Abstract:
A swing cylinder such as those used to offset an agricultural implement may experience larges forces as it reaches the ends of its travel. A cushioning system to mitigate these forces comprises a piston with wear rings engaged thereto. The wear rings block off a usual passageway for the hydraulic fluid to flow, and provide their own, much smaller passageway. The flow of hydraulic fluid is thereby restricted in the neighborhood of the extremes of piston travel. An additional aspect of the invention is that the wear rings are pushed out of their position blocking the passageway when hydraulic fluid pressure is applied to move the piston away from the extreme position, thereby completely removing the restriction to flow in that direction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    U.S. patent application Ser. No. 11/927,866 filed Oct. 30, 2007 (Our Reference 2-5169-110), U.S. patent application Ser. No. 11/928,010 filed Oct. 30, 2007 (Our Reference 2-5169-111) and U.S. patent application Ser. No. 11/928,082 filed Oct. 30, 2007 (Our Reference 2-5169-112) are hereby incorporated by reference herein in their entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO MICROFICHE APPENDIX 
       [0003]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The present invention relates generally to a mower used in agricultural applications. More particularly, the present invention relates to an improved swing cylinder used in appropriately orienting a tongue of an agricultural mower for transport and for mowing. 
         [0006]    2. Background Art 
         [0007]    Some agricultural implements, notably mowers and mower-conditioners, require that the implement be offset from the tractor when in operation so the tractor does not knock down crop before it can be processed, and also that the implement be centerable behind the tractor for transport. The use of a hydraulic swing cylinder is known in the prior art. In U.S. Pat. No. 7,047,714, a swing cylinder arrangement is disclosed providing the ability to both offset a mower-conditioner for operation and center the mower-conditioner behind the tractor for transport. 
         [0008]    Another swing cylinder is disclosed in U.S. Pat. No. 6,907,719. The swing cylinder is shown in FIGS. 3-5 in U.S. Pat. No. 6,907,719 denoted with reference numeral 7. 
         [0009]    As an agricultural implement tongue is rotated about a pivot axis, the swing cylinder retracts or extends depending on the direction of rotation. The maximum and minimum angle the tongue can be positioned relative to the frame is thereby determined by the stroke range of the cylinder. The cylinder is pivotally mounted to the frame at a pivot point which is not coincident with the pivot point of the tongue, but offset in a transverse direction and possibly in the longitudinal direction. Abrupt deceleration at the extreme ends of the swing cylinder&#39;s stroke can be significant. Dynamic forces resulting from the rotation of the tongue can be sufficient to cause structural damage to the tongue, frame, or swing cylinder when the cylinder reaches its maximum or minimum stroke. 
         [0010]    There is, therefore, a need for a method and apparatus to reduce the magnitude of the deceleration at the extreme ends of the swing cylinder&#39;s stroke to reduce dynamic forces and consequent damage. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    An object of the present invention is to provide a swing cylinder, for tongued agricultural implements, for which stroke speed is restricted at the extreme ends of its stroke in the direction of the extreme ends. Another object is, then, when traveling away from the extreme ends, the cylinder&#39;s stroke speed is not limited, even when the hydraulic cylinder position is at an extreme. 
         [0012]    To effect the instant invention, wear rings are provided at each end of a piston about the hydraulic swing cylinder ram. These wear rings are permitted to slide in an axial direction due to forces encountered when the piston is moving axially. When the piston approaches either extreme end of its travel, the wear rings pass the port at that extreme end. Passageways are provided in the piston through which hydraulic fluid may pass. Additionally, splits are provided in the wear rings. The hydraulic fluid may pass from the passageways in the piston, through the splits in the wear ring in order to exit the port. The split in the wear rings is very small, and presents a significant restriction to the flow of hydraulic fluid. Hence, the flow rate of the hydraulic fluid is reduced, consequently reducing the cylinder&#39;s stroke speed. 
         [0013]    Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of a center pivot mower of the present invention having a tongue pivotally connected to the frame with a relative angle controlled by a swing cylinder; 
           [0015]      FIG. 2  is a top plan view of the center pivot mower with the mower swung in a first direction for operation; 
           [0016]      FIG. 3  is a top plan view of the center pivot mower with the mower swung in a second direction for operation; 
           [0017]      FIG. 4  is a top plan view of the rear of the center pivot mower; 
           [0018]      FIG. 5  is a geometric schematic of the mower from the top showing the tongue at a minimum, maximum, and perpendicular angle to the frame; 
           [0019]      FIG. 6  is a first cross sectional view of the cushioned swing cylinder in an extended position; 
           [0020]      FIG. 7  is a second cross sectional view of the cushioned swing cylinder in a retracted position; 
           [0021]      FIG. 8  is a third cross sectional view of the cushioned swing cylinder in a midpoint position; 
           [0022]      FIG. 9  is a first detail of the cross section of a piston within the swing cylinder with wear rings; 
           [0023]      FIG. 10  is a second detail of the cross section of the piston with wear rings; 
           [0024]      FIG. 11  is a detail view of the piston and lower wear ring in the vicinity of a hydraulic fluid port; 
           [0025]      FIG. 12   a  is a perspective view of a wear ring exhibiting a first form of a split; 
           [0026]      FIG. 12   b  is a perspective view of a wear ring exhibiting a second form of a split; 
           [0027]      FIG. 12   c  is a perspective view of a wear ring exhibiting orifices for the passage of hydraulic fluid; 
           [0028]      FIG. 13  is a plan view showing the piston, cylinder ram, and passages; 
           [0029]      FIG. 14   a  shows a hydraulic piston in a first position relative to an extreme end of travel, the hydraulic cylinder tube having a variable inside diameter; 
           [0030]      FIG. 14   b  shows the hydraulic piston in a second position relative to the extreme end of travel, the hydraulic cylinder tube having a variable inside diameter; and 
           [0031]      FIG. 14   c  shows the hydraulic piston at the extreme end of travel, the hydraulic cylinder tube having a variable inside diameter. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Referring now to the drawings wherein like reference numerals correspond to the same or similar parts throughout the drawings, the present invention makes use of a cushioned cylinder as a swing cylinder  17 , as seen in all the figures, on a center-pivot agricultural mower  1 . As shown in  FIGS. 1-5 , the swing cylinder  17  controls the rotation of a tongue  2  about a vertical axis  30  such that the tongue  2  can be positioned at a variable angle, θ, relative to a mower frame  15  on either side of a centerline  52  of the agricultural mower  1 . The way θ is measured is illustrated in  FIG. 5 . 
         [0033]    As the tongue  2  is rotated about the pivot axis  30 , the swing cylinder  17  retracts or extends depending on a direction of rotation. The maximum and minimum angle, θ=θ max , the tongue  2  can be positioned relative to the frame  15  is thereby determined by a stroke range (compare  FIGS. 6 and 7 ) of the cylinder  17 . Dynamic forces resulting from the rotation of the tongue  2  can be sufficient to cause structural damage to the tongue  2  and/or frame  15  when the cylinder  17  reaches its maximum ( FIG. 6 ) or minimum ( FIG. 7 ) stroke. At intermediate positions ( FIG. 8 ), no potentially damaging forces are encountered. The cylinder  17  is pivotally mounted to the frame  15  at a pivot point  29  which is not coincident with the pivot point  30  of the tongue, but offset in a transverse direction and preferably in a longitudinal direction. The swing cylinder  17  of the present invention preferably strokes at a constant rate, resulting in a variable angular speed, dθ/dt, of the tongue  2  relative to the frame  15 . This concept is illustrated in  FIG. 5  and in Table 1 for the mower of  FIGS. 1-3 , where a counterclockwise rotation of the tongue is considered positive, by convention. When the stroking speed, dL/dt, of the swing cylinder  17  is constant, the rotational speed, dθ/dt, of the tongue  2  relative to the frame  15  must be proportional to the derivative, dθ/dL, of the angle, θ, with respect to the cylinder length, L. In other words: 
         [0000]    
       
         
           
             
               
                  
                 θ 
               
               
                  
                 t 
               
             
             = 
             
               
                 
                   
                      
                     θ 
                   
                   
                      
                     L 
                   
                 
                  
                 
                   
                      
                     L 
                   
                   
                      
                     t 
                   
                 
               
               = 
               
                 C 
                  
                 
                   
                      
                     θ 
                   
                   
                      
                     L 
                   
                 
               
             
           
         
       
     
         [0000]    where C is the constant of proportionality and is equal to the constant stroking speed, dL/dt. 
         [0034]    The relationship between the angle, θ, and the cylinder length, L, is: 
         [0000]        L (θ)=√{square root over (( B+R  cos θ− D  sin θ) 2 +( C+R  sin θ+ D  cos θ) 2 )}{square root over (( B+R  cos θ− D  sin θ) 2 +( C+R  sin θ+ D  cos θ) 2 )} 
         [0000]    while the derivative of the angle, θ, with respect to the cylinder length, L, is: 
         [0000]    
       
         
           
             
               
                  
                 θ 
               
               
                  
                 L 
               
             
             = 
             
               
                 
                   
                     
                       ( 
                       
                         B 
                         + 
                         
                           R 
                            
                           
                               
                           
                            
                           cos 
                            
                           
                               
                           
                            
                           θ 
                         
                         - 
                         
                           D 
                            
                           
                               
                           
                            
                           sin 
                            
                           
                               
                           
                            
                           θ 
                         
                       
                       ) 
                     
                     2 
                   
                   + 
                   
                     
                       ( 
                       
                         C 
                         + 
                         
                           R 
                            
                           
                               
                           
                            
                           sin 
                            
                           
                               
                           
                            
                           θ 
                         
                         + 
                         
                           D 
                            
                           
                               
                           
                            
                           cos 
                            
                           
                               
                           
                            
                           θ 
                         
                       
                       ) 
                     
                     2 
                   
                 
               
               
                 
                   
                     
                       
                         
                           ( 
                           
                             B 
                             + 
                             
                               R 
                                
                               
                                   
                               
                                
                               cos 
                                
                               
                                   
                               
                                
                               θ 
                             
                             - 
                             
                               D 
                                
                               
                                   
                               
                                
                               sin 
                                
                               
                                   
                               
                                
                               θ 
                             
                           
                           ) 
                         
                          
                         
                           ( 
                           
                             
                               
                                 - 
                                 R 
                               
                                
                               
                                   
                               
                                
                               sin 
                                
                               
                                   
                               
                                
                               θ 
                             
                             - 
                             
                               D 
                                
                               
                                   
                               
                                
                               cos 
                                
                               
                                   
                               
                                
                               θ 
                             
                           
                           ) 
                         
                       
                       + 
                     
                   
                 
                 
                   
                     
                       
                         ( 
                         
                           C 
                           + 
                           
                             R 
                              
                             
                                 
                             
                              
                             sin 
                              
                             
                                 
                             
                              
                             θ 
                           
                           + 
                           
                             D 
                              
                             
                                 
                             
                              
                             cos 
                              
                             
                                 
                             
                              
                             θ 
                           
                         
                         ) 
                       
                        
                       
                         ( 
                         
                           
                             R 
                              
                             
                                 
                             
                              
                             cos 
                              
                             
                                 
                             
                              
                             θ 
                           
                           - 
                           
                             D 
                              
                             
                                 
                             
                              
                             sin 
                              
                             
                                 
                             
                              
                             θ 
                           
                         
                         ) 
                       
                     
                   
                 
               
             
           
         
       
     
         [0035]    Based on this last equation and the data of Table 1, the rotational speed must increase as the cylinder  17  extends when the swing cylinder&#39;s  17  stroke speed is constant. Geometric considerations may accentuate this, or alleviate it. Therefore, it is deemed desirable to have cushioning effects near both extreme ends—both extreme retraction and extreme extension. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 (+ = CCW) 
                 θ (deg) 
                 L (in) 
                 dθ/dL (deg/in.) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Retracted 
                 127 
                 36.08 
                 3.26 
               
               
                   
                 Centered 
                 90 
                 46.83 
                 3.84 
               
               
                   
                 Extended 
                 53 
                 54.62 
                 6.49 
               
               
                   
                   
               
             
          
         
       
     
         [0036]    For the values of Table 1, R=40 in, B=16.7 in, C=5.5 in, and D=5.6 in (see  FIG. 5 .) Full extension is assumed to occur at θ=53° and full retraction when θ=127° (or θ=180−53°). As those of ordinary skill know, the dimensions may be varied without compromising the instant invention. 
         [0037]    The present invention involves the use of a cushioned cylinder as the swing cylinder  17 , which will slow the stroke speed of the cylinder ram  33  as it approaches the extreme ends of the swing cylinder&#39;s stroke to decrease dynamic forces and eliminate the problem of structural damage. The cushioning mechanism, most visible in  FIGS. 9-11 , is a piston  32  surrounding the cylindrical ram  33  such that, as the cylinder ram  33  approaches the extreme retracted or extreme extended position, flow through a port  31  at the associated end becomes increasingly restricted. On either end of the piston  32  there are grooves in which wear rings  43  rest freely. Also on either end of the piston  32 , as best seen in  FIG. 13 , are four passages  50  arranged in a polar array about the central axis of the piston  32  which allow oil to flow from the end of the piston  32  to its side. As the cylinder ram  33  slides toward either extreme position, friction forces the wear ring  43  to the end of its groove in a direction opposite that of travel, as can best be seen in  FIG. 11 . This wear ring  43  then blocks the path of oil from the passages  50  in the piston  32  to the port  31  as the cylinder ram  33  nears its extreme position. As illustrated in  FIGS. 12   a - 12   c , each wear ring  43  has a narrow split  55  in it such that it acts like a temporary, restricting orifice in the port  31 . This causes the flow rate of oil to reduce as the piston approaches the extreme position thereby slowing the cylinder ram&#39;s  33  travel (see  FIG. 9 ). As illustrated in  FIG. 10 , when the operator demands the piston  32  leave a given extreme position, the change in oil flow direction causes the wear ring  43  to move out of the way while oil travels through the passages  50  freely to move the piston  32  immediately and with no speed restriction. Therefore, the travel of the piston  32  is cushioned at the extreme retracted and extreme extended ends while the piston  32  experiences full speed motion when leaving the extreme position, as contrasted in  FIGS. 9 and 10 . 
         [0038]    The split  55  in the wear ring  43  may take on a variety of forms. A simple discontinuity in the wear ring  43  is shown in  FIG. 12   a . A more complex split  55  is shown in  FIG. 12   b  that would disallow the split from widening past a predetermined diameter. 
         [0039]    In  FIG. 12   c , the wear ring  43  possesses axially-oriented orifices  57  to limit the restriction to the flow of hydraulic fluid. 
         [0040]    An aspect of the instant invention is the fraction of the swing cylinder&#39;s  17  stroke wherein flow is restricted. This fraction is a function of the length of the cylinder ram  33  and the positioning of the working fluid ports  31 , as shown in  FIGS. 6-8 . Positioning the port  31  nearer the extreme end of the hydraulic cylinder  17  results in a lesser fraction of the travel having flow restriction than if the port  31  is placed farther away from the extreme end. The choice of port  31  location depends on the application. 
         [0041]    In the present invention, the cushioned portions of the travel on both ends of the cylinder travel have been designed to provide adequate movement and time to decelerate the tongue swing from full speed to the reduced speed, and then to the stopped position at the end of travel. The choice of length of the restricted flow portion of the swing cylinder&#39;s  17  stroke is designed to provide adequate time for proper deceleration and minimized to avoid unnecessary delay in the operation of swinging the tongue  2 . This restricted portion of travel can vary, but is expected to be within a range of 0.5% to 15% of the overall cylinder stroke at each end of the swing cylinder&#39;s  17  stroke. For the preferred embodiment illustrated herein, with the dimensions given above, 5.3% of the full stroke is cushioned on extension and 9.2% of the full stroke is cushioned on retraction. With a nominal full stroke of 19 inches, this translates to 1 inch of restricted travel on the extended stroke and 1.75 inches of restricted travel on the retracted stroke. 
         [0042]    It may be clearly seen that other geometries and applications require other values, and the instant invention is not limited to any particular dimensions or percentages. 
         [0043]    Note that the application of the instant invention is not limited to an agricultural mower or mower conditioner, nor is the working fluid limited to hydraulic fluid. Any linear actuator  17  with any working fluid in any application may be outfitted with piston  32 , sealing ring  60  and wear rings  43  as disclosed herein to reduce the forces occurring when the linear actuator  17  reaches either extreme of its travel. 
         [0044]    The rate that the wear ring can cushion can be determined by machining the inside diameter of the hydraulic cylinder tube. When the cylinder tube has a uniform inside diameter, the actuator piston starts to slow down as the wear ring begins to close the exit port off to fluid flow. By varying the inside diameter of the hydraulic cylinder, as shown in  FIGS. 14   a - 14   c , the rate of piston deceleration is predetermined by the amount of machining done to the tube. Fluid is permitted to flow around the outside diameter of the wear ring until the wear ring nears the extreme edge of the machined area. 
         [0045]    The above embodiment is the preferred embodiment, but this invention is not limited thereto. It is, therefore, apparent that many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.