Patent Application
20170159796
The present disclosure generally relates to lubrication, and more particularly, to a spline lubrication system that includes a vent.
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.
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.
In operation, the spline joint may need lubrication from time to time.
According to one embodiment, a gear box assembly is disclosed. The gearbox 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 and a reservoir dam that separates the interior region into a reservoir volume and a spline volume. The reservoir dam has a vent hole formed therein that passes through it such that a surface of the dam is in fluid communication with a region defined by the outer housing and outside of the gear box shaft.
According to another embodiment, a power delivery system is disclosed. The system 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 and connected by a spline joint to the driven shaft. The gear box shaft includes an interior region and a reservoir dam that separates the interior region into a reservoir volume and a spline volume. The reservoir dam has a vent hole formed therein that passes through it such that a surface of the dam is in fluid communication with a region defined by the outer housing and outside of the gear box shaft.
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:
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.
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.
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.
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.
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).
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.
With reference now to
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).
With reference now to
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.
With reference now to
With reference to
One manner in which the pressure difference may be reduced is to allow pressure from the case to enter the interior region 107 through vent 170 formed through the reservoir dam 112 as shown in
The size of the vent 170 needs to allow for the desired pressurization of the interior region 107 while not allowing too much lubricant to flow back to the case and not over dam 112. That is, if the vent 170 is too small and the required pressurization of the interior region 107 may not occur and if the vent 170 is too large, the lubricant may escape the interior region 107 when the shaft 104 stops spinning without reaching the spline volume 116 during normal operation.
According to one embodiment, the vent 170 is realized by one or more (and in particular, four) equally spaced holes size of Dia 0.125″+/−0.010″ at an angle of 50° off the centerline axis. The length (L) of such vents (which affects the pressure drop) is approximately 0.630″ in such an embodiment.
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.
