Abstract:
A hybrid spiroid and worm gear is formed as a gear body having an axis of rotation. The gear body has a plurality of spiroid gear teeth formed in opposing surfaces of the body formed generally radially relative to the axis of rotation. The gear body further has a plurality of worm gear teeth formed in a hub portion, between, separate and apart from the spiroid teeth. The worm gear teeth are formed generally longitudinally relative to the axis of rotation. A method for making the hybrid spiroid and worm gear is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION DATA 
       [0001]    This application claims the benefit of priority of Provisional U.S. Patent Application Ser. No. 61/158,801, filed Mar. 10, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an enveloping gear arrangement and more particularly, to an enveloping gear arrangement that uses a spiroid and worm gear arrangement. 
         [0003]    Gears are one of the fundamental mechanical machines and have been in use for centuries. Gears are used to, among other things, transmit power from one device to another and change the direction of force. 
         [0004]    Many types of gears are known—straight gears, angle gears, bevel gears, worm gears, combinations of these and others. Also known are SPIROID® brand gears that use a curved gear tooth. Such a configuration permits larger loads to be transferred due to the increased surface area of gear tooth relative to a straight gear formed on a similar blank. 
         [0005]    Certain applications require gears that must withstand high loads (forces). Generally, the ability to withstand such forces is accomplished by using larger gears to increase the area on the gear teeth over which the forces are exerted. The ability to withstand forces must be balanced against the size requirements, or conversely the size limitations, of the gear assembly. While the spiroid gear accomplishes this, at times, even smaller size requirements must be met. One such gear tooth form is disclosed in Saari, U.S. Pat. No. 3,631,736, commonly assigned with the present application and incorporated herein by reference. 
         [0006]    Accordingly, there is a need for a gear system that can withstand high loads/forces in a limited or small size application. Desirably, such a gear can be formed from non-metallic, e.g., polymeric materials. 
       SUMMARY OF THE INVENTION 
       [0007]    A hybrid spiroid and worm gear is formed as a gear body having an axis of rotation. The gear body has a plurality of spiroid gear teeth formed in a surface of the body, formed generally radially relative to the axis of rotation and a plurality of worm gear teeth formed in the body separate and apart from the spiroid teeth. The worm gear teeth are formed generally longitudinally relative to the axis of rotation of the gear. 
         [0008]    It has been found that the present hybrid spiroid and worm gear provides a significant increase in torque capability for gearing without increasing the size of the gears. 
         [0009]    In a preferred embodiment, the gear body is formed having a pair of substantially opposing surfaces in which the spiroid gear teeth are formed a central hub, with the worm gear teeth formed between the opposing surfaces in the hub. The gear can be formed with a gap between the spiroid gear teeth and the worm gear teeth. 
         [0010]    A present gear body is formed as two parts joined to one another at the hub. The two parts can be substantially identical to one another. The parts can be joined by press-fitting, welding, adhesive, fasteners or the like. 
         [0011]    The worm gear teeth can be formed having a profile that is different from or the same as the profile of the spiroid gear teeth, where the profile is defined by a height and/or a pitch of the gear teeth. 
         [0012]    A preferred gear is formed from a polymeric material, such as acetal material or the like. 
         [0013]    The hybrid spiroid and worm gear is configured to mesh with a pinion disposed at an angle that is other than normal to an axis of the gear body. The pinion can be formed with first and third spaced apart thread forms configured to mesh with the opposing surface spiroid gear teeth and an intermediately disposed, second thread form configured to mesh with the gear worm teeth. The pinion first and third thread forms are preferably identical. The second thread form can be different from or identical to the first and third thread forms. The first, second and third thread forms can also be formed as a continuous thread form in the pinion. 
         [0014]    One method for making the hybrid spiroid and worm gear is to form the first gear body part, form the second gear body part and join the first and second gear body parts to form the hybrid spiroid and worm gear. The first and second body parts can be formed identical to one another. 
         [0015]    These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE PHOTOGRAPHS 
         [0016]    The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein: 
           [0017]      FIG. 1  is a top perspective view of a hybrid enveloping spiroid and worm gear (shown without the complementary pinion) embodying the principles of the present invention; 
           [0018]      FIG. 2  is an enlarged view similar to  FIG. 1 ; 
           [0019]      FIG. 3  is a top view into the center of the gear assembly, looking at the central worm gear; 
           [0020]      FIG. 3A  is an enlarged view of a tooth on the worm gear; 
           [0021]      FIG. 4  is a view similar to  FIG. 3  and also illustrating one pinion that can be used with the hybrid spiroid and worm gear; 
           [0022]      FIG. 5  is a view of the pinion in place in the hybrid spiroid and worm gear, the pinion being skewed relative to the hybrid spiroid and worm gear axis; 
           [0023]      FIG. 6  is an enlarged view of the pinion and hybrid spiroid and worm gear of (and as seen from an angle rotated about 90 degrees relative to)  FIG. 5 ; 
           [0024]      FIGS. 7A ,  7 B and  7 C are sectional views taken along lines  7 A- 7 A,  7 B- 7 B, and  7 C- 7 C, respectively, in  FIG. 6 ; 
           [0025]      FIG. 8  is a view looking substantially along the pinion as it resides in the hybrid spiroid and worm gear; and 
           [0026]      FIG. 9  is an illustration of a testing apparatus used to obtain torque data for the hybrid spiroid and worm gear and pinion assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated. 
         [0028]    It should be understood that the title of this section of this specification, namely, “Detailed Description Of The Invention”, relates to a requirement of the United States Patent Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein. 
         [0029]    Referring now to the figures and in particular to  FIG. 1 , there is illustrated a hybrid enveloping spiroid and worm gear (the gear assembly  10 ) embodying the principles of the present invention. The gear assembly  10  is a double gear  11  in which two facing (opposing) surfaces  12 ,  14  have gear teeth  16 ,  18  formed therein. The assembly  10  includes a central hub region  20  that interconnects the opposing gears surfaces  12 ,  14 . 
         [0030]    The opposing gear surfaces  12 ,  14  have teeth  16 ,  18  that extend from the periphery  22 , partially downward toward the central hub region  20 . In a present hybrid spiroid and worm gear  10 , the opposing surfaces  12 ,  14  are formed with a spiroid gear form  24  and the central hub portion  20  is formed with a worm gear form  26 . A gap  27  is defined between the spiroid  24  and worm  26  gear forms. The spiroid gear form  24  has a curved tooth profile as indicated at  28 . In the illustrated embodiment, the worm gear  26  has lower gear tooth profile. It will, however, be appreciated that the worm gear  26  tooth profile can be the same as the spiroid  24  profile insofar as the pitch, tooth height and like tooth characteristics. 
         [0031]    Referring to  FIG. 3 , the assembly  10  is formed as a pair of elements  30 ,  32 , each element having the spiroid face gear face or profile  24  and one-half  26   a,b  of the worm gear  26  profile. The two elements  30 ,  32 , which are defined by a parting line  40  in the gear assembly  10 , are then joined to one another (e.g., by press-fitting, welding, adhesive, fasteners or the like) to form the double gear element  11 . In a present element  11 , the two half-gear elements  30 ,  32  each include one-half of the worm gear  26  so that a single gear profile (and, for example, a single gear mold) can be used for each element or half  30 ,  32 . 
         [0032]    The illustrated gear system (the gear assembly  10  and a pinion  34 ) has a pinion  34  that has two different and separate tooth profiles  36 ,  38 . Two outer pinion (worm) tooth profiles  36  are designed to engage the larger opposing spiroid gear profiles  24 , while the inner pinion (worm) tooth profile  38  is designed to engage the central worm gear tooth profile  26 . It will, however, be appreciated that the pinion  34  can be configured with a single tooth (worm pinion) profile and can also be formed having a continuous tooth profile along the length of the pinion. Alternately, the pinion can be formed tapering (with a decreasing diameter) toward the center of the pinion from the ends, as indicated at P in  FIG. 4 . The illustrated pinion is formed from metal, but, of course can be formed from other suitable materials. 
         [0033]    As seen in  FIGS. 4-8 , the present enveloping spiroid and worm gear assembly  10  uses a pinion  34  that has an axis A 34  that is skewed (at skew angle α) relative to the axis A 10  of the gear assembly  10 . In this manner, a first portion  36   a  of the pinion  34  rests again one of the spiroid gear faces  24   a  while a second (or other) portion  36   b  of the pinion  34  rests against the other spiroid gear face  24   b . And, the central portion  38  of the pinion  34  engages the central worm gear formation  26 . 
         [0034]    Tests were conducted to compare the torque capability of the hybrid gear to that of a double spiroid gear (without the central worm gear) and a worm gear. This was conducted by measuring the maximum torque at failure which was determined to be when the gear teeth fail under applied torque. 
         [0035]    Testing was carried out using an ITW Intron device T as illustrated, in part, in  FIG. 9 . The test gear  10  was held in a fixed position and an input torque was applied to rotate the pinion  34 . The pinion shaft was linked to the center of a 5 inch diameter disk D. The input torque on the pinion was provided by a steel cord, and was determined to be equal to the force exerted on the disk by the cord C engaging the periphery P of the disk D and rotating the disk D, multiplied by the radius of disk r D , which is 2.5 inches. 
         [0036]    The force was increased slowly until the gear teeth failed. 
         [0037]    Three sets of test were conducted. The first set of tests was carried out on three worm gear samples. The calculated results of the test are shown in Table 1, below, which show the maximum load indicated for the worm gear. 
         [0038]    The second set of tests was carried out on six double spiroid gear samples. The calculated results of the test are shown in Table 2, below, which show the maximum load indicated for the double spiroid gears. 
         [0039]    The third set of tests was carried out on six hybrid enveloping spiroid and worm gear samples. The calculated results of the test are shown in Table 3, below, which show the maximum load indicated for the hybrid spiroid and worm gear. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 MAXIMUM TESTED LOAD FOR WORM GEAR 
               
             
          
           
               
                   
                   
                 Load at 
                   
                   
               
               
                   
                 Maximum 
                 Break 
                 Energy at Break 
                 Load at Preset Point 
               
               
                 Sample 
                 Load 
                 (Standard) 
                 (Standard) 
                 (Tensile extension 
               
               
                 No. 
                 (lbf) 
                 (lbf) 
                 (ft-lbf) 
                 0.5 in) (lbf) 
               
               
                   
               
               
                 1 
                 15.31 
                 9.13 
                 4.57 
                 3.84 
               
               
                 2 
                 14.15 
                 9.21 
                 3.29 
                 4.11 
               
               
                 3 
                 14.45 
                 9.54 
                 3.46 
                 3.61 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 MAXIMUM TESTED LOAD FOR DOUBLE SPIROID GEAR 
               
             
          
           
               
                   
                   
                 Load at 
                   
                   
               
               
                   
                 Maximum 
                 Break 
                 Energy at Break 
                 Load at Preset Point 
               
               
                 Sample 
                 Load 
                 (Standard) 
                 (Standard) 
                 (Tensile extension 
               
               
                 No. 
                 (lbf) 
                 (lbf) 
                 (ft-lbf) 
                 0.5 in) (lbf) 
               
               
                   
               
               
                 1 
                 70.06 
                 62.25 
                 22.75 
                 5.82 
               
               
                 2 
                 76.09 
                 65.24 
                 24.11 
                 3.88 
               
               
                 3 
                 75.21 
                 66.20 
                 24.14 
                 4.44 
               
               
                 4 
                 76.14 
                 66.75 
                 24.01 
                 7.27 
               
               
                 5 
                 72.66 
                 60.23 
                 22.90 
                 6.26 
               
               
                 6 
                 72.06 
                 62.10 
                 22.62 
                 9.36 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 MAXIMUM TESTED LOAD FOR HYBRID SPIROID AND WORM 
               
               
                 GEAR 
               
             
          
           
               
                   
                   
                 Load at 
                   
                 Load at 
               
               
                   
                 Maximum 
                 Break 
                 Energy at Break 
                 Present Point 
               
               
                 Sample 
                 Load 
                 (Standard) 
                 (Standard) 
                 (Tensile extension 
               
               
                 No. 
                 (lbf) 
                 (lbf) 
                 (ft-lbf) 
                 0.5 in) (lbf) 
               
               
                   
               
               
                 1 
                 81.46 
                 68.35 
                 30.16 
                 5.72 
               
               
                 2 
                 79.91 
                 63.70 
                 28.13 
                 6.56 
               
               
                 3 
                 84.21 
                 68.96 
                 30.86 
                 5.16 
               
               
                 4 
                 84.82 
                 70.35 
                 30.41 
                 5.35 
               
               
                 5 
                 81.68 
                 61.66 
                 27.94 
                 2.14 
               
               
                 6 
                 88.80 
                 74.40 
                 33.03 
                 4.04 
               
               
                   
               
             
          
         
       
     
         [0040]    In each case, the maximum load was calculated as the test device force multiplied by the disk radius (2.5 inches) and multiplied by the RPM ratio of 19. The RPM ratio is the ratio of rotational speed of the pinion to the tested gear. Thus, the maximum load is calculated as the test device force (in pounds) multiplied by 47.5 inches. All of the gears were made from the same material, Acetal 100. 
         [0041]    With respect to the worm gear, the average (of three samples) maximum load at failure for the three tests was found to be 14.64 lbs, which corresponds to an average torque limit for the worm gear of 14.64×2.5×19=694.4 in-lbs. 
         [0042]    With respect to the double spiroid gear samples, the average (of six samples) maximum load at failure was found to be 73.7 lbs. This corresponds to an average torque limit for the double spiroid gear of 73.7×2.5×19=3500.75 in-lbs. 
         [0043]    And with respect to hybrid spiroid and worm gear samples, the average (of six samples) maximum load at failure was found to be 83.48 lbs. This corresponds to an average torque limit for the hybrid spiroid and worm gear of 83.48×2.5×19=3965.3 in-lbs. 
         [0044]    As can be seen from the test results, the maximum load of the present hybrid gear, compared to that of similar size and material gears is considerably higher than the comparable worm gear (over 470 percent) and higher than the comparable double spiroid gear (13.3 percent). Thus, the present hybrid spiroid worm gear has been found to provide a significant increase in torque capability for gearing, without increasing the size of the gears. 
         [0045]    It will be understood by those skilled in the art that the present hybrid enveloping spiroid and worm gear assembly  10  permits a gear application in those instances where high torque handling is required and a physically small gear set is needed. Importantly, it has been found that the present hybrid enveloping spiroid and worm gear assembly  10  can be formed from polymeric (e.g., plastic, resin) materials and still withstand high or out of the ordinary loads such as thrust loads (longitudinally along the pinion or normal to the gear assembly axis), without stripping the gear teeth  16 ,  18 . It has also been found that higher torque loads can be accommodated since the load is distributed over both the spiroid gear surfaces  24 , as well as the worm gear  26 . 
         [0046]    Although not exhaustive nor limiting, it is anticipated that the present hybrid enveloping spiroid and worm gear system  10  can be used in (medical) pump and valve applications, aerospace systems and robotics applications, automobile and transportation systems, power systems, wind energy, mining systems, as well as general manufacturing uses. 
         [0047]    All patents referred to herein, are hereby incorporated herein by reference, whether or not specifically done so within the text of this disclosure. 
         [0048]    In the disclosures, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. 
         [0049]    From the foregoing it will be observed that numerous modification and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.