Patent Publication Number: US-6986519-B2

Title: Low profile chassis and suspension

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part application of my application Ser. No. 09/193,501, filed Nov. 17, 1998 now abandoned, entitled LEAF SPRING WHEEL SUSPENSION SYSTEM, which is a continuation of Ser. No. 08/792,972, filed Jan. 31, 1997, entitled LEAF SPRING WHEEL SUSPENSION SYSTEM, which issued as U.S. Pat. No. 5,839,750 on Nov. 24, 1998. This application also claims priority to U.S. provisional patent application Ser. No. 60/238,790, filed Oct. 6, 2000 and entitled LOW PROFILE CHASSIS AND SUSPENSION. This application is a continuation in part and also claims priority to my application Ser. No. 09/318,428, filed May 25, 1999 now U.S. Pat. No. 6,398,251. All of the above-referenced applications are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   Field of the Invention 
   This invention relates to the field of wheel suspensions, and particularly to wheel suspension systems that independently support the wheels of a vehicle in which a wide and low cargo floor is desired. This invention is an improvement to the wheel suspension systems described in my earlier patents, namely, U.S. Pat. No. 4,878,691, issued on Nov. 7, 1989, U.S. Pat. No. 4,934,733, issued on Jun. 19, 1990, U.S. Pat. No. 5,016,912, issued on May 21, 1991, U.S. Pat. No. 5,275,430, issued on Jan. 4, 1994, and U.S. Pat. No. 5,839,750, issued on Nov. 24, 1998, all incorporated herein by reference. 
   For a variety of reasons, it is frequently desirable to have the cargo floor of a trailer, van, or similar vehicle as low as reasonably possible. A low floor provides for more efficient transportation of cargo, giving a vehicle more useable, internal space for given exterior dimensions. Also, a low floor placed close to the road surface makes for easier access to the vehicle. These and other advantages of a low cargo floor have motivated various proposals for low vehicle floors. 
   SUMMARY OF THE INVENTION 
   One embodiment of the present invention is a unique apparatus for placing the floor of a cargo compartment or payload section of a vehicle close to the roadway surface. Examples of cargo compartments and payload sections include the aft section of delivery trucks, airport shuttle buses and ambulances. 
   In another embodiment of the present invention, there is a novel configuration for a vehicle which includes a cab section with a high mounted engine and high placed cab floor coupled to a low profile chassis. 
   In yet another embodiment of the present invention, there is a novel manner of supporting an exhaust pipe within a frame that rides close to the road surface. 
   In a still further embodiment of the present invention, there is an apparatus for a road vehicle which includes a pair of frame sections with substantially planar top surfaces, and a planar bottom surface on one of the frame sections which provides increased ground clearance. A still further embodiment of the present invention pertains to a frame section of a vehicle placed below the rotational axes of the rear wheels, the frame section defining a recessed pocket adapted and configured to provide wheelchair access to the vehicle from a ramp. 
   In another embodiment of the present invention, there is a front suspension for a road vehicle which includes a pair of trailing arm supports attached to a driven front axle, and a pivotal member which links a trailing arm on one side of the vehicle with a frame member on the other side of the vehicle. 
   Yet another embodiment of the present invention pertains to a hydraulic brake assembly for use on a wheel whose rotational axis is above the top surface of a frame section. The hydraulic ports and hydraulic lines for the brake assembly are oriented such that they do not extend inward of the inboard surface of the brake assembly. 
   In yet another embodiment of the present invention, a vehicle including a rear frame with a top surface below rotational axes of the rear wheels is coupled to a driven front axle. The front axle receives power from an engine which is located aft of the front axle. 
   Accordingly, one object of the present invention is to provide a unique apparatus for transporting people and/or cargo in a vehicle. 
   Further objects, embodiments, forms, benefits, aspects, features, and advantages of the present invention can be obtained from the description, drawings, and claims provided herein. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a pair of wheel suspension systems constructed in accordance with one embodiment of the present invention. 
       FIG. 2  is a side elevational view of the wheel assemblies and wheels of  FIG. 1  mounted to a vehicle frame, viewing outwardly from inboard of the assemblies. 
       FIG. 3  is a top plan view of the wheel assemblies of  FIG. 1 . 
       FIG. 4  is a side elevational view of a frame and suspension section of a vehicle according to another embodiment of the present invention. 
       FIG. 5  is a top plan view of the vehicle section of  FIG. 4  as taken along line  5 — 5  of  FIG. 4 . 
       FIG. 6A  is a cross-sectional view of the vehicle section of  FIG. 5  as taken along line  6 — 6  of  FIG. 5 . 
       FIG. 6B  shows the vehicle section of  FIG. 6A  supporting a cargo compartment. 
       FIG. 7  is a partial cross-sectional view of a portion of the vehicle section of  FIG. 5  as taken along the line  7 — 7  of  FIG. 5 . 
       FIG. 8A  is a side elevational view of a wheel support and a portion of the vehicle section of  FIG. 5  as viewed along line  8 A— 8 A of  FIG. 5 . 
       FIG. 8B  is a side elevational view of the wheel support and portion of the vehicle section of  FIG. 8A  including a reinforcing doubler. 
       FIG. 9  is a perspective view of a wheel support according to one embodiment of the present invention. 
       FIG. 10A  is a side elevational view of a pivotal attachment according to one embodiment of the present invention. 
       FIG. 10B  is a side elevational view of another pivotal attachment according to one embodiment of the present invention. 
       FIG. 11  is an enlargement of the area within dotted oval  189  of  FIG. 5 . 
       FIG. 12  is a perspective view of a two-wheeled embodiment of the present invention as used within a van. 
       FIG. 13  is a perspective view of a four-wheeled embodiment of the present invention as used within a trailer. 
       FIG. 14  is a top plan view of a vehicle section in accordance with another embodiment of the present invention. 
       FIG. 15  is a partial side view of the vehicle section of  FIG. 14  as taken along line  15 — 15  of  FIG. 14 . 
       FIG. 16  is a top plan view of a vehicle section in accordance with another embodiment of the present invention. 
       FIG. 17  is a top plan view of a wheel support according to one embodiment of the present invention. 
       FIG. 18  is a side elevational view of the wheel support of  FIG. 17 . 
       FIG. 19  is a cross-sectional, perspective view of another embodiment of the present invention. 
       FIG. 20  is a top plan view of a frame and suspension system according to another embodiment of the present invention. 
       FIG. 21  is a top plan view of a frame and suspension system according to another embodiment of the present invention. 
       FIG. 22  is a top plan view of a frame and suspension system according to another embodiment of the present invention. 
       FIG. 23  is a top plan view of a frame and suspension system according to another embodiment of the present invention. 
       FIG. 24  is a front, left side, and top perspective view of another embodiment of the present invention. 
       FIG. 25A  is a front elevational view of the embodiment of  FIG. 24 . 
       FIG. 25B  is a rear elevational view of the embodiment of  FIG. 24 . 
       FIG. 25C  is a left side elevational view of the embodiment of  FIG. 24 . 
       FIG. 26  is a bottom planar view of the embodiment of  FIG. 26 . 
       FIG. 27  is a rear, top, and right side photograph of another embodiment of the present invention. 
       FIG. 28  is a front, top, and left side photograph of the embodiment of  FIG. 27 . 
       FIG. 29  is a partly sectional schematic representation of a side elevational view of another embodiment of the present invention. 
       FIG. 30  is a top plan view of an apparatus according to another embodiment of the present invention. 
       FIG. 31  is an end elevational view of the apparatus of  FIG. 30  as taken along line  31 — 31  of  FIG. 30 . 
       FIG. 32  is a side elevational view of the apparatus of  FIG. 30  as taken along line  32 — 32 . 
       FIG. 33  is a top, side perspective view of a portion of the apparatus of  FIG. 30 . 
       FIG. 34  is a side elevational view of another embodiment of the present invention. 
       FIG. 35  is a top plan view of an apparatus according to another embodiment of the present invention. 
       FIG. 36  is a side and rear perspective view of a vehicle incorporating the apparatus of  FIG. 35 . 
       FIG. 37  is a top, front, left side perspective view of the apparatus of  FIG. 30 . 
       FIG. 38  is an enlargement of a portion of the apparatus of  FIG. 37 . 
       FIG. 39  is a top perspective view of a portion of the apparatus of  FIG. 37 . 
       FIG. 40  is a rear, side perspective view of a portion of the apparatus of  FIG. 37 . 
       FIG. 41  is a side true perspective view of a wheel support according to another embodiment of the present invention. 
       FIG. 42  is a top true perspective view of the wheel support of  FIG. 41 . 
       FIG. 43  is a bottom true perspective view of a mirror-image wheel support of the wheel support of  FIG. 41 . 
       FIG. 44  is a side perspective and cutaway view of a portion of a wheel support, wheel, brake, and stub axle assembly according to one embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
   The present invention provides a wheel suspension system which has an extremely low profile. The suspension system utilizes a wheel support that is connected with the vehicle frame at points of attachment on the frame which are spaced apart laterally, thereby providing lateral support for the wheel. The wheel support is pivotable between an uppermost position and a lowermost position. One or two biasing means are included to maintain the wheel support in an intermediate position and to absorb loads from the wheel. 
   Referring in particular to  FIG. 1 , there is shown a wheel suspension system constructed in accordance with the present invention. The system includes a pair of wheels mounted to a vehicle frame by respective wheel supports. The wheel supports are maintained in position by a leaf spring secured between the wheel support and the frame. 
   The two wheels are shown mounted on the same side of the vehicle, and of course similar wheels and suspension systems are used on the opposite side of the vehicle. It will further be appreciated that the present invention is equally useful when only one wheel is supported on each side of the vehicle. Also, the embodiment of  FIG. 1  utilizes a single leaf spring, but could equally use separate biasing means serving the function of the spring. 
   The wheels are attached to cross members of the vehicle frame by wheel supports. The wheel supports attach to the cross member at a pair of pivot points, with one pivot point being inboard of the other pivot point. This lateral displacement of one pivot point relative to the other promotes the lateral stability of the wheel support. The frame cross members are held in position by a longitudinal member of the frame. 
   The wheel support connects to the frame cross member on a portion of the support that is largely horizontal and parallel to the roadway. The wheel support also has a section that is largely vertical relative to the roadway, to which the wheel, spring and shock absorber are attached. The spring and shock absorber attach to the vertical portion of the wheel support and also a vertical member of the frame. The upright portion of the wheel support is adaptable to springs such as the coil type, air bag type, or any other type of spring that creates a spring force when its attachment points are displaced relative to each other. 
   There is an additional spring that acts between the wheel support and the frame. This spring is of the leaf type, and attaches to both the horizontal portion of the wheel support and also to the frame. In a preferred embodiment, the attachment of the spring to the wheel support permits relative sliding of the spring within the wheel support in the fore and aft directions, but otherwise transmits spring forces created by the pivoting of the wheel support relative to the frame cross member. Alternative attachments of the leaf spring may be used, including an attachment by which one end of the spring is secured to a wheel support and the portion connected with the vehicle frame is allowed to slide relative thereto. Additionally, a spring configuration and attachment could be employed in which all attachments of the spring prevent or allow for sliding movement. 
   It is a feature of the leaf spring design that a biasing device is provided that fits generally within the typical vehicle frame. The leaf spring is located interior of the frame perimeter. It is also positioned below the upper surface of the frame, and thereby does not intrude into space available above the frame for the bed of the vehicle, i.e., the floor of a trailer or van. As shown in  FIG. 1 , the leaf spring is conveniently received through an opening in a frame member, thus accommodating the position of the leaf spring and minimizing the space required for the spring. 
   This leaf spring may be used simultaneously with adjacent wheels. The spring can attach, slidably or not, to two wheel supports and also be attached to a cross member of the frame in-between the two wheel supports. 
   The present invention provides a wheel suspension system useful in a variety of applications. The preferred embodiment is characterized by a wheel support with a largely vertical portion and a largely horizontal portion. The vertical portion is generally outboard of the vehicle frame. The horizontal portion is below or within much of the vehicle frame. Also, the shock absorber and springs of the preferred embodiment are similarly situated either outboard of much of the vehicle frame, or below or within much of the vehicle frame. This general arrangement permits maximum utilization of the area inboard and above most of the frame as useful cargo area. The wheel suspension system is useful, for example, for mounting the wheels of a trailer, or for the rear wheels of a front-wheel drive vehicle, such as a van. 
   Referring in particular to  FIG. 1 , there is depicted a preferred embodiment of the present invention in a perspective view. Frame outboard longitudinal member  2 , shown with an “L” cross section, is a major structural member of the vehicle frame traversing fore and aft along one side of the vehicle and defining an outer perimeter of the frame. Attached to it are frame cross members  4  and  6 , located fore and aft of each other, respectively. These cross members traverse the width of the vehicle, and typically terminate at the mirror image wheel suspension system on the other side of the vehicle frame. The frame cross members include frame vertical members  5  and  7 , respectively, located outboard of longitudinal member  2 . 
   Wheel suspension systems according to the present invention are mounted to the vehicle frame in the following manner. The wheel suspension systems include, for example, wheel supports  24  and  26 . The supports carry stub axles or the like to support wheels thereon. In turn, the wheel supports are mounted to the vehicle frame for pivoting about a horizontal axis, thereby allowing the carried wheel to move up and down with respect to the vehicle frame. 
   Located just aft of the cross members are wheels  8  and  10 . These wheels are attached to the wheel supports  24  and  26 , respectively, and are free to rotate about respective hubs. For example, wheel  8  is mounted to hub  16  and is free to rotate about a horizontal axis  12  ( FIG. 3 ). This hub is attached to upright portion  20  of wheel support  24 . 
   The wheel support further includes means for attaching pivotally to the vehicle frame. The support preferably has a generally flat, horizontal portion  21  attached pivotally to frame cross member  4  at inboard pivotal attachment  28  and outboard pivotal attachment  30 . The attachments preferably comprise a bracket secured to the frame, and a bolt and nut received through apertures in the bracket and the associated portion of the wheel support. These two pivotal attachments are aligned to provide for pivoting about a horizontal axis extending therethrough. The pivotal attachments are also displaced laterally to enhance the lateral stability of the wheel support, and therefore of the first wheel  8 . 
   A similar method is used to attach wheel  10  to frame cross member  6 . Hub  18 , about which second wheel  10  is free to rotate, is attached to upright portion  22  of wheel support  26 . This wheel support further includes a horizontal portion  23  which is pivotally attached to frame cross member  6  at pivotal attachments  32  and  34 . The wheel support  26  is thereby pivotal with respect to the frame about a horizontal axis extending through the pivotal attachments  32  and  34 , and the wheel  10  is rotatable about an axis  14  ( FIG. 3 ) which extends parallel to the pivoting axis. 
   The upright portions of the wheel supports attach not only to the hubs, but also continue around the forward upper quadrant of the respective wheels and attach to spring and shock absorber assemblies. As shown in  FIGS. 2 and 3 , air spring (air bag)  50  and shock absorber  56  both connect support upright portion  20  to frame vertical member  5 . Air spring  50  is attached at face  51  of first wheel support  24 , and also at face  52  of first frame vertical member  5 , in conventional fashion. Shock absorber  56  is mounted in a typical manner along side air spring  50 , to first wheel support  24  at pivotal attachment  57 , and to first frame vertical member  5  at pivotal attachment  58 . As wheel support  24  rotates about pivots  28  and  30 , the distance between upright portion  20  and vertical member  5  changes. The air bag and shock absorber accommodate this movement and cushion the pivoting of the wheel support. 
   An alternate to the spring and shock absorber arrangement utilizes a coil spring  60 , as shown attached between wheel support  26  and frame vertical member  7  in conventional fashion. This spring attaches to front spring mount  62  of vertical member  7 , and to rear spring mount  61  of wheel support  26 . When utilizing a coil spring, the shock absorber could be attached alongside the spring, similar to the positioning shown for shock absorber  56 , or it could be attached coaxially with the coil spring. Shock absorber  66  is shown mounted between frame vertical member  7  and wheel support  26  inside the coils of coil spring  60 . 
   Additionally spring support for the wheel occurs in respect to the horizontal portions of the wheel support members. The horizontal portion is configured to be substantially flat and to underlie the vehicle frame. It is a feature of the present invention that such a compact wheel support is also supportable in a manner to further enhance the low profile of the overall suspension in comparison to the vehicle frame. 
   The wheel support engages a leaf spring  70  that is secured between the support and the vehicle frame. Each wheel support can be combined with an individual leaf spring. Alternatively, pairs of wheel supports can be accommodated by a single leaf spring, as shown in the drawings. In general, a wheel support includes a leaf spring receiving member for connection with an end of the leaf spring. Leaf spring  70  is shown having a forward portion received within a narrow slot comprising a leaf spring forward attachment  78 . Leaf spring  70  continues in the aft direction, attaching to the frame by means of the frame attachment  74  through which it passes. Aft of that location the leaf spring includes a portion received within the rear attachment  72  defined by the wheel support  26 . 
   Frame attachment  74  prevents lateral, longitudinal or vertical motion of the leaf spring at the point of attachment. However, pivoting is permitted about the lateral access established by frame attachment  74 . 
   As wheel support  24  pivots about the axis defined by the attachments  28  and  30 , forward attachment  78  of the wheel support moves in an arc relative to cross member  4 . The distance between attachments  74  and  78  changes as the wheel support pivots. Attachment  78  permits sliding of leaf spring  70  in the fore and aft directions. Thus, a change in the fore/aft distance between attachments  74  and  78  does not result in the creation of spring load from spring  70 . However, attachment  78  does resist any change in the vertical distance between attachments  78  and  74 . Thus, rotation of the wheel support results in a change in spring load of spring  70  for the vertical component of movement. 
   Although the preferred embodiment depicts a single leaf spring attached near its center in providing support to wheel supports both in front and behind it, it is also possible to use a single leaf spring for each wheel support. For example, it would be possible to remove all portions of leaf spring  70  aft of attachment  74 , and have the remainder support only first wheel support  24 . Similarly, it would also be possible to remove all portions of leaf spring  70  forward of attachment  74 , thus providing support only to second wheel support  26 . Thus, leaf spring  70  could provide independent support for each wheel support, and the attachment of that independent leaf spring, could either be forward or aft of the respective wheel rotational axis. 
   Alternate embodiments of the present invention shown in  FIGS. 4–18  also provide a wheel suspension system which has an extremely low profile. These alternate embodiments utilize a wheel support that is connected by a pair of pivotal attachments to the vehicle frame. The wheel support supports a wheel for rotation about a rotational axis. The rotational axis is located above the pivotal attachments and above the transverse frame structure which lowers the profile of the wheel support and permits additional cargo-carrying volume above the wheel support. The pivotal attachments are spaced apart laterally, thereby providing lateral support for the wheel. The wheel support is pivotal between a first, uppermost position and a second, lowermost position. The pivot axes of the two pivotal attachments are generally coincident, and are preferably arranged such that the wheel support pivots in a pitching direction relative to the vehicle. 
   Some of these embodiments incorporate a spring such as an airbag, leaf spring, or coil spring for biasing the wheel support to a position intermediate of the first and second positions. The spring is placed between a spring support of the vehicle frame and a spring support of the wheel support, and is placed beneath the rotational axis of the wheel and preferably inward of the wheel and tire. This placement of the spring helps increase useable cargo carrying volume for the vehicle and simplifies the structural support necessary to support the biasing loads by utilizing planar portions of the vehicle frame to support the spring. In addition, some embodiments orient the shock absorber in a generally horizontal position beneath the rotational axis of the wheel. This placement of the shock simplifies the structure of the wheel support and also the upright structures of the frame that houses the wheels. In some of those embodiments with horizontal shock absorbers placed below the wheel rotational axis, the biasing mechanism includes either an air bag, or one or more leaf springs coupled to both a wheel support and a cross member of the vehicle frame. In yet other embodiments, a leaf spring couples to adjacent wheel supports and to the vehicle frame. 
   Referring to  FIGS. 4–6 , a vehicle frame and suspension section  98  with a longitudinal axis X includes a wheel support  100  which rotatably supports a wheel  102  and tire  104 . Wheel support  100  is pivotally attached to a cross member  106  of a transverse frame structure  116  by a first pivotal attachment  108  and a second pivotal attachment  110 . Pivotal attachments  108  and  110  couple wheel support  100  to frame section  98 , and are displaced laterally from one another so as to provide stability to wheel support  100 . Pivotal attachments  108  and  110  are pivotal about first axis  109  and second axis  111 , respectively. Pivotal axes  109  and  111  are preferably coincident with each other and are preferably oriented transverse to the direction of motion of the vehicle. Wheel support  100  is thus pivotally attached so as to permit pitching motion of wheel support  100 . Wheel support  100  includes a generally upright portion  112  which supports a spindle, or stub axle,  114  about which wheel  102  rotates. The present invention contemplates spindles, hubs, stub axles, and other similar devices known to those of ordinary skill in the art as means for rotatably supporting a wheel on the wheel support. 
   Frame and suspension section  98  includes a row of tires  104  on either side of a transverse frame structure  116 . Transverse frame structure  116  generally supports the vehicle cargo or utility section directly above it, as best seen in  FIGS. 12 and 13 . Referring again to  FIGS. 5 and 6A , transverse frame structure  116  includes laterally disposed transverse frame sides  118  and  120 . Attached to first transverse frame side  118  is a first upright frame structure  122 . Attached to second transverse frame side  120  is a second upright frame structure  124 . Frame structures  124 ,  116 , and  122  form a generally U shape, as best seen in  FIG. 6A , with transverse structure  116  being attached to the bottoms of the opposing upright frame structures  124  and  122 . The top surface of transverse structure  116  preferably defines a plane that is located generally at or below the rotational axis of the wheels. 
   Wheels  102 , shock absorbers  136 , spindles  114 , and upright portion  112  of wheel support  100  are disposed within upright structures  122  and  124 . Spindle  114  supports one or more wheels  102  disposed within the upright frame structures. Spindle, or stub axle,  114  is not an axle that extends across transverse frame structure  116 . By not having an axle spanning between upright frame structures  122  and  124 , it is possible to have more cargo-carrying volume within the vehicle. Transverse frame structure  116  can thus be located below the rotational axes of the wheels  102 , and cargo can be carried below the rotational axes also. 
   Transverse frame structure  116  preferably includes a cross member  106  for each pair of wheel supports  100 . Cross members  106  are attached to longitudinal members  126  and sides  120  and  118  by comer reinforcements  128 . In addition, longitudinal members  126  are also interconnected to members  106  preferably with reinforcements  130 . Frame spring supports  132  of transverse frame structure  116  are generally planar portions in one embodiment which extend inward preferably from either first side  118  or second side  120  to longitudinal members  126 . Preferably, spring supports  132  are laterally disposed inwardly from the wheel being supported. Portions of wheel supports  100  for supporting a spring are located below frame spring supports  132 . Disposed between each wheel support  100  and frame spring support  132  in one embodiment is an air spring  133 . Frame spring support  132  provides a support for air spring  133 . 
   Although what has been shown and described is a specific arrangement of cross members and longitudinal members with reinforcements, the present invention also contemplates other arrangements for a transverse frame structure as would be known to one of ordinary skill in the art. Although welding is a preferable means of joining various members of frame and suspension section  98 , the present invention also contemplates other joining and integrating methods, including fusion, bonding, brazing, bolting, casting, molding, and similar methods known in the art. Also, those of ordinary skill in the art will recognize that the cross members and longitudinal members can have a variety of cross sectional shapes, such as for C channels, I beams, L shapes, rectangular shapes, and others. 
   Wheel support  100  is pivotally attached to cross member  106  by a pair of pivotal supports  108  and  110 . Supports  108  and  110  permit pivoting of wheel support  100  in a pitching direction about a pivotal axis that coincides with first axis  109  of support  108  and second axis  111  of support  110 . Inboard pivotal attachment member  180  of support  100  is preferable releasably fastened to inner pivot  108   a  of support  108 . Inner pivot  108   a  is coupled to outer support housing  108   c  through a rubber bushing  108   b . Inner pivot  108   a  is able to pivot relative to housing  108   c  by twisting rubber bushings  108   b . In a similar fashion, an inner pivot  110   a  of pivotal attachment member  110  is able to pivot relative to the housing  110   c  by twisting a rubber bushing  110   b . 
   Wheel support  100  supports a wheel for rotation about a rotational axis  158 , and is arranged and constructed such that there is usable cargo volume below the rotational axis of the wheel, as best seen in  FIGS. 6A ,  12 , and  13 . Horizontal portion  168  of wheel support  100  lies generally below the volume useful for cargo. Pivotal attachments  108  and  110 , which pivotally support wheel support  100 , have pivot axes  109  and  111 , respectively, that are located below rotational axis  158 . In one embodiment of the present invention, pivot axes  109  and  111  are preferably parallel to rotational axis  158 , as best seen in  FIG. 8A . 
   Wheel support  100  pivots about pivot axis  109  and  111  in a pitching direction relative to the vehicle, and is pivotal between an uppermost position and a lowermost position. Wheel support  100  is biased to a position between the uppermost and lowermost positions, preferably by air spring  133 . However, the present invention also contemplates the use of other means for biasing the wheel support, including by way of example one or more coil springs or one or more leaf springs. The one or more springs bias wheel support  100  to a position between the uppermost and lowermost positions by urging spring support  156  of wheel support  100  apart from frame spring support  132  of the vehicle frame. 
   In one embodiment, spring supports  156  and  132  generally face each other and are part of a structural load path for the spring forces from spring  133 . Preferably, spring supports  156  and  132  are disposed laterally inward from the wheel being supported, although the present invention also contemplates spring supports disposed laterally inward from the tire being supported. Spring supports  156  and  132  are preferably generally planar in those embodiments utilizing air springs with planar attachment surfaces. However, the present invention also contemplates those embodiments in which spring supports  156  and  132  are constructed and arranged to compatibly support other types springs, including, for example, leaf springs and coil springs. 
   Referring to  FIG. 7 , upright frame  124  is joined to transverse frame structure  116  along second side  120  of frame structure  116 . In one embodiment, vertical wall section  144  of upright structure  124  is angled outwardly about 4 degrees from the vertical, so as to permit additional cargo space. Wall section  144  is preferably fused to a longitudinal member  150  in the shape of a C channel that extends along side  120 . 
   Air spring  133  is preferably fastened to attachment plate  152  by fasteners (not shown) along upper contact face  154   a  of air spring  133 , contact face  154   a  being one end of air spring  133 . Attachment plate  152  is preferably fastened to spring support  132  of frame section  116  by fasteners (not shown). One side of spring support  132  is preferably welded to a longitudinal member  126 , and the other side of spring support  132  is preferably welded to longitudinal member  150 , the present invention contemplating other means known to those of ordinary skill in the art for coupling the spring support to the transverse fame section. 
   Air spring  133  is preferably fastened by fasteners (not shown) to spring support  156  of wheel support  100  along a lower contact face  154   b  of air spring  133 , contact face  154   b  being the other end of air spring  133 , this end of air spring  133  being between the second spring support  156  and the rotational axis of the wheel. Thus, upper contact face  154   a  is coupled to and in contact with a first spring support  132  and lower contact face  154   b  is coupled to and in contact with a second spring support  156 . 
   Although it is preferable to couple lower face  154   b  of the air spring with fasteners to attachment member  156 , coupling is not necessary provided lower face  154   b  is in contact with spring support  156 . Attachment members  156  and  132  support biasing loads from spring  133 . 
   Upright portion  112  of wheel support  100  supports spindle  114 . Spindle  114  is attached at a fastener attachment pattern  160  to upright portion  112 . Spindle  114  defines a rotational axis  158  that is generally horizontal and preferably parallel to the pivotal axis of wheel support  100 . However, the present invention also contemplates those embodiments in which the rotational axis of the wheel and the pivotal axis of the wheel support are not parallel. A hub  162  is mounted to spindle  114  by a pair of bearings  163 . A brake drum  164  is fastened to hub  162 , and provides a braking surface for a pair of brake shoes  166 . 
   Upright portion  112  of wheel support  100  in one embodiment includes a support structure  134 . A shock absorber  136  is pivotally coupled to support structure  134  by a coupling end  138  that attaches to ears  140  of support structure  134 . Attachment ears  140  for coupling to shock absorbers  136  are attached to support plate structure  183  of support structure  134  as best seen in  FIGS. 8A and 8B . As seen in  FIGS. 6A–7 , the other coupling end  142  of shock absorber  136  is pivotally coupled within upright frame structures  124  and  122 . Shock absorber  136  and support structure  134  are located forward of the rotational axis of wheel  102 , and above the pivot axis of wheel support  100  in some embodiments. 
   Support structure  134  preferably provides features for attachment of various components, including braking system components (not shown). As best seen in  FIG. 9 , support  134  includes support plates  183  which incorporate fastening patterns  182  and  184  for support and attachment of various components, including braking system components (not shown). Top support plate  183  also defines a slot  186  through which brake system linkages (not shown) pass onto the braking system components for wheel  102 . 
   Referring to  FIG. 8A , a side elevational view of wheel support  100  and a portion of frame  116  is shown. Some embodiments of wheel support  100  include a stiffening member  167  generally in the shape of a “W” to provide stiffness and strength along spring support  156  and to better distribute loads from air spring  133  into wheel support  100 . However, the present invention also contemplates those wheel supports  100  in which alternative structure is used to provide sufficient support for spring biasing loads imposed upon spring support  156 , including by way of example only, increased thickness for spring support  156 , stiffening ribs attached or incorporated into spring support  156 , V-shaped and I-shaped structural members, and various other equivalents known to those of ordinary skill in the art. 
     FIG. 8B  depicts a side elevational view of an embodiment of wheel support  100  capable of supporting two wheels. A doubler plate  167  is installed on upright section  112  between section  112  and wheel spindle  114 . Doubler plate  167  provides an improved distribution of load from spindle  114  within upright section  112 . In one embodiment of the present invention, upright section  112  is constructed from A-36 steel plate of about one and one quarter inch thickness. Doubler plate  167  is constructed from A-36 steel plate of approximately one half inch thickness. In other embodiments the doubler may not be needed, upright portion  112  being fabricated from thicker material or higher strength material, incorporating reinforcing ribs, or otherwise suitably strengthened. 
     FIG. 9  is a perspective view of a wheel support according to one embodiment of the present invention. Wheel support  100  includes a generally horizontal portion  168  attached to upright portion  112 . Horizontal portion  168  includes spring support  156  for supporting air spring  133 . In one embodiment, spring support  156  includes a fastener pattern  174  for fastening air spring  133  to wheel support  100 . However, in some embodiments of the present invention spring support  156  is not fastened to air spring  133 . Horizontal portion  168  also preferably includes a slot  176  or other means to provide clearance for an air line for pressurizing and depressurizing air spring  133 . In some embodiments, the center of air spring  133  is located between the rotational axis of the wheel and the pivotal axis of the wheel support, as best seen in  FIG. 4 . 
   Referring again to  FIG. 9 , a reinforcing member  170 , which may include one or more distinct pieces, has a generally square cross-section in one embodiment and supports some of the edges of spring support  156 . A reinforcing member  171  with a C-shaped cross-section is attached to one end of reinforcement member  170  and also to upright portion  112 . Reinforcement member  171  includes a pair of inboard pivotal attachment members  180  and a pair of outboard pivotal attachment members  178 . Inboard attachment members  180  define holes  181  for coupling to second pivotal attachment  108 . Outboard pivotal attachment members  178  preferably define threaded holes  179  for fastening to first pivotal attachment  110 . In one embodiment, holes  179  are oriented about ninety degrees from holes  181 . 
   Multiple comer reinforcements  172   a  and  172   b  attach reinforcement member  170  to upright portion  112  in one comer. A comer reinforcement  172   a  similarly attaches member  171  to upright portion  112 . A reinforcement plate  173  is fused to one end of reinforcement member  171  near upright portion  112  so as to better distribute stresses within support  100 . Plate member  173  and comer reinforcement  172   a  enhance the stiffness and strength of the load path from spindle  114  to outboard pivotal attachment members  180 . In one embodiment of the present invention, the included angle  175  from upright section  112  to spring support  156  is about ninety and three fourths degrees, so as to provide about three fourths of a degree of positive camber when not loaded by the weight of the vehicle. Although a specific arrangement of reinforcement members has been shown and described for wheel support  100 , those of ordinary skill in the art will recognize equivalent methods of providing sufficient strength and stiffness. 
     FIGS. 10A and 10B  depict side elevational views of pivotal attachments according to one embodiment of the present invention. Pivotal attachments  108  and  110  include pivotal inner support members  108   a  and  110   a , respectively, that are supported from stationary outer members  108   c  and  110   c , respectively, by elastomeric bushings  108   b  and  110   b , respectively. Inner supports  108   a  and  110   a  are able to pivot about pivot axes  109  and  111 , respectively. Inner pivotal member  108   a  includes a pair of through holes  108   d  for coupling attachment assembly  108  by fasteners to attachment members  180  of wheel support  100 . In one embodiment fastener holes  108   d  are oriented such that their centerlines are inclined from the horizontal as indicated by angle  188 . Fastener holes  110   d  of pivotal inner member  110   a , likewise used for fastening pivotal attachment  110  to attachment members  178  of support  100 , are inclined from vertical in one embodiment as indicated by angle  188 . In one embodiment of the present invention angle  188  is about seven and one half degrees, and may be as large as about fifteen degrees. The offset angle  188  of the pivotal attachments preferably corresponds to a similar offset angle for wheel support  100 ′, as seen in  FIG. 4 , as will be discussed later. In other embodiments, angle  188  is about zero degrees. 
   Although what has been shown and described are pivotal attachment assemblies in which an inner pivoting member is elastomerically mounted to an outer housing, the present invention contemplates other types of pivotal attachment assemblies. By way of example only, the present invention also contemplates pivotal attachment assemblies in which a pivotal inner member is coupled by a bearing, such as a ball bearing or plane bearing, to an outer casing. By further way of example, the outer casing may be a cast, molded, adhered, welded, or otherwise fixedly attached member to the transverse frame section  116 . By further way of example, the inner pivoting member may be cast, molded, adhered, welded, or otherwise fixedly attached or otherwise made integral with wheel support  100 , thus eliminating the need for attachment members such as members  180  and  178 . Yet other varieties of pivotal attachments are known to those of ordinary skill on the art. It is preferable that the pivotal attachments include a feature that permits spacing apart of the pivotal attachment from either frame section  116  or wheel support  110  so as to permit adjustment of wheel camber and toe-in. One embodiment of the present invention which includes such adjustment features will now be described. 
   Pivotal attachments  108  and  110  are preferably attached by readily removable fasteners  177  to cross member  106 , as seen in  FIG. 11 . Pivotal attachment  110  supports the outboard side of wheel support  100  via outboard pivotal attachment members  178 . Pivotal attachment  108  supports the inboard side of wheel support  100  through L-shaped inboard pivotal attachment members  180 . Pivotal attachment members  178  and  180  are preferably welded or otherwise attached, cast, or molded within channel member  171  of wheel support  100 , as best seen in  FIGS. 8A and 9 . 
   Referring again to  FIG. 11 , pivotal attachment  110  is capable of being spaced apart from cross member  106  of frame  116  so as to move pivot axis  111  in a longitudinal direction relative to the vehicle. This spacing may be accomplished, for example, by insertion of a shim between pivotal attachment  110  and cross member  106 . In addition, wheel support  100  may be spaced apart from pivotal attachment  110  by insertion of shims between attachment members  180  and pivotal inner member  110   a . By spacing apart attachment assembly  110  from frame  116 , and/or spacing apart wheel support  100  from attachment assembly  110   a , the toe-in of the supported wheel  102  can be adjusted. 
   Second pivotal attachment  108  is similarly coupled to cross member  106  of frame  116 , and may be spaced apart from frame  116  so as to move pivot axis  109  longitudinally relative to the vehicle. Thus spacing apart pivotal attachment  108  from frame  116  adjusts the toe-in of the wheel  102  supported by support  100 . In one embodiment the present invention contemplates the use of shims for adjusting both camber and toe-in, including shims fabricated from sheet or plate material, and also shims in which the shim faces are not parallel, but are angled in proportion to the desired toe-in or camber angle. Further, the pivotal attachments are releaseably coupled to the transverse frame section and also to the wheel support so that the shimming may be performed easily and repeatedly, as desired, without the need, for example, to remove welded attachments. 
   Fastener attachment holes  108   d  are positioned about ninety degrees relative to fastener holes  110   d . Also, fastener holes  181  of inboard attachment members  180  are oriented about ninety degrees relative to fastener holes  179  of outboard attachment members  178 , as best seen in  FIG. 9 . As a result, spacing apart inner pivotal member  108   a  from attachment members  180  moves wheel support  100  in a different direction than that achieved by shimming between inner member  110   a  and attachment members  178 . Spacing apart inner pivot  108   a  from attachment members  180  adjusts the camber of the wheel  102  supported by wheel support  100 . 
   Although what has been described is an embodiment which includes a pivotal attachment  108  which can be shimmed or otherwise manipulated so as to adjust camber or toe-in and another pivotal attachment  110  which can be manipulated to adjust toe-in, the present invention also contemplates those embodiments in which there are two pivotal attachments each permitting adjustment of camber or toe-in or two pivotal attachments each permitting adjustment of only camber or toe-in. Further the present invention also contemplates embodiments in which neither pivotal attachment permits adjustment of either camber or toe-in, or in which only one pivotal attachment permits adjustment of either camber or toe-in. 
   In one embodiment of the present invention, spring support  156  of wheel support  100  is preferably inclined from the horizontal for improved airbag characteristics, as indicated by angle  188  of  FIG. 4 . Wheel support  100   x  is shown in the inclined position during operation of frame and suspension section  98  on a level surface. The tire rotatably supported from wheel support  100   y  is shown at full jounce over an irregularity in the roadway such that wheel support  100   y  has pitched up and second spring support  156   y  is generally parallel to first spring support  132   y  and also to roadway  190 . 
   In this embodiment pivotal attachments  108  and  110  include inner pivoting members  108   a  and  110   a , respectively, which have an included angle  188 , as best seen in  FIGS. 10A and 10B . By incorporating an offset angle  188  into pivotal attachments  108  and  110  that is the same as the offset angle  188  of wheel support  100 ′, stress within elastomeric bushing  108   b  and  110   b  is kept to a minimum during normal operation. Other embodiments of pivotal attachments incorporating by way of example plane, roller, or ball bearings in place of the elastomeric bushings would not need an offset angle  188 . The present invention also contemplates pivotal attachments  110  and  108  in which the offset angle of the pivotal attachments is different than the offset angle of the wheel support relative to the roadway during normal operation, with the difference in the pivotal attachment offset angle and the wheel support offset angle being provided by angled attachment faces to attachment members  180  and  178 . 
   One embodiment of the present invention contemplates an angle  188  of about 7.5 degrees between first spring support  132  and second spring support  156  during typical operation of the suspension system on a level roadway  190 . Having an included angle  188  of about 7.5 degrees provides an acceptable range of air spring characteristics and internal air pressure in one embodiment, and permits placement of certain types of air springs below the cargo compartment of the vehicle. However, the present invention contemplates a range for angle  188  from about 0 degrees to about 15 degrees. For example, a cast wheel support with different dimensions provides equally acceptable air spring characteristics and internal pressure with an angle  188  of about zero degrees, such that faces  154   a  and  154   b  of air spring  133  are generally parallel during operation of the suspension on a level road. 
   In another embodiment of the present invention, there is a suspension control system for maintaining the ride height of the vehicle as the weight of the vehicle changes, and also for changing the air pressure in the air spring in response to pivoting of the wheel support. A linkage (not shown) attached to both wheel support  100  and the upright frame structure provides a control input to a pneumatic valve (not shown), such as a Neway Model 9005-4007 leveling valve. In response to movement of the linkage, the valve places air spring  133  in fluid communication with either ambient air or with a source of air pressure such as air tank  192 , which is provided pressurized air from an air compressor. Movement of wheel support  100  relative to the vehicle frame causes the valve to increase or decrease the air pressure in air spring  133 . The control system adjusts the air pressure within air spring  133  so as to maintain the wheel support at a predetermined angle relative to the vehicle frame, and also to maintain a predetermined orientation of the vehicle. 
   Although  FIGS. 4 ,  5  and  6 A depict an embodiment of the present invention which includes six wheel supports  100  supporting six wheels  102 , some embodiments of the present invention include a single wheel support  100  supporting a single wheel  102 . Other embodiments of the present invention, such as frame and suspension section  98 ′ shown as part of a van vehicle  200  in  FIG. 12 , include two wheel supports  100  each supporting a single wheel  102 . In yet another embodiment of the present invention shown in  FIG. 13 , a frame and suspension section  98 ″ including four wheel supports  100  supporting four wheels  102  is shown in a trailer section of a vehicle  202 . Further, some other embodiments of the present invention include a wheel support  100  that support a pair of wheels  102  to maintain adequate load margin in the tires when supporting a heavy cargo load. 
   The frame and suspension sections shown herein may be built modularly and slidingly coupled to a cargo compartment. As shown in  FIG. 6B , some embodiments of frame and suspension section  98  include a pair of rails  117  coupled to upright frame structures  122  and  124 . These rails  117  slidingly engage a pair of receiving C-channels  119  arranged on the underside of the trailer section of vehicle  202 . After the sliding insertion, the floor of the trailer section is below the rotational axes of the wheels, the C-channel of longitudinal member  150  being replaced with an L-angle longitudinal member. The coupling of rails  117  and C-channels  119  limits lateral and vertical motion of the frame and suspension section relative to the cargo compartment. A locking arrangement (not shown) such as a plurality of locking shear pins inserted through matched holes limits fore and aft relative movement. Although a particular arrangement has been shown for coupling a frame and suspension section of the present invention to a trailer, those of ordinary skill in the art will recognize other arrangements, including those in which the frame and suspension section and trailer are not slidingly coupled. 
     FIGS. 14–16  depict another embodiment of the present invention in which the shock absorber is located below the rotational axis of the wheel. A wheel support  100 ′ includes a horizontal portion  168 ′ coupled to an upright section  112 ′. Horizontal portion  168 ′ includes a spring support  156 ′ receiving and coupling to a spring which urges wheel support  100  away from transverse frame structure  116 . The use of (′) and (″) indicate elements of the invention substantially the same as previously described for that element, except for the changes as noted. 
     FIGS. 14–15  depict an embodiment in which a leaf spring  70  urges a pair of wheel supports  100 ′ from transverse frame structure  116 . Leaf spring  70  includes a first end  70   a  clamped by a pair of bolts to spring support  156 ′. A second end  70   b  is in sliding contact with spring support  156 ′ of the aft-most wheel support. Ends  70   a  and  70   b  are located between their respective second spring support  156 ′ and the rotational axis of the wheel. The center  70   c  of leaf spring  70  is fastened to a portion of cross-member  106  of transverse frame structure  116  which is the frame spring support. Pitching movement of either the forward-most wheel support  100 ′ or the aft-most wheel support  100 ′ is resisted by a biasing force from the center of the leaf spring. 
   Although a particular arrangement for contacting leaf spring  70  with wheel supports  100  and transverse frame structure  116  has been shown and described, those of ordinary skill in the art will recognize other suitable arrangements. For example, both ends of spring  70  could be clamped to the wheel supports, or both ends could be slidable on the wheel support. Further, the method of clamping leaf spring  70  can be one or more through fasteners, an example of which is depicted at  70   c , or a fastened strap, as depicted at  70   a , or other methods known in the art for clamping a leaf spring to a structure. As another example, spring  70  can pass through a frame attachment  74  as shown in  FIG. 1 . Further, although  FIG. 14  depicts a leaf spring  70  acting upon two adjacent wheel supports, the present invention also contemplates those embodiments in which a leaf spring acts upon a single wheel support. As depicted in  FIG. 16 , an alternate embodiment includes an air spring  133  acting on both spring support  156 ′ of wheel support  100 ′ and also on spring support  132 ′ of transverse frame structure  116 . 
   Referring to  FIGS. 14–15 , shock absorber  136  is located beneath the rotational axis of the wheel so as to further simplify the structure of the wheel support, upright frame structures  122  and  124 , and to further increase the cargo-carrying capability of the vehicle. Placement of shock absorber  136  is such that it acts upon horizontal portion  168 ′ at wheel support  100 ′, and permits elimination of support structure  134  and a generally simplified upright structure  112 ′. Shock absorber  136  is actuatable about an axis  137   a , which is generally oriented horizontally as best seen in  FIG. 15 . 
   Shock absorber  136  has a first end  136   a  which is pivotally coupled to a portion of transverse frame structure  116 , such as cross-member  106  or longitudinal member  126 ′, through an attachment ear  140 . A second end  136   b  of shock absorber  136  is pivotally attached to one end of a lever arm  222 . Lever arm  222  is pivotally secured to pivot  224  which is attached to transverse frame structure  116 , such as by a bracket  226  in a manner well known in the art. Lever arm  222  pivots about pivot axis  221 . The other end of lever arm  222  defines a slot  228 . Pinned bushing  229  is slidable in slot  228 . Pinned bushing  229  is secured into a boss  220  of wheel support  100 ′. 
   Upward pitching of wheel support  100 ′ results in compression of shock absorber  136  and sliding of pin  229  within slot  228 . Downward pitching of wheel support  100 ′ relative to transverse frame section  116  results in extension of shock absorber  136 . Pinned bushing  229  and lever arm  222  are fabricated from hardened steel so as to minimize wear from sliding. Further, although an embodiment has been described and depicted in which shock absorber  136  compresses during upward pitching of wheel support  100 ′, those of ordinary skill in the art will recognize other arrangements of pivoting lever arms that will suitably dampen the motion of wheel support  100 ′ by extending during upward pitching. 
     FIGS. 17–18  depict a substantially cast wheel support  100 ″ according to another embodiment of the present invention. Wheel support  100 ″ includes a horizontal portion  168 ″ cast integrally with an upright portion  112 ″. A spring support  156 ″ within horizontal portion  168 ″ receives loads from a spring, and is reinforced by a plurality of cast stiffening ribs  169 ″. A cast reinforcing member  170 ″ stiffens and strengthens wheel support  100 ″. Attachment members  178 ″ and  180 ″ are cast integrally with wheel support  100 ″. 
   A support structure  134 ″ for attaching a shock absorber and brake system components is integrally cast with upright portion  112 ″. Upright portion  112 ″ also includes a cast spider  239  which includes an attachment pattern of holes  240 ,  242 , and  244  for support of brake system components (not shown) including brake shoes and an S-cam. The toe-in of wheel support  100 ″ is adjustable by shimming in a manner as previously described. Camber is adjustable by incorporating slots in stationary outer members  108   c  and/or  110   c  of the pivotal attachments. The slots permit the orientation of outer member  108   c  or  110   c  to be adjusted relative to cross-member  106 . This orientation is maintained by a friction fit provided by fasteners  177 . 
   Yet other alternate embodiments of the present invention include a wheel support and a disc brake as part of a wheel suspension system. As shown in  FIG. 19 , an upright section  112 ′ is bolted to a spindle  114  by fasteners through fastener attachment pattern  160 . A rotating hub  162  is bearingly supported on spindle  114 . Coupled to hub  162  is a vented disc assembly  165  comprised of opposing rotor plates  165   a  and  165   b . A caliper assembly  159  supported by upright portion  112 ′ includes two friction pads  161  which are actuated against vented disc  165  so as to slow the vehicle. For sake of clarity, only one friction pad  161  is shown. Those of ordinary skill in the art will recognize the applicability of disc brakes to the many embodiments of the present invention. 
     FIGS. 20 ,  21  and  22  depict variations of the suspension systems shown in  FIGS. 3 ,  5  and  14 , respectively, in which the wheels on one side of the vehicle are longitudinally staggered, or spaced apart, relative to wheels on the other side of the vehicle. By staggering the wheels as shown, a softer ride can be presented to the cargo or occupants, and less wear is imposed upon the roadway, especially a roadway with a disturbance that passes under the wheels on both sides of the vehicle 
   In the embodiments depicted in  FIGS. 20 and 22  wheel supports on a given side of the vehicle (same-side wheel supports) include one or more springs that couple the forward wheel support to the aft wheel support. In these embodiments, the motion of a same-side wheel support thereby depends, at least partly, on the motion of the other same-side wheel support. However, the present invention also includes embodiments such as the one depicted in  FIG. 21 , in which the motion of each wheel support is substantially independent of the motion of each other wheel support. 
   In some embodiments of the present invention, the extent of stagger between opposite side wheels is as great as half the distance between rotational axes of same-side wheels. However, the present invention also includes those embodiments in which the extent of stagger is less. 
   In the embodiments depicted in  FIGS. 20–22 , an even total number of rotational axes are arranged on both sides of the vehicle in an alternating longitudinal pattern, with no rotational axis being coincident with any other rotational axis. However, those of ordinary skill in the art will recognize that the present invention contemplates not only embodiments in which there is a forward-most wheel on the right side of the vehicle with an aft-most wheel on the left side, but also embodiments in which the forward-most wheel is located on the left side and the aft-most wheel is located on the right side. Further, the present invention also contemplates those embodiments in which both the forward-most and aft-most wheels are on the same side of the vehicle, and also those embodiments in which one side of the vehicle has an even number of wheels and the other side of the vehicle has an odd number of wheels, such as by way of example, a vehicle with two wheels on one side and one wheel on the other side. Further, the total number of rotational axes per frame section is as low as two, and is as great as required in the particular application. 
   The use of element numbers the same as numbers previously used, including element numbers with letter suffixes, indicates that the element referred to is the same, except as described. 
     FIG. 20  depicts an embodiment of the present invention to which the discussion herein relative to  FIGS. 1 ,  2  and  3  is applicable, except as now described. Although a description of the “a” side components is given, those of ordinary skill in the art will recognize applicability of the description to the “b” side components. Frame and suspension section  398  of a vehicle frame includes a forward-most wheel  8   a  and a rear-most wheel  10   a  located on one side of the vehicle frame. Wheels  8   a  and  10   a  are pivotally supported by wheel supports  24   a  and  26   a , respectively, in a manner as previously described. Wheel supports  24   a  and  26   a  are coupled together by a leaf spring  70   a , also in a manner as previously described. Further, biasing members  50   a ,  56   a  and  60   a  are located generally above the rotational axes of the wheels, also as previously described. 
   The rotational axes  12   a  and  14   a  of wheels  8   a  and  10   a , respectively, are staggered, or longitudinally spaced apart, from the rotational axes  12   b  and  14   b  of wheels  8   b  and  10   b , respectively. In one embodiment, the four rotational axes are arranged in an alternating longitudinal pattern, with no rotational axis being coincident with any other rotational axis. Rotational axis  12   a  is located in this embodiment aft of rotational axis  12   b , and forward of rotational axis  14   b . Rotational axis  14   a  is located aft of all other rotational axes. 
     FIG. 21  depicts an embodiment of the present invention to which the description herein relative to  FIG. 5  and related figures is applicable, except as now described. Although a description of the “e” components is given, those of ordinary skill in the art will recognize applicability of the description to the “a,” “b,” “c,” “d,” and “f,” components. As previously described, frame and suspension section  498  of a vehicle frame includes a wheel  102   e  and tire  104   e  rotatably supported by a spindle  114   e  coupled to a wheel support  100   e . The wheel support is pivotally attached to frame section  498  by pivotal attachments  108   e  and  110   e . An air spring  133   e  biases wheel support  100   e  and wheel  102   e  to a position intermediate of an uppermost position and a lowermost position. An optional shock absorber  136   e  for dampening motion of wheel  102   e  is pivotally coupled to both wheel support  100   e  and frame structure  416 . The rotational axes  158   a ,  158   c , and  158   e , of wheels  104   a ,  104   c , and  104   e , respectively, are staggered, or longitudinally spaced apart, from the rotational axes  158   b ,  158   d , and  158   f , of wheels  104   b ,  104   d , and  104   f , respectively. The present invention also contemplates patterns of stagger other than that shown in  FIG. 21 , for example, including an asymmetric pattern in which rotational axis  158   b  is located forward of rotational axis  158   a , or in which rotational axis  158   e  is located aft of rotational axis  158   f.    
     FIG. 22  depicts an embodiment of the present invention that is the same as the embodiments described herein relative to  FIGS. 14 ,  15  and  16 , except as now described. Although a description of the forward-most “b” components is given, those of ordinary skill in the art will recognize applicability of the description to the “a,” “c,” and “d,” components. Further, although an embodiment with a leaf spring linking adjacent, same-side wheel supports is shown, those of ordinary skill in the art will recognize that the present invention also includes the embodiments depicted in  FIG. 16 , which include an air spring. 
   As shown in  FIG. 22 , a wheel set comprising a pair of wheels  104   b ′ and  104   b ″ rotatable about an axis  158   b  are supported by a wheel support  100   b ′ pivotally attached to frame structure  516  by pivotal attachments  108   b  and  110   b . The pitching movement of wheel support  100   b ′ is dampened by shock absorber  136   b , which is pivotally coupled to both frame section  516  and wheel support  100   b ′. Shock absorber  136   b  is substantially horizontal. 
   The rotational axes  158   b  and  158   d  of wheels  104   b ′ and  140   d ′, respectively, are staggered, or longitudinally spaced apart, from the rotational axes  158   a  and  158   c  of wheels  104   a ′ and  104   c ′. As shown, the four rotational axes are arranged in an alternating or longitudinally spaced apart pattern, with no rotational axis of any one wheel set being coincident with the rotational axis of any other wheel set. Those of ordinary skill in the art will recognize that the present invention also contemplates those embodiments in which only wheel sets “a,” “b,” and “d,” are present. 
     FIG. 23  depicts an embodiment of the present invention that is the same as the embodiments described herein relative to  FIGS. 14 ,  15  and  16 , except as now described. The wheel support described herein may be pivotally attached to a frame as trailing-arm wheel supports, in which the pivotal attachment of the wheel support to the frame is located forward of the rotational axis of the wheel, or as leading-arm wheel supports, in which the pivotal attachment of the wheel support to the frame is located rearward of the rotational axis of the wheel. 
   As seen in  FIG. 23 , a first wheel support  100 ′ a  rotatably supporting a wheel  104   a  on a first side of frame  516  has inboard pivotal attachment  108  and outboard pivotal attachment  110  located forward of rotational axis  158   a . A spring, preferably an air spring  133   a , urges first wheel support  100 ′ a  apart from a portion of frame  516 . An end of air spring  133   a  is coupled to frame  516  below rotational axis  158   a.    
   A second wheel  104   b  is pivotally supported by a second wheel support  100 ′ b  on the other side of frame  516  in a manner similar to that for the “a” components described above. However, inboard pivotal attachment  108  and outboard pivotal attachment  110  of wheel support  100 ′ b  are placed rearward of rotational axis  158   b . By this arrangement of a trailing arm wheel support  100 ′ a  on one side of the frame and a leading-arm wheel support  100 ′ b  on the other side, it is possible to use an identical wheel support for opposing sides of the vehicle, and thus benefit from a reduction in cost of the frame and suspension section  698 , and also a reduction in the number of different parts for building a frame and suspension section  698 . 
   The present invention also contemplates those embodiments in which other combinations of leading and trailing wheel supports are utilized on a frame and suspension section. Wheels  104   a  and  104   c  are shown supported by wheel supports  100 ′ a  and  100 ′ c , respectively, both wheel supports being pivotally supported by a common portion of frame  616 . Other embodiments of the present invention include wheel supports arranged as shown in  FIG. 23  with wheels  104   b  and  104   d . Those wheels, supported by wheel supports  100 ′ b  and  100 ′ d , respectively, may be placed close together by arranging the pivot axes of the respective wheel supports as shown. Those of ordinary skill in the art will recognize that frame and suspension section  698  as shown in  FIG. 23  is but one arrangement combining leading and trailing wheel supports, and that many other arrangements are contemplated by the present invention. 
   The inventions described in my other patent applications, namely U.S. patent application Ser. No. 09/318,428, filed May 25, 1999 and entitled AXLELESS VEHICLE SUSPENSION SYSTEM; U.S. patent application Ser. No. 09/654,584, filed Sep. 1, 2000, and entitled STAGGERED INDEPENDENT SUSPENSION; U.S. Provisional Patent Application Ser. No. 60/202,237, filed May 5, 2000, and entitled ELECTRIC CAR SUSPENSION; and U.S. Provisional Patent Application 60/222,478 filed Aug. 2, 2000 and entitled SINGLE ARM VEHICLE SUSPENSION; are incorporated herein by reference. 
   In another embodiment, the present invention relates to a low profile chassis section for the center and rear portion of a vehicle. The chassis section includes a low profile suspension system that supports the rear wheels with independent trailing arm wheel supports. Preferably, the trailing arm wheel support has a pivot axis below the rotational axis of the wheels. The chassis includes a frame section having a substantially planar top surface. Trailing arm wheel supports according to the present invention permit the top surface of the frame section to be located below the rotational axes of the rear wheels. Preferably, the rear wheels are not powered by the engine of the vehicle, and are not steerable. Preferably, the rear wheels are constrained to pitching motion describable with a single degree of freedom. 
   A chassis section according to the present invention preferably is rigidly coupled to a cab section having a high profile sub-frame and floor. The cab section preferably includes steerable front wheels, an engine to drive the front wheels, and a driver&#39;s seat and controls. In one embodiment of the present invention the cab section is separated from an existing vehicle which typically includes a high profile frame throughout the length of the existing vehicle. The center and rear portion of the high profile frame section of the existing vehicle is separated from the cab section, and the low profile chassis section according to an embodiment of the present invention is rigidly coupled to the high profile cab section, resulting in a new vehicle. 
   A separate payload section, such as an ambulance compartment, passenger compartment, or cargo compartment can be coupled to the top of the center and rear chassis section and also to the rear of the cab section. The payload compartment can have a floor that is close to the roadway by placement of the top surface of the underlying chassis section below the rotational axes of the rear wheels, in the case of an ambulance compartment, having a low floor permits easier entrance and exit from the compartment as compared to a standard ambulance with a high profile floor. A low profile chassis according to the present invention permits easier movement of wheelchairs and gurneys into and out of the ambulance compartment. As another example, a payload compartment for carrying passengers around airports and hotels can have a low profile floor which makes ingress and egress easier for elderly and handicapped passengers. As another example, a payload compartment comprising a low profile floor cargo compartment such as for a short haul delivery truck permits the delivery person to bring cargo into and out of the compartment with less fatigue. A payload compartment attached to a chassis according to the present invention can also have a lower overall height than an existing vehicle with high profile chassis, yet have a useful interior height from floor to ceiling that is about the same as for an existing vehicle. Therefore the present invention permits the use of a payload compartment with a large interior that can pass underneath a low hanging obstruction, such as those found at the arrival and departure areas of some hotels. 
   In one embodiment of the present invention, the chassis section is fastened by bolts or other fasteners to a sub-frame of the cab section. Fastening is useful where the members of the cab sub-frame are heat treated, in which cases welding the chassis to the cab subframe lessens the material properties of the subframe. 
   Referring to  FIGS. 24–29 , vehicle chassis  1020  according to one embodiment of the present invention includes a substantially planar forward frame portion  1040 , a substantially planar rearward frame portion  1060 , and an intermediate frame portion  1050  located therebetween. Chassis  1020  further includes a support section  1150  located forward of forward frame portion  1040 , section  1150  bolting to a front sub-frame  1220  supporting a front suspension/engine module  1230 . Forward frame  1040 , intermediate frame  1050 , and rearward frame  1060  are preferably of the ladder-type, each comprising a plurality of lateral structural members  1070 , longitudinal structural members  1072 , and/or diagonal structural members  1074 . The various structural members  1070 ,  1072 , and  1074  are preferably welded together into a ladder-type or box structure such that the top surfaces of the structural members define a substantially planar top surface  1022  that extends generally across frame sections  1040 ,  1050 , and  1060  (as best seen in  FIG. 25   c ). Chassis  1020  preferably includes hollow structural members  1042  and  1062  which run in a generally longitudinal direction. Structural members  1042  and  1062  provide housing and protection for an exhaust pipe  1053  carried therein. 
   Although a ladder-type or box structure has been shown and described, the present invention also contemplates other configurations of frame structure, with the top surface of the frame portions being generally located below the rotational axes of the rear wheels. A separable vehicle body or payload portion  1300  including an interior with a floor  1302  and exterior body panels attaches to frames section  1040 ,  1050 , and  1060 , preferably by bolting or use of other fasteners, including riveting, or by welding or other attachment methods. 
   Intermediate frame  1050  preferably includes a substantially planar center frame section  1054  and left and right wheel housings  1100  and  1101 , respectively, on either side of section  1054 . Left and right rear wheels  1130  and  1131  for the vehicle are located within their respective wheel housings. A left wheel  1130  is pivotally supported from intermediate section  1050  by a wheel support  100 ″ which pivotally couples to a forward portion  1120  of intermediate frame portion  1040  by inboard and outboard pivot joints  108  and  110 , respectively. The pivotal attachment of the wheel support to the frame permits pivoting motion of the supported wheel in a pitching direction only, and constrains the wheel against yawing motion such as the type necessary for steering control. Although what has been shown and described is a wheel support  100 ″ pivotally coupled to intermediate section  1050 , the various embodiments of the present invention shown and described herein contemplate use of any of the various wheel supports shown and described herein. 
   In one embodiment, a spring  133  such as an inflatable air spring is placed between a portion of the wheel support and the bottom side of spring support member  1140 . The spring provides resilient support of the vehicle from the roadway, the spring urging apart the frame from the wheel support. Spring support  1140  has a top surface within frame section  1054  that is at or below plane  1022 . Although what has been shown and described pertains to the left wheel, it is understood that there is preferably a mirror image wheel support supporting the vehicle from a right wheel  1131  located within wheel housing  1101 , right wheel  1131  being pivotally supported from portion  1121  of frame  1050 . 
   In one embodiment of the present invention, the wheel supports are trailing arm supports, such that the pivot axes  109  and  111  of the wheel supports  100 ″ are forward of the rotational axes  158  of the wheels  1130  and  1131 . Further, as can be best seen in  FIG. 29 , rotational axes of the wheels are located above plane  1022 . Preferably, a wheel support according to the present invention supports a stub axle  114 , and stub axle  114  supports one or more wheels from a single side in cantilever fashion such that the wheel is located outboard of the wheel support, leaving the space inboard of the wheel and stub axle for the wheel support, spring, and cargo compartments. Further, pivot joints  108  and  110  which pivotally couple the wheel support to the frame are located inboard of the supported wheel. Preferably, the pivot axes  109  and  111  of the wheel support are parallel to the rotational axis of the supported wheel, but the present invention also contemplates a wheel support pivotable about an axis that is not perpendicular to the longitudinal centerline of the vehicle and not parallel to the rotational axis of the supported wheel. The present invention also contemplates suspension systems located generally within the wheel housings, such as the type shown in my issued patents referenced above and incorporated herein by reference. 
   A support section  1150  is preferably coupled to sub-frame  1220  which supports front suspension and engine module  1230  located in front of forward frame  1040 . Support section  1150  includes a pair of support members  1160  and  1161  which are cantilevered from the forward portion of forward frame  1040  and which are further supported by a pair of lateral braces  1162  and  1163 . Support arms  1160  and  1161  preferably include a plurality of holes  1170 . Sub-frame  1220  and other structural components which support the front suspension and engine module  1230  are rigidly coupled to frame portion  1150  by the use of fasteners  1171  in conjunction with holes  1170 . In one embodiment of the present invention the subframe supporting the engine and front suspension is cut away from or otherwise removed from an existing vehicle. The frame portion of the existing vehicle aft of the cab section is discarded, and the sub-frame of the cab section is bolted to chassis  1020 . 
   Sub-frame  1220  of cab section  1200  provides “high profile” support of at least one of the engine or front suspension of cab section  1200 . Typically, the structural members of sub-frame  1220  are above rotational axis  1206  of front wheel  1204 . The floor  1222  of cab section  1200  is also located above the rotational axis  1206 . As can be seen in  FIG. 29 , a vehicle  1400  according to one embodiment of the present invention includes a top surface  1221  of the frame of the cab section that is above rotational axes  1206  and  158  of wheels  1206  and  1130 , respectively, and a top surface  1022  of the frame supporting the payload section  1300  that is below rotational axes  1206  and  158 . The combined frame for vehicle  1400  includes a forward-most sub-frame  1220  with a top surface that is at a first elevation above the rotational axes of the wheels, and a center and rear-most frame section  1020  with a top surface that is at a second elevation below the rotational axes of the wheels. 
   Although what has been shown and described is a support section that couples the front frame section to the sub-frame of the cab section, the present invention also contemplates those embodiments in which portions of the sub-frame and vehicle chassis section are unitary. For example, the present invention contemplates those embodiments in which the one or more central longitudinal frame members of the rear vehicle chassis are integrally formed with longitudinal frame members of the sub-frame. In another embodiment, one or more frame members of the rear vehicle chassis are welded to one of more frame members of the sub-frame, and the welded assembly is heat treated as a unitary assembly. 
     FIGS. 27 and 28  are photographs of a chassis coupled to a cab section according to another embodiment of the present invention.  FIG. 29  is a partly sectional and partly side schematic representation of a cab section coupled to a chassis which supports a payload section according to another embodiment of the present invention. Vehicle chassis  1020  is shown coupled to a cab section  1200 . Cab section  1200  includes an engine and a pair of front wheels  1204  and  1205  which are both steerable and which both apply the power provided by the engine to the roadway. Cab section  1200  includes a driver&#39;s seat  1210 , windshield  1215 , and other features necessary for the powering and control of the vehicle. Cab section  1200  includes a cab floor  1222  that is at an elevation above the rotational axes of the front and rear wheels, and also above plane  1022  of chassis  1020  and floor  1302  of payload compartment  1300 . In the embodiment depicted in  FIGS. 27 and 28  a passenger compartment, cargo compartment, ambulance section, or other payload section  1300  can be attached above chassis section  1020  and behind cab section  1200 .  FIG. 29  schematically shows a payload section  1300  attached to a chassis section  1020 .  FIG. 29  also shows cab section  1200  in part sectional view, with the front suspension and engine module  1230  visible, and being supported by sub-frame  1220 . 
   The use of two thousand prefixes (2XXX) or three thousand prefixes (3XXX) designate the same element as the one thousand prefix (1XXX) previously described except as shown and described differently. 
     FIGS. 30 ,  31 , and  32  depict top plan, rear and side elevational views of an apparatus  2021  including a vehicle chassis  2020  coupled to a simplified cab section  2200 . Cab section  2200  is shown with a front suspension and engine module  2230 , a front axle  2208 , left and right wheels  2204  and  2205 , respectively, and left and right brake assemblies  2207   a  and  2207   b , respectively. These features of cab  2200  are shown schematically. Other features of cab section  2200  have been removed for sake of clarity. 
   Referring to  FIGS. 30–33 , vehicle chassis  2020  according to one embodiment of the present invention includes a substantially planar forward frame portion  2040 , a substantially planar rearward frame portion  2060 , and an intermediate frame portion  2050  located therebetween, and also between wheel housings  2100  and  2101 . Chassis  2020  further includes a support section  2150  located forward of forward frame portion  2040 , section  2150  bolting to a front sub-frame  2220  supporting a front suspension/engine module  2230 . 
   Forward frame  2040 , intermediate frame  2050 , and rearward frame  2060  are preferably of the ladder-type, each comprising a plurality of lateral structural members  2070 , longitudinal structural members  2072 , and/or diagonal structural members  2074 . The various structural members  2070 ,  2072 , and  2074  are preferably welded together into a ladder-type or box structure such that the top surfaces of the structural members define a substantially planar top surface  2022  that extends generally across frame sections  2040 ,  2050 , and  2060  (as best seen in  FIGS. 31 and 32 ). 
   Forward frame portion  2040  includes a plurality of lateral structural members  2070   a  that extend transversely from the outboard surface of one of the central longitudinal members  2042   a  or  2042   b  to the inboard surface of the adjacent outboard longitudinal member  2072   a  or  2072   b , respectively. As best seen in plan view  30 , forward frame portion  2040  resembles a pair of “ladder-type” structures that extend from either side of the central “backbones”  2042   a  and  2042   b . In one embodiment, frame members  2041 ,  2042   a ,  2042   b ,  2072   a  and  2072   b  have closed-off, rectangular cross-sections. Preferably, transverse structural members  2072   a  have an “I” or “H” cross-sectional shape. However, the present invention further contemplates various types of common cross-section structural members. 
   Chassis  2020  preferably includes a pair of hollow structural members  2042   a  and  2042   b  which run in a generally longitudinal direction from forward-most transverse beam  2041  to aftmost transverse beam  2072   e . Structural members  2042   a  and  2042   b  provide protection for an exhaust pipe  2053  carried therebetween. As best seen in  FIG. 30 , exhaust pipe  2053  begins at the forwardmost end of forward frame portion  2040 , passing through a hole within transverse beam  2041 . Exhaust pipe  2053  extends fore to aft down the longitudinal centerline of chassis section  2020 , to a point just aft of intermediate frame portion  2050 . Exhaust pipe  2053  has a diameter which is less than the height of central structural members  2042   a  and  2042   b . Exhaust pipe  2053  is located below the top surface of members  2042   a  and  2042   b , and above the bottom surface of members  2042   a  and  2042   b . By being nested between members  2042   a  and  2042   b , exhaust pipe  2053  is protected from many types of debris and irregularities on the road surface. 
   Pipe  2053  has a round cross section in portion  2053   a  which extends through front frame portion  2040  and a portion of intermediate frame portion  2054 . This circular cross section changes to an oval cross section within portion  2053   b , which begins within intermediate frame portion  2054  and extends a short distance into rear frame portion  2060 . Exhaust pipe  2053   b  includes a right angle section, such that the exhaust exits at a location aft of wheel housing  2100 . 
   Intermediate frame  2050  preferably includes a substantially planar center frame section  2054  and left and right wheel housings  2100  and  2101 , respectively, on either side of section  2054 . Left and right rear wheels  2130  and  2131  for the vehicle are located within their respective wheel housings. Although what has been shown and described are various chassis sections that include wheel housings, the present invention also contemplates those embodiments in which the wheel housings are not part of the chassis, but are integrated into the separable vehicle body or payload portion which is supported by the chassis. 
   A left wheel  2130  is pivotally supported from intermediate section  2050  by a wheel support  100 ″ which pivotally couples to a forward portion  2120  of intermediate frame portion  2040  by inboard and outboard pivot joints  108  and  110 , respectively, in a manner as previously described herein. The pivotal attachment of the wheel support to the frame permits pivoting motion of the supported wheel in a pitching direction, and preferably constrains the wheel against yawing motion such as the type necessary for steering control. The various embodiments of the present invention shown and described herein contemplate use of any of the various wheel supports shown and described herein. 
   In one embodiment, a spring  133  such as an inflatable air spring is placed between a portion of the wheel support and the bottom side of spring support member  2140 , in a manner as previously described herein. The spring provides resilient support of the vehicle from the road surface, the spring urging apart the frame from the wheel support. Spring support  2140  has a top surface within frame section  2054  that is at or below plane  2022 . Although what has been shown and described pertains to the left wheel, it is understood that there is preferably a mirror image wheel support supporting the vehicle from a right wheel  2131  located within wheel housing  2101 , right wheel  2131  being pivotally supported from portion  2121  of frame  2050 . 
   In one embodiment of the present invention, the wheel supports are trailing arm supports, such that the pivot axes  109  and  111  of the wheel supports  100 ″ are forward of the rotational axes  158  of the wheels  2130  and  2131 . Further, as can be best seen in  FIGS. 31 and 32 , the rotational axes of the wheels are located above plane  2022 . Preferably, a wheel support according to the present invention supports a stub axle  114 , and stub axle  114  supports one or more wheels from a single side in cantilever fashion such that the wheel is located outboard of the wheel support, leaving the space inboard of the wheel and stub axle for the wheel support, spring, and cargo compartments. Further, pivot joints  108 ,  109 ,  110  and  111  which pivotally couple the wheel supports to the frame, are located inboard of the supported wheel. Preferably, the pivot axes of the wheel supports are parallel to the rotational axis of the supported wheel, but the present invention also contemplates a wheel support pivotable about an axis that is not perpendicular to the longitudinal centerline of the vehicle and not parallel to the rotational axis of the supported wheel. The present invention also contemplates suspension systems located generally within the wheel housings, such as the type shown in my issued patents referenced above and incorporated herein by reference. 
   Rearward frame portion  2060  extends aft from wheel housings  2100  and  2101 , and supports the aftmost part of a separable vehicle body or payload portion. Forward longitudinal frame members  2042   a  and  2042   b  terminate just aft of intermediate frame section  2050 , where each frame member is welded to an aft longitudinal frame member  2062   a  and  2062   b , respectively. These aft longitudinal frame members extend through rear portion  2060 , and are welded to rear transverse member  2072   e . A pair of outboard longitudinal members  2072   c  and  2072   d  interconnect wheel housings  2100  and  2101 , respectively, to aft transverse member  2072   e . A plurality of interconnecting transverse members  2070   b  are welded at one end to outboard longitudinal members  2072   c  or  2072   d , and at the other end to central longitudinal members  2062   a  or  2062   b , respectively. 
   In a preferred embodiment, chassis section  2020  has a substantially planar top surface which extends throughout frame sections  2040 ,  2050 , and  2060 . For example, the top surfaces of forward and intermediate members  2042   a ,  2042   b ,  2072   a ,  2072   b ,  2070   a ,  2120 ,  2140 , and  2141  are preferably located in a single plane  2022  which is lower than rotational axes  158  of the rear wheels, as best seen in  FIG. 31 . The top surfaces of aft members  2062   a ,  2062   b ,  2070   b ,  2072   c ,  2072   d , and  2072   e  are preferably also located in a plane  2022 . However, in one embodiment of the present invention, the lower surfaces of these same members are preferably arranged such that the bottom surfaces of the aft members have increased clearance from the road surface. The bottom surface of the forward and intermediate members are closer to the road surface, thus allowing the forward and intermediate sections to include channel sections with a greater vertical height and thus stronger cross-sectional properties. 
   Referring to  FIGS. 30 and 32 , the bottom surfaces of forward and intermediate members  2042   a ,  2042   b ,  2072   a ,  2072   b ,  2070   a ,  2120 ,  2140 , and  2141  are preferable located in a single lower plane  2022   b . Further, the bottom surfaces of aft members  2062   a ,  2062   b ,  2070   b ,  2072   c ,  2072   d , and  2072   e  are preferably located in a single plane  2022   c  that is elevated more above the road surface than plane  2022   b . Preferably, plane  2022   c  including the bottom surfaces of the aft members is spaced apart and parallel to plane  2022  containing the top surfaces of the same aft members (refer to  FIG. 32 ). Similarly, the bottom surfaces of the forward and intermediate members located in plane  2022   b  are spaced apart and parallel to plane  2022  containing the top surfaces of the same forward and intermediate members. 
   Thus, chassis  2220  includes a forward section with a preferably planar body surface  2022   b  spaced apart from top planar surface  2022  by a first amount, and a bottom planar surface  2022   c  which is spaced apart from top surface  2022  by a second amount. Preferably the second amount is less than the first amount, thereby giving increased ground clearance to the aft portion  2060  of the chassis. This increased ground clearance makes it less likely that a road vehicle incorporating this embodiment of the present invention will strike or rub against the road surface when the road vehicle begins to climb an elevated road surface. In one embodiment, the distance between top plane  2022  to bottom plane  2022   b  is about 4–6 inches, and top plane  2022  is about 10–12 inches from the road surface. However, the present invention also contemplates those embodiments in which the top surfaces of structural members  2042   a ,  2042   b ,  2070   a ,  2072   a , and  2072   b  do not lie in a common top plane, but are all beneath the rotational axes of the rear wheels. 
   In one embodiment of the present invention, forward frame portion  2040  includes unique provisions for incorporating a ramp to facilitate wheelchair access to a payload portion of the road vehicle. As best seen in  FIGS. 32 and 33 , frame portion  2040  defines a recessed pocket  2180  on one side of forward frame portion  2040 . Recessed pocket  2180  includes a bottom boundary established by the top surface of structural members  2071   a ,  2071   b , and  2071   c . These three members transition on a downward angle from an inboard portion of frame section  2040 , such as from the outboard surface of central longitudinal member  2042   b . The other end of members  2071   a ,  2071   b , and  2071   c  are attached to an outboard portion of frame  2040 , such as outboard longitudinal member  2073 . 
   As best seen in  FIG. 33 , longitudinal member  2073  has a vertical height which is less than that of adjacent longitudinal member  2072   b . This cutaway portion along the outboard side of chassis  2020  presents a lower height for those passengers boarding on wheel chairs. In one embodiment of the present invention, the bottom boundary of recessed pocket  2180  is inclined more than about 11.5 degrees and less than about 17.5 degrees, as indicated by angle  2181  of  FIG. 34 . More preferably, angle  2181  is more than about 14 degrees and less than about 15 degrees. This angle is chosen so that the subsequent vertical rise of the bottom boundary, as would be experienced by a person in a wheelchair entering the vehicle, is about 1 inch for every 4 inches of lateral travel. 
   In another embodiment of the present invention, the bottom surface  2022   b  of frame portion  2040  is established to facilitate use of recessed pocket  2180  as part of a wheelchair ramp. In this embodiment, bottom surface  2022   b  is about 6.5 inches from the road surface. Using the previously mentioned ratio of a 4:1 declining angle, a ramp pivotably hinged to longitudinal member  2073  would have to be about 25–27 inches long. By maintaining the bottom surface of the chassis close to the road surface, it is possible to incorporate a ramp of moderate length, which can be hinged from beam  2073 . When not in use, the ramp can be stored inside the vehicle, being supported on the top of beams  2071   a ,  2071   b  and  2071   c . When in use, the ramp can be folded out to extend from the edge of beam  2073  to the ground. Thus by being low to the ground, it is possible to incorporate a folding wheelchair ramp for ingress and egress of disabled passengers. The weight, complexity and cost of a lifting device is not required. 
   A support section  2150  is preferably coupled to sub-frame  2220  which supports front suspension and engine module  2230  located in front of forward frame  2040 . Support section  2150  includes a pair of support members welded  2160  and  2161  which are cantilevered from the forward transverse beam  2041 . Support arms  2160  and  2161  preferably include a plurality of holes  2170 . Sub-frame  2220  and other structural components which support the front suspension and engine module  2230  are rigidly coupled to support section  2150  by the use of fasteners  2171  in conjunction with holes  2170 . 
   In some embodiments of the present invention, some portions of sub-frame  2220  are heat treated for improved strength. In these embodiments, the use of fasteners such as bolts, rivets, and related fasteners obviates the need to weld a portion of chassis  2020  to sub-frame  2220 . Welding of a sub-frame  2220  that has been heat treated could result in an undesirable change to the heat treated properties. Therefore, some embodiments of the present invention include joining of a chassis to a sub-frame by methods that do not use sufficient heat to change the heat treated properties. However, the present invention also contemplates those embodiments in which there is a negligible or acceptable affect of welding support section  2150  to forward frame portion  2040 . 
   In one embodiment of the present invention the sub-frame supporting the engine and front suspension is cut away from or otherwise removed from an existing vehicle. The rear frame portion of the existing vehicle aft of the cab section is not used, and the sub-frame of the cab section is bolted to chassis  2020 . In other embodiments of the present invention, the sub-frame, engine and front suspension unit, and other forward portions of the vehicle are taken from several different existing vehicles, or fabricated specifically for use with chassis section  2020 . 
   Sub-frame  2220  of cab section  2200  provides “high profile” support of at least one of the engine or front suspension of cab section  2200 . In some embodiments, the structural members of sub-frame  2220  are above rotational axis  2206  of front wheel  2204 . The floor of cab section  2200  is also located above the rotational axis  2206 . A vehicle  2400  according to one embodiment of the present invention includes a top surface of the frame of the cab section that is above rotational axes  2206  and  158  of wheels  2206  and  2130 , respectively, and a top surface  2022  of the frame supporting the payload section that is below rotational axes  2206  and  158 . The combined frame for a vehicle includes a forward-most sub-frame  2220  with a top surface that is at a first elevation above the rotational axes of the wheels, and a center and rear-most frame section  2020  with a top surface that is at a second elevation below the rotational axes of the wheels. 
   What follows now are specific dimensions for a particular embodiment of the present invention which is related to apparatus  2021  of  FIGS. 30 ,  31 ,  32 , and  33 . However, it is understood that these particular dimensions are provided as examples only and are not limiting. 
   In a specific embodiment, the height of plane  2022  above the road surface is from 10–12 inches and preferably about 11 inches. The distance from the road surface to underneath planar surface  2022   b  is 5–8 inches and preferably about 6.5 inches. The distance form the road surface to planar surface  2022   c  on aft frame portion  2060  is 7–10 inches and preferably about 8 inches. 
   The vertical height of frame portions  2042   a ,  2042   b ,  2072   a ,  2072   b , and  2070   a  is 4–6 inches, and preferably about 5 inches. The width of these same beams is preferably from 2–3 inches. The vertical height of beams  2070   b ,  2072   c ,  2072   d ,  2072   e ,  2062   a , and  2062   b , is preferably from about 2–4 inches and most preferably about 3 inches. The vertical height of front transverse beam  2041  is preferably from about 7–9 inches and most preferably about 8 inches. The width of beam  2041  ranges from about 1–3 inches and preferably about 2 inches. 
   The lateral width of pocket  2180  from the outboard edge of the pocket along the outer surface of beam  2073  to the inboard edge of the pocket along the outboard surface of beam  2042   b  is from about 38–42 inches and preferably about 40 inches. The width of pocket  2180  from the inner surface of beam  2141  to the front face of beam  2072   b  is from about 33–37 inches and most preferably about 35 inches. The vertical distance from plane  2022  to the top surface of beam  2073  is from about 3–5 inches and preferably about 4 inches. The distance from the longitudinal centerline of the chassis to the outboard edge of beam  2072   b  is from about 45–50 inches and preferably about 47.5 inches. Beams  2041 ,  2072   a ,  2072   b ,  2072   c ,  2072   d ,  2072   e ,  2042   a ,  2042   b ,  2062   a , and  2062   b  are preferably of a closed channel construction with a rectangular cross section. Beams  2070   a  and  2070   b  are preferably of an open channel construction with a “c” cross section, or I-beams. 
     FIG. 34  shows a side elevational view of another embodiment of the present invention.  FIG. 35  shows an apparatus  2021 ′ which includes a chassis section  2020  as previously described, and a modified cab section  2200 ′. The use of a prime (′) mark by an element number indicates an element substantially similar to the non-prime element, except for those differences which are shown or described. 
   Cab section  2200 ′ includes a subframe  2220 ′ and a front suspension and engine module  2230 ′ that have been modified to permit a lowering of the driver&#39;s seat and floor of the cab compartment. Front suspension and engine module  2230 ′ includes an engine  2232 ′ and transmission  2234 ′ located aft and lower than the location shown and described for engine  2232  and transmission  2234 . Engine  2232  is located over the centerline  2206  of wheel  2205 , as best seen in  FIG. 32 . The rotational centerline and power takeoff for engine  2232  is above the axis of the front wheels, and must be brought to the lower level of front axle  2208  by a transfer case  2236 . The rotational centerline of the engine and transmission, as well as the various housings of the engine and transmission, generally establish lower boundaries for the floor of the cab section. Therefore, apparatus  2020  can include one or more steps which the driver uses to climb from road level to the driver&#39;s seat. Climbing a large distance is undesirable in some applications, such as for delivery trucks which make frequent starts and stops. In these situations, the height and number of steps that must be climbed leads to increased injuries and problems for the delivery drivers. 
   Apparatus  2021 ′, shown in  FIG. 34 , includes a mounting arrangement for the engine  2232 ′ and transmission  2234 ′ that reduces the height of the floor of cab section  2200 ′. Front suspension and engine module  2230 ′ includes an engine  2232 ′ placed aft of front axle  2208 ′. Engine  2232 ′ is also rotated 180 degrees so that its power takeoff is toward the front of apparatus  2021 ′. Transmission  2234 ′ is located between engine  2232 ′ and front axle  2208 ′. The centerline  2232   a ′ of the engine is preferably co-planar with axis  2206 ′ of the front axle. Apparatus  2021 ′ does not need a transfer case because the centerline of the engine is close to, or intersects the centerline of the front axle. The present invention also contemplates those embodiments in which the power input of the front axle is offset slightly from the rotational centerline of the axle. Therefore, the height of the floor of cab section  2200 ′ is lower, and fewer steps are required for entry of the driver from the road surface. 
     FIG. 35  is a top plan view of an apparatus according to another embodiment of the present invention. A vehicle chassis  3020  is similar to inventive chassis  1020  and  2020  as previously described, but with the following differences. Chassis  3020  includes three central longitudinal members  3042   a ,  3042   b , and  3042   c , that traverse the length of forward frame section  3040 . Three longitudinal frame members  3062   a ,  3062   b , and  3062   c , traverse the length of rear frame portion  3060 . Intermediate frame portion  3050  in between the forward and aft frame portions supports a plurality of rear wheels on each side of the chassis. The left side of chassis  20  includes forward and rear wheels  3130   a  and  3130   b , respectively, housed under a common wheel housing  3100 . The right side of chassis  3020  includes forward and rear wheels  3131   a  and  3131   b , respectively, housed under a common wheel housing  3101 . Further, chassis  3020  includes upper spring supports  3140   a  and  3140   b  which are in contact with the top surface of the springs held by the wheel supports (not shown). Further, chassis  3020  includes upper spring supports  3141   a  and  3141   b  which are in contact with the top surface of the springs held by the wheel supports (not shown). 
     FIG. 37  shows a front, left, top true perspective view of chassis section  2020  coupled to a portion of a cab section  2200 . Various portions of cab  2200 , such as the body, seats, windshield, and other features have been removed for sake of clarity. Cab section  2200  includes a subframe  2220  which supports a front suspension and engine module  2230 . Module  2230  includes a front axle  2208  which provides power to driven front wheels  2204  and  2205 . Wheels  2204  and  2205  rotate about a common centerline  2206  which, in one embodiment of the present invention, is located below engine rotational axis  2232   a . Power is provided to the driven front wheels by a transfer case  2236 , which in turn receives power from a transmission  2234  coupled to engine  2232 . 
   Subframe  2220  includes a pair of longitudinally extending front frame members  2240  and  2241 , located on the left and right sides, respectively, of subframe  2220 . Each side of front axle  2208  is pivotally coupled to a respective frame member  2240  and  2241  by trailing arm supports  2242  and  2243 , respectively. Each trailing arm support is pivotally coupled to the frame member by a single degree of freedom pivot joint. For example, trailing arm support  2242  is coupled to frame member  2240  by a pivot joint  2244   a  located within a housing  2244   b . Likewise, trailing arm support  2243  is coupled to frame member  2241  by a pivot joint  2245   a  located within a housing  2245   b . In the description that follows, reference will be made to the trailing arm support and other features of the left side of cab section  2200 , it being understood that identical and/or mirror-image features are used on the right side, except as noted. 
     FIGS. 38 ,  39 , and  40  are enlarged views of the various components in the vicinity of trailing arms support  2242  from side, top, and rear viewpoints, respectively.  FIG. 38  shows trailing arm support  2242  pivotally coupled to longitudinal frame member  2240  by a pivot joint  2244   a  attached within a joint housing  2244   b . Pivot assembly  2244   a  permits rotation of trailing arm support  2242  about a pivot axis  2244   c  which is generally parallel to the rotational axis  2206  of front axle  2208 . Pivot assembly  2244   a  includes a stationary member, preferably bolted to housing  2244   b , and a pivoting inner member which is attached to the forward-most end of arm  2242 . 
   In one embodiment, the inner pivoting member of assembly  2244   a  includes an inner molded elastomeric collar which is integrally molded within the stationary member of pivot assembly  2244   a . Preferably, the inner surface of the joint stationary member includes a plurality of grooves, such that during molding of the elastomeric collar, complimentary shaped ribs are molded into the elastomeric material. 
   Referring to  FIGS. 38 ,  39  and  40 , trailing arm support  2242  extends aft from pivot joint  2244   a  preferably underneath front axle  2208 , with the aftmost end of support  2242  being coupled to the bottom side of an air spring  2248 . The top side of air spring  2248  is in contact with static members which are rigidly attached to front longitudinal frame member  2240 . Air spring  2248  is pressurized with a gas such as air, and urges apart the aftmost end of arm  2242  from frame member  2240 . Although what has been shown and described is an air spring, the present invention also contemplates the use of other biasing members, including for example, coil springs and leaf springs. 
   Arm  2242  is coupled to the left side of front axle  2208 , such as by a plurality of U-bolts, as shown. In a preferred embodiment, the support of front axle  2208  by trailing arm support  2242  occurs at a longitudinal position inbetween pivot joint  2244   a  and air spring  2248 . However, the present invention contemplates those embodiments in which the support of the front axle by the trailing arm support occurs at a longitudinal position aft of both the pivot joint and the air spring. 
   Referring to  FIG. 40 , front axle assembly  2208  includes a power input coupling  2208   a . This power input coupling rotates about an input axis  2208   b , which is largely perpendicular to the central axis  2206  of the front axle and front driven wheels. However, the present invention also contemplates those embodiments in which the axis of power input is displaced vertically up or down from wheel axis  2206 , as is common in some front axles. 
   As best seen in  FIG. 37 , front suspension module  2230  includes a pivotal member  2260  that pivotally couples trailing arm  2243  to longitudinal frame member  2240 . Rod  2260 , sometimes referred to as a panhard rod, is pivotally coupled at one end by a pivot joint  2260   a  supported within a pivot housing  2260   b , the latter being rigidly attached to trailing arm support  2243 . Pivot joint  2260   a  permits pivoting movement of one end of rod  2260  about a pivot axis that is generally perpendicular to pivot axes  2244   c  and  2243   c  of trailing arm supports  2242  and  2243 , respectively. 
   Referring to  FIG. 37 , pivotal member  2260  extends laterally from its pivotal attachment to trailing arm  2243  toward the longitudinal centerline of engine and suspension module  2220 , and then transitions vertically up toward longitudinal frame member  2240 . As best seen in  FIG. 39 , member  2260  is pivotally connected by a pivot joint  2260   c  supported by a pivot joint housing  2260   d  rigidly attached to an inboard surface of frame member  2240 . Pivot joint  2240   c  permits pivoting of the second end of member  2260  about a pivot axis that is perpendicular to the pivot axes of trailing arms  2243  and  2242 , and generally parallel to the pivot axis of the other end of member  2260 . 
     FIGS. 41–43  depict a substantially cast wheel support  100 ′″ according to another embodiment of the present invention. Element numbers designated with three prime marks (′″) designate elements that are the same as the non-prime, single prime, or double prime elements, except as described and depicted differently. 
   Wheel support  100 ′″ includes a horizontal portion  168 ′″ cast integrally with an upright portion  112 ′″. A spring support  156 ′″ within horizontal portion  168 ′″ receives loads from a spring, and is reinforced by a plurality of cast stiffening ribs  169   a ′″. Spring support  156 ′″ preferably includes two mounting holes  174 ′″ placed laterally and generally parallel to the rotational axis of the wheel. For the configurations of wheel supports shown herein, it is possible to dispense with a form bolt pattern for attachment of the airspring, since the pitching-type movement of the wheel support reduces loads on the airspring which act to cause the airspring to move fore and aft. Therefore, a simplified, two bolt lateral pattern is sufficient in some embodiments to prevent side to side motion of the airspring. By simplifying the attachment pattern from four fasteners to two fasteners, the reliability of the airspring and wheel support is increased by lessening the number of attachment points that can fail. 
   A cast reinforcing member  170 ′″ stiffens and strengthens wheel support  100 ′″. A plurality of cast stiffening ribs  169   b ′″ reinforces upright portion  112 ′″. Attachment members  178 ′″ and  180 ′″ are cast integrally with wheel support  100 ′″. Upright portion  112 ′″ includes mounting provisions  134 ′″ for attachment of a shock absorber and brake system components. 
   The toe-in of wheel support  100 ′″ is adjustable by shimming in a manner as previously described. Camber is adjustable by incorporating slots in stationary outer members  108   c ′″ and/or  110   c ′″ of the pivotal attachments. The slots permit the orientation of outer member  108   c ′″ or  110   c ′″ to be adjusted relative to a cross-member of the frame. This orientation is maintained by a friction fit provided by fasteners  177 ′″. 
   Yet other alternate embodiments of the present invention include a wheel support and a disc brake assembly including bleed and pressure ports oriented to maximize the lateral extent of the payload compartment between wheel housings.  FIG. 44  is a top perspective view, shown in partial cutaway, of a wheel  2102  rotatably supported about a stub axle  2114  which is cantilevered from an upright portion  112 ′″ of a wheel support  100 ′″. For sake of clarity, the wheel housing, tire, and other components have been removed. It is understood that the upright portion  112 ′″ lies immediately outboard of the inner surface of the vertical, inboard-most portion of wheel housing  2100 . 
   As shown in  FIG. 44 , an upright section  112 ′″ is bolted to a spindle  114  by fasteners through fastener attachment pattern  160 ′″. A rotating hub  162  is bearingly supported on spindle  114 . Coupled to hub  162  is a vented disc assembly  165  comprised of opposing rotor plates  165   a  and  165   b . A brake caliper assembly  2159  supported by upright portion  112 ′″ includes two friction pads  161  which are actuated against vented disc  165  so as to slow the vehicle. For sake of clarity, only one friction pad  161  is shown. Those of ordinary skill in the art will recognize the applicability of disc brakes to the many embodiments of the present invention. 
   As is common in the art, brake assembly  2159  includes one or more ports which are in fluid communication with an internal hydraulic cylinder. For example, there can be one port which provides flow into and out of the internal wheel cylinder, for purposes of brake application and release, respectively. There can be another fluid port for removal of trapped air and outward flow of hydraulic fluid, commonly called a bleed port. For sake of clarity,  FIG. 49  is shown with a single port  2159   a , which represents either the fluid actuation port or the bleed port. 
   In order to get the maximum lateral distance between wheel housings, it is necessary to place the inboard vertical walls of the wheel housings as close to the upright portion of the wheel supports as possible. However, other portions of the wheel, stub axle, and brake assemblies must also be located outboard of the inner vertical surface of upright portion  112 ′″, so as to not interfere with the wheel housing or, for those embodiments in which the wheel housings are integrated into the payload section, to not interfere with the payload section itself. 
   Therefore, some embodiments of the present invention utilize a brake assembly  2159  which incorporates one or more fluid ports that are oriented so that neither the ports, nor any equipment attached to it, protrude inward of the innermost surface of the brake assembly. As shown in  FIG. 44 , brake assembly  2159  includes a port  2159   a , preferably located on a top surface of the brake assembly, and preferably oriented with an axis that is generally parallel to the longitudinal axis of the chassis. A hydraulic fitting  2159   b  part of a hydraulic fluid line  2159   c  is threadably coupled into port  2159   a . Hydraulic line  2159   c  provides hydraulic fluid into and out of the internal cylinder of brake assembly  2159 , or provides a bleed of trapped air and hydraulic fluid from the internal cylinder. Preferably, port  2159   a  is located on assembly  2159  and adapted and configured such that no portion of hydraulic line  2159   c , including hydraulic fitting  2159   b , is located inward of innermost portion  2159   d . As shown in  FIG. 49 , the brakes can be actuated or bled from a hydraulic line, including the fittings, that does not come closer to the wheel housing than the upright portion of the wheel support. As shown and described, port  2159   a  is oriented vertically upwards. However, the present invention also contemplates those embodiments in which port  2159   a  can have any orientation, so long as hydraulic line  2159   c  and fitting  2159   b  do not extend inward of the innermost surface of the brake assembly. 
   While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.