Abstract:
Gears are known to have a whine that can be unpleasant to operators or occupants of vehicles. A gear set is disclosed in which the pressure angle of the teeth varies along the periphery of the gear. A mating gear also has teeth with varying pressure angle. The teeth that mate have an identical pressure angle so that present disclosure is applicable only to 1:1 or integer ratio gears: 2:1, 3:1, etc. Because the teeth meet differently as a function of the pressure angle, the fundamental vibration frequency is not reinforced as would be the case with all teeth having the same pressure angle.

Description:
FIELD 
       [0001]    The present disclosure relates to gear pairs that have varying pressure angle among teeth on a single gear. 
       BACKGROUND 
       [0002]    Gear noise is a common issue for which solutions have been sought for decades. Rattle is prevalent when meshing teeth impact each other due to separation between the teeth. Rattle can be reduces by minimizing teeth backlash. In operation, the contact forces lead to vibrations in the gear pair due to the frequencies of teeth meshing. When tooth backlash is minimized, whine increases. A fundamental frequency develops and reinforced by each tooth engagement during rotation of the mating gears. One solution is to use a scissor-type gear, in which one of the gear pair has two gears with the same number of teeth, but with the teeth offset from each other slightly by spring loading. The backlash is taken up by the teeth of the spring-loaded gears. However, this doesn&#39;t address the whine issue. Furthermore, such a solution introduces complications and additional parts. An inexpensive solution to address gear whine, particularly for applications, such as automotive, where the noise is perceived by a nearby individual is desired. 
       SUMMARY 
       [0003]    A crankshaft that reduces the fundamental frequency of vibration by introducing other frequencies presents an improvement over the prior art. One disclosed embodiment has a gear set with a first gear having a first portion of teeth having a first pressure angle and a second portion of teeth having a second pressure angle; and a second gear having a first portion of teeth having the first pressure angle and a second portion of teeth having the second pressure angle. The first portion of first gear teeth mesh with the first portion of second gear teeth. The second portion of first gear teeth mesh with the second portion of second gear teeth. 
         [0004]    Some embodiments further include a third portion of teeth on the first gear having a third pressure angle and a third portion of teeth on the second gear having the third pressure angle. 
         [0005]    In some cases, total number of teeth on the first gear equals total number of teeth on the second gear; a number of teeth in the first portion of teeth of the first gear is one greater than number of teeth in the first portion of the second gear; and the second gear has a transition tooth in which the pressure angle on a first side of the tooth is the first pressure angle and the pressure angle on a second side of the tooth is the second pressure angle. In other embodiments, total number of teeth on the first gear divided by total number of teeth on the second gear yields a quotient of one of: two, three, four, five, one-half, one-third, one-quarter, and one-fifth; number of teeth in the first portion of the first gear equals the quotient times the number of teeth of the second gear; when the quotient is greater than one, the first portion of teeth on the first gear is separated into evenly-spaced regions with the number of regions equal to the quotient; and when the quotient is less than one, the first portion of teeth on the second gear is separated into evenly-spaced regions with the number of regions equal to the reciprocal of the quotient. When the quotient is greater than one, the first portion of teeth on the second gear are mutually adjacent; and when the quotient is less than one, the first portion of teeth on the first gear are mutually adjacent. 
         [0006]    In some embodiments, the first portion of teeth of the first gear are arranged randomly on the periphery of the first gear; and the first portion of teeth of the second gear are arranged so that the first portion of teeth of the second gear mesh with the first portion of the teeth of the first gear when the gears are rotated. 
         [0007]    And in other embodiments, the first portion of teeth of the first gear are evenly arranged on the periphery of the first gear; the second portion of teeth of the first gear are evenly arranged on the periphery of the first gear; the first portion of teeth of the second gear are arranged so that the first portion of teeth of the second gear mesh with the first portion of the teeth of the first gear when the gears are rotated; and the second portion of teeth of the second gear are arranged so that the second portion of teeth of the second gear mesh with the second portion of the teeth of the first gear when the gears are rotated. 
         [0008]    A first shaft, a second shaft arranged in parallel with the first shaft, a first index on the first gear, and a second index on the second gear may also be included. The first gear is mounted on the first shaft. The second gear is mounted on the second shaft. The first and second index are lined up when the driving and second gears are enmeshed. 
         [0009]    Also disclosed in a gear set having a first gear in which teeth in a first sector have a first pressure angle and teeth in a second sector have a second pressure angle and a second gear in which teeth in a third sector have the first pressure angle and teeth in a fourth sector have the second pressure angle wherein the first and second gears are enmeshed. The first pressure angle does not equal the second pressure angle. 
         [0010]    In some embodiments, the first gear further includes a fifth sector in which the teeth have a third pressure angle and the second gear further includes a sixth sector in which the teeth have the third pressure angle. 
         [0011]    The teeth of the first gear and the second gear that sit on an overlap between the two sectors are transition teeth in which the pressure angle on one side of the tooth differs from the pressure angle on the other side of the tooth. 
         [0012]    The number of whole teeth in the first sector of the first gear is within one of the number of whole teeth in the third sector of the second gear. 
         [0013]    In some cases, the second gear is twice the diameter of the first gear. The second gear further comprises a fifth sector in which the teeth have the first pressure angle. The second gear further comprises a sixth sector in which the teeth have the second pressure angle. The fifth sector is located between the third and fourth sectors. When the gears rotate, the teeth of the first sector mesh with the teeth of the third and fifth sectors. The teeth of the second sector mesh with the teeth of the fourth and sixth sectors. 
         [0014]    The gear set may further include: a first shaft and a second shaft arranged in parallel with the first shaft. The first shaft is inserted into a centrally-defined opening on the first gear. The second shaft is inserted into a centrally-defined opening on the second gear. 
         [0015]    The first shaft, the second shaft, the centrally-defined opening on the first gear, and the centrally-defined opening on the second gear each have a keyway, in some embodiments. A first key is inserted into the keyways of the first shaft and the keyway on the first gear; and a second key is inserted into the keyways of the second shaft the keyway on the second gear. 
         [0016]    Also disclosed is a method to manufacture a gear set that includes machining a first gear having a first plurality of gear teeth having a first pressure angle and a second plurality of gear teeth having a second pressure angle and machining a second gear having a first plurality of gear teeth having the first pressure angle, a second plurality of gear teeth having the second pressure angle, and at least one transition tooth with the first pressure angle on one side and the second pressure angle on the second side. 
         [0017]    The method may also include machining a third plurality of teeth on the first gear with a third pressure angle, machining a third plurality of teeth on the second gear with a third pressure angle, and machining a transition tooth on one of the first and second gears where ever a change in pressure angle occurs. A transition tooth is one that has one pressure angle on one side of the tooth and another pressure angle on the other side of the tooth. 
         [0018]    The first plurality of gear teeth in the first gear engage with the first plurality of gear teeth in the second gear when the gears rotate; and the second plurality of gear teeth in the second gear engage with the second plurality of gear teeth in the second gear when the gears rotate. 
         [0019]    By providing a varying pressure angle around the periphery of the gear, the fundamental frequency changes and thus is not reinforced by all of the gear teeth. The total sound level may be similar to a gear set in which all the teeth have the same pressure angle, but having the frequencies spread out makes the noise less annoying to humans. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows two separated gears; 
           [0021]      FIG. 2  shows a detail of a single tooth of a gear defining parameters relevant to the present disclosure; 
           [0022]      FIG. 3  shows two gears with enmeshed teeth; 
           [0023]      FIGS. 4-6  show single gears with teeth having varying pressure angles; and 
           [0024]      FIG. 7  is a process by which gears can be fabricated. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0026]    A pair of gears  10  and  30  are shown in  FIG. 1 . Driving gear  10  and driven gear  30  are shown separated. Driving gear  10  is mounted on a shaft  12 , shown in cross section, using a key  14  wedged into a keyway in gear  10  and a keyway in shaft  12 . Gear  10 , by way of non-limiting example, has 24 teeth. In a first sector  22  of gear  10 , the teeth have a first pressure angle. In a second sector  24  of gear  10 , the teeth have a second pressure angle, the second pressure angle being different than the first pressure angle. In a third sector  24  of gear  10 , the teeth have a third pressure angle. The example in  FIG. 1  shows eight teeth in each of the first, second, and third sectors,  20 ,  22 , and  24 , respectively, i.e., sectors  20 ,  22 , and  24  are identical in size. Alternatively, the sectors are non-uniform in size. In another alternative, a different number of sectors is used: 2, 4, 5, as examples. Particularly when the number of teeth is not divisible by the number of sectors must the sectors be of unequal size. 
         [0027]    Also shown is a driven gear  30  which also has 24 teeth. Gear  30  is mounted on a shaft  30  and prevented from slipping with respect to shaft  32  by a key  34  . When the two gears are engaged and rotating, they provide a 1:1 ratio. Meshing teeth are to be of the same pressure angle. Thus, gear  30  is provided with three sectors  40 ,  42 , and  44 , which have first, second, and third pressure angles, respectively. When gear  10  rotates counterclockwise and is enmeshed with gear  30 , gear  30  rotates clockwise. 
         [0028]    The teeth in gears  10  and  30  in  FIG. 1  have varying pressure angle. However, such detail is not visible. In  FIG. 2 , a detail of a gear tooth  200  is shown that has a pitch circle  202 . Tooth  200  has a first side  210  and a second side  220 . Lines  212  and  222  are radii of the gear (not shown) associated with tooth  200 . Lines  216  and  226  are tangents of pitch circle  202  at their respective pitch points. (The pitch point is on the surface of first side  210  where lines  214 ,  216 , and pitch circle  202  intersect. The other pitch point is on the surface of second side  220  where lines  224 ,  226 , and pitch circle  202  intersect.) Line  214  is perpendicular to the tangent (not shown for clarity purposes) of side  210  that travels through its associated pitch point. Similarly,  224  is perpendicular to the tangent (also not shown) of side  220  that travels through its associated pitch point. The pressure angle for side  210  is defined by angle  218  and the pressure angle for side  220  is defined by angle  228 . The pressure angles on the two sides of the teeth may differ. Typical pressure angles in gears are in a non-limiting range of 15-25 degrees. 
         [0029]    During rotation, each gear tooth contacts two teeth from the mating gear. Referring back to  FIG. 1 , all eight teeth in sector  20  have the same pressure angle on each side of the teeth. However, a tooth  46  on gear  30  is a transition tooth with half of the tooth in sector  40  and half of the tooth being in sector  42 . Tooth  46  has the pressure angle associated with the sector in which it is located, i.e., the half in sector  40  has a first pressure angle and the half in sector  42  has a second pressure angle. Tooth  46  is a transition tooth that makes the transition from meshing sectors  20  with  40  to meshing sectors  22  with  42  proceed smoothly. For every change in pressure angle around the periphery of one gear, one tooth on a mating pair of gears has a transition tooth, which is defined herein as having one pressure angle on one side of the tooth and a different pressure angle on the other side of the tooth. 
         [0030]    The present disclosure can be applied to other than 1:1 ratio gears. In  FIG. 3 , a first gear  10 , has three sectors  20 ,  22 , and  24  that have first, second, and third pressure angles, respectively. A second gear  50  that has teeth enmeshed with teeth of first gear  10  has double the number of teeth as first gear  10 , that is,  48  teeth. Gear  50  is mounted on shaft  52  by a key  54  that engages with keyways formed in both shaft  52  and gear  50 . When gear  10  rotates counterclockwise twice, gear  50  rotates once. In such a period, the teeth in sector  20  of gear  10  enmesh twice with teeth on gear  50 . Thus, gear  50  has two sectors,  60 , which are diametrically opposed and have the first pressure angle. Teeth of two diametrically-opposed sectors  62  are formed with the second pressure angle. Teeth of two diametrically-opposed sectors  64  are formed with the third pressure angle. As described above, in other embodiments, sectors  20 ,  22 , and  24  of gear  10  need not all be identical in size. However, the number of teeth in sector  20  is the same as the number of teeth in both of sectors  60 . Teeth numbers in sectors  22  and  62  are identical. And, a similar correspondence occurs in sectors  24  and  64 . 
         [0031]    The present disclosure can be applied to any pair of driving/driven gears in which the ratio involves integers: 1:2; 3:1, 1:4, as examples. The teeth that mesh should be of the same pressure angle. For this to happen, there is a transition tooth between sections of different pressure angles on one of the two meshing gears. Gears in which different teeth mesh during each revolution, do not benefit from the present disclosure. 
         [0032]    A 12-toothed gear  70  is shown in  FIG. 4  in which the pressure angle is changed for each tooth. Teeth  80 ,  80 ′,  80 ″, and  80 ′″ have a first pressure angle. Teeth  82 ,  82 ′,  82 ″ and  82 ′″ have a second pressure angle. Teeth  84 ,  84 ′,  84 ″, and  84 ′″ have a third pressure angle. All teeth of a gear that meshes with gear  70  are transition teeth: a tooth having the first pressure angle on one side and the second pressure angle on the other side followed by a tooth having the second pressure angle on one side and the third pressure angle on the other side followed by a tooth having the third pressure angle on the one side and the first pressure angle on the other side, in succession. Other regular patterns may alternatively be employed as well as different numbers of teeth. In other alternatives, two pressure angles are used in a regular pattern, or more than three, as is shown in the example in  FIG. 4 . 
         [0033]    Gear  70  in  FIG. 4  is not shown mounted on a shaft and the opening  72  to accommodate a shaft as well as a keyway  74  formed in the gear to accept a key are shown. 
         [0034]    Shown in  FIG. 5  is a 12-toothed gear  90  having teeth of three pressure angles, but the arrangement is random. Teeth  100 ,  100 ′,  100 ″, and  100 ′″ all have the same pressure angle. It turns out that  100  and  100 ′ are adjacent to each other simply due to the random nature. 
         [0035]    In  FIG. 6 , a 12-toothed gear is shown having four sectors:  120 ,  122 ,  124 , and  126 , each having a pressure angle assigned to the teeth within its sector. A gear that Transition teeth  130 ,  132 ,  134 , and  136  (not shown in Figure) have two pressure angles, e.g., a side  150  of tooth  130  and a side  142  of tooth  132  have the pressure angle associated with sector  120 . Analogously, sides  152  and  144  have the pressure angle associated with sector  122 ; sides  154  and  146  have the pressure angle associated with sector  124 ; sides  156  and  140  have the pressure angle associated with sector  126 . A gear that mates with gear  110 , if it were a 1:1 ratio, would also have 12 teeth, three each have pressure angles associated with sectors  120 ,  122 ,  124 , and  126  on both sides of the teeth. Sectors  120  and  124  may have the same pressure angle that is different than  124  and  126 . 
         [0036]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.