Abstract:
A hydraulic fluid coupling for attaching two hydraulic hoses that comprises an inline swivel joint to prevent twisting of the hoses. The coupling comprises a first and second coupling portion, with the second coupling portion rotatable relative to the first coupling portion. There are two bearings and a ring shaped piston that slides toward the second bearing in response to fluid pressure inside the coupling. Engagement of the piston with the second bearing urges the second coupling portion towards the first coupling portion, against the action of fluid pressure between the first and second couplings. This reduces the load on the first bearing and transfers some of that load to the second bearing, thereby making it easier to rotate the second coupling portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Patent Application 61/418,385, filed Nov. 30, 2010, the contents of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to hydraulic fluid couplings. In particular, the invention relates to hydraulic fluid couplings comprising an inline swivel joint to prevent twisting of hydraulic hoses connected via the coupling. 
       BACKGROUND OF THE INVENTION 
       [0003]    Hydraulic fluid couplings are used to connect hydraulic hoses as part of hydraulic fluid power systems on both mobile and stationary power equipment. In instances where the hoses are attached to equipment components that move or twist relative to one another, the coupling must accommodate torsional movement to prevent binding and/or kinking of the hoses. An inline swivel joint is normally employed in these situations. 
         [0004]    Prior art hydraulic fluid couplings comprising inline swivel joints have suffered from the problem that, when loaded with internal hydraulic fluid pressure, the swivel becomes difficult to turn. This leads to binding and kinking of the hoses and ultimately hose or coupling failure. The prior art couplings are also prone to excessive bearing wear due to the high loads imparted to the bearings by fluid pressure; this leads to premature bearing failure with the result that the swivel becomes more difficult to turn, exacerbating the hose twisting problem. 
         [0005]    As a result, there remains a need for an improved hydraulic fluid coupling, particularly a hydraulic fluid coupling comprising an inline swivel joint. Such a coupling would desirably be easy to turn and not be prone to premature bearing failure. 
       SUMMARY OF THE INVENTION 
       [0006]    The inventive hydraulic fluid coupling is for attaching two hydraulic hoses and comprises an inline swivel joint to prevent twisting of the hoses. The coupling comprises a first and second coupling portion, with the second coupling portion rotatable relative to the first coupling portion. There are two bearings and a ring shaped piston that slides toward the second bearing in response to fluid pressure inside the coupling. Engagement of the piston with the second bearing urges the second coupling portion towards the first coupling portion, against the action of fluid pressure between the first and second couplings. This reduces the load on the first bearing and transfers some of that load to the second bearing, thereby making it easier to rotate the second coupling portion. 
         [0007]    According to an aspect of the present invention, there is provided a hydraulic fluid coupling comprising an inline swivel joint, the coupling comprising: a first coupling portion having a central conduit axis; a second coupling portion co-axially aligned with the first coupling portion and having a coupling face perpendicular to the conduit axis abutting the first conduit portion; a central conduit passing through the first and second coupling portions along the central conduit axis; a dynamic seal between the first and second coupling portions; a first bearing between the first and second coupling portions co-axial with the central conduit axis; a ring shaped piston circumferentially disposed about an exterior of the second coupling portion and axially moveable therealong, the piston comprising a piston driving surface and a bearing engaging face; a fluid receiving chamber bounded by at least the piston driving surface and the second coupling portion; at least a radial conduit through the second coupling portion between the central conduit and the fluid receiving chamber; a second bearing circumferentially disposed about an exterior of the second coupling portion and co-axial with the central conduit axis, the second bearing engageable by the piston and supporting rotational and axial movement of the second coupling portion. 
         [0008]    The coupling may comprise a retaining cap secured to the first coupling portion and extending over the second coupling portion, the second bearing and the piston located between the retaining cap and the second coupling portion. The second bearing may be engaged with the retaining cap by axial movement of the piston in response to fluid pressure in the fluid receiving chamber. Accordingly, forces exerted by the piston on the second bearing may be resisted by the retaining cap, causing the second coupling portion to move axially toward the first coupling portion in response thereto. To facilitate engagement between the piston and the second bearing, the bearing engaging face may have a shape complementary to a curvature of a ball of the second bearing. To facilitate axial movement of the second coupling portion towards the first coupling portion, the fluid receiving chamber may be bounded by a driving surface of the second coupling portion with an area that is selected to be complementary to the area of the piston driving surface. For example, the area of the driving surface of the second coupling portion may be equal to the area of the piston driving surface. 
         [0009]    The area of the piston driving surface and/or the driving surface of the second coupling portion may be sized to transfer a predetermined proportion of an axial load on the first bearing to the second bearing through action of the hydraulic fluid on the piston. For example, the area of the piston driving surface and/or the driving surface of the second coupling portion may be sized to substantially equalize the axial load on the first bearing and the second bearing. The axial load on the first bearing may be due to shear between the first coupling portion and the second coupling portion caused by action of hydraulic fluid pressure on a pressurized portion of the coupling face of the second coupling portion. The axial load on the second bearing may be entirely due to action of the piston. Since the second bearing is immovable, engagement of the piston with the second bearing may cause the second coupling portion to move axially toward the first coupling portion, countering the shear forces on the first bearing, due to fluid pressure against the driving surface of the piston and/or second coupling portion. 
         [0010]    The area of the driving surfaces may be from 0.3 to 1.5 times the pressurized area of the coupling face. The pressurized area of the coupling face is the area perpendicular to the conduit axis bounded by the dynamic seal. The area of the driving surfaces may be a fraction x of the pressurized area of the coupling face determined, within a tolerance of 25%, according to the formula: x=N 2 d 2 /(N 2 d 2 +N 1 d 1 ) where, N 2  is a number of balls in the second bearing; N 1  is a number of balls in the first bearing; d 2  is a diameter of the balls in the second bearing; and, d 1  is a diameter of the balls in the first bearing. When the diameter of the balls in the two bearings, d 2  and d 1 , are the same size, the formula for x simplifies to x=N 2 /(N 2 +N 1 ). N 2  may be larger than N 1 . 
         [0011]    The coupling may further comprise a static seal between the second coupling portion and the piston. The coupling may further comprises two static seals between the second coupling portion and the piston on either side of the fluid receiving chamber spaced apart along the conduit axis by a distance sufficient to maintain sealing of the chamber regardless of movement of the piston. The static seals may be disposed within enlarged circumferential grooves to accommodate axial movement of the seals with the piston. The coupling may comprise a single dynamic seal. This may advantageously reduce the torque required to rotate the second coupling portion relative to the first coupling portion as compared with multiple dynamic seals. The dynamic seal may be located between the first and second coupling portions proximal the coupling face in order to reduce the pressurized area of the coupling face and thereby reduce the load on the bearings. The first and second bearings may be on the same side of the dynamic seal and may be spaced apart along a length of the second coupling portion in order to stabilize it during rotation. 
         [0012]    Hydraulic hoses may be connected to the first and second coupling portions by any suitable means, including crimp or compression fittings, threaded connections, or slidingly releasable hose attachments. 
         [0013]    Further features of the invention will be described or will become apparent in the course of the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    In order that the invention may be more clearly understood, embodiments thereof will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
           [0015]      FIG. 1   a  is a sectional side view of an embodiment of a hydraulic fluid coupling comprising an inline swivel according to the present invention; 
           [0016]      FIG. 1   b  is an enlarged view of the portion of  FIG. 1   a  denoted by the circle B; 
           [0017]      FIG. 1   c  is an enlarged view of the portion of  FIG. 1   a  denoted by the circle C; 
           [0018]      FIG. 2   a  is a side view of the coupling of  FIG. 1   a , shown connecting two hydraulic hoses; 
           [0019]      FIG. 2   b  is a side sectional view of  FIG. 2   a;    
           [0020]      FIG. 3   a  is a sectional side view of another embodiment of a hydraulic fluid coupling comprising an inline swivel according to the present invention; and, 
           [0021]      FIG. 3   b  is an end view of the hydraulic fluid coupling of  FIG. 3   a.    
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    In describing the figures, like features are referred to by like reference numerals. Although not all features indicated on a particular drawing are necessarily described with reference to that drawing, all of the features are described with reference to at least one of the drawings. 
         [0023]    Referring to  FIGS. 1   a  to  1   c , a hydraulic fluid coupling according to the invention comprises a first coupling portion  1  and a second coupling portion  2 . Each coupling portion comprises connection means for hydraulic hoses in the form of female threads  3   a  on the first coupling portion and male threads  3   b  on the second coupling portion. A hydraulic fluid conduit  4  is formed through the first and second coupling portions  1 ,  2  that has a central conduit axis  5 . The first coupling portion  1  comprises an axial recess  6  into which a complementary nose  7  of the second coupling portion  2  is fitted. The nose  7  has a coupling face  8 , at least a portion of which adjoins with an interior face  9  of the recess  6 . The coupling face  8  has a pressurized area that is perpendicular to the conduit axis  5  that defines the hydraulic force acting on the second coupling portion  2 . The hydraulic forces acting to force apart the first and second coupling portions  1 ,  2  are equally applied to both coupling portions and are proportional to the diameter of the nose  7 . 
         [0024]    A dynamic seal  10  is provided between the first and second coupling portions. In the embodiment shown, the dynamic seal  10  is fitted within an annular recess  11  in the first coupling portion  1 , although it could alternatively have been provided within an annular recess on the second coupling portion. The seal  10  comprises an elastomeric portion  12  and a glide element  13 , in a configuration as is known in the art; other known dynamic seal configurations may also be used. The dynamic seal  10  is of a type that permits rotational movement of the second coupling portion  2  relative to the first coupling portion  1  (or vice versa), while still maintaining a sealing relationship between the first and second coupling portions. Fluid pressure is applied to both coupling portions  1 ,  2  in a pressurized region from the conduit up to the dynamic seal  10 . The dynamic seal  10  is shaped such that fluid pressure causes it to deform radially in a manner that increases its contact with the second coupling portion  2 ; the degree of sealing therefore increases with increasing fluid pressure. When placed under pressure, this type of seal usually imparts a relatively high degree of friction to the rotational movement and, in order to reduce that friction and allow the coupling portions  1 ,  2  to rotate more freely relative to one another, it is desirable to reduce the number of dynamic seals  10 . Accordingly, in a preferred embodiment, the hydraulic coupling is provided with a single dynamic seal  10 . The dynamic seal is able to resist hydraulic fluid pressures of up to 2000 psi, preferably up to 5000 psi, more preferably up to 8,000 psi, yet more preferably up to 10,000 psi. 
         [0025]    A first bearing  15  is located between the first and second coupling portions  1 ,  2  co-axial with the conduit axis  5  and comprises a plurality of balls loaded into a first bearing recess  16  via a fill port  17 . The first bearing recess  16  is mutual to both the first and second coupling portions and, by loading the balls, the coupling portions  1 ,  2  are locked together against axial movement, but still permitted to rotate about the central conduit axis  5  relative to one another. Hydraulic fluid pressure applied to the coupling face  8  that forces apart the conduit portions  1 ,  2  places the first bearing  15  in shear, which axially loads the bearing and makes it difficult to turn. It would therefore be desirable to relieve some of the load on the first bearing  15  in order to make it easier to turn and to reduce wear, thereby prolonging the lifetime of the hydraulic fluid coupling. 
         [0026]    A second bearing  18  is provided to relieve some of the load applied to the first bearing  15 . The second bearing  18  is circumferentially disposed about an exterior of the second coupling portion  2  and is co-axial with the central conduit axis  5 . The second bearing  18  comprises a plurality of balls resting within a bearing spacer  19  having complementary curvature. In this embodiment, the spacers are abutted within a retaining cap  21  that is threaded to the first coupling portion  1  and extends over the exterior of the second coupling portion  2 . Removal of the retaining cap  21  allows the spacer  19  and the balls of the second bearing  18  to be inserted through the open end and lubricated; however, once threaded to the first coupling portion  1 , forces applied to the retaining cap  21  are transmitted to the first coupling portion. A dust seal  22  is provided in the retaining cap  21 , but this serves no hydraulic fluid sealing function and imparts relatively little rotational friction to the second coupling portion  2 . 
         [0027]    A ring shaped piston  23  is circumferentially disposed about the exterior of the second coupling portion  2  in a manner that permits sliding axial movement. Both the second bearing  18  and the piston  23  are located in the annular space between the retaining cap  21  and the second coupling portion  2 . The piston  23  is sized with close tolerance to the exterior of the second coupling portion  2  so that engagement is provided with a pair of static seals  24 ,  25  located within circumferential grooves  26 ,  27  on the second coupling portion. This tends to cause the piston  23  to rotate with the second coupling portion  2 . The grooves  26 ,  27  are spaced apart by a distance sufficient to maintain sealing regardless of movement of the piston  23 . The static seals  24 ,  25  are of the O-ring type and comprise a backup ring to prevent extrusion of the O-ring from the groove in response to fluid pressure. The static seals  24 ,  25  are therefore not dynamic seals; they have no special shape or design features causing them to deform radially in response to hydraulic fluid pressure. As such, the rotational friction imparted to the second coupling portion  2  by the seals  24 ,  25  is significantly less than that imparted by dynamic seals. 
         [0028]    The seals  24 ,  25  are provided on either side of a fluid receiving chamber  28  formed between a piston driving surface  29  of the piston  23  and a complementary driving surface  30  formed by a radially enlarged area of the second coupling portion  2 . The driving surfaces  29 ,  30  each have an area that is perpendicular to the conduit axis  5 ; this is considered the driving area of the piston, regardless of the specific shape of the surface. The area thus defined of the driving surfaces  29 ,  30  is equal. The axial forces exerted by fluid pressure in the receiving chamber  28  on the piston  23  and the second coupling portion  2  are therefore equal in magnitude but opposite in direction. Fluid pressure is provided to the receiving chamber  28  through one or more radial conduits  31  through the second coupling portion  2 , linking the central conduit  4  with the receiving chamber  28 . In the embodiment shown, there are four radial conduits  31 . 
         [0029]    The piston  23  has a bearing engaging face  32  with a shape complementary to the balls of the second bearing  18 . Fluid pressure in the receiving chamber  28  causes the piston  23  to axially move into engagement with the second bearing  18 , which is urged toward the bearing spacer  19  that abuts the retaining cap  21 . An axial load is thus imparted to the second bearing  18  through action of hydraulic fluid pressure on the piston driving surface  29 . An equal axial load is imparted in an opposite direction to the second coupling portion  2  through action of hydraulic fluid pressure on the second coupling portion driving surface  30 . Since the bearing spacer  19  and retaining cap  21  cannot move relative to the first coupling portion  1 , the second coupling portion  2  is urged towards the first coupling portion  1 . This relieves some of the axial load imparted to the first bearing  15  by action of fluid pressure on the coupling face  8 . The first bearing  15  is thus relieved of load, reducing its resistance to rotation of the second coupling portion  2  about the conduit axis  5 . 
         [0030]    This, of course, comes at the expense of an axial load imparted to the second bearing  18 . Since both the driving force on the piston  23  and the coupling face  8  are a function of hydraulic fluid pressure in the conduit  4 , the area of the driving surfaces  29 ,  30  can be sized to transfer a pre-determined proportion of the axial load on the first bearing  15  to the second bearing  18 . Through careful selection of the area of the driving surfaces  29 ,  30 , the axial loads and/or the resistance to torsion of the first and second bearings  15 ,  18  can be substantially equalized, thus making it easier overall for the second coupling portion  2  to rotate about the axis  5  and reducing wear on the bearings. For example, in one embodiment, the area of the driving surfaces  29 ,  30  is preferably in the range of from 0.3 to 1.5 times the pressurized area of the coupling face  8 . 
         [0031]    The frictional resistance to torsion of the bearings  15 ,  18  is a function of both axial load and area being loaded; since, in the embodiment shown, the second bearing  18  has a diameter that is larger than the first bearing  15 , in order to equalize the resistance to torsion the axial loads are not necessarily equal. The area of the bearings is roughly proportional to the number of balls in the bearing, particularly in cases where the diameter of all balls are equal. Therefore, in one embodiment, the area of the driving surfaces  29 ,  30  is a fraction x of a pressurized area of the coupling face  8  determined, within a tolerance of 25%, according to the formula: 
         [0000]        x=N   2   d   2 /( N   2   d   2   +N   1   d   1 ) 
         [0000]    where, 
         [0032]    N 2  is a number of balls in the second bearing; 
         [0033]    N 1  is a number of balls in the first bearing; 
         [0034]    d 2  is a diameter of the balls in the second bearing; and, 
         [0035]    d 1  is a diameter of the balls in the first bearing. 
         [0036]    In cases where the diameter of the balls in the first and second bearings  15 ,  18  are equal, the formula simplifies to x=N 2 /(N 2 +N 1 ). When N 2  is larger than N 1 , the value of x is greater than 0.5. When N 2  equals N 1 , the value of x equals 0.5. 
         [0037]    Referring to  FIGS. 2   a  and  2   b , the hydraulic fluid coupling is shown interconnected with a pair of hydraulic hoses  33  connected to the female and male threads  3   a ,  3   b  of the first and second coupling portions  1 ,  2 , respectively. The hoses are therefore able to rotate about the conduit axis  5  relative to one another with reduced propensity for kinking and binding due to the features of the hydraulic coupling described above, which provide reduced torsional requirements for rotation. Although shown here with threaded connections, other means of connecting hydraulic hoses known to persons skilled in the art may be employed. 
         [0038]    Referring to  FIGS. 3   a  and  3   b , another embodiment of the fluid coupling is shown that is similar in all respects to the coupling described with reference to  FIGS. 1 and 2 , except that the bearing spacer  19  is integrated with the retaining cap  21 . The retaining cap  121  of this embodiment is thus provided with an interior curvature complementary to the curvature of the balls selected for the second bearing  115 . Although this reduces flexibility in the choice of ball diameter, it reduces cost and complexity from a manufacturing perspective. 
         [0039]    Other advantages which are inherent to the structure are obvious to one skilled in the art. The embodiments are described herein illustratively and are not meant to limit the scope of the invention as claimed. Variations of the foregoing embodiments will be evident to a person of ordinary skill and are intended by the inventor to be encompassed by the following claims.