Abstract:
A method of manufacturing and/or providing a gearbox for rotating a propeller in a selected single one of a first and second direction is disclosed. The gearbox includes a many common components, selected irrespective of desired propeller direction, and a few unique components selected based on desired propeller direction. In one aspect the method includes casting a casing of the gearbox and machining the casing according to a selected configuration of the gear stages of the gearbox used to achieve direction of the propeller in the selected direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a divisional of U.S. patent application Ser. No. 10/817,857 filed Apr. 6, 2004, the entire specification of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to gas turbine engines, and most particularly to gearboxes of such engines.  
       BACKGROUND OF THE INVENTION  
       [0003]     In a typical turboprop engine, the propeller rotates in only one direction and the gearbox is designed to handle the associated reacted propeller loads accordingly, in addition to transmitting the driving power. However, because the gas turbine direction is generally fixed the propeller loads are somewhat asymmetric, and the gearbox design will vary depending on which direction the propeller is intended to rotate. Thus, if a gas turbine manufacturer wishes to provide a generic gas turbine engine capable or spinning a propeller in either direction depending on the customer&#39;s preference, two different gearbox designs must be available. Providing two gearboxes, however, increases the costs of production, inventory, etc. and, accordingly, there is a need for an improved gas turbine gearbox design adapted to drive a propeller either direction.  
       SUMMARY OF THE INVENTION  
       [0004]     It is therefore an aim of the present invention to provide an improved method of manufacturing a gearbox for a gas turbine engine which minimizes duplication for different turboprop applications having differing directions of rotation.  
         [0005]     Therefore, in accordance with one aspect of the present invention, there is provided a method of manufacturing a gearbox for rotating a propeller of a gas turbine engine in a selected one of a first and second direction, the method comprising the steps of casting a casing, selecting one of a first and second configuration corresponding to the selected one of the first and second direction, machining the casing according to the selected one of the first and second configuration, partially inserting an input shaft and an output shaft within the casing, providing in the casing a gear train adapted to drive the output shaft, a mating gear meshed with the gear train, an input pinion coupled to the input shaft, a multiple member gear, and a plurality of accessory drive gears each adapted to drive one accessory, at least one accessory drive gear being meshed with each member of the multiple member gear, providing in the casing at least one element corresponding to the selected one of the first and second configuration, the at least one element of the first configuration consisting in a first idler gear and an accessory pinion, and the at least one element of the second configuration consisting in a second idler gear, and arranging an interaction between the input pinion, the mating gear, the multiple member gear and the at least one element according to the selected one of the first and second configuration, the interaction of the first configuration consisting in meshing the input pinion with the mating gear, meshing the multiple member gear with the first idler gear, meshing the first idler gear with the accessory pinion, and coupling the accessory pinion with the input pinion, the interaction of the second configuration consisting in meshing the input pinion with the second idler gear, meshing the second idler gear with the mating gear, and coupling the multiple member gear with the mating gear.  
         [0006]     There is further provided, in accordance with another aspect of the present invention, a method of providing a single-propeller turboprop engine, the method comprising: providing a gas turbine; and providing a reduction gearbox, the gearbox mounted to an output shaft of the gas turbine, the gearbox having an output propeller shaft and at least first and second gear stages coupled to one another, the first gear stage adjacent and coupled to the output shaft of the turbine, the second gear stage adjacent and coupled to the output propeller shaft, wherein the step of providing the reduction gearbox includes the steps of: selecting a first gear stage configuration from a group consisting of a first gear set adapted to permit clockwise propeller operation and a second gear set adapted to permit counter-clockwise propeller operation; providing a second gear stage configuration operable with both the first and second gear sets of the first gear stage; selecting a desired direction of rotation for the propeller; and selecting the corresponding first gear stage configuration.  
         [0007]     Throughout this application, the term “standard rotation” will be used to refer to a first direction of rotation (e.g. one of clockwise or counter-clockwise) and the term “opposite direction of rotation” will be used to refer to a second, or opposite, direction of rotation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof and in which:  
         [0009]      FIG. 1  is a side cross-section view of a gas turbine engine having an offset gearbox according to a preferred embodiment of the present invention;  
         [0010]      FIG. 2  is a side cross-section view of a “standard rotation” offset gearbox, according to a preferred embodiment of the present invention;  
         [0011]      FIG. 3  is a partial schematic aft view of the gearbox of  FIG. 2  showing main drive gears thereof;  
         [0012]      FIG. 4  is a partial schematic aft view of the gearbox of  FIG. 2  showing an accessory drive;  
         [0013]      FIG. 5  is a sectional view of the accessory drive of  FIG. 4  taken along line  5 - 5 ;  
         [0014]      FIG. 6  is a side cross-section view of a gearbox similar to  FIG. 2  but configured according to a preferred embodiment of the present invention for rotation in the opposite direction;  
         [0015]      FIG. 7  is a partial schematic aft view of the gearbox of  FIG. 6  showing main drive gears thereof;  
         [0016]      FIG. 8  is a partial schematic aft view of the gearbox of  FIG. 6  showing an accessory drive; and  
         [0017]      FIG. 9  is a sectional view of the main drive gears of  FIG. 7  taken along line  9 - 9 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]      FIG. 1  illustrates a turboprop engine  10  having an offset gearbox  30 , 130  for driving a propeller. The engine  10  comprises a first rotating assembly including a low pressure (LP) turbine  16  and a LP compressor  18  mounted on an LP turbine shaft  19 , and a second rotating assembly including a high pressure (HP) turbine  17  and a HP compressor  15  mounted on a HP turbine shaft  21 . Power turbines  20  drive a power turbine output shaft  22 , which provides rotational input into the gearbox  30 , 130 .  
         [0019]     The LP and HP compressors  18 , 15  draw air into the engine  10  via an annular air inlet passage  24 , increasing its pressure and delivering the compressed air to a combustor  26  where it is mixed with fuel and ignited for generating a stream of hot combustion gases. The LP and HP turbines  16 , 17  extract energy from the hot expanding gases for respectively driving the LP and HP compressors  18 , 15 . The hot gases leaving the LP and HP compressor turbines are accelerated again as they expand through the power turbines  20 . The power turbines  20  provides rotational energy to drive the gearbox via the power turbine output shaft  22 .  
         [0020]     A gearbox  30 , 130  reduces the speed of the power turbine  20  to one suitable for the propeller. In the present invention, the gearbox can either be a “standard rotation” gearbox  30  or an “opposite rotation” gearbox  130 , depending on the desired direction of rotation for the propeller. The gearboxes  30 , 130  of the present invention advantageously may both be provided from substantially the same components, as will be explained further below.  
         [0021]     Referring to  FIG. 2 , the “standard rotation” gearbox  30  is shown in more details. A gearbox housing  32 , front cover  34  and accessory drive cover  36  forms a casing containing the various gearbox components. A flange  37  on the gearbox housing  32  provides the turbomachinery/gearbox interface. A flexible input drive shaft  38  couples the gearbox  30  to the turbine shaft  22 . An output shaft  40  includes a flange  42  to which the propeller is attached. The output shaft is supported by a front ball bearing  68  and a roller bearing  70  which are mounted in the front cover  34  and by a rear roller bearing  72  which is mounted in the accessory drive cover  36 .  
         [0022]     The gearbox  30  is preferably a two stage reduction gearbox with an offset first stage  28  and a planetary second stage  29 , indicated for description purposes by dotted lines in the Figures.  
         [0023]     Referring to  FIGS. 2-3 , the first stage consists of an input pinion  44  coupled to the drive shaft  38  and meshing with a first stage gear, or mating gear,  46  which is coaxial with the output shaft  40 . The first stage gears  44  and  46  are double helical gears. The first stage  28  is supported by front bearings  48  which are attached to a support housing  50  mounted into the gearbox housing  32 , and by rear bearings  52  which are attached to the gearbox housing  32 .  
         [0024]     The second stage  29  is epicyclic and preferably composed according to the following description. A sun gear  54 , coaxial with the output shaft  40  and coupled to the first stage gear  46  by a free spline  56 , is meshed with a plurality of planet gears  58 . The planet gears  58  are supported on a planet carrier  60 , which they drive. The planet carrier  60  is coupled to the output shaft  40  by a fixed spline coupling  62 . A stationary ring gear  64  is meshed with the planet gears  58  such as to allow an orbiting motion thereof. The stationary ring gear  64  is coupled to the support housing  50  by a free spline coupling  66 . The second stage is preferably made in accordance with U.S. application Ser. No. 10/628,573, filed Jul. 29, 2003 by the applicant, which is incorporated herein by reference.  
         [0025]     The gearbox  30  includes three accessory drives, each preferably rotating at different speeds in the clockwise direction looking from the rear of the engine. Referring to  FIGS. 2, 4  and  5 , an accessory pinion  74  is coupled to the pinion  44 . The accessory pinion  74  is meshed with an idler gear  76  which is in turn meshed with a triple accessory gear  78 . The triple accessory gear  78  is an idler mounted onto the output shaft  40  by, for example, a needle roller bearing  76  and is thus free to rotate about its axis. Three accessory drive gears  82   a, b, c  mesh with the corresponding member of the triple accessory gear  78  such as to each drive an accessory.  
         [0026]     The first stage gears of both gearboxes  30 ,  130  are typically more suitable for driving the engine accessories than the second stage gears. The selection of the input drive to the accessories is thus reduced to the choice of either the pinion  44  or the gear  46 . Although driving the accessories from the gear  46  is possible, such design cannot be easily adapted for use in a gearbox  130  designed for opposite direction rotation. The configuration of the present invention, in selecting pinion  44  as the driver, presents a design which, although in appearance seems more complex, will actually allow for a great deal or commonality between the two gearboxes  30 , 130 , as will be explained further below.  
         [0027]     Referring to  FIG. 6 , the opposite rotation gearbox  130  is shown in more details. All the components with identical reference numerals are preferably identical to the corresponding components in the standard rotation gearbox  30 , while corresponding components having slight differences are identified by similar reference numerals to  FIGS. 1-5 , but incremented by  100 . As with the standard rotation gearbox  30 , the opposite rotation gearbox  130  includes a gearbox housing  132 , a front cover  34 , an accessory drive cover  36 , a flange  37 , a flexible input drive shaft  38  to couple the gearbox  130  to the turbine shaft  22 , and an output shaft  40  with shaft flanges  42  to receive the propeller. Like in the standard rotation gearbox  30 , the output shaft is supported by the front ball bearing  68  and the roller bearing  70  and by the rear roller bearing  72 . Slight differences exist between the gearbox housings  32 , 132 , which will be detailed further below.  
         [0028]     The gearbox  130  is also preferably a two stage reduction gearbox with an offset first stage  128 . Referring to  FIGS. 6-7 , the first stage  128  is composed of an input pinion  144  coupled to the drive shaft  38  and meshing with two idler gears  145 . The two idler gears  145  are then meshed with a first stage gear, or mating gear,  146  which is coaxial with the output shaft  40 . The gears  144 ,  145  and  146  are also double helical gears. The first stage  128  is supported by front bearings  148  which are attached to a support housing  150  mounted into the gearbox housing  132 , and by rear bearings  152  which are attached to the gearbox housing  132 .  
         [0029]     The second stage  29  of the opposite rotation gearbox  130  is identical to the second stage  29  of the standard rotation gearbox  30  and therefore need not be described again here.  
         [0030]     The pinion  144  and gear  146  are smaller than, respectively, the pinion  44  and the gear  46  of the standard rotation gearbox  30 . However, the rotational speed and the centre distance between the input and output drives is preferably the same between the two gearboxes  30 ,  130 . Because the power from the input shaft  38  is split between two gears (idler gears  145 ), lower bearings loads are transmitted on the bearings  148 , 152 , which are thus smaller than the bearings  48 , 52  of the standard rotation gearbox  30 . Because of the different configuration of the first stage, the gearbox housings  32 ,  132  and support housings  50 ,  150  are slightly different at the location supporting the pinion  44 ,  144  and bearings  48 ,  52  and  148 ,  152 . However, these differences are minor and both sets of housings can be machined from an identical casting, which is preferred. All other components of the first stage  128  are preferably identical to corresponding components of the standard rotation gearbox  30 . Smaller bearings and smaller gears somewhat compensate for the addition of the idler gears, and the weight difference between the two gearboxes  30 ,  130  is minimal.  
         [0031]     As with the standard rotation gearbox  30 , the opposite rotation gearbox  130  has three accessory drives, each preferably rotating at different speeds in the clockwise direction looking from the rear of the engine. Referring to  FIGS. 6, 8  and  9 , a triple accessory gear  178  is directly coupled to the first stage gear  146  by a fixed spline  179 . The triple accessory gear  178  thus differs from the triple accessory gear  78  of the standard rotation gearbox  30  which was free to rotate about its axis. However, the gear teeth members of the gears  78 ,  178  are preferably identical: the only difference here is in the hub of the gear. Three drive gears  82   a ,  82   b  and  82   c , identical to the drive gears of the standard rotation gearbox  30 , mesh with the corresponding member of the triple accessory gear  178  such as to each drive an accessory.  
         [0032]     The accessory drive of the opposite rotation gearbox  130  thus differs from that of the standard rotation gearbox  30  in that the accessory pinion  74  and idler gear  76  are not present, and that the hub of the triple accessory gear  178  is adapted for receiving a spline instead of a bearing. However, the location, size and rotational speed of the triple accessory gears  78 ,  178  and accessory drive gears  82   a ,  82   b , and  82   c  is the same for both gearboxes  30 ,  130 .  
         [0033]     There is no need for an idler for the right rotational direction, in case of the gearbox  130 , but driving accessories directly from the first stage gear  146  would make accessory gears excessively large (transmission ratios range between 1 and 2.5) and is therefore not preferred. Selection of the pinion  144  or the idler gear  145  for the same purpose also offers few benefits compared to the scheme of the present invention. In the present invention, the triple accessory gear  78 ,  178  is driven by the pinion  44  in the case of the standard rotation gearbox  30 , and by the first stage gear  146  in the case of the opposite rotation gearbox  130 . However, in both cases the triple accessory gear  78 ,  178  is preferably at the same location and is driven in the same direction and speed. The accessory drive gears  82   a ,  82   b  and  82   c  in both gearboxes  30 ,  130  can thus be identical and at the same location. This allows for the configuration of the accessory drive elements of the two gearboxes  30 ,  130  to be the same, and for the accessory drive covers  36  and portions of the gearbox housings  32 ,  132  supporting the accessory drives to be identical.  
         [0034]     The two gearboxes  30 ,  130  can thus be provided with components having a high degree of commonality, with the exceptions being the first stage gears and the input components of the accessory drive. The support and gearbox housings may also be slightly different, but the similarity is sufficiently close that both housings can be machined from the same casting, which represents savings in fabrication. The present design thus allows for the construction of either a standard rotation gearbox or an opposite rotation gearbox with few unique components, thus reducing the costs of manufacturing and inventory.  
         [0035]     The embodiments of the invention described above are intended to be exemplary. Those skilled in the art will therefore appreciate that the foregoing description is illustrative only, and that various alternatives and modifications can be devised without departing from the spirit of the present invention. For example, the specific design of the first and second stages may be altered without departing from the scope of the teachings contained herein. Casing and accessory design may also be modified. Still other changes will be apparent to the skilled reader. Accordingly, the present invention, as defined by the appended claims, is intended to embrace all such alternatives, modifications and variances.