cavities for receiving connector sets  106  (shown in  FIG. 1 ). 
   Referring again to  FIG. 2 , each paired set of support flanges  117  extends from an underside of the floor plate  102  to the ground plane level and is bisected by a square cross-section side peripheral support  114   a  extending down from the floor plate  102  to the ground plane and under the portion of the floor plate  102  where side square peripheral cavities  107  (in  FIG. 1 ) are located. Two opposite vertices of each side peripheral support  114   a  are connected with one of the support flanges  117 . 
   The underside cavity beneath the floor plate  102  comprises bridge flanges  116  connecting sides of all the downward extensions from the floor plate  102 . Said bridge flanges  116  extend from the underside of the floor plate  102  to a depth of one half or less of the distance from the underside of the floor plate  102  to the ground plane. 
     FIGS. 3 ,  4 ,  5 ,  6  and  7  show the above features in other views. 
     FIG. 8  shows blocks  100   a ,  100   b  and  100   c  interlocked with connectors of blocks  100   b  and  100   c  secured in the structure of the cavity under the floor plate of block  100   a . Blocks  100   b  and  100   c  are first arranged abutting one another along adjacent sides of their outer sidewalls. Block  100   a  is impressed upon the tops of blocks  100   b  and  100   c.    
     FIG. 9  shows a cutaway view of the assembly of  FIG. 8 , where bridging flanges  116  of block  100   a  are supported from the top surfaces  110  of the connectors of blocks  100   b  and  100   c . In addition, the cylindrical pins with sidewalls  122  are shown supported from closed end  112  of the cylindrical bore of the connectors of blocks  100   b  and  100   c . A portion of the outer sidewalls  101  of block  100   a  are supported on a portion of the floor plate of blocks  100   b  and  100   c . A part of the support flanges  117  of block  100   a  are supported from the floor plates of blocks  100   b  and  100   c . For each of one of the adjacent connector sets on the tops of blocks  100   b  and  100   c , a row of two corner peripheral supports  114  and a side peripheral support  114   a  extending from the underside of block  100   a  are secured within, respectively, two corner peripheral receiving cavities  104  and one side peripheral receiving cavity  107 . Finally, the bottom edges of sidewalls  118  of central support square  119  and support flanges  117  of block  100   a  are supported from the floor plates  102  of both blocks  100   b  and  100   c.    
   Therefore, block  100   a  is connected to block  100   b  by way of the extensions of eight cylindrical pins, four connectors and three peripheral connectors, which is also true of the connection with block  100   c . The central support square, support flanges and bridge flanges are all supported on flat top surfaces of both blocks  100   b  and  100   c . This type of connection is very strong and secure. 
   The above design options will sometimes present the skilled designer with considerable and wide ranges from which to choose appropriate apparatus and method modifications for the above examples. However, the objects of the present invention will still be obtained by that skilled designer applying such design options in an appropriate manner.