Patent Publication Number: US-10766398-B2

Title: Tie down with automatic strap tension adjustment

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/900,587 of the same title and filed Feb. 20, 2018, which application is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Field 
     The subject disclosure relates to tie down mechanisms and more particularly to a tie down mechanism featuring automatic adjustment of the tension applied to a strap component of the mechanism. 
     Description of Related Art 
     Various tie down mechanisms have been constructed in the past and have been employed, for example, to tie down a load to a trailer or other transport vehicle. In such applications, such tie down mechanisms typically have a first strap which is secured to the load and a second strap which is attached to the trailer. 
     SUMMARY 
     According to an illustrative embodiment, a tie down apparatus includes a drum comprising first and second drum pins separated by a space, the space being shaped to receive and hold a tie down strap as well as first and second ratchet wheels, the first and second ratchet wheels each comprising a plurality of ratchet teeth. 
     First and second spiral load springs are each mounted adjacent an outside surface of one of the first and second ratchet wheels. Each spiral load spring has a center leg and a tab at an outer end thereof. In the illustrative embodiment, the center leg of each spiral load spring is inserted in the space between the first and second drum pins, and the first end of each tab of each spiral load spring is fixedly attached to a respective one of the first and second ratchet wheels, such that as the ratchet wheels are rotated, a preload is applied to the first and second load springs. 
     Further in the illustrative embodiment, first and second circular plates are mounted in a central opening in each ratchet wheel and have first and second openings shaped to respectively receive opposite ends of the first and second drum pins. The ratchet wheels have inwardly projecting nubs positioned to come into engagement with outwardly projecting nubs on the first and second circular plates as each ratchet wheel rotates with respect to its respective circular plate. In an illustrative embodiment, these nubs interact so as to limit the amount of pre-load applied to each load spring. 
     According to the illustrative embodiment, rotation of the ratchet wheels to tighten the tie down strap pre-loads the spiral load springs to the same tension applied to the strap up to a limit established by the interaction of the respective nubs of the ratchet wheels and circular plates. If the strap were to lose tension below the preload spring rate of the spiral springs, then the springs act to force the drum pins to rotate and increase tension on the strap until the preload tension of the springs and the strap tension are in equilibrium or until the springs have lost all of their preload. 
     According to another aspect of the disclosure, a method of strap tension adjustment for a tie down apparatus is provided comprising attaching an outer end of first and second load springs to respective outside surfaces of respective first and second ratchet wheels, inserting an inner leg of each load spring into a space between respective rotating pins of the tie down apparatus, positioning a plate within a central opening in each ratchet wheel, and configuring each plate to rotate in unison with the respective rotating pins. Further according to the method, an inner periphery of each of the ratchet wheels and an outer periphery of a respective one of the plates are shaped such that the inner periphery and outer periphery interact so as to stop rotation of the first and second ratchet wheels with respect to the plates at a selected point so as to limit an amount of pre-load force applied to the load springs. 
     According to another aspect of the disclosure, first and second plates are each sandwiched between the outside surface of a respective one of first and second ratchet wheels and an inside surface of corresponding spiral load springs, each spiral load spring having a center leg and a tab at an outer end thereof, wherein the tabs and respective ratchet wheels are configured to rotate in unison together through a first range of motion and wherein the center leg of each of the first and second load springs is positioned in the space between the drum pins of a tie down apparatus. Each of the first and second plates has a cut-out arc portion in its perimeter having first and second end surfaces, and the tab of each spiral load spring is positioned to move within the cut-out arc from the first end surface to the second end surface, such that, as the first and second ratchet wheels are driven in a direction so as to tighten a tie down strap, the tab of each spiral load spring is driven toward the second surface until it abuts that second surface. After such abutment, the first and second ratchet wheels are constrained to rotate in unison with the first and second plates such that no further load is applied to the spiral load springs. In one embodiment, each tab is fixedly attached in a slot in each respective ratchet wheel. In another embodiment, each tab engages a bump formed on each respective ratchet wheel. In another embodiment, each tab is step-shaped and is inserted into a mating step-shaped opening in a respective ratchet wheel 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is front perspective view of a tie down apparatus according to an illustrative embodiment in a first position; 
         FIG. 2  is a rear perspective view of the tie down apparatus of  FIG. 1 ; 
         FIG. 3  is an exploded view of the tie down apparatus according to the illustrative embodiment; 
         FIG. 4  is a perspective view of tension adjustment apparatus according to an illustrative embodiment in an assembled state; 
         FIG. 5  is an exploded view of the tension adjustment apparatus of  FIG. 4 ; 
         FIG. 6  is a front perspective view of the tie down apparatus of the illustrative embodiment in a second position; 
         FIG. 7  is a rear perspective view of the tie down apparatus of  FIG. 6 ; 
         FIG. 8  is a perspective view of the tie down apparatus of the illustrative embodiment in a third position; 
         FIG. 9  is a perspective view of the tie down apparatus in a fourth position; 
         FIG. 10  is a side view of the tension adjustment apparatus of  FIGS. 4 and 5 . 
         FIGS. 11 and 12  are perspective views illustrating another embodiment of tension adjusting apparatus; 
         FIG. 13  is a perspective view illustrating another embodiment of tension adjusting apparatus; and 
         FIG. 14  is a perspective illustrating another embodiment of tension adjusting apparatus. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-10  show an illustrative embodiment of a self-adjusting tie down apparatus  11 . The illustrative embodiment  11  includes a base frame  13 , which is attached to a fixed strap  112  ( FIG. 7 ) secured by a bolt  15  and nut  17 . A “drum”  18 , which comprises two drum pins  19 ,  21 , rotates in respective circular openings  50  in respective end plates  29 ,  31  of the base frame  13 . This drum  18  is caused to rotate by respective center legs  123  of respective main load springs  125 , one spring  125  on each side of the drum  18  and positioned adjacent the outer sides of respective first and second ratchet wheels  135 . A tab  136  at the outer end of each main load spring  125  is inserted into a slot  142  in the side of each ratchet wheel  135  and, in one embodiment, is fixedly attached to the respective ratchet wheel  135 , for example, by welding. 
     In an illustrative embodiment, each main load spring  125  is a spiral wound spring. A circular plate  148  is centered within each ratchet wheel  135 , as shown for example in  FIG. 5 . In the illustrative embodiment, each circular plate  148  is positioned between a respective load spring  125  and one of the end plates  29 ,  31  of the base frame  13  and is thereby held in place axially. 
     In the illustrative embodiment, the interior circular periphery of each ratchet wheel  135  has three radially positioned inwardly projecting nubs  151 ,  153 ,  155  formed thereon separated from one another by 120 degrees. Correspondingly, each circular plate  148  has three radially positioned outwardly projecting nubs  152 ,  154 ,  156  formed on its outer circular periphery and separated from one another by 120 degrees. The components are sized such that the nubs  152 ,  154 ,  156  of each circular plate  148  will come into contact with the nubs  151 ,  153 ,  155  of the respective ratchet wheels  135  if the ratchet wheels  135  are rotated through a selected arc with respect to the circular plates  148 . Each circular plate  148  further has slots  232 ,  234 , which receive the ends  20 ,  22  of the drum pins  19 ,  21  and are shaped conformably such that the circular plates  148  are forced to rotate in unison with the drum pins  19 ,  21 . 
     In assembly of the apparatus of  FIG. 5  according to an illustrative method of assembly, the drum pins  19 ,  21  are first inserted into the openings  50  in the end plates  29 ,  31  of the base frame  13 . Each load spring tab  136  is then welded or otherwise attached to its respective ratchet wheel  135 . Each circular plate  148  is then slid onto the opposite ends of the drum pins  19 ,  21 . The springs  125  with ratchet wheels  135  attached are then mounted onto opposite ends of the drum pins  19 ,  21  by placing the leg  123  of each spring  125  in the slot  57  between the drum pins  19 ,  21  and pushing the legs  123  into the slot  57 , while allowing each circular plate  148  to come into position within its respective ratchet wheel  135 . In one embodiment, an end cover  126  may be slid over the outer periphery of the load spring  125  and ratchet wheel  135  to cover the assembly. 
     Each side of the base frame  13  has an angled slot  37  into which fits respective wings  40  of a main latch  39 . The main latch  39  can slide in the slots  37  and engage the teeth, e.g.  41 , of each ratchet wheel  135  and is spring loaded toward each ratchet wheel  135  by a main latch spring  43  ( FIGS. 3, 8 ). The main latch spring  43  is mounted on a pin  146  projecting from a rear side of the main latch  39  and is held in place by an upright projection  42  on the base frame  13 , which has a slot  44  ( FIG. 3 ) through which the pin  46  fits. 
     A handle frame  45  has circular openings  150  ( FIG. 3 ) through which project the respective ends, e. g.  20 ,  22 , of the drum pins  19 ,  21 . Two pins  47  respectively inserted through the drum pins  19 ,  21  on either side of the device serve to hold the mechanism together. 
     The handle frame  45  has a handle  49  at one end that is easy to grip and a pair of slots  51  in which fit respective wings  54  of a handle latch  53 . The handle latch  53  slides in the slots  51  and engages respective teeth, e.g.  41   b  ( FIG. 1 ), of each ratchet wheel  135 . The handle latch  53  is spring loaded toward the ratchet wheel  135  by a handle spring  55  ( FIG. 3 ). The handle latch  53  has a slot  56  in which fits one end  58  of the handle spring  55 , while the coiled end  60  of the handle spring  55  fits over and is retained by a pin  62  formed in the slot  51  of the handle frame  45 . 
     The tie down  11  is used by inserting a strap  12  through the slot  57  in between the two drum pins  19 ,  21 , as shown in  FIG. 6 . As shown in  FIG. 2 , in a first position, the main latch  39  is engaging a tooth  41   c  of each of the ratchet wheels  135 , specifically by engagement with the front surface of those two ratchet teeth, e.g.  41   c.  As shown in  FIGS. 1 and 2 , in the first position, the handle frame  45  is at its lowest point of rotation, lying generally parallel to the base frame  13 . In this position, rear surfaces  160  of the respective recesses  59  ( FIG. 3 ) of the handle frame  45  engage the respective wings  40  of the main latch  39  and prevent the main latch  39  from disengaging from the ratchet wheel teeth, e.g.  41   c.    
     Additionally, in the first position shown in  FIGS. 1 and 2 , each surface  74  of the spring loaded handle latch  53  is engaging each ratchet wheel  135  via engagement with the front surface of a respective oppositely disposed pair of ratchet teeth, e.g.  41   b.  In this position, the respective surfaces  74  on the handle latch  53  are also locked behind a respective step  61  formed on the circumference of the base frame  13 , which prevents the handle latch  53  from rotating around the drum  18 . 
     As illustrated in connection with  FIG. 6 , by pulling the handle  68  of the handle latch  53  against its spring bias away from the base frame  13  in the direction of arrow  70 , the surfaces  74  on the handle latch  53  will clear the steps  61  in the base frame  13 , and the handle frame  45  can then rotate into a second position shown in  FIGS. 6 and 7 . This action also clears wings  40  of the main load latch  39  from engagement with the rear surfaces  160  of the recesses  59  such that the main load latch  39  is now free to slide back and forth in its respective slots  37  while engaging the teeth, e.g.  41   c,  on each ratchet wheel  135 . 
     By rotating the handle frame  45  through an arc from the second position to the third position shown in  FIG. 8 , each ratchet wheel  135  will rotate through the same arc. In an illustrative embodiment, this arc amounts to three ratchet teeth out of eleven total=an arc of approximately 98 degrees. This rotation causes each main load spring  125  to rotate the drum pins  19 ,  21  through the same angle, as long as there is no tension load on the strap  12 . At the same time, the main load latch  39  shuttles back and forth following the rear cammed or contoured surfaces  76  ( FIGS. 2, 4, 5 ) of three successive ratchet teeth  41  of each ratchet wheel  135 , thus “ratcheting” three times in the illustrative embodiment. At the end of this ratcheting action, the main load latch  39  again engages behind the flat surface of the next successive ratchet tooth of each ratchet wheel  135 , as shown in  FIG. 2 . 
     After the handle frame  45  reaches the third position of  FIG. 8 , it is rotated from the third position back to the second position while the handle latch  53  slides back and forth following the rear profile  76  of each ratchet wheel tooth, again “ratcheting” three times and engaging at the end of the travel behind the flat surface of another pair of ratchet teeth. During travel from the third position back to the second position, the drum pins  19 ,  21  do not rotate, and the tension on the strap is maintained by the main load latch  39 . 
     This process of rotating the handle frame  45  between the second and third positions will continue and in turn will put additional load on the strap  12 , and therefore each main load spring  125  will also be preloaded to the same level of tension. As each main load spring  125  is preloaded, each nub  151 ,  153 ,  155  of each ratchet wheel  135  begins to rotate toward the corresponding nub  154 ,  156 ,  152  of each circular plate  148  as illustrated in  FIG. 10 . In this respect, nub  151  approaches and eventually comes into abutment with nub  154 , nub  153  approaches and eventually comes into abutment with nub  156 , and nub  155  approaches and eventually comes into abutment with nub  152 . 
     In an illustrative embodiment, if the nubs are each 10 degrees “wide,” (Tab  1 , Tab  2  angles), then the maximum angular rotation of the ratchet wheels  135  before the nubs of the ratchet wheels  135  engage the nubs of the circular plates  148  is 120 degrees minus 20 degrees equals 100 degrees. When the nubs so engage, the ratchet wheels  135  are prevented from rotating further with respect to the circular plates  148  and the pins  19 ,  21 , and further loading of the load springs  125  ceases. At this point, the load springs  125  have reached the maximum preload permitted by the particular design of the device. In an illustrative embodiment, the maximum angular rotation during which preload is applied is 100 degrees, but may range from 40 to 340 degrees in other embodiments, depending, for example, on the type of spring tension selected, number of nubs, and the application for which the tie down is used. In other embodiments, the circular plates  148  and ratchet wheels  135  could each have less than three nubs respectively, for example, two nubs on each of the circular plates  148  and ratchet wheels  135 , or one nub. Thus, for example, each circular plate  148  may have at least one outwardly protruding nub and each ratchet wheel  135  may have at least one inwardly protruding nub. 
     Once each main load spring  125  has gone through an approximately 100 degrees preload angle, further preload on the main load springs  125  ceases in order to prevent overloading those springs  125 , and any further tension generated by rotating the handle frame  45  from the second to the third position will now in turn directly rotate the drum pins  19 ,  21 , and add additional load tension to the strap  12 . When the tie down operation is complete, the tie down  11  is in the locked position shown in  FIGS. 1 and 2 . 
     In the event that the strap  12  were to lose tension below the preload spring rate of the main load springs  125 , then the main load springs  125  will force the drum pins  19 ,  21 , to rotate and increase tension on the strap  12  until the preload tension of the main load springs  125  and the strap tension are in equilibrium or until the main load springs  125  have lost all of their preload. 
     As shown in connection with  FIG. 9 , when the apparatus is in the position shown in  FIG. 8 , pulling on the handle latch handle  68  against its spring bias further in the direction of the arrow  70  allows the handle frame  45  to move into a fourth position shown in  FIG. 9 . This action disengages the handle latch  53  from the ratchet wheel teeth completely. At the same time, a ramp  101  on the exterior of the handle frame  45  also pushes the main load latch  39  away from the ratchet wheel teeth  41 . This effectively allows the drum pins  19 ,  21  completely free rotation, removes the tension on the strap  12 , and releases any remaining tension on the main load springs  125 . 
       FIGS. 11-14  illustrate alternative embodiments for enabling the ratchet wheels of the tie down mechanism to first rotate freely with respect to the load pins  19 ,  21  and to thereafter stop that free rotation at a point after the spiral springs have been loaded to a degree which enables maintaining tension on the strap of the tie down mechanism. In an embodiment illustrated in  FIGS. 11 and 12 , a plate  248  has a cut-out arc  249 , which provides two surfaces designated “A” and “B.” A first tab  236  at the end of a spiral load spring  225  is fixedly attached in a notch or opening  242  in a ratchet wheel  235 , while the inner end  223  of the spiral load spring  225  is inserted into the gap  57  between the load pins  19 ,  21 . As illustrated in  FIG. 12 , each plate  248  is sandwiched between its respective ratchet wheel  235  and spiral load spring  225 . In this configuration, as the ratchet wheels  235  are driven in the direction of the arrow  250  ( FIG. 11 ), the tab  236  will be driven rotationally from surface A toward the surface B until it abuts that surface B. Thereafter, the ratchet wheels  235  are constrained to rotate in unison with the plates  248  and pins  19 ,  21 , and no further load is applied to the spiral load springs  225 . 
     The embodiment of  FIG. 13  is constructed and functions similarly to that of  FIGS. 11-12 , the only difference being that each tab  336  of each spiral load spring  325  engages its respective ratchet wheel  325  through abutment with the bottom edge  338  of a “bump”  337 , which is fixedly attached to, or integrally formed as part, of each ratchet wheel  335 . The embodiment of  FIG. 14  is similarly constructed with the exception that the tab  436  of the spiral load spring  425  is formed as a stepped edge, which mates with a stepped opening  442  in the ratchet wheel  435 . In various embodiments, the tab  436  may slide fit together with the stepped opening  442 , may press-fit into that opening  442 , or may be welded in place in the opening  442 . 
     From the foregoing, those skilled in the art will appreciate that various adaptations and modifications of the just described illustrative embodiments can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.