Patent Publication Number: US-8992192-B2

Title: Input shaft lubrication for gear pump

Description:
BACKGROUND 
     The present disclosure relates to a pump, and more particularly to a fuel gear pump for gas turbine engines. 
     Fuel gear pumps are commonly used to provide fuel flow and pressure for gas turbine engines and other systems on aircrafts. The gear pump must perform over a wide system operating range and provide critical flows and pressures for various functions. Typically, these pumps receive rotational power from an accessory gearbox through a drive shaft. 
     In a dual gear stage pump, rotational power is transferred from one gear stage to the other gear stage through an input shaft and coupling shaft. Each shaft usually has splines to transfer input shaft rotation into the respective gear stages. To minimize wear and meet all performance requirements throughout the pump service life, the splines may be lubricated during operation. 
     SUMMARY 
     A shaft assembly according to an exemplary aspect of the present disclosure includes a shaft with a first radial shoulder and a second radial shoulder, an axial separation between the first radial shoulder and the second radial shoulder defines an axial distance SA along an axis and each of said radial shoulders defines an outer diameter SD, a ratio of SA/SD defined between 0.19 -0.45. 
     A shaft assembly according to an exemplary aspect of the present disclosure includes a gear with a gear bore having a splined bore section adjacent to an oil dam. A shaft includes a first splined end section and a second splined end section, the first splined end section engageable with the splined inner diameter, the shaft having a bore with a bore diameter greater than a diameter of the oil dam, a first set of radial apertures axially inboard of the first splined end section in communication with the shaft inner bore and a second set of radial apertures axially inboard of the second splined end section in communication with the shaft inner bore. 
     A gear pump according to an exemplary aspect of the present disclosure includes a gear with a gear bore having a splined bore section adjacent to an oil dam. A shaft includes a first splined end section and a second splined end section, the first splined end section engageable with the splined inner diameter, the shaft having a bore with a bore diameter greater than a diameter of the oil dam, a first set of radial apertures axially inboard of the first splined end section in communication with the shaft inner bore and a second set of radial apertures axially inboard of the second splined end section in communication with the shaft inner bore. A coupling shaft is located along a coupling shaft axis parallel to the input shaft axis. 
     A method of lubricating a shaft within a housing according to an exemplary aspect of the present disclosure includes communicating a lubricant into a shaft inner bore, transferring the lubricant between a first splined end section and a second splined end section, collecting the lubricant within the shaft inner bore, and draining the lubricant from the shaft inner bore when the level of the lubricant reaches an oil dam inner aperture. 
     A method of installing a shaft according to an exemplary aspect of the present disclosure includes installing a shaft having a shaft inner bore into a gear, the shaft inner bore having a diameter greater than an oil dam. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a block diagram of a gear pump driven by an accessory gearbox to communicate a fluid such as fuel to a gas turbine; 
         FIG. 2  is an end view of a gear pump; 
         FIG. 3  is a sectional view of the gear pump taken along line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a sectional view of the gear pump taken along line  4 - 4  in  FIG. 2 ; 
         FIG. 5  is a perspective view of the gear pump with the housing removed; 
         FIG. 6  is another perspective view of the gear pump with the housing removed; 
         FIG. 7  is another perspective view of the gear pump with the housing removed; 
         FIG. 8  is a perspective view of the gear pump from the same perspective as in  FIG. 5 ; 
         FIG. 9  is a perspective view of the gear pump from the same perspective as in  FIG. 7 ; 
         FIG. 10  is a perspective view of the gear pump from the same perspective as in  FIG. 6 ; 
         FIG. 11  is an expanded sectional view of an input shaft assembly of the gear pump; 
         FIG. 12  is an end view of a retainer plate of the input shaft assembly; 
         FIG. 13  is an expanded sectional view of an input shaft assembly of the gear pump in an operational position; 
         FIG. 14A  is an expanded sectional view of an input shaft assembly of the gear pump in an operational position; and 
         FIG. 14B  is an expanded, isolated view from  FIG. 14A  of a gear and oil dam. 
         FIG. 15  is an expanded side view of the input shaft assembly illustrating a dimensional relationship between radial shoulders. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gear pump  20  driven by an accessory gearbox  22  to communicate a fluid such as fuel to a gas turbine  24 . It should be appreciated that the present application is not limited to use in conjunction with a specific system. Thus, although the present application is, for convenience of explanation, depicted and described as being implemented in an aircraft fuel pump, it should be appreciated that it can be implemented in numerous other systems. In addition, although a dual stage gear pump is disclosed, other machines with a shaft will also benefit herefrom. 
     With reference to  FIG. 2 , the gear pump  20  generally includes a housing  30  that includes an input shaft assembly  32  and a coupling shaft assembly  34  to power a main stage  36  and a motive stage  38  ( FIGS. 3 and 4 ). Rotational power is transferred from the gas turbine  24  to the accessory gearbox  22  then to the gear pump  20  through the input shaft assembly  32 . In the disclosed, non-limiting embodiment, the input shaft assembly  32  interfaces with the accessory gearbox  22  and receives a lubricant therefrom while the coupling shaft assembly  34  is lubricated with fuel. 
     With reference to  FIG. 3 , the input shaft assembly  32  is defined along an input axis A and the coupling shaft assembly  34  is defined along a coupling axis B parallel to the input axis A. The main stage  36  generally includes a main drive gear  40 , a main driven gear  42 , a main drive bearing  44  and a main driven bearing  46 . The motive stage  38  generally includes a motive drive gear  50 , a motive driven gear  52 , a motive drive bearing  54  and a motive driven bearing  56  ( FIG. 4 ). 
     The main drive gear  40  is in meshed engagement with the main driven gear  42  and the motive drive gear  50  is in meshed engagement with the motive driven gear  52  ( FIGS. 5-7 ). The input shaft assembly  32  drives the coupling shaft assembly  34  through the main stage  36  to drive the motive stage  38 . A boost stage  58  is also driven by the input shaft assembly  32  to define a centrifugal pump with an impeller and integrated inducer. 
     The stages  36 ,  38 ,  58  work mostly independently. Each stage  36 ,  38 ,  58  includes a separate inlet and discharge ( FIGS. 8-10 ). As the meshed gears  40 ,  42  and  50 ,  52  rotate, respective volumes of fluid are communicated from the main stage inlet MI to the main stage discharge MD and from a motive stage inlet ml to a motive stage discharge mD such that the main stage  36  communicates a main fuel flow while the motive stage  38  supplies a motive fuel flow. The main stage inlet MI and main stage discharge MD as well as the motive stage inlet ml and motive stage discharge mD are respectively directed along generally linear paths through the respective gear stage  36 ,  38 . 
     In the disclosed non-limiting embodiment, an aircraft fuel system provides flow and pressure to the boost stage inlet BI. A portion of the boost stage discharge is routed internally to the motive stage inlet mI. The remainder of the boost stage discharge is discharged from the gear pump  20  to the aircraft fuel system, then returns to the main stage inlet MI. The motive stage discharge mD is communicated to the aircraft fuel system. The main stage discharge MD is also communicated to the aircraft fuel system to provide at least two main functions: actuation and engine burn flow. There may be alternative or additional relatively minor flow directions and functions, but detailed description thereof need not be further disclosed herein. 
     With reference to  FIG. 11 , the input shaft assembly  32  includes an input shaft  60 , a spring  62  and a retainer plate  64 . The input shaft  60  is a hollow shaft with splined end sections  66 A,  66 B and radial shoulders  68 A,  68 B therebetween. The splined end section  66 A plugs into a gear G of the accessory gearbox  22 . The splined end section  66 B interfaces with the main drive gear  40 . The splined end sections  66 A,  66 B need to be properly lubricated during operation to minimize wear and meet all performance requirements throughout service life. Using a fluid lubricant such as oil from within the accessory gearbox  22 , the lubrication is continually supplied, drained and replenished at the spline interfaces  66 A,  66 B. 
     The radial shoulders  68 A,  68 B are generally aligned with the housing  30  to receive the retainer plate  64  therebetween. The retainer plate  64  is attached to the housing  30  through fasteners  70  such as bolts (also illustrated in  FIG. 2 ) to position an interrupted opening  65  between the radial shoulders  68 A,  68 B. The interrupted opening  65  in one disclosed non-limiting embodiment is an arcuate surface with an interruption less than 180 degrees ( FIG. 12 ). The axial position of the input shaft  60  is thereby axially constrained by the interaction of the radial shoulders  68 A,  68 B and to the retainer plate  64 . 
     With reference to  FIG. 13 , the spring  62  biases the input shaft assembly  32  to position the input shaft assembly  32  during gear pump operation. That is, the spring  62  allows the input shaft assembly  32  to move in the housing  30  in response to impact loads, until the input shaft assembly  32  bottoms out on the retainer plate  64 , but during operation, the spring  62  positions the input shaft assembly  32  such that the radial shoulders  68 A,  68 B are spaced from the retainer plate  64 . This assures there are no rotational to stationary part contact during operation. 
     With reference to  FIGS. 14A and 14B , the gear G includes a splined bore  80  with an oil dam  82 , a splined section  84  axially inboard of the oil dam  82  and a smooth bore section  86  axially inboard of the splined section  84 . The oil dam  82  generally includes a shoulder  88  and an inner aperture  90 , having a diameter  90 A, along the shaft axis A which communicates with the accessory gearbox  22 . 
     The input shaft  60  includes a first and second set of radial apertures  94 A,  94 B adjacent to splines  66 A,  66 B. A radial seal structure  96 A,  96 B extends from the input shaft  60  in an axial inboard position relative to a set of radial apertures  94 A,  94 B to seal the shaft  60  respectively to the gear G and the main drive gear  40 . The radial seal structure  96 A interfaces with the smooth bore section  86  of the gear G and the radial seal structure  96 B interfaces with the main drive gear  40  such that lubricant circulates over the splines  66 A,  66 B and communicates therebetween through a hollow inner bore diameter  92  of the input shaft  60 . 
     Lubricant initially radially enters the input shaft  60  hollow inner bore diameter  92  through either the first set of radial apertures  94 A or through the spline  66 A. Because the inner bore diameter  92  of the shaft  60  is greater than the diameter  90 A of the inner aperture  90 , lubricant collects in a reservoir  82 A of the oil dam  82  until the lubricant reaches the hollow inner bore diameter  92 . That is, as the shaft  60  rotates, the lubricant is thrown radially outwards with respect to the axis A and thus collects in the reservoir  82 A until it exceeds the level of the shoulder  88 . As the lubricant collects in reservoir  82 A of the oil dam  82 , the lubricant cannot escape through the inner aperture  90  until there is enough lubricant in the reservoir to flow over the shoulder  88 . Lubricant thus collects in the reservoir  82 A, at the spline  66 A. and in the input shaft  60  such that lubricant also flows down the hollow inner bore diameter  92  and lubricates the spline  66 B through either the second set of radial apertures  94 B or through an end section of the hollow inner bore diameter  92  and end of the input shaft  60 . Rotation of the input shaft  60  further facilitates radial flow of the lubricant through the sets of radial apertures  94 A,  94 B. When the lubricant level surpasses the shoulder  88 , the lubricant flows over the shoulder  88  of the oil dam  82  and drains into the accessory gearbox  22 . A predetermined quantity of lubricant is thereby maintained within the input shaft  60  and through rotation, circulates radially to the spline  66 A,  66 B through the sets of radial apertures  94 A,  94 B and end sections of the input shaft  60 . Thus, the oil dam  82  facilitates the continual supply, draining, and replenishing of lubricant to the splines  66 A,  66 B for proper spline lubrication. It should further be understood that the lubricant flow may be in either direction such that the flow can also exit through the sets of radial apertures  94 A,  94 B or from the end sections of the hollow inner bore diameter  92 . That is, the lubricant flows along the least path resistance which may change dynamically. 
     With reference to  FIG. 15 , the separation between the radial shoulders  68 A,  68 B defines an axial distance SA along the axis of rotation A and each of the radial shoulders  68 A,  68 B defines a diameter SD of each of the radial shoulders  68 A,  68 B. 
     The axial dimension SA in one disclosed non-limiting dimensional embodiment is 0.210-0.410 inches (5.3-10.4 mm) with a nominal dimension 0.310 inches (7.9 mm). The diameter SD in this disclosed non-limiting dimensional embodiment is 1.100-0.900 inches (28.0-22.9 mm) and a nominal diameter of 1.000 inches (25.4 mm). In this disclosed non-limiting dimensional embodiment, a ratio of SA/SD is defined between 0.19-0.45. 
     The disclosed ratios permit axial movement of the input shaft  60  defined in part by the distance between the radial shoulders  68 A,  68 B yet assures proper lubricant flow and effective splined engagement. 
     It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
     Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
     The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.