Abstract:
A leveling system for a load hauling trailer which will improve the stability of a payload having a high center of gravity, thereby allowing loads, which would otherwise not be transportable, to be moved over roadways. The leveling system includes a base member with a curved upper surface, a slide member with a curved lower surface, and a hydraulic cylinder for sliding the slide member relative to the base member. As the slide member moves from side-to-side across the base member, the angle between the axis of slide member varies with respect to the axis of the base member. When installed at each end of a double gooseneck trailer, the leveling system will reduce or eliminate torsional stresses in the trailer as the front running gear traverses a road surface having a cross grade different from the surface being traversed by the rear running gear.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a leveling system for a trailer. More particularly, but not by way of limitation, the present invention relates to a bed leveling system for a load hauling trailer to stabilize a payload and mitigate torsional stress on the trailer due to differences in the cross slope between the front and rear of the trailer. 
     2. Background of the Invention 
     Generally speaking, trailers for hauling a payload are well known in the art. Typically such trailers are connected to a tractor, commonly known as a“semi tractor”, through a fifth-wheel type connector. Usually such trailers have no provision for leveling the payload while the trailer is being towed. This lack of leveling can cause loads with a high center of gravity to become unstable under certain conditions. 
     Stability problems can take on an even greater dimension when hauling exceptionally large, heavy loads. Specialty trailers for hauling such loads are well known in the art. Typically these trailers may include a relatively large number of axles to reduce the load per axle to an acceptable level. In a typical arrangement, such trailers include front running gear which includes a fifth wheel connector for attaching the trailer to a tractor for hauling; rear running gear; and a load unit, or bed, suspended by front and rear goosenecks from the front and rear running gear, respectively. The load unit is often configured to support the load fairly close to the ground, sometimes referred to as a “low boy” trailer, to provide greater head room when passing beneath overhead obstacles, such as power lines and overpasses. In addition, maintaining the load unit as close as possible to the ground provides improvement in the stability of the load, as well as facilitating loading and unloading of the trailer. Such trailers may be generically referred to as “double gooseneck” trailers. 
     As used herein, the term “running gear” is used to describe a combination of jeeps and/or dollies used to support a gooseneck. 
     Generally speaking, trailer connections may be broadly grouped into connections which are articulated to allow side-to-side rotation between the trailer and the towing vehicle, referred to herein as a “pivotal connection” and connections which do not allow side-to-side rotation referred to herein as a “moment connection” or “structural connection”. Thus, a conventional trailer connected to a tractor by a fifth wheel connector would employ a pivotal connection while a double gooseneck trailer could have either type of connection at the front gooseneck and either type of connection at the rear gooseneck. 
     While the stability of the load is a concern with either type of connection, when moment connections are employed, torsional stresses may be induced in the trailer, or load unit, by unevenness in the road surface (i.e. different cross grade under the front and rear portions of the trailer). Such torsional stresses may be particularly damaging to double gooseneck trailers having moment connections at both the front and rear of the trailer. Cornering is known to compound problems with both the stability of the load and the introduction of unwanted torsional stresses in the load unit. 
     It is thus an object of the present invention to provide a leveling system for a trailer bed which will level, from side-to-side, at least one end of a trailer to improve the stability of loads having a high center of gravity. 
     It is still a further object of the present invention to provide a leveling system for trailers designed to haul large, heavy loads which will simultaneously level the front and rear portions of a load unit to improve the stability of payloads having a high center of gravity and to reduce torsional stresses in the load unit and the payload. 
     SUMMARY OF THE INVENTION 
     The present invention provides a leveling system for trailers of the type used to carry a payload. In one embodiment, the leveling system provides a base member, having a curved upper surface attached to the frame of a trailer and a slide member, having a mating, curved lower surface, attached to the bed of the trailer, or a gooseneck. Preferably, both curved surfaces have the same radius so that the curved surface of the slide member will have substantially full engagement with the curved surface of the base member when the leveling system is assembled. Hydraulic cylinders move the slide relative to the base such that the angle between the axis of the base and the axis of the slide may be controlled to level the bed of the trailer. 
     The system may be operated manually by providing a manual hydraulic valve to control flow of hydraulic fluid to each cylinder or, alternatively, an electronic level may be provided to automatically actuate electrically operated valves to adjust the hydraulic cylinders to maintain the attitude of the trailer bed. 
     When the system is installed on a conventional fifth wheel-type trailer having a pivotal connection, the leveling device is preferably located at the rear of the bed. It is also preferable that, in such a configuration, the curvature of the base member and the slide member is such that the center of gravity of the loaded bed remains substantially concentric with the center line of the rear axle. 
     When the inventive device is included on a double gooseneck trailer, front and rear leveling systems may be provided to reduce torsional stresses on the trailer when the trailer is moved over surfaces where the cross grade under the front running gear differs from the cross grade under the rear running gear. Such a system is particularly advantageous when both goosenecks connect to the front and rear running gear through moment connections. 
    
    
     Further objects, features, and advantages of the present invention will be apparent to those skilled in the art upon examining the accompanying drawings and upon reading the following description of the preferred embodiments. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the general environment of the inventive leveling system. 
     FIG. 2 provides a top view of the base member of the inventive leveling system. 
     FIG. 3 provides a cross-sectional view of the base member as seen from perspective  3 — 3  of FIG.  2 . 
     FIG. 4 provides a partial cut away side view of the base member as seen from perspective  4 — 4  of FIG.  3 . 
     FIG. 5 provides a front view of a slide member incorporated in the inventive leveling system. 
     FIG. 6 provides a top view of the slide member. 
     FIG. 7 provides a partial side view of the slide member as seen from perspective  7 — 7  of FIG.  5 . 
     FIG. 8 provides a top view of an assembled leveling system. 
     FIG. 9 provides a cross-sectional view of the inventive leveling system as seen form perspective  9 — 9  of FIG.  8 . 
     FIG. 10 provides a front view (or rear view) of the inventive leveling system mounted on a trailer. 
     FIG. 11 provides a partial front view of a trailer having the inventive system and a visual level for adjusting the system. 
     FIG. 12 provides a block diagram for a system to automatically maintain the trailer bed in a level attitude. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the construction illustrated and the steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation. 
     Referring now to the drawings, wherein like reference numerals indicate the same parts throughout the several views, the general environment of the inventive leveling system is shown in FIG. 1. A trailer  10 , having a leveling system  20  (FIG.  9 ), is typically towed by a tractor  12 . Trailer  10  is a double gooseneck trailer (also commonly known as a “low boy”) having: front running gear  14  consisting of front jeep  150 , steering dolly  152 , and transfer beam  158 ; rear running gear  16  having front steering dolly  154 , rear steering dolly  156 , and transfer beam  160 ; a load unit  18  suspended between the front and rear running gear  14  and  16  by front and rear goosenecks  22  and  24 , respectively. As will be described in more detail hereinbelow, trailer  10  includes first and second leveling systems  20  under the front and rear towers  88 . While the preferred embodiment of the inventive leveling system  20  is shown and described as incorporated on a double gooseneck trailer, it will be apparent to those skilled in the art that the system may be installed on virtually any load hauling trailer or vehicle. It should also be noted that, while the preferred embodiment is described and shown in connection with a double gooseneck trailer having front and rear moment connections, the invention is not so limited. Double gooseneck trailers may be found which utilize one or more pivotal connections between the load unit and the running gear, the inventive system may be used with trailers having any combination of pivotal and moment connections. 
     The term “running gear” is used herein to describe a combination of jeeps and/or dollies used to support a gooseneck. While a typical configuration for a double gooseneck trailer is shown in FIG. 1, it should be understood that running gear may be provided in a large number of alternate configurations and the particular selection of running gear is not material to the present invention. 
     Referring next to FIG. 9, leveling system  20  comprises a base member  30  mounted to the frame  26  of either front transfer beam  158  or rear transfer beam  160 ; a slide member  32  slidably secured to base member  30  by a pair of guide pins  34  and  36 ; and a plurality of hydraulic cylinders (better seen in FIG. 8)  38 ,  40 ,  42 , and  44  for adjusting the position of slide member  32  with respect to base member  30 . Preferably, slide member  32  is attached to front and rear towers  88 . 
     Referring now to FIGS. 2-4, base member  30  includes: a top plate  46  having a convex upper surface  60  and registering slots  48  and  50 ; bottom plate  52 ; hinge elements  54   a-j  projecting downward from plate  52 ; front base lug  56  and rear base lug  58  affixed between bottom plate  52  and top plate  46  at the front and rear of base member  30 , respectively; and left and right stops  62  and  64 , respectively, located along the outer sides of top plate  46 . Front base lug  56  includes cylinder devises  66   a  and  66   b  and, similarly, rear base lug  58  includes cylinder devises  68   a  and  68   b . Ribs  69   a-d  extend from bottom plate  52  to top plate  46  to support top plate  46 . 
     Turning now to FIGS. 5-7, slide member  32  includes: a bottom plate  70  having a concave lower surface  72 ; left and right slide lugs  74  and  76 , respectively; left and right registering pins  34  and  36 , respectively; braces  82 ,  84 , and  86 ; jacking tower  88  and front rod devises  90   a  and  90   b  and rear rod devises  92   a  and  92   b . With further reference to FIG. 1, front and rear goosenecks,  22  and  24  are received over jacking towers  88  to allow the raising and lowering of load unit  18  to facilitate loading and unloading as well as to allow adjustment of the ground clearance of load unit  18 . Typically, in such a construction, jacking cylinders  94   a-c  (FIG. 9) may be attached to braces  82 ,  84 , and  86  to control the height of goosenecks  22  and  24 . 
     Referring to FIGS. 8 and 9, to assemble the leveling system  20 , slide member  32  is placed over base member  30  such that registering pins  34  and  36  project through registering slots  48  and  50 , respectively. It should be noted that, most preferably, concave surface  72  (FIG. 5) of slide member  32  is of the same radius as convex surface  60  (FIG. 3) of base member  30 . Thus, it can be seen that slide member  32  is free to slide from side-to-side on base member  30 , at least within the limits imposed on the right side by contact between slide lug  76  and stop  64 , and on the left side by contact between slide lug  74  and stop  62 . Registering pins  34  and  36 , and registering slots  48  and  50 , work in concert to prevent longitudinal movement between base member  30  and slide member  32 . As will be apparent to those skilled in the art, when slide member  32  is centered on base member  30 , jacking tower  88  will be substantially perpendicular to bottom plate  52 . As slide member  32  moves to the right, the angle between the jacking tower  88  and the right side of bottom plate  52  will become progressively smaller. Likewise, as slide member  32  moves to the left, the angle between the jacking tower  88  and the left side of bottom plate  52  will become progressively smaller. Thus, it can be seen that, by controlling the side-to-side position of slide member  32  relative to base member  30 , it is possible to maintain the jacking tower  88  in a plumb position while base member  30  rocks in response to changes in the cross grade of a road surface. 
     To control the side-to-side position of slide member  32 , hydraulic cylinder  38  is mounted between clevis  66   a  and clevis  90   a , cylinder  40  is mounted between clevis  66   b  and clevis  90   b , cylinder  42  is mounted between clevis  68   a  and clevis  92   a , and cylinder  44  is mounted between clevis  68   b  and clevis  92   b . By proper application of hydraulic fluid under pressure to the various cylinders, the precise position of slide member  32 , and hence the angle of jacking tower  88 , may be controlled. It should be noted that hydraulic cylinders are generally available in either single acting, or double acting models. Either type of hydraulic cylinder is suitable for use with the present invention. It should also be noted that a number of alternatives could also be employed for positioning slide member  32 . By way of example and not limitations, such slide means could also include pneumatic cylinders, electromagnetic linear actuators, rack and pinion mechanisms, and the like. 
     Continuing with FIG. 9, preferably retainers  96  and  98  are attached to the ends of registering pins  34  and  36  to ensure pins  34  and  36  remain in their respective slots. The assembled leveling system  20  is typically attached to a turntable  100  by way of hinge  104  comprising hinge elements  54   a-j  and hinge pin  102 . Turntable  100  is, in turn, attached to the frame  26  of the transfer beam  158  or  160  to allow turning of the running gear  14  or  16  relative to load unit  18 . Hinge  104  allows front-to-back angular displacement between the running gear  14  or  16  and tower  88 . As will be appreciated by those skilled in the art, allowing rotational freedom by way of the turntable  100  and hinge  104  is most preferable to allow trailer  10  to negotiate a typical roadway. 
     Referring to FIG. 11, goosenecks  22  and  24  are slidingly received over towers  88 , cylinders  94   a-c  are connected between the leveling system  20  and jacking frame  89  to allow the lifting and lowering of goosenecks  22  and  24 . In practice, cylinders  94   a-c  would typically be collapsed to fully lower goosenecks  22  and  24  for loading and unloading load unit  18 . For hauling a load, cylinders  94   a-c  would typically be extended to raise load unit  18  to achieve a desired ground clearance and blocks would be placed between gooseneck  22  or  24  and side lugs  74  and  76  to maintain the desired height. 
     As will be apparent to those skilled in the art, a number of modifications could be made to the inventive leveling system without departing from the scope or spirit of the present invention. For example, the slide member could be provided with a convex surface while providing the base member with a concave surface. While such a modification is withing the scope of the present invention, the method of the preferred embodiment is somewhat more advantageous. Referring to FIG. 10, it can be seen that, by a judicious selection of the radius of slide member  32  and base member  30 , that the slide may move in an arc concentric about the center of axle  106 . Thus, as the leveling system  20  is adjusted to keep the force vector aligned with jacking tower  88 , the vector will pass roughly through the center of axle  106  to best distribute the load across the tires. 
     It should also be noted that, as mentioned previously, the inventive leveling system may be adjusted manually (i.e., using manual valves to control the flow of hydraulic fluid to the cylinders) or automatically. The connection of the hydraulic cylinders through manual valves is well within the skill level of one of ordinary skill in the art. With double acting cylinders, for example, the rod side of cylinders  38  and  42  (FIG. 8) would be connected with the chamber side of cylinders  40  and  44  in a first hydraulic circuit. Likewise, the rod side of cylinders  40  and  44  would be connected with the chamber side of cylinders  38  and  42  in a second hydraulic circuit. Thus, when pressure is applied to the first circuit and fluid is drawn from the second circuit, the cylinders will push slide member  32  to the right. When hydraulic pressure is applied to the second circuit, and fluid is drawn from the first circuit, slide member  32  will instead move to the left. 
     In a manual configuration, as shown in FIG. 11, a liquid level  110  may be attached to the front of tower  88  so that the level is in view of an operator. Typically, at least the outer ends  112  and  114  of tube  110  are formed of a transparent, or translucent material. Obviously, as an unlevel road surface is encountered, the height of the fluid on one side of level  110  will be higher than in a level condition, while the fluid on the opposite side will be lower than in a level condition. Graduations  116  are provided on each side of level  110  to assist the operator in determining the degree of correction required. Thus the operator may simply operate manual hydraulic valves to adjust the leveling system  20  to maintain even fluid heights between the left and right sides of level  110 . 
     In an automatic system, as shown in FIG. 12, switches  120  and  122  are used to detect an unlevel condition and operate solenoid valves  124  and  126 , in response, to return the load unit to a level condition. A number of methods may be used to determine an out-of-level condition. By way of example and not limitation, an led/photodetector pair could be placed to detect a rise in the fluid level on either side of level  110  of FIG.  11 . Upon detecting the rise in fluid level, the appropriate valve would be opened to correct the unlevel condition. Alternatively, a pair of mercury switches could be positioned such that a clockwise rotation would cause one mercury switch to close while a counterclockwise rotation would close the other switch. Each mercury switch would control a valve to control the hydraulic fluid to correct the unlevel condition. An inclinometer or electronic vial level are other examples of electronic level detecting means which could be employed in an automatic leveling system. 
     In a situation where the road under the front running gear a cross grade significantly different than the road under the rear running gear, independently acting front and rear leveling systems will reduce, or eliminate, torsional forces in the load unit. In addition, it is possible that, if a load is securely tied to the load unit, unwanted torsional forces could also be transferred to the payload. In the preferred embodiment, front and rear leveling systems are preferred as depicted in FIG.  1 . However, it should be noted that where one or two pivotal connections are employed, a single system could be used to improve leveling of the load over prior art trailers. 
     It should also be noted that the inventive device is suitable for use with a conventional fifth wheel trailer having a single pivotal connection at the front of the trailer. Preferably, the base member would be attached above the rear axle. The bed of the trailer would attach to the top of the slide member allowing leveling of the trailer from the rear. As will be apparent to those skilled in the art, the fifth wheel connection allows some variation in pitch angle between the tractor and trailer so that a single leveling system could level the entire trailer from the back end of the trailer without inducing significant torsional stresses. 
     Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those skilled in the art. Such changes and modifications are encompassed within the spirit of this invention.