Patent Application
20060024172
This invention relates to a sealing system for a swinging yoke hydrostatic unit. Swinging yoke hydrostatic units are very well known in the art as can be seen in U.S. Pat. No. 6,203,283 to Fleming et al. and the U.S. Pat. No. 6,257,119 to Ryken et al. The prior art utilizes a sealing system in its trunnion and manifold that utilizes three seals. Fluid cavities within the trunnion are spaced apart from one another and represent two separate hydraulic fluid lines. Prior art teaches the sealing of these two fluid cavities by using three seals to prevent fluid from these passages from seeping out of the fluid cavities or in between the fluid cavities. This three seal arrangement has proven problematic.
The area of deficiency in the three seal arrangement is related specifically to the center seal. During operation of the swinging yoke hydrostatic unit the pressure in the fluid cavities fluctuates, causing a significant difference in the pressure between the two cavities. Because of this fact, the cavity containing high pressure fluid transitions between the cavities. Thus, the center seal is required to shuttle from one side of the seal mounting groove to the other depending upon which cavity contains the high pressure fluid. Currently in the art, to handle this shuttling back and forth within the mounting groove, seals are designed to have radial grooves on their sideface to facilitate the infusion of pressurized fluid against the side of the seal and into the area where the seal energizer ring is located to hasten the movement of the seal across the groove. Simultaneously, the radial grooves on the opposite side of the seal facilitate the evacuation of fluid from the seal cavity as the seal moves across the groove. Unfortunately, because of the current design, when used, the seal material will flow to form a uniformly extruded lip in the clearance area between the hydrostatic transmission manifold and the swinging yoke and thus, will effectively seal the path that pressurized fluid must flow to generate the required force to cause the seal to shuttle to the other side of the mounting groove. Consequently, when the seal fails to move, pressure builds upon the seal and eventually the seal can no longer hold back the high pressure and the seal is lifted and thus, a leak path between the high pressure and low pressure side of the hydrostatic loop is created. This condition of the seal being thrust out of the area between the yoke and the housing and lifted thus allowing for the leak is known as “blow-by”.
There is a need in the art to provide for an improved seal design that alters the flow of the seal material such that a uniform extrusion will no longer be created between the manifold and the yoke so that “blow-by” does not occur within the hydrostatic transmission. Thus, it is a primary object of the present invention to provide a seal for a hydrostatic transmission that alters the sideface of the seal to disrupt the flow of the seal into a uniform extrusion and thus, improves upon the state of the art.
Yet another object of the present invention is to provide a seal that will immediately shuttle from one side of a mounting groove to another while maintaining a leak proof seal on the sealing surface when a pressure reversal within the hydrostatic transmission occurs.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.
The present invention is an improved sealing system for a hydrostatic transmission. The sealing system utilizes an improved seal that is to be placed in a mounting groove of the manifold and is in sealing contact with the swinging yoke trunnion of a hydrostatic transmission. The improved seal has a sideface with a chamfered portion therein and has an irregular shape. The irregular shape can be created by placing a notch in the chamfered portion or by cutting the sideface to form a different angle for the chamfered portion in relation to the sideface. Thus, when pressure reversal within the hydrostatic transmission occurs, the seal will immediately shuttle to the opposite side of the mounting groove and the seal will not flow to create a uniform extrusion.
The yoke 11 has a central bucket portion 24 adapted to swingably carry the cylinder block kit 18 of the bent axis unit 14. The yoke 11 also includes a trunnion bearing portion or arm 22 for swinging control on one side of the bucket portion 24 and a trunnion 26 for fluid porting on the other side of the bucket portion 24.
The trunnion 26 has a pair of fluid passages or conduits 28 and 30 that intersect the running surface 32 in the area 34. The conduits 28 and 30 extend separately and are entirely within the bottom wall 36, the side wall 38, and the trunnion for fluid porting 26. One of the fluid conduits 28, 30 normally carries high pressured fluid (in the range of 0-550 BAR) when the cylinder block kit 18 rotates in one direction. Meanwhile, the other of the fluid conduits 28, 30 normally carries relatively low pressure fluid, such as control or charge pressure (in the range of 0-25 BAR). Of course, the normal pressures of the bent axis unit 14 may vary, depending upon the system requirements. The invention is applicable to other system pressure requirements with only minor modifications.
The conduits 28, 30 extend across the bottom wall 36 of the yoke 11. Then the conduits 28, 30 extend upwardly within the side wall 38. Near the top of the yoke 11, gauge ports 40, 42 can be provided. The gauge ports 40, 42 extend into the yoke 11 adjacent to the open top 44 so that they intersect the fluid conduits 28, 30 respectively. The fluid conduits 28, 30 curve and extend into the trunnion 26 for fluid porting.
The sealing system of the present invention can be seen as seals 46, 48, and 50 located on the manifold 17 adjacent to the trunnion 26. Each seal is disposed within a seal mounting groove 54. For convenience, only seal 48 will be discussed. Seal 48 is located on the exterior side of conduit 28 and on the interior side of fluid conduit 30 thus, representing a center seal. One should appreciate that seal 48 seals fluid from fluid conduits 28 and 30 thus preventing fluid communication therebetween.
Mounting groove 54 is disposed within the manifold 17 around the yoke trunnion 26 and has a top or outer surface 56 with an inner open end 58. Disposed within the mounting groove 54 is an energizer ring 60 that contacts the outer surface 56 and functions to force the seal 48 against the yoke trunnion 26. Additionally, the space between the yoke trunnion 26 and the manifold 17 forms a clearance space or fluid conduit 62 therebetween.
The seal 48 can best be seen in
In operation, all of the modifications to the seal and manifold as seen in
It will be appreciated by those skilled in the art that other various modifications could be made to the device without the parting from the spirit in scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby.
