Patent Abstract:
A sub-trailer is provided having an attachment frame removably connected to a vehicle or trailer, an intermediate frame pivotally connected about a horizontal axis to the attachment frame to, and a subframe with two axles to support the subframe. The subframe is pivotally connected to the intermediate frame about another horizontal axis located between the first and second axles, and provides adequate load distribution from a load carried by the vehicle or trailer to the axles of the sub-trailer. Another sub-trailer is provided and is similar to the first sub-trailer, with the attachment frame removably and pivotally connected to the vehicle ro trailer about a vertical axis. Yet another sub-trailer is provided having a frame extending rearwards and being a vehicle, trailer, or attachment thereof; and a subframe pivotally connected to the frame about a horizontal axis, the subframe having two axles, each with a suspension system.

Full Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    Embodiments of the invention relate to a sub-trailer for attachment to a vehicle or a trailer, to distribute load therefrom. 
         [0003]    2. Background Art 
         [0004]    The prior art has provided various ways to transport and distribute a load to the ground using a vehicle or trailer. Additional load distribution is warranted when the vehicle or trailer cannot fully support the load it is required to carry. Efforts to better distribute a load began with a vehicle and then progressed to adding a trailer, and now include connecting an attachment to the vehicle or trailer such as an auxiliary axle or other assembly. One of the issues in using many of these systems occurs when the attachment traverses rough terrain or terrain having a steep or changing grade and the wheels lose contact with the ground. 
       SUMMARY 
       [0005]    An embodiment of the present invention discloses a sub-trailer having an attachment frame that can be removably and pivotally connected to a vehicle or trailer about a vertical axis, an intermediate frame extending rearward of the attachment frame, and a subframe with first and second axles connected to the subframe to support the subframe for travel upon an underlying support surface. The subframe is pivotally connected to the intermediate frame about a horizontal axis that is located between the first and second axles to provide load distribution from the vehicle or trailer to the first and second axles. 
         [0006]    Another embodiment of the present invention discloses a sub-trailer having an attachment frame that can be removably connected to a vehicle or a trailer, an intermediate frame extending rearward of the attachment frame and pivotally connected to the attachment frame about a first horizontal axis, and a subframe with first and second axles connected to the subframe to support the subframe for travel upon an underlying support surface. The subframe is pivotally connected to the intermediate frame about a second horizontal axis. The second horizontal axis is spaced apart from the first horizontal axis and located between the first and second axles to provide load distribution from the vehicle or trailer to the first and second axles. 
         [0007]    Yet another embodiment discloses a sub-trailer having a frame extending rearwards and being one of a vehicle, a trailer, or an attachment thereof; and a subframe with first and second axles connected to the subframe for rotation relative thereto to support the subframe for travel upon an underlying support surface. The subframe is pivotally connected to the frame about a horizontal axis located between the first and second axles to provide load distribution from the vehicle or trailer to the first and second axles. A first suspension system extends between the subframe and the first axle, and has a pair of trailing arms, a pair of shock absorbers, and a pair of airbags. A second suspension system extends between the subframe and the second axle, the second suspension having a second pair of trailing arms, a second pair of shock absorbers, and a second pair of airbags. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of one embodiment of a sub-trailer illustrated connected to a vehicle and trailer; 
           [0009]      FIG. 2  is a side view of the sub-trailer of  FIG. 1 ; 
           [0010]      FIG. 3  is a top plan view of another embodiment of a sub-trailer illustrating a portion of an intermediate frame and a subframe; 
           [0011]      FIG. 4  is a side elevation view of the sub-trailer of  FIG. 3 ; and 
           [0012]      FIG. 5  is a perspective view of the sub-trailer of  FIG. 1  illustrated descending from flat terrain to a downhill grade. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for the claims and/or as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0014]    Now referring to  FIG. 1 , a sub-trailer  10  is illustrated and is connected to a vehicle  12 . The vehicle  12  could be a truck, a trailer for a truck, or another piece of heavy equipment according to the invention. The sub-trailer  10  allows for distribution of a load placed on the truck  12  to the wheels  16  connected to the axles of the sub-trailer  10 . The sub-trailer  10  is depicted with two axles, a front axle  18  and a rear axle  20 , but additional axles are possible. The sub-trailer  10  is designed such that it is capable of being driven over terrain with potentially steep and extreme grades while keeping the wheels  16 , which are connected to the axles  18 ,  20 , in contact with the ground. The sub-trailer  10  can distribute a load from the truck  12  to both the front axle  18  and rear axle  20  of the sub-trailer  10 , and in one embodiment evenly distributes the load between the axles  18 ,  20 . 
         [0015]      FIG. 2  shows a side view of the sub-trailer  10  connected to the vehicle  12 . In one embodiment the sub-trailer  10  has three primary frame components. The first frame component is an attachment frame  22  that can be connected and disconnected from the back of the vehicle  12 . The attachment frame  22  is attached to the vehicle  12  using a pivotal connection  24  with a vertical axis of rotation  26 , such that the sub-trailer  10  can follow the truck  12  through a turn. The pivotal connection  24  can be a fifth wheel coupling, pintle and gudgeon, or other similar device that allow for the sub-trailer  10  to be removably connected to the vehicle  12  and have rotation about a vertical axis  26 . 
         [0016]    The second frame component shown in  FIG. 2  is an intermediate frame  28 . The intermediate frame  28  is connected to the attachment frame  22  via a pivotal connection  30 , which allows for motion about a horizontal axis of rotation  32 . The intermediate frame  28  is also connected to the attachment frame  22  by a hydraulic loading system  34 . The hydraulic loading system  34  is controllable such that it can exert a force on the intermediate frame  28  under specified conditions. The force exerted by the hydraulic loading system  34  on the intermediate frame  28  will cause it to rotate either away or towards the attachment frame  22  about the horizontal axis  32 . The hydraulic loading system  34  may be a self-contained unit and an example of one that could be used in this application is an oil over nitrogen accumulator system. When engaged, the hydraulic loading system  34  can lift the wheels  16  of the sub-trailer  10  from contact with the ground or other underlying surface. This may allow for better maneuverability of the truck  12  and sub-trailer  10  assembly while reversing, undergoing difficult turns, or the like. 
         [0017]    The third frame component shown in  FIG. 2  is a subframe  36 , which is connected to the intermediate frame  28  by another pivotal connection  38 . This pivotal connection  38  allows for motion about a horizontal axis of rotation  40  located at a different location than the previously described horizontal axis of rotation  32 . The intermediate frame  28  arches and extends rearward over the forward portion of the subframe  36  to the attachment point on an upper surface and in a central region of the subframe  36 . The axles  18 ,  20  connect to the subframe  36  at two locations, both of which are lower than the subframe pivotal connection  38 . The front axle  18  connects to the subframe  36  at a position forward of the pivotal connection  38 . The rear axle  20  connects to the subframe  36  at a location behind the pivotal connection  38 . The wheels  16  are attached to the ends of the axles  18 ,  20  and are in contact with the ground as the sub-trailer  10  is towed by the truck  12 . Each wheel  16  can be a single wheel, a tandem wheelset, or a combination of the two, if needed. There can also be a transverse connector bar  46  connected to a rear surface of the subframe  36  in one embodiment. Attached to the rear transverse connector bar  46  may be a taillight assembly  48 , or the taillight assembly could be directly attached to a rear surface of the subframe  36 . The lights of the taillight assembly  48  are used to indicate braking, turning, and/or hazards. 
         [0018]    As the sub-trailer  10  moves in relation to the ground, the two horizontal axes of rotation  32 ,  40  allow for the wheels  16  to stay in contact with the ground. This can lead to a better and more equal distribution of the load carried by the truck  12  to the front and rear axles  18 ,  20 , through the wheels  16  and to the ground. The sub-trailer  10  can distribute the load while it is being towed over uneven ground or a graded terrain such as uphill or downhill. For example, pivotal motion about the two horizontal axes  32 ,  40 , can evenly distribute a load to the axles  18 ,  20  while the vehicle  12  and sub-trailer  10  are on different grades, such as the vehicle on a even surface and the sub-trailer on a hill, the vehicle on a hill and the sub-trailer on a flat surface, the vehicle and the sub-trailer on different percentage graded hills, or any other combination. 
         [0019]      FIGS. 3 and 4  are views of another embodiment of a sub-trailer  10 ; in these figures, like elements to previous embodiments retain the same reference numerals and new elements are assigned new reference numerals.  FIGS. 3 and 4  illustrate a subframe  36  and a portion of an intermediate frame  49 . The intermediate frame  49  may be the same as the intermediate frame  28  or it can extend directly from a portion of a trailer or vehicle  12  structure. The intermediate frame  49  extends rearward to a pivotal connection  38  where it attaches to the subframe  36  at an intermediate portion of the subframe  36  and has a horizontal axis of rotation  40 . The subframe  36  extends both forward and rearward from the pivotal connection  38 . Attached to the subframe  36  is a front axle  18  and a rear axle  20  with a pair of tandem wheel sets  16  attached to each axle. At the rearward portion of the subframe  36 , a rear transverse connector bar  46  is attached. This connector bar  46  may have a tail light assembly  48  attached to it, which can indicate braking, turn, and/or emergency signals. The transverse connector bar  46  also provides a mounting point for a license plate or mud flaps. 
         [0020]      FIGS. 3 and 4  also show a top view of a bar  50  which extends from the intermediate frame  49  in a downward direction and is engaged to slide with respect to the subframe  36 . The sliding bar  50  interacts with and extends through a slot  56  in the subframe  36 . The sliding bar  50  acts to prevent a twisting motion of the subframe  36  relative to the intermediate frame  49  and the sliding motion allows for the subframe  36  to move mainly in one vertical plane of motion in relation to the intermediate frame  49  as the subframe pivots on its connection  38  with respect to the intermediate frame  49 . A pair of bumpers  58  are used to prevent direct contact of the subframe  36  with the intermediate frame  49 . In one embodiment the bumpers  58  are attached to the intermediate frame  49 , and alternatively could be attached to the subframe  36 . The bumpers  58  can be made from rubber, a plastic, or other type of resilient material, and also may be replaceable with use and wear. 
         [0021]      FIGS. 3 and 4  also show an embodiment of a suspension system that may be used. In this suspension system, the front axle  18  is attached to the forward portion of the subframe  36  by first and second trailing arms  52 , one each side of the subframe  36 . Each trailing arm  52  is pivotally connected to the subframe  36  and interacts with the end of the axle  18 , allowing it to move with respect to the subframe  36 . Each trailing arm  52  also interacts with a respective vibrational absorption system  54 , which in one embodiment may be a combination of an airbag and a shock absorber. The rear axle  20  is also attached to the subframe by a suspension system. In the rear axle  20  suspension system, third and fourth trailing arms  52  are pivotally connected to each side of the rearward portion of the subframe  36  and interact with the ends of the rear axle  20  allowing it to move with respect to the subframe  36 . Each of these rear trailing arms  52  interact with a respective vibrational absorption system  54  between the trailing arm and the subframe which in one embodiment may be an airbag system and shock absorber. The four trailing arms  52  interact with the outboard ends of both axles  18 ,  20  to allow the axle to rotate. The four trailing arms  52  can independently move to react to the ground surface, and act as an independent suspension system. This allows for better load distribution and ride quality as the sub-trailer is on the road or going over rougher terrain. 
         [0022]      FIG. 5  shows a perspective view of the sub-trailer  10  on graded terrain as the vehicle  12  descends from flat terrain onto a downhill grade while towing a sub-trailer  10 . As can be seen in the figure, all of the wheels  16  remain in contact with the ground or other underlying surface while the vehicle  12  and its sub-trailer  10  are on differently graded terrain. In  FIG. 5 , all of the wheels  16  of the sub-trailer  10  remain in contact with the ground, which is due in large part to the two horizontal axes  32 ,  40 . The first horizontal axis  32  is located at the pivotal connection  24  of the attachment frame  22  to the intermediate frame  28 . The second horizontal axis  40  is located at the pivotal connection  38  of the intermediate frame  28  to the subframe  36 . These two pivotal connections  30 ,  38  are spaced apart and allow for the intermediate frame  28  and the subframe  36  to independently pivot with respect to the attachment frame  22  which is either directly attached to the vehicle  12  or a portion of the vehicle  12  itself. This figure also illustrates the taillight assembly  48  that may be connected to the rear transverse connector bar  46 . 
         [0023]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

Technology Classification (CPC): 1