Abstract:
A method of fabricating a motorhome, wherein the motorhome comprises a chassis, a vehicle frame, and a coach body. In one embodiment, the method begins by prefabricating the frame by joining a plurality of parallel elongate members with cross-tie members. The frame is prefabricated separate from the chassis, and in one embodiment, the frame is prefabricated upside down such that the underside of the frame is accessible for attachment of a plurality of bulkheads. Then, the frame is rotated upright and positioned atop the chassis. In one embodiment, the rails of the chassis lie inside a channel defined by the plurality of bulkheads. Next, additional bulkheads are joined to the frame and chassis to further interconnect the frame and chassis. Preferably, the additional bulkheads comprise an opening such that the additional bulkheads can surround the chassis on all sides. Finally, the coach body is assembled on the frame.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. application Ser. No. 10/857,408 filed May 28, 2004, which is a divisional of U.S. application Ser. No. 09/965,463 filed Sep. 26, 2001 (issued on Oct. 26, 2004 as U.S. Pat. No. 6,807,735), which is a continuation-in-part of U.S. application Ser. No. 09/728,946 filed Dec. 1, 2000 (issued on Apr. 1, 2003 as U.S. Pat. No. 6,540,285); and this application also claims the benefit of U.S. Provisional Application No. 60/318,136 filed Sep. 7, 2001. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to the field of recreational vehicle fabrication and, in particular, to methods of prefabricating a motorhome frame and then joining the frame to a prefabricated vehicle chassis to provide a motorhome with increased structural strength and interior ceiling height with improved production efficiency and reduced cost and time of production.  
         [0004]     2. Description of the Related Art  
         [0005]     Motorhomes have become an increasingly popular and common means of recreation. Motorhomes are self-propelled vehicles that include a living space inside. Motorhomes typically provide sleeping areas, cooking facilities, and self-contained water supplies and toilet facilities. More elaborate motorhomes can include refrigerator/freezer units, showers and/or bathtubs, air conditioning, heaters, built in generators and/or power inverters, televisions, VCRs, and clothes washers and dryers. Motorhomes provide many of the amenities of a residential home while on the road away from home and are popular for this reason. Motorhome users will typically use the motorhome to travel to a recreational area and live in the motorhome for some period of time. It is not unusual for people, particularly retired persons, to use a motorhome as their primary residence. Motorhome users often have families with children and, as their trips are often of a recreational nature, will often invite friends or family along on the trip.  
         [0006]     It can be understood that since a motorhome will often be used by a large number of people and often for an extended period of time, the motorhome manufacturers and customers will seek as many amenities and as much interior living space as possible. A major goal of motorhome manufacturers and their customers is to maximize the amount of usable living space inside their motorhomes. However, the overall size of an motorhome is limited both by vehicle code regulations and by practical limitations on what is reasonable to drive and maneuver. Vehicle codes restrict the maximum height, width, and length of vehicles that may be driven on public roads. Also, as a vehicle increases in size, it becomes increasingly difficult to drive and can become physically too large to pass through locations that the driver may wish to go. In addition, as the motorhome gets physically larger, more fuel is required to move it, which increases the cost of operation. Accordingly, many motorhomes are provided with slide-out room structures which are extendable so as to increase the motorhome&#39;s footprint and interior living space once the vehicle comes to rest.  
         [0007]     An additional design constraint on the construction and design of motorhomes is their overall weight. Since an motorhome is intended to be mobile, an integral power plant is provided and the engine and drive-train have an upper design limit on the weight it is capable of moving. In addition, the chassis, suspension, wheels, and brakes of a motorhome also have upper design limits as to how much weight they can safely accommodate. These weight limits are established after careful engineering analysis and the weight ratings are endorsed and enforced by responsible governmental agencies. Exceeding the established weight limits of a power-train or chassis component can lead to excessive wear and failure, unacceptable performance, and exposure to liability in case of an accident. It is also highly desirable that as much payload as possible is available to accommodate passengers and cargo, i.e. available weight load between the wet weight of the motorhome and the total maximum gross weight of the motorhome.  
         [0008]     A particular issue with the weight of a motorhome is its distribution along a vertical axis. The distance of the vehicle&#39;s center of mass from the road surface has a dramatic effect on the handling characteristics of the vehicle. The closer the center of mass is to the road surface, the shorter the moment arm between the center of mass and the roll axis of the vehicle. The shorter the moment arm between the center of mass and the roll axis of the vehicle, the less tendency the vehicle will have to lean in turns. Leaning in turns is uncomfortable for the occupants and typically places uneven loads on the tires and suspensions, compromising turning ability. Motorhomes, typically being quite tall, often exhibit significant leaning in turns. However, within the height available in a motorhome, the weight should be concentrated as low as possible. For this reason, heavy items, such as generators, storage and holding tanks for water and fuel, and the engine are optimally placed low in the chassis.  
         [0009]     Since motorhomes are mobile structures, they are typically exposed to the stresses of driving over roads that are in places quite rough. In addition, an motorhome will often have to travel over some distance of dirt surface to reach a camping space. Since an motorhome is typically used outdoors, it is exposed to the stresses of inclement weather and high winds. It can be appreciated that structural integrity is highly desired in an motorhome. However, the weight and size limitations previously mentioned place a limit on the strength of an motorhome. Accordingly, motorhomes are constructed to be as strong, but as light as possible.  
         [0010]     The chassis of a motorhome is typically constructed on a steel ladder frame chassis. The chassis is a partially complete vehicle and is generally procured from a manufacturer such as Freightliner or Ford Motor Company. The chassis typically consists of two parallel frame rails extending the length of the chassis and interconnected with several perpendicular cross-braces to form a ladder frame. An engine, transmission, and fuel tank(s) are generally placed between the frame rails near one end. Suspension, steering, brake, and road wheel assemblies are attached outboard of the frame rails.  
         [0011]     The coach bodywork, which provides and encloses the living space of the motorhome, is typically made from a laminate that can include light gauge sheet metal, plywood, vinyl, and insulation. The laminate is built to be strong, lightweight, weather resistant, and durable. The coach bodywork may also include a supporting framework. The floor of the coach typically rests indirectly on the chassis frame and the vertical walls extend upwards from the floor. The roof of the coach rests on and depends on the vertical walls of the body for structural support.  
         [0012]     A completed motorhome may be up to 45′ long and 13′6″ high in most states. The chassis is generally on the order of 1′ high and is elevated some distance above the ground by the suspension and wheels to provide ground clearance for suspension movement and clearing obstacles in the road. The interior flooring in current art motorhomes is typically elevated a significant amount above the upper face of the chassis in order to facilitate installing ancillary equipment. In addition, many prior art motorhomes route cooling or heating air ducts adjacent the roof structure or mount air-conditioning units on the roof. Under the overall height limit previously mentioned, these structures in or on the roof intrude into the available interior height envelope and limit the usable interior vertical space. Current motorhomes typically offer interior ceiling heights of 6′9″ or less. The slide-outs in current art motorhomes do not typically provide sufficient room inside for adults to stand upright. As the slide-out area is a living space in the extended position, it can be appreciated that to be forced to stoop or crouch inside the slide-out is an inconvenience for the users of such motorhomes.  
         [0013]     An additional difficulty arises with motorhomes of the construction described above when the vehicle drives over rough terrain. Motorhomes are essentially rectangular and are thus susceptible to twisting deflection as opposed to a triangulated structure such as a trailer or a fifth wheel. Motorhomes of the construction described above are not particularly strong under torsional forces such as arise when one corner of the vehicle drops or rises compared to the others, for example when a wheel drops into a pothole or rut or the vehicle drives over a curb or speed bump at an angle. Such maneuvers “cross-up” the rectangular frame and impose twisting forces. These forces, exerted over the relatively large dimensions of a typical motorhome, can cause significant displacement in the coach. This can cause cracks to appear in the coach, jam door and window openings, dislodge interior fitments, and generally cause wear and tear on the vehicle.  
         [0014]     Furthermore, as stated, a motorhome is typically constructed on an unfinished vehicle chassis procured from a separate manufacturer, such as Freightliner or Ford Motor Company. As such, the motorhome manufacturer is dependent on delivery of the preassembled chassis before motorhome fabrication can begin. This results in a series production that has increased assembly time as compared to a parallel process. expensive to purchase and inventory.  
         [0015]     From the foregoing, it can be appreciated that there is a continuing need for a stronger motorhome coach construction that also provides increased interior living space. The structure should minimize weight to the motorhome and should also maintain as low a center of gravity as possible to benefit vehicle handling characteristics. There is also a need for a method of fabricating the motorhome with increased efficiency and reduced cost and construction time.  
       SUMMARY OF THE INVENTION  
       [0016]     The aforementioned needs are satisfied by the invention which, in one aspect, is a method of manufacturing a motorhome comprising the steps of assembling a three-dimensional space frame wherein the space frame defines a generally planar floor area, interconnecting the space frame with an unfinished vehicle chassis, and attaching living structure to the interconnected space frame and vehicle chassis so as to define an interior living area. In one aspect, assembling the three-dimensional space frame comprises assembling a planar ladder frame and attaching planar bulkheads to the ladder frame and in certain aspects interconnecting the space frame with the vehicle chassis comprises attaching the ladder frame to the vehicle chassis along first horizontal regions of the vehicle chassis and attaching the bulkheads along second vertical regions of the vehicle chassis.  
         [0017]     Further aspects of the invention include installing a heating, ventilation, and air conditioning (HVAC) system such that the majority of the weight of the HVAC system is positioned below the floor area and/or installing the HVAC system such that the heating and air-conditioning portions of the HVAC system share a common air return.  
         [0018]     Other aspects of the invention include installing the HVAC system such that the furnace and air-conditioning portions of the HVAC system are positioned outside the living area. Certain aspects of the invention include assembling the living structure such that an outside roof structure has a convex exterior contour and attaching an extensible slide-out structure to the interconnected space frame and vehicle chassis wherein the slide-out is constructed such that an adult of above-average height can stand upright inside the slide-out. In particular aspects of the invention, the frame is assembled in an upside-down orientation and inverted to a right-side-up orientation prior to attachment to the unfinished vehicle chassis.  
         [0019]     The invention is also a method of lowering the center of mass of a motorhome comprising the steps of assembling a planar ladder frame wherein the ladder frame defines a floor plane, attaching planar structural members to the ladder frame such that, in an assembled configuration, the planar structural members extend downwards from the ladder frame, and attaching the space frame to an unfinished vehicle along an attachment plane such that the floor plane is adjacent the attachment plane less the thickness of the ladder frame and so as to create a three-dimensional space frame wherein the space frame extends below the floor plane. Certain of these aspects further comprise installing a heating, ventilation, and air conditioning (HVAC) system such that the majority of the weight of the HVAC system is positioned below the floor plane. The invention can include installing the HVAC system such that the heating and air-conditioning portions of the HVAC system share a common air return and the aspect wherein the planar structural members form storage areas positioned below the attachment plane.  
         [0020]     Yet another aspect of the invention is a method of increasing production efficiency of motorhome manufacture, the method comprising assembling a motorhome frame separately from an unfinished vehicle chassis, attaching the frame to the unfinished vehicle chassis so as to define an interconnected space frame among the frame and unfinished vehicle chassis, and constructing a motorhome coach on the interconnected frame and vehicle chassis. These aspects can include installing a heating, ventilation, and air-conditioning (HVAC) system wherein the HVAC system has a common air return. Yet other aspects of the invention include assembling the motorhome frame separately from the unfinished vehicle chassis and attaching the frame to the unfinished vehicle chassis so as to define the interconnected space frame between the frame and unfinished vehicle chassis comprising attaching bulkheads to the frame and the vehicle chassis such that the bulkheads are structural components of the space frame and form storage areas. These and other objects and advantages will become more fully apparent from the following description taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is an isometric view of a preassembled vehicle frame mounted on a preassembled chassis forming the framework for a motorhome with a high interior ceiling including an HVAC system with common air return;  
         [0022]      FIG. 2  is an exploded, isometric view of a partially assembled vehicle frame and a preassembled chassis;  
         [0023]      FIG. 3  is a perspective view of a partially complete preassembled frame;  
         [0024]      FIG. 4  is a perspective view of the frame of  FIG. 3  with a plurality of bulkheads attached forming a three dimensional space frame;  
         [0025]      FIG. 5  is an end section view of a motorhome including the vehicle frame and a slide-out;  
         [0026]      FIG. 6  is a perspective view of a completed motorhome; and  
         [0027]      FIG. 7  is a top view of one embodiment of an interior build-out in a motorhome. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     Reference will now be made to the drawings wherein like numerals refer to like parts throughout.  FIG. 1  shows an preassembled vehicle frame  100  mounted to a preassembled chassis  102 . The vehicle frame  100 , mounted to the chassis  102  in the manner that will be described in greater detail below, facilitates the construction of a motorhome  104  ( FIGS. 5 and 6 ) with a greater interior ceiling height, which in this embodiment, is at least 7′-6″ in a reduced time span. The vehicle frame  100  also facilitates, in a manner described below, building a slide-out  122  ( FIGS. 5 and 7 ) with a greater interior height. The vehicle frame  100  also facilitates mounting of relatively massive items, such as generators, furnaces, storage and holding tanks, and the like low to the ground so as to provide a lower center of mass for the motorhome  104 .  
         [0029]     The vehicle frame  100  provides a strong three dimensional space frame  118  to inhibit twisting of the vehicle frame  100  under torsional forces such as would arise when the motorhome  104  drives over uneven terrain so as to lift or drop a wheel  116  with respect to the other wheels  116 . The vehicle frame  100  further defines integral storage areas  106  as part of the structure of the vehicle frame  100  in a manner that will be described in greater detail below. The vehicle frame  100  further facilitates routing of a heating, ventilation, and air conditioning (HVAC) system  110  below the beltline of the frame  100  so as to avoid intrusion of the HVAC system  110  into the interior living space of the motorhome  104  to further enable increased interior ceiling height of the motorhome  104  employing the vehicle frame  100 . The HVAC system  110  comprises a furnace  164  and air conditioning unit  162  including evaporator, condenser, and compressor. These relatively heavy portions of the HVAC system  110  are installed below the beltline of the frame  100  thereby maintaining a lower c.g. than other designs.  
         [0030]     As can be advantageously seen in  FIG. 2 , the chassis  102  of this embodiment, is a split rail or raised rail chassis  102  of a type known in the art. The chassis  102  of this embodiment is a diesel pusher type and is available commercially from Freightliner, LLC. of Portland, Oreg. as Model XC. The chassis  102  comprises a pair of raised rails  112  and two pairs of lower rails  114 . The raised rails  112  and lower rails  114  are rigid elongate members formed of c-channel steel approximately 2¾″ by 9″ and approximately ¼″ thick. The raised rails  112  and the lower rails  114  are all substantially parallel. A first and second end of each center rail  112  overlies a lower rail  114  over a length of approximately 402″ in one embodiment and is attached along the overlying extent to the lower rail  114  in a known manner. Each pair of interconnected raised rails  112  and attached lower rails  114  are displaced a lateral distance of approximately 34″ and are further interconnected by a plurality of orthogonally extending cross-beams (not illustrated) rigidly attached so as to form a ladder frame structure of a type well known in the art. The upper surfaces of the raised rails  112  defines a generally horizontally disposed attachment plane for attachment of the frame  100  to the chassis  102  in a manner that will be described in greater detail below. The rails  112 ,  114  also present vertically arranged surfaces for further attachment of the frame  100  to the chassis  102 .  
         [0031]     The chassis  102  also comprises a plurality of road wheels  116  with corresponding suspension, brake systems, steering, and drive mechanisms of types known in the art that are positioned at substantially the front and rear corners of the chassis  102  in the manner illustrated in  FIG. 2 . The road wheels  116  enable the motorhome  104  to roll along the road and to be steered and braked in a well understood manner. The road wheels  116  are positioned adjacent the overlapping raised rails  112  and lower rails  114 . The chassis  102  further comprises an engine assembly, transmission, drive axle, fuel system, and electrical system (not illustrated) of types known in the art to provide the motive power for the motorhome  104 . These items are advantageously located substantially within the plane of the rails  112  to lower the center of mass of the chassis  102  and thus the motorhome  104 .  
         [0032]     The chassis  102  of this embodiment is highly resistant to bending along longitudinal and transverse axes. However, the chassis  102 , by itself, is susceptible to twisting along the plane of the longitudinal and transverse axes due to torsional forces. Such torsional force may arise when a road wheel(s)  116  at one corner of the chassis  102  is displaced either above or below the plane of the remaining road wheels  116 . Additionally, the torque of the engine exerts a torsional force on the chassis  102 .  
         [0033]     The motorhome  104  of this embodiment is assembled on and around the interconnected vehicle frame  100  and the chassis  102 . The motorhome  104  provides users with a vehicle having a variety of living spaces and amenities fitted within the motorhome  104 . The partitioning of the interior living spaces and placement of interior amenities can be readily implemented by one of ordinary skill in the art. One embodiment of interior partitioning and furnishing of the motorhome  104  is illustrated in  FIG. 6 . The construction and features of the motorhome  104  will be described in greater detail below.  
         [0034]     As is illustrated in  FIGS. 1, 2 ,  3 , and  4 , the vehicle frame  100  comprises a floor section  101  which is formed from a plurality of L-channel elongate members  174 , C-channel elongate members  176 , and square tubing elongate members  180 . The L-channel elongate members  174  of this embodiment are approximately 1½″ wide, 6⅜″ tall, and 34′ long and are made of sheet steel approximately 0.0897″ thick. The C-channel elongate members  176  of this embodiment are approximately 1½″ wide, 3½″ tall, and 34′ long and are made of sheet steel approximately 0.0897″ thick. The square channel elongate members  180  of this embodiment are approximately 2″ square in cross section, approximately 97″ long, and are made of sheet steel with a wall thickness of approximately ⅛″. It should be appreciated that the configurations of the elongate members  174 ,  176 ,  180  herein described are simply one embodiment and that other configurations of the elongate members  174 ,  176 ,  180  could be employed by one of skill in the art without detracting from the spirit of the present invention.  
         [0035]     The L-channel elongate members  174  and the C-channel elongate members  176  extend substantially the length of the vehicle frame  100 . The C-channel elongate members  176  define a cavity  182  and the L-channel elongate members  174  define an inside corner  184  as illustrated in  FIGS. 3, 4 , and  5 , Detail B. The square channel elongate members  180  are fixedly attached via welding in a known manner to the L-channel elongate members  174  such that a first and second end of each square channel elongate member  180  is flush with the inside corner  184  of an L-channel elongate member  174  such that the two L-channel elongate members  174  are parallel, the plurality of square channel elongate members  180  extend perpendicular to each of the L-channel elongate members  174 , and the plurality of square channel elongate members  180  are thus all respectively parallel.  
         [0036]     As can be seen in  FIG. 3 , a C-channel elongate member  176  is fixedly attached via welding in a known manner to each L-channel elongate member  174  such that the C-channel elongate member  176  abuts a first or second end of the square channel elongate members  180  and further such that the cavity  182  of the C-channel elongate member  176  is adjacent the L-channel elongate member  174 . Thus, the L-channel elongate members  174  enclose the cavities  182  and thus create closed structures. The abutment of the C-channel elongate members  176  against the square channel elongate members  180  inhibits displacement and bending of the square channel elongate members  180  with respect to the L-channel  174  and C-channel  176  elongate members. The interconnection of the L-channel  174  and C-channel  176  elongate members also defines two shelves  186  extending the length of the L-channel  174  and C-channel  176  elongate members. The interconnected L-channel  174 , C-channel  176 , and square channel  180  elongate members thus define a preassembled rigid ladder frame  100  structure that is highly resistant to bending and flexing.  
         [0037]     In one embodiment, a plurality of Z-channel elongate members  190  extend longitudinally and are positioned so as to be parallel to, aligned with, and between the rails  112 .  
         [0038]     The abutment of the C-channel elongate members  176  against the square channel elongate members  180  increases the stiffness of the joint between the square channel elongate members  180  and the L-channel elongate member  174 . This is because loads, which would be otherwise carried solely by the joint between the square channel elongate members  180  and the L-channel elongate members  174 , can now be distributed through the C-channel elongate members  176 . The interconnected L-channel  174 , C-channel  176 , and square channel  180  elongate members thus define a rigid ladder frame structure that is highly resistant to flexure. By making the frame  100  more rigid, the overall motorhome  104  will subsequently be more stiff to thereby enhance the performance of the motorhome  104 . The upper surface of the frame  100  defines a floor plane to which additional structure of the motorhome  104  is attached as described below. Areas of the lower surface of the frame  100  are attached along the attachment plane of the chassis  102  in a manner that will be described in greater detail below.  
         [0039]     As shown in  FIG. 3 , the elongate members  174 ,  176 ,  180 ,  190  are joined to form the vehicle frame  100  such that the frame  100  is assembled upside down. The frame  100  is assembled in an upside down orientation to facilitate attachment of other elements as will be described in greater detail below with reference to  FIG. 4 . The elongate members  174 ,  176 ,  180 ,  190  are held in position during attachment by a jig in a known manner. Thus, the frame  100  can be assembled without a chassis  102  present.  
         [0040]     The vehicle frame  100  also comprises a plurality of transversely extending bulkheads  120  illustrated in  FIGS. 1, 2 , and  4 . In one embodiment, the bulkheads  120  are rigid, planar pieces of steel approximately 0.0897″ thick. The bulkheads  120  are rectangular, triangular, or compound rectangular in shape as can be seen in  FIGS. 2 and 4 . Approximately 2″ of the outer edges of the bulkheads  120  are folded via known sheet metal forming techniques so as to extend generally perpendicular to the major plane of the bulkheads  120  thereby forming attachments areas  121  and also so as to increase the stiffness of the bulkheads  120 . The bulkheads  120  are attached to the frame  100  so as to extend generally perpendicular to the major plane of the frame  100  in the next step in the fabrication process, illustrated in  FIG. 4 . As the frame  100  is upside down, the bulkheads  120  can rest on the frame  100  during attachment rather than needing to be held up if the frame  100  were in its final right side up orientation. A particular advantage of the frame  100  of this embodiment, is that the frame  100  defines a three-dimensional space frame  118  prior to attachment of the frame  100  to the chassis  102 . Thus, the frame  100  is highly resistant to bending and twisting forces even if not attached to the chassis  102 .  
         [0041]     Following attachment of the bulkheads  120 , the frame  100 , as shown in  FIG. 4 , is then inverted and placed on the chassis  102  as illustrated in  FIG. 1 . The frame  100  is attached to the chassis  102  along the attachment plane, in this embodiment, at the points of intersection of the transversely extending elongate members  180  and the longitudinally extending rails  112 . The bulkheads  120  of the frame  100  are also fixedly attached to the vertical sides of the rails  112 ,  114  of the chassis  102  to further interconnect the chassis  102  and the vehicle frame  100 . The bulkheads  120  are attached to the vehicle frame  100  and the chassis  102  so as to extend downward from the vehicle frame  100  and the chassis  102 . The rigid interconnection of the bulkheads  120  with the chassis  102  and the vehicle frame  100  boxes in the rails  112 ,  114  of the chassis  102  further defining a three-dimensional space frame structure  118  adjacent the chassis  102 . The rigidly interconnected vehicle frame  100  and chassis  102 , boxed in by the bulkheads  120 , are much more resistant to twisting forces than the chassis  102  by itself. In addition, the floor plane of the frame  100  is advantageously positioned immediately adjacent the upper surface of the chassis  102  less the thickness of the ladder portion of the frame  100 . This maximizes the available vertical extent of the motorhome  104  available for interior living space within a set total exterior height.  
         [0042]     As stated above, the motorhome  104  manufacturer ordinarily orders the incomplete vehicle chassis  102  from another manufacturer, like Freightliner. The chassis  102  is a significant fraction of the overall material cost of the motorhome  104 . With the fabrication method described above, the frame  100  can be prefabricated to completion before the chassis  102  is obtained. More specifically, a major portion of the assembly of the motorhome  104  can be completed before the chassis  102  is received, and then the comparatively quick task of joining the completed frame  100  to the chassis  102  can be achieved once the chassis  102  is received. This aspect of the invention facilitates a just-in-time manufacturing capability thereby reducing the time capital is tied up in the chassis  102  prior to completion of the motorhome  104 . This aspect of the invention results in cost savings for the manufacturer of the motorhome that can be passed on as price reductions to the consumer and/or increase the manufacturer&#39;s profit margin.  
         [0043]     The motorhome  104  also comprises a front loop  192  as shown in  FIG. 1 . The loop  192  is a generally rectangular structure attached at the front of the motorhome  104  to the frame  100 . The loop  192  provides structural support for interior body assemblies in the driver&#39;s and front passenger&#39;s area as well as the front exterior bodywork of the motorhome  104  and the front windshield. The loop  192  is assembled from a plurality of elongate steel members via welding in a similar manner to that previously described with respect to the frame  100 .  
         [0044]     The motorhome  104  of this embodiment comprises a slide-out  122  ( FIGS. 5 and 7 ). The slide-out  122  is a movable structure contained within the motorhome  104  that is extensible between a retracted, travel position and an extended, live-in position. The slide-out  122  is a generally rectangular structure closed on the top and bottom and three sides and open on the remaining fourth side. The slide-out  122  of this particular embodiment is approximately 3½′ deep, 13′-4″ long, and of 6′-1″ interior height. The slide-out  122 , in the extended, live-in position, provides additional interior living space to the users of the motorhome  104 .  
         [0045]     In particular, the slide-out  122  provides an additional 45½ square feet of living space when the slide-out  122  is extended. A particular advantage of the slide-out  122  of this embodiment is that the interior ceiling height is approximately 6′1″ as referred above. This enables a person of above average height to stand up within the slide-out  122 . This greatly increases the convenience and livability of motorhomes  104  employing the vehicle frame  100  which enables the slide-out  122  as herein described. As will be described in greater detail herein below, the increased living space in the main section of the motorhome  104  and in the slide-out  122  is due, in part, to the configuration of the vehicle frame  100 .  
         [0046]     The slide-out  122  includes a slide-out mechanism  124 . The slide-out mechanism  124 , of this particular embodiment, is an electro-mechanical assembly of a type known in the art. The slide-out mechanism  124  extends and retracts the slide-out  122  between the retracted, travel position and the extended, live-in position in response to user commands. The slide-out mechanism  124  also physically supports the slide-out  122  in transition between the travel and live-in positions. The slide-out mechanism  124  may comprise other mechanisms such as manual, pneumatic, or hydraulic without departing from the spirit of the present invention. However, the electro-mechanical mechanism of the preferred embodiment of the present invention affords advantages over other means. In particular, the slide-out mechanism  124  of this embodiment offers greater user friendliness than known mechanisms for extending slide-out rooms which are manually actuated. Furthermore, the slide-out mechanism  124  of this embodiment is lighter and requires less maintenance than known pneumatic or hydraulic slide-out extension mechanisms.  
         [0047]     The slide-out  122  and slide-out mechanism  124  are attached to the vehicle frame  100 . The vehicle frame  100 , when interconnected with the chassis  102  and the bulkheads  120  as previously described, is highly resistant to bending and twisting. Thus, the slide-out  122  and slide-out mechanism  124 , attached to the rigid structure of the vehicle frame  100  has a low susceptibility to jamming or sticking due to flexing of the motorhome  104  as it is driven about. The slide-out  122  is also able to support a significant amount of weight, such as furniture and occupants. It should be appreciated that alternative embodiments of the invention include additional slide-outs  122 .  
         [0048]     The vehicle frame  100  also comprises seat supports  126 . The seat supports  26  are, in one embodiment, rectangular structures formed from sheet steel approximately ⅛″ thick and are approximately 12 13/16″ by 22½″. The seat supports  126  are fixedly attached to the vehicle frame  100  via a plurality of bolts and/or welding in a known manner adjacent the front end of the vehicle frame  100 . The seat supports  126  provide a support and attachment structure for passenger seats  128  of known types. The passenger seats  128  provide seating accommodations for driver and passengers in a known manner.  
         [0049]     The vehicle frame  100  of this embodiment, also comprises two storage area floors  130 . The storage area floors  130  are rigid composite rectangular members approximately 3¼″ thick, 95″ wide, and 98″ long and 3¼″ thick, 65″ wide, and 44″ long. The storage area floors  130  are a composite of tube steel, foam, and Luan vacuum bonded together. The storage area floors  130  are fixedly attached along the attachment areas  121  along lower edges of the bulkheads  120  with welds and/or bolts in a known manner. The storage area floors  130 , together with the bulkheads  120 , define storage areas  106 . The storage areas  106  of this embodiment extend substantially the full width of the motorhome  104 . The storage areas  106  of this embodiment are two rectangular spaces approximately 95″ by 98″ by  25½″ and  65″ by 42″ by 25½″. The storage areas  106  of this embodiment are approximately 8″-9″ higher than comparable storage areas would be in an embodiment employing a straight rail design chassis. In particular, the raised rails  112  of the chassis  102  are 8″-9″ higher than the lower rails  114  and thus provide 8″-9″ additional height to the storage areas  106 .  
         [0050]     The storage area floor  130 , comprising a rigid member fixedly attached along the length of the lower edges of the bulkheads  120 , further defines the three-dimensional structural space frame  118 . The structural space frame  118 , comprising a plurality of rigid panels and rigid elongate members fixedly interconnected along their adjoining edges and arranged at right angles to each other, forms a structurally rigid space structure. It will be appreciated that distorting the space frame  118  would require separation of the joints between component members and/or bending of the rigid members. This further increases the torsional rigidity of the interconnected vehicle frame  100 , chassis  102 , bulkheads  120 , and storage area floor  130  assembly.  
         [0051]     The vehicle frame  100  also comprises a plurality of storage area doors  132  ( FIG. 5 ). In one embodiment, the storage area doors  132  are rectangular, rigid structures approximately 2⅜″ thick by 25½ by 8′ long. The storage area doors  132  are a vacuum bonded composite of fiberglass, Luan plywood, block foam insulation, and aluminum. The storage area doors  132  enclose the storage areas  106 . The storage area doors  132  have an insulation value of R 11  and thus provide thermal insulation to the interior of the storage areas  106 . The storage area doors  132  also retain objects placed in the storage areas  106  from falling out as the motorhome  104  moves about or from unintentional removal by curious children or thieves. The storage area doors  132  also inhibit intrusion of pests and windblown dirt, dust, and rain into the interior of the storage areas  106  thereby befouling the interior and possibly damaging items stored therein.  
         [0052]     The storage area doors  132  are hingedly attached along either a top edge or a vertical edge of the storage area doors  132  to the vehicle frame  100 . The storage area doors  132  can be raised to an elevated position to facilitate placing items into or removing items from the interior of the storage areas  106 . The storage area doors  132  are further positionable in a closed position to seal the interior of the storage areas  106 . The storage area doors  132 , in a preferred embodiment, further comprise weather seals  133  and a latching mechanism  135 . The weather seals  133  are resilient, tubular structures of a type known in the art that are attached with adhesive to the periphery of the storage area doors  132  on the side of the storage area doors  132  facing the motorhome  104 . The weather seals  133  improve the seal between the storage area doors  132  and the storage areas  106  in a known manner. The latching mechanism  135  is a lock mechanism of a type well known in the art which lockably secures the storage area doors  132  in the closed position to further inhibit unintentional opening of the storage area doors  132 .  
         [0053]     The motorhome  104  also comprises a coach floor  134 . The coach floor  134  of this embodiment is formed from a plurality of rectangular pieces of ¾″ tongue and groove plywood, placed so as to abut each other in a coplanar fashion. The coach floor  134  is a planar, rectangular structure approximately 97¼″ by 420⅝″. The coach floor  134  is placed directly on the floor section  101  of the vehicle frame  100  so as to rest on the shelves  186 . The coach floor  134  is attached to the floor section  101  of the vehicle frame  100  via a plurality of screws and adhesive in a known manner. The coach floor  134  provides a continuous flooring surface for the motorhome  104  to support occupants and furniture in the interior of the motorhome  104 . The coach floor  134  also provides a support and attachment surface for padding, carpeting, tile, linoleum, or other interior floor finishings.  
         [0054]     As is illustrated in  FIGS. 1, 2 , and  5 , the floor section  101  of the vehicle frame  100  is mounted such that the bottom surface of the floor section  101  is positioned directly on the rails  112 . As such, the coach floor  134  is elevated above the rails  112  of the chassis  102  by a distance substantially equal to the thickness of the members comprising the floor section  101 . This results in the upper surface of the coach floor  134  being flush with driver platform from front to back. The substantially planar floor section  101  yields a better bond between the floor section  101  and the chassis  102 .  
         [0055]     Moreover, the floor section  101  is attached to the upper surface of the raised rails  112  and is also connected to the sides and the bottom side of the raised rails  112  and the lower rails  114  via the bulkheads  120  that are also connected to the floor section  101 . As is illustrated in  FIGS. 1 and 2 , the floor section  101  is attached to the raised rails  112  and the lower rails  114  at periodic intervals along the length of the floor section  101  of the vehicle frame  100 . By interconnecting the floor section  101  to the raised rails  112  and the lower rails  114  using the space frame  118  that encloses the raised rails  112  and the lower rails  114  along the top and sides, twisting of the frame  100  when the wheels  116  of the motorhome  104  are vertically displaced from each other is reduced.  
         [0056]     The motorhome  104  also comprises coach walls  136 . The coach walls, in one embodiment,  136  are generally planar, rectangular structures approximately 2⅜″ thick, 90″ tall, and 416⅞″ long. The coach walls  136  are made from a laminated composite of fiberglass, phenolic Luan plywood, foam insulation, and interior decor panel which are vacuum bonded together with an aluminum frame. The coach walls  136  provide physical structure to the motorhome  104 . The coach walls  136  also insulate the interior of the motorhome  104  against heat transfer and sound. The coach walls  136 , of this embodiment, are approximately ½″ thicker than walls typically used in the art and have a higher insulation rating than other known walls. The insulation rating of the coach walls  136  of this embodiment is R 11 . The coach walls  136  also comprise various openings to accommodate windows, doors, slide-outs  122 , vents, etc. the formation and placement of which are readily realized by one skilled in the art.  
         [0057]     The motorhome  104  also comprises a coach roof  140 . The coach roof  140 , in one embodiment, is a planar, rectangular structure approximately 97¼″ wide by 371″ long. The coach roof  140  is formed from a laminate of a rubber outer roofing layer, Luan plywood, ultra-light high-density block foam insulation core, and a one-piece carpeted inner ceiling layer bonded with an extruded aluminum welded superstructure  138 .  
         [0058]     The coach roof  140  is substantially planar along a lower face  142  and convexly contoured along an upper face  144 . The coach roof  140  is approximately 5½″ thick at the thickest region near the center of the coach roof  140  and convexly tapers off to the sides and towards the front and back to a thickness of approximately 2½″ along the edges of the coach roof  140 . Thus, the upper face  144  of the coach roof  140  has a crowned contour. The crowned contour of the upper face  144  of the coach roof  140  inhibits pooling of water and accumulation of snow and debris on the coach roof  140 . Thus, the motorhome  104 , fitted with the coach roof  140  as herein described, can more readily shed water, snow, and debris and minimize the deleterious effects of retaining water or debris in contact with the materials of the coach roof  140 . The crowned contour of the upper face  144  also improves the structural durability of the coach roof  140  because avoiding accumulation of water and snow will minimize the vertical weight loads of heavy snow or water which could potentially otherwise bow the coach roof  140  leading to distortion, cracking, or separation of joints. The crowned contour of the coach roof  140  also improves the aesthetics of the motorhome  104  because more readily shedding debris helps to minimize adhesion of dirt and thus maintains a cleaner appearance to the exterior of the motorhome  104 .  
         [0059]     The motorhome  104  also comprises a plurality of attachment assemblies  146 . The attachment assemblies  146  are extruded from aluminum alloy in a known manner. The attachment assemblies  146  are elongate members that extend substantially the length of the motorhome  104 . The attachment assemblies  146  interconnect the coach walls  136 , a storage area skirt frames  132   a , the coach roof  140 , and the vehicle frame  100  in a manner that will be described in greater detail below.  
         [0060]     As viewed in a perpendicular cross-section (as shown in  FIG. 5 ) the attachment assemblies  146  comprise a planar attachment area  150 , a hollow rounded, closed rectangular channel  152  region, and an inner partition  154 . It should be appreciated that the attachment assemblies  146  are unitized, extruded assemblies and the planar attachment area  150 , the rectangular channel  152 , and the inner partition  154  herein described are regions of the attachment assemblies  146  and are materially and structurally continuous with each other.  
         [0061]     The attachment area  150  is a rectangular, planar region of the attachment assemblies  146  that is long as the length of the coach and extends vertically from the rectangular channel  152  approximately 2⅛″ and provides a convenient structure for attaching the attachment assemblies  146 . The rectangular channel  152  is a closed, structural element of the attachment assemblies  146  approximately 2″ by 34″ and increases the stiffness of the attachment assemblies  146  to bending and twisting according to well understood structural principles. The inner partition  154  extends vertically approximately ⅝″ within the rectangular channel  152  and spans and internally partitions the rectangular channel  152  and further stiffens the attachment assemblies  146 . The inner partition  154  is substantially coplanar with the attachment area  150 .  
         [0062]     The attachment assemblies  146  are fixedly attached to an upper and lower edge of the coach walls  136  such that the rectangular channels  152  are positioned between outer layers of the coach walls  136  as shown in  FIG. 3 , details A and B. The attachment assemblies  146  are further attached to the coach walls  136  such that the rectangular channels  152  are positioned flush with upper and lower edges of the coach walls  136 . The attachment areas  150  of the attachment assemblies  146  thus extend beyond the edges of the coach walls  136  approximately 2⅛″. The attachment assemblies  146  are attached to the coach walls  136  with an adhesive, such as MA425 from Plexus of Danvers, Mass. in a known manner.  
         [0063]     The coach walls  136  with the attachment assemblies  146  attached are placed on the coach floor  134  such that the attachment area  150  is adjacent the edge of the coach floor  134  and the rectangular channel  152  rests on the coach floor  134 . This placement of the coach walls  136  and attached attachment assemblies  146  results in the edge of the coach floor  134  occupying the corner defined between the attachment area  150  and the rectangular channel  152 . This placement further results in the coach walls  136  straddling the coach floor  134  such that approximately half of the thickness of the coach walls  136  is overlying the coach floor  134 . This enables the coach walls  136  to partially rest on the coach floor  134  for additional vertical load support while still maintaining clearance for recessed attachment of the coach walls  136  such that the attachment devices do not protrude beyond the outer face of the coach walls  136 .  
         [0064]     The attachment assemblies  146  in one embodiment are attached to the coach floor  134  and the vehicle frame  100  via a plurality of screws  156  positioned approximately every 5″ along the length of the attachment assemblies  146 . The screws  156  of this embodiment are 10-16×1″ of a type known in the art and installed in a known manner.  
         [0065]     The coach roof  140  is positioned on the coach walls  136  such that the attachment areas  150  are adjacent the edges of the coach roof  140  and such that the coach roof  140  partially overlies the coach walls  136 . The attachment areas  150  are attached to the coach roof  140  via a plurality of screws  156  placed approximately every 5″ along the length of the edges of the coach roof  140 .  
         [0066]     The motorhome  104  also comprises a plurality of trim pieces  160 . The trim pieces  160  are elongate members of semi-rigid material, such as vinyl, approximately 20′ long, 5″ wide and 1/16″ thick. The trim pieces  160  are arc-shaped in cross section and are attached to the aluminum superstructure  138  via a friction fit achieved in a known manner. The trim pieces  160  are positioned to abut each other so as to extend the full length of the coach roof  140 . The outer rubber roofing layer of the coach roof  140  overlies the trim pieces  160 .  
         [0067]     The trim pieces  160  cover the screws  156  attaching the coach roof  140  to the coach walls  136 . The trim piece  160  obscures the view of the screws  156  to thereby improve the aesthetics of the motorhome  104 . The trim piece  160  also shields the screws  156  and the upper edges of the coach walls  136  from rain, snow, and debris. Thus the trim piece  160  inhibits accumulation of water and debris adjacent the screws  156  and the upper edges of the coach walls  136  so as to inhibit corrosion and fouling of the screws  156  and the coach walls  136 . The trim piece  160  also inhibits intrusion of water and debris into the interior of the coach walls  136  which could compromise the strength and structural integrity of the coach walls  136 .  
         [0068]     The HVAC system  110  in this embodiment comprises the air conditioning unit  162 , the furnace  164 , a manifold  166 , a duct  170 , at least one register  172 , an intake  171 , and a filter  173  as illustrated in  FIG. 1 . The intake  171  (shown in section view in  FIG. 1 ) commonly directs air from the interior of the motorhome  104  to the air conditioning unit  162  and the furnace  164 . The filter  173  is positioned within the intake  171  and filters the air entering the HVAC system  110 . The air conditioning unit  162  receives air from the interior of the motorhome  104  via the intake and cools this filtered incoming air and directs the cool air into the interior of the motorhome  104 . The furnace  164  warms incoming air and directs the warm air into the interior of the motorhome  104 . The manifold  166  receives air from both the air conditioning unit  162  and the furnace  164  and routes the air to the duct  170 . The duct  170  extends substantially the length of the interior of the motorhome  104 . The duct  170  carries the warm or cool air to at least one register  172 . The registers  172  direct cool or warm air, received from the duct  170 , into the interior of the motorhome  104 . The registers  172  includes a screen to inhibit objects falling into the interior of the registers  172  and the duct  170 .  
         [0069]     The common intake  171  is advantageously formed on two sides by wood paneling that serves both to direct the air inside the intake  171  and also provide interior trim in the interior of the motorhome  104 . In addition, by directing air to both the air-conditioning unit  166  and the furnace  164 , the common intake  171  of this embodiment, obviates the need for the separate air intakes for the A/C unit and the furnace of other designs. The common intake  171  of this embodiment also facilitates the use of a single filter  173  for the HVAC system  110 . This single filter  173  reduces the time and expense of maintaining the HVAC system  110  by the end user as compared to other designs with multiple filters for the separate A/C and furnace systems. This commonality reduces the time and expense of construction of the HVAC system  110  as well as reducing the weight thereof.  
         [0070]     The HVAC system  110 , of this embodiment, is located within or below the plane of the chassis  102 . Positioning the air conditioning unit  162  and the furnace  164 , which are both relatively heavy items, within or below the plane of the chassis  102  further lowers the center of mass of the motorhome  104  to thereby improve the road handling of the motorhome  104 . The placement of the HVAC system  110  of this embodiment also distances the duct  170  and registers  172  from the coach roof  140 . Other known motorhome designs rout HVAC ducting adjacent the roof of the vehicle which exposes the cool air to thermal heating from sunlight incident on the roof of the vehicle. In the motorhome  104  of this embodiment, the duct  170 , register  172 , and air conditioning unit  162  are shaded from incident sunlight by the motorhome  104 . Thus, the HVAC system  110  can more efficiently provide cool air to the interior of the motorhome  104 . This improves the occupant&#39;s comfort in hot weather and reduces fuel costs for powering the HVAC system  110 .  
         [0071]     A further advantage of the HVAC system  110  of this embodiment is that the air conditioning unit  162 , duct  170 , and register  172  which carry cool air are located below the living space of the motorhome  104 . As is well understood by those of ordinary skill in the art, a cooler than ambient surface, such as the air conditioning unit  162 , duct  170 , and register  172  induces liquid water to condense out of the atmosphere if the temperature of the surface is at or below the dew point. When air conditioning ducting is routed above the living space of a motorhome, liquid water that condenses on the ducting is drawn downwards by gravity. This can induce liquid water to intrude into walls, ceilings, and other interior materials. It can be appreciated that liquid water can readily damage the structural integrity of typical motorhome building materials. Liquid water can also stain and warp interior materials, damaging the aesthetics of a motorhome. The air conditioning unit  162 , duct  170 , and registers  172  of this embodiment are positioned below the living space of the motorhome  104  and thus water that condenses out during use of the HVAC system  110  is drawn downwards and away from the motorhome  104  without intruding into the living spaces of the motorhome  104 .  
         [0072]     An additional advantage of the HVAC system  110  of this embodiment is that placement of the HVAC system  110  adjacent and below the beltline of the chassis  102  obviates the need to place portions of an HVAC system on the roof of the motorhome  104 . Other known HVAC systems place portions of the system on the exterior roof of a motorhome. This requires that the major plane of the outer roof be lowered with respect to the roof of the present invention so as to maintain the overall height restrictions previously mentioned. Lowering the exterior roof height results in corresponding lowering of the interior ceiling height and a corresponding reduction in the interior space and livability of such a motorhome.  
         [0073]     Yet another advantage of the HVAC system  110  of this embodiment is that placement of the HVAC system  110  adjacent and below the beltline of the chassis  102  distances the furnace  164  and air conditioning unit  162  from the interior of the motorhome  104 . The air conditioning unit  162  and furnace  164  are relatively noisy in operation. Placing the HVAC system  110  outside the interior of the motorhome  104  distances the noise sources of the air conditioning unit  162  and the furnace  164  and thus provides a quieter, more comfortable living environment for users of the motorhome  104 .  
         [0074]     Although the preferred embodiments of the present invention have shown, described and pointed out the fundamental novel features of the invention as applied to those embodiments, it will be understood that various omissions, substitutions and changes in the form of the detail of the device illustrated may be made by those skilled in the art without departing from the spirit of the present invention. Consequently, the scope of the invention should not be limited to the foregoing description but is to be defined by the appended claims.