Patent Publication Number: US-11655890-B2

Title: Axle system with a planetary support structure

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to U.S. Provisional Application No. 63/152,775, entitled “AXLE SYSTEM WITH A PLANETARY SUPPORT STRUCTURE”, and filed on Feb. 23, 2021. The entire contents of the above-listed application are hereby incorporated by reference for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an axle system with a planetary support that structurally grounds a ring gear in a planetary gearset. 
     BACKGROUND AND SUMMARY 
     Axle assemblies have incorporated gear reductions, such as planetary gearsets, that are attached to a differential to enhance drivetrain performance. In some designs, a gearbox housing may be profiled to directly ground the planetary gearset. Because the gearbox housing grounds the planetary assembly, the housing reacts the driving gear forces. The housing may therefore carry loads from the planetary assembly, which may demand additional gearbox housing reinforcement, in certain designs. 
     U.S. Pat. No. 9,777,816 B2 to Petersen et al. discloses an electric drive axle with a transmission and differential gearing unit. In the axle assembly, the electric motor is arranged coaxial to the differential gearing unit. The transmission includes a two-stage planetary gear reduction that is coupled to a spur gear differential. In the load stage, a ring gear is directly attached to the transmission&#39;s housing. 
     The inventors have recognized several drawbacks with Petersen&#39;s electric drive axle. For instance, attaching the ring gear directly to the gearbox housing may lengthen the axle&#39;s manufacturing duration due to the added complexity brought about by mounting the planetary gearset in the gearbox housing. Hence, previous gearbox designs have been encumbered by lengthy and convoluted manufacturing processes. Customer appeal of the axle may be reduced due to long manufacturing duration. Further, certain axle assemblies have been unable to achieve a relatively high gear ratio. Due to the lower gear ratio, the size and strength of the components upstream of the planetary gearset may be increased due to the higher torque transfer therethrough. 
     To address at least a portion of the abovementioned issues, the inventors have developed an axle system. The axle system includes, in one example, a gearbox housing that at least partially encloses a gearbox. The system further includes a planetary gearset rotationally coupled to an output of the gearbox. The planetary gearset is further positioned co-axial with an axle shaft in a differential. The planetary gearset includes a ring gear grounded by a planetary support that is coupled to the gearbox housing. In this way, the planetary gearset may be efficiently radially, axially, and rotationally supported using a reinforcement structure that is distinct from the gearbox housing. Consequently, the housing&#39;s structural complexity may be reduced, thereby simplifying manufacturing. Further, grounding the ring gear, allows the planetary gearset to achieve a comparatively high gear ratio, if wanted. The high gear ratio enables upstream components to be reduced in sized, if desired. This allows the size and weight of the axle system to be reduced thereby increasing the system&#39;s appeal and applicability. 
     Further, in one example, the planetary support includes a bridge section that extends between two opposing pillars which include central openings. The axle system further includes attachment devices that extend through the central openings of the two opposing pillars. Incorporating the bridge into the planetary support structure allows said structure to be strengthened while maintaining a relatively compact profile. 
     In yet another example, the gearbox housing may partially surround the differential. Shaping the housing in this manner allows the profile of the system to be further reduced and the packaging constraints imposed by the system on surrounding vehicle components to be reduced. 
     Still further in another example, the ring gear may be slip fit or splined into the planetary support. Both of these attachment techniques may simplify axle assembly, thereby increasing manufacturing efficiency. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is an illustration of a vehicle with an axle system. 
         FIG.  2    is a perspective view of a first example of an axle system with a planetary gear reduction that is grounded by a planetary support. 
         FIG.  3    is a first cross-sectional view of an axle system. 
         FIG.  4    is a second cross-sectional view of the axle system, depicted in  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION 
     An axle system with a planetary support that bolts or otherwise attaches to a gearbox housing is described herein. This planetary structure radially, axially, and rotationally supports a ring gear of a planetary reduction in a differential. By incorporating a fixed-ring planetary gearset into differential, a relatively high ratio can be achieved by the planetary gearset, if desired. This comparatively high gear ratio, allows upstream components to be downsized. The downsizing may result in a more space efficiency and lower cost axle assembly. Further, the planetary support serves to carry loads from the planetary reduction. Because of the support&#39;s load carrying capacity, the housing&#39;s structural complexity may be decreased, if wanted. In this way, the system&#39;s components may be tailored to meet anticipated loading in selected locations of the axle without unduly increasing the system&#39;s profile and weight, for instance. This in effect allows the system&#39;s structural features to be more granularly reinforced to decrease the chance of axle structural degradation. The planetary support structure may include a bridge that extends between two opposing columns. Bolts and/or other suitable attachment devices may extend through the columns, in one example. The bolts serve to attach the support to the gearbox housing which partially surrounds the differential. This allows the planetary support structure to be efficiently tied into the gearbox housing using a gearbox housing which is shaped to facilitate simplified installation of the structure, if so desired. 
       FIG.  1    schematically illustrates a vehicle with an axle system that efficiently incorporates a planetary gearset into a differential.  FIG.  2    shows a first example of an axle system with a planetary support structure that grounds a ring gear in a planetary assembly.  FIG.  3    shows a first cross-sectional view of the axle system with a differential and the planetary gearset that is space efficiently packaged and structurally reinforced.  FIG.  4    shows a second cross-sectional view of the axle system with the planetary gearset and the planetary support structure. 
       FIG.  1    shows a vehicle  100  with an axle system  102 . The vehicle  100  may be a light, medium, or heavy duty vehicle that may be designed for on-road and/or off-road travel. The axle system  102  may include an electric machine  104  such as an electric motor or an electric motor-generator, in one example. Additionally or alternatively, the axle system may include an internal combustion engine coupled to a gearbox  106 . Thus, in one example, the vehicle may be a battery electric vehicle (BEV) or a hybrid electric vehicle (HEV) that incorporates an electric motor and internal combustion engine. For instance, the vehicle may include another axle system with an internal combustion engine. Even further in other examples, the axle system  102  may be a non-steerable axle which, in certain cases, may be a solid beam axle, in vehicle where greater vehicle articulation, a relatively high load carrying capacity, and durability may be desired. However, axles with independent suspension systems have also been contemplated. 
     The electric machine  104  may include conventional components (e.g., a rotor, a stator, and the like) that electromagnetically interact to generate rotational energy and generate electrical energy, in some cases. The electric machine  104  may be a high voltage motor. For instance, the motor may be operated at a voltage equal to or greater than 24 Volts (V). For instance, the motor may be a 3-phase, 6-phase or 9-phase style motor. Nevertheless, numerous types of motors have been envisioned and may be selected based on vehicle performance targets, expected vehicle loads, gearbox range, and the like. The electric machine&#39;s rotational axis  108  is indicated for reference. Further, the electric machine  104  may be incorporated into the gearbox  106 , in one example. 
     An output shaft  110  of the electric machine  104  is further illustrated in  FIG.  1   . The output shaft  110  is attached to the gearbox  106  which is included in the axle system  102 . The gearbox  106  may be a shiftable gearbox with at least two selectable gears. However, other types of gearboxes have been contemplated, such as a fixed ratio gearbox or a continuously variable gearbox. 
     The gearbox  106  may include an input shaft  112  that is rotationally coupled to (e.g., splined, welded, fastened, press-fit, combinations thereof, and the like) the electric machine&#39;s output shaft  110 . The gearbox  106  may further include an output shaft  114 . In other instances, the gearbox may include a layshaft. The gearbox  106  is depicted with multiple selectable gear reductions  116 ,  118 . These gear reductions may be first stage gear reductions. However, other gearbox arrangements with the selectable gear reductions arranged in downstream locations have been contemplated. The gear reduction  116  includes a gear  120  on the input shaft  112  coupled to a gear  122  on an output shaft  114 . Likewise, the other selectable gear reduction  118  includes a gear  124  on the input shaft  112  coupled to a gear  126  on the output shaft  114 . As described herein gears which are coupled to one another include teeth meshing with each other to facilitate rotational energy transfer therebetween. Although two gear reductions are specifically illustrated in  FIG.  1   , the gearbox may include additional gear reductions if end-use design goals demand additional available gear ratios. 
     Rotational axes  128 ,  130  of the input and output shafts  112  and  114 , respectively are indicated for reference. Further, rotational axes  132  of axle shafts  134 ,  136 , discussed in greater detail herein are further provided for reference. As illustrated, the axes  128 ,  130  are radially offset from one another and offset from the axle shafts  134 ,  136 . Further, in one example, the rotational axis of the electric machine  104  and the input shaft  112  may be coaxial to decrease the longitudinal length of the system. In this way, the electric machine  104  may be space efficiently arranged in the system. Alternatively, the electric machine  104  may be arranged perpendicular to the input shaft, in certain vehicle systems. 
     The gearbox  106  may further include a shifting mechanism  138  designed to place the gear reductions  116 ,  118  in an activated state as well as a neutral state. In the activated state, power travels through the active gear reduction while the other gear reduction(s) remains inactive and power transfer through the other gear reduction does not occur. In this way, one of the selectable gear reductions may be placed in an active state. This shifting mechanism  138  may include a clutch (e.g., dog clutch, friction clutch, and the like), a shift fork, a piston, and the like to achieve the gear selection functionality. Further in one example, a power take-off (PTO) may be included in the gearbox at the end of the shaft  112 . 
     The gearbox  106  may include a parking mechanism  140  or parking brake system designed to lock-up the gearbox and prevent rotation of the gearbox&#39;s input and output shafts. The parking mechanism  140  may include a pawl, a gear, rods, cams, and the like that enable the mechanism to implement gearbox locking and unlocking functionality. 
     Another gear  142  on the output shaft  114  may be rotationally coupled to an output gear  143  of the gearbox  106 . However, alternate gearbox arrangements are possible. The output gear of the transmission may be arranged on the output shaft  114 , for instance. 
     The output gear  143  may be rotationally coupled to a planetary gearset  144 . Specifically, the output gear  143  may be coupled to a sun gear in the planetary assembly, in one example. Further, the planetary assembly&#39;s ring gear may be grounded by a planetary support and the carrier may be coupled to a case in a differential  145 . Further, the planetary gearset may be a simple planetary gearset that includes solely a ring gear, a plurality of planet gears, a carrier, and a sun gear. In this way, the planetary may achieve a relatively high gear ratio, in a compact arrangement. However, planetary gearsets with multiple ring gears, sets of planet gears, etc. have been envisioned, which may add manufacturing complexity to the system. 
     A planetary support  146  schematically depicted in  FIG.  1   , described in greater detail herein with regard to  FIGS.  2 - 4   , may be used to support (e.g., radially, axially, and rotationally support) the planetary gearset and specifically ground the ring gear. It will be understood that the planetary support includes greater structural complexity than is depicted in  FIG.  1    and is elaborated upon herein. The planetary support may be coupled to a gearbox housing  147 , schematically depicted in  FIG.  1   . In this way, the planetary support  146  may be tailored to react forces from the planetary assembly rather than the gearbox housing. Consequently, loads from the planetary gearset may be carried by the planetary support rather than the gearbox housing. As a result, the structural complexity of the gearbox housing may be reduced, if wanted. Further, the gearbox housing  147  may at least partially surround a portion of the gears, shafts, mechanisms, and the like in gearbox  106 . The gearbox housing  147  may also partially enclose the differential  145 . 
     The differential  145  is designed to allow speed differentiation between axle shafts  134 ,  136 , under some conditions. To that end, the differential  145  may include a case, spider gears, side gears, and the like, for example. Further, in certain examples, the differential may be a locking type or a limited slip type differential. However, the differential may be an open differential, in some instances, which may streamline manufacturing at the expense of traction, during some operating conditions, for instance. The axle shafts  134 ,  136  may be coupled to one or more drive wheels. 
     A control system  150  with a controller  152  may further be included in the vehicle  100  and/or axle system  102 . The controller  152  includes a processor  154  and memory  156 . The memory  156  may store instructions therein that when executed by the processor cause the controller  152  to perform the various methods, control strategies, etc., described herein. The processor  154  may include a microprocessor unit and/or other types of circuits. The memory  156  may include known data storage mediums such as random access memory, read only memory, keep alive memory, combinations thereof, etc. Further, the memory  156  may include non-transitory memory. 
     The controller  152  may receive vehicle data from sensors positioned in different locations in the vehicle  100  and/or axle system  102 . The sensors may include a motor speed sensor  160 , shaft speed sensors  162 , a parking mechanism sensor  164 , wheel speed sensors, and the like. 
     The controller  152  may send control commands to an actuator in the shifting mechanism  138  and in response the clutch may be engaged or disengaged to alter the system&#39;s operating gear ratio. The other controllable components in the transmissions system include the electric machine  104 , parking mechanism  140 , the differential in the case of a controllable locking type differential, and the like. These controllable components may function similarly with regard to receiving control commands and adjusting an output and/or state of a component responsive to receiving the command via an actuator. 
     The vehicle  100  may include an input device  170  (e.g., an accelerator pedal, a gear selector, a gear stick, a control-stick, buttons, combinations thereof, and the like). The input device  170 , responsive to operator input, may generate a gear shift request for transitioning between two of the available gears in the gearbox. Alternatively, the transmission system may automatically shift between two of the available gears responsive to changes in operator torque request, vehicle load, etc. 
     The shifting mechanism  138  may be commanded to selectively place the gear reduction  116  or the gear reduction  118  in the gearbox&#39;s power path. As such, the power path, in a first gear mode may travel through the input shaft  112 , the gear reduction  116 , the gear  142 , the gear  143 , the planetary gearset  144 , the differential  145 , and then the axle shafts  134 ,  136 . Conversely, the power path in second gear mode may first travel through the input shaft  112  and then to the gear reduction  118 , etc. In this way, gearbox adaptability may be increased and may enable the motor to be more efficiently operated, if wanted. 
     The active gear in the gearbox may be automatically determined based on vehicle operating conditions or selected by an operator through interaction with a gear selector. As such, the controller may determine whether or not shifting between the two gear modes is demanded. As such, the aforementioned shifting strategy may be carried out as instruction stored in memory  156  executable by the processor  154  in the controller. 
     An axis system is further provided in  FIG.  1    as well as  FIGS.  2 - 4    for reference. In one example, the z-axis may be parallel to a gravitational axis, the x-axis may be a lateral axis, and the y-axis may be a longitudinal axis. However, other orientations of the axes may be used, in other examples. 
       FIG.  2    shows a first example of an axle system  200 . The axle system  200  again includes a planetary gearset, schematically depicted at  202 . Although, the planetary gear set is schematically illustrated in  FIG.  2   , it will be appreciated that it is supported by a planetary support structure and may be coupled to a differential (e.g., a differential case). Further structural details of the planetary gear set and the support structure are expanded upon herein with regard to  FIGS.  3 - 4   . It will be appreciated that the axle system  200  shown in  FIG.  2    may share common structural and/or functional features with the axle system  102 , depicted in  FIG.  1    and vice versa. Redundant description is therefore omitted for concision.  FIG.  2    is approximately drawn to scale, although other relative dimensions may be used, in other embodiments. 
     The planetary gearset  202 , schematically depicted in  FIG.  2   , may include a sun gear  350  with a central opening through which one of the axle shafts may extend. The planetary gearset  202  may further include a carrier on which a plurality of planet gears rotate as well as a ring gear. 
     The axle system  200  includes a planetary support  210  coupled to and grounding the ring gear of the planetary gearset  202 . The planetary support  210  is shown including a bridge section  212  that extends between two opposing pillars  214 . For the purpose of structural reinforcement, a rib may extend across the bridge section  212  which curves away from the rotational axis of the planetary gearset  202 . The bridge&#39;s curvature allows the ring gear to be efficiently reinforced. The opposing pillars  214 ,  215  may be symmetrically arranged on a first and second side  220 ,  222  of the planetary support. Conceptually, the bridge may have a sombrero shape. 
     The planetary support  210  may further include recessed sections adjacent to the pillars  214 ,  215 . Because of the recessed section location, the weight and size of the support may be reduced without unduly impacting the load carrying capacity of the support. 
     Further, the pillars  214 ,  215  may each include flanges  224  on opposing ends of the respective pillar. Accordingly, bolt heads or other suitable attachment device heads may seat on one side of the pillars. Bolts  228  or other suitable attachment devices (e.g., pins, screws, and the like) may extend through openings in the pillars  214 ,  215 . Ribs, for the purpose of structural reinforcement, may extend lengthwise down the pillars. As depicted, the ribs may have a substantially constant thickness and/or widths along their length. However, ribs with varying thicknesses and/or widths along their length have been envisioned. 
     Further, in the illustrated example, the bolts  228  include a head on one side and a threaded section of the other side. The threaded section of the bolts may threadingly engage with openings in a gearbox housing  232 . To form an interface between the ring gear  308 , shown in  FIG.  3   , and the planetary support  210  splines, pins, bolts, welds, stakes, adhesive, an interference fit, combinations thereof, and the like may be utilized, which may simplify the system&#39;s assembly process. This interface  450  is schematically depicted in  FIG.  4   . The planetary support may further include recessed sections  233  positioned between an interior flange and the pillars  214 ,  215 . These recessed sections allow the support&#39;s weight to be reduced. 
     Continuing with  FIG.  2   , to achieve the abovementioned structural features, the planetary support  210  may be at least partially constructed via machining. However, other suitable manufacturing techniques for the planetary support have been contemplated. Specifically, in one example, the gearbox housing  232  may be constructed out of a cast metal while, the planetary support  210  may be constructed using another manufacturing process such as machining, in one example. In this way, the support may achieve a more accurate profile than the gearbox housing, to decrease tolerances in the support and decrease the likelihood of misalignment of the support with regard to planetary assembly and/or the housing. 
     The gearbox housing  232  may partially enclose a differential. Further, the gearbox housing  232  may be constructed out of a cast metal, to decrease manufacturing costs when compared to other manufacturing techniques such as machining. 
     The planetary reduction may further include a sun gear that acts as an input which is coupled to a gear on an output shaft of the gearbox. Even further, the planetary reduction may include a carrier rotationally coupled to a differential case. In this way, the planetary gear reduction may achieve a relatively high gear ratio, if wanted. 
     Cutting plane A-A′ corresponds to the cross-sectional view illustrated in  FIG.  3    and cutting plane B-B′ corresponds to the cross-sectional view illustrated in  FIG.  4   . 
       FIG.  3    depicts a first cross-sectional view of the axle system  200 . The gearbox&#39;s output gear  300  is illustrated along with the planetary gearset  202  and the differential  204 . A sun gear  350 , the carrier  304 , the planet gears  306 , and the ring gear  308  are further illustrated in FIG.  3 . The grounding of the ring gear is schematically illustrated. However, as previously discussed the ring gear may be grounded by the planetary support  210 , depicted in  FIG.  2   . 
     The ring gear  308  may be positioned axially between the output gear  300  and the differential case  352 . In this way, the axle system&#39;s compactness may be increased. However, alternate axle assembly layouts have been contemplated. Further, the output gear  300  may radially extend beyond and outer surface of the ring gear  308 . This allows the output gear to be profiled for attachment to the sun gear  350 . 
     The differential case  352 , axle shafts  316 , spider gears  310 , and side gears  312  are depicted in  FIG.  3   . The carrier  304  is shown coupled (e.g., directly coupled) to one side of the differential case  352 . In this way, the planetary assembly&#39;s output may be space efficiently attached to the differential case. Bearings  314  may be coupled to the case  352  and constrain rotation thereof. Axle shafts  316  may further be coupled to the side gears  312 , as previously discussed. Bearing  318  may be coupled to the sun gear  350  and one of the side gears  312  to allow the sun gear to independently rotate with regard to the side gear. Further, bearing  321  may be included in the axle system. The bearing  321  may be coupled to the sun gear  350  and the differential case  352  and allows independent rotation therebetween. The sun gear may function as a planetary input. To realize the planetary input functionality, the sun gear may include an extension  319  coupled (e.g., directly coupled) to the output gear  300 . The extension may axially traverse the length of the axle shaft away from the side gear. A bearing  320  (e.g., a needle bearing) may be provided between the axle shaft  316  and the sun gear  350  to allow rotation therebetween. The bearing  320  may enable a gap  323  between the axle shaft and the sun gear to be achieved to prevent unwanted interaction therebetween. 
     Bearing  322  may be coupled to the output gear  300  or the sun gear  350  to constrain rotation thereof. As described herein, a bearing, as described herein, may include races, roller elements (e.g., cylinders, balls, tapered cylinders, etc.), and the like to achieve the aforementioned functionality. 
       FIG.  4    shows a second cross-sectional view of the axle system  200  and specifically the planetary gearset  202 , the planetary support  210 , and the gearbox housing  232 . The bolts  228  are shown extending through openings  400  in the pillars  214 ,  215 . Further, the bolts may include threaded sections  402  at one end that threadingly engage threaded sections  404  in the gearbox housing  232 . Further, as illustrated in  FIG.  4   , the bolt heads  405  seat on flanges  224 . However, other suitable types of attachment devices or methods used to couple the support structure to the housing, may be used, in other examples. The face  451  of the housing  232  is shown contacting an inner surface  407  of the support  210 . In this way, the support may be efficiently attached to the gearbox housing. 
       FIG.  4    again shows the sun gear  350 , the planet gears  306  on the carrier  304 , and the ring gear  308 . The ring gear  308  may be press fit into an opening  406  in the planetary support  210 , in one example. Alternatively, an outer surface  408  of the ring gear  308  may be splined and mate with an inner surface  410  of the planetary support  210 . Additionally or alternatively, the ring gear may be coupled to the planetary support via welds, pins, bolts, combinations thereof, and the like. Thus, a splined or press fit interface may be formed between the planetary support and the ring gear. Using splines or an interference fit between the ring gear and the support may allow the manufacturing efficiency of the axle assembly to be increased. The inner surface of the planetary support may be machined to efficiently achieve a desired interference fit between the ring gear and the support. However, this interference fit may be achieved via other suitable manufacturing techniques. 
       FIGS.  1 - 4    show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Additionally, elements co-axial with one another may be referred to as such, in one example. Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example. In other examples, elements offset from one another may be referred to as such. 
     The invention will be further described in the following paragraphs. In one aspect, an axle system is provided that comprises: a gearbox housing at least partially enclosing a gearbox; and a planetary gearset rotationally coupled to an output of the gearbox and positioned co-axial with a rotational axis of an axle shaft in a differential, wherein the planetary gearset comprises: a ring gear grounded by a planetary support; wherein the planetary support is coupled to the gearbox housing. 
     In another aspect, an electric axle system is provided that comprises: a gearbox housing at least partially enclosing a shiftable gearbox; and a planetary gearset rotationally coupled to an output of the gearbox and positioned co-axial with a rotational axis of an axle shaft in a differential, wherein the planetary gearset comprises: a ring gear grounded by a planetary support; wherein the planetary support is coupled to the gearbox housing via a plurality of attachment devices. 
     In any of the aspects or combinations of the aspects, the planetary support may include a bridge section that extends between two opposing pillars that include central openings and wherein the axle system further comprises attachment devices that extend through the central openings of the two opposing pillars. 
     In any of the aspects or combinations of the aspects, the ring gear may form an interference fit with the planetary support. 
     In any of the aspects or combinations of the aspects, the axle system may further comprise a splined interface formed between an outer surface of the ring gear and an interior surface of the planetary support. 
     In any of the aspects or combinations of the aspects, the gearbox housing may partially surround the differential. 
     In any of the aspects or combinations of the aspects, the gearbox housing may be constructed out of a cast metal. 
     In any of the aspects or combinations of the aspects, the gearbox may comprise: an input shaft rotationally coupled to an electric machine output; and an output shaft rotationally coupled to the ring gear. 
     In any of the aspects or combinations of the aspects, a rotational axis of the differential, a rotational axis of the electric machine, and rotational axes of the input shaft and the output shaft in the gearbox may be arranged parallel to one another. 
     In any of the aspects or combinations of the aspects, wherein the gearbox may comprise: a parking mechanism coupled to the output shaft; and a shifting mechanism activating a first gear reduction and a second gear reduction during different operating conditions. 
     In any of the aspects or combinations of the aspects, the electric machine may be an electric motor-generator. 
     In any of the aspects or combinations of the aspects, the output of the gearbox may be a gear coupled to an output shaft. 
     In any of the aspects or combinations of the aspects, the planetary gearset may be a simple planetary gearset that includes a sun gear coupled to an output gear of the gearbox. 
     In any of the aspects or combinations of the aspects, the planetary support may include two opposing pillars that include central openings and wherein the plurality of attachment devices extend through the central openings. 
     In any of the aspects or combinations of the aspects, the shiftable gearbox may include at least two selectable gear reductions and a shifting mechanism placing the shiftable gearbox in the two selectable gear reductions during different operating conditions. 
     In any of the aspects or combinations of the aspects, the shiftable gearbox may comprise: an input shaft rotationally coupled to an electric machine output; an output shaft rotationally coupled to the ring gear; and a parking mechanism coupled to the output shaft. 
     In any of the aspects or combinations of the aspects, the gearbox housing may partially surround the differential and wherein the gearbox housing is constructed out of a cast metal. 
     In any of the aspects or combinations of the aspects, the planetary gearset may be a simple planetary gearset with a sun gear coupled to a gearbox output and a carrier coupled to a case in the differential. 
     In any of the aspects or combinations of the aspects, the plurality of attachment devices may include two bolts positioned on opposing sides of the planetary gearset. 
     In any of the aspects or combinations of the aspects, the planetary support may include a curved bridge section that extends away from a face of the gearbox housing and wherein the gearbox housing may partially surround the differential. 
     In any of the aspects or combinations of the aspects, the ring gear may be coupled to the planetary support via one or more of an interference fit, a weld, a stake, a pin, and a bolt. 
     In another representation, an electric drive axle is provided. The electric drive axle comprises a simple planetary gearset with a ring gear directly coupled to and radially, axially, and rotationally supported by a planetary reinforcement structure with an arced section that is coupled to the ring gear via a press fit or splined interface. The simple planetary gearset further includes a carrier directly coupled to a case of a differential. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms without departing from the spirit of the subject matter. The embodiments described above are therefore to be considered in all respects as illustrative, not restrictive. 
     Note that the example control and estimation routines included herein can be used with various axle system and/or vehicle configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other axle system and/or vehicle hardware. Further, portions of the methods may be physical actions taken in the real world to change a state of a device. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example examples described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the vehicle and/or transmission control system, where the described actions are carried out by executing the instructions in a system including the various hardware components in combination with the electronic controller. One or more of the method steps described herein may be omitted if desired. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific examples are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to powertrains that include different types of propulsion sources including different types of electric machines, internal combustion engines, and/or transmissions. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure. 
     As used herein, the term “approximately” is construed to mean plus or minus five percent of the range, unless otherwise specified.