Patent Application
20160356372
The present disclosure relates generally to differential assemblies for use in motor vehicle drivelines. More particularly, the present disclosure relates to differential assemblies configured to permit use of a single weldment junction to rigidly interconnect the two case members of a two-piece differential case and a ring gear.
This section provides background information related to the present disclosure which is not necessarily prior art to the inventive concepts disclosed and claimed herein.
A conventional drive axle assembly typically includes an axle housing from which a pair of axleshaft extend to support a pair of wheels positioned on opposite sides of the motor vehicle. Drive torque generated by the vehicle's powertrain is delivered to the axle assembly via an input shaft. The input shaft drives a hypoid gearset for transmitting drive torque to a differential assembly having a differential gearset drivingly connected to the axleshafts. The hypoid gearset typically includes a pinion gear driven by the input shaft and which is meshed with a crown or ring gear which, in turn, is rigidly secured to a differential case of the differential assembly. The differential gearset is disposed within the differential case and includes at least one pair of pinion gears rotatably mounted on a pinion post or cross-pin fixed to the differential case, and a pair of side gears each being meshed with the at least one pair of pinion gears. Each side gear is also coupled to a corresponding one of the axleshafts such that driven rotation of the differential case via the hypoid gearset causes drive torque to be transmitted to the differential gearset in a manner permitting relative rotation between the axleshafts.
At one time, a majority of the differential cases were made as a one-piece iron casting. Iron castings have lower ductility and yield strength compared to most steels and, therefore, cast differential cases typically require thick wall dimensions which detrimentally impact weight and packaging and results in reduced powertrain efficiency. To address the shortcomings of cast differential cases, development has been directed to two-piece differential cases having a pair of case members made from higher strength steel using cold-forming processes. Examples of differential assemblies equipped with such two-piece differential cases are disclosed in U.S. Pat. Nos. 4,125,026; 6,045,479; 6,176,152; 6,945,898; and 7,261,664. In each of these configurations, the two case members of the differential case are initially connected together with a first weld seam and the ring gear is subsequently connected to the welded two-piece differential case using a second weld seam and/or bolts.
As a further advancement, efforts have been directed to development of differential assemblies configured to utilize a single weld seam to interconnect the two-piece differential case and the ring gear. For example, U.S. Publication No. US2009/0266198 and U.S. Pat. No. 8,444,522 each disclose a differential assembly having a first case member disposed between a radial flange portion of a second case member and a radial flange portion of the ring gear, with the weld seam only interconnecting the ring gear to the radial flange portion of the second case member. As a further alternative, U.S. Publication No. US2012/0325047 discloses a differential assembly having an “integral” end cap and ring gear component that is welded to a one-piece differential case.
In view of the above, there remains a continuing need to develop further improvements to differential assemblies and, in particular, to two-piece differential case arrangements which overcome the shortcomings of conventional single-piece and two-piece differential case arrangement and provide improvements in weight savings, packaging space requirements and reduced assembly complexity.
This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its aspects and features. The description and specific examples disclosed in this summary are not intended to limit the scope of the inventive concepts disclosed herein.
It is an aspect of the present disclosure to provide a differential assembly of the type adapted for use in motor vehicle driveline applications and which is equipped with a two-piece differential case and a ring gear that are interconnected to each other along a common weldment junction via a single weld seam.
It is another aspect of the present disclose to provide a two-piece differential case for use with a differential assembly, the two-piece differential case being defined by a first case member and a second case member that are mechanically interconnected via an interlocking feature. The interlocking feature establishes a differential case weldment surface that is configured to be aligned with a ring gear weldment surface for establishing the common weldment junction therebetween.
In accordance with these and other aspects of the present disclosure, a differential assembly is provided which includes a two-piece differential case, a differential gearset disposed within a gearset chamber formed within the differential case, and a ring gear. The two-piece differential case includes a first case member having first locking elements and a second case member having second locking elements that are interdigitated with the first locking elements to provide a mechanical interconnection between the first and second case members and which together establish a differential case weldment surface. The ring gear includes a rim segment which surrounds the mechanically interconnected first and second case members and defines a ring gear weldment surface that is configured to be aligned with the differential case weldment surface. A single seam of weld material is provided between and along the aligned weldment surfaces for rigidly securing the ring gear to both case members of the differential case as well as for rigidly securing the first case member to the second case member.
The drawings described herein are for illustrative purposes only of selected embodiments and are not intended to limit the scope of the present disclosure. Accordingly, the inventive concepts associated with the present disclosure will be more readily understood by reference to the following description in combination with the accompanying drawings, where:
Common reference numerals are used through the several figures to identify corresponding components.
Example embodiments will now be described more fully with reference to the accompanying drawings. Each of the example embodiments is directed to a differential assembly. The example embodiments only are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
In general, the present disclosure is directed to one or more embodiments of a differential assembly of the type well suited for use in power transfer devices such as, for example, drive axles and transaxles, to transmit drive torque from the powertrain of a motor vehicle to a pair of ground-engaging wheels. The differential assemblies of the present disclosure each include a two-piece differential case, a differential gearset operably disposed between the differential case and a pair of axleshafts, and a ring gear adapted to be rigidly secured to the differential case. The two-piece differential case is configured to include first and second case members adapted to be mechanically interconnected via an interlocking arrangement in a manner to define a common differential case weldment surface. The ring gear is configured to engage an outer surface of at least one of the first and second case members and define a ring gear weldment surface that is adapted to be aligned with the differential case weldment surface. The ring gear is welded to the differential case by providing a weld seam along a weldment junction established by the aligned weldment surfaces. The specific interlocking arrangements disclosed herein each include a plurality of first locking elements formed on the first case member that are configured to be alternatively interleaved or interdigitated with a plurality of second locking elements formed on the second case member.
With particular reference to
First case member 18 is configured, in this non-limiting example, to include a larger diameter first cylindrical segment 26, a smaller diameter second cylindrical segment 28, and a semi-spherical segment 30 interconnecting first and second cylindrical segments 26 and 28. A first open end surface 32 is associated with first cylindrical segment 26 while a second open end surface 34 is associated with second cylindrical segment 28. First case member 18 is configured to define a portion of the gearset chamber including a pinion chamber 38 within first cylindrical segment 26, a first side gear chamber 40 within semi-spherical segment 30, and a first axleshaft chamber 42 within second cylindrical segment 28.
Second case member 20 is configured, in this non-limiting example, to include a semi-spherical segment 50 and a cylindrical segment 52. A first open end surface 54 is associated with semi-spherical segment 50 while a second open end surface 56 is associated with cylindrical segment 52. Second case member 20 also defines a portion of the gearset chamber including a second side gear chamber 58 formed within semi-spherical segment 50 and a second axleshaft chamber 60 formed within cylindrical segment 52. Cylindrical segment 28 of first case member 18 and cylindrical segment 52 of second case member 20 define a pair of laterally-spaced hub segments on which bearing assemblies (not shown) are mounted for supporting two-piece differential case 20 for rotation within an axle housing (not shown) in a manner known in the art.
Mechanical interlocking feature 22 is shown, in this first non-limiting embodiment, to include a plurality of axially-extending and circumferentially-spaced first locking elements, hereinafter referred to as fingers 64, and which extend outwardly from first open end surface 32 of first case member 18. A plurality of circumferentially-aligned first retention apertures, hereinafter referred to as slots 66, are also formed in first case member 18 between adjacent fingers 64. Interlocking feature 22 further includes a plurality of radially-extending and circumferentially-spaced second locking elements, hereinafter referred to as lugs 70, and which extend radially in a co-planar arrangement from first open end surface 54 of second case member 20. A plurality of circumferentially-aligned second retention apertures, hereinafter referred to as pockets 72, are also formed between adjacent lugs 70. As will be understood, each finger 64 is configured to be positioned within a corresponding one of pockets 72 while each lug 70 is concurrently configured to be positioned within a corresponding one of slots 66. In a preferred, but non-limiting embodiment of interlocking feature 22, terminal end surfaces 74 of fingers 64 are configured to be aligned with first face surfaces 76 of lugs 70 while second face surfaces 78 of lugs 70 are configured to be aligned with open end surface 32. Thus, upon mechanical interconnection, end surface 32 of first case member 18 is located in close proximity to end surface 54 of second case member 20. Additionally, the arcuate profile of the outer surface of axially-extending fingers 64 is configured to be aligned with the top edge surface of lugs 70 so as to define a continuous cylindrical interconnection between the interdigitated fingers 64 and lugs 70.
As best shown in
Ring gear 14 is shown, in this non-limiting example, to include a cylindrical rim segment 120, a toothed gear segment 122, and a radial web segment 124 interconnecting rim segment 120 to gear segment 122. As is known, gear segment 122 of ring gear 16 includes gear teeth 125 configured to be meshed with a pinion gear (in an axle system) or a final drive gear (in a transaxle system) to transmit drive torque to differential case 12. Rim segment 120 has an inner surface 126 configured to be press-fit onto an outer surface 128 of first cylindrical segment 26 of first case member 18. Rim segment 120 further includes a planar edge or face surface 130 defining a ring gear weldment surface. Ring gear weldment surface 130 is adapted to be aligned with a differential case weldment surface, shown best in
As will be understood, differential gearset 16 is initially assembled into differential case 12 and thereafter interlocking feature 22 is engaged to mechanically couple first and second case members 18 and 20. Following assembly of differential case 12, ring gear 16 is installed (i.e., press-fit) thereon and positioned for subsequent weld processing. It will also be understood that the specific number, location, and physical dimensions of the interdigitated locking elements associated with interlocking feature 22 can be varied from the non-limiting example shown to accommodate alternative configurations. The inventive concepts of the present disclosure provide an arrangement for establishing a continuous weldment junction allowing the three components to be welded to one another. Case members 18 and 20 can be formed via stamping, net forging, spin forging, cold forming or any other suitable forming technologies currently available for manufacturing differential case components.
Turning now to
Two-piece differential case 12′ includes first case member 18 and a second case member 20′ that has been slightly modified in comparison to second case member 20 to accommodate the alternative configuration associated with interlocking feature 22′. Second case member 20′ is still configured to include semi-spherical segment 50 and tubular segment 52 which again define second side gear chamber 58 and second axleshaft chamber 60, respectively. However, instead of having lugs 70 extending radially from first open end surface 54, second case member 20′ now includes a plurality of axially-extending and circumferentially-spaced second locking elements or lugs 70′ extending outwardly from end surface 54′. Additionally, a plurality of second retention apertures or pockets 72′ are formed between adjacent axial lugs 70′. Thus, interlocking feature 22′ is configured to include a series of axial fingers 64 extending from first case member 18 that are adapted for retention in pockets 72′ formed in second case member 20′ and a series of axial lugs 70′ extending from second case member 20′ that are adapted for retention in slots 66 formed in first case member 18. In a preferred, but non-limiting embodiment of interlocking feature 22′, terminal end surfaces 74 of fingers 64 are configured to engage end surface 54′ of second case member 20′ while terminal end surfaces 140 of lugs 70′ are configured to engage end surface 32 of first case member 18. Additionally, the arcuate profile of axial fingers 64 and axial lugs 70′ define a continuous cylindrical mechanical interconnection area between first case member 18 and second case member 20′. Line 132′ identifies a differential case weldment surface established by two-piece differential case 12′.
Similar to that previously described, following assembly of differential gearset 16 into two-piece differential case 12′, ring gear 16 is pressed onto outer surface 128 of first cylindrical segment 26 on first case member 18 until ring gear weldment surface 130 of rim segment 120 on ring gear 16 is aligned with differential case weldment surface 132′. Thereafter, a weld seam 134 of weld material is provided therebetween to establish the single and continuous weldment junction and interconnect the three components to one another.
As previously mentioned, being able to secure first and second case members 18 and 20, 20′ and ring gear 16 to one another by one continuous weld seam along the weldment junction provides for a number of advantages. Among these include reduced fabrication costs since minimal time is needed by fabricators and few tools are required to perform the welding operation. Further, material costs are reduced since the fastening components (i.e., bolts) used to secure prior art differential assemblies are not required. Additionally, since the weld seam takes up minimal space, differential assembly 10, 10′ has a reduced packaging volume and mass. Furthermore, because of the simple design of the overall assembly, differential case members 18 and 20, 20′ may be metal components formed of high strength steels using the latest stamping, net forging or spin forming processes, therefore providing increased strength of the differential assembly.
It should be appreciated that any type of welding method could be utilized along the weldment junction such as, but not limited to, laser, electronic beam, MIG (Metal in Gas) and TIG (Tungsten Inert Gas) welding. Other methods of fixedly connecting components could be used, e.g., brazing, soldering or high-strength adhesives. It should further be appreciated that the concepts described herein could be applied to open or closed style differential assemblies. Finally, it should also be pointed out that the specific configurations provided for the first and second case members of the differential cases disclosed herein are merely intended to be examples and any alternative configuration providing a mechanical interconnect and a pair of weldment surfaces alignable along a weldment junction are within the scope of the present disclosure.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varies in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of disclosure.
