Abstract:
A tow truck carrier with sub frame rails above the carrier chassis frame rails that also reduces platform height thereby presenting a lower center of gravity. Sub frame rails of rectangular steel tubing with the wider dimension of the tubing are used in a horizontal, low profile orientation, with the direct attachment of the lift cylinder ends to the sub frame rails or to a cross beam to lower the platform. The sub frame rails form a descending ladder frame with cross members attached via brackets so that they are lowered into the recess between the chassis side frame. A lifting bracket is welded to the underside of each sub frame rail underneath the overhang and adjacent to the chassis frame to accept the end of a lifting cylinder rod while leaving some space for sliding engagement of a platform beam which engages three edges of the sub frame rail.

Description:
FIELD OF THE INVENTION 
     The present invention relates to tow truck carriers with lowered platform height and lower center of gravity. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to tilting platform carriers in which the platform also slides in relation to the vehicle frame. These carriers are most often used to pick up and carry disabled vehicles transporting them to repair centers; they may also be used to transport industrial and agricultural equipment. 
     The basic motion of the platform relative to the truck frame is well illustrated in U.S. Pat. No. 3,485,400 of Pewthers.  FIGS. 1-3  show the sequence of starting with the platform in a horizontal forward transporting position, to sliding the platform rearward, and finally raising the front of the platform with a hydraulic cylinder pivoting its distal overhanging end to ground contact. While these basic moves do not equate to modern carriers with additional disabled vehicle handling equipment, other patents in the prior art do relate to them. 
     Examples of patents relating to carriers of the present invention include the following: the Car Carrier of Lapiolahti (U.S. Pat. No. 4,750,856), Disabled Car Carrier Vehicle of Moore et al. (U.S. Pat. No. 4,756,658), Vehicle Carrier With Wheel Lift of Nespor (U.S. Pat. No. 5,061,147), and Wrecker Truck With Sliding Deck of Pinkston (U.S. Pat. No. 5,871,328). None of these prior art patents relate specifically to the objective of lowering the platform height. 
     The patent of Jaeger et al. entitled Low Center Of Gravity Carrier (U.S. Pat. No. 8,348,586) does meet this objective by moving the sub frame rails (which support the tilting platform and permit its sliding action) from above the vehicle frame rails sideways to between the chassis frame rails and the rear wheels. The bottoms of these sub frame rails are also moved down below the top surface of the adjacent chassis frame to reduce platform height. 
     The prior art does not reveal a carrier with sub frame rails above the carrier chassis frame rails that also reduces platform height thereby offering the associated advantages of lower center of gravity for better dynamic road handling, shallower load angle, and an increase in maximum payload height. 
     SUMMARY OF THE INVENTION 
     As opposed to the prior art, the present invention uses sub frame rails of rectangular steel tubing with the wider dimension of the tubing used in a horizontal (low profile) orientation. By itself, this change lowers the platform several inches. Other changes such as the direct attachment of one or more lift cylinder ends to the sub frame rails as opposed to using a lifting crossbar underneath the sub frame rails account for further lowering. 
     The sub frame rails form a true ladder frame with cross members attached via brackets so that they are lowered into the recess between the chassis side frame. The space between the top surface of the sub frame rails and the tops of the cross members is well utilized to house both the platform sliding cylinder as well as the carrier chain, such as an Igus Energy Chain™, guiding and protecting hydraulic hoses and cables. 
     The sub frame rails are wider than the top surface of the chassis frame; they are aligned so that their inner edge is aligned with the inner edge of the chassis frame members and their outer edges overhang by a few inches. A lifting bracket is welded to the underside of each sub frame rail underneath the overhang and adjacent to the chassis frame to accept the end of a lifting cylinder rod while leaving some space for sliding engagement of a platform beam which engages three edges of the sub frame rail. This direct bracket attachment also minimizes the height of the platform surface. When the platform is in the horizontal (transporting) position, the sub frame can actually rest atop the carrier chassis frame side members with no wasted space between. While the preferred embodiment has a pair of lift cylinders, it is noted that one or more lift cylinders can be employed in lifting the vehicle or other load supporting platform. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can best be understood in connection with the accompanying drawings. It is noted that the invention is not limited to the precise embodiments shown in the drawings, in which: 
         FIGS. 1-3  are schematic rear elevations of carriers comparing and contrasting the elements directly affecting the platform height while in the horizontal position. All three figures are assumed to have the same carrier chassis frame position and rear axle; 
         FIG. 1  is a rear elevation of a prior art carrier with a normal (higher) platform height; 
         FIG. 2  is a rear elevation of a prior art carrier which achieves a lower platform height using techniques different from the present invention; 
         FIG. 3  is a rear elevation of a lower platform height carrier of the present invention; 
         FIG. 3A  is an enlarged detail of part of  FIG. 3 . 
         FIG. 3B  is an enlarged detail of an alternate embodiment for  FIG. 3 . 
         FIG. 3C  is an enlarged detail view of a further alternate embodiment for the rear view of  FIG. 3 . 
         FIG. 3D  is an enlarged detail view of another further alternate embodiment for the rear view of  FIG. 3 . 
         FIG. 4  is a perspective detail of a normal (higher) platform height prior art carrier showing one of the two sub frame rails horizontal atop a lifting crossbar atop the chassis frame; 
         FIG. 5  is a perspective detail of the same region of a prior art carrier as in  FIG. 4 , but the sub frame rail is now raised by the hydraulic cylinder; 
         FIG. 6  is a perspective detail of current invention showing the outer edge of a sub frame rail overhanging the outer edge of a chassis frame, and also showing the attached wear strip on top; 
         FIG. 7  is a perspective detail showing a slightly raised sub frame rail, a hydraulic lift cylinder, and a cantilevered cylinder top bracket welded to the overhanging underside of one of the sub frame rails; 
         FIG. 8  is an end perspective view of the two sub frame rails during assembly showing the cross members attached via drop down brackets forming a true ladder frame; 
         FIG. 9  is a perspective detail showing part of the carrier chain for hydraulic hoses as well as part of the platform sliding hydraulic cylinder; both share the space between and under the two sub frame rails above the cross members; 
         FIG. 10  is a perspective view of the platform with vehicle on top, platform at an angle in the rearward position, and hydraulic lifting cylinders extended; and, 
         FIG. 11  is a perspective side view of a carrier platform in a horizontal position with vehicle in transporting position atop platform; platform height is indicated. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The salient features dictating differences in platform height and means by which they are achieved is illustrated by the various figures that follow. Obvious means such as attempts to use smaller wheels or high strength steel to reduce platform thickness or height of carrier chassis side frame members will not be discussed as the economics dictate that the starting point for such vehicle carriers as these is a “standard” flatbed truck chassis as supplied by a major manufacturer. 
       FIGS. 1-3  compare the differences in structural elements used in two prior art carriers as compared and contrasted with those of the present invention. These are mere rear view schematic illustrations leaving out essential items such as cross members tying together sub frame rails to clarify the images of elements directly involved in platform height determination. The same truck chassis with rear axle  3  and side frame members  4  is assumed in each case. 
       FIG. 1  shows a prior art carrier  2  using two upright sub frame rails  10  which lift platform  6  tilting it down toward the rear for loading and unloading. Hydraulic cylinders  18  are the lift cylinders lifting the front of sub frame  10  rails through lifting bar  12  which is attached by brackets  14 . Rails  10  have a wear strip attached to the top surface to provide a low friction sliding surface which interacts with I-beams  16  enclosing three sides of sub frame rails  10 . I-beams  16  are attached longitudinally to the underside of platform  6  and provide a sliding surface. It is noted that brackets  14  must provide clearance between lifting bar  12  and the lower flange of I-beams  16 . While these parts work well in providing a secure attachment and proper articulation of platform  6  relative to carrier  2 , the platform height Hh is not as low as can be achieved. More details are shown in  FIGS. 4 and 5 . 
     For example,  FIG. 4  shows sub frame in horizontal position with lifting bar  12  resting on frame  4 . Hose carrier chain  36  is shown housed between sub frame rails  10 . 
       FIG. 5  shows sub frame raised revealing attachment of I-beam  16  to underside of the platform; lifting bar bracket  14  shows spacing between bar  12  and sub frame rail  10  to provide clearance for the lower flange of I-beam  16 . 
       FIG. 2  shows the prior art carrier  5  which moves the upright sub frame rails  20  outward to the side of carrier frame  4  and lower with their lower surface below the top surface of frame  4  members. Some inner side space of sub frame beams  20  must be reserved above the top of chassis frame members  4  to attach cross members (not shown in this view); this limits the amount by which rails  20  can be lowered. U-beams  22  attached longitudinally to the underside of platform  6  enclose three sides of sub frame beams  20  providing a sliding engagement. It is noted that the crowding between frame  4  and the rear wheels almost dictates moving hydraulic lift cylinders  24  to a center position as shown between frame  4  members. The platform height Hi is reduced several inches as compared to carrier  2  of  FIG. 1 . 
       FIG. 3  shows the lowered platform height carrier  7  of this invention. It uses a pair of sub frame rails  30  with their larger crossection dimension in the horizontal (low profile) orientation atop chassis frame members  4 . Rails  30  are aligned with the inner edge of frame  4  members on the inside, but preferably overhang the top of frame  4  on the opposite side. This overhang provides space for direct attachment of cantilevered brackets for hydraulic lift cylinders  34  and also for engagement slider elements, such as, for example, provided on three sides of U-beams  32  attached longitudinally to the underside of platform  6 , thereby locating platform  6  onto the rails  30  in a sliding assembly. U-beams  32  cradle an outer edge of sub-frame rails  30  on three sides in a spaced apart relationship, so that low friction wear strip  40 , which is attached to the outer top edge of sub-frame rails  30 , can provide a sliding surface for the top edge of U-beams  32 . As also shown in  FIG. 3 , platform  6  has a height H L , which is several inches lower than the height Hh of the prior art of  FIG. 1 . 
       FIG. 3A  is an enlarged detail of the right side sub frame and associated items shown in  FIG. 3 . It is easier to understand the arrangement permitting resting of sub frame rail  30  on chassis frame  4  while functioning as required. It is noted that cross members  44  are dropped down to a space below the top of chassis frame member  4  via welded drop brackets  46  (this is also shown in the view in  FIG. 8 ). Removable low friction wear strip  40  is attached to the top surface of sub frame rail  30  adjacent the outer edge thereof, so that low friction wear strip  40  provides a sliding surface under top flange of U-beam  32 , so that vehicle towing support platform  6  and U-beam  32  attached thereto, can slide on low friction wear strips  40  and sub-frame rails  30  during towing operations. Cantilevered cylinder bracket  42  is welded to the underside of rail  30  adjacent to the side of chassis frame  4 , and is bent outward as shown, for providing clearance sliding space for the lower flange of U-beam  32  to securely engage the lower surface of the end of rail  30  thereby straddling three surfaces of the overhanging rail end. Rod clevis  35  of hydraulic cylinder  34  is pivoted on bracket  42 . The hydraulic cylinder  34  exerts force upward via bracket  42  connected to sub-frame rail  30 , to lift platform  6 , as well as sub-frame rail  30 , connected via drop down bracket  46 , which is connected to cross member  44 , which is connected to a mirror-image assembly on the left side sub-frame (not shown). Cross member  44  insures that the left side assembly acts in unison with the right side assembly shown in  FIG. 3A . 
       FIG. 3B  is an enlarged detail of the lifting portion for the carrier shown in  FIGS. 3 and 3A , except that the lifting force of the hydraulic cylinders  34  is shifted inward of chassis frame rails  4  and is exerted against cross member  44  and drop down brackets  46  connected to sub-frame rails  30 , and, as also shown in  FIG. 3A , sub-frame rails  30  also have removable low friction wear strip  40 , which is attached to the top surface of sub frame rail  30  adjacent the outer edge thereof, so that low friction wear strip  40  also provides a sliding surface under top flange of U-beam  32 , so that vehicle towing support platform  6  and U-beam  32  attached thereto, can slide on low friction wear strips  40  and sub-frame rails  30  during towing operations. As in  FIG. 3A , in  FIG. 3B , cross member  44  insures that the left side assembly acts in unison with the right side assembly shown in  FIG. 3B . In this embodiment of  FIG. 3B , cylinder brackets  43  are welded to the underside of cross member  44 . Use of the lifting assembly as in  FIG. 3B  can be used if the fuel tank is not located between chassis rails  4 , which allows the space then for positioning the lifting cylinders  34  to the inside of chassis frame rails  4 . 
       FIG. 3C  is an enlarged detail view of an alternate embodiment for the rear view of  FIG. 3 , showing left and right sub frames  30  and associated items. Cross member  44  is positioned below the top of chassis frame members  4 , and inside and between the location of the two sets of tires on each side of the towing vehicle, which are shown in  FIG. 3 . As in the embodiment of  FIG. 3B , hydraulic cylinders  34  are placed inward of chassis frame rails  4 . 
     Unlike  FIGS. 3A and 3B , where the U-beam nests over the outside portion of sub frame rail tube  30 , in  FIG. 3C , the respective U-beams  32  of  FIG. 3C  are instead relocated to nest over the inside portion of sub frame rail tube  30 , adjacent to an inner edge thereof. Sub frame rails  30  each have low friction wear strips  40  to provide a sliding surface under a top flange of U-beams  32 , so that vehicle support platform  6  and U-beams  32  attached thereto, can slide on low friction wear strips  40  and sub frame rails  30  during towing operations. Hydraulic cylinders  34  each have a respective pivotable pin clevis  35 , which is attached via cylinder brackets  42  to lift cross member  44 . Cross member  44  is attached to the underside of each sub frame rail tube  30  via welded straight drop down brackets  46 . 
       FIG. 3D  is an enlarged detail view of yet an alternate embodiment for the rear view of  FIG. 3 , showing left and right sub frames  30  and associated items. Cross member  44  is positioned below the top of chassis frame members  4 , and inside and between the location of the two sets of tires on each side of the towing vehicle, which are shown in  FIG. 3 . However in the embodiment of  FIG. 3D , although the sub frame rail tubes  30  are on top of chassis frame members  4 , and not located on the side of chassis frame members  4  between chassis frame members  4  and the wheels of the vehicle, hydraulic cylinders  34  are placed outside of chassis frame rails  4 . 
     Unlike  FIGS. 3A and 3B , where the U-beam nests over the outside portion of sub frame rail tube  30 , in  FIG. 3D , the respective U-beams  32  of  FIG. 3D  are instead relocated to nest over the inside portion of sub frame rail tube  30 , adjacent to an inner edge thereof. Sub frame rails  30  each have low friction wear strips  40  to provide a sliding surface under a top flange of U-beams  32 , so that vehicle support platform  6  and U-beams  32  attached thereto, can slide on low friction wear strips  40  and sub frame rails  30  during towing operations. Hydraulic cylinders  34  each have a respective pivotable pin clevis  35 , which is attached via cylinder brackets  42  being attached by bracket extension  41  to left and right sub frame rail tubes  30  located on top of chassis frame members  4  to lift support platform  6 . Cross member  44  is attached to the underside of each sub frame rail tube  30  via welded straight drop down bracket  46 . 
     It is known that the position of U-beams  32  can be located on either side of sub frame rail tubes  30 , which are located on top of, and not beside chassis frame members  4 , and the position of hydraulic cylinders can be located in other combinations, as long as sub frame rail tubes  30  are located on top of chassis frame members  4 . 
     When sub frame rail tubes  30  are raised, they convey this motion to vehicle support platform  6  through U-beams  32  during lifting of a vehicle for transport. 
       FIG. 6  shows a close-up of the end of sub frame rail  30  resting atop side frame member  4  while overhanging the outer edge of frame  4 . Optional wear strip  40  attached to the top outer edge of sub frame rail may be greased to further lower the coefficient of friction with the mating U-beam  32 , of  FIGS. 3 and 3A , attached to platform  6  as the two surfaces slide. 
       FIG. 7  shows a close-up of the cantilevered bracket  42  that pivotally attached to the clevis  35 , shown in  FIG. 3A , at the end of the rod of lifting hydraulic cylinder  34 . Bracket  42  is welded to sub frame rail  30  on the bottom surface adjacent to the outer side of frame  4 , shown in  FIGS. 3, 3A and 6 , thereby also providing clearance for the lower flange of U-beam  32  to slide by. 
       FIG. 8  shows an end view of the two sub frame rails  30  attached together by cross members  44  via drop down brackets  46  forming a rigid ladder frame. Carrier chassis cross member  52  is also in this view. 
     As shown in assembly  FIG. 9 , the space under platform  6  and above cross members  44 , shown in  FIGS. 3A and 10 , is used to house hydraulic hose carrier chain  48  as well as platform sliding cylinder  50 ; these items must move with the sub frame. 
       FIG. 10  shows a partial view of carrier  7  looking rearward with platform  6  at ground level at the rear and hydraulic lift cylinders  34  extended. This depicts the position for loading or unloading carried vehicle  56 . 
       FIG. 11  shows a side view of the back end of carrier  7  showing carried vehicle  56  on platform  6 . Lowered platform  6  height H L  in this transporting configuration is indicated. 
     In the foregoing description, certain terms and visual depictions are used to illustrate the preferred embodiment. However, no unnecessary limitations are to be construed by the terms used or illustrations depicted, beyond what is shown in the prior art, since the terms and illustrations are exemplary only, and are not meant to limit the scope of the present invention. 
     It is further known that other modifications may be made to the present invention, without departing the scope of the invention, as noted in the appended Claims.