Abstract:
An improved locking mechanism for a movable subframe of a tractor-trailer has a pair of transversely-spaced main members extending longitudinally beneath a body of the tractor-trailer, at least one cross member extending between and being attached to the main members, and an axle/suspension system attached to and depending from the main members. At least one clamping mechanism is attached to the subframe and mechanically engages a longitudinally extending rail of the body of the tractor-trailer to enable efficient selective positioning of the subframe relative to the body. Undesirable movements between the subframe and the tractor-trailer body are minimized by fore-aft and/or vertical clamping loads exerted on the body rail and the subframe by the clamping mechanism. This secure positioning allows portions of the trailer body and/or subframe to be constructed of lightweight materials which in turn permits the tractor-trailer to carry larger payloads.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/703,910, filed on Jul. 29, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field  
         [0003]     The invention relates to tractor-trailer subframes and, in particular, to movable subframes for tractor-trailers. More particularly, the invention is directed to a movable subframe for tractor-trailers which includes a clamping arm mechanism for locking the movable subframe into a selected position relative to the tractor-trailer body, wherein the movable subframe is effectively clamped to the trailer body rails so that gyrations of the subframe are reduced or minimized after the subframe is locked into position and during operation of the vehicle, thereby enabling the use of weight-saving aluminum trailer body rails and cross sills and enhancing the advantages of an aluminum slider box.  
         [0004]     2. Background Art  
         [0005]     Specifically, movable subframes, typically referred to as slider boxes, slider subframes, slider undercarriages, or slider secondary frames, have been utilized on tractor-trailers or semi-trailers for many years. One or more axle/suspension systems usually are suspended from a single slider box. For purposes of clarity, hereinafter the movable subframe incorporating the improved locking mechanism of the present invention will be referred to as a slider box. It is understood that a slider box outfitted with usually two axle/suspension systems typically is referred to as a slider or slider tandem, and again, for purposes of clarity will hereinafter be referred to as a slider tandem. The slider tandem in turn is mounted on the underside of the trailer primary frame or floor structure, and is movable longitudinally therealong to provide a means for variable load distribution and vehicular maneuverability. Specifically, the slider tandem can be used on flatbeds having a primary frame, van trailers having a floor structure, and the like.  
         [0006]     More specifically, the amount of cargo that a trailer may carry is governed by local, state and/or national road and bridge laws, and is dependent on proper load distribution. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as limit the maximum load that can be supported by individual axles. A trailer having a slider tandem gains an advantage with respect to laws governing maximum axle loads. More particularly, proper placement of the slider tandem varies individual axle loads or redistributes the trailer load so that it is within legal limits.  
         [0007]     Conventional or prior art slider box designs were developed before the advent of air suspension systems for trailers. At that time, leaf spring suspension systems were the suspension of choice for van trailers with slider boxes. However, the leaf spring suspension system was unable to provide adequate load equalization between the axles of the slider tandem and therefore was subject to possible overload situations.  
         [0008]     Moreover, the subsequent development of air suspension systems provided load equalization among multiple axles for tractor-trailers, with or without the utilization of slider boxes, as well as improved ride quality for individual axles. Of course, the combination of a movable slider box and an air suspension system provided maximum versatility with respect to variable load distribution and load equalization in a trailer and increased maneuverability. Unfortunately, prior art slider boxes equipped with air suspensions add unwanted weight to the trailer, primarily because those slider boxes were originally built to support leaf spring suspensions and adapting them to incorporate air suspensions required additional bracing and support.  
         [0009]     Additionally, vehicles containing more than one non-steerable axle, including tractor-trailers, are subject to lateral or side loads. Lateral loads can act through the slider box in opposite directions, and the effect of such lateral or bending loads on the slider box can be significant. Moreover, a slider box is subjected to strong vertical and longitudinal or fore-aft loads. Thus, the loads to which the slider box is subjected must be controlled by the slider box design. Prior art slider box designs control vertical loads by utilizing rigid, and therefore heavy, main members and cross members typically made of steel. This increases the weight of the frame, thereby reducing the amount of payload that can be carried by the tractor-trailer as governmental weight limitations remain constant irrespective of the weight of the vehicle.  
         [0010]     Thus, within the trucking industry, reducing the weight of carrier equipment without sacrificing durability directly improves productivity by increasing the available payload that can be transported by the vehicle. Slider boxes made of steel have contributed to the excessive weight problems that have plagued slider tandems in the past. Although certain prior art slider boxes formed of steel have exhibited weight and durability improvement over other prior art steel slider boxes, as well as improvements to the structure and operation of prior art retractable pin mechanisms, the trucking industry is continually striving for improvement in slider box design. However, attempts to utilize materials that are lighter than steel to construct slider boxes, such as aluminum, have been largely unsuccessful and inefficient.  
         [0011]     Turning now to the manner in which a slider tandem operates, once properly positioned, the slider tandem heretofore typically has been locked into place on the underside of the trailer by a retractable pin mechanism. The retractable pin mechanism of the prior art generally includes two or more, and typically four, retractable pins which may be interconnected by a usually manually operated crank mechanism. When the pins are in their extended or outboardmost position, they each pass through a respective opening formed in the slider box and a selected aligned one of a plurality of openings formed in rails of the trailer body. The pins thereby lock the slider tandem in the selected position relative to the trailer body. However, these pins can become jammed. The mechanical advantage enjoyed by the manual operator of the pin mechanism, which is used for retracting the pins when it becomes necessary to reposition the slider tandem, is designed to overcome spring forces which bias the pins to the locked position. The mechanical advantage is not designed to free or retract jammed pins from their locked position. Since the mechanical advantage is sometimes inadequate, prior art slider tandem pin mechanisms rely on either the brute force of the tractor-trailer operator or add-on devices designed to release jammed pins.  
         [0012]     In assessing the causes for jammed pins, it has been discovered that shear forces are imposed on the individual pins. The shear forces operate on the pin perpendicular to the longitudinal axis of each cylindrical pin. More specifically, slight movement of the slider tandem relative to the trailer body during operation of the tractor-trailer can cause slight misalignment between the respective slider box and trailer body openings through which each pin extends or passes when in the locked position. This misalignment can in turn cause contact pressure points between each pin and its respective trailer body rail opening, aligned slider box opening, and the mounting bracket opening located adjacent to the inboard end of the pin. The contact pressure points in turn cause the above-mentioned shear forces on the pins. Such whipsaw-like or jamming forces can become greater than the force that a tractor-trailer operator is able to manually apply through the crank mechanism to free the pins.  
         [0013]     Thus, when prior art pins become jammed, the operator of the tractor-trailer risks personal injury due to overexertion in attempting to manually free jammed pins, and further risks damaging the retractable pin mechanism. Specifically, a typical method of attempting to release prior art jammed pins is for the tractor-trailer operator to rock the trailer fore and aft, while an assistant operates the retractable pin mechanism. The rocking motion momentarily realigns the misaligned openings, so that the assistant can retract the pins during the brief period of realignment. The process has been simplified by a prior art quick-release device which allows the vehicle operator to maneuver the trailer while the quick release device automatically frees the jammed pins, thus effectively obviating the need for another person to operate the crank mechanism. However, such quick release devices add expense to the slider box, and such an exercise can be time-consuming and also can create wear on the retractable pin mechanism.  
         [0014]     Yet another problem associated with prior art locking pins, which is related to the pin jamming problem, is that the holes formed in the trailer body rails and through which the slider box pins protrude when in the locked position, are approximately 0.25″ oversized to allow the pins to pass through the respective holes after tolerances and deflections are accounted for. This relatively sloppy fit allows the slider box pins to gyrate back and forth and up and down within the holes during trailer operation. Such movements, in turn, can cause each pin to forcibly contact, or bang, the trailer body rail opening at the interface of the slider pin and the trailer body rail. Such movement and pin banging, in turn, causes lateral movement and misalignment of the slider tandem, which can adversely affect tracking, cause excessive tire wear, and exacerbate the jamming of pins. This movement also places additional and undesirable stresses on the slider box and the trailer body rails, and dictates that those components be made of steel, as opposed to a lighter material such as aluminum, to provide acceptable component life. The steel body rails alone add approximately 100 lbs. apiece to the weight of the trailer and further dictate the use of steel cross sills in trailers having a floor structure frame, which enables easy welding of the steel rails to the steel floor structure but also adds additional undesirable weight. As there are approximately 17 cross sills on a typical trailer floor structure in the slider area, substantial weight savings could be achieved through the use of sills made of aluminum, as opposed to steel.  
         [0015]     Thus a need exists in the art for an improved locking mechanism for a slider box that overcomes the problems and deficiencies of the prior art, mainly unwanted movement, gyrations and pin jamming, and yet still allows the slider box to be constructed of lightweight materials in order to provide vehicle operators an improved slider box that can carry larger payloads.  
       BRIEF SUMMARY OF THE INVENTION  
       [0016]     An objective of the present invention is to provide a slider box incorporating an improved locking mechanism that securely fastens a slider tandem to the trailer body rails of a tractor-trailer.  
         [0017]     Another objective of the present invention is to provide a slider box incorporating an improved locking mechanism that allows the operator to easily lock and unlock the slider tandem for easy repositioning of the slider tandem with respect to the trailer body rails, while effectively substantially minimizing the stresses associated with the relatively loose fit of prior art locking pin mechanisms.  
         [0018]     Yet another objective of the present invention is to provide a slider box incorporating an improved locking mechanism that allows for the use of lighter materials, such as aluminum, in constructing the trailer body rails, cross sills, and other components of the slider box, and which in turn significantly reduces the overall weight of the trailer, thereby improving cargo-carrying efficiency.  
         [0019]     A further objective of the present invention is to provide a slider box incorporating an improved locking mechanism that reduces the amount of effort expended by the operator when repositioning the slider tandem, and further permits the operator to easily determine whether the slider box is properly engaged, thereby improving safety for the operator and the traveling public.  
         [0020]     These objectives and advantages are obtained by the movable subframe for a tractor-trailer which includes a pair of transversely spaced-apart main members extending longitudinally relative to a longitudinally-extending trailer body of the tractor-trailer, at least one cross member extending between and being attached to the main members, at least one axle/suspension system mounted on and depending from the subframe, and at least one clamping mechanism mounted on the subframe for clampingly engaging the trailer body for selectively positioning the subframe relative to the trailer body. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0021]     The preferred embodiment of the invention, illustrative of the best mode in which applicant has contemplated applying the principles of the invention, is set forth in the following description and is shown in the drawings, and is particularly and distinctly pointed out and set forth in the appended claims.  
         [0022]      FIG. 1  is a driver&#39;s-side top-front fragmentary perspective view of a prior art slider box for a tractor-trailer, showing the retractable pin mechanism used to selectively position the slider box along the underside of a trailer body, and further showing depending hangers for suspending axle/suspension systems from the slider box;  
         [0023]      FIG. 2  is an enlarged fragmentary driver&#39;s-side elevational view of a prior art slider tandem, including the prior art slider box shown in  FIG. 1 , and showing two axle/suspension systems, with portions broken away and hidden portions represented by broken lines;  
         [0024]      FIG. 3  is a reduced-size rear fragmentary elevational view of the prior art slider tandem shown in  FIG. 2  movably mounted on the underside of a trailer body, with portions thereof represented by broken lines;  
         [0025]      FIG. 4  is a greatly-enlarged fragmentary view taken from the circled area in  FIG. 3 , showing one of the pins of the retractable pin mechanism in the locked position;  
         [0026]      FIG. 5  is a greatly-enlarged fragmentary top view of the retractable pin mechanism of the prior art slider box shown in  FIG. 1 , with portions thereof in section and hidden portions represented by broken lines, and showing one of the pins of the retractable pin mechanism in an unlocked position and showing the pin opening of the slider box slightly mis-aligned with the pin opening of the trailer body;  
         [0027]      FIG. 6  is a view similar to  FIG. 5 , showing one of the pins of the retractable pin mechanism of the prior art slider box in a locked position and showing contact pressure points imparted on the pin as a result of the ordinary movement of the slider box relative to the trailer body during operation of the vehicle;  
         [0028]      FIG. 7A  is an enlarged outboard perspective view of the driver&#39;s side improved locking mechanism for a slider box of the present invention, showing the clamping arm mechanism including the housing, the arm base, and the clamping arms;  
         [0029]      FIG. 7B  is a condensed view similar to  FIG. 7A  with a portion of the arm base and one of the front L-shaped plates removed, showing the front opening in the spacer, and with the outboard housing plate removed and showing the location of the air spring, the coil springs, and the locking mechanism within the housing;  
         [0030]      FIG. 8A  is a top driver&#39;s side perspective view of the improved locking mechanism of the present invention incorporated into a slider tandem, and showing the clamping arm mechanism locking the tandem into a selected position on the rails of a trailer body;  
         [0031]      FIG. 8B  is an enlarged fragmentary top-front outboard perspective view of the improved locking mechanism for a slider box of the present invention with portions of the trailer body rail removed, showing the manner in which the upper arms of one of the clamping arm mechanisms engages its respective trailer body rail for locking a slider tandem in a selected position beneath the trailer;  
         [0032]      FIG. 9  is an outboard elevational view of the improved locking mechanism for a slider box of the present invention, with the outboard housing plate removed and showing the slider box main member and trailer body rail in section, and further showing the clamping arm mechanism in an unlocked position;  
         [0033]      FIG. 10  is a view similar to  FIG. 9 , but showing the clamping arm mechanism in a partially locked position; and  
         [0034]      FIG. 11  is a view similar to  FIGS. 9 and 10 , but showing the clamping arm mechanism in a locked position. 
     
    
       [0035]     Similar numerals refer to similar parts throughout the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0036]     So that the structure, operation and advantages of the improved locking mechanism for a slider box of the present invention can be best understood, a slider box for a tractor-trailer having a prior art retractable locking pin mechanism is indicated generally at  20  and is shown in  FIG. 1 . Slider box  20  includes a pair of longitudinally extending main members  21 , a plurality of cross members  22 A through F, and a retractable pin mechanism  24 . Front and rear pairs of hangers  23 A and  23 B, respectively, are attached to and depend from slider box main members  21  for suspending axle/suspension systems.  
         [0037]     Specifically, and as further shown in  FIG. 2 , each main member  21  is an elongated, generally C-shaped beam made of a metal such as steel or other suitable material. The open portion of each main member  21  is opposed to the open portion of the other main member and faces inboard relative to slider box  20 . Main members  21  are connected to each other in spaced-apart parallel relationship by cross members  22 A-F, which extend between in fore-aft spaced-apart parallel relationship and are perpendicular to main members  21 . Each end of each cross member  22  nests in the open portion of a respective one of main members  21 , and is secured therein by any suitable means such as welding or mechanical fastening. Each cross member  22  is a generally C-shaped beam also made of a metal such as steel or other suitably robust material, and has a plurality of openings  29  formed in its vertically extending surface. Openings  29  are aligned with corresponding openings formed in the other cross members  22  to provide for passage of air and/or fluid conduits, electrical lines, and the like, used in the operation of the tractor-trailer (not shown). Each front hanger  23 A is attached by welding or other suitable means, to the lowermost surface of a respective one of main members  21  at a location directly beneath cross members  22 A, B. Each rear hanger  23 B similarly is attached to main members  21  at a location directly beneath cross members  22 D, E.  
         [0038]     Each main member  21  has a pair of rail guides  25  mounted on its outboard surface by bolts  26 , or other suitable means of attachment, such as welding. Each rail guide  25  is mounted adjacent to a respective one of the ends of main member  21 . A low friction strip  27  is attached to the uppermost surface of each main member  21  by recessed fasteners  28 , and extends generally the entire length of main member  21 . Low friction strip  27  is formed of any suitable low-friction material, such as ultra-high molecular weight polyethylene.  
         [0039]     As mentioned hereinabove, and as best shown in  FIG. 2 , slider box  20  supports front and rear axle/suspension systems  30 A and  30 B, respectively, wherein the slider box and axle/suspension systems combine to form a slider tandem, which is indicated generally at  70  in  FIG. 2 . Inasmuch as each axle/suspension system  30 A,B is suspended from slider box  20 , but does not form an integral part thereof, only the major components of system  30  will be cited for aiding in the description of the environment in which the slider box and prior art retractable pin mechanism  24  operates. Each axle/suspension system  30 A,B includes generally identical suspension assemblies  31  suspended from respective pairs of hangers  23 A,B. Each suspension assembly  31  includes a suspension beam  32  which is pivotally mounted on hanger  23  in a usual manner. An air spring  33  is suitably mounted on and extends between the upper surface of the rearwardmost end of suspension beam  32  and main member  21  at a location directly beneath a certain one of the cross members  22 C,F. A shock absorber  34  extends between and is mounted on suspension beam  32  and the certain cross member  22 C,F. One or more reinforcement struts  60  are strategically attached within each cross member  22 C,F to strengthen the cross member for supporting suspension assemblies  31 . Other components of suspension assembly  31 , mentioned herein only for the sake of relative completeness, include an air brake  35  and a height control valve  36 . An axle  37  extends between and is captured in the pair of suspension beams  32  of each axle/suspension system  30 A,B. Wheels  38  are mounted on each end of axle  37 .  
         [0040]     Slider tandem  70  is movably mounted on trailer body  40  ( FIGS. 3 and 4 ) by slidable engagement of rail guides  25  with spaced apart, parallel, and generally Z-shaped rails  41 , which are mounted on and depend from the underside of a floor structure  61  of the trailer body. More specifically, each Z-shaped rail  41  preferably is typically formed of a metal such as steel and weighs about 100 pounds. Since steel Z-shaped rails  41  conventionally are welded to floor structure  61  of a trailer body  40 , cross sills  55  of the floor structure also conventionally are formed of steel to facilitate welding. Cross sills  55 , which support floor structure  61  of the trailer, typically number about 17 within the area directly above Z-shaped rails  41 . Each low friction strip  27  abuts the bottom surface of the uppermost portion of a respective one of Z-shaped rails  41  to provide a smooth, generally friction-free contact surface for slidable movement of slider tandem  70  beneath trailer body  40 .  
         [0041]     As is well-known in the art, slider tandem  70  can be selectively positioned relative to trailer body  40  for optimum load distribution by retractable pin mechanism  24 . As best shown in  FIGS. 1 ,  3  and  4 , pin mechanism  24  includes a generally L-shaped handle  42 , which passes through an opening  39  formed in a selected one of main members  21 , but usually on the driver&#39;s side of the tractor-trailer. It can be seen that the bent end portion of handle  42 , which extends outwardly from the outboard side of main member  21 , is accessible for easy grasping by an operator of the tractor-trailer. The inboard end of handle  42  is pivotally attached to an arm or a lever  43 , which in turn is pivotally attached to a pair of arms  44  which extend in opposite outboard directions from lever  43 . Lever  43  further is attached to an elongated, longitudinally extending pivot rod  45  which passes rearwardly through a plurality of aligned openings  46  formed in cross members  22 . The rear end of pivot rod  45  remote from lever  43  similarly is attached to a remote lever  47 , which in turn is pivotally attached to a pair of arms  48  which extend in opposite outboard directions from the remote lever. The outboard end of each one of arms  44 ,  48  is bent ( FIG. 5 ) and is pivotally attached to the inboard end of a prior art locking pin  49 .  
         [0042]     The inboard end of each prior art locking pin  49  is slidably mounted ( FIG. 5 ) in an opening  50  formed in a bracket  51  which is attached by suitable means such as welding to a respective one of cross members  22 A and  22 F. The enlarged cylindrical outboard end of each locking pin  49  passes through a generally round or circular-shaped opening  52  formed in a respective one of main members  21 . When it is desired to lock slider tandem  70  in a selected position relative to trailer body  40 , the slider box main member openings  52  are aligned with selected ones of a plurality of correspondingly sized openings  53  formed in Z-shaped rails  41  of the trailer body. Each locking pin  49  automatically passes through the selected aligned openings  52 , 53  since the locking pin is biased in an outboard direction by a coil spring  54  captured between bracket  51  and the enlarged outboard end of locking pin  49 . When it is again desired by the operator of the tractor-trailer to move slider tandem  70  beneath trailer body  40 , the parking brake of the trailer is engaged, handle  42  is pulled in an outboard direction to retract pins  49  out of trailer rail openings  53  and against the bias of springs  54 , and slider  20  is moved longitudinally along Z-shaped rails  41  until slider box main member openings  52  align with selected trailer rail openings  53  and prior art locking pins  49  engage therewith as described hereinabove for maximizing load distribution.  
         [0043]     Due in part to the aforementioned problems associated with the use of prior art locking pins, including gyrations of slider tandem  70  due to the relatively sloppy fit of locking pins  49  in aligned openings  52 , 53  as the vehicle travels over-the-road, the above-described prior art Z-shaped rails  41  and cross sills  55  of floor structure  61  are formed of steel. Forming such components from steel enables trailer body  40  and Z-shaped rails  41  to withstand such gyrations, but using the steel material increases the overall weight of the trailer which is undesirable and inefficient.  
         [0044]     Moreover, as is best shown in  FIGS. 4 and 5  and especially  FIG. 6 , it can be appreciated that prior art locking pins  49  can become jammed during routine operation of retractable pin mechanism  24 . More particularly, shear forces are caused to operate on pins  49  when they are in the extended or locked position, because of slight movement of prior art slider box  20  and its main members  21  relative to trailer body  40  and its Z-shaped rails  41 , causing misalignment as indicated by arrows M in  FIG. 6 . Specifically, this movement results in slight misalignment between slider box openings  52  and trailer body rail openings  53 . The misalignment in turn causes contact pressure points between each pin  49  and its respective trailer body rail opening  53 , slider box main member opening  52 , and bracket opening  50 , as represented by arrows PP. The contact point pressure in turn causes the shear forces which operate on the pin perpendicular to the longitudinal axis of each pin to resist retraction of the pins to the unlocked position.  
         [0045]     The mechanical advantage enjoyed by the manual operator of retractable pin mechanism  24  must be greater than the combined shear forces acting on jammed pins  49  in order to retract or free the pins to the unlocked position shown in  FIG. 5 . However, the mechanical advantage often is inadequate, and so the operator must personally exert additional physical force to free the jammed pins. This type of overexertion by the operator can cause personal injury and/or damage to retractable pin mechanism  24 . Specifically, a typical method of attempting to release prior art jammed pins is for the operator to rock trailer body  40  fore and aft, while an assistant operates the retractable pin mechanism. The rocking motion briefly realigns misaligned openings  52 , 53  so that the assistant can retract the pins during the period of realignment. Also, add-on devices designed to release jammed pins, such as a prior art quick-release device which allows the operator to maneuver the trailer while the quick-release device automatically frees the jammed pins, eliminates the need for another person to operate the retractable pin mechanism. While the quick-release device does make freeing jammed pins a one-person job, it still requires the operator to rock the trailer which is time consuming, can cause damage to the retractable pin mechanism, and adds weight and additional installation and maintenance expense.  
         [0046]     The improved locking mechanism for a slider box of the present invention eliminates the undesirable stresses and jamming associated with prior art retractable pin mechanism  24  by replacing the mechanism with the clamping arm locking mechanism of the present invention, thereby permitting the use of lighter materials, such as aluminum, to construct the trailer body rails and cross sills and enhancing the advantages of an aluminum slider box.  
         [0047]     The improved locking mechanism for a slider box of a tractor-trailer of the present invention is indicated generally at  80  and is shown in  FIGS. 7 through 11 . The environment in which locking mechanism  80  of the present invention operates is generally identical to that described above for prior art retractable pin mechanism  24 , with any differences in structure and operation between the environment adapted for use with the present invention and that of the prior art being particularly described below. Inasmuch as a pair of clamping arm mechanisms  80  are utilized on a slider box, but are generally identical in structure and operation, only one will be described herein.  
         [0048]     Specifically, clamping arm mechanism  80  ( FIGS. 7A and 7B ) includes a housing  90 , a coil spring  82 , an arm base  100 , a pair of front and rear clamping arms  110 A,B, respectively, an air spring  120 , a locking mechanism  130 , and an up-stop  160  ( FIG. 9 ). Unless otherwise indicated, all components of clamping arm mechanism  80  are made of a metal such as steel, aluminum, or other suitable material.  
         [0049]     Housing  90  further includes a generally longitudinally extending elongated U-shaped base  91 , an inboard plate  92  and an outboard plate  96 , which combine to form a generally rectangular-shaped box-like structure having a top opening  99 . Inboard plate  92  and outboard plate  96  are vertically disposed in spaced-apart parallel relationship, abut the inboard and outboard edges, respectively, of U-shaped base  91 , and are removably connected to each other and to slider box main member  21  by pins or bolts  105  ( FIG. 8B ) that pass through outer metal sleeves  98 , as described more fully below. U-shaped base  91  includes a first vertically-disposed wall  94 A, a second vertical wall  94 B and a horizontal bottom wall  95 , and is positioned between abutting inboard and outboard plates  92 , 96 , respectively, as illustrated in  FIG. 7A , to complete the structure of housing  90 . U-shaped base  91  further includes an opening  91 A for the receipt of a lower end of air spring  120  and an aperture  91 B for receipt of a lower end of coil spring  82  ( FIG. 7B ). More specifically, coil spring  82  is vertically disposed and is captured between the bottom wall  95  of U-shaped base  91  and the lowermost portion of arm base  100 , and is in biased tension in a generally vertical direction so as to assist in the lowering of arm base  100  relative to bottom wall  95 , as will be described in greater detail hereinbelow. Inboard plate  92  is formed with a plurality of openings  93  for receipt of tabs  135 , as described more fully below and illustrated in  FIG. 9 . Similarly, outboard plate  96  is formed with a plurality of openings  97  for receipt of tabs  135  ( FIG. 7A ), also as described more fully below. Housing  90  serves to shield coil spring  82 , air spring  120 , locking mechanism  130  and, when clamping arm mechanism  80  is in the unlocked position, arm base  100 , from debris and the elements, such as rain and snow, and also serves as a mounting structure for the coil spring, air spring, locking mechanism and clamping arm mechanism.  
         [0050]     As best shown in  FIG. 7B , locking mechanism  130  includes a dividing plate  131 , an actuator  132 , a locking plate  133  and a coil spring  136 . More particularly, dividing plate  131  is a flat plate and is generally perpendicular to, abuts and extends vertically upwardly from bottom wall  95  of U-shaped base  91 , to which it is fixedly attached by any suitable means such as welds, between air spring  120  and actuator  132 . Actuator  132  is positioned horizontally between and is fixedly attached at its respective ends to dividing plate  131  and locking plate  133  by any suitable means. Actuator  132  preferably is an air spring, but could be any device or mechanism capable of moving locking plate  133  in the direction of and against the bias of coil spring  136  until the coil spring is compressed and the locking plate is disengaged from the lowermost portion of arm base  100  (see  FIG. 10 ). Locking plate  133  is an inverted generally L-shaped plate having a top horizontal flange  134  and a lower vertical portion  137 . The plurality of tabs  135  protrude outwardly from locking plate lower portion  137  in both the inboard and outboard directions and perpendicular to inboard and outboard housing plates  92 , 96 , respectively. When housing  90  is fully assembled, tabs  135  extend through inboard housing plate openings  93  and outboard housing plate openings  97 . When in the locked position, as shown in  FIG. 11 , locking plate  133  is generally perpendicular to, and extends vertically upwardly from, bottom wall  95  of U-shaped base  91 . Coil spring  136  is captured between and fixedly attached to locking plate lower portion  137  and second wall  94 B of U-shaped base  91 , and is in biased compression against the locking plate lower portion. The operation of locking mechanism  130  also will be described in greater detail hereinbelow.  
         [0051]     Arm base  100  ( FIGS. 7A and 7B ) is also a generally U-shaped structure having a generally horizontal bottom wall  101 , an inboard generally vertical side wall  102  and an outboard generally vertical side wall  104 , and can be formed, extruded, or fabricated without affecting the overall concept of the invention. Arm base bottom wall  101  is fixedly attached to the upper portion of air spring  120  by any suitable means, and further includes a spring aperture  106  for receipt of the upper portion of coil spring  82 . As more fully described below, as airspring  120  is inflated it overcomes the tension in coil spring  82  and elevates arm base  100  in the direction of trailer body rails  41 ′.  
         [0052]     Inboard side wall  102  and outboard side wall  104  each is formed with a pair of longitudinally spaced-apart openings, with the inboard openings not shown and the outboard openings indicated at  104 A,B, for receipt of a base pin  107  therein. The inboard openings and outboard openings  104 A,B each generally is a longitudinally elongated opening to permit its respective base pin  107  to move longitudinally therein during the operation of clamping arm mechanism  80 , as described more fully below. Arm base  100  preferably is extruded, but also can be formed or fabricated without affecting the overall concept of the invention.  
         [0053]     Each one of front and rear clamping arms  110 A,B, respectively, further includes an upper arm  112 A,B and a lower arm  116 A,B as best shown in  FIGS. 7A and 7B . More particularly, front lower arm  116 A includes a pair of generally L-shaped front plates  117 A which are disposed in transversely-spaced parallel relationship to one another and are pivotally attached to arm base  100  by base pin  107 . Similarly, rear lower arm  116 B includes a pair of generally L-shaped rear plates  117 B which are also disposed in transversely-spaced parallel relationship to one another and are also pivotally attached to arm base  100  by base pin  107 . Each of front L-shaped plates  117 A include a generally rounded rearward extension  119 . A spacer  118  formed with a front opening  300  and a rear opening (not shown), is disposed between the front and rear pairs of spaced-apart L-shaped plates  117 A,B, respectively, which in turn are disposed between the inboard and outboard side walls  102 , 104 , respectively, of arm base  100 . More specifically, the rearward end of spacer  118  is disposed between and fixedly attached to rear L-shaped plates  117 B. The forward end of spacer  118  is disposed between and pivotally attached to the rearward extensions  119  of front L-shaped plates  117 A by a pin (not shown), or other suitable means of pivotal attachment. The pivotal connection of the forward end of spacer  118  to front L-shaped plates  117 A in conjunction with the fixed connection of the rearward end of the spacer to rear L-shaped plates  117 B forces front and rear clamping arms  110 A,B, respectively, to clamp in unison with one another. Front L-shaped plates  117 A each is formed with an opening (not shown) which is aligned with a selected pair of the aligned inboard openings (not shown) and outboard openings  104 A formed in side walls  102 , 104 , respectively, of arm base  100  for the receipt of base pin  107  in the aligned openings. Rear L-shaped plates  117 B each is formed with an opening (not shown) which is aligned with a selected pair of the aligned inboard openings (not shown) and outboard openings  104 B formed in side walls  102 , 104 , respectively, of arm base  100 , and the rear opening of spacer  118  (not shown) for the receipt of base pin  107  in the aligned openings. More particularly, each one of front and rear lower arms  116 A,B, respectively, is pivotally mounted on arm base  100  by insertion of base pin  107  in the inboard direction through outboard side wall opening  104 A,B, and the aligned openings formed in the outboardmost L-shaped plate  117 A,B, the inboard most L-shaped plate  117 A,B, and the inboard side wall opening (not shown). Alternatively, base pin  107  can be inserted through the same components in the outboard direction without affecting the overall concept of the invention. Once base pin  107  is in place it can be secured by any suitable means such as a nut (not shown).  
         [0054]     Each one of front and rear upper arms  112 A,B in turn is pivotally connected to a respective one of lower arms  116 A,B by arm pin  140 , as best illustrated in  FIGS. 7A  and B. Each one of upper arms  112  is a generally S-shaped plate formed with an opening (not shown) for receipt of arm pin  140 . Each one of upper arms  112  further includes a mounting tube  115  that is perpendicular to, and extends outwardly from, the upper arm in both the inboard and outboard directions. Mounting tube  115  preferably is cylindrical in shape and is hollow for receipt of a fastener  122  for rotatably mounting clamping arm mechanism  80  to slider box main members  21 ′, as best shown in  FIGS. 8A and 8B , and described more fully below.  
         [0055]     Having described the structure of clamping arm mechanism  80 , the preferred location of clamping arm mechanism  80  on slider box  20  will now be described. To accommodate and mount clamping arm mechanism  80  of the present invention, main members  21  and Z-shaped rails  41  of prior art slider box  20  must also be modified as described below. Inasmuch as each one of the pair of clamping arm mechanisms  80  mounted on respective ones of slider box main members  21 ′ of the present invention is generally identical in structure and operation, only one of the mechanisms and its attachment to its respective main member now will be described. In the preferred embodiment of the present invention, main member  21 ′ is an inverted generally Y-shaped structure defining a continuous channel  215  ( FIG. 8B ). More particularly, main member  21 ′ includes an inboard leg  211 , an outboard leg  212  and a top mounting structure  213 . Main member  21 ′ can be formed, fabricated, or extruded without affecting the overall concept of the present invention, and preferably is extruded of a light material such as aluminum. Top mounting structure  213  has a generally U- 5  shaped profile with a flat, generally vertical upper portion  216  on the inboard side and an inboardly facing, groove-defining upper portion  217  on the outboard side for engaging trailer body rail  41 ′ of the present invention, as best illustrated in  FIG. 8B . More particularly, rail  41 ′ of the present invention is extruded and includes a pair of transversely spaced-apart, generally Z-shaped members  411 A,B. Z-shaped member  411 A is located on the inboard side of rail  41 ′, and Z-shaped member  411 B is located on the outboard side of rail  41 ′ and further includes an outboardly-extending tongue portion  413  for engaging groove-defining upper portion  217  of main member  21 ′ as illustrated in  FIG. 8B . The tongue and groove relationship of groove-defining upper portion  217  and tongue portion  413  permits movement of main members  21 ′ and slider tandem  70  in the longitudinal direction relative to trailer body rails  41 ′, but prevents the slider box from disengaging from the rails, when clamping arm mechanism  80  is in the unlocked position. In the preferred embodiment of the present invention, a low friction strip  170  is attached to portions of the uppermost surface of top mounting structure  213  and the inboard side of upper portion  216  with interlocking dovetails, and extends generally the entire length of the top mounting structure. Strip  170  is formed of any suitable low friction material, such as ultra-high molecular weight polyethylene, and assists in enabling generally smooth movement of slider box  20  along trailer body rails  41 ′ and, unlike the prior art, generally prevents sticking along the sides of the rails.  
         [0056]     Clamping arm mechanism  80  preferably is mounted on main member  21 ′ adjacent to and forwardly of rear hanger  23 B and between inboard leg  211  and outboard leg  212 , as best illustrated in  FIGS. 8A and 8B , and described more fully below. An up-stop  160  ( FIG. 9 ) also is mounted with a bolt  161  on main member  21 ′ between upper arms  112  of mechanism  80  and between inboard leg  211  and outboard leg  212  of main member  21 ′. More particularly, up-stop  160  preferably is formed of aluminum or steel and is mounted on the lowermost surface of and depends from top mounting structure  213 , by any suitable means such as welding or with fasteners, and preferably with a bolt  161 . Upstop  160  prevents the further upward movement of arm base  100  when clamping arm mechanism  80  is in the locked position ( FIG. 11 ).  
         [0057]     As previously described, clamping arm mechanism  80  is mounted on main member  21 ′, between inboard leg  211  and outboard leg  212 , by fasteners  122 , each one of which extends through respective aligned openings (not shown) formed in the inboard leg, mounting tube  115  of each one of upper arms  112 , and the outboard leg; and by pins  105  which extend through outer metal sleeves  98  of housing  90 , inboard leg  211 , and outboard leg  212 . Fastener  122  preferably is a threaded or shoulder bolt, but could also be a rivet or a pin without affecting the overall concept of the present invention. A second clamping arm mechanism  80  and up-stop  160  are mounted on the opposite main member  21 ′ at the same location, and in the same manner, so that the two clamping arm mechanisms  80  are in spaced-apart parallel relationship to one another. It also is contemplated that clamping arm mechanisms  80  can be located at other locations along main members  21 ′ without affecting the overall concept of the present invention.  
         [0058]     Having described the structure and location of the present invention, the operation of clamping arm mechanism  80  in the preferred embodiment of the present invention now will be described. As slider box  20  is being selectively slidably positioned beneath trailer body  40 , clamping arm mechanism  80  is in the unlocked position as best illustrated by  FIG. 9 . When clamping arm mechanism  80  is in the unlocked position, air spring  120  is fully deflated and arm base  100  is in its lowermost position due to the biased tension in coil spring  82  which pulls the arm base down toward bottom wall  95  of U-shaped base  91 . Additionally, when clamping arm mechanism  80  is in the unlocked position, actuator  132  is fully inflated, which clears locking plate  133  from contact with bottom plate  101  of arm base  100  by overcoming the bias in coil spring  136 .  
         [0059]     After slider box  20  is positioned in its desired location relative to trailer body  40 , the operator will activate the clamping arm mechanism  80  of the present invention by any suitable means such as by flipping a switch (not shown) or turning a key (also not shown). Once clamping arm mechanism  80  is activated, air spring  120  begins to inflate and actuator  132  begins to deflate. As air spring  120  inflates, it overcomes the biased tension in coil spring  82  and elevates arm base  100  in an upward direction toward rail  41 ′, as best shown in  FIG. 10 . For the convenience of the reader, and looking at clamping arm mechanism  80  shown in the foreground in  FIG. 8A , from the outboard direction in  FIGS. 9 through 11 , only the movement of the front clamping arm  110 A will be described, though it is understood that the rear clamping arm  110 B moves in the same manner, only in an opposite pivotal direction. As arm base  100  and front lower arm  116 A move upward in the direction of rail  41 ′, the lower arm rotates in a counterclockwise direction which, by virtue of its connection to front upper arm  112 A by arm pin  140 , in turn causes front upper arm  112 A to pivot about fastener  122  in a clockwise direction as it moves through a selected one of a plurality of openings  214  formed in main member top mounting structure  213 , and further through an opening  162  formed in rail  41 ′, as best illustrated in  FIGS. 8B and 10 . Of course, it is understood that a plurality of pairs of openings  162  are formed along rail  41 ′ for receiving upper arms  112 , to allow for a large number of possible positions for slider box  20  beneath trailer body  40 . Upon full inflation of air spring  120 , a hook portion  114  of front upper arm  112 A is in mating contact with a top surface of rail  41 ′ as best shown in  FIG. 11 . As an important feature of the present invention, clamping arm mechanism  80  is designed so that upper arms  112  come into contact with the top surface of rail  41 ′ at approximately the same time as up stop  160  comes into contact with lower arms  116 A,B as shown in  FIG. 11 , thereby securely attaching clamping arm mechanism  80  and slider box  20  to rail  41 ′.  
         [0060]     As yet another important feature of the present invention, actuator  132  is deflated simultaneously with the inflation of air spring  120  and elevation of arm base  100 . As actuator  132  is deflated, the biased tension of coil spring  136  causes locking plate  133  to move in the direction of dividing plate  131  to the upright position, and the top portion  134  of locking plate  133  mates with the lowermost surface of bottom plate  101  of arm base  100 , as shown in  FIG. 11 . When in the locked position, locking plate  133  prevents the downward movement of arm base  100 , thereby further securing the attachment of slider box  20  to rails  41 ′.  
         [0061]     Similarly, when the operator desires to reposition slider box  20 , or otherwise disengage clamping arm mechanism  80 , the operator disengages clamping arm mechanism  80  by any suitable means such as flipping a switch (not shown) or turning a key (also not shown), which in turn causes actuator  132  to inflate and disengage locking plate  133  from its contact with bottom plate  101  of arm base  100  by pushing locking plate  133  in the direction of and against the bias of coil spring  136 . Once locking plate  133  is disengaged from arm base  100 , air spring  120  is deflated which in turn permits the biased tension in coil spring  82  to pull arm base  100  downward in the direction of bottom wall  95 . As arm base  100  is being lowered, front lower arm  116 A pivots in a clockwise direction which, by virtue of its connection to front upper arm  112 A by arm pin  140 , in turn causes front upper arm  112 A to pivot about fastener  122  in a counterclockwise direction as it moves downward through opening  162  in rail  41 ′ and corresponding aligned opening  214  in main member  21 ′. It is understood that the same movements are simultaneously occurring on the other clamping arms of mechanism  80  nearest rear hanger  23 B, only in the opposite pivotal direction. More specifically, as arm base  100  is lowered, rear lower arm  116 B nearest rear hanger  23 B pivots in a counterclockwise direction which, by virtue of its connection to rear upper arm  112 B by arm pin  140 , in turn causes rear upper arm  112 B to pivot about fastener  122  in a clockwise direction as it moves downward through rail opening  162  and main member opening  214 . Moreover, unlike prior art pins which had to be closely aligned to be engaged, hooks  114  have ample clearance within openings  162  and  214  to allow for slight misalignment, and are much less likely to become jammed.  
         [0062]     In accordance with another important feature of the present invention, the operator of the vehicle can easily determine whether clamping arm mechanism  80 , and in particular locking mechanism  130 , are in the locked position by viewing the location of tabs  135  within openings  97  in outboard plate  96 . More specifically, when the operator is viewing clamping arm mechanism  80  in the foreground of  FIG. 8A , if tabs  135  are in the leftmost or frontwardmost portion of opening  97 , as shown in  FIG. 7A , the operator will know that clamping arm mechanism  80  is in the locked position and it is safe to operate the vehicle. If, however, tabs  135  are on the rightmost or rearwardmost side, or any location other than the leftmost portion of opening  97 , the operator will know that clamping arm mechanism  80  is in the unlocked position. Similarly, when the operator is viewing passenger-side clamping arm mechanism  80  in the background of  FIG. 8A  also from the outboard position, if tabs  135  are in the rightmost or frontwardmost portion of opening  97 , the operator will know that clamping arm mechanism  80  is in the locked position and it is safe to operate the vehicle. If, however, tabs  135  are on the leftmost or rearwardmost side, or any location other than the rightmost portion of opening  97 , the operator will know that clamping arm mechanism  80  is in the unlocked position.  
         [0063]     As yet another important feature of the present invention, when clamping arm mechanism  80  is in the locked position, upper arms  112  and hooks  114  are in secure contact with rails  41 ′ and slider box main members  21 ′, thereby eliminating the banging of the slider box against floor structure  61  of trailer body  40 , and the stresses associated therewith, which is common in the prior art, and thereby permitting the use of lighter materials such as aluminum. More particularly, when in the locked position, hooks  114  of clamping arm mechanism  80  exert a fore-aft clamping force F/A ( FIG. 11 ) on their respective trailer body rail  41 ′, causing the trailer body rail to be clamped in a secure position to its respective slider box main member  21 ′ in the fore-aft direction, and thereby reducing, minimizing, or eliminating unwanted movement and gyrations. More specifically, and depending on the orientation of clamping arm mechanism  80  on its respective slider box main member  21 ′, each one of upper arms  112  and its associated hook  114  exert a force in the fore direction against trailer body rail  41 ′ and its associated slider box main member, and the other upper arm and its associated hook exerts a force in the aft direction against the trailer body rail and slider box main member. Additionally, when clamping arm mechanism  80  is in the locked position, hooks  114  of the clamping arm mechanism also exert a vertical clamping force V ( FIG. 11 ) on their respective trailer body rail  41 ′, thereby causing the trailer body rail to be clamped in a secure position to its respective slider box main member  21 ′ in a vertical direction, and further reducing, minimizing, or eliminating unwanted movement and gyrations. More specifically, each one of upper arms  112  and its associated hook  114  exert a force in the vertical direction against trailer body rail  41 ′ and its associated slider box main member  21 ′. It is understood, although both fore-aft and vertical forces are preferred, that the manner in which upper arms  112  and associated hooks  114  engage trailer body rails  41 ′ and main members  21 ′ can be adjusted so that only vertical forces or only fore-aft forces are applied without affecting the overall concept.  
         [0064]     Therefore, it can be seen that clamping arm mechanism  80  of the present invention overcomes the disadvantages of the prior art retractable pin mechanisms such as mechanism  24 , and permits the use of a lightweight, economical slider box that is capable of being easily and securely repositioned relative to the trailer body, and that is relatively easy to manufacture. Clamping arm mechanism  80  also allows for use of aluminum rails  41 ′, rather than heavier steel, in certain applications, which also contributes to weight savings. Mechanism  80  may also enable use of lighter weight materials on the trailer body itself in certain applications, such as aluminum for cross sills  55  in van-type trailers. The clamping arm mechanism of the present invention has a wide range of potential applications including, without limitation, virtually any application that contemplates the use of a slider box.  
         [0065]     The present invention has been described with reference to a specific embodiment. It shall be understood that this illustration is by way of example and not by way of limitation. Other clamping mechanisms that include different structural components and/or clamping means, including those utilizing: hydraulics, pneumatics, or electrical solenoids, are also contemplated by the present invention. Furthermore, the use of a reduced number or an increased number of clamping mechanisms on the slider box, for example, a single clamping arm mechanism or three, four or more clamping arm mechanisms, as well as different locations for placement of the clamping arm mechanism on the slider box, or even on the trailer body, are also contemplated by the present invention. Further potential modifications and alterations will occur to others upon a reading and understanding of this disclosure, and it is understood that the invention includes all such modifications and alterations and equivalents thereof.  
         [0066]     Accordingly, the improved locking mechanism for a slider box of a tractor-trailer is simplified, provides an effective, safe, inexpensive, and efficient structure which achieves all the enumerated objectives, provides for eliminating difficulties encountered with prior art retractable pin locking mechanisms, and solves problems and obtains new results in the art.  
         [0067]     In the foregoing description, certain terms have been used for brevity, clearness and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed.  
         [0068]     Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described.  
         [0069]     Having now described the features, discoveries and principles of the invention, the manner in which the improved locking mechanism for a slider box is construed, arranged and used, the characteristics of the construction and arrangement, and the advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts and combinations are set forth in the appended claims.