DIFFERENTIAL APPARATUS AND METHOD OF MAKING

Abstract: An integral differential case (10) for a cross axis, compound planetary gear differential that includes end portions (10a, 10b) each defining an axle receiving bore (14, 28) and trunnions (12, 26) by which the case is rotatably supported within a housing, and, an intermediate portion (10c) located between the end portions. The intermediate portion includes a through passage (50) defining transfer gear windows (52, 54) at each end. Each transfer gear window is defined at least partially by spaced apart window wall sections (56), disposed in planes that extend on either side of an axis of rotation (20) for the differential case. Intermediate wall sections (58) are disposed along the passage intermediate the transfer gear windows (52, 59) and are disposed in parallel planes that intersect the axis of rotation at substantially 90<o>. The passage is finish formed by a broaching process in which a broaching tool (80) concurrently machines the intermeidate wall sections and window wall sections in a single broaching cycle. The broached window wall sections and broached intermediate wall sections provide locating and reaction surfaces for transfer gears (60) mounted within the windows and axle drive gears (62) mounted inside the differential.

Description: Description Differential Apparatus and Method of Making CROSS REFERENCES TO RELATED APPLICATIONS Application of Vernon E. Gleas an and Keith E. Gleasman, Serial No. ; _, (Attorney Docket 8- 961) entitled Differential Gear Apparatus, filed con¬ currently herewith, the disclosure of which is hereby incorporated by reference. Application of Vernon E. Gleasman, Serial No. , (Attorney Docket 9-417) entitled Differential Gearing Assembly, filed concurrently herewith, the dis¬ closure of which is hereby incorporated by reference. Application of Gene A. Stritzel, Serial No. , (Attorney Docket 9-418) entitled Improved Differential Apparatus and Method of Making, filed con¬ currently herewith, the disclosure of which is hereby incorporated by reference. Technical Field The present invention relates generally to-differen- tial mechanisms and in particular to a new and improved differential case for use with a cross axis compound planetary gear differential assembly. Background Art Patent No. 2,859,641 to Gleasman, which is hereby incorporated by reference discloses a worm gear differen¬ tial mechanism, termed a "cross-axis compound planetary gear complex". The disclosed differential includes a differential case that mounts g-ear elements which couple rotation of the differential case to axles extending into the case. In particular, a pair of axle drive gears (also termed traction or side gears) are located within the differential and are received and rotatably coupled with ends of the axles. Pairs of balancing gears are mounted in windows disposed in the case and split driving torque between the side gears. In the embodiment illustrated in this Gleasman patent, the differential case is actually an assembly held together by spacer bolts and other fasteners. In addition, three pairs of balancing gears are employed and hence the differential case assembly includes three windows. Al¬ though the differential, disclosed in this Gleasman patent, operates extremely well, it is nevertheless desirable to reduce its manufacturing cost. Some attempts have been made to reduce the cost of this differential. One such attempt included the sub¬ stitution of a one piece casting for the individual components that made up the original differential case. Although the cost of producing the differential was reduced by fabricating the differential case from a casting, significant expense was still incurred in machin¬ ing the raw casting. In particular, each of the three windows required separate machining steps to provide the necessary surface finish to the balancing gear moun¬ ting and locating surfaces. In addition, side thrust surfaces for the axle drive gears and/or thrust bearings necessitated the internal machining of the casting to provide the required surface finish. In short, although some cost in producing the differential was saved by the utilization of the cast differential case, the con¬ struction of the differential case did not lend itself to high speed production methods. Disclosure of the Invention A new and improved differential is disclosed which includes an integral differential case that simplifies the construction and assembly of the differential and significantly reduces its manufacturing cost. The present invention also encompasses a process for making the case and in particular includes a process for finishing O PI the requisite machined surfaces that coact with or locate the gear components in the differential assembly. According to the preferred embodiment, the differen¬ tial case is a unitary casting and comprises end portions disposed on either side of an intermediate portion. One end portion defines a ring gear mounting flange and a laterally extending trunnion disposed centrally with respect to the flange. The trunnion includes an axle receiving bore through which an axle is inserted to engage internal gear components supported within the differential case. The other end portion includes another laterally extending trunnion which also includes an axle receiving bore. As is conventional, the trunnions are adapted to receive bearings by which the differential case is rotatably mounted to a differential housing. The trunnions define an axis of rotation for the case which is typically coincident with the central axis of the ring gear mounting flange. According to the invention, the intermediate por¬ tion of the differential case defines a through passage which in the illustrated and preferred embodiment, is four sided. The ends of the through passage form windows in which transfer gearing is mounted. Each gear window is defined, at least in part, by opposed, * spaced apart window wall sections, the sections being disposed in parallel planes that extend on either side of the axis of rotation of the differential case. In the exemplary embodiment, these wall sections provide locating and reaction surfaces for the gears mounted within the window. In accordance with the invention, the passage is further defined by another pair of spaced apart wall sections located along the passage intermediate the transfer gear windows. The wall sections are disposed in parallel planes that intersect and are substantially OMPI orthogonal to the axis of rotation of the differential case. These intermediate wall sections define locating and reaction surfaces for axle drive gears and/or thrust bearings disposed between inside of the the case and the axle drive gears. The construction of the differential case is dis¬ closed for use with a cross axis compound planetary gear differential of the type described in Gleasman Patent No. 2,859,641, but in which two pairs of balan¬ cing gears are used to cross couple the axle drive gears instead of three pairs as disclosed in the Gleasman patent. The unitary case reduces assembly time of the differential and even more importantly, the cost of producing the case is substantially -less than the cost of producing a differential case comprised of individual components. According to additional features of the invention, the .intermediate portion defines pairs of aligned bores located at the transfer gear windows that extend per¬ pendicularly with respect to the window wall sections. The bores accept shafts which rotatably carry the transfer gears. In addition, the case preferably defines integ¬ rally formed lugs constructed to receive a retaining arrangement for securing the transfer gear shafts in position. The present invention also provides a new and im¬ proved method for making the differential case. In accordance with the preferred embodiment, a broaching process is used to machine at least two sides, but pre¬ ferably four sides, of the passage simultaneously. In particular, a four sided broaching tool is driven through the passage to finish machine the window wall sections and the intermediate or side gear wall sections. De¬ pending on the broach construction, both ends of the passage may be finished machined in a single broaching OMPI cycle, or alternately, the differential case may be finished machined in a two step process in which a broaching tool is sequentially inserted from both ends of the passage to individually finish each transfer gear window. The disclosed differential case construction and method greatly reduces the expense associated with pro¬ ducing the differential described above. The casting from which the differential case is ultimately formed requires minimal machining to produce a finished product. By using the disclosed broaching method, high speed production of the differential can be achieved. According to still another feature of the invention, each end portion of the differential case includes radial gusset-like ribs that radiate outwardly from the asso¬ ciated trunnion. The ribs provide added rigidity to the case and trunnion location without a substantial increase in overall weight. Additional features will become apparent and a fuller understanding of the invention will be obtained by reading the following detailed description made in connection with the accompanying drawings. Brief Description of the Drawings Figure 1 is a side elevational view of a differen¬ tial case constructed in accordance with the preferred embodiment of the invention; Figure 2 is a left end view of the differential case shown in Figure 1; Figure 3 is a right end view of the differential case shown in Figure 1; Figure 4 is a sectional view of the " differential as seen from the plane indicated by the line 4-4 in Figure 1, shown with differential gear components. Figure 5 is another side elevational view of the differential case shown with a broaching tool in position; Figure 6 is a sectional view as seen- from the plane indicated by the line 6-6 in Figure 5; Figure 7 is a sectional view of an alternate differen¬ tial case embodying the present invention as seen from the plane indicated by the line 7-7 in Figure 8; Figure 8 is an end view of the alternate differential case; Figure 9 is a side elevational view of the alternate differential case, rotated 90° from the position shown in Figure 7; and. Figure 10 is a sectional view of the case as seen from the plane indicated by the line 10-10 in Figure 9. Detailed Description of a Preferred Embodiment of the Invention The overall construction of a differential case 10, constructed in accordance with the preferred embodi¬ ment of the invention is illustrated in Figures 1-3. The case 10 is formed from an integral casting and in¬ cludes end portions 10a, 10b disposed on either side of an intermediate portion 10c. The end portion 10a includes a trunnion 12 defining, at least in part, an internal bore 14 through which a drive axle (not shown) extends into engagement with internal gear components. The trunnion 12 is typically a machined annulus adapted to receive a bearing by which the differential case is rotatably mounted to a dif¬ ferential housing (not shown) . The trunnion extends outwardly from a larger diameter, unmachined hub 16 that defines a shoulder 16a against which the bearing (not shown) seats. The left end portion 10a (as viewed in Figure 1) also defines a flange 18 that includes a plurality of apertures 18a by which a ring gear (not shown) is mounted to the differential case. The flange 18 defines an axis of rotation 20 for the case 10. In the illustrated embodiment, a plurality of re¬ inforcing, gusset-like ribs 22 radiate outwardly from the unmachined hub 16 and merge with the base of the mounting flange 18. The ribs 22 reinforce the end portion 10a and rigidize the location of the trunnion 12. The right end portion 10b is similarly configured and includes a trunnion 26 defining, at least partially, an axle receiving bore 28. The trunnion 26 is defined by a machined annulus that extends outwardly from an unmachined hub 30, of larger diameter, thereby defining a shoulder 30a against which a bearing (not shown) seats. Like the end portion 10a, in the disclosed embodi¬ ment, radial ribs 32 radiate outwardly from the un¬ machined hub 30, to reinforce the right end portion 10b and the position of the trunnion 26. As seen in both Figures 2 and 3, reliefs 36, 38 are formed in the hubs 16, 30, respectively, to provide clearance for a suitable bearing removal tool, in the event replacement of the differential bearings is required. The intermediate portion 10c is located between the end portions 10a, 10b. According to the invention, the intermediate portion defines a through passage 50, which in the preferred and illustrated embodiment is of a four sided configuration. Opposite ends of the passage (only one end is shown in Figure 1) define aligned open¬ ings 52, 54 or "windows" in which gear components, to be described, are operatively carried (shown in Figure 4). Each window 52, 54 is defined by opposed, machined window wall sections 56. The wall sections 56 are paral¬ lel and disposed in planes that extend on either side of the center line 20. The passage 50 is further defined by spaced apart wall sections 58 disposed intermediate the window wall sections 56, which provide mounting and reaction surfaces for axle drive differential gearing components to be described. The intermediate wall sections 58 define sur¬ faces disposed in parallel planes that extend orthogonally with respect to the axis of rotation 20. Referring also to Figure 4, the window wall sec¬ tions 56 define mounting and/or thrust surfaces for transfer gears 60 mounted in the windows. The opera¬ tion of the transfer gears are fully described in Patent No. 2,859,641, which is hereby incorporated by reference. By way of summary, each transfer gear 60 includes an "irreversible" gear portion formed as a worm wheel 60a, for example, and a pair of "reversible" balancing gears such as spur gears 60b disposed at opposite ends of the worm wheel (only one spur gear of the pair is shown in Figure 4) . Axle drive gears 62 formed as "worm" gears are disposed centrally within the differential case and rotatably engage the ends of axles (not shown) which extend through the bores 14, 28. In the embodiment shown, the axle drive gears 62 each include a splined internal bore 62a which is adapted to engage external splines formed on the axle end (not shown) . The worm wheel portions 60a of the transfer gears 60 engage the axle drive gears 62. The transfer gears 60 that form a pair, as seen in Figure 4, are coupled to each other by the spur gears 60b. The pairs of transfer gears 60 thus cross couple the axles to each other and split torque between the axles. It should be noted that the axle drive gears no. 62 and the irreversible gear portions 60a of the transfer gears 60 can be cross axes helical gears. As seen best in Figure 4, the transfer gears 60 rotate on shafts 66. Referring also to Figures 1 and 6, the shafts 66 span the windows 52, 54, their ends being supported by aligned bores 68 that open on one end into the windows. The other ends of the bores 68 open into relieved areas 70 formed on the periphery of the inter¬ mediate section 10c of the differential case at spaced locat i ons. A lug-like structure 72 separates -^tJ EΛ the adjacent relieved areas and includes a bore 74 (shown best in Figure 3) adapted to receive a pin 76 (shown in Figure 1) for maintaining the position of a shaft 66 in its associated bores 68. It should be noted that other arrangements can be used to maintain the shafts 66 in position. In the embodiment shown, to install a pair of trans¬ fer gears 60 in the window of the differential case, the gears are positioned between the wall sections 56 in alignment with the bores 68. The shafts 66 are passed from one bore 68 through the transfer gear 60 and into its associated, spaced bore 68. The position of the shaft is then fixed by the pin 76. As seen in Figure 4, the axle drive gears 62 are disposed side-by-side within the differential case and are engaged by associated worm wheel portions 60a of -the transfer gears 60. Each of the axle drive gears 62 includes an outward end face 63 that abuts a respective one of the intermediate wall sections 58. Thus, the intermediate wall sections 58 locate the axle drive gears within the housing and can receive side loading or end thrust from the gears. According to a feature of the invention, a broaching process is used to machine the passage 50, and in particu¬ lar to simultaneously finish machine the window wall sections 56 and the intermediate wall sections 58. Turning now to Figures 5 and 6, the differential is shown with a broaching tool 80 in position. As viewed in Figure 5, the broach includes a plurality of vertical and trans¬ verse teeth 80a, 80b, respectively. According to the method, the cross-section of the broach defines the finish dimension of the passage 50. The vertically oriented teeth (as viewed in Figure 5) cut the interme¬ diate wall sections 58 and the transversely oriented teeth 80b cut the window wall sections 56. In accord- OMPI ance with the method, the broach 80 is inserted from one end of the passage 50. As it passes through the passage 50, during a broaching cycle or cutting stroke, the window and intermediate wall sections 56, 58 are finish sized. In the preferred method, the broaching process provides the final surface finish for all of wall sections. As is conventional, the cross-section of the broach typically tapers from one end to the- other so that material is gradually cut from the passage 50. Depending on the type of broach and broaching machine used, the passage 50 in the differential case can be finish machined in one step or multiple steps. For example, a roughing broach may initially be used to rough machine the passage followed by a finishing broach. The window wall sections 56 of both windows 52, 54 may be machined in one broaching cycle or, alternately, the broach 80 may be inserted from one end to finish one window opening 52 and then removed and reinserted from the other window to finish machine the window wall sec¬ tions 56 of the second window 54. The disclosed invention greatly reduces the manufac¬ turing cost of a differential case of the type that includes transfer gearing mounted in window openings that cross-couple axle drive gears. The integral cast¬ ing used for the differential case eliminates the cost incurred in assembling a differential case from indivi¬ dual components. By machining the passage 50 with a broach or similar method, precision locating and thrust surfaces for the transfer gears 60 and the axle drive gears 62 are obtained without undue expense. The "broached surfaces" in the passage eliminate the need for complex and expensive internal machining of the differential case that would otherwise be required. The differential case 10 illustrated in Figures 1-6 depicts my invention as originally conceived by me. MPI Figures 7-10 illustrate an alternate differential case, embodying my invention but which also includes improve¬ ments made by Gene A. Stritzel. The improvements are described and claimed in the co-pending application filed concurrently herewith in the name of Gene A. Stritzel, entitled "Improved Differential Apparatus and Method of Making" which has been incorporated by refer¬ ence. Figures 7 and 9 illustrate the overall construction of the alternate embodiment of a differential case 110. The case comprises end portions 110a, 110b disposed on either side of an intermediate portion 110c. The three case portions comprise an integral casting. The left end portion 110a (as viewed in Figure 7) includes a trunnion 112 formed by a machined annulus which is adapted to receive a bearing by which the trun¬ nion, and hence the differential case, is rotatably mounted to a differential housing. The trunnion 112 defines an internal, axle receiving bore 114 that extends through the trunnion and opens into the interior of the differential case. The end portion 110a also includes a flange 118 including a plurality of apertures 118a by which a ring gear (not shown) is mounted to the differen¬ tial case. The right end portion 110b (as viewed in Figure 7) includes a trunnion 126 that also defines, at least partially, an internal axle receiving bore 128 that opens into the interior of the case. The trunnion 126 also comprises a machined annulus adapted to receive a bearing by which the right end of the differential case is rotatably mounted to a differential housing. The trunnions 114, 126 and ring gear flange 118 define an axis of rotation 120 for the differential case. As seen in Figure 8, unmachined portions of the trunnion hub, indicated by the reference character 130 include relief notches 132, spaced 180° apart, to.provide access for a bearing removing tool should replacement of a differential bearing be necessary. The end portion 110b includes similar notches or reliefs (not shown) . As seen best in Figure 7 and 10, the intermediate portion 110c defines spaced apart, aligned openings, 140 which for purposes of explanation will be termed "windows", in which gear components are located and carried. As seen in Figure 7, the openings appear to define a through-passage 150 extending through the in¬ termediate portion 110c of the differential case. As viewed in Figure 7, each window is defined by vertical, preferably unmachined, walls 152 and spaced apart, transverse walls 154 which preferably include unmachined portions 154a on either side of a machined portion 154b. The intermediate portion 110c also includes an additional pair of openings 156 (shown in Figures 9 and 10) which are rotated 90° with respect to the windows 140. The intermediate portion 110c also includes re¬ cesses or relieved areas 158 between the windows 140 and the openings 156 so that, in section, and as seen in Figure 10, the intermediate section appears to comp¬ rise four L-shaped posts which, for purposes of explana¬ tion, shall be individually designated by the reference character 160. Each post defines a pair of parallel, through bores 166 that extend from the recess 158 and open into an associated window 140 and also includes a pair of smaller diameter bores 168 oriented 90° with respect to the bores 166, which extend from the recess 158 to the differential case openings 156. Referring to Figure 7, the bores 166 of the posts 160 are machined or formed in alignment with each other for the purpose of receiving shafts 170 by which transfer gears 172 (only one shaft and one gear are shown) are rotatably OMPI carried within the window 140. The smaller diameter bores 168 receive shaft retainers 174, such as friction pins to maintain the transfer gear shafts 170 in position. Returning to Figures 7 and 10, locating and reac¬ tion (thrust receiving) surfaces for axle drive gears 176 (only one gear is shown in Figure 7) are provided by respective annular, inwardly extending extensions 180, 182 of the end portions 110a, 110b. The annular extensions 180, 182 are preferably formed concentric with respective axle receiving bores 114, 128 and as seen in Figure 7, the extensions define machined end faces which abuttably engage an outer end face 176a of ' the side gears 176 or, alternately, the side of a thrust bearing disposed between the side gear 176 and the exten¬ sion 180 (not shown). As seen best in Figure 7, the transverse dimension of the windows (the distance between the window walls 152), as indicated by the arrow 186, is greater than the distance between the internal end faces of the extensions 180, as indicated by the arrow 188. The machined surface portions 154b of the trans¬ verse window wall sections 154 extend inwardly towards the center of the window 140. In the preferred method, the finished surfaces are formed by a broaching process. By appropriate design and construction of a broaching tool (such as shown in Figures 5 and 6) the machined portions 154b of the window walls 154 as well as the end faces of the extensions 180, 182 can be finish machined in one broach cutting cycle. In addition, only those- differential case sur¬ faces, requiring a machine finish, are actually con¬ tacted by the broach. With the disclosed differential case construction, the amount of material removed during the broaching process is reduced and, in addition, the unmachined portions 154a of the transverse wall sections 154 (as viewed in Figure 7) as well as the additional clearance defined by the added spacing between the verti¬ cal wall sections 152, provide chip relief for the broach¬ ing process. As described earlier, one or both windows 140 may be finish machined in a single broaching cycle depending on the broach construction. The use of a broaching process to manufacture the disclosed differential case, results in broached mounting and locating surfaces for the axle drive gears and the transfer gears. In addition, since all surfaces can be concurrently cut with a single tool, critical tolerances between the surfaces can be easily maintained resulting in a precisionally manufac¬ tured differential case at a substantially reduced cost as compared to assembled differential cases or cases requiring a multitude of machining steps. It should be appreciated by those skilled in the art, that the present invention is adaptable to a variety of differential assemblies. The invention has been disclosed in connection with a differential that includes a single pair of transfer gears 60 located in each window 140. The present invention can also be used to produce a differential case for use with a differential that includes additional gearing within the windows such as the differential assembly disclosed in co-pending appli¬ cation. Serial No. , filed concurrently here¬ with in the name of Vernon E. Gleasman and entitled "Differential Gearing Assembly". Although the present invention has been described with a certain degree of particularity, it should be understood that various changes can be made to it by those skilled in the art without departing from the spirit or scope of the invention as hereinafter claimed.

Claims: Claims 1. A differential case for a cross axis, compound planetary gear differential comprising a unitary casting having integrally formed end portions disposed on either side of an intermediate portion, each end portion defining a trunnion including an axle receiving bore, said trunnions defining an axis of rotation for said differential case, said intermediate portion defining a through passage and transfer gear windows at each end of said passage, each transfer gear window defined at least in part by opposed, parallel window wall sections disposed in planes that extend on either side of said axis of rotation, • said passage further defined by another pair of spaced apart wall sections located along said passage, intermed¬ iate said windows, said intermediate wall sections disposed in planes that intersect said axis of rotation. 2. The differential case of Claim 1 wherein said end portions include radial ribs for rigidizing the position of said trunnions. 3. The differential case of Claim 1 wherein said intermediate portions further include pairs of aligned bores located at said windows and extending perpendicu¬ larly with respect to said window wall sections. 4. The differential case of Claim 1 wherein said intermediate portion further includes integrally formed lugs for receiving a shaft retaining means. 5. The differential case of Claim 1 wherein at least two of said wall sections defining said passage are formed by a broaching process. OMPI 6. The differential case of Claim 1 wherein said passage is formed by broaching said window wall and intermediate wall sections in a single broaching cycle. 7. An intregal differential case for a cross axis, compound planetary gear differential or the like, comprising: a) an end portion defining a trunnion having an axle receiving bore; b) another end portion defining another trunnion, having an axle receiving bore, said other end portion spaced axially from said one end portion? c) an intermediate case portion disposed between said end portions; d) said intermediate portion including spaced, aligned transfer gear windows, each window defined at least partially by a pair of window wall sections dis¬ posed in parallel planes that extend on either side of an axis of rotation for said differential case; and, e) said intermediate portion further includ¬ ing spaced apart intermediate wall sections located intermediate said transfer gear windows and defining locating surfaces for axle drive means, said surfaces disposed in parallel planes that intersect said axis of rotation, substantially at an angle of 90°. 8. The differential case of Claim 7 wherein said window wall sections and said intermediate wall sections define machined surfaces formed by a broaching process. 9. The differential case of Claim 7 wherein said window wall sections and said intermediate wall sections are formed by driving a broach having cutting teeth sized to define the spaced apart distance for said window wall sections and said intermediate wall sections, into one of said window openings and moving it along a path defined by said aligned window openings. 10. An integral differential case for a cross axis, compound planetary gear differential or the like, comprising: a) an end portion defining an axle receiving bore and structure for rotatably supporting said end portion; b) another end portion, spaced from said one end portion, including another axle receiving bore and means for rotatably supporting said other end por¬ tion; c) an intermediate portion disposed between said end portions; d) said intermediate portion including a pair of spaced apart transfer gear windows; e) each window defined at least partially by a pair of spaced apart wall sections, each of said window wall sections including a broached mounting surf¬ ace for locating and coacting with transfer gears; f) said intermediate portion further includ¬ ing intermediate wall sections, located intermediate said transfer gear windows, each of said intermediate wall sections defining a broached machined surface for locating and coacting with respective axle drive gears located within said intermediate portion.

Inventors: GLEASMAN VERNON E, GLEASMAN, VERNON, E.
Applicants: GLEASON WORKS, THE GLEASON WORKS
Application year: 1984
Main classification: F16H1
IPC codes: B23D43, F16H1, F16H48, F16H57