Abstract:
A compact, modular, portable vehicle lifting and holding apparatus comprising either an individual lifting tower assembled from independent components, or one or more pairs of independent lifting tower assemblies interconnected by torsionally stiff support crossmembers, thereby forming a complete apparatus. Each lifting tower assembly is provided with redundant lifting carriage locking features, lifting means comprising a cable pulling device of conventional type, and further provided with ground traversing means whereby said complete apparatus is capable of ambulatory motion while supporting a load. Said apparatus includes means to engage and elevate a vehicle body independent of its frame, or elevate an entire vehicle or part thereof in a horizontal position relative to the level surface supporting said apparatus, thereby facilitating restoration, repair, and customization processes. Said complete apparatus has dimensions allowing operation within the confines of a conventional one-car residential garage, and disassembles completely for compact storage or transport.

Description:
REFERENCES CITED  
       [0001]    
       
         
               
               
               
               
             
           
               
                   
               
               
                   
               
             
             
               
                 U.S. Pat. No. 3,999,739 
                 Vick, et al. 
                 May 19, 1975 
                 254/409 
               
               
                 U.S. Pat. No. 4,235,420 
                 Ross, et al. 
                 Nov. 20, 1978 
                 254/218 
               
               
                 U.S. Pat. No. 4,008,881 
                 Ross, et al. 
                 Mar. 17, 1975 
                 254/369 
               
               
                   
               
             
          
         
       
     
     
    
     FIELD OF SEARCH  
       [0002]     269/9,17,900,901,909  
         [0003]     187/203,210,219,240,250,266,401,404,406,411  
         [0004]     254/45,47,89R,389,390,397,399,401,402  
         [0005]     212/175,176,180  
         [0006]     248/351,352  
         [0007]     211/175,209  
         [0008]     414/222,223,678  
       BACKGROUND OF THE INVENTION  
       [0009]     The present invention relates to the art of vehicle lifting apparatus and, more particularly, the present invention relates to a method and an apparatus for lifting and holding automotive vehicles and vehicle bodies for the repair and restoration thereof.  
         [0010]     In the fields of automotive repair, restoration, and customization/modification the most commonly found automotive lifting systems capable of elevating the entire vehicle are the single-post, twin-post, and four-post varieties. Generally, vehicle-lifting systems of these types are extremely bulky, require considerable space to operate, and restrict access to various areas of the vehicle surface or undercarriage. Vehicle lifting systems that support the vehicle on a platform provide limited access to the vehicle undercarriage, while systems employing wheel lifts or that support the vehicle on arms positioned underneath the vehicle frame may restrict access to the vehicle interior, doors, and side panels.  
         [0011]     Approximately half of automotive repair shops use a twin-post lift, the vast majority of which employ hydraulic systems powered by electrical pumps as lift means. In addition to the previously detailed disadvantages of twin-post lifts, hydraulic lifts present further disadvantages relating to their electrical power requirements and the hydraulic fluid itself. Typically, these lifts require a 220-volt electrical outlet, as do air compressors, welders, plasma cutters, and other shop tools and equipment. Due to the limited number of these outlets usually found in smaller shops, wiring of additional 220-volt outlets, and the associated costs, may be necessary to provide a number sufficient to optimize use of the equipment and tools. Routine service and maintenance of hydraulic lifts includes the removal and disposal of used hydraulic fluid, known to be environmentally hazardous. Hydraulic fluid, while for the most part comprising an oil-based hydrocarbon, includes certain caustic and heavy metal additives including iron, lead, copper, nickel, tin, aluminum, cadmium, and phosphorus. As a result, removal and disposal of the used fluid requires special procedures and the involvement of governmental hazardous materials oversight agencies and other organizations.  
         [0012]     Many of the tasks and processes involved in automotive restoration and customization or modification cannot be performed until the vehicle body has been removed from the frame. Use of a twin-post lift to accomplish this task involves balancing the vehicle body on the bottom edge of the pinch welded flanges that mate the floor to the rocker panels, a surface usually less than one quarter of an inch wide, these surfaces being supported by the lift arms. The extremely tight clearances between the vehicle body and frame make this task even more difficult. A condition where the body is not correctly balanced on the lift arms can be dangerous because the body may slip or fall off the lift, causing damage to the vehicle and injury to any persons who may be near or under the lift. As a result of these considerations the common practice is to promptly remove the vehicle body from the lift, once separated from the frame, and place it on some type of mobile work holder. This allows it to be moved around the shop while various processes, such as metalwork, sanding, welding, etc., are performed. While conventional twin-post lifts do not efficiently or effectively lend themselves to the process of vehicle body removal, use of conventional single-post or four-post lifting systems is not possible. Hence, the need exists for a vehicle lift that facilitates this process.  
         [0013]     Another disadvantage of these conventional automotive lifts is the permanence of their installation. Most need to be professionally installed in a permanent location and generally require between one and two bays of shop floor space whether in use or not, while most collapsible types require as much as half of a bay when not in use, a standard shop bay having dimensions of approximately 15 feet times 30 feet. A surprisingly large percentage of commercial businesses providing automotive repair, restoration, or customization services operate from facilities having no more than four bays of floor space. Consequently, maximizing the productivity of such limited workspace is a critical factor in the ability of such businesses to achieve financial success. Regardless of issues concerning equipment workspace usage, most shops require a vehicle lift as well as many other pieces of bulky equipment including mobile work holders, which are a necessity when vehicles or parts thereof must be moved to different locations in the shop in order to complete various processes. A compact vehicle lift incorporating the functionality of a mobile work holder is therefore desirable.  
         [0014]     Additionally, the minimum ceiling height required to accommodate the majority of automotive lifts is greater than the ceiling height used as the industry standard in construction of residential garages, thus prohibiting the use of such lifts in most non-commercial buildings.  
         [0015]     While conventional automotive lifts may be suitable for their intended use, none can be operated within the confines of a residential garage of standard dimension while providing a sturdy and stable lifting system capable of elevating the entire vehicle, facilitating vehicle body removal, functioning as a mobile work holder when loaded, and that can be stored in a minimal amount of space when not in use.  
         [0016]     Circumstances necessitating a vehicle lifting system having these characteristics and free from the aforementioned disadvantages and restrictions of conventional lifts required that an embodiment of the present invention be reduced to practice in the year 2002.  
         [0017]     The apparatus according to the invention, summarized herewithin, fulfills a long felt need for a compact vehicle lifting system that provides for quick, efficient vehicle body removal as well as stable whole vehicle lifting, that adjusts to differing vehicle dimensions, functions as a mobile work holder, is easily transportable, and can be stored compactly.  
       BRIEF SUMMARY OF THE INVENTION  
       [0018]     The primary object of the present invention is to provide a compact vehicle lifting apparatus in which individual components are easily brought into cooperation to complete an operative apparatus and removed from cooperation for storage or transport, whereby use of the lifting apparatus is possible in a greatly increased range of circumstances.  
         [0019]     Another object of the present invention is to provide a lifting apparatus free from the previously discussed disadvantages and limitations of conventional vehicle lifts.  
         [0020]     An additional object of the present invention is to provide a vehicle lifting system comprised of easily manufacturable lightweight components whereby shipping is greatly simplified so as to reduce shipping and handling expense.  
         [0021]     One preferred embodiment of the present invention comprises one pair of lifting tower assemblies, each lifting tower assembly having a base, upright support member, at least one diagonal support member, lifting carriage, load supporting assembly, pulley component, lifting means, ground traversing means, and at least one horizontally disposed longitudinal support crossmember. Said embodiment further comprises at least 2 torsionally stiff structural support crossmembers interconnecting said lifting tower assemblies which form said pair thereby forming an apparatus of generally rectangular structure.  
         [0022]     Each lifting tower assembly is provided with ground traversing means, having a base component being movably supported on a plurality of wheels for ambulatory motion over a horizontal surface. Extending in a generally vertical direction from said base is a torsionally stiff upright support member. A lifting carriage is vertically slidable along the longitudinal axis of said upright support member, said lifting carriage being provided with a mounting site for attachment or connection of a conventional cable-engaging pulley device of an appropriate sort thereto One type of such conventional cable-engaging pulley device is commonly referred to as a snatch-block, an example of which is manufactured under U.S. Pat. No. 3,999,739, however an other appropriate type of cable-engaging pulley device may be employed in lie thereof.  
         [0023]     Lift is provided to the lifting carriage assembly by a lifting means in cooperation with a pulley component located adjacent the uppermost end of the upright support member and a cable having sufficient strength and appropriate material composition. Said pulley component includes a cable engaging pulley device of appropriate conventional type connected thereto and is further provided with a cable locking means such that a cable passing through the locking means can be secured in a substantially immovable position relative to said pulley component thereby preventing movement in either direction. A lifting means is detachably connected or attached to one tail of said cable, the opposite tail passing through the locking device and extending around the lifting carriage pulley and extending over the pulley component pulley, is detachably connected or attached to same said lifting means in such manner that said lifting means interconnects both tails of said cable with said base. This configuration greatly increases the lifting capacity provided to the lifting carriage assembly by the cooperation of the lifting means and the cable, however an alternate embodiment of the present invention including other manner of cable configuration to provide interconnection between the lifting means, the pulley component, the lifting carriage assembly, and the base is possible.  
         [0024]     In one embodiment of the present invention lifting means comprises a cable-pulling device of the ratcheting type known as a power pull, commonly referred to as a come-along, an example of which is manufactured by American Power Pull under U.S. Pat. Nos. 4,235,420 and 4,008,881. Said embodiment of the apparatus according to the invention provides the advantage that use of the vehicle lifting apparatus does not require an electrical power source, thereby eliminating any restrictions or expenses resulting from access to 220 volt or 110 volt outlets or lack thereof. It is to be understood that said power pull is representative of but one type of cable-pulling device and as the lifting means is detachably connected to the other lifting system components an alternate type of cable-pulling device, such as the type commonly known as an electric winch for example, can be utilized in lieu thereof without departing from the scope of the invention.  
         [0025]     At least one vertically disposed diagonal support member having an upper end and a lower end interconnects the upright support member of each lifting tower assembly with the longitudinal crossmember attached thereto. An upper circumferential collar surrounding a segment of said upright support member and a lower circumferential collar surrounding a segment of said longitudinal crossmember connect the upper end and the lower end of the diagonal support member to the upright support member and the longitudinal crossmember respectively, the upper collar being positionable along the longitudinal axis of said upright support member and the lower collar being positionable along the length of said longitudinal crossmember. Said diagonal support member greatly increases the stability of the lifting system thereby minimizing the possibility of said upright support member tilting, twisting, or rotating relative to said longitudinal crossmember. Said upper circumferential collar is secured to the upright support member in a location upwards of the lifting carriage and has dimension in proportion to the lifting carriage whereby said upper collar limits movement of the lifting carriage towards the uppermost end of the upright support member thereby defining the uppermost position of the lifting carriage. Thus, said upper collar functions as a safety means and additionally, being positionable along the length of the upright support member, allows the operator to set the raised or uppermost position of the lifting carriage to the desired elevation by positioning and securing said upper collar in an appropriate location on the upright support member.  
         [0026]     The apparatus according to the invention includes a load supporting assembly having sufficient strength and appropriate material composition and provided with means of attachment to the lifting carriage, and which in one embodiment comprises a main body, adjustable mounting brackets, and body attachment arms provided with a projecting portion shaped to fit within the channel existing adjacent the body mount locations of a full-frame automobile. The projecting portion is further provided with a connection means such that said projecting portion can be secured to the underside of the vehicle body in a manner whereby a body being lifted is supported from underneath by said projecting portion of the body attachment arms. Once said body attachment arms have been attached to the vehicle body the lifting tower assembly is moved into a position whereby the mounting brackets of the load supporting assembly are attachable to the body attachment arms. Consequently, the lifting apparatus automatically adjusts to fit vehicles of differing dimensions.  
         [0027]     Said load supporting assembly in an alternate embodiment includes vehicle supporting arms having an upper surface forming a generally horizontal surface of sufficient size and strength whereby the vehicle being lifted is supported on the flat upper surfaces of the vehicle supporting arms which are placed in appropriately reinforced and stable points on the vehicle&#39;s undercarriage. The lifting tower assembly is assembled in a desired location adjacent the vehicle and moved into a position such that elevating the lifting carriage assembly results in contact between the upper flat surfaces of said vehicle supporting arm and an appropriate point on the vehicle undercarriage. Thus, the apparatus according to the invention provides the capability to lift a vehicle body off its frame or lift an entire vehicle by employing the appropriate load supporting assembly.  
         [0028]     Additional alternate embodiments of said load supporting assembly provided with means to appropriately engage and support loads other than those specifically herein referenced are also possible.  
         [0029]     The apparatus according to the invention includes at least two horizontally disposed torsionally stiff structural support crossmembers, each having sufficient strength and appropriate material composition, interconnecting the lifting tower assemblies which form a pair, thereby forming a stable structure. Said crossmembers interconnect the lifting tower assemblies in a manner such that a lower transverse crossmember is detachably attached to the base component of each of said lifting tower assemblies and an upper transverse crossmember is detachably attached to the lifting carriage assembly of each of said lifting tower assemblies.  
         [0030]     When an embodiment of the apparatus according to the invention is used to lift a vehicle body off its frame, load attachment arms of an appropriate type are secured to the vehicle body and to the assembled lifting tower assemblies, then the lower transverse crossmember is attached. After disconnection from the frame, the vehicle body is elevated separately and the frame is then removed from underneath the elevated body. The capability of the apparatus to elevate a load in a stable and secure manner before attachment of the upper transverse crossmember allows the vehicle body to be lifted off its frame without obstruction. Said upper transverse crossmember is then attached and the lower transverse crossmember is removed from the lifting system, thereby allowing the frame, suspension, and etceteras to be removed from beneath the lifting system, there being no lower crossmember interfering with access. Said lower transverse crossmember is again attached, resulting in a single sturdy and stable structure having a vehicle body supported thereby.  
         [0031]     Alternately, assembly of the complete apparatus including attachment of the previously herein defined vehicle supporting embodiment of said load supporting assembly provides the apparatus the ability to lift an entire vehicle or other suitable load. Additional alternate embodiments of said load supporting assembly are possible, whereby the apparatus according to the invention is able to engage and support a wide variety of loads having varying dimensions and differing requirements for appropriate engagement, support, and securing.  
         [0032]     The apparatus includes ground-traversing means and, once all crossmembers are attached and secured, can be moved while supporting a load whereby the vehicle or part thereof can be conveniently relocated when necessary without removal from the lifting apparatus. Said apparatus supports loads from below in a manner providing unrestricted access to the upper surfaces and interior of the supported vehicle and greatly increased access to the lower surfaces or undercarriage. Thus, the apparatus functions as a mobile workholder and facilitates repair, restoration, and customization processes.  
         [0033]     The preferred embodiment of the invention previously described herein comprises one pair of lifting tower assemblies, however, an alternate embodiment comprising a single lifting tower assembly may be desirable for certain applications, each lifting tower assembly having the same or similar characteristics as those defined in the description of the previous preferred embodiment.  
         [0034]     An alternate preferred embodiment of the present invention comprises more than one pair of lifting tower assemblies, each pair having the same or similar characteristics as those previously defined, said alternate embodiment further comprising a multiplicity of torsionally stiff structural support crossmembers interconnecting said pairs of lifting tower assemblies thereby forming a complete apparatus having a stable structure.  
         [0035]     For the purpose of clarity of explanation a vehicle to be lifted is defined as having a front, a rear, a left side corresponding to the driver side of the vehicle, a right side corresponding to the passenger side, a longitudinal axis extending in a horizontal direction between the vehicle front and the vehicle rear and located equidistant from the right and left sides of the vehicle, and a transverse axis extending in a direction perpendicular to the defined longitudinal axis when viewed in a horizontal plane.  
         [0036]     Each pair of lifting tower assemblies is positioned such that one lifting tower assembly of each pair is located adjacent the right side of the vehicle and the second lifting tower assembly of each pair is located adjacent the left side of the vehicle and the pairs of lifting tower assemblies are spaced apart along an axis in parallel relationship to the longitudinal axis of the vehicle and at locations determined appropriate for the application to be performed.  
         [0037]     Horizontally disposed crossmembers extending in a direction parallel to the transverse axis of the vehicle interconnect the two lifting tower assemblies of each pair in a manner such that a lower transverse crossmember is detachably attached to the base component of each of said lifting tower assemblies and an upper transverse crossmember is detachably attached to the lifting carriage assembly of each of said lifting tower assemblies. Each two pair of adjacent lifting tower assemblies are interconnected by two horizontally disposed crossmembers extending in a direction parallel to the longitudinal axis of the vehicle, each longitudinal crossmember being detachably attached to the base component of two lifting tower assemblies located on a single side of the vehicle.  
         [0038]     The embodiment of the apparatus comprising more than one pair of lifting tower assemblies as described herein provides the ability to conveniently and easily perform restoration processes on vehicles having unusually large dimensions or excessive weight, such as limousines for example, or to lift the entire vehicle for repair, maintenance, or customization purposes.  
         [0039]     Additionally, the apparatus disassembles completely into the separate components that have been described herewithin. The minimal size and lightweight nature of each component greatly improves the ability of the operator to quickly and easily assemble the complete apparatus and operate it without assistance, and allows the disassembled apparatus to be stored compactly when not in use or easily transported in a light duty vehicle such as a pickup truck or SUV. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0040]     For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference is made by way of example to the accompanying drawings, which show an apparatus according to the preferred embodiment of the present invention and in which:  
         [0041]      FIG. 1  is an elevated perspective view of a preferred embodiment of a complete apparatus according to the invention.  
         [0042]      FIG. 2  is an elevated perspective view of an individual lifting tower assembly.  
         [0043]      FIG. 3  is a perspective view of an individual lifting tower assembly.  
         [0044]      FIG. 4  is a side plan view of an individual lifting tower assembly.  
         [0045]      FIG. 5  is a front plan view of an individual lifting tower assembly.  
         [0046]      FIG. 6  is an enlarged, vertical cross-sectional view of the pulley component.  
         [0047]      FIG. 7  illustrates a preferred embodiment of a load supporting assembly.  
         [0048]      FIG. 8  is an end view of a pair of lifting tower assemblies interconnected by crossmembers, illustrating placement and attachment of a supported vehicle body.  
         [0049]      FIG. 9  is a side view of a lifting tower assembly illustrating cable placement and angle.  
         [0050]      FIG. 10  is a partial view of crossmembers attached to a base component.  
         [0051]      FIG. 11  is an elevated perspective view of an alternate preferred embodiment of a complete apparatus according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0052]     It is to be understood that the embodiments of the present invention disclosed herein are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting.  
         [0053]     Referring now to the drawings, in which some proportions have been exaggerated for the purposes of conceptual illustration, the description of the invention is best understood by commencing with reference to  FIGS. 1, 2 , and  3 . Attention is first directed to  FIG. 1  where a complete lifting apparatus according to the invention is shown and is indicated generally as  1  and may be seen to include one pair  2  of lifting-tower assemblies  3 , 4 . It is to be understood that the components forming one lifting tower assembly of pair  2  are the same as said components forming the second lifting tower assembly of the pair. Said lifting apparatus further includes horizontally disposed lower crossmember  13 , and horizontally disposed upper crossmember  12 .  
         [0054]     An individual lifting-tower assembly, illustrated in FIGS.  2 ,  3 , 4 , 5 , is assembled in a desired location and includes a base  20 , upright support member  21 , pulley component  25 , cable  34 , at least one diagonal support member  26 , upper collar  27 , at least one lower collar  28 , lifting carriage  23 , load supporting assembly  22 , and is provided with lifting means  35 .  
         [0055]     As shown in  FIG. 5 , base  20  includes a vertically oriented receiver portion  85 . Upright support member  21  is provided with a receiver portion  77  and further includes a shank portion  78  that is vertically inserted into receiver  85 .  
         [0056]     As shown in  FIGS. 4,9 , lifting carriage  23  includes a receiver portion  74  and is provided with a main body shaped to form a circumferential sleeve  75  having inner dimension  80  and longitudinal length  81 . Upright support member  21  has longitudinal axis  32  and outer dimension  82 , sleeve  75  slidably mounted thereabout. The inner dimension  80  and length  81  of sleeve  75  are proportioned relative to outer dimension  82  such that the values of inner dimension  80  and outer dimension  82  differ by no more than 0.75 percent of sleeve length  81 , and preferably less than 0.35 percent, the values of inner dimension  80  and outer dimension  82  being sufficiently different as to allow unimpeded motion of lifting carriage  23  along the length of upright support member  21 . Thus, an allowable range of proportional relationship is defined between sleeve length  81 , inner dimension  80 , and outer dimension  82 , thereby further defining an allowable tolerance range existing between upright support member  21  and lifting carriage  23  when mounted theresurrounding. Lifting carriage  23  further includes mounting site  31 , for attachment of a pulley device of conventional type  30 .  
         [0057]     An upper circumferential collar  27  is slidably mounted surrounding a segment of upright support member  21  and is secured at a location upwards of lifting carriage  23  by means of a threaded aperture passing through upper collar  27  and a mating bolt  46 , as indicated in  FIG. 2 .  
         [0058]     Pulley component  25  includes shank portion  76  that is slidably inserted into receiver  77  of upright support member  21 , shown in  FIG. 5 . A cross-sectional view of pulley component  25  is illustrated in  FIG. 6  and can be seen to include a conventional pulley device of the bearing type  60 , comprising a cable guide  61 , bearing  62 , and a center  63  having bolt  52  passing therethrough, thereby securing pulley  60  between outer spacer  58  and inner spacer  57  which are located between and immediately adjacent the pulley component outer body  50  and the inside locking plate  56 , respectively. A cable passing through locking device  53  is supported by cable spacer  55  and is positioned between inside locking plate  56  and the outer locking-pin plate  54 . Said bolt  52  passes through the outer locking-pin plate  54 , pulley component inner body  51 , cable spacer  55 , inside locking plate  56 , inner spacer  57 , pulley device  60 , and outer spacer  58 , each having an aperture passing therethrough. Said mating bolt  52  then passes through threaded aperture  59  in the pulley component outer body  50  thereby extending completely through said pulley component  25  in such manner that sufficient tightening of bolt  52  provides the result that cable  34  passing through locking device  53  is secured between the outer locking-pin plate  54  and inside locking plate  56  in a stationary position relative to pulley component  25 , and further provides secure positioning of the pulley device  60  relative to pulley component  25 .  
         [0059]     Referring again to  FIGS. 2,3 , base  20  is further provided with mounting site  36  for attachment of a lifting means  35 , comprising a conventional cable-pulling device of the ratcheting type hereinafter referred to as a come-along  37 . Cable  34  has one tail attached to the winch portion  39  of come-along  37  and has opposite tail extending over pulley device  60  and then extending around pulley device  30  and then passing through locking device  53 , said opposite tail being attached to the come-along body  38 . Both tails of cable  34  are connected to come-along  37  using means recommended by the manufacturer thereof. Operation of come-along  37  is performed as per manufacturer instructions, whereby winching in or winching out cable  34  causes lifting carriage  23  to move upwards or downwards, respectively, along the vertical length of upright support member  21 , said lifting carriage  23  being freely movable about upright support member  21  due to the tolerance existing therebetween as previously defined herein. Base  20  limits downward movement of lifting carriage  23  and upward movement thereof is limited to the desired height by said aforedescribed upper collar  27 .  
         [0060]     Lifting carriage  23  further includes a safety feature comprising a securing means such that said lifting carriage  23  can be secured to upright support member  21  at a desired height and in a generally immovable position, said securing means comprising a threaded aperture passing through lifting carriage  23  and a mating bolt  43 , thereby preventing upward or downward movement of lifting carriage  23  regardless of whether or not a load is being supported. Hence, a vehicle or part thereof can be lifted to and maintained at a height preferred by the operator or convenient for the task to be performed.  
         [0061]     As shown in  FIG. 9 , base  20  is provided with mounting site  36  having location such that an axis  66  defined by the segment of cable  34  extending between pulley device  60  and ratchet  39 , and the longitudinal axis  32  of upright support member  21  intersecting therewith, forms an angle alpha of not less than 4 degrees but not more than 9 degrees, and preferably between 6 degrees and 7 degrees, thereby defining an allowable range of angle alpha. Mounting site  31  has location on lifting carriage  23  such that an axis  67  defined by the segment of cable  34  extending between pulley device  30  and pulley device  60 , and axis  32  intersecting therewith, forms an angle beta of not less than 2 degrees and not more than  17  degrees, and preferably between 3 degrees and 15 degrees, thereby defining an allowable range of angle beta. Mounting site  31  includes three points for attachment of pulley device  30 , each of said points corresponding to a pre-determined range of allowable load weight and having location determined such that angle beta is maintained within the allowable range when pulley device  30  is attached to the attachment point which is appropriate for the weight of the load to be lifted.  
         [0062]     Each lifting tower assembly further includes a safety feature, inherent in its design, for the purpose of preventing a catastrophic accident in the event of failure of cable  34  or come-along  37  or the lifting carriage safety feature  43 , and that acts to secure lifting carriage  23  against upright support member  21  immovably in such event. Said safety feature is provided by the interrelationship between the angle of cable  34  relative to upright support member  21  (angle beta) and the aforedefined allowable tolerance range between lifting carriage sleeve  75  and upright support member  21 . A failure of cable  34  or come-along  37  while the lifting tower assembly is under load results in sleeve  75  tilting or twisting relative to upright support member  21  causing a portion of the inner surface of sleeve  75  to contact and wedge against a portion of the exterior surface of upright support member  21  due to the limited tolerance existing therebetween, whereby lifting carriage  23  is prevented from continued movement along the length of upright support member  21 . The previously defined tolerance range is determined such that a relatively small amount of tilting or twisting of sleeve  75  will cause lifting carriage  23  to become immobile relative to upright support member  21 . The range of values allowed for angles alpha and beta, respectively, ensure sleeve  75  is maintained in an orientation relative to axis  32  such that under normal operating circumstances movement of lifting carriage  23  is unimpeded, however, events including cable failure, lifting means failure, excessive load shift, and etc., will cause lifting carriage  23  to lock against upright support member  21  before significant downward movement can occur, thereby providing a secondary safety means for preventing catastrophic accident.  
         [0063]     A base component  20  and attached crossmembers  10 , 13  are illustrated in  FIG. 10 . Base  20  is provided with a receiver portion  83  and a receiver portion  84  that define a transverse axis  65  and a longitudinal axis  64  respectively. As shown in  FIGS. 5,10 , the upright support member  21  connected to a base component  20  and the longitudinal crossmember  10  connected thereto are interconnected by at least one diagonal support member  26  having an upper end attached to said upper collar  27  and a lower end attached to a lower circumferential collar  28  slidably mounted surrounding said crossmember  10  and secured thereto by means of a threaded aperture passing through collar  28  and a mating bolt  47 . Said lower collar  28  in a preferred embodiment is further provided with ground traversing means comprising wheels  9  mounted to a lower surface of said collar. Both ends of said diagonal support member  26  are secured to their respective collars by means of an aperture passing through each of said collars and each end of said diagonal support member  26  for insertion of pin  48  and  49 , respectively, however an alternate method of securing each end of diagonal support member  26  to its respective collar is possible.  
         [0064]     A load supporting assembly having sufficient strength and appropriate material composition is provided with attachment means whereby said load supporting assembly can be connected and secured to lifting carriage  23 , said attachment means in a preferred embodiment comprising a shank portion shaped to allow slidable insertion within lifting carriage receiver  74  and secured thereto by means of a threaded aperture passing through lifting carriage  23  and a mating bolt, however alternate attachment means may be used to connect said load supporting assembly to lifting carriage  23  and securing means other than a threaded aperture and mating bolt are possible, such as an aperture and locking pin, for example.  
         [0065]     One embodiment of the aforedescribed load supporting assembly, indicated generally as  22  in  FIGS. 1, 4 ,  7 , includes a main body  110 , mounting brackets  112 , and load attachment arms  24 . Main body  110  is provided with shank portion  111  shaped to allow slidable insertion within lifting carriage receiver  74 , said shank  111  being secured thereto by means of a threaded aperture passing through lifting carriage  23  and a mating bolt  45 , as noted in  FIG. 3 . Each mounting bracket  112  includes a portion shaped such that it forms a circumferential collar  114  having dimensions allowing said collar to be slidably mounted surrounding a positionally appropriate segment of main body  110 , said collar  114  being provided with means of securing thereto, said means in a preferred embodiment comprising a threaded aperture passing through collar  114  and mating bolt  93 , as illustrated in  FIG. 7 . Said mounting bracket  112  is further provided with a receiver portion  115  shaped to allow slidable insertion of shank  73  therewithin, said receiver  115  including means for securing shank  73  thereto, said means comprising a threaded aperture passing through receiver  115  and mating bolt  94 .  
         [0066]     Each load attachment arm  24  is provided with a shaped portion that allows a vehicle body of the full-frame type to be attached and secured thereto in a manner whereby the vehicle body is supported from underneath by load attachment arm  24  and attached thereto at a suitably reinforced and appropriate location on the body, said shaped portion comprising a projection  79 . Said projection  79  is shaped such that it can be inserted within a channel existing between the vehicle body and frame of a full-frame vehicle, and can be secured at the location of a pre-existing attachment site on the body underside commonly referred to as a body mount, said body mount including a threaded aperture  91  and mating bolt  92  whereby the vehicle body is secured to the frame, as illustrated in  FIG. 8 . Said body mount thereby provides a suitably reinforced and stable point for attachment of said load attachment arm  24  to the vehicle body. Projection  79  includes means for securing load attachment arm  24  to said body mount, comprising an elongated aperture  90  passing through projection  79  whereby alignment of said aperture  90  with body mount aperture  91  allows body mount mating bolt  92  to be inserted into aperture  90  and extended through projection  79  before entering the body mount threaded aperture  91 , thereby securing load attachment arm  24  to the body underside when said mating bolt  92  is tightened sufficiently. Lifting carriage  23  is then raised to an elevation such that receivers  115  are at substantially the same height as each load attachment arm shank  73  and each mounting bracket  112  is positioned and secured at an appropriate location on main body  110  whereby movement of the assembled lifting tower in a direction towards said load attachment arms  24  and alignment therewith results in the slidable insertion of each shank  73  within a receiver  115 . The position of the lifting tower assembly and the elevation of lifting carriage  23  may be adjusted to achieve proper insertion of shanks  73  within receivers  115 , such that each shank  73  can be secured to a mounting bracket  112  by means of the aforedescribed threaded aperture mating bolt  94 . Means other than a threaded aperture and mating bolt for attaching and securing said load attachment arms to said mounting brackets or said mounting brackets to said main body may be used.  
         [0067]     An alternate load supporting assembly embodiment having the ability to support an entire vehicle from underneath the frame or undercarriage is also possible, wherein each load attachment arm includes a projecting portion having an upper surface forming a generally horizontal plane shaped to allow a vehicle frame or undercarriage to be supported thereupon in a stable manner. Additional alternate embodiments of said load-supporting assembly provided with means to engage and support loads of a type other than those mentioned herein, such as unibody vehicles for example, are also possible without departing from the underlying ideas or principals of this invention.  
         [0068]     As shown in  FIGS. 8,10 , the two lifting tower assemblies  3 , 4 , forming pair  2  are interconnected by a lower transverse crossmember  13  having ends slidably inserted within receiver  83  of each base  20 , and secured thereto by means of a threaded aperture passing through receiver  83  and a mating bolt  42 . A single torsionally stiff crossmember  13  is comprised of three segments  70 ,  71 ,  72 , assembled and secured together by means of two threaded apertures passing through segment  71  and mating bolts  88 ,  89  to form a single crossmember wherein the length of said crossmember is adjustable, said crossmember  13  being shaped in such manner as to allow disassembly and removal from pair  2 , and assembly and installation, while said pair  2  is supporting a load. An alternate embodiment of the present invention including a lower transverse crossmember formed as a single piece (not shown) having ends slidably inserted within and passing completely through receiver  83  of base  20  is possible, thereby providing an other method of adjusting the distance between the two lifting tower assemblies  3 , 4  forming pair  2 .  
         [0069]     An upper transverse crossmember  12  further interconnects pair  2 , having ends slidably inserted within receiver  33  of each lifting carriage  23  and in a manner whereby upper crossmember  12  may be removed or installed between tower assembly  3  and  4  while pair  2  is supporting a load, the aforementioned outward tilt of tower assemblies  3 , 4  providing a means whereby said insertion and removal of crossmember  12  is possible. Said crossmember  12  is secured to lifting carriage  23  by means of a threaded aperture passing therethrough and mating bolt  44 , shown in  FIG. 2 .  
         [0070]     Said upper crossmember  12  further provides an additional redundant safety feature in the event of failure of both primary and secondary safety features in one tower of a pair, said previously herein described primary and backup safety features each comprising a method whereby lifting carriage  23  is secured to upright support member  21  and in a generally immovable relationship therewith. Said upper crossmember  12 , being a torsionally stiff component having ends secured to lifting carriage  23  of tower assemblies  3  and  4 , operatively interconnects tower assemblies  3 , 4 , in a manner such that in the event of failure of both safety features in one tower of pair  2 , tower assembly  3  for example, crossmember  12  will transfer the load to tower assembly  4  and will further result in the descending lifting carriage  23  tilting relative to upright support member  21 , causing the secondary lifting carriage safety feature to become operative, thereby preventing said lifting carriage  23  from further descent. Thus, the apparatus according to the invention includes several redundant safety features.  
         [0071]     Referring again to  FIG. 9 , base  20  is further provided with ground traversing means comprising wheels  29  mounted to a lower surface of base  20 , said wheels  29  being positioned at locations whereby axis  32  of upright support member  21  defines a direction differing from a true vertical axis, and intersecting therewith forms an angle of not more than 3 degrees but not less than 0.5 degrees when viewed in a vertical plane having an axis in parallel relationship to axis  65  of base  20 , as noted in  FIG. 8 . An assembled lifting tower assembly supported by base  20  having wheels  29  is thereby provided with a small but measurable tilt in an outward direction indicated by arrow  68 , that is to say, the two lifting tower assemblies  3 , 4 , forming pair  2  tilt away from each other slightly. This outward tilt provides additional stability to each pair of lifting tower assemblies, thereby reducing the possibility of a lifting tower assembly tilting or toppling toward a load being supported.  
         [0072]     When the apparatus according to the invention is used to lift a vehicle body off its frame, the load attachment arms  24  are secured to the vehicle body and to the assembled lifting tower assemblies  3 ,  4 , and lower horizontal crossmember  13  is attached. The vehicle body is then lifted off the frame and elevated, each lifting carriage locking means  43  is engaged, and the upper horizontal crossmember  12  is installed. Lower transverse crossmember  13  is then removed, allowing the vehicle frame, suspension, wheels, and etc., to be rolled out from beneath the body and lifting apparatus. Once the frame is removed the lower transverse crossmember is again installed, resulting in a complete lifting apparatus which is a single stable structure having a vehicle body supported thereby. Adjustment or alteration of the load elevation may be made at any point hereafter. Said apparatus, being movably supported by wheels  29 , is capable of ambulatory motion over a generally level surface while supporting said load, thereby acting as a mobile workholder.  
         [0073]     An alternate embodiment of the apparatus according to the invention is shown in  FIG. 11 , indicated generally as  101 , and can be seen to include four lifting tower assemblies  104 ,  105 , and  106 ,  107 , forming two pair of lifting tower assemblies  102 ,  103  respectively. Said pairs  102  and  103  are interconnected by two longitudinal crossmembers  14 ,  15 , each having ends slidably inserted within receiver  84  of base  20  and secured by means of the two threaded apertures passing through receiver  84  and mating bolts  40 ,  41 , said receiver  84  shaped forming an aperture passing completely through base  20  whereby said longitudinal crossmember is slidably positionable within base  20  such that the distance between pairs  2  and  3  may be increased or decreased.  
         [0074]     Alternate embodiments of said apparatus utilizing means other than a threaded aperture and mating bolt for attaching or securing crossmembers  10 ,  12 ,  13 ,  14 , and  15  are possible without departing from the underlying ideas or principals of this invention, said means comprising an aperture and securing pin, for example.  
         [0075]     The interconnection of assembled lifting tower assemblies  104 ,  105 ,  106 , and  107  by horizontal crossmembers  12 ,  13 ,  14 , and  15 , and each diagonal crossmember  26  further interconnecting therewith, forms a complete apparatus which is a single stable structure capable of ambulatory motion over a generally level surface while supporting a load, said apparatus being movably supported by wheels  29 .  
         [0076]     Although a particular preferred embodiment of the apparatus according to the invention and a number of alternate embodiments have been described herein and illustrated in the figures, the principles of the present invention are not limited to those specific embodiments, and within said embodiments certain changes may be made in the form or arrangement of the parts without departing from the underlying ideas or principles of this invention.