Abstract:
An improvement to a collapsible stanchion on a railcar for supporting semi-trailers thereon. The improvement consists of a linkage which is activated by the pulling of a handle away from the stanchion during the operation of raising it from a resting position to an upright position. The linkage exerts a force on a diagonal support member of the stanchion to urge it into a position where the stanchion&#39;s locking mechanism may be engaged to lock the stanchion in an upright position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/548,446, filed Feb. 27, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The intermodal transport of semi-trailers on ocean going barges and flatbed railcars is well known in the prior art. One known method of attaching or “tying down” semi-trailers for transport on railcars utilizes a collapsible stanchion having a “fifth wheel” mounted thereon which mimics the connection point on the rear of a typical on-road tractor. This apparatus operates as illustrated in  FIGS. 1 through 3 .  
         [0003]      FIG. 1  shows stanchion  40  in a collapsed position about to be pulled erect. The erection is accomplished using an operable hook  12  pivotally mounted to the rear of a terminal tractor  10 . Tractor  10  is positioned over stanchion  40  and hook  12  is pivoted down into engagement with an opening (not shown) defined in vertical strut  42  of stanchion  40 .  FIG. 1  shows hook  12  lowered and engaged in the opening.  
         [0004]     In  FIG. 2 , stanchion  40  has been pulled partially erect by the forward motion of tractor  10 . The four main parts of stanchion  40  are now exposed. Stanchion  40  is comprised of vertical strut  42 , which will bear the weight of semi trailer  8  when erect; diagonal strut lower portion  46 , which is fixed to railcar deck  18  by a pinned connection; a shorter diagonal strut upper portion  44 , which is pivotally mounted to both vertical strut  42  and diagonal strut lower portion  46 ; and top plate  48 , which will bear the weight of semi trailer  8  and lock onto the kingpin of trailer  8  to keep trailer  8  and railcar  18  together during travel over the railway.  
         [0005]      FIG. 3  shows stanchion  40  in its fully erect position. Stanchion  40  is locked in this position by diagonal strut  45  formed by upper diagonal strut portion  44  and lower diagonal strut portion  46 . When fully erect, the joint between upper diagonal strut portion  44  and lower diagonal strut portion  46  is locked against rotation and will remain locked until an abutting plate on terminal tractor  10  is backed against release trigger  14  shown in  FIG. 3 . Through suitable linkage, the backward motion of tractor  10  against release trigger  14  will unlatch the joint of diagonal strut  45 , simultaneously releasing the kingpin and permitting the collapse of stanchion  40  back into the position of  FIG. 1 .  
         [0006]     While the collapsible stanchion as illustrated in  FIGS. 1-3  is operable, it suffers from a serious design flaw. To be locked into place, the upper and lower portions  46  and  44  respectively of diagonal strut  45  must be moved slightly beyond their straight line position as defined by the end fastening pins of the two portions  46  and  44 , and the center pivot pin all having their centers in one straight line. The reason for this is that a hard stop of high strength is provided to prevent folding of the strut in the wrong direction. By latching the strut slightly over center (i.e., wherein the diagonal strut is beyond its straight line position), any longitudinal compressive force imparted to the diagonal strut by, for example, switching impacts to the car, or slack action when traveling in a train, will force the strut to fold slightly against its hard stop instead of placing the load on the latching mechanism, thereby freeing the latch mechanism from having to bear these very high forces.  
         [0007]     Because no amount of statically applied pull on the ends of diagonal strut  45 , even up to the breaking strength of diagonal strut  45  could cause this over center alignment to occur, the instructions usually given to operators simply advises that to lock diagonal strut  45  the motion of vertical strut  42  must be rapid enough that diagonal strut  45 , because of inertia, will “snap”, that is, travel beyond the straight line condition, and lock into place at the over center position.  
         [0008]     This is shown in  FIG. 4 .  FIG. 4 ( a ) shows strut  45  before upper portion  44  and lower portion  46  are situated in a straight line. Spring operated latch  50 , mounted on upper portion  44 , is just touching fixed catch  52 , mounted on lower portion  46 .  FIG. 4 ( b ) shows strut  45  closer to its straight-line position. Note that that the closer strut  45  gets to its straight line position, the lesser is the force exerted to move it further into its straight line position. For example, in the position shown in  FIG. 4 ( b ) a tension of 250# will only produce a force of about 23# operating to straighten the strut.  FIG. 4 ( c ) shows strut  45  in a completely straight position, but with latch  52  no yet engaged. Finally,  FIG. 4 ( d ) shows strut  45  moved past the straight position by approximately 3/16″ at  54 . At this position, latch  52  is forced into position by springs  51  and stanchion  1  will remain safely erect.  
         [0009]     Unfortunately the conditions under which the portion of diagonal strut  46  and  44  will lock into place are seldom, if ever, well defined, and no method exists for assuring the speed necessary to bring about the desired locked up condition. The variables affecting this operation (weather, temperature, cleanliness or lack thereof, lubrication, fit and condition of parts, initial manufacturing tolerances and wear, to name the most obvious) are so varied and variable that the perfect tractor speed on one day might fail the next. Regrettably, the drivers who must load trailers cannot know or control any of the variables except for tractor speed, and in trying to assure lockup of the stanchion, have a tendency to pull harder on stanchion  40  than may be necessary to bring about the locked condition. This can result in failure of the stanchion, and, if the car and the stanchion are made strong enough to resist the resulting forces, damage to the tractor can result. Therefore, it would be desirable to provide an improvement to this design in which the two portions of diagonal strut  45  become locked under conditions that are better defined, can be inspected in service and which do not require the “snapping” of the portions into place.  
         [0010]     With the need for high speed pull-ups of the stanchion eliminated from the tractor operating protocol, a maximum speed during pull-up can be imposed (either by the driver or through some form of automatic control) and the hitch and tractor failures mentioned above can be reduced or eliminated.  
       SUMMARY OF THE INVENTION  
       [0011]     The improvement to the prior art stanchion described herein addresses the deficiencies identified above, and provides a system which will assure that when a well-defined and sufficient force is applied to the hook, regardless of speed, the diagonal strut will lock and allow the stanchion to be used in an otherwise normal way. With this end accomplished, a simple tractor control can be implemented which will assure that, when the hook is in the down position and engaged with the stanchion, operating speeds low enough to avoid damage to both the railcar and the tractor are sufficient to engage the stanchion lock.  
         [0012]     The improvements described herein are achieved with a modification to the prior art stanchion consisting of the addition of linkages between the vertical strut and upper diagonal strut of the prior art stanchion. The linkages include a handle, located in the same position and having the same profile as the existing opening in the vertical strut. This handle is engaged by the hook on the rear of the terminal tractor, and pivots outwardly from the vertical strut as the tractor moves forward. The pivoting motion of the handle activates a linkage located inside the vertical strut, which moves a lock rod upward. This lock rod in turn is connected to a toggle link near the center thereof. The toggle link is pivoted to the vertical strut at one end while its other end is connected to a second toggle called the input link, which is pivoted to the input lever, which is simply an integral part of the upper diagonal strut portion. Thereby, the upper portion of the diagonal strut is urged into a position wherein the locking mechanism can engage between the upper strut portion and the lower strut portion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0013]      FIG. 1  diagrammatically shows a prior art tractor semi-trailer arrangement utilizing a hook for stanchion pull-up.  
         [0014]      FIG. 2  shows the prior art stanchion of  FIG. 1  in a intermediate position.  
         [0015]      FIG. 3  shows the prior art stanchion of  FIG. 1  in the full up and locked position.  
         [0016]     FIGS.  4 ( a - d ) show close up views of the upper and lower portions of a prior art diagonal strut as it is pulled beyond its straight line position and locked into that position.  
         [0017]      FIG. 5  shows a side view of the preferred embodiment of the invention.  
         [0018]     FIGS.  6 ( a - b ) show top views of the stanchion of  FIG. 5  in resting position and in up and locked position, respectively.  
         [0019]      FIG. 7  shows an enlarged view of the stanchion in its resting position.  
         [0020]      FIGS. 8   a  and  8   b  show enlarged views of the stanchion in first and second intermediate positions, respectively.  
         [0021]      FIGS. 9   a  and  9   b  show enlarged views of the stanchion in first and second nearly erect positions, respectively.  
         [0022]      FIG. 10  shows the embodiment of  FIG. 5  with the stanchion in a fully erect position.  
         [0023]      FIG. 11  diagrammatically shows a stanchion with the condition of a diagonal strut over center.  
         [0024]     FIGS.  12 ( a - c ) show a hydraulic cylinder control of the tractor for controlled pull-up of the stanchion.  
         [0025]      FIG. 13  diagrammatically shows an alternate electro optic speed control for a tractor to allow controlled pull-up of the stanchion. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     The preferred embodiment of the invention is shown in cross sectional view in  FIG. 5  and consists primarily of a linkage added to vertical strut  42  which is engaged when stanchion  1  is raised from the rail deck to its upright and locked position. Handle  60  resides in the area of opening  58  in vertical strut  42  and is engaged by hook  12  positioned on the back of tractor  10 , as shown in  FIG. 1 . The forward motion of tractor  10  causes vertical strut  42  to begin to raise from the deck of the railcar. As vertical strut  42  travels from its collapsed position on deck  18  of the railcar, upper diagonal strut  44  begins to pivot outwardly from vertical strut  42  toward its final latched position as shown in  FIG. 5 , allowing input lever  70  to rotate about pivot point  71 . As a result, handle  60  slowly begins to pivot outwardly away from vertical strut  42 . Near the end of the travel of upper diagonal strut  44 , further movement of the linkage caused by the continued forward motion of tractor  10 , and the force exerted on handle  60  as a result thereof, forces upper diagonal strut  44  beyond a straight line relationship with lower diagonal strut  46 , thereby allowing the locking mechanism to engage.  
         [0027]     Handle linkage  62  is preferably integral with and perpendicular to handle  60  and moves in unison with the motion of handle  60  as handle  60  pivots away from vertical strut  42 . Handle linkage  62  urges lock rod  64  towards the upper end of vertical strut  42 . Toggle link  66  is pivotably attached at one end to vertical strut  42 . Lock rod  64  engages toggle link  66  in the middle thereof, causing it to rotate about pivot point  65 . The other end of toggle link  66  is coupled to input link  68 , and the opposite end of input link  68  is coupled with input lever  70 . The position of these components in their collapsed position is best shown in  FIG. 7 .  
         [0028]     As lock rod  64  is urged toward top plate  48  by the motion of handle  60  and handle linkage  62 , toggle link  66  pivots on pivot point  65  and causes input link  68  to move in a direction designed to urge input lever  70  to rotate about pivot point  71 , in the same direction of rotation as upper strut  44 . Preferably, pivot point  71  of input lever  70  is coincidental with the point about which upper diagonal strut  44  rotates. Input lever  70  engages upper diagonal strut  44  and urges upper strut  44  to pass beyond a straight line relationship with lower strut  46 , thereby allowing the locking mechanism to lock the strut into place in this position. As a result of the assistance provided by the linkage, the engagement of the locking mechanism occurs regardless of the speed at which the apparatus is raised from deck  18  of the railcar.  
         [0029]      FIG. 6  shows a top view of stanchion  1  is its resting position in  FIG. 6   a  and in its raised position, in  FIG. 6   b.    
         [0030]      FIG. 7  shows the linkages in their stowed position when stanchion  1  is collapsed on deck  18  of the railcar, showing hook  12  engaging handle  60 .  FIGS. 8   a  and  8   b  show the position of the linkages as the stanchion is being raised off of the railcar deck. Note that hook  12  is still engaging handle  60 , however, handle  60  has not yet pivoted in a direction away from vertical strut  47 . The movement of handle  60  away from vertical strut  47  is prevented by the position of input lever  70 , which cannot rotate because of the position of upper strut  44 , which is still folded close to vertical strut  47 . In  FIGS. 9   a  and  9   b , vertical strut  47  has moved to an almost vertical position and the position of upper diagonal strut  44  allows input lever  70  to rotate in a clockwise direction, further rotation of upper diagonal strut  44  toward its final portion is assisted by the linkage. As handle  60  pivots further away from vertical strut  42 , lock rod  64  begins to rotate toggle link about pivot point  65 , thereby urging input link  68  in an upward direction and thereby also urging input lever  70  in a clockwise rotation about point  71 . This causes the upper portion of upper diagonal portion  44  to also move in a counterclockwise direction without the need for any type of inertia which would be required absent the new linkage.  
         [0031]      FIG. 10  shows the stanchion in the complete upright and locked position. After diagonal strut  45  is locked into position, the force on handle  60  may be released and hook  12  removed. This relaxes the linkage comprising lock rod  60 , toggle link  62 , input link  64  and input lever  70 . However, once diagonal strut  45  is locked into place by the engagement of the locking mechanism, the components comprising the linkage are no longer needed to keep the stanchion in the upright and locked position. The only purpose of the linkage is to urge upper diagonal strut  44  into a position where the locking mechanism may engage lower diagonal strut  46  without the need of inertia moving the components past their completely straight positions.  
         [0032]     The kinematics of this setup and it&#39;s geometry during pull-up operation are illustrated in  FIGS. 6, 7 ,  8   a  and  9   a , along with the forces acting to lift the stanchion and acting on the components of the linkage.  
         [0033]     Initial Pull Up Force  
         [0034]     This condition is illustrated in  FIG. 7 . It is assumed for these calculations that a vertical force of 600.5#, applied at the centerline of the kingpin of top plate  48 , would raise top plate  48  and attached struts  42  and  45  against both gravity and friction. Therefore, the 600.5 # downward force in the diagram represents the resistance of stanchion  1  to being pulled up at the pivot point of top plate  48 . Top plate  48  itself is not shown in  FIGS. 7-10 , but is represented by the 600.5# weight vector.  
         [0035]     The geometry included in  FIG. 7  and referenced in the relevant calculation in the Appendix shows that this 600# force will be supplied when a drawbar force along the axis of the connection between hook  12  and tractor  10  is approximately 4000 pounds. This required drawbar force, as shown in the subsequent figures, decreases as the vertical strut rises, becoming essentially zero at the vertical position.  
         [0036]     Also shown in the calculations associated with  FIGS. 7, 8   a ,  9   a  and  10  are the forces in the added linkage acting to open diagonal strut  45  toward its final, over center, locked position. These calculations are to properly size the linkage, and at the end, to assure that the force on upper diagonal strut  44  exerted by linkage will be adequate to assure movement of diagonal strut  45  to its locked position without requiring any potentially damaging dynamic input.  
         [0037]     First Intermediate Position  
         [0038]     This position is shown in  FIG. 8   a , which was chosen as the point where significant motion of the toggle links to force the upper diagonal strut outward begins. At this point, the required drawbar (hook) force has dropped to 2124#, both because of the increasing lever arm of hook  12 , and the decreasing lever arm of top plate  48 . The associated calculation in the Appendix also shows that, at this point, the linkage is exerting a force of only a little more than 1.5# on upper diagonal strut  44 , as reflected at that strut&#39;s central pin.  
         [0039]     Thus, at the position (more or less half elevated) shown in  FIG. 8   a , the linkage has had almost no influence on the operation of the stanchion.  
         [0040]     Second Intermediate Position  
         [0041]     In this position, as shown in  FIG. 9   a , stanchion  1  is nearly erect, and the figure shows that the lever arm through which the 600.5# force is acting is less than one inch. A drawbar force of only 41 pounds is required to balance it but at this point toggle link  66  and input link  68  are beginning to straighten and exert meaningful force on upper diagonal strut  44 . This force is calculated in the Appendix as about 5 pounds at the center pin connecting upper and lower diagonal strut halves  44  and  46  respectively.  
         [0042]     Diagonal Strut Stretched—Stanchion Erect but Not Locked  
         [0043]     The condition, shown in  FIG. 10 , is the end of travel of vertical strut  42  where the rotation upward of vertical strut  42  has been stopped by the straightening of diagonal strut  45 . At this point several important things occur. First, with diagonal strut  45  fully extended, drawbar force is no longer a function of the weight of top plate  48 , but acts directly into diagonal strut  45 . Thus, any drawbar force that tractor  10  is capable of producing may now be applied to the lever and will cause a proportional reaction force in diagonal strut  45 .  
         [0044]     Second, while diagonal strut  45  is assumed not to have gone over center due to lack of dynamic input, the linkage at this point is becoming much more capable and is exerting a force to take diagonal strut  45  toward the locked-up position. Because all forces at and beyond this point are proportional to drawbar force, an arbitrarily chosen drawbar force of 1000# is used to determine all the other forces involved in the linkage.  
         [0045]     To determine any actual force then, the force shown may be multiplied by the ratio of the actual drawbar force to 1000# and the actual force determined. At a thousand pounds, the axial force in diagonal strut  45  is calculated in the appendix as 539# and the force available to push diagonal strut  45  to lock (at right angles to the axial force) as 260#. To determine whether this force should be adequate, the force opposing it that would obtain at 3/16″ beyond center was calculated using the geometry of  FIG. 11 .  
         [0046]     As can be seen from  FIG. 11 , the force at right angles to the pivot pin of diagonal strut  45 , resulting from a thousand pound drawbar pull is only 7.7#, whereas the force available from the linkage to overcome this and move diagonal strut  45  into lock position is about 260#. This will force strut  45  into place and permit the springs in the locking mechanism to move it into engagement.  
         [0047]     From the above it should be clear that, because the drawbar force and hence the position of the linkage may be held for as long as desired, a low temperature which might cause the lock latch to move too slowly to dynamically lock up, would not be deleterious to this design. Likewise there is limited potential of someone hitting the linkage so hard that diagonal strut  45  would spring through the position wherein engagement of the locking mechanism could occur and bounce back before the locking mechanism could engage.  
         [0048]     Control of the Terminal Tractor  
         [0049]     The elimination of the requirement for “snapping up” stanchion  1  allows two important changes to be made in the technology of trailer tie down. One is that the operation of stanchion  1  can be verified with static methods such as using a simple spring scale to verify proper stanchion operation, thus permitting quick inspection and maintenance and adjustment of stanchions to be made at convenient times when trains are not loading or unloading trailers. The other is that the performance of tractor  10  can be repeatably controlled during the erection of stanchion  1  to eliminate excessive forces, thus reducing wear and tear on both railcar and tractor equipment for a significant savings in both loading time and repair costs and delays.  
         [0050]     Because the horizontal distance the tractor must travel to erect a stanchion is only about  17 1/2 inches, a stop 80 could be affixed to deck 18 of the railcar at a convenient point at or ahead of the vertical strut mounts and a retracted hydraulic cylinder 82 affixed to the tractor such as shown in FIGS. 12(   a - c ) could be lowered to the deck at the same time that hook  12  is lowered to acquire stanchion pull-up handle  60 . The action of operating the hook control to lower hook  12  and cylinder  82 , as shown in  FIG. 12 ( a ), could also, through separate controls, restrict the speed of the tractor engine to idle. The position of the stop and the relationship of the cylinder position to the position of the hook could be arranged such that when the tractor moves forward and the hook engages pull-up handle  60 , the end of cylinder  82  would move over stop  80  to a position an inch or so ahead of it, as shown in  FIG. 12 ( b ). At this point, tractor  10  would stop, because it takes nearly 4000 pounds of drawbar pull to begin to raise stanchion  1  and this force is not available when the engine speed is at idle. At this point, the operator could supply hydraulic cylinder  82  with fluid at a rate to move tractor  10  forward at a rate of approximately 8-16 inches per second, as shown in  FIG. 12 ( c ), and reaction force would cause pressure in cylinder  82  to rise and fall in accord with the resistance to motion caused by the varying drawbar force requirement. With the stanchion locked up, the cylinder would not be capable of continuing to move tractor  10  forward, at which point the operator should disengage the hydraulic fluid from the cylinder and raise the hook. This arrangement would provide one simple means of controlling loads and dynamics for the entire erection and lock up operation.  
         [0051]     Alternatively, a perforated or radially slotted disc  90  could be fixed to prop shaft  92  of tractor  10  and the edge of the disc could be straddled by an optical switching unit  94  or photonic detector. The slots would then pass between the source and photodiode of the detector as disc  90  rotated, thus producing an output signal which would switch a definite number times per revolution of shaft  92  no matter how low the shaft speed might be, This detector in turn would signal one input of a programmable logic controller (PLC)  96  to supply power to a first solenoid air valve  97  when the speed of prop shaft  92  corresponded with a tractor speed of approximately 8-12 inches per second, and to supply power to a second such valve  98  as tractor speed got to or above approximately 16-20 inches per second. A second input to PLC  96  would be provided by a hook position indicator  99  and would prevent any signal to the solenoids when hook  12  was retracted, thus preventing interference with normal tractor operation when the hook is in the raise position. A schematic representation of such a system is shown in  FIG. 13 .  
         [0052]     Each of the solenoid valves would supply air via a double check valve  95  to a small actuator  93  on or beneath the cab floor, which would urge the throttle control pedal upward to its idle position. First solenoid  97  would supply air at a low enough pressure that the operator could, by exerting an increase in effort, maintain the throttle open above idle. The second valve  98  would admit air at a higher pressure to actuator  93  and would be more capable of moving pedal  91  back to idle than the operator could be in forcing it down. The operator then, could speed the engine up to provide the increased drawbar pull necessary to start the stanchion up, but would not be able to cause a tractor over speed during the stanchion erection operation. The double check valve  95  would send the higher pressure to actuator  93 , and permit its exhaustion when both solenoids  97  and  98  were off.  
         [0053]     As has been shown, the invention can be practiced in a number of ways with various loads and forces involved, and is not limited to the linkage shown, which is described merely as an example of one linkage design that satisfies the requirements of the invention. The following example uses some typical forces as one example. It is also to be understood that this example is only one of many load/force embodiments that could be practiced within the scope of the invention claimed, shown, and described herein.  
         [0000]     Appendix—Calculations Relative to  FIGS. 7-11   
         [0054]     Forces Acting on Stanchion and Linkage— FIG. 7   
         [0055]     A vertical cylinder  4 ′ diameter with a 1″ rod can be attached to top plate  48  at the kingpin centerline, and would raise top plate  48  vertically when pressure exceeding 51 psi was supplied to the cylinder. 
        Force produced by this cylinder then is found from:     Piston area=0.785*15=11.775 sq in.     Vertical force=11.775*51=600.5 #    Moment required about vertical strut anchor pin then is:     600.5*41.62=24992.81 # in.     Force on hook to provide this moment is: Initial lever arm to hook=6.29 as shown.     Initial Hook force required is: 24992/6.29=3973.2 #    Internal forces on diagonal strut lock assurance linkage torque on input handle to generate internal force=lifting force x handle length: 3973*2.75=10925.75 # in     Force on lock rod=10925.75/3.9=2801.4 #       
 
         [0065]     Force on Upper Diagonal Strut 
        Compressive force in toggle link     2801*1.53/2.81=1525#    Torque on upper diagonal strut: 1525*0.063=96.0#in (to close)     Resultant force at pin connecting upper and lower diagonal strut: 96/17.81=5.4 # working against strut opening up (negligible)     Ratio Input/output: 3972/−5.4=−735.5        
 
         [0071]     Forces Acting on Stanchion and Linkage— FIG. 8   a  
        Torque required about vertical strut anchor pin     600.4*32.8/9.27=hook force of 2124.39 #    Internal forces on diagonal strut lock assurance linkage:     Force on lock rod=2124*4.02/3.9=2189.8 #       
 
         [0076]     Force on Upper Diagonal Strut 
        Compressive force in toggle link     2189*1.52/2.95=1128.3 #    Torque on upper diagonal strut: 1128.3*0.02=22.56 # in (to open)     Resultant force at pin connecting upper and lower diagonal strut:     22.56/17.81=1.26 # working to open the strut up (negligible)     Ratio Input/output: 2124.4/1.26=1686.0        
 
         [0083]     Forces Acting on Stanchion and Linkage— FIG. 9   a  
        Hook force is 600.4*0.961/13.777=41.88 #    Internal forces on diagonal strut lock assurance linkage;     Force on lock strut=41.88*7.34/3.93=78.21 #       
 
         [0087]     Force on Upper Diagonal Strut 
        Force in control link: 41.88*1.653/2.231=31.02 #    Force at pivot pin to lower diagonal strut: 31.02*2.845/17.813=4.954 # to open     Ratio input/output is 41.88/4.954=8.453        
 
         [0091]     Calculations for  FIG. 10  
        Tension force in diagonal strut from 1000# drawbar=1000*13.487/25.007=539.3 #    Force in Lock Strut 
            539.3*7.033/3.894=974.03 #   
            Force in control link=974.0*1.565/0.927=1644.3 #    Force at pivot pin to lower diagonal strut 1644.3*2.821/17.813=260.4 # to open     Ratio input/output+1000/260.4=3.840        
 
         [0098]     Calculations for  FIG. 11   
         [0099]     With diagonal strut under 539.3 # tension and strut control linkage straightened to force the center pin over center by 3/16 in., the proportional triangles of  FIG. 10  give the restoring force which must be overcome by the action of the linkage. 
        For the larger triangle the restoring force is: 539.3*0.187/49.41=2.041 #    For the smaller triangle the restoring force is; 539.3*0.187/17.813=5.661 #    The total restoring force then is: 2.041+5.661=7.702 #    Thus the force available to move the diagonal strut over center against pin friction, latch friction, and latch spring load, so as to allow the latch to engage will be: 
            260.4-7.7=252.3 # (for each 1000# imposed on the pull-up handle by the drawbar)