Patent Publication Number: US-2020300348-A1

Title: Differential overmolded ring gear

Description:
FIELD OF INVENTION 
     The present invention relates to a differential assembly. In particular, the present invention relates to an overmolded ring gear for a differential assembly configuration suitable for a wide variety of applications including, but not limited to, a differential for an automobile. 
     BACKGROUND 
     A differential is part of a power train of a vehicle that allows an engine to transmit torque and rotation to wheels. The differential allows an outer drive wheel to rotate at a different rate than an inner drive wheel when the vehicle turns. It includes gears or a gear train that are driven by an input shaft to drive output shafts connected to the gears. 
     A drive shaft connects to a pinion, and the pinion drives a ring gear of the differential. The ring gear is attached to a differential case or housing and may include teeth for driving other gears or pinions. Traditionally, bolts connect the ring gear with a differential case to prevent movement of the ring gear with respect to the differential case. In other examples, ring gears may be welded or brazed to the differential case. 
     Welding or brazing traditionally puts limitations on the number and type of materials that can be used. Bolts and other fasteners add weight and complexity to assembly. Further, these methods require additional parts, materials, steps, and the like. 
     SUMMARY 
     The following presents a summary of this disclosure to provide a basic understanding of some aspects. This summary is intended to neither identify key or critical elements nor define any limitations of embodiments or claims. Furthermore, this summary may provide a simplified overview of some aspects that may be described in greater detail in other portions of this disclosure. 
     A differential assembly may include a ring gear and a case. The ring gear may comprise a ferrous material and the case may comprise a non-ferrous material. The ring gear may comprise curved teeth operatively engaging with pinions or gears of a drive train. The ring gear may be overmolded with the case. The non-ferrous case may reduce weight while meeting operable standards for strength and resilience. 
     A method of manufacturing a differential assembly may allow for coupling a case with a ring gear without the need for fasteners. The method may include forming a ring gear from a ferrous material. The ring gear may be overmolded with a non-ferrous case. Teeth may be formed in the ring gear. The teeth may be hardened via a localized heating process. The method may further include machining the case and ring gear after joining the ring gear and the case. 
     The following description and the drawings disclose various illustrative aspects. Some improvements and novel aspects may be expressly identified, while others may be apparent from the description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate various systems, apparatuses, devices and related methods, in which like reference characters refer to like parts throughout, and in which: 
         FIG. 1  illustrates a side view of a differential assembly comprising a ring gear joined with a case in accordance with embodiments disclosed herein; 
         FIG. 2  is a side, cross-sectional view of the differential assembly of  FIG. 1  in accordance with embodiments disclosed herein; 
         FIG. 3A  is a front view of a ring gear for a differential assembly comprising protrusions in accordance with embodiments disclosed herein; 
         FIG. 3B  is a cross-sectional view of the ring gear of  FIG. 3A  taken along line BB in accordance with embodiments disclosed herein; 
         FIG. 4  illustrates a side, cross-sectional view of the ring gear of  FIG. 3A  taken along line AA in accordance with embodiments disclosed herein; 
         FIG. 5  illustrates a side, cross-sectional view of a ring gear comprising a plurality protrusion from an inner surface in accordance with embodiments disclosed herein; 
         FIG. 6  illustrates a side, cross-sectional view of a ring gear comprising a plurality of protrusion from an inner surface in accordance with embodiments disclosed herein; 
         FIG. 7  illustrates a side, cross-sectional view of a ring gear comprising a roughened inner surface in accordance with embodiments disclosed herein; 
         FIG. 8  illustrates a front view of a ring gear comprising a plurality protrusion extending from an inner surface in accordance with embodiments disclosed herein; 
         FIG. 9  illustrates a front view of a ring gear comprising a plurality apertures formed through an inner surface of the ring in accordance with embodiments disclosed herein; 
         FIG. 10  illustrates a front view of a ring gear comprising a plurality circular apertures formed through an inner surface of the ring in accordance with embodiments disclosed herein; 
         FIG. 11  illustrates a front view of a ring gear comprising a plurality grooves formed through an inner surface of the ring in accordance with embodiments disclosed herein; 
         FIG. 12  is a front view of the differential assembly of  FIG. 1  in accordance with embodiments disclosed herein; 
         FIG. 13  is a front, cross-sectional view of the differential assembly of  FIG. 1  in accordance with embodiments disclosed herein; and 
         FIG. 14  illustrates an exemplary method of manufacturing a differential in accordance with embodiments disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to exemplary embodiments, examples of which are illustrated in the accompanying drawings. It is to be understood that other embodiments may be utilized, and structural and functional changes may be made. Moreover, features of the various embodiments may be combined or altered. As such, the following description is presented by way of illustration only and should not limit in any way the various alternatives and modifications that may be made to the illustrated embodiments. In this disclosure, numerous specific details provide a thorough understanding of the subject disclosure. It should be understood that aspects of this disclosure may be practiced with other embodiments not necessarily including all aspects described herein, etc. 
     As used herein, the words “example” and “exemplary” mean an instance, or illustration. The words “example” or “exemplary” do not indicate a key or preferred aspect or embodiment. The word “or” is intended to be inclusive rather than exclusive, unless context suggests otherwise. As an example, the phrase “A employs B or C,” includes any inclusive permutation (e.g., A employs B; A employs C; or A employs both B and C). As another matter, the articles “a” and “an” are generally intended to mean “one or more” unless context suggest otherwise. 
     While embodiments and examples describe a differential for a vehicle, it is noted that the systems, apparatuses, and methods described herein may be applied to a variety of applications, including automobiles, aircrafts, personal transport systems (e.g., motorized scooters), or the like. As such, references to a vehicle are used as exemplary embodiments for purposes of explanation and clarity. It is noted that the present teachings may not be limited to such examples. 
     A differential generally includes a housing or case, and a number of gears, pinions, and the like. The gears and pinions may be referred to as a gear set. This gear set may allow for operation of wheels of a vehicle at different speeds. For example, when a vehicle turns, a first or inner wheel (e.g., the wheel at the inner curve of the turn) may be driven at a lower speed than a second or outer wheel. This may result in increased control of the vehicle in comparison to vehicles that do not include a differential. 
     In some systems, such as automotive systems, the components of the differential may be subject to forces that require the components to have a certain or defined strength. For instance, automobiles (e.g., cars, trucks, farm equipment, etc.) may require components to be formed of ferrous materials (e.g., iron, cast iron, steel, etc.). In some applications, one or more components of the differential may not need to have the strength of such ferrous materials. One such application, may allow a differential housing to be made of a lighter weight material such as aluminum, magnesium, copper, lead, nickel, tin, titanium, zinc, alloys, or the like. Such materials may not have the same strength as ferrous materials, but may be lighter weight, cheaper, and/or more than sufficient for certain applications. 
     As an example, as consumers become more conscious of fuel saving automobiles, vehicle weight becomes more important. Moreover, lighter weight vehicles may place a reduced amount of stress on a differential in comparison with heavier, traditional vehicles. For these and other reasons, components of a differential may be made of lighter weight materials than conventionally called for. In another aspect, disclosed apparatuses and methods may reduce production steps, costs, and/or reduce the number of components of the differential. 
     In at least one embodiment, a differential case may comprise a castable metal that is cast within and/or about a portion of a ring gear. The ring gear may comprise steel or another ferrous metal having a desired strength for driving pinions and/or wheel axles. The ring gear may be formed as a substantially circular ring, having an internal or inner surface. The ring gear may be placed in a mold. Material may be deposited into the mold to form the case so that the case directly contacts the internal surface of the ring gear. This may bond or join the ring gear directly with the case. It is noted that the ring gear may or may not have teeth formed thereon during the casting process. For instance, if the teeth are formed prior to casting, care should be taken so that the teeth are not damaged or deformed during the casting process. In other examples, the teeth may be formed after casting. When formed after casting, the teeth may be subsequently hardened, such as through an induction hardening process. 
     In an induction hardening process, the teeth may be selectively heated by induction heating and then quenched. The quenched teeth undergo a martensitic transformation that may harden the teeth. It is noted that other areas or components of the differential (e.g., the case) may be generally not affected by the induction heating. In an example, a method may include placing teeth comprising conductive material into a sufficiently strong alternating magnetic field. Current may flow through the material to create heat. It is noted that the depth of the hardening process may be controlled by properties associated with the induction, such as the frequency of the alternating field, the surface power density, the permeability of the material, the heat time and the diameter of the material, or material thickness. In another aspect, quenching the heated teeth may include applying water, oil, or a polymer based quench to alter the teeth and form a martensitic structure. 
     It is noted that the teeth may be formed prior to casting and may be protected by a protective member or otherwise protected. For instance, a shield member may mate with the teeth of the ring gear to protect the teeth during casting. In another example, casting may be accomplished without placing pressure on the teeth, or otherwise exposing the teeth to harmful contact with casting equipment or other potentially damaging materials. 
     Turning now to the figures,  FIGS. 1, 2, and 12-13  illustrate an exemplary ring gear  110  and case  140  of a differential apparatus  100 .  FIG. 1  is a side view of the differential apparatus  100  with line QQ, and  FIG. 13  is a cross-sectional view taken along line QQ.  FIG. 12  is a front view of the differential apparatus  100  showing line PP, and  FIG. 2  is a cross-sectional view taken along line PP. It is noted that the differential apparatus  100  may include various other components and/or dimensions in accordance with various disclosed aspects. In an example, the differential apparatus  100  may be utilized in a vehicle as described herein. 
     According to embodiments, the ring gear  110  and the case  140  may comprise disparate materials that may comprise different properties. For instance, the ring gear  110  may comprise ferrous materials and the case  140  may comprise non-ferrous materials. The non-ferrous material may allow for reduced weight in comparison with a ferrous case. It is noted that the non-ferrous case  140  may be removably or irremovably attached to the ferrous ring gear  110 . For instance, the non-ferrous case may be attached via one or more fasteners, a press-fit, friction-fit or self-broaching process, and/or over-molding or casting process. In an exemplary embodiment, the ring gear  110  may be at least partially formed and then may be placed into a mold or die-cast. The case  140  may then be molded or cast into the mold, such that the case  140  is overmolded with the ring gear  110 . This may reduce assembling cost, weight, required components (e.g., fasteners), increase efficiency of assembly processors, or the like. 
     It is noted that the casting process may account for the differences in the properties of the ferrous and non-ferrous materials. Such properties may include the coefficient of thermal expansion for the different materials. For instance, the non-ferrous case  140  and the ferrous ring gear  110  may have coefficient of thermal expansion mismatch. The non-ferrous case  140  and the ring gear  110  may be subject to a relatively broad range of temperatures due to the typical uses of automobiles in cold and hot environments. The mismatch may mean that the fractional change in size per degree change in temperature between the ring gear  110  and non-ferrous case  140  differ. It is noted that alloys may be selected that match more closely such that the ferrous and non-ferrous materials have a lesser difference in the coefficient of thermal expansion mismatch. 
     In an example, the case  140  may comprise aluminum or an aluminum alloy. Aluminum has a relatively high coefficient of thermal expansion relative to other metals, such as steel. Thus, a ring gear  110  comprising steel and a case  140  comprising aluminum may have a large mismatch. This mismatch may lead to bending, stress, and/or fracture of joint  120 . Embodiments described herein may reduce or alleviate bending, stress, or fracturing. For instance, joint  120  may comprise one or more coatings or layers of materials disposed between the case  140  and the ring gear  110 . The coating may include a material selected to alleviate thermal stress at one or more ranges of temperatures. This may be achieved by gradually transitioning mismatch from steel to aluminum (or from other ferrous materials to non-ferrous materials) through layers of intermediate materials. In another example, the casting and/or joining process may be selected based on the type of materials utilized for one or more of the case  140  and/or gear  110 . For instance, magnesium and steel may be joined utilizing a hot chamber process, and where the case  140  is aluminum or an aluminum alloy, a cold chamber process. 
     Turning to  FIGS. 3A-4 , ring gear  310  is depicted.  FIG. 4  depicts a cross-section of ring gear  110  along line AA. Ring gear  310  may comprise an inner surface comprising geometric formations that may alter properties, e.g., increased strength, decreased breakage, etc., of a joint with a case, such as joint  120  of  FIG. 1 . It is noted that ring gear  310  may comprise similar aspects as ring gear  110 . 
     Ring gear  310  may comprise a body  312  that may comprise a non-ferrous material. The body  312  may include a first side  314 , a second side  316 , an inner surface  318  and an outer surface  322 . The first side  314  may generally face towards a main body of a case, such as similarly shown in  FIG. 1 —first side  114  of ring gear  110  faces towards a main body  142  of case  140 . Likewise, the second side  316  may be generally opposed to the first side  314 . The inner surface  318  may operatively abut a case, such as similarly shown in  FIG. 1 —inner surface  118  abuts case  140 . In an aspect, the inner surface  318  may comprise or may form a portion of a joint (e.g., joint  120 ) when attached to a case. 
     Inner surface  318  may further include one or more protrusions or nodes  324  that may form a geometric feature. Each node  324  may allow molten material of a case to interlock and permanently affix the ring gear  310  to the case. The node  324  may provide increased surface area, an anchor, or the like for a joint between the ring gear  310  and a differential case. In another aspect, the nodes  324  may prevent or reduce slippage between ring gear  310  and a case (e.g., case  140 ) when assembled. It is noted that ring gears comprising various other geometric features are considered in the scope and spirit of this disclosure. Such features may include protrusions, cavities, channels, roughened or scored surfaces, and the like. 
     It is noted that ring gear  310  may comprise i nodes, where i is a number. In  FIG. 3A , ring gear  310  comprises eight nodes. Nodes  324  may be separated by ridges  332 . Each node may comprise similar dimensions and may be spaced evenly about the inner surface  318 . Nodes  324  may comprise rounded corners  326 . Rounded corners  326  may reduce stress on portions of the ring gear  310  or a case in comparison with squared corners. In some embodiments, ring gear  310  may comprise nodes having different shapes, non-evenly spaced nodes, nodes with squared corners, or the like. 
     Each node  324  may comprise formations on its surface. For instance, node  324  may comprise one or more reliefs  328  and  329 . As shown, relief  328  may face towards second side  216 , and relief  329  may face towards first side  314 . The reliefs  328  and  329  may comprise areas relieved of material (e.g., dimples, groves, etc.). This may alter the bonding of ring gear  310  with a case. For instance, during casting of a case, material may flow into the reliefs  328  and  329 . This may create a more efficient bond between the ring gear  310  and a case (e.g., case  140 ).  FIG. 3B  shows a cross-sectional view of ring gear  310  taken at line BB. It is noted that reliefs  328  and  329  may comprise other shapes, such as grooves that extend across the nodes  324 . 
       FIG. 4  illustrates a cross-sectional view of ring gear  310  taken at line AA. Ridge  332  may extend a first distance  342  from inner surface  318  and node  344  may extend a second distance  344  from inner surface  318 . In an aspect, first distance  342  may be generally less than second distance  344 . While each node  324  are illustrated as extending generally the same distance from inner surface  318 , it is noted that nodes may extend at different distance relative each other. Similarly, while each ridge  332  are illustrated as extending generally the same distance from inner surface  318 , it is noted that ridges may extend at different distance relative each other. Moreover, while corners  334  and  336  are shown as generally rounded, it is noted that corners  334  and  336  may be tapered, squared, or the like. 
     Turning back now to  FIGS. 1 and 2 , ring gear  110  may be formed or pre-manufactured without teeth. This may prevent damage to teeth during casting of the case  140 . Thus, after the case  140  is cast and joined to the ring gear  110 , the teeth (not shown) may be formed in the body  120  of ring gear  110 . For example, the teeth may comprise curved grooves formed in body  120  and proximal first side  114 . These teeth may interact with pinions or gears that may drive an axle of a vehicle. 
     In at least one embodiment, the teeth may be hardened after they are formed or machined. In an aspect, the ferrous ring gear  110  and the non-ferrous case  140  may be subjected to coefficient of thermal expansion mismatch. Because of this mismatch, some hardening techniques would weaken and/or damage joint  120 . As such, localized hardening techniques may be utilized to harden the teeth. For instance, induction hardening may target the teeth with localized heat treatment. This will localize the heat or hardening process such that the case  140  and/or joint  120  maintain their integrated and desired properties. 
     It is noted that the case  140  and ring gear  110  may be further machined after being joined. For instance, case  140  may include one or more apertures  144 ,  146 ,  148 , and  150 . The apertures or features of the apertures may be machined after a casting process. It is further noted that the case  140  may be machined with various other geometric features. 
     The various described embodiments may allow for a reduction in assembly cost, reduction in weight, ability to utilize different materials (e.g., light-weight materials, heavier/stronger materials, etc.), reduced production steps, or the like. It is further noted that while embodiments describe a non-ferrous case, any desired castable material may be utilized. Such castable materials may include, for example, aluminum, magnesium, iron, alloys, or the like. In at least one example, the material is a non-ferrous material. In another aspect, ring gears may comprise non-ferrous materials, ferrous materials coated with non-ferrous materials, or the like. In another aspect, a non-ferrous case  140  may be press-fit with a ring gear comprising a splined inner surface in a self-breaching process. 
     In view of the subject matter described herein, methods that may be related to various embodiments may be better appreciated with reference to the flowchart of  FIG. 7 . While the method is shown and described as a series of blocks, it is noted that associated methods or processes are not limited by the order of the blocks. It is further noted that some blocks and corresponding actions may occur in different orders or concurrently with other blocks. Moreover, different blocks or actions may be utilized to implement the methods described hereinafter. Various actions may be completed by one or more of users, mechanical machines, automated assembly machines (e.g., including one or more processors or computing devices), or the like. 
     Turning to  FIGS. 5-7 , with reference to  FIGS. 1-2 , there are ring gears  510 ,  610 , and  710 , respectively. It is noted that each of the ring gears  110 ,  310 ,  510 ,  610 , and  710  may comprise similar aspects or features, unless context suggests otherwise. For example, each of the above referenced ring gears may comprise a ferrous material and may be configured to be received by a die-cast. A non-ferrous case (e.g., case  140 ) may then be attached to each of the ring gears as described herein. The ring gears  110 ,  310 ,  510 ,  610 , and  710  are provided to illustrate exemplary inner surfaces with geometric features. 
     For instance,  FIG. 5  illustrates ring gear  510  comprising a plurality of protrusions extending from inner surface  518 . The protrusions may include one or more vertical protrusions  526  and one or more horizontal protrusions  524 . The differently oriented protrusions may provide for altered (e.g., increased) strength of a joint for forces acting in different directions. 
     As another example,  FIG. 6  illustrates ring gear  610  comprising an inner surface  618  that may include a plurality of protrusions, such as ridges or ribs  624 . The ribs  624  may receive molten material of a case during a casting process. The material may cool and/or harden within the ribs  624  to form a joint. 
       FIG. 7  illustrates an exemplary embodiment of ring gear  710  having an inner surface  718  that may include roughened surface  724 . While inner surface  718  is shown as substantially covered by roughened surface  724 , it is noted that the inner surface  718  may include surface areas that are generally smooth and areas that are roughened to make a mosaic-like surface. 
     Turning to  FIGS. 8-11 , with reference to  FIGS. 1-2 , there are ring gears  810 ,  910 ,  1010 , and  1110 , respectively. It is noted that each of the ring gears  110 ,  310 ,  510 ,  610 ,  710 ,  810 ,  910 ,  1010 , and  1110  may comprise similar aspects or features, unless context suggests otherwise. For example, each of the above referenced ring gears may comprise a ferrous material and may be configured to be received by a die-cast. A non-ferrous case (e.g., case  140 ) may then be attached to each of the ring gears as described herein. Ring gears  810 ,  910 ,  1010 , and  1110  provide exemplary 
       FIG. 8  illustrates ring gear  810  comprising a plurality of protrusions or nodes  824  extending from an inner ring  836  disposed proximal inner surface  818 . The nodes  824  may be separated by cutouts  832 . When a case is casted, it may fill the cutouts  832  and interlock with nodes  824 . 
       FIG. 9  illustrates ring gear  910  comprising a plurality of cutouts  924  disposed within an inner ring  936 . The inner ring may extend from inner surface  918  of the ring gear  910 . When a case is casted, it may fill the cutouts  924  to interlock with the ring gear  910 . The cutouts  924  may comprise any desired shape, such as polygonal, rectangular, elliptical, irregular in shape, or the like. For instance,  FIG. 10  illustrates a ring gear  1010  comprising a plurality of generally circular cutouts  1024 . 
       FIG. 11  illustrates ring gear  1110  that may comprise depressions  1124  and  1132  formed in an inner ring  1136 . In an aspect, the depressions  1124  and  1132  may alternate sides of the inner ring  1136 . The depressions  1124  and  1132  may comprise any desired shape, such as polygonal, rectangular, elliptical, irregular in shape, or the like. When material is cast around the depressions  1124  and  1132  the material may fill the depressions  1124  and  1132 . This may allow a case to be cast into the ring gear  1110  and lockable secure thereto. 
     In view of the subject matter described herein, a method that may be related to various embodiments may be better appreciated with reference to the flowchart of  FIG. 14 . While method  1400  is shown and described as a series of blocks, it is noted that associated methods or processes are not limited by the order of the blocks. It is further noted that some blocks and corresponding actions may occur in different orders or concurrently with other blocks. Moreover, different blocks or actions may be utilized to implement the methods described hereinafter. Various actions may be completed by one or more of users, mechanical machines, automated assembly machines (e.g., including one or more processors or computing devices), or the like. 
       FIG. 14  is a flow chart of an exemplary method  1400  of manufacturing a differential as described herein. The method  1400  may be utilized to form a differential having a light-weight case and a heavier-weight or stronger ring gear. For example, the differential may comprise a ferrous ring gear and a non-ferrous case. 
     At  1402 , a manufacturer may manufacture a ring gear (e.g., ring gear  140 ,  340 , etc.) that does not comprise teeth. This ring gear may comprise a ferrous material that may or may not be subject to a hardening process. In an aspect, the ring gear may be pre-manufactured then provided to another party that may cast materials. 
     At  1404 , the ring gear may be positioned in a die-cast, such as a die-cast for a differential case. It is noted that positioning the ring gear may include other or additional steps, such as coating the die-cast, coating the ring gear, or the like. 
     At  1406 , the ring gear may be overmolded with molten material that will form a case of a differential. As described herein, the molten material may include non-ferrous material (e.g., aluminum, magnesium, and/or alloys thereof). It is noted that the molten material may be cooled, quenched, or otherwise allowed to cool. 
     In an example, as shown in  FIG. 13 , material  113  forming at least a portion of the case  140  may be deposited within a mold that has ring gear  110  positioned therein. The body  112  of the ring gear  110  may include nodes  124  and ridges  134 . As material  113  is cast, it may fill space around the nodes  124  and ridges  134 . 
     At  1408 , teeth may be formed in the ring gear. The teeth may comprise curved teeth appropriately shaped to drive pinions or gears of a differential system. In an aspect, the teeth may be machined into a portion of the ring gear by a precision machining system. 
     At  1410 , the teeth may be hardened so that they resist damage during operation. Hardening may include a localized hardening process, such as induction hardening. For example, inductive current may be directed in or through the teeth. This may heat the teeth without directly heating and/or substantially heating the case. 
     What has been described above includes examples of the present specification. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present specification, but one of ordinary skill in the art may recognize that many further combinations and permutations of the present specification are possible. Each of the components described above may be combined or added together in any permutation to define embodiments disclosed herein. Accordingly, the present specification is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.