Abstract:
A gear box assembly includes an outer housing and a gear box shaft at least partially disposed in the outer housing. The gear box shaft includes an interior region, a reservoir dam that separates the interior region into a reservoir volume and a spline volume and one or more gear box shaft venting holes formed through the gear box shaft near an end thereof. The assembly also includes a regulator disposed at least partially within the gear box shaft, the regulator including one or more regulator vent holes, wherein at least one of the regulator venting holes is in fluid communication with one of the one or more gear box shaft vent holes.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to lubrication, and more particularly, to a spline lubrication system that includes a vent. 
       BACKGROUND 
       [0002]    Certain mechanical systems include a driving shaft and a driven shaft. The driving shaft may be part of, for example, a gear box and the driven shaft may be part of an accessory of receives rotational energy from the driving shaft. The two shafts may be joined by a spline joint. 
         [0003]    A spline joint may include splines (ridges or teeth) on a drive shaft that mesh with grooves in a mating piece and transfer torque to it, maintaining the angular correspondence between them. For instance, the driving shaft may include a male spline on the shaft that matches the female spline on the driven shaft or vice versa. 
         [0004]    In operation, the spline joint may need lubrication from time to time. 
       BRIEF DESCRIPTION 
       [0005]    According to one embodiment, a gear box assembly that includes an outer housing and a gear box shaft at least partially disposed in the outer housing is disclosed. The gear box shaft includes an interior region, a reservoir dam that separates the interior region into a reservoir volume and a spline volume and one or more gear box shaft venting holes formed through the gear box shaft near an end thereof. The assembly also includes a regulator disposed at least partially within the gear box shaft, the regulator including one or more regulator vent holes, wherein at least one of the regulator venting holes is in fluid communication with one of the one or more gear box shaft vent holes. 
         [0006]    Also disclosed is a power delivery system that includes a driven shaft and a gear box assembly. The gear box assembly includes an outer housing and a gear box shaft at least partially disposed in the outer housing is disclosed. The gear box shaft includes an interior region, a reservoir dam that separates the interior region into a reservoir volume and a spline volume and one or more gear box shaft venting holes formed through the gear box shaft near an end thereof. The assembly also includes a regulator disposed at least partially within the gear box shaft, the regulator including one or more regulator vent holes, wherein at least one of the regulator venting holes is in fluid communication with one of the one or more gear box shaft vent holes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The subject matter which is regarded as the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIGS. 1A and 1B  show, respectively, a cross-sectional side view of a gear box driving an accessory and a magnified section thereof; 
           [0009]      FIG. 2  is a perspective view of a reservoir according to one embodiment; 
           [0010]      FIG. 3  is a partial view of the cross-section of the gear box of  FIG. 1  illustrating a lubricant torus formed when a gear box shaft is rotating; 
           [0011]      FIG. 4  is a view of the cross-section of the gear box of  FIG. 1  illustrating a lubricant pool formed when a gear box shaft initially stops rotating; 
           [0012]      FIG. 5  is a view of the cross-section of the gear box of  FIG. 1  illustrating the lubricant pool formed after the gear box shaft stops rotating at a time after the lubricant has flowed back through the feed holes; 
           [0013]      FIG. 6  is a cross-sectional side view of a gear box driving an accessory illustrating various pressures during operation; 
           [0014]      FIG. 7  is a cross-sectional side view of a gear box driving an accessory illustrating various pressures during operation and how lubricant may leak out through the gear box shaft; 
           [0015]      FIG. 8  is a cross-sectional side view of a gear box shaft with a regulator according to one embodiment; 
           [0016]      FIG. 9  is an exploded perspective view of the regulator of  FIG. 8  and the gear box shaft that includes regulator retaining ring; 
           [0017]      FIG. 10  is a cut-away side of the a regulator and gear shaft that shows air and lubricant paths; and 
           [0018]      FIG. 11  is a cross-section of  FIG. 8  taken along line  11 - 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Disclosed herein are systems and methods that can lubricate a joint between two shafts and that is resistance to failures in a sealing element (e.g., an o-ring) that seals oil or other lubricants from leaving the system through the joint between the shafts. It shall be understood that while a spline joint is used in the following description, the teachings herein can be applied to any type of connection between two shafts that need to be connected together. 
         [0020]    As described above, a spline joint may need lubrication. One manner to provide such lubrication is to utilize a so-called “one shot” lubrication system that provided lubrication every time the connected shafts stop spinning. The inventors hereof have found that such lubrication systems may have limitations when a sealing element fails that result in a loss of lubricant during operation of the system/joint at high altitude. To best understand the inventive nature of the system/method disclosed herein a brief description of an example one shot system is first provided and described in the context of a gear box shaft connected to an accessory shaft in an air craft. The accessory shaft as the term is used herein may refer to an input or output of any element on an aircraft that either generates of receives rotational energy. Examples include, but are not limited to, starters, constant speed drives, generators, hydraulic pump(s), and the hydromechanical engine fuel controls. The gear box shaft may be an input to or an output from a gear box. Depending on the context, either of the accessory or gear box shafts may be referred to as the driving shaft with the other being referred to as the driven shaft. However, for simplicity the following description may describe systems where the gear box shaft is the driving shaft and the accessory shaft is the driven shaft. 
         [0021]      FIG. 1A  shows a system  100  with a gear box  102  having a gear box (or driving) shaft  104  connected to an accessory (or driven) shaft  106 . The gear box  102  may be connected to an aircraft turbine or a ram air fan in one embodiment and may be referred to as an accessory gear box denoting that it provided rotational energy to an accessory. Further, the gear box  102  may define a closed cavity within which some or all of the gear box shaft  104  is housed. An exterior gear  111  is coupled to or integrally formed around an outer surface of the gear box shaft  104  such that it can receive and re-transmit rotational energy received, for example, from the turbine or ram air fan and provide to another element such as accessory  108 . 
         [0022]    For example, and now referring to the gear box shaft  104  as the driving shaft and the accessory shaft  106  as the driving shaft, the driving shaft  104  is coupled to the driven shaft  106  by a spline joint  110  such that rotational energy is transferred to the driven shaft  106 . The particular configuration of the spline joint  110  can be selected from all known configurations of such joints. The spline joint  110  is sealed by a sealing element such as o-ring  112  to prevent a fluid (e.g., lubricant) from escaping an interior region  107  of the driving shaft  104 . Such fluid may otherwise be lost to the atmosphere if not sealed. If enough fluid is lost, mechanical errors may occur. 
         [0023]    The interior region  107  includes two volumes, a reservoir volume  114  and spline volume  116 . The two volumes are separated and defined by a reservoir dam  112 . More particularly, the reservoir volume  114  is defined by the torus formed during rotation and having a thickness (e.g., height) as defined by Rh and, similarly, the spline volume  116  is defined by the torus formed during rotation and having a thickness (e.g., height) as defined by Sh. The precise volume and how to determine such is known in the art and may be determined by the skilled artisan. Further, the heights Rh and Sh may be selected (as well as the lengths of the volumes where the length is measured in the axial direction) such that a specific amount of lubricant is delivered to the spline joint  110  each time the system restarted. For example, the height and lengths may be selected such that each time an aircraft takes off a particular amount of lubricant is delivered to the joint  110  as is more fully described below. 
         [0024]    The driving shaft  104  is supported by bearings  120  and  121  which allow for the driving shaft  104  to rotate within the gear box  102 . It shall be understood that fluid from the interior region  107  of the driving shaft  104  or introduced upstream of the driving shaft  104  may return to an interior region of the gear box  102  through bearing  120  as it may settle in the direction of gravity (shown by arrow g) when the aircraft is not operating (e.g., when the driving shaft is not turning). 
         [0025]    The gear box  102  includes a lubrication jet  122  that provide a lubricant into the system (e.g., into shaft  104 ). The end of the driving shaft  104  opposite the spline joint  110  includes a lubricant regulator (or regulator)  103 . 
         [0026]    With reference now to  FIGS. 1A-1B and 2 , details of the regulator  103  are described. The regulator  103  is a generally circular element that includes a perforated base  105  that includes one or more feed holes  130  formed therein. The regulator  103  also includes a tubular sidewall  124 . As will be understood from the below, the feed holes  130  are locate a distance Fh from the sidewall  124 . At an opposite end of the regulator  103  from the base  105  a lip referred to as a feed dam  126  is provided on the regulator  103 . As more fully described below, the length of the sidewall  124  and the height of the feed dam  126  define a feed volume  134 . In one embodiment, a regulator retaining ring  132  holds the regulator  103  in place and a regulator sealing ring  120  may also be provided. 
         [0027]    During operation (e.g., while an aircraft is running), lubrication jet  122  may direct lubricant towards the regulator  103 . Some of this lubricant may enter the interior region  107  as described below. The amount is dependent on the sever factors including Fh, and a distance from an interior wall of the interior region  107  to the top of the feed dam  126  that defines an entry height (shown as Eh). 
         [0028]    With reference now to  FIGS. 1-3 , during operation the lubricant will form a regulator torus  134  and a reservoir torus  140 . The feed dam  126  and the sidewall  124  define the volume of the regulator torus  134 . The entry height Eh and a length from the base  105  to the reservoir dam  112  defines the volume of the reservoir torus  140 . As will be understood, while spinning the distance from a centerline of the driving shaft to an internal diameter of both the regulator torus  134  the reservoir torus  140  and is set by the height of the feed dam  126 . Also, the volume of the reservoir torus  140  is depending on the entry height Eh and a distance from the base  105  to the reservoir dam  110 . 
         [0029]    Stated differently, lubrication is supplied through the feed jet  124  that such that the feed volume  134  fills defining a torus of lubrication (regulator torus  134 . Further, the lubricant drains through feed holes  130  into the interior region  107 . As discussed above, the reservoir volume  114  fills to the level of feed dam  126  (e.g., Eh) as reservoir torus  140 . Any excess lubricant flows back over feed dam  126  into the gear box  102 . In this manner, the levels of the regulator torus  134  and a reservoir torus  140  remain constant while the driving shaft  104  is spinning. 
         [0030]    With reference now to  FIGS. 4 and 5 , when the reservoir Torus  140  collapses into chordal volume  150  which is higher than reservoir height Rh. In one embodiment, the feed holes  130  are sized small enough that a majority of the lubricant flows over the reservoir dam  110  into spline volume  116  to form lubrication volume  202 . Any remaining lubricant is the reservoir volume not flowing into the spline volume  116  will flow back though the feed holes  130  until the level of the fluid in the reservoir volume is equal to Eh. As illustrated, the amount that remains in the reservoir volume is shown as volume  204 . As will be understood, based on the volume the reservoir torus and the spline height Sh, the volume  202  will be at or near the same level on every shut down. 
         [0031]    With reference to  FIGS. 6 and 7 , while the aircraft is operating Pcase is at a first level and the pressure (Pres) in the internal region  105  is lower than Pcase. It has been discovered that if Pcase is substantially higher than Pres a manometer mode may arise causing lubricant to be forced over the reservoir dam  112  from the reservoir volume  114  in the spline volume  116 . Such fluid is shown as fluid  160 . Such a condition may exist if the o-ring  112  is damaged or missing. In such a case, Pres may approach atmospheric pressure Patm. At high altitudes, the Patm may be enough below Pcase that the manometer effect occurs. Further, this extra oil in the spline volume  116  may escape (see fluid  160 ) to the atmosphere and not be recovered leading to a constant drain on the lubricant tanks (e.g., the aircraft could lose substantial amounts of lubricant). 
         [0032]    One manner in which the pressure difference may be reduced is to vent case pressure into the interior region  107 . With reference now to  FIGS. 8-11  several views of an alternative regulator  203  are shown that allow for such venting. The regulator  203  of this embodiment allows for the flow of lubricant in the same manner as the regulator  103  described above. To that end, regulator  203  is a generally circular element that includes a perforated base  205  that includes one or more feed holes  230  formed therein. The regulator  203  also includes a tubular sidewall  224 . Feed holes  230  are locate a distance Fh from the sidewall  224 . The regulator  203  includes a lip referred to as a feed dam  226 . As above, the length of the sidewall  224  and the height of the feed dam  226  define a feed volume. In one embodiment, a regulator retaining ring  262  holds the regulator  203  in place and is seated in a groove  280  formed on an inner surface of the shaft  104 . The regulator  203  may also include alignment tabs  260  that time the regulator to the driving shaft  104  and are received by slots  270 . 
         [0033]    According to this embodiment, the driving shaft  104  includes shaft venting holes  250  formed therein. The regulator  203  includes regulator venting holes  290  that corresponding to at least some of the shaft venting holes  250 . In the disclosed embodiment, there are four regulator venting holes  290  and correspond to four of the eight shaft venting holes  250 . For clarity, an air path (e.g., vent path) is shown by path A and an oil path is show by path B in  FIG. 10 . 
         [0034]    With reference to  FIG. 11 , where the four regulator venting holes  290  correspond shaft venting holes  250  a direct venting path D is formed and for the remaining four shaft venting holes  250  an indirect venting path ID is formed. The paths D and ID may reduce the difference between the Pcase and Pres such that the manometer effect does not occur, even if o-ring  112  is damaged or missing. While different paths have been shown it shall be understood that only one venting path needs to be formed. As such, the venting path can be formed as long as each of the shaft  102  and the regulator  203  includes one venting hole formed therein. The tabs  260  may ensure that at least one path D is formed. 
         [0035]    During operation (e.g., while an aircraft is running), lubrication jet  122  may direct lubricant towards the regulator  203 . Some of this lubricant may enter the interior region  107  as described above. The amount is dependent on the sever factors including Fh, and Eh. 
         [0036]    While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.