Patent Publication Number: US-2016238120-A1

Title: Spiral Bevel and Pinion Gear

Description:
FIELD 
     The subject matter disclosed herein relates to a gear assembly and, more particularly, to a two-piece bevel gear assembly for use in a gear box. 
     BACKGROUND 
     Misalignment of the gears within a gear train relative to a shaft, bearings, or other components, may increase wear and stress on the gears and contribute to a reduction in gear durability. For instance, axial misalignment of the gears may cause uneven wear of the gear teeth and eventually necessitate replacement. Therefore, bevel gears require a tooth profile uniquely customized for each application to ensure proper tooth contact between meshing gears. Unique tailoring of the gear tooth profiles will limit the effects of movement, tolerance, and thermal expansion on the gear interface. 
     SUMMARY 
     According to one embodiment of the invention, a gear is provided including a generally conical base having an inner end and an outer end at two different positions along a rotational axis. A plurality of teeth extends from the surface of the base between the inner end and the outer end. Each tooth has a root, a pitch, and a face. The outside diameter of the gear is about 5.1924 inches. The outer cone distance of the gear is about 4.3738 inches. The face width of the gear is about 1.31 inches. 
     According to another embodiment of the invention, a gear is provided including a generally conical base having an inner end and an outer end at two different positions along a rotational axis. A plurality of teeth extends from the surface of the base between the inner end and the outer end. Each tooth has a root, a pitch, and a face. The outside diameter of the gear is about 5.1924 inches. The outer cone distance of the gear is about 4.3738 inches. The face width of the gear is about 1.31 inches. The ratio of the outside diameter to a length parallel to the axis of rotation between the crown and the pitch apex of about 1.47. 
     According to yet another embodiment of the invention, a gear set is provided including a first bevel gear having a first rotational axis and a second bevel gear having a second rotational axis. The second gear can be driven by the first gear or the first gear can be driven by the second gear. The outside diameter of the first gear is about 5.1924 inches. The outside diameter of the second gear is about 7.3363 inches. The outer cone distance of both the first gear and the second gear is about 4.3738 inches and the face width of both the first gear and the second gear is about 1.31 inches. The ratio of the outside diameter to a length parallel to the axis of rotation between the crown and the pitch apex of about 3.08. 
     According to yet another embodiment of the invention, a method is provided for installing a gear set in a gearbox of an aircraft including mounting a first gear on a first shaft. A second gear is mounted in meshing engagement with the first gear to a second shaft driven by the first shaft. The first gear has an outside diameter of about 5.1924 inches and the second gear has an outside diameter of about 7.3363 inches. The first gear and second gear have a ratio of the outside diameter to a length parallel to the axis of rotation between the crown and the pitch apex of about 1.47 and about 3.08, respectively. The first gear and second gear have an outer cone distance of about 4.3738 inches and a face width of about 1.31 inches. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, 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 invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  illustrates a cross-sectional view of an exemplary gearbox with a gear assembly according to an embodiment of the invention; 
         FIG. 2  is a perspective view of the gear assembly of  FIG. 1  according to an embodiment of the invention; 
         FIG. 3  is a cross-sectional view of the gear assembly of  FIG. 1  according to an embodiment of the invention; 
         FIG. 4  is a cross-sectional view of the first gear in the gear assembly of  FIG. 1  according to an embodiment of the invention; 
         FIG. 5  is a cross-sectional view of the second gear in the gear assembly of  FIG. 1  according to an embodiment of the invention; and 
         FIG. 6  is an elevation view of the first gear of  FIG. 4 ; 
         FIG. 7  is an elevation view of the second gear of  FIG. 5 ; 
         FIG. 8  is a planar view of the mated gear set according to an embodiment of the invention; 
         FIG. 9  is a contact pattern check of the gear set according to an embodiment of the invention; and 
         FIG. 10  is an ease-off grid of the normalized tooth profile of the gear set according to an embodiment of the invention. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION 
     Embodiments of a bevel gear assembly disclosed herein include a first gear coupled to a second gear in a gearbox. Further embodiments are directed to the first and second gears separately. 
     Referring to the drawings,  FIG. 1  illustrates an exemplary gearbox  100 . The gearbox  100  may be attached to an engine (e.g., a turbine engine) and includes a gear set  102  as part of a gear train for driving any of a number of accessories such as a fuel pump, generator, hydraulic pump, and deoiler, for example. In one embodiment, the gear set  102  includes a first gear  120  (also referred to as a “pinion”) coupled to a second gear  130 , and the tolerances for gears  120 ,  130  are defined by guidelines established by the American Gear Manufacturers Association (AGMA) for a specific class of gear. The gearbox  100  includes an engine shaft  124  that rotates about a first axis A 1  and is supported by at least one bearing assembly  126 . In one example, the engine shaft  124  may receive rotational power from an engine such as a turbine engine on an aircraft. The engine shaft  124  supports the first gear  120  that is engaged with the second gear  130 . The second gear  130  is supported within the gearbox  100  by a second shaft  134  rotatable about an axis A 2  transverse to the engine shaft  124 . The second shaft  134  is supported by at least one bearing assembly  136 . 
     The first gear  120  and the second gear  130  mesh to provide the desired transmission of power from the engine shaft  124  to the second shaft  134  and finally to the associated accessories. In one embodiment, rotation of the engine shaft  124  in the direction indicated by arrow  128  causes rotation of the second shaft  134  in the direction of arrow  138 . The first gear  120  includes a plurality of teeth  122  that engage a plurality of teeth  132  of the second gear  130 . The number of teeth on each of the first gear  120  and the second gear  130  can be selected to provide a desired speed of the second shaft  134 , responsive to the input of the engine shaft  124 , to drive the accessories. In one embodiment, the first gear  120  has  32  teeth and the second gear  130  includes  47  teeth. In another embodiment, the number of teeth on the first gear  120  and the second gear  130  may vary. Also, variations in part fabrication and assembly can result in some relative movement between the first gear  120  and the second gear  130 . Consequently, such movements and variations are accommodated in the design of the mating interface between the first and second gears  120 ,  130 . 
     Referring now to  FIGS. 2 and 3 , the first gear  120  and the second gear  130  forming gear set  102  are shown in relation to each other without their respective shafts  124 ,  134  ( FIG. 1 ) for clarity. The first gear  120  and second gear  130  are generally conical in shape based on an axis, A 1  and A 2  respectively, that serves as a rotational center. 
     Each gear  120 ,  130  has a small diameter end section and a large diameter end section at two different positions along their rotational axes A 1 , A 2 , respectively. The small diameter end section forms the toe  144  of the teeth and the large diameter end section of a gear forms the heel  146  of the teeth. The teeth  122  of the first gear  120  and the teeth  132  of the second gear  130  each share a common face width  142 . The face width  142  is the length taken along the pitch P of the gear teeth  122 ,  132  of each of the first gear  120  and the second gear  130 . In one embodiment, the face width  142  of both the first gear  120  and the second gear  130  is about 1.31 inches, or about 3.327 centimeters. It shall be understood that while the face width  142  is illustrated as being the same in both the first and second gears  120 ,  130 , each could have a unique width. 
     The pitch apex  140  (also shown in  FIGS. 4 and 5 ) of the gear set  102  is the point where the axis A 1  of the engine shaft  124  ( FIG. 1 ) and the axis A 2  of the second shaft  134  ( FIG. 1 ) intersect. Each of the first gear  120  and the second gear  130  are mounted a distance from the pitch apex  140 . The mounting distance is a function of the required meshing between the teeth of each of the first gear  120  and the second gear  130 . The mounting distance is also a function of the angular relationship between the engine shaft  124  ( FIG. 1 ) and the second shaft  134  ( FIG. 1 ). The engine shaft ( FIG. 1 ) rotates about axis A 1  at an angle  139  relative to the axis A 2  of the second shaft  134  ( FIG. 1 ). In the illustrated example, the angle  139  is about 90 degrees. 
     A cross-sectional view is shown for both the first gear  120  and the second gear  130  in  FIGS. 4 and 5 , respectively. Each of the first gear  120  and the second gear  130  has a length parallel to the axis of rotation between a crown of the gear and the pitch apex  140 . In this example, the first gear  120  includes a length  150  parallel to the axis of rotation A 1  between pitch apex  140  and the crown, and the second gear  130  includes a length  184  parallel to the axis of rotation A 2  between the pitch apex  140  and the crown. In one embodiment, the length  150  is approximately 3.5237 inches, 8.9502 centimeters and the length  184  is approximately 2.384 inches, 6.055 centimeters. The first gear  120  has an outside diameter  148  and the second gear has an outside diameter  180 . In one embodiment, the outside diameter  148  of the first gear  120  is about 5.1924 inches (about 13.1887 centimeters) and the outside diameter  180  of the second gear  130  is about 7.3363 inches (about 18.6342 centimeters). Alternately, each gear may be measured by the ratio of the outside diameter to the length parallel to the axis of rotation between the crown and the pitch apex. In one embodiment, this ratio for the first gear  120  is about 1.47 and for the second gear  130  is about 3.08. Both the first gear  120  and the second gear  130  also have an outer cone distance extending from the crown to the pitch apex  140  parallel to the pitch cone P. In this example, the first gear  120  has an outer cone distance  152  and the second gear  130  has an outer cone distance  182  which are equal and about 4.3738 inches (about 11.1095 centimeters). 
     Gears  120 ,  130  include respective root cones R 1 , R 2  extending along the conical root of a tooth and respective face cones F 1 , F 2  extending along the conical face of a tooth. The root cones R 1 , R 2  and face cones F 1 , F 2  intersect the respective rotational axes A 1 , A 2  of the respective gears  120 ,  130  to form a root angle and a face angle. In one embodiment, the first gear  120  has a root angle  156  of about 32.99 degrees and a face angle  158  of about 36.76 degrees. The second gear  130  has a root angle  188  of about 53.24 degrees and a face angle  190  of about 57.01 degrees. Each gear  120 ,  130  has a respective pitch axis P 1 , P 2  that forms an angle with the respective rotational axes A 1 , A 2  of each respective gear  120 ,  130 . In one embodiment, the pitch angle  154  of the first gear  120  is about 34.25 degrees and the pitch angle  186  of the second gear  130  is about 55.75 degrees. 
     The location where each respective root cone R 1 , R 2  and each respective face cone F 1 , F 2  intersects a respective rotational axis A 1 , A 2  can be measured as a distance from the pitch apex  140 . For the first gear  120 , the crossing point of the root cone RI is a distance  162  from pitch apex  140  and the crossing point of the face cone F 1  is a distance  160  from pitch apex  140 . Distance  196  is the distance between the pitch apex  140  and the crossing point of the root cone R 2  and length  194  is the distance between pitch apex  140  and the crossing point of the face cone F 2  of the second gear  130 . In one embodiment, distance  162 , where the root cone R 1  crosses axis A 1 , is about 0.0492 inches (about 0.1250 centimeters) before the pitch apex  140  and distance  160 , where the face cone F 1  crosses axis A 1 , is about 0.0481 inches (about 0.1222 centimeters) before the pitch apex  140 . Similarly, the distance  196 , where root cone R 2  crosses rotational axis A 2 , is about 0.0001 inches (about 0.0002 centimeters) before the pitch apex  140  and the distance  194 , where the face cone F 2  crosses axis A 2 , is about 0.0025 inches (about 0.0064 centimeters) past the pitch apex  140 . In this example, the pitch axes P 1 , P 2  for both the first and second gear  120 ,  130  cross the respective rotational axes A 1  and A 2  through the pitch apex  140 . 
       FIGS. 6 and 7  depict elevation views of the first gear  120  and the second gear  130 . In one embodiment, the first gear  120  and the second gear  130  are bevel gears having complementary spiral teeth. As such, the teeth  122  of the first gear  120  may have a left-handed spiral and the teeth  132  of the second gear  130  may have a right-handed spiral. A spiral angle is the angle of a gear tooth relative to the pitch cone and is selected to provide a desired length of contact balanced with the thrust load generated by the torque on each gear. The spiral angle may be measured at various points along the face of the tooth. For example, the outer spiral angle, θ O , is measured at the outer cone distance, the inner spiral angle, θ I , is measured at the inner cone distance, and the mean spiral angle, θ M , is measured at the mean cone distance. For the teeth of the first gear  120  and the second gear  130  to mate properly, the spiral angle is common to both the first gear  120  and the second gear  130 . In one embodiment, the inner spiral angle θ I  is about 18.59 degrees, the outer spiral angle, θ O  is about 36.48 degrees and the mean spiral angle, θ m , is about 27.5 degrees. 
     Referring now to  FIG. 8 , the whole depth  198  of a gear tooth is the distance from the root of the tooth to the face of the tooth. The whole depth  198  is equal to the sum of the length of the addendum AD and the length of the dedendum DD. In one embodiment, the first gear  120  and the second gear  130  have a whole depth of about 0.2856 inches (about 0.7254 centimeters). The dedendum DD of a gear is the radial distance from the root of a tooth to the pitch cone P as measured at the heel. The addendum AD is the radial distance from the pitch cone P to the face cone F of a tooth as measured at the heel. In one example, the first gear  120  has a dedendum DD 1  of about 0.1227 inches (about 0.3117 centimeters) and an addendum AD 1  of about of 0.1629 inches (about 0.4138 centimeters) and the second gear  130  has a dedendum DD 2  of about 0.1918 inches (about 0.4872 centimeters) and an addendum of about 0.0938 inches (about 0.2383 centimeters). The clearance  200  of a gear is the distance between the root of a first gear  120  and the face of the second gear  130  when mated. In one embodiment, the first gear  120  and the second gear  130  have a clearance of about 0.0289 inches (about 0.0734 centimeters). The working depth  202  of a gear is the difference between the whole depth  198  of a gear and the clearance  200 . Therefore, the working depth  202  of the first and second gear  120 ,  130  is about 0.2567 inches (about 0.6520 centimeters). The dedendum angle is the angle formed between the pitch cone P and the root cone R of a gear. In one embodiment, the dedendum angle  301  of the first gear  120  is about 1.26 degrees and the dedendum angle  192  of the second gear  130  is about 2.51 degrees. 
     Each tooth includes a topland  210 , a convex tooth flank  212  and a concave tooth flank  214 . Root cone  216  is continuously formed at the tooth root between the convex and concave flanks  212 ,  214  of adjacent teeth. In general, the topland  210  connects to the convex and concave tooth flanks  212 ,  214  by a tooth crest arc  218  and the concave and convex tooth flanks  212 ,  214  connect to the root cone  216  by a tooth root arc  220 . The width of the topland  210  may vary along the length of the tooth. The width of the topland is measured at the toe, the heel, and halfway between the toe and the heel. In one embodiment, the first gear  120  has an inner topland, measured at the toe, of about 0.0796 inches (about 0.2022 centimeters), an outer topland, measured at the heel, of about 0.0736 inches (about 0.1869 centimeters) and a mean topland of 0.0756 inches (about 0.1920 centimeters). Similarly, the second gear  130  may have an inner topland, measured at the toe, of about 0.0841 inches (about 0.2136 centimeters), and an outer topland, measured at the heel, of about 0.0810 inches (about 0.2057 centimeters), and a mean topland of 0.0875 inches (approximately 0.2223 centimeters). The mean circular thickness  222  of a tooth is the average width of a tooth measured along the arc of the pitch circle. In one embodiment, the mean circular thickness  222  of the first gear  120  is approximately 0.2208 inches (approximately 0.5608 centimeters) and the second gear  130  is approximately 0.1741 inches (approximately 0.4422 centimeters). 
       FIG. 9  illustrates a contact pattern check of the gear set  102  and the maximum amount that the first gear  120  may be moved relative to the second gear  130  to maintain sufficient contact for clean visual inspection. These maximum tolerances regarding the positioning of the first gear  120  relative to the second gear  130  are listed in Table 1. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 IN * 1000 
                 MEAN 
                 TOE 
                 HEEL 
                 TOTAL 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 CX E(V) 
                 0 
                 10 
                 −42 
                 52 
               
               
                   
                 CX P(H) 
                 10 
                 11 
                 28 
                 17 
               
               
                   
                 CV E(V) 
                 0 
                 −13 
                 66 
                 79 
               
               
                   
                 CV P(H) 
                 −10 
                 −13 
                 −36 
                 23 
               
               
                   
                   
               
            
           
         
       
     
     In one embodiment, when the first gear  120  is shifted about 0.010 inches (about 0.025 centimeters) along axis E (see  FIG. 2 ) relative to the second gear, the first gear  120  contacts the convex flank  212  of the second gear  130  near the toe  144  of the second gear  130 . Similarly, if the first gear  120  is shifted about −0.042 inches (about −0.1067 centimeters) along axis E and about 0.028 inches (about 0.0711 centimeters) along axis A 1 , the first gear  120  will contact the convex flank  212  of the second gear  130  near the heel  146  of the second gear  130 . Shifting the first gear  120  about −0.013 inches (about −0.0330 centimeters) along the E axis and about −0.013 inches (about 0.0330 centimeters) along the A 1  axis will cause the first gear  120  to contact the concave flank  214  of the second gear  130  near the toe  144  of the second gear  130 . If the first gear  120  is shifted about 0.066 inches (about 0.0838 centimeters) along axis E, the first gear  120  will contact the concave flank  214  of the second gear  130  near the heel  146  of the second gear  130 . If the first gear  120  is shifted about 0.066 inches (about 0.0838 centimeters) along axis E, and about −0.036 inches (about −0.0914 cm) along axis A 1 , the first gear  120  will contact the concave flank  214  of the second gear  130  near the heel  146  of the second gear  130 . Various other translations are further indicated in Table 1. 
     Referring now to  FIG. 10 , an ease-off grid illustrates the normalized tooth profile of a first gear  120  overlapped with the normalized tooth profile of a second gear  130 . A profile modification is added to each contact corner to create a smooth overlapping surface. In an exemplary embodiment, the profile modifications for the concave flank (generally shown at  212 ) include about 0.0024 inches (about 0.0061 centimeters) at the top of the toe  144 , about 0.0054 inches (about 0.0137 centimeters) at the root of the toe  144 , about 0.0080 inches (about 0.02032 centimeters) at the top of the heel  146 , and about 0.0077 inches (about 0.01956 centimeters) at the root of the heel  146 . The profile modifications for the convex flank (generally shown at  214 ) may be about 0.0060 inches (about 0.0152 centimeters) at the top of the toe  144 , about 0.0015 inches (about 0.0387 centimeters) at the root of the toe  144 , about 0.0086 inches (about 0.0983 centimeters) at the top of the heel  146 , and about 0.0056 inches (about 0.0142 centimeters) at the root of the heel  146 . The profile modification at each corner may be split between the first gear and the second gear. For example, the first gear may be modified the total profile modification amount, the second gear may be modified the total profile modification amount, or the first gear and the second gear may each be modified an amount totaling the profile modification amount at that corner. 
     The above description details particular dimensions of gears in a set according to one embodiment. One or ordinary skill will realize that additional dimensions could be specified and the values of those could be modified without departing from the present invention. Examples of additional dimensions of the first gear  120  and the second gear  130  and their approximate values may be found in included Table 2. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 First Gear 
                 Second Gear 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Pitch Diameter 
                 4.9231″ 
                 7.2308″ 
               
               
                 Outer Slot Width 
                 0.0736″ 
                 0.0750″ 
               
               
                 Mean Slot Width 
                 0.0736″ 
                 0.0750″ 
               
               
                 Inner Slot Width 
                 0.0736″ 
                 0.0750″ 
               
               
                 Pitch Apex to Crown 
                 3.524″ 
                 2.38″ 
               
               
                 Edge Radius 
                 0.0250″ 
                 0.0350″ 
               
               
                 Maximum Allowable Edge Radius 
                 0.0250″ 
                 0.0350″ 
               
               
                 Maximum Edge Radius Geometry 
                 0.0479″ 
                 0.0479″ 
               
               
                 Maximum Edge Radius Mutilation 
                 0.0784″ 
                 0.0810″ 
               
               
                 Maximum Edge Radius Interference 
                 0.0259″ 
                 0.0397″ 
               
               
                 Crown to Crossing Point 
                 3.5237″ 
                 2.3840″ 
               
               
                   
               
            
           
         
       
     
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention 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 invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.