Abstract:
A scissor jack assembly with double-lead Acme threaded screw. Through use of urethane or similar material as a braking means, the jack assembly is operable with a self locking action over a wider range of loads and especially at lower loads where an Acme loading phenomenon that results in said self locking action has previously been unattainable. Faster and smoother jack operation is made possible by employing a thrust bearing, including a plurality of roller or ball bearings, with the jack assembly. A spacing washer is also provided to retain the threaded shaft within the trunnions of the jack assembly, in order that the ends of each of the trunnions need not be machined or stamped to retain the trunnions within the jack assembly. Utilizing such a spacing washer decreases the costs involved with manufacturing the jack assembly, while increasing the ability to repair the jack assembly.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a continuation of copending application Ser. No. 09/200,375, which was filed on Nov. 24, 1998, which in turn, is a further continuation of copending application Ser. No. 09/843,975, filed on Apr. 26, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to mechanical jacks used for raising heavy objects and, more specifically, to a screw-operated scissorjack having an expanded range of load lifting capabilities provided by use of urethane or similar material as a braking means and having faster, smoother operation made possible by use of thrust bearing that includes a plurality of ball or roller bearings.  
         BACKGROUND OF THE INVENTION  
         [0003]    Screw-operated scissor jacks have long been known to be useful in lifting applications and especially in situations where it may be desired to level heavy objects. A particular type of well known screw-operated scissor jack employs a double lead Acme screw which traditionally has proven to be particularly advantageous where extremely massive objects need to be raised quickly. One industry in which jacks having the double lead Acme screw have been widely used is the railroad industry, where the need often has arisen to lift locomotives and rail cars from train tracks. For this and similar types of lifting jobs, the double lead Acme screw has been shown to be capable of raising loads up to three times faster than a standard SAE screw that has been used in other jacks.  
           [0004]    In addition to providing a faster operating jack, the Acme double lead screw exhibits a further operational advantage that derives from the physical characteristics which are unique to the Acme screw thread. Such operational advantage is the ability for the Acme screw to become self-locking when the jack is subjected to loads generally in excess of one thousand pounds. Where loading is above the stated level, it has been determined that frictional forces developed among the thread lands or roots become sufficiently large to prevent the vertically downward directed force of the lifted object from causing the screw to unwind and prematurely allow the lifted object to descend. As already suggested, the described advantage, which also may be termed an “Acme loading phenomenon,” requires that a minimum load be lifted by the jack before the Acme loading phenomenon takes effect and becomes of any benefit to the jack operator. Thus, the advantage to be gained from discovery of a means to lower the minimum load at which the jack will become self-locking has been recognized, and the present invention provides a simple and inexpensive jack construction that is aimed at achieving that end.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with a preferred embodiment of the present invention, there is provided a screw-operated scissor jack assembly including a double lead Acme screw, used for lifting and on some occasions, leveling a heavy object; the jack assembly being capable not only of raising the object at a faster rate than conventional SAE screws used for the same purposes, but also of becoming advantageously engaged in a self-locking state at loads that are markedly lower than those heretofore required to cause traditionally available scissor jack assemblies to achieve self-locking operation. The jack assembly of the present invention is comprised of: a base member having a plurality of foot-like projections provided for resting the jack assembly against a relatively hard, flat, stationary surface; a first movable arm member rotatably connected at a first end of said first movable arm member to said base member by a first bolt or similar fastening means; a second movable arm member rotatably connected at a first end of said second movable arm member to a second end of said first movable arm member by a first trunnion; a third movable arm member rotatably connected at a first end of said third arm member to said base member by a second bolt or similar fastening means; a fourth movable arm member rotatably connected at a first end of said fourth movable member to a second end of said third movable member by a second trunnion; a first and a second load supporting bracket, each of which brackets is rotatably connected to a second end of each of said second and fourth movable arm members by a third and a fourth bolt or similar fastening means; a rotatable shaft member extending within said first, second, third and fourth movable arm members and having a double lead Acme threaded screw engaged with a threaded bore provided in said second trunnion; and a turning means affixed to an unthreaded end of said rotatable shaft member and located proximate to said first trunnion, said turning means including an operating handle receiver, a thrust bearing, a ring-like braking means comprised of urethane or a similar substance; a first and second washer and a locking pin.  
           [0006]    It is therefore an object of the present invention to provide an improved screw-operated scissor jack assembly with a double lead Acme screw, which assembly is operable at high speed and with smooth action.  
           [0007]    It is yet another object of the present invention to provide an improved screw-operated scissor jack assembly with a double lead Acme screw, which assembly is operable with a self locking action over a wider range of loads and especially at lower loads in a range of 700-1200 pounds where an Acme loading phenomenon that results in said self locking action has previously been unattainable. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1A is a perspective view of a jack assembly of the present invention in a raised condition;  
         [0009]    [0009]FIG. 2 is a side view of a jack assembly of the present invention in a raised condition;  
         [0010]    [0010]FIG. 3 is a enlarged perspective view of the turning means of the jack assembly of the present invention wherein portions of the turning means are shown in a spatially separated state;  
         [0011]    [0011]FIG. 4 is a yet another enlarged perspective view of the turning means of the present invention wherein selected portions of the turning means are shown in a spatially separated condition;  
         [0012]    [0012]FIG. 5 is a side view of the turning means of the present invention, depicted in a non-spatially separated state.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    A screw-operated jack assembly in accordance with a preferred embodiment of the present invention is indicated generally in FIG. 1 by the reference numeral  10 . The jack assembly  10  is comprised of a base member  11  employed for resting the jack assembly  10  against a flat, stationary surface such as a concrete floor or some other relatively firm material; a first movable arm member  12  rotatably connected at a first of its two ends to the base member  11  by a first bolt  1 ; a second movable arm member  13  rotatably connected by a first pin or trunnion  17  at a first of its two ends to the second end of the first movable arm member  12 ; a third movable arm member  14  rotatably connected at a first of its two ends to the base member  11  by a second bolt  2 ; a fourth movable arm member  15  rotatably connected by a second pin or trunnion  18  at a first of its two ends to the second end of the third movable arm member  14 ; a pair of load supporting brackets  16 , each of the brackets  16  making up the pair being connected by bolts  3  and  4  (the bolt  4  shown in FIG. 2) to the second ends of the second and the fourth movable arm members  13  and  15  in a manner so that the second and fourth arm members  13  and  15  are rotatable in relation to each of the load supporting brackets  16 . The jack assembly  10  is further comprised of a horizontally extending, rotatable shaft member indicated generally by the numeral  20  in FIGS. 1 and 2. The rotatable shaft member  20  is provided on its outer circumference with a double lead Acme thread  22  that continuously extends from one end of the shaft member  20  and across approximately two-thirds to three-fourths of the length of the shaft member  20 ; and a turning means generally indicated in the drawings by the reference numeral  30  and situated on the end of the unthreaded portion  23  of the rotatable shaft member  20 . Each of the trunnions  17  and  18  are provided with a bore (bore in the trunnion  17  indicated in FIG. 3 the reference numeral  17   a  and bore in the trunnion  18  not shown in the drawings) that extends perpendicularly through the center portion of the turnings  17  and  18 . In the case of the trunnion  17 , the bore  17   a  provided therethrough is unthreaded and is slightly larger than the diameter of the threaded portion  22  of the shaft member  20 . In the case of the trunnion  18 , the provided bore is threaded with a double lead Acme thread that is dimensionally compatible with the threading provided on the threaded portion  22  of the shaft member  20 . As indicated in the drawings, when the jack  10  is in an assembled state, the threaded portion  22  of shaft member  20  is rotatably received by the threaded bore in trunnion  18  and the unthreaded portion  23  of the shaft member  20  is rotatably received by the bore in trunnion  17 . At the ends of each of the movable arm members  12 ,  13 ,  14  and  15 , that receive one of the bolts  1 ,  2 ,  3  and  4 , there is provided a plurality of tab-like teeth  19 . As shown in FIG. 2, the teeth on opposing ends of the arm members  12 ,  13 ,  14  and  15  mesh and permit the load supporting brackets  16  to be raised or lowered as the shaft member  20  is rotated in one direction or the other. The base member  11  is supplied with foot-like projections  11   a.  The projections  11   a  provide a means for resting the jack assembly  10  in a stable manner against a stationary surface during operation.  
         [0014]    Turning to FIG. 3, an enlarged perspective view is provided of a portion of the jack assembly  10  where movable arms  12  and  13  are joined by the trunnion  17 , and the unthreaded portion  23  of the shaft member  20  passes through the unthreaded bore  17   a.  Also shown in FIG. 3, in a spatially separated (laterally) state, are the elements that comprise the turning means  30 . Collectively, the turning means  30  includes: an operating handle receiver  31 ; a thrust bearing  32 ; a ring-like breaking means  33 ; a first washer  34 ; a second washer  35  and a locking pin  36 .  
         [0015]    The operating handle receiver  31  is cylindrically shaped and is provided as an enlarged diameter extension at the end of the unthreaded portion  23  of the shaft member  20 . A longitudinally extending central bore  31   a  is provided in the handle receiver  31  along with a radially extending side bore  31   b  that passes through the wall of the handle receiver  31  at one location on its periphery. The central bore  31   a  receives an end of a known shaft-like, rotation causing tool (not shown) equipped with a radially projecting, spherical locking means (not shown) that engages the side bore  31   b  to prevent relative rotation between the handle receiver  31  and the rotation causing tool.  
         [0016]    The thrust bearing  32  is located on the unthreaded portion  23  of the shaft member  20 , immediately next to the operating handle receiver  31 . The bearing  32  is annularly shaped, and its central opening, the diameter of which is smaller than the outside diameter of the handle receiver  31 , but is larger than the diameter of the portion  23  where it is joined to the receiver  31 , is provided with a plurality of bearings (ball or roller) that project toward and make contact with the outer surface of the unthreaded portion  23  lying inside of the central opening of the bearing  32 .  
         [0017]    Positioned immediately adjacent to the thrust bearing  32  is the braking means  33 , which in the preferred embodiment of the invention, is in the form of an O-ring that fits snugly about the circumference of the unthreaded portion  23  of the shaft  20 . Preferably, the braking means  33  is fabricated from urethane, employing known production techniques; however, any other substance having properties similar to urethane may be used as a braking means, and all such substances are intended to be within the scope of the present invention.  
         [0018]    The first washer  34  is situated immediately beside the braking means  33  and to the outside of the trunnion  17 . The first washer  34  is made of a sturdy metal such as steel and has an outer diameter that significantly exceeds the outer diameters of the receiver  31 , the bearing  32  and the braking means  33 , but that will allow the washer  34  to fit in the space -provided at the end of the movable member  12  where it is joined by the trunnion  17  to the movable member  13 . Such sizing of the washer  34  also permits it to make firm tangential contact with the trunnion  17  when the jack  10  is in its fully assembled state.  
         [0019]    First washer  34  also acts as a spacer to properly maintain shaft member  20  and trunnion  17  between movable arms  12  and  13 . Upon assembly of the jack  10 , the combination of the shaft member  20 , the locking pin  36  and first washer  34  holds jack  10  in its assembled position. In prior art scissor jacks, processing steps were required to hold a trunnion within the arms of the jack, while having the shaft member positioned within the trunnion. Such prior art processes include machining the lateral ends of the trunnion to provide slots for accepting snap rings on each end of the trunnion, or stamping each end of the trunnion to create an upset region or ridge, about the circumference of each end of the trunnion. Spacers, such as first washer  34 , eliminate the need to machine or stamp the ends of each trunnion thereby decreasing the costs associated with manufacturing the scissor jack  10 . Furthermore, using first washer  34  as a spacer to hold shaft member  20  and trunnion  17  between movable arm  12  and  13 , allows for easier repair of jack  10 , in contrast to stamping the ends of trunnions  17  and  18 , which increases the time, effort and expense of repairing jack  10 .  
         [0020]    The second washer  35  is also made of metallic material like steel and is provided on the unthreaded portion  23  at a position that lies immediately to the inside of the trunnion  17 . Like the first washer  34 , the second washer  35  also makes tangential contact with the trunnion  17  when the jack  10  is fully assembled.  
         [0021]    A hook-like locking pin  36  completes the turning means  30 . The locking pin  36  is clearly shown in FIG. 4, where there is provided yet another spatially separated perspective view of the of components of the turning means  30 . (It should be noted that the second washer  35  has been omitted from FIG. 4 for clarity purposes only.) The locking pin  36  is received by a radial bore  37  that passes through a region  23   a  of the unthreaded portion  23 . The region  23   a  extends toward the operating handle receiver  31  and has a diameter that is somewhat enlarged over that of the unthreaded portion  23 . As shown in FIG. 3, the pin  36  abuts the second washer  35  and thus cooperates with the operating handle receiver  31  to maintain physical contact among the components of the turning means  30  and to prevent axial translation of the unthreaded portion  23  relative to the trunnion  17 .  
         [0022]    In FIG. 5, the operating handle receiver  31 , the thrust bearing  32 , the braking means  33 , the washer  34 , the washer  35  and the locking pin  36  are shown in a non-spatially separated state, i.e., as said components would actually appear relative to the trunnion  17  and the unthreaded portion  23  of the shaft  20  when the jack  10  is in an assembled state.  
         [0023]    In operation, the jack  10  will cause a load in contact with the load supporting brackets  16  to be raised when a rotation causing tool is engaged in the central bore  31   a  of the operating handle receiver  31  and the shaft member  20  with threaded portion  22  is caused to rotate within the threaded bore of the trunnion  18  in a direction that will cause the trunnion  18  to be drawn along the threaded portion  22  toward the trunnion  17 . During a typical load-raising process, the jack  10  will first be positioned beneath the load to be lifted such that at least a small clearance space will exist between the load supporting brackets  16  and object to be raised. Next, the shaft member  20  will be turned so that the load supporting brackets  16  make contact with the object and the clearance space is eliminated. As contact is made, load from the object will be increasingly shifted to the load supporting brackets  16  and cause forces to be developed in and transmitted through the second and fourth movable arm members  13  and  15  and the trunnions  17  and  18 . The force transmitted through the trunnion  18  will be transferred at the threaded bore to the double lead Acme threads  22  there within. Similarly, the force transmitted through the trunnion  17  will be directed against the washer  34  and then transferred to ring-like braking means  33 , thrust bearing  32  and operating handle receiver  31 . The force transmitted through the trunnion  18  to the Acme threads  22  assumes the form of a frictional force that acts between the opposing Acme thread faces and that increases in magnitude as the load of the object being lifted increases. In general, traditional screw-operated scissor jacks having double lead Acme threads need to be subjected to a load in excess of approximately 3,000 pounds before the frictional force among the threads becomes large enough to cause the conventional jack to become self-locking and thus prevent the it from lowering of its own accord if the turning force provided by the rotation causing tool against the operating handle receiver  31  is relieved. In accordance with the present invention, the magnitude of the load required to cause the jack assembly  10  to become self-locking is markedly reduced by the braking means  33  and the action of the force transferred to it through the washer  34 . Recalling that in the preferred embodiment of the invention the braking means  33  is comprised of a urethane material, the force transmitted to the braking means  33  by the washer  34  causes the braking means  33  to become deformable compressed between the washer  34  and the transfer bearing  32  and to expand radially outward and inward toward the unthreaded portion  23  of the shaft  20 . The expansion increases the surface areas of contact among the braking means  33  and the washer  34  and the transfer bearing  32  and at the same time causes the braking means to constrict against the unthreaded portion  23  of the shaft  20 . These combined actions cause frictional forces to develop that resist lowering of the jack  10  and that combine with the frictional forces developed at the trunnion  18  among the Acme threads. The combination of the frictional forces created by the braking means  33  and the interaction of the Acme threads  22  thus causes the jack  10  to become self-locking at loading which is less than conventional jacks. By way of example, loads in the range of  700  to  1200  pounds have been found to cause the jack  10  of the present invention to engage in a self-locking condition.  
         [0024]    Another aspect of the present invention is the transfer bearing  32 . Conventional screw-operated scissor jacks generally have been long known for their slow, laborious manner of operation and for their non-fluid or erratic lifting action. The transfer bearing  32  with its plurality of ball or roller bearings that project toward and contact the outer surface of the unthreaded portion  23  of the shaft  20  has been found to eliminate these drawbacks by reducing the frictional forces that would otherwise act tangentially to the unthreaded portion  23 .  
         [0025]    While the preferred embodiment of the invention has been described above, it will be recognized and understood that various modifications may be made therein and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.