Abstract:
A frame for recreational vehicles having a pair of oppositely spaced longitudinal frame members, having notches completely therethrough. The longitudinal frame members have a foam core in direct contact with a woven fiber fabric on an exterior of the longitudinal frame members with fabric flaps extending therefrom. The frame has a plurality of transverse stringers having a foam core in direct contact with a woven fiber fabric on an exterior of stringers that rest in notches of the longitudinal members. The stringers are complementary to the notches in the longitudinal members and the stringers have fabric flaps that extend along their length on opposite sides. The stringers extend completely through the longitudinal frame members. The flaps on the longitudinal frame members and the stringers are in overlapping contact. A deck having a layer of fabric covers the stringers, the flaps, and the longitudinal frame members and is impregnated with resin.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/466,300, filed Mar. 22, 2011, the disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Frames for vehicles, especially towable recreational vehicle trailers and motorized recreational vehicles (RVs), are typically made of steel. Steel is certainly a durable material for producing a frame, but it does have disadvantages. Weight is a primary drawback to using steel for framing an RV. The weight in a steel frame is due to the considerable weight of the material itself and also due to its shape. Generally, RV frames are made from readily available I-beams or tubular sections of a standard size. These I-beams and tubes are of a constant cross section along their entire length. However, this does not place the most material in areas of high stress where it is needed most nor does a constant cross sectional beam reduce material where less is needed as in areas of low stress. 
     Assembling a steel vehicle frame is difficult. During assembly there will typically be two longitudinal beams running the length of the RV and stringers or cross members will be placed across the longitudinal beams. At each junction of the stringers and longitudinal beams a connection must be made. These connections are made by welding or mechanically fastening the beams and stringers together. This takes a great deal of time and provides potential for mistakes. After the beams and stringers are mated, an additional step of attaching a deck must be made so that an RV may be built upon the frame. The deck that is attached to the steel frame may be made of wood, aluminum, or could structural steel. Attaching the deck to the frame is accomplished with many screws driven through the deck into the frame. This method of joining the deck to the frame is not only time consuming, but does not produce a continuously integrated deck and frame. In the case that the deck is wood, it must be protected from the elements below. 
     The geometry of a steel frame for an RV is not ideal. As mentioned above, uniform cross sections have the same height at the ends and at the middle. Ideally, less material would be placed at the ends so that more adequate ground clearance could be had at the front and rear of the vehicle. Also, in attaching the stringers to a traditional longitudinal beam, height is added to the vehicle as the stringers rest on top of the beams. This is height that is not available for living space within the vehicle due to height restrictions. This added height can also raise the center of gravity of the vehicle, which may be detrimental to the handling of the vehicle. 
     SUMMARY OF THE INVENTION 
     The present invention is for a frame for recreational vehicles having a pair of oppositely spaced longitudinal frame members, having notches completely therethrough. The longitudinal frame members have a foam core in direct contact with a woven fiber fabric on an exterior of the longitudinal frame members. The longitudinal frame members have fabric flaps that extend from them. The frame has a plurality of transverse stringers having a foam core in direct contact with a woven fiber fabric on an exterior of the stringers. The stringers rest in the notches of the transverse members. The stringers are complementary to the notches in the longitudinal members and the stringers have fabric flaps that extend along their length on opposite sides. The stringers extend completely through the longitudinal frame members. The flaps on the longitudinal frame members and the stringers are in overlapping contact. A deck covers the stingers and the longitudinal frame members. The deck has a layer of fabric and the flaps on the stringers and the flaps on the longitudinal members contact the deck. The stringers, the flaps, and the longitudinal frame members being impregnated with resin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of the composite RV frame without upper deck; 
         FIG. 2  is a top view of the frame shown in  FIG. 1  with the upper deck removed; 
         FIG. 3  is an exploded perspective view of the frame shown in  FIGS. 1 and 2 ; 
         FIG. 4  is a perspective view of a forward gooseneck portion of the frame shown in  FIGS. 1-4 ; 
         FIG. 5  is a sectional view taken about the line  5 - 5  in  FIG. 2 ; 
         FIG. 6  is a sectional view taken about the line  6 - 6  in  FIG. 2 ; 
         FIG. 7  is a broken top view of another embodiment having the longitudinal beams placed at the ends of the stringers; 
         FIG. 8  is a sectional view taken about the line  8 - 8  in  FIG. 7 ; 
         FIG. 9  is a sectional view taken about the line  9 - 9  in  FIG. 4 ; and 
         FIG. 10  is a perspective view of a longitudinal beam and stringers without the resin cured into the fibrous fabric; and 
         FIG. 11  is a perspective exploded view of a longitudinal beam exploded. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The frame  10  of the present invention is particularly well suited to a fifth wheel recreational vehicle RV. The overall design may also be used with other types of RVs as well. Although, a fifth wheel trailer is shown, it is not necessarily limited to being used in a fifth wheel configuration, but may be used for a ball type hitch trailer as well. Any trailer needing a long flat expanse will benefit from the construction of this invention. Examples of such trailers may be horse trailers and cargo trailers as well as others. The frame  10  has longitudinal beams  12  running most of the length of the frame  10  in its main section  14 . The longitudinal beams  12  are substantially parallel to each other and are made of a composite material. The composite material may be a fiberglass thermoset polymer composite, or can also be carbon fiber in a polymer matrix. The polymer of either type of composite is typically sprayed on fabric  21  made of the desired fibers. In the case of the frame  10  shown in the FIGS., the fabric  21  is woven fiberglass. Carbon fiber or other fibers may be woven into fabric that will be suitable for the present invention, however, woven fiberglass is an extremely cost effective choice that provides ample strength necessary for the frame  10 . The longitudinal beams  12  are of a lesser height at the ends and taller near the middle. This is done to optimize weight of the beams  12 . More material and a greater cross sectional moment of inertia is provided near the middle where the bending stresses are greatest. Less material is provided near the ends where the bending stresses are the least. The longitudinal beams  12  may also be tapered laterally, in addition to the vertical taper shown in  FIG. 1 .  FIG. 6  shows a cross section of the longitudinal beam, however, this particular beam is not tapered laterally. 
     An additional benefit of the shape of the longitudinal beams  12  is that the vehicle can be lower to the ground than would be possible if the longitudinal beams  12  were of uniform height along their entire length. In a completed RV the wheels will be placed near the center of the longitudinal beams  12 . As such, increased ground clearance will be achieved at the ends of the beams  12 . 
       FIG. 5  shows a composite layer  16  over a foam core  18 . The foam core  18  is the desired shape of the final beam  12 , minus the thickness of the composite layer  16 . The foam may be extruded polystyrene, expanded polystyrene, Styrofoam®, or other similar lightweight foam products. Although the foam core  18  does not have great mechanical strength, its combination with the composite layer  16  produces structure that is extremely strong per its unit weight.  FIG. 10  shows a portion of a beam  12  before resin is cured into the fibrous fabric  21 . The foam core  18  directly contacts the woven fiberglass fabric  21 . 
     The longitudinal beams  12  have a series of notches  20 , that are shown in  FIG. 1 , for accepting stringers  22 . Each stringer  22  extends completely through the longitudinal beams  12 . The stringers  22  are constructed similarly to the longitudinal beams  12 . Each has a composite layer  24  and a foam core  26 .  FIG. 10  shows stringers  22  before the resin is cured into the fabric  21 . Large lateral flaps  27  extend from the sides of each stringer  22  near the widest portion of each stringer  22 , which is the upper side of the stringers  22 . The lateral flaps  27  of the stringers  22  are woven fiberglass fabric  21  and are extensions of the fabric surrounding the foam core  26  of the stringers  22 . As can also be seen flaps  27  on the stingers  22  overlap with flaps  29  on the longitudinal beam  12 . The flaps on the longitudinal beams  12  are also extensions of the woven fiberglass fabric  21 . As such, the overlapping flaps  27 ,  29  as seen in  FIG. 10  will provide direct contact between woven layers of the fiberglass fabric  21 . This provides a very secure interlock and fully integrates the stringers  22  with the longitudinal beams  12  when both are cured with resin to form a continuous composite layer  16 . The stringers  22  have a consistent cross section along their length. As can be seen in  FIG. 5 , the stringers have a trapezoidal cross sectional shape. This is to optimize their strength to weight because the composite layer  24  is stronger in tension than compression, thus, less material is needed on the lower portion of the stringers  22 . 
     The frame  10  is built as an assembly of pieces connected by resin sprayed on fabric that connects individual pieces. The pieces begin as molded preforms filled with foam, with the fabric containing no resin. The stringers  22  and longitudinal beams  12  hold their shape before being impregnated by resin due to the fact that they are filled with foam that is in direct contact with the woven fabric. The stringers  22  extend completely through the longitudinal beams  12  and are placed through the longitudinal beams  12  dry. The fabric on the pieces may be saturated with resin by other methods of application such as rolling the resin onto the pieces, but typically a spray on application is most desirable for rapid mass production. The longitudinal beams  12  are made of three separate pieces, a front end piece  28 , a middle piece  30  and a rear end piece  32 .  FIG. 11  shows the pieces  28 ,  30 ,  32 . Some of the pieces  28 ,  30 ,  32  have fabric flaps  34  that are placed over an adjacent piece  28 ,  30 ,  32  and sprayed with resin to bond them to the adjacent piece  28 ,  30 ,  32 .  FIG. 11  shows how the pieces  28 ,  30 ,  32  are assembled to faun a longitudinal beam  12 . Flaps  34  near the ends are used to join adjacent pieces  28 ,  30 ,  32  of the longitudinal beams  12 . Flaps  29  near the upper portions of the pieces  28 ,  30 ,  32  are used to join deck  50  that will be placed over the top of the beams  12 . 
     The front portion of the frame  10  has a stepped up gooseneck portion  38  that is designed to have a fifth wheel hitch mounted to it. The gooseneck portion includes an upper deck  50 ′ that will be placed on top of the gooseneck portion. The gooseneck portion has upper longitudinal beams  42  that support stringers  22 . The upper longitudinal beams  42  are attached to longitudinal beams  12  with vertical supports  43 . The upper longitudinal beams  42  fabric flaps that extend from them similarly to the flaps  29  on longitudinal beams  12 . Because this area of a finished RV will have a great deal of stress from weight of the vehicle and towing force placed upon it, reinforcement beams  40  are placed between the outer beams  42  of the gooseneck  38 . These beams  40  are angled toward the midpoint of the forward most stringer  22 ′ and are connected to stringer  22 ′ at their forward ends. The reinforcement beams  40  have angled notches  44  to receive the stringers  22  that pass through them and are joined to the upper longitudinal beams  42  behind the forward most stringer  22 ′. 
     Deck  50  is integral with the tops of all the stringers  22  and the longitudinal beams  12  for the entire length of the frame  10 . The deck  50  is also applied to the gooseneck portion  38 . The deck is a composite made of the fibers mentioned above and cured resin. When making the frame  10 , a sheet of the woven fabric made from the fibers is placed on a mold and the rest of the frame  10  is assembled upon the fabric, after it is wetted with resin. The flaps  27 ,  29  on the stringers  22  and beams  12  cure into the deck to form an integral structure. This forms a continuous bond with the deck  50  everywhere it contacts the stringers  22  and beams  12 . The flaps  29 ,  27  on the longitudinal beams  12  and stringers  22  are integrally bonded within the deck  50  as the resin soaks through both the flaps  29 ,  27  and the deck  50 . The flaps  27 ,  29  form layers of the deck that are additional to layers of woven fabric that is applied on top of the stringers  22  and longitudinal beams  12 , and thus form a unibody structure. The unibody structure meaning that all of the parts are integrally joined to form a single unit lacking any separate pieces. This unibody structure forms a more rigid structure for a given amount of weight than could be had with separately joining pieces mechanically or using adhesive bonding. 
     Each part below the deck  50  has its fibers contributing to the material in the deck in areas not directly supported by underlying beams  12  or stringers  22 . The longitudinal beams  12  have their flaps  29  that extend inwardly. The stringers  22  have their flaps  21  that overlap and extend between respective adjacent stringers. Thus, there are at least three layers of bonded woven fabric adjacent to the longitudinal beams excluding the fabric in the deck  50  is applied. This relationship is illustrated in  FIG. 10 . With the deck fabric applied, the deck  50  will have four layers of woven fabric in contact adjacent to the longitudinal beams  12 . It is contemplated that the flaps  29  on the longitudinal beams may extend until they meet between the longitudinal beams  12 , and thus, it is possible to have 4 layers of contacting integrally bonded fabric throughout the deck using only one sheet of fabric on the top of the deck. 
     An additional embodiment may be made as shown in  FIGS. 7 and 8 . In this version of the frame  10 ′, the longitudinal beams  12  are placed at the ends of the stringers  22 . This provides an opportunity to bond vertical walls directly to the longitudinal beams  12  of the frame  10 ′. Construction of this manner forms an extremely rigid vehicle. 
     When making the frame  10  of this invention. A first step is to place a sheet of fabric used to form the deck  50  on a flat form. The flat form is placed so that the frame  10  will be constructed upside down. Then stringers  22  are placed on the deck  50  appropriately spaced to fit within notches  20  of the longitudinal members  12 . The flaps  27  on the stringers are placed so they overlap, and the flaps  29  on the longitudinal members  12  are place so they overlap the overlapping flaps  27 , as shown in  FIG. 10 . The upper deck  50 ′ fabric is placed on a deck that is lower than that of the form used to form the first deck  50 . Stringers  22  are placed onto the upper deck  50 ′ fabric and the reinforcement beams  40  are placed on top of the stringers  22  along with the upper longitudinal beams  42 . Supports  43  are placed so they span the longitudinal members  12  and upper longitudinal members  42 . When the individual pieces of the frame  10  are placed, the entire frame  10  is coated with resin to impregnate all of the fabric and cured. Once cured, the frame  10  is removed from the forms and flipped right side up. 
     The invention is not limited to the details given above, but may be modified within the scope of the following claims.