DIFFERENTIAL APPARATUS AND METHOD OF MAKING

Abstract: An integral differential case (110) for a cross axis, compound planetary gear differential that includes end portions (110a), (110b) each defining an axle receiving bore (114), (128) and trunnions (112), (126) by which the case is rotatably supported within a housing, and, an intermediate portion (110c) located between the end portions. The intermediate portion includes a pair of spaced apart, aligned transfer gear windows (140) defined by side walls (152) and window wall sections (154) that each include inwardly projecting broached machined surfaces (154b) for coacting with transfer gears (172) rotatably carried within the window. The end portions define respective inwardly extending extensions (180), (182) having end faces for coating with axle drive gears located inside the differential case. The end faces are disposed in parallel planes which are substantially orthogonal to the planes of the broached window wall surfaces and which are located inwardly with respect to window side walls (152). The intermediate portion (110a) also defines elongate openings (156) spaced 90 degrees from thetransfer gear windows and recesses (158) between the windows and the elongate openings so that in section the intermediate portion appears to comprise four L-shaped posts (160). Each post includes aligned bores for receiving transfer gear shafts and bores (168) for receiving shaft retaining pins (174).

Description: DIFFERENTIAL APPARATUS . AND METHOD OF MAKING Technical Field The present invention relates generally to differ- ential mechanisms and in particular to a new and im¬ proved differential case for use with a cross axis com¬ pound planetary gear differential assembly. Bac g ' round Art Patent No. 2,859,641 to Gleasman, which is hereby incorporated by reference discloses a worm gear differ¬ ential mechanism, termed a "cross-axis compound planet¬ ary gear complex". The disclosed differential includes a differential case that mounts gear 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. Although 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 substitution of a one piece casting for the individua l components that made up the original differentia l SUBSTITUTE SHEET OMPI case. Although the cost of producing the differential was reduced by * fabricating the differential case from a casting, significant expense was still incurred in machining the raw casting. In particular, each of the three windows required separate machining steps to provide the necessary surface finish to the balancing gear mounting 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 differ¬ ential was saved by the utilization of the cast diff¬ erential case, the construction 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 sim¬ plifies the construction and assembly of the differ- ential 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 the requisite machined surfaces that coact with or locate the gear components in the diff- erential assembly. According to the preferred embodiment, the differ¬ ential 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. SUBSTITUTE SHEET 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 5 which is typically coincident with the central axis of the ring gear mounting flange. According to the invention, the intermediate portion of the differential case defines spaced apart, aligned peripheral openings, which for purposes of explanation 10 are termed "transfer gear windows". Preferably, a common centerline through the windows intersects the axis of rotation for the differential case. Each transfer gear window is defined by a pair of spaced apart, preferably parallel side walls and a pair r- of spaced apart transverse window wall sections that extend between and merge with the side walls . In accordance with the invention, each transverse window wall section defines a machined surface that serves as a locating and reaction surface for transfer gears 0 mounted within the window. The machined surface of each window wall section projects outwardly from and towards a center plane of the window, so that other portions of the window wall section are disposed in a plane spaced further from the center plane than the 5 plane of the machined surf ces. With the disclosed invention, the amount of finish machining for a transfer gear window is reduced. In the exemplary embodiment, only the locating/reaction surfaces for the transfer gears are actually finish ° machined; the remainder of the wall sections and side walls defining the window opening are left unmachined. According to the invention, each end portion includes an annular extension, that extends inwardly into the inside of the differential case. The 5 annular extensions are preferably formed concentric ' SUBSTITUTE SHEET with the axle receiving bores of the respective case end postions. Each extension defines a locating and reaction surface for an axle drive gear or axle drive gear bearings, disposed within the differential. 5 The reaction surface for each extention is defined by a machined end face. In the preferred and illustrated embodiment, the distance between the end faces of the extensions is less than the distance between the side walls of 10 the window openings. When viewed from a window, the extensions appear to project towards the center line of the windows and are disposed in parallel planes that are orthogonal to the planes of the machined surf ces of the window wall sections. In the preferred 15 method of making the differential case, a broaching tool is inserted through a window opening to finish machine the projecting surfaces of the window wall sections and the end faces of the inner extensions of the case end portions. With this preferred process, 20 broached window surfaces and broached extension end faces for the transfer gears and axle drive gears, respectively, are provided in a single broaching cycle. In addition, the added clearance provided by the unmachined portions of the windows provide chip 5 relief for the broaching process. According to a feature of the invention, the intermediate portion defines additional openings that are positioned substantially 90 degrees from the transfer gear windows. These additional openings -*- *0 provide added access to the interior of the differ¬ ential wall while at the same time reducing the overall weight of the case. According to still another feature of the inven¬ tion, the intermediate portion defines recesses between 35 the transfer gear windows and the additional openings, so that in section, the intermediate portion appears SUBSTITUTE SHEET to be defined by four L-shaped posts. According to this feature, each post defines shaft receiving bores aligned with associated bores on the adjacent L-shaped posts which together support shafts by which transfer gears are rotatably carried within the window. Each post preferably includes a means for retaining the shafts which in the preferred embodiment comprises relatively small diameter bores for receiving a retaining pin or similar arrangement. The construction of the differential case is disclosed for use with a cross axis compound planet¬ ary gear differential of the type described in Gleasman Patent No. 2,859,641, but in which two pairs of bal¬ ancing 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. 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 sectional view of a differential case embodying the present invention as seen from the plane indicated by the line 1-1 in Figure 2; Figure 2 is an end view of the differential case; Figure 3 is a side elevational view of the differ¬ ential case, rotated 90 degrees from the position shown in Figure 1; and, Figure 4 is a sectional view of the case as seen from the plane indicated by the line 4-4 in Figure 3. SUBSTITUTE SHEET / O PI Detailed Description of a Preferred Embodiment of the Invention The overall construction of a differential case 110, constructed in accordance with the preferred embodiment of the invention is illustrated in Figures 1-3 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 1) includes a trunnion 112 formed by a machined annulus which is adapted to receive a bearing by which the trunnion, and hence the differential case, is rotat- ably 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 differential case. The right end portion 110b (as viewed in Figure 1) 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 differ¬ ential case is rotatably mounted to a differential housing. The trunnions 114, 126 and ring gear flange 118 define an axis of rotation 20 for the differential case. As seen in Figure 2, unmachined portions of the trunnion hub, indicated by the reference charac ¬ ter 130 include relief notches 132, spaced 180 degrees apart, to provide access for a bearing removing tool should re p lacement of a differential bearing be necessary. The end portion 110b includes similar notches or reliefs (not shown). As seen best in Figure 1 and 4, 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 1, the openings appear to define a through-passage 150 extending through the intermediate portion 110c of the differential case. As viewed in Figure 1, 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 3 and 4) which are rotated 90 degrees with respect to the windows 140. The intermediate portion 110c also includes recesses or relieved areas 158 between the windows 140 and the openings 156 so that, in section, and as seen in Figure 4, the intermediate section appears to comprise four L-shaped posts which, for purposes of explanation, shall be individually desig¬ nated 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 degrees with respect to the bores 166, which extend from the recess 158 to the differential case openings 156. Referring to Figure 1, 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 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. O PI Returning to Figures 1 and 4, locating- and reac¬ tion (thrust receiving) surfaces for axle drive gears 176 (only one gear is shown in Figure 1) are provided b y 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 1, 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 extension 180 (not shown) . As seen best in Figure 1, 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 transverse window wall sections 154 extend inwardly towards a center plane of the window 140, parallel to a v/indow centerline 178 (shown in Figure 4), whereas the extensions 180, 182 project towards the centerline, the end faces being disposed in parallel planes that are ortho¬ gonal to the planes of the machined surface portions 154b of the windows. In the preferred method, the finished surfaces are formed by a broaching process. By appropriate design and construction of a broaching tool 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 surfaces, requiring a machine finish, are actually contacte d b y t h e broach. With the disclosed differential case construction, the amount of material remove d during the broaching process is reduced an d , in a dd ition, SUBSTITUTE SHEET ^J Ϊ _T A the unmachined portions 154a of the transverse wall sections 154 (as viewed in Figure 1) as well as the additional clearance defined by the added spacing between the vertical wall sections 152, provide chip relief for the broaching 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 diff- erential 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 toler¬ ances between the surfaces can be easily maintained resulting in a precisionally manufactured 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 172 located in each window 140. The present invention also can 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 application, Serial No. 475,526, filed concurrently herewith 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 herinafter claimed. SUBSTITUTE SHEET

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 inter¬ mediate portion defining a pair of aligned transfer gear windows, each transfer gear window defined at least in part by opposed, parallel window wall sec¬ tions, said wall sections defining inwardly projecting machined surfaces disposed in planes that extend on either side of said axis of rotation, said end portions defining inwardly extending spaced apart extensions including respective end faces disposed in planes that intersect said axis of rotation and disposed inwardly of window side walls. 2. An integral 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, said sections having respective broached surfaces disposed in parallel planes that extend on either side of an axis of rotation for said differ- ential case; and, SUBSTITUTE SHEET e) said end portions defining respective, inwardly extending, spaced apart extensions, said extensions including respective end faces for 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 degrees and which are disposed inwardly with respect to side walls of said transfer gear windows. 3. 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 portion; 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, including a broached mounting surfaces projecting towards a centerpiece of said windows, for locating and coacting with transfer gears; f) said end portions including inwardly extending extensions each having a broached end face for defining a locating surface for respective axle drive gears located within said intermediate portion, said end faces disposed in planes that extend inwardly of side walls defining said windows. 4. The differential case of claim 3 wherein s.aid intermediate portions define peripheral elongate openings spaced substantially 90 degrees from said transfer gear windows. 5• The differential case of claim 4 wherein said case further defines recesses between said elongate openings and said transfer gear windows such that in section, said intermediate portion appears to comprise four L-shaped posts. 6. The differential case of claim 5 wherein each post includes at least two bores positioned in align¬ ment with bores in adjacent posts for supporting shafts that rotatably carry transfer gear in said windows. 7. The differential case of claim 6 wherein said posts include means for retaining said shafts in position. SUBSTITUTE SHEET C FI

Inventors: STRITZEL GENE A, STRITZEL, GENE, A.
Applicants: GLEASON WORKS, THE GLEASON WORKS
Application year: 1984
Main classification: F16H1
IPC codes: B23D43, F16H1, F16H48, F16H57, F16M1