Abstract:
A method of assembling an integrated drive generator includes the steps of providing a bore in a center housing portion, pressing a bearing liner into the bore, with a portion of the bearing liner extending proud of a surface of the center plate, and machining the surface around and adjacent to the bearing liner to provide a machined surface parallel to the surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This disclosure is a continuation of U.S. patent application Ser. No. 13/542,776 filed Jul. 6, 2012. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to a housing for an integrated drive generator for a gas turbine engine, for example. The disclosure also relates to a mounting configuration for a hydraulic unit of the integrated drive generator relative to its housing. 
         [0003]    One example type of integrated drive generator (IDG) includes a generator, a hydraulic unit and a differential assembly arranged in a common housing. The differential assembly is operatively coupled to a gas turbine engine via an input shaft. The rotational speed of the input shaft varies during the operation of the gas turbine engine. The hydraulic unit cooperates with the differential assembly to provide a constant speed to the generator throughout engine operation. 
         [0004]    In one example, the housing includes generator, center and input housing portions, which may be constructed from a magnesium alloy. The hydraulic unit is mounted to the center housing portion, which is sealed relative to the generator and input housing portions with seal plates. 
         [0005]    The center housing has spaced apart lateral sides. The hydraulic unit includes a structural can that is mounted to one of the sides. It can be difficult to maintain the flatness in a machined magnesium surface. The sides have been machined flat in the area of the hydraulic unit across the center housing portion in the area of the hydraulic unit and the surrounding surface, which maintains flatness of the center housing portion to ensure that it adequately seals relative to the other housing portions. A bearing liner is pressed into a bore in the center housing portion to support a hydraulic unit shaft. The bearing liner is flush with the lateral surface opposite the can. The surface is subsequently machined right over the bearing liner, better ensuring flatness. 
       SUMMARY 
       [0006]    In one exemplary embodiment, a method of assembling an integrated drive generator includes the steps of providing a bore in a center housing portion, pressing a bearing liner into the bore, with a portion of the bearing liner extending proud of a surface of the center plate, and machining the surface around and adjacent to the bearing liner to provide a machined surface parallel to the surface. 
         [0007]    In a further embodiment of the above, the method includes the step of installing a bearing onto a shaft, and inserting the bearing into the bearing liner. 
         [0008]    In a further embodiment of any of the above, the method includes machining a recess in an opposite side of the center housing portion to provide a second machined surface, and securing a hydraulic unit to the second machined surface, the hydraulic unit having the shaft. 
         [0009]    In a further embodiment of any of the above, the method includes arranging a seal on the machined surface and sealing the center housing portion relative to another housing portion with the seal plate. In a further embodiment of any of the above, the method includes the steps of securing generator, center and input housing portions to one another. The center housing portion is sealed relative to the generator and input housing portions with seal plates. The center housing portion is arranged between the generator and input housing portions. The seal plates are arranged on opposing sides of and in engagement with the center housing portion. A hydraulic unit is mounted to the center housing portion. The center housing portion includes first and second parallel surfaces, and the machined surface is parallel to and recessed into one of the first and second surfaces in an area of the hydraulic unit. 
         [0010]    In a further embodiment of any of the above, the method includes the steps of securing generator, center and input housing portions to one another. The center housing portion is sealed relative to the generator and input housing portions with seal plates. A hydraulic unit is mounted to the center housing portion. The center housing portion includes first and second parallel surfaces. The machined surface is parallel to and recessed into one of the first and second surfaces in an area of the hydraulic unit. The hydraulic unit includes a can having a flange secured to the machined surface. The can houses a shaft supported by a bore in the center housing portion. 
         [0011]    In a further embodiment of any of the above, the can houses first and second pumping elements separated by a pump plate and configured to provide a fixed rotational speed to a generator within the housing. 
         [0012]    In a further embodiment of any of the above, a first lateral thickness is provided between the first surface and the machined surface. A second lateral thickness is provided between the first and second surfaces. A ratio of the second lateral thickness to the first lateral thickness is 1.05. 
         [0013]    In a further embodiment of any of the above, the hydraulic unit includes a shaft supported by a bearing in the center housing portion. The machined surface surrounds the bearing. 
         [0014]    In a further embodiment of any of the above, the method includes the steps of securing generator, center and input housing portions to one another. The center housing portion is sealed relative to the generator and input housing portions with seal plates. A hydraulic unit is mounted to the center housing portion. The center housing portion includes first and second parallel surfaces. The machined surface is parallel to and recessed into one of the first and second surfaces in an area of the hydraulic unit. The hydraulic unit includes a shaft supported by a bearing in the center housing portion. The machined surface surrounds the bearing. The bearing includes a bearing liner extending proud of the machined surface. 
         [0015]    In a further embodiment of any of the above, the bearing liner is in an interference fit in a bore in the center housing portion. 
         [0016]    In a further embodiment of any of the above, the bearing liner includes first and second flanges opposite one another. The second flange engages the second surface. The first flange is proud of the first surface and engages the bearing. 
         [0017]    In a further embodiment of any of the above, the bearing is a roller bearing. 
         [0018]    In a further embodiment of any of the above, the machined surface may provide a lip circumscribing the bearing liner. 
         [0019]    In a further embodiment of any of the above, the center housing portion is a magnesium alloy. 
         [0020]    In a further embodiment of any of the above, the machined surface is provided by a milled surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0022]      FIG. 1  is a highly schematic view of a generator system. 
           [0023]      FIG. 2  is a cross-sectional schematic view of an example integrated drive generator. 
           [0024]      FIG. 3  is a schematic perspective view of a generator, a hydraulic unit and a differential assembly of the integrated drive generator shown in  FIG. 2 . 
           [0025]      FIG. 4  is a cross-sectional view through the hydraulic unit. 
           [0026]      FIG. 5  is an enlarged cross-sectional view of in an area of a bearing supporting a hydraulic unit shaft relative to a center housing portion. 
           [0027]      FIG. 6  is an enlarged cross-sectional view of the hydraulic unit mounted to the center housing portion. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    An example generator system  10  is schematically illustrated in  FIG. 1 . The system  10  includes a gas turbine engine  12  that provides rotational drive to an integrated drive generator (IDG)  16  through an accessory drive gearbox  14  mounted on the gas turbine engine  12 . The accessory drive gearbox  14  is coupled to a spool of the engine  12 , and the speed of the spool varies throughout engine operation. 
         [0029]    Referring to  FIGS. 2 and 3 , an example IDG  16  is illustrated. In the example, the IDG  16  includes a housing  18  having generator, center and input housing portions  20 ,  22 ,  24  secured to one another. A generator  40  is arranged in the generator housing portion  20 . Seal plates  23  are provided on either side of the center housing  22  to seal the center housing  22  relative to the generator and input housing portions  20 ,  24 . 
         [0030]    An input shaft  26  receives rotational drive from the accessory drive gearbox  14 . The rotational speed of the input shaft  26  varies depending upon the operation of the engine  12 . To this end, as a result, a hydraulic unit  32  cooperates with the differential assembly  28  to convert the variable rotational speed from the input shaft  26  to provide a fixed rotational output speed to the generator  40 . 
         [0031]    The input shaft  26  rotationally drives a differential input gear  30  that is coupled to a hydraulic input gear  34  of the hydraulic unit  32 . The differential input gear  30  is operatively coupled to the input shaft  26  by the disconnect assembly  27 . The hydraulic output gear  36  is coupled to a differential speed trim gear  38 . The hydraulic unit  32  increases or decreases the rotational speed provided to the differential unit  28  from the hydraulic input gear  34  to provide a fixed rotational output speed, such as a 12,000 rpm speed. The variable rotational speed of the differential input gear  30  combines with the speed of the differential speed trim gear  38  to provide a fixed rotational speed to a gear input shaft  42 . 
         [0032]    In the example, a gear train  44  cooperates with the generator input shaft  42 , which rotates at a constant speed to rotationally drive a charge pump  46 , deaerator  48 , main scavenge pump  50 , inversion pump  52  and generator scavenge pump  54 . Thus, these components may be designed efficiently to operate at a fixed speed. 
         [0033]    Referring to  FIG. 4 , the hydraulic unit  32  includes a can  60  that houses and provides structural support for the hydraulic unit components. Fixed and variable speed shafts  62 ,  64  are arranged coaxially with and nested relative to one another on one side of the hydraulic unit  32 . The hydraulic input gear  34  is provided by the variable speed shaft  64 , and the hydraulic output gear  36  is provided by the trim speed shaft  62 . 
         [0034]    A speed change shaft  72  is also arranged within the can  60  and is coaxial with the trim and variable speed shafts  62 ,  64 . A pump plate  66  separates first and second pumping assemblies  68 ,  70 , which each include a wobbler and pistons. The pumping assemblies cooperate with one another to increase or decrease the rotational speed of the trim speed shaft  62 . 
         [0035]    A first bearing  74  supports the trim speed shaft  62  relative to the can  60 , and a second bearing  76  supports the other end of the trim speed shaft  62  relative to the pump plate  66 . Another second bearing  76  supports the speed change shaft  72  relative to the pump plate  66 , and a third bearing  78  supports the other end of the speed change shaft  72  relative to the center housing  22 . A fourth bearing  79  supports the variable speed shaft  64  relative to the input housing  24 . 
         [0036]    Referring to  FIGS. 4 and 5 , the center housing portion  22  includes a bore  80  that receives the third bearing  78 . A bearing liner  82 , which may be steel, is press-fit into the bore  80 . The bearing liner  82  includes first and second flanges  84 ,  86  adjoined by a wall  88  that is received in the bore  80  to provide the press-fit. It is desirable to press-fit the bearing liner  82  into the bore  80  prior to machining, since press-fitting may distort the magnesium center housing portion  22 . The center housing portion  22  includes first and second surfaces  98 ,  100  that are laterally spaced apart from one another. The first and second surfaces  98 ,  100  may be provided by an initial machining operation that may provide sufficiently flat surfaces for adequate sealing of the seal plates  23 . The second flange  86  abuts the second surface  100  to limit the installation depth of the bearing liner  82  during press-fitting. 
         [0037]    The first flange  84  extends proud or beyond the first surface  98 , which is necessary to accommodate the width of the third bearing  78 . The third bearing  78  includes an outer race  90  received by the bearing liner  82  in abutting relationship with the first flange  84 . Rollers  92  are spaced circumferentially about an inner race  96 , which is provided by the speed change shaft  72 , and engage the outer and inner races  90 ,  96 . The circumferential spacing of rollers  92  are maintained by a cage  94 . 
         [0038]    The center housing portion  22  is machined to a thinner width than provided by the first and second surfaces  98 ,  100 . This may enable a longer hydraulic unit to be accommodated in the same sized housing envelope as previously used IDGs. However, desired flatness of the center housing portion  22  must be maintained to ensure proper sealing of the center housing portion  22  relative to the generator and input housing portions  20 ,  24 . To this end, the first surface  98  is machined, for example, using a milling operation, to provide a machined surface  102  that is parallel with the second surface  100 . The bearing liner  82  is installed before machining. 
         [0039]    The can  60  includes a flange  106  that is secured to the center housing portion  22 . The flange  106  includes holes  108  aligned with holes  110  in the center housing portion  22 . Fasteners  112  are received by the holes  108 ,  110  and secure the flange  106  to the center housing portion  22 . A machined surface  114 , provided for example using a milling operation, is recessed into the second surface  100  to accommodate the longer hydraulic unit and provide a first lateral thickness T 1 . The first lateral thickness T 1  is provided between the first surface  98  and the machined surface  114 , which are parallel to one another. A second lateral thickness T 2  is provided between the first and second surfaces  98 ,  100 . The ratio of the second lateral thickness T 2  to the first lateral thickness T 1  is 1.05. 
         [0040]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.