Patent Abstract:
A slip joint includes a structure that prevents a negative pressure situation from occurring within a sealed lubricant chamber during operation thereof. The slip joint includes a male splined member having a plurality of external splines formed thereon that cooperate with a plurality of internal splines formed on a female splined member. The cooperating splines are disposed within a lubricant chamber defined at one end by a seal assembly and at the other end by a pressure regulator assembly that maintains a positive pressure situation within the lubricant chamber during operation thereof (i.e., a situation where the fluid pressure within the lubricant chamber is greater than or equal to than the fluid pressure outside of the lubricant chamber). To accomplish this, the pressure regulator assembly includes a housing having an open end that faces toward the lubricant chamber. A spring urges the pressure compensator assembly toward the lubricant chamber. As a result, the pressure compensator assembly compresses the lubricant disposed within the sealed lubricant chamber and, accordingly, functions to maintain a positive pressure situation within the lubricant chamber. This positive pressure situation deters contaminants from passing through the seal assembly into the region of the cooperating splines.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/314,125, filed Aug. 22, 2001, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to a slip joint, such as is commonly used in a driveshaft assembly for transmitting rotational force or torque from an engine/transmission to an axle assembly in a vehicle drive train system. In particular, this invention relates to a pressure regulator assembly for use with such a slip joint that compresses a volume of lubricant disposed within a sealed lubricant chamber defined within the slip joint so as to maintain a positive pressure situation within the lubricant chamber and thus deter the entry of contaminants therein. 
     Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The front and rear universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts. 
     Not only must a typical drive train system accommodate a limited amount of angular misalignment between the source of rotational power and the rotatably driven device, but it must also typically accommodate a limited amount of relative axial movement therebetween. For example, in most vehicles, a small amount of relative axial movement frequently occurs between the engine/transmission assembly and the axle assembly when the vehicle is operated. To address this, it is known to provide a slip joint in the driveshaft assembly. A slip joint includes first and second members that have respective structures formed thereon that cooperate with one another for concurrent rotational movement, while permitting a limited amount of axial movement to occur therebetween. A typical sliding spline type of slip joint includes male and female members having respective pluralities of splines formed thereon. The male member is generally cylindrical in shape and has a plurality of outwardly extending splines formed on the outer surface thereof. The male member may be formed integrally with or secured to one of the end fittings described above to form a slip yoke. The female member, on the other hand, is generally hollow and cylindrical in shape and has a plurality of inwardly extending splines formed on the inner surface thereof. The female member may be formed integrally with or secured to an end of the driveshaft tube described above. To assemble the slip joint, the male member is inserted within the female member such that the outwardly extending splines of the male member cooperate with the inwardly extending splines of the female member. As a result, the male and female members are connected together for concurrent rotational movement. However, the outwardly extending splines of the male member can slide relative to the inwardly extending splines of the female member to allow a limited amount of relative axial movement to occur between the engine/transmission assembly and the axle assembly of the drive train system. 
     Frequently, the cooperating splines of the male and female splined members are disposed within a lubricant chamber that is defined between a pair of sealing structures provided on the slip joint. To accomplish this, the slip joint typically includes both an external sealing structure and an internal sealing structure. The exterior sealing structure is usually supported on the outer surface of the female splined member and extends inwardly into sliding and sealing engagement with the male splined member to prevent contaminants from entering into the region of the cooperating splines from the exterior environment. The interior sealing structure is often supported within the female splined member to prevent contaminants from entering into the region of the cooperating splines from the interior of the female splined member. A variety of such external and internal sealing structures are known in the art. The sealed lubricant chamber is usually filled with a lubricant that not only reduces the amount of sliding friction between the cooperating splines of the male and female splined members, but also substantially fills the volume of the lubricant chamber to further deter the entry of contaminants therein. 
     Although the use of such external and internal sealing structures has been effective, it has been found that during normal operation of the driveshaft assembly, the axial movement of the male splined member relative to the female splined member causes the volume of the lubricant chamber to vary. Such changes in the volume of the lubricant chamber can, in some instances, result in a pumping action that can discharge lubricant from the lubricant chamber and thereafter create a negative pressure situation within the lubricant chamber (i.e., a situation where the fluid pressure within the lubricant chamber is less than the fluid pressure outside of the lubricant chamber). This negative pressure situation tends to undesirably draw contaminants through either or both of the sealing structures and into the region of the cooperating splines of the male and female splined members. To prevent this from occurring, it is known to form a vent hole through one of the male and female members. The vent hole communicates with the lubricant chamber to prevent this negative pressure situation from occurring. However, the formation of a vent hole has been found to be undesirable for other reasons. Thus, it would be desirable to provide an improved structure for a slip joint that prevents a negative pressure situation from occurring within the lubricant chamber during operation thereof. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved structure for a slip joint that includes a structure that prevents a negative pressure situation from occurring within the lubricant chamber during operation thereof. The slip joint includes a male splined member having a plurality of external splines formed thereon and a female splined member having a plurality of internal splines formed thereon. The external splines of the male splined member cooperate with the internal splines of the female splined member to provide a rotational driving connection therebetween, while accommodating a limited amount of relative axial movement. The cooperating splines are disposed within a lubricant chamber defined at one end by a seal assembly and at the other end by a pressure regulator assembly that maintains a positive pressure situation within the lubricant chamber during operation thereof (i.e., a situation where the fluid pressure within the lubricant chamber is greater than or equal to than the fluid pressure outside of the lubricant chamber). To accomplish this, the pressure regulator assembly includes a housing having an open end that faces toward the lubricant chamber. A spring urges the pressure compensator assembly toward the lubricant chamber. As a result, the pressure compensator assembly compresses the lubricant disposed within the sealed lubricant chamber and, accordingly, functions to maintain a positive pressure situation within the lubricant chamber. This positive pressure situation deters contaminants from passing through the seal assembly into the region of the cooperating splines. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The sole FIGURE is a side elevational view, partially in cross section, of a portion of a driveshaft assembly including a sealed slip joint and a pressure regulator assembly in accordance with this invention that prevents a negative pressure situation from occurring within the slip joint during operation thereof. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing, there is illustrated a portion of a driveshaft assembly, indicated generally at  10 , that can be used, for example, in the drive train system (not shown) of a land vehicle for transmitting rotational force or torque from an engine/transmission assembly to an axle assembly. However, the driveshaft assembly  10  may be used to transmit power from type of any source of power to any type of driven mechanism. Furthermore, although this invention will be described in the context of the illustrated driveshaft assembly  10 , it will be appreciated that this invention may be practiced in a variety of applications other that driveshaft assemblies. 
     The driveshaft assembly  10  includes a slip yoke, indicated generally at  12 , and a driveshaft tube, indicated generally at  14 . The slip yoke  12  can be embodied as any end fitting or other member that is adapted to be connected or otherwise coupled with a cooperating component (not shown) to transmit power therebetween. For example, the slip yoke  12  can form a portion of a front universal joint (not shown) that connects an output shaft of an engine/transmission assembly to one end of the driveshaft tube  14 , as described above. The other end of the driveshaft tube  14  (not shown) may be connected to a rear end fitting that forms a portion of a rear universal joint (not shown) that connects the rear end of the driveshaft tube to an input shaft of an axle assembly, as also described above. 
     The slip yoke  12  includes an end portion  16  having a generally cylindrical shaft portion  18  extending therefrom. The shaft portion  18  of the slip yoke  12  has a plurality of longitudinally extending external splines  20  formed thereon. The purpose for such external splines  20  will be described below. If desired, a tubular sleeve  22  can be supported on the slip yoke  12  so as to extend concentrically about the end portion  16  thereof. The tubular sleeve  22  has a first end  23  that is engaged with and supported on a shoulder formed on the end portion  16  of the slip yoke  12 . The first end  23  of the tubular sleeve  22  can be secured to the slip yoke  12  in any desired manner, such as by welding, adhesives, or frictional engagement. The tubular sleeve  22  has a second end  24  that is located opposite the first end  23 . The purpose for the tubular sleeve  22  will be explained below. An annular space  28  is defined between the tubular sleeve  22  and the shaft portion  18  of the slip yoke  12 . 
     The driveshaft tube  14  is generally hollow and cylindrical in shape, having a first end  31  that is attached to a transition member  32  in any desired manner, such as by a circumferential weld (not shown). The transition member  32  is generally hollow and cylindrical in shape and includes a tapered portion  36  and a reduced diameter end portion  42  that extends concentrically within the driveshaft tube  14 , thereby defining an annular space therebetween. If desired, a support member  32   a  may be provided on the transition member  32  for slidably supporting the tubular member  22  thereon. The end portion  42  of the transition member  32  is formed having a plurality of internal splines  44 . Although the illustrated driveshaft tube  14  and transition member  32  are formed as separate components that are secured together, it will be appreciated that the internal splines  44  could be formed directly on the driveshaft tube  14 , thus eliminating the need for the transition member  32  as a separate piece. The internal splines  44  of the transition member  32  cooperate with the external splines  20  of the shaft portion  18  of the slip yoke  12  to provide a rotational driving connection between the slip yoke  12  on the one hand and the transition member  32  and the driveshaft tube  14  on the other hand, while accommodating a limited amount of relative axial movement to occur therebetween. The end portion  42  of the transition member  32  is also formed having an external circumferential ridge  42   a  that supports an elastomeric seal  42   b . The purpose for the external circumferential ridge  42   a  and the elastomeric seal  42   b  will be explained below. 
     A first seal assembly, indicated generally at  46 , is provided on the second end  24  of the tubular sleeve  22  for preventing dirt, water, and other contaminants from entering into the annular space  28  defined between the tubular sleeve  22  and the shaft portion  18  of the slip yoke  12 . The illustrated first seal assembly  46  can be press fit or otherwise retained within the second end  24  of the tubular sleeve  22 . The first seal assembly  46  extends inwardly into sliding and sealing engagement with an outer cylindrical surface  48  provided on the driveshaft tube  14  to prevent the contaminants from entering the annular space  28  between the tubular sleeve  22  and the shaft portion  18  of the transition member  32 . To accomplish this, the first seal assembly  46  can include any suitable seal structure that provides for a sealing relationship between the inner surface of the sleeve  22  and the outer cylindrical surface  48  of the driveshaft tube  14 , while permitting a limited amount of relative axial movement to occur therebetween. For example, the first seal assembly  46  can include a metal annular retaining member  50  that supports an annular elastomeric lip seal  52 . The lip seal  52  is supported on the metal retaining member  50  and preferably includes one or more inwardly extending wiper portions  56  that sealingly engage the outer cylindrical surface  48  of the driveshaft tube  14 . 
     A second seal assembly, indicated generally at  60 , is provided for preventing the contaminants from passing from the annular space  28  defined between the tubular sleeve  22  and the shaft portion  18  of the slip yoke  12  into the region of the cooperating splines  20  and  44 . The illustrated second seal assembly  46  is preferably press fit within the end of the transition member  32  and slidably and sealingly engages an outer cylindrical surface  62  of the shaft portion  18  of the slip yoke  12 . The second seal assembly  60  can include any suitable seal structure that provides for a sealing relationship between the inner surface of the transition member  32  and the outer cylindrical surface  62  of the shaft portion  18  of the slip yoke  12 , while permitting a limited amount of relative axial movement to occur therebetween. For example, the second seal assembly  60  can include a metal annular retaining member  64  that supports an annular elastomeric lip seal  68 . The lip seal  68  is supported on the retaining member  64  and preferably includes one or more inwardly extending wiper portions  70  that slidably and sealingly engage the outer cylindrical surface  62  of the shaft portion  18  of the slip yoke  12 . 
     Lubricant is preferably provided in the region of the cooperating splines  20  and  44  to reduce the amount of sliding friction between the slip yoke  16  and the transition member  32 , and further to minimize the undesirable entry of dirt, water, and other contaminants into that region. The second seal assembly  60  defines one end of a lubricant chamber  74  that extends at least partially, and preferably completely, throughout the region of the cooperating splines  20  and  44 . The other end of the lubricant chamber  74  is defined by a pressure compensator assembly, indicated generally at  80 . The pressure compensator assembly  80  is generally cylindrical in shape (although such is not required) and includes a generally cup-shaped housing defined by a hollow cylindrical wall portion  84 , a circular end portion  86 , and an annular retainer portion  88 . The hollow cylindrical wall portion  84  of the housing for the pressure compensator assembly  80  extends concentrically within the annular space defined between the outer surface of the transition member  32  and within the inner surface of the driveshaft tube  14 . As mentioned above, the elastomeric seal  42   b  is supported on the external circumferential ridge  42   a  of the end portion  42  of the transition member  32 . The elastomeric seal  42   b  extends outwardly into sealing engagement with the inner surface of the hollow cylindrical wall portion  84  of the pressure compensator assembly  80 . Thus, the hollow cylindrical wall portion  84  and the circular end portion  86  of the pressure compensator assembly  80 , together with the elastomeric seal  42   b , define the other end of the lubricant chamber  74 . 
     The circular end portion  86  of the pressure compensator assembly  80  is secured to one end of the hollow cylindrical wall portion  84  and is disposed adjacent to the end portion  42  of the transition member  32 . The annular retainer portion  88  of the pressure compensator assembly  80  is secured to the other end of the hollow cylindrical wall portion  84  and is disposed about the outer surface of the end portion  42  of the transition member  32 . Thus, the entire pressure compensator assembly  80  is slidably supported about the end portion  42  of the transition member  32  for axial movement relative thereto. A spring  90  or other biasing structure is disposed in the annular space defined between the outer surface of the end portion  42  of the transition member  32  and the inner surface of the hollow cylindrical wall portion  86  of the pressure compensator assembly  80 . This spring  90  reacts between the retainer portion  88  of the pressure compensator assembly  80  and the external circumferential ridge  42   a  formed on the end portion  42  of the transition member  32 . The spring  90  urges the pressure compensator assembly  80  toward the lubricant chamber  74  (toward the left when viewing the illustrated embodiment). Thus, the pressure compensator assembly  80  defines a portion of the lubricant chamber  74 , and the spring  90  urges the pressure compensator assembly  80  in a direction that tends to reduce the volume of the lubricant chamber  74  and compress the lubricant therein. 
     As a result of this urging by the spring  90 , the pressure compensator assembly  80  causes a positive pressure situation to occur within the lubricant chamber  74  (i.e., the fluid pressure within the lubricant chamber  74  is at least equal to, and preferably is somewhat greater than, the fluid pressure outside of the lubricant chamber  74 ). This positive pressure situation in the lubricant chamber  74  deters contaminants from passing through the second seal assembly  60  and into the region of the cooperating splines  20  and  44 . Preferably, the magnitude of the fluid pressure within the lubricant chamber  74  is only slightly greater than the magnitude of the fluid pressure outside thereof so that the lubricant contained within the lubricant chamber  74  is not (at least to a significant extent) urged outwardly therefrom through the second seal assembly  60 . 
     During normal operation of the driveshaft assembly  10 , the slip yoke  12  will move axially relative to the transition member  32  and the driveshaft tube  14 . As a result, the volume of the lubricant chamber  74  will vary. Such changes in the volume of the lubricant chamber  74  can, without the pressure compensator assembly  80 , result in a pumping action that can discharge lubricant from the lubricant chamber  74  and thereafter create a negative pressure situation within the lubricant chamber  74  (i.e., a situation where the fluid pressure within the lubricant chamber  74  is less than the fluid pressure outside of the lubricant chamber). This negative pressure situation can undesirably draw contaminants through the first and second sealing assemblies  46  and  60  and into the region of the cooperating splines  20  and  44 . 
     By providing the above-described pressure compensator assembly  80 , however, the fluid pressure within the lubricant chamber  74  can be maintained at least equal to (and preferably somewhat greater than) the fluid pressure outside of the lubricant chamber  74  (i.e., in the annular space  28  on the other side of the second seal assembly  60 ). The magnitude of this pressure differential is determined, among other ways, by the strength of the spring  90  reacting against the pressure compensator assembly  80  and, therefore, the amount of force that is exerted by such spring  90  against the pressure compensator assembly  80 . If desired, however, the strength of the spring  90  can be selected to be relatively small so as to simply minimize the occurrence of the negative pressure situations in the lubricant chamber  74 , as opposed to completely eliminating such negative pressure situations. In either event, as the slip yoke  12  moves axially relative to the transition member  32  and the driveshaft tube  14 , the pressure compensator assembly  80  moves axially under the urging of the spring  90  relative to the housing of the pressure compensator assembly  80  to automatically exert pressure against the lubricant contained in the lubricant chamber  74  and thereby maintain a relatively constant positive pressure situation within the lubricant chamber  74 . 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Technology Classification (CPC): 5