Functional indexing in multiple gear differential
United States Patent n 1 Benjamin FUNCTIONAL INDEXING IN MULTIPLE GEAR DIFFERENTIAL Robert N. Benjamin, 1830 Kathryn Dr., Westlake, Ohio 44l45 [22] Filed: July 19, I974 [2]] Appl. No.: 490,069  
 Related U.S. Application Data [60] Division of Ser. No. 385,834, Aug. 6, 1973, which is a continuation-in-part of Ser. No. 265247. June 22, l972. abandoned.  
 [76] Inventor:  
 Primary Examiner-Samuel Scott Assistant E.\&#39;uminerlohn Reep Attorney, Agent, or Firm-Baldwin, Egan, Walling &amp; Fetzer Apr. 8, 1975 [57] ABSTRACT This invention relates to a differential gear mechanism utilizing two substantially identical gear sets in a housing or cage adapted to be driven by a drive shaft. Each set has a central worm or traction gear, sometimes called a side gear, adapted to be keyed in one instance to one of the stub shafts leading to a rear wheel of an automotive vehicle. Each of these side gears is in mesh with a plurality of transfer gear complexes, each having located centrally thereof a worm wheel in mesh with the side gear and having a reversible balancing gear at each end of the worm wheel rigidly connected with the associated worm wheel and coaxial therewith. In use, the balancing gears in one set are in mesh with the balancing gears of the other set. The worm gear has an index point near its periphery, and each complex has an indicator at a fixed point thereon, the index point and indicators being used cooperatively, during assembly, to obtain proper meshing relationship of the gears.  
 2 Claims, 6 Drawing Figures PMENTEDAPR 81975 SEIIET 1 OF 3 FIG?) FIG.2  
 PMENTEUAPR 81975 FUNCTIONAL INDEXING IN MULTIPLE GEAR DIFFERENTIAL This application is a division of my copending application Ser. No. 385.834. filed Aug. 6. I973 which in turn is a continuation of application Ser. No. 265.247, filed June 22, 1972. now abandoned.  
  This invention relates to a differential gear mechanism somewhat similar to that shown in U.S. Pat. No. 2.859.641. granted Nov. 1 l, 1958 to Vernon E. Gleasman, to which reference may be had for a more detailed description of the operation of this type of differential. This patented differential mechanism was satisfactory for accomplishing the purposes set forth and claimed therein, but it was somewhat noisy under certain test conditions and somewhat inefficient in delivery of power therethrough. and did not always give a good division of power between the left and right rear wheels. or drive wheels. of an automotive vehicle.  
  It is. therefore. an object of the present invention to efficiently mesh a plurality of transfer gear worm wheels in mesh with a side gear worm and to efficiently mesh together two half differential mechanisms so assem bled.  
  Other objects and advantages of the present invention will be apparent from the accompanying drawings and description and the essential features thereof will be set forth in the appended claims.  
 In the drawings.  
  FIGS. 1 and 2 are diagrammatic sketches illustrating the method of assembling first and second transfer gear complexes in a set of three in a half differential mechanism;  
  FIG. 3 is a top plan view taken along the line 33 of FIG. 4 and showing three transfer gear complexes assembled in a half differential mechanism as taught herein;  
  FIGv 4 is a side elevational view of two half differential mechanisms of the character shown in FIG. 3 completely assembled in a case; while FIGS. 5 and 6 show another case into which this invention may be assembled, FIG. 5 being a perspective view of parts which hold three gear complexes. and FIG. 6 being a perspective view showing the embodiment completely assembled.  
  This invention is not limited to any specific number of transfer gear complexes composing a set of the same assembled in a differential mechanism as taught herein. The embodiments described herein involve three such transfer gear complexes as composing a complete set in a half differential gear mechanism. Two transfer gear complexes may be used. or more than three. if desired. Also. the invention is disclosed herein where each transfer gear complex consists of a centrally located worm wheel of six helices. on each end of which is a re versible balancing gear. here shown as spur gears with ten teeth each. These need not be spur gears and the number of teeth may vary according to the mechanical problem. Each side gear shown herein is a worm having ten teeth of helical configuration. Geometrically, three of such transfer gear complexes meshing with a side gear worm and utilizing balancing gears which may have varying number of teeth usually are not equally divisible into three identical meshing arrangements and it is one ofthe objects of the present invention to overcome this difficulty so that all of the gears involved will mesh evenly and efficiently so that in operation the power is transmitted smoothly.  
  Referring now to FIGS. 1, 2 and 3, a central or side gear worm 10, sometimes referred to as a worm traction gear. is shown having internal splines for driving connection to a stub shaft going to one of the drive wheels of an automotive vehicle. It is understood that a side gear and its associated stub shaft may be integral. The worm wheel I0 of the upper half differential shown in FIG. 4 is provided with a suitable bearing (not shown) in the portion 11 of the housing. The worm wheel 10 of the lower half differential is provided with a gearing (not shown) in the housing portion 12. Referring to FIG. I, the central worm 10 is provided with a reference index point 13, preferably at the end 10b of one of the helices of the worm I0. Each of the transfer gear complexes to be placed in mesh with the central worm 10 consists of a unitary structure of which the central portion I4 is a worm wheel adapted to mesh with the worm l0 and having at opposite ends thereof reversible balancing gears 15. Each complex 14, I5. i5. is mounted for rotation about a shaft 16 which is housed in the half differential case 17 and held in position by any suitable means such as a pin indicated at 19. Those familiar with the manufacture of gears having helical worm threads recognizes that a driving key is positioned at one end of the threads to determine the initiation of the cutting operation. In this case. an indicator or reference point 18 marks this driving key position in the case of each of the worm wheels I4. In using the method of this invention. the reference index point 13 is placed in a predetermined position relative to the gear complex 14. I5. 15. here shown as substantially the central point of the worm wheel 14. The driving key position indicator or reference point I8 is then set at a preferred radial position. here pointing directly upwardly toward the person assembling the gearing. and the shaft 16 for this first transfer gear complex is placed in position to hold the gear complex in the gear half case 17. Next the central worm I0 is turned in the direction of the arrow of FIGS. 1 and 2 so that the index point I3 is now positioned as shown in FIG. 2. Meanwhile. the first gear complex A is allowed to turn as propelled by the mesh between worm l0 and worm wheel 14 of the first complex. With the index point 13 in the position of FIG. 2, centrally of worm wheel 14b. the second transfer gear complex B is positioned with the driving key position indicator 18 of worm wheel 14]) in the same relative position as when setting the complex A, namely, vertically upwardly as shown in FIG. 2. Complex B is then fixed in the case by a shaft 16. The next step is to turn the worm 10 another 120 in the direction of the arrow of FIG. 2 to the dot-dash position of index 13 corresponding to the placing of the transfer gear complex C which is shown at the bottom of FIG. 3. Here. with the index point 13 at the midpoint of the worm wheel 14c, the third gear complex is positioned by a shaft 16 with the indicator or reference point 18 vertically upward as shown in FIG. 3. It will be understood that in locating of the gear complexes at positions B and C, in each case the shaft or pin I6 is inserted in the differential half case 17 and fixed in position by a pin 19. While turning the index point 13 from the location of gear complex B to the location of the complex C. the worm wheels 14 and 14b are permitted to turn freely in mesh with the central worm 10.  
  The half differential mechanism just described, as assembled in the half case 17, is the lower portion of the differential shown in FIG. 4. Then the upper portion 170 is assembled in an identical manner. The two half differentials in case portions 17 and [7a are thereafter assembled in a unit as shown in FIG. 4 with complexes A, B and C in the two half cases mutually in registration. The two half cases are held in position by stud bolts 20 that pass through openings 21a in the gear case half 17a registering with other openings 21 in the case half 17 as shown in FIG. 3. The openings 21 may be provided with threads to receive the threaded end of the stud bolt 20. The portion 12 of the differential casing is preferably formed integrally with the half case portion 17 and the portion 11 is held in the assembled position of FIG. 4 by the bolts 20. The flange 22 shown in FIG. 4 is provided with a plurality of bolt holes 220 for the attachment to the ring gear which forms part of the differential driving mechanism.  
  In a production line, one would not wish to go through the procedure outlined herein with respect to FIGS. 1, 2 and 3 and this may be avoided very simply. It is clearly seen in FIGS. 3 and 4 that window openings 23 and 23a are provided opposite the gear complexes A, B and C and when the gear complexes have been all assembled as shown in FIG. 3, one may note on each of the complexes of a given set the position of the indicator 18 where it is visible through the windows 23 and 230 or, if it is not visible in a given instance, then a point 180 from position 18 may be indicated in such case so that the gears may be properly assembled looking through the windows 23 and 230 having noted the position of the indicators 18 of FIG. 3 when looked at horizontally. Thus assembled, the mechanism clearly embodies the present invention.  
  It was mentioned hereinabove that the differential case halves l7 and 170, as described in connection with FIG. 3. are placed together in final assembly as shown in FIG. 4. If the balancing gears 15, 15b and 150 have an odd number of teeth, then they will mesh directly with similar gear teeth in the other half case. If the balancing gears have an even number of teeth, then the central worm 10 should be turned slightly in one of the half differential mechanisms to advance the balancing gears thereof by the amount of one-half tooth before the upper and lower half sets are placed together.  
  In some differential mechanisms, what has been described herein as half of a gear mechanism in case portion 17 and another half portion in 170 are all housed in a single housing which must be assembled from the top. With this type of mechanism, the gear complexes are first assembled in the lowermost portion of the housing by placing the central worm 10&#39; in position and orienting the transfer gear complexes A, B and C as taught herein. Then, with the index point 13 returned to the position of FIG. 1 of the drawings accompanying this description. another Central worm I&#34; is placed directly on the first worm with a reference index point like 13 vertically above point 13 of the lower set. The upper set of three transfer gear complexes is then placed in position around worm 10&#34; by repeating the operation as in the lower set, thus placing the complexes like A, B and C over similarly indicated complexes on the lower level of the mechanism.  
  A housing for carrying out the assembly operation described in the preceding paragraph is shown in FIGS. 5 and 6. Three identical sector shape portions 24 each have a flange member 24a and an upstanding member 24b. In the above mentioned method of assembly of the preceding paragraph, the flange portions 24a are bolted to a ring 25 to which also is bolted a ring gear 26 lying above the flange members 240. Those familiar with this art will understand that the ring gear meshes with a bevel gear on the end of the propeller drive shaft of the vehicle. Referring to FIG. 6, three transfer gear complexes are assembled as just described evenly spaced around the central worm 10. Each of these transfer gear complexes comprises an intermediate worm gear 14, at opposite ends of which, and unitarily connected with the worm wheel are two balancing gears 15 like the assembly shown in FIG. 3. The upper set of gears includes a central worm 10&#34; about which three gear complexes are assembled also as above described, and each complex includes a central worm gear 14&#34;, at each end of which is a balancing gear 15&#34;. A shaft 16 or 16&#34; passes through each transfer gear complex, as in the first described embodiment, and these are received in suitable openings 24c in the upstanding portions 24b of the three members 24. Then a member (not shown) is secured to the underside of ring member 25 as seen in FIG. 6 and this holds a bear&#39; ing 27 for a stub shaft running to one of the drive wheels of the vehicle, A cap 28 holds the entire struc ture together by means of three bolts 29 which pass through the cap 28, then through openings 24d in the members 24 and then through the structure shown in FIG. 6 as the ring 25 and the members supported therebelow. The cap 28 carries a bearing 30 for a drive shaft extending to the opposite wheel of the vehicle. It will be noted that certain portions of the ring gear 26 are cut away in FIG. 6 to more clearly show how the present invention is assembled in the portions 24.  
  In any case, no matter how assembled, this invention presents a set of gears including a central worm, sometimes called a side gear, around which are assembled a plurality of transfer gear complexes, each of which is a unitary structure including a worm wheel meshing with the side gear with a balancing spur gear at each end of the worm wheel, characterized in that during rotation of the side gear, a fixed index or reference point thereon passes through the same reference point of each transfer gear complex in the same positional relation. Also, each set of the differential mechanism, as described herein, sometimes called a half differential mechanism, separately goes through the same cycle, no matter how assembled. This invention substantially cancels out errors which occur in the machining of the gears, worms and worm wheels forming elements of the differential herein described and establishes the correct index relation to facilitate proper assembly. Thereby eccentric oscillation of side or traction gears 10 is eliminated.  
  The differential mechanism disclosed herein can be caused to run even in a more smoothly related manner, if desired, by utilizing a gear arrangement disclosed and claimed in the US. Pat. of Vernon E. Gleasman. No. 3,735,647, granted May 29. 1973, which teaches that the balancing gears 15 at opposite ends of the worm wheel 14 should have the teeth of one of these balancing gears indexed relative to the teeth of the other balancing gear of the same unitary structure by an amount between one-half of the circular pitch and full registration whereby when these are meshed with the coacting balancing gears in the other differential half mechanism, the teeth of only one of the pair of matching gears is in full mesh with its coacting gear at any given time.  
  Other than as described herein. the differential gear mechanism as shown in the drawings and described in the specification operates in the same manner as the invention described in US. Pat. No. 2,859,641, to which reference may be bad if further information is needed.  
  The present invention teaches the assembly of the differential gear mechanism so that all parts of inter meshing teeth and gears take their share of the load so that the mechanism provides a smoother action and has a longer life than that disclosed in US. Pat. No. 2.859.641.  
  As used in the specification and claims herein, the term worm or worm gear also includes a helical gear, regardless of the helix angle.  
 What is claimed is:  
  1. In a differential mechanism. a differential gear case adapted to be driven by a source of power. two gear assemblies in said case, each assembly including a central worm traction gear, a set of transfer gear complexes operatively associated with said traction gear,  
 each complex comprising centrally a worm wheel with a reversible balancing gear at each end thereof coaxial with and rotatable with the associated worm wheel. each said complex being rotatably journaled in said case. each of said complexes being mounted in said case with the axis parallel to a tangent to said worm gear and with its worm wheel in meshing engagement with its associated worm traction gear, each of said complexes having an indicator at a fixed point thereon, said worm gear having an index point near its periphery, and said transfer gear complexes being so assembled in said case that they correspond to the positions arrived at by rotating said worm gear to move said index point thereon progressively past said transfer gear complexes, when said index point reaches the same relative position relative to each of its associated worm wheels, then said indicator of each of said complexes in turn arrives at a predetermined radial position which is the same for each worm wheel 2. A differential gear mechanism as defined in claim 1, wherein said reversible balancing gears are spur