Abstract:
A gearbox for an aircraft has a first side wall, a second side wall, a gear train, and an aircraft accessory. The aircraft accessory has a housing, an input attaching to the gear train for receiving rotative input from the gear train, and a first shaft for selectively coupling and uncoupling the gear train from the input. The housing attaches to the first side wall and the second side wall.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/284,454, filed Dec. 18, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    An aircraft&#39;s power requirements for various flight systems and passenger comfort are usually provided by a gas turbine engine. Such systems and accessories may include a fuel pump, engine lube pump, an electrical generator and a PMA, a small permanent magnet alternator (“PMA”) that provides power for electrical systems. The gas turbine engine can be an engine that provides thrust to the aircraft, an auxiliary power unit (“APU”) or both in some instances. 
         [0003]    A conventional arrangement for transferring rotational energy from the gas turbine engine to accessories is by means of a geared transmission. Usually, the accessories mount on the face of an accessory gear box. The accessory gear box is often connected to a rotative engine output by beveled gearing. An accessory mounting gear box usually includes a drive shaft extending from gearing connected to the engine core and the drive shafts rotating the engine lube pump, fuel pump, the engine control, hydraulic pumps, generators etc. 
         [0004]    Some accessories are needed for engine operation and must be highly reliable so that the engine maintains propulsive power. For instance, the PMA is used to power the electrical controls for the engine. Other accessories are not essential loads for flight, and mechanical disconnects are often incorporated inside the accessory to allow manual or automatic decoupling of the accessory drive shaft should the accessory malfunction. The decoupling of a faulty accessory reduces damage to the accessory that would occur with continued operation, and prevents overloads of the drive line should the accessory damage progress to shaft seizure. Some accessories incorporate shear sections that fracture and stop accessory rotation should a fault (such as a bearing failure inside the accessory) develop inside the accessory that exceeds normal operating torque. 
       SUMMARY OF THE INVENTION 
       [0005]    According to an exemplary embodiment herein, a gearbox for an aircraft has a first side wall, a second side wall, a gear train, and an aircraft accessory. The aircraft accessory has a housing, an input attaching to the gear train for receiving rotative input from the gear train, and a first shaft for selectively coupling and uncoupling the gear train from the input. The housing attaches to the first side wall and the second side wall. 
         [0006]    According to a further exemplary embodiment herein, a gearbox has a first side wall, a second side wall, a gear train, and an accessory driven by the gear train. The accessory has a housing, an input attaching to the gear train for receiving rotative input from the gear train, and a first shaft for selectively coupling and uncoupling the gear train from the input. The housing attaches to the first side wall and the second side wall. 
         [0007]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a prior art arrangement of a gear train coming from an engine such as an engine that provides thrust or an auxiliary power unit. 
           [0009]      FIG. 2  shows an accessory such as a generator wherein the housing of the generator is degraded with a housing of the gearbox. 
           [0010]      FIG. 3  shows a first embodiment of a jack shaft gearing arrangement incorporating a disconnect. 
           [0011]      FIG. 4  is a second embodiment of a jack shaft as disclosed herein. 
           [0012]      FIG. 5  is a still further embodiment of a jack shaft as provided herein. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    Referring now to  FIG. 1 , a prior art gear train  10  is shown within a gearbox  15 . The gear train  10  has a plurality of gears  20  mounted on a plurality of rotating shafts  25 . The gearbox  15  has a wall  30  and a wall  35  in which the gears  20  are mounted. The right wall  35  is reinforced and a heavier gauge is shown herein, to support an accessory  40  that projects from outside the right wall  35 . 
         [0014]    The accessory  40  may be mounted in a housing  45  and includes an accessory input shaft  50 , a shear neck  55  and a rotating device  60  in the accessory  40 . The accessory can be any of an engine lube pump, a fuel pump, a PMA, engine hydraulic pumps, and generators, etc. Though the accessory  40  shown herein is supported by the right wall  35  of the gearbox  15 , an accessory can hang off of either side of the gearbox  15  so long as that side of the gearbox  15  is reinforced to hold that accessory  40  securely. The accessory housing  45  has an L-shaped flange  65  extending from a cylindrical body  70  to attach securely to the right wall  35 . The L-shaped flange  65  and the right wall  35  are reinforced to support the hanging moment of the accessory  40  off the right wall  35 . 
         [0015]    To save generator and gearbox weight, an accessory such as a generator may be incorporated into a gearbox. This reduces the overhung moment of the generator which is normally cantilevered off of one face of the gearbox and allows the gearbox and generator to partially share the same housing. Reduced cantilever simplifies and allows the gearbox housing to be of lighter weight and may also reduce loads of a gearbox mount links, reducing their weight. Reduced cantilever and gearbox/accessory combined weight is a particular importance when the extreme engine dynamic load cases are considered that have many times a normal acceleration of gravity. 
         [0016]    Referring now to  FIG. 2 , the accessory housing  47  is shown having a first portion  75  extending through the wall  31  and a second portion  80  extending through the right wall  37  of the gearbox  15 . The weight of the accessory housing  45  is supported by both walls  30 ,  35  almost entirely normal to a longitudinal axis of each wall. As such, any torquing moment that requires the walls  30 ,  35  to be reinforced is eliminated thereby minimizing the weight of the gearbox walls because reinforcement may be reduced or eliminated. Moreover, because the accessory housing  45  also has a reduced torquing moment on it, flange  85 , which attach by conventional means to the right wall  35 , may not have to be reinforced, thereby further reducing weight. 
         [0017]    In the embodiment shown in  FIG. 2 , an accessory  41  such as a generator or the like is supported on an input shaft  90  attaching to an input gear  95  which is driven by the gear train  10 . The generator  41  may have several other components installed on the shaft  90  including a permanent magnet generator (“PMG”)  100  located outboard of the input gear  95  that provides power to an electronic controller (not shown) or the like, and an exciter  105  located on the right side of the accessory  41 . The shaft  90  is supported on bearings within the housing  47 . 
         [0018]    Referring now to  FIG. 3 , an embodiment is shown in an engaged position above Axis A and a disengaged position below Axis A (as is also true in the subsequent drawings). It should be appreciated that the split view of the Axis A is for illustrative purposes only and that the parts shown herein are in register with each other above and below Axis A if the embodiment is in either the engaged or disengaged position. Referring now to  FIG. 3 , portion  110  that attaches to wall  31  extending from first portion  75 , portion  115  extending from a middle of body  70 , and portion  120  extending from the second portion  80  and attaches to wall  37  are shown supporting a plurality of bearings,  125 ,  130 ,  135 , and  140 . A shaft  90  rotatively mounted between bearings  125  and  130  supports input gear  95  and rotates therewith that meshes with a gear in a gear train  10  as is known in the art. The shaft  90  has a plurality of axially teeth  155  that engage with axial teeth  160  (see above axis A) connected to a jack shaft  165  that is disposed within and engages an output gear  170 . The jack shaft  165  has a plurality of jack shaft splines  175  that engage internal splines  180  of the output gear  170  shaft which is supporting by bearings  135 ,  140 . The output gear  170  has teeth  185  that mesh with teeth (not shown) depending from a gear (not shown) that drives an accessory  41  such as a generator or the like. 
         [0019]    The jack shaft  165  has a spiral ramp  190  disposed on extension  195  that extends beyond bearings  140 . A disengagement pawl  200  is arranged transversely to the spiral ramp  190 . Should the disengagement pawl  200  be pushed upwardly into engagement with the spiral ramp  190 , the jack shaft  165  moves axially with the rotation of the spiral ramp  190  to the right in the drawing (see below Axis A in  FIG. 3 ) to disengage its axial teeth  160  from the axial teeth  155  extending from the input shaft  90  to disconnect the accessory  41  from the input gear train  10 . Input gear  95  and shaft  90  rotate freely without providing input to the accessory  41  through the jack shaft  165 . The disengagement pawl  200  may be driven by a mechanical, electrical or hydraulic means acting in response to a signal received by a controller (not shown) in response to a stimulus that the accessory  41  is malfunctioning and should be withdrawn from gear train  20  to minimize damage to the accessory  41  or overloading of the gear train  20 . 
         [0020]    Referring now to  FIG. 4 , a jack shaft  265  is shown attaching to a hydraulic or pneumatic actuator  270 , or the like (e.g., an electromechanical device such as a solenoid), via piston head  275 , piston rod  280  and bearing  285 . The jack shaft  265 , instead of disconnecting from the axial teeth  155  (see  FIG. 3 ) of the input shaft  90 , disconnects from the output gear  170  by moving axially along the axis of rotation A as urged by the actuator  270  as will be discussed herein. 
         [0021]    The actuator  270  has the piston head  275  disposed within a cylinder  290  outside of the second portion  80  in line with the axis of rotation A. The piston rod  280  extends from the actuator  270  through the second portion  80  and engages the jack shaft  265  via the bearing  285  that attaches to an outer end  295  of the piston rod  280  and an inner end  300  of the jack shaft  265 . To disengage the jack shaft  265  from the output gear  170 , a pump  305  impels fluid such as air or hydraulic fluid, into the right side  310  of the cylinder  290  via line  315  while drawing fluid from the left side of the cylinder  290  via line  331 . The piston head  275  is driven axially to the left (see below the Axis A) and in turn drives the piston rod  280 , the bearing  285  and the jack shaft splines  175  out of engagement with the interior spline teeth  180  of the output gear thereby protecting the accessory from continued input torque. To reverse the effect, (recouple the shaft) the pump  305  impels fluid into the left side  320  of the cylinder  290  while drawing fluid from the right side  310 . The piston head  275  is driven axially to the right and in turn drives the piston rod  280 , the bearing  285  and the jack shaft splines  175  re-engage the interior spline teeth  180  of the output gear. 
         [0022]    Referring now to  FIG. 5 , the jack shaft  265  is shown having a shear section  330  having a smaller diameter than the rest of the jack shaft  265 . In extreme situations, where the pneumatic actuator or the disengagement paw do not act quickly enough to disengage the accessory from the input torque of the gear train  20 , the shear section  330  protects the accessory  41  (see  FIG. 2 ) from catastrophic situations by breaking before the accessory  41  does. Upon breaking, the jack shaft  265  has separate sections that rotate independently of each other there by stopping the accessory from rotation and potential breakage thereof. The shearing force necessary to cause the shear section  330  to break is normally greater than three times the maximum operating load. For instance, if the maximum operating load is 113 newton meters the shear section will break at about 339 newton meters. The ratio of three times the maximum operating load is suggested to avoid nuisance shearing where sudden unexpected loads that occur normally are encountered. 
         [0023]    Referring further to  FIG. 5 , a hydraulic or pneumatic actuator  370 , or the like is shown as an integral component of the second portion  80  of the housing  47 . 
         [0024]    Though the input shaft  90  (see also gear from the gear train  20  is shown on the left and the output gear  170  to the accessory  41  is shown to the right in the drawings, one of ordinary skill would recognize that the input shaft  90  could be on the right and the output gear  170  could be on the left depending on the requirements of the application. Moreover, the actuator  270  may be used with the embodiment shown in  FIG. 3  and the spiral ramp  190  of  FIG. 3  may be used to move the piston rod  280  of  FIGS. 3 and 4 . 
         [0025]    Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
         [0026]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.