Patent Publication Number: US-11648837-B2

Title: Axle assembly having a rotor bearing assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 17/227,620, filed Apr. 12, 2021, which is a continuation of U.S. application Ser. No. 16/733,070, filed Jan. 2, 2020, the disclosures of which are hereby incorporated in their entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to an axle assembly that may have one or more rotor bearing assemblies that may rotatably support a rotor on a drive pinion. 
     BACKGROUND 
     An axle assembly having an electric motor module is disclosed in U.S. Patent Publication No. 2019/0054816. 
     SUMMARY 
     In at least one embodiment, an axle assembly is provided. The axle assembly may include an electric motor module, a drive pinion, and a rotor bearing assembly. The electric motor module may have a rotor that may be rotatable about a first axis. The drive pinion may extend through the rotor and may be rotatable about the first axis. The rotor bearing assembly may rotatably support the rotor on the drive pinion. The rotor bearing assembly may extend from the drive pinion to the rotor. 
     In at least one embodiment, an axle assembly is provided. The axle assembly may include an electric motor module, a drive pinion, a rotor coupling, a gear reduction module, and a rotor bearing assembly. The electric motor module may have a rotor that may be rotatable about a first axis. The drive pinion may extend through the rotor and may be rotatable about the first axis. The rotor coupling may be received inside the rotor and may engage the rotor. The rotor coupling may be fixedly positioned with respect to the rotor. The gear reduction module may operatively connect the rotor coupling to the drive pinion. The rotor bearing assembly may rotatably support the rotor and the rotor coupling. The rotor bearing assembly may extend from the drive pinion to the rotor coupling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an axle assembly having an electric motor module and a gear reduction module. 
         FIG.  2    is a section view of the axle assembly along section line  2 - 2 . 
         FIG.  3    is a section view of another configuration of the axle assembly. 
         FIG.  4    is a section view of another configuration of the axle assembly. 
         FIGS.  5 - 7    show examples of how a rotor coupling may be coupled to a gear reduction module. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Referring to  FIG.  1   , an example of an axle assembly  10  is shown. The axle assembly  10  may be provided with a motor vehicle like a truck, bus, farm equipment, mining equipment, military transport or weaponry vehicle, or cargo loading equipment for land, air, or marine vessels. The motor vehicle may include a trailer for transporting cargo in one or more embodiments. The axle assembly  10  may provide torque to one or more traction wheel assemblies that may include a tire mounted on a wheel. The wheel may be mounted to a wheel hub that may be rotatable about an axis. 
     One or more axle assemblies may be provided with the vehicle. As is best shown with reference to  FIGS.  1  and  2   , the axle assembly  10  may include a housing assembly  20 , a drive pinion  22 , an electric motor module  24 , at least one rotor bearing assembly  26 , a gear reduction module  28 , a differential assembly  30 , and at least one axle shaft  32 . 
     Referring to  FIG.  1   , the housing assembly  20  may receive various components of the axle assembly  10 . In addition, the housing assembly  20  may facilitate mounting of the axle assembly  10  to the vehicle. In at least one configuration, the housing assembly  20  may include an axle housing  40  and a differential carrier  42 . In addition, the housing assembly  20  may include portions that may receive and/or facilitate mounting of the electric motor module  24 , the gear reduction module  28 , or both. 
     The axle housing  40  may receive and may support the axle shafts  32 . In at least one configuration, the axle housing  40  may include a center portion  50  and at least one arm portion  52 . 
     The center portion  50  may be disposed proximate the center of the axle housing  40 . The center portion  50  may define a cavity that may receive the differential assembly  30 . A lower region of the center portion  50  may at least partially define a sump portion that may contain a first lubricant. Splashed lubricant may flow down the sides of the center portion  50  and may flow over various internal components of the axle assembly  10  and gather in the sump portion. 
     One or more arm portions  52  may extend from the center portion  50 . For example, two arm portions  52  may extend in opposite directions from the center portion  50  and away from the differential assembly  30 . The arm portions  52  may have substantially similar configurations. For instance, the arm portions  52  may each have a hollow configuration or tubular configuration that may extend around and may receive a corresponding axle shaft  32  and may help separate or isolate the axle shaft  32  or a portion thereof from the surrounding environment. An arm portion  52  or a portion thereof may be integrally formed with the center portion  50 . Alternatively, an arm portion  52  may be separate from the center portion  50 . In such a configuration, each arm portion  52  may be attached to the center portion  50  in any suitable manner, such as by welding or with one or more fasteners. An arm portion may rotatably support an associated wheel hub. It is also contemplated that the arm portions  52  may be omitted. 
     Referring to  FIGS.  1  and  2   , the differential carrier  42 , which may also be called a carrier housing, may be mounted to the center portion  50  of the axle housing  40 . The differential carrier  42  may support the differential assembly  30 . In at least one configuration, the differential carrier  42  may facilitate mounting of the electric motor module  24 . 
     Referring to  FIG.  2   , the drive pinion  22  may provide torque to a ring gear that may be provided with the differential assembly  30 . Moreover, the drive pinion  22  may help operatively connect the gear reduction module  28  to the differential assembly  30 . The drive pinion  22  may extend along and may be rotatable about a first axis  60 . In addition, the drive pinion  22  may extend through a hole or opening in the differential carrier  42  and into the axle housing  40 . In at least one configuration, the drive pinion  22  may include a gear portion  70  and a shaft portion  72 . 
     The gear portion  70  may be disposed at or near an end of the shaft portion  72 . The gear portion  70  may have a plurality of teeth that may mate or mesh with corresponding teeth on the ring gear of the differential assembly  30 . The gear portion  70  may be integrally formed with the shaft portion  72  or may be provided as a separate component that may be fixedly disposed on the shaft portion  72 . 
     The shaft portion  72  may extend from the gear portion  70  in a direction that extends away from the axle housing  40 . The shaft portion  72  may extend along the first axis  60 . 
     The shaft portion  72  may be rotatably supported by one or more drive pinion bearings  80 . In the configuration shown, the shaft portion  72  is illustrated as being rotatably supported by a pair of drive pinion bearings  80 . For convenience in reference, the drive pinion bearing located closest to the gear portion  70  may be referred to as a first drive pinion bearing  80  while the drive pinion bearing located furthest from the gear portion  70  may be referred to as a second drive pinion bearing  80 . The drive pinion bearings  80  may have any suitable configuration. For example, a drive pinion bearing  80  may be configured as a roller bearing assembly that may include a plurality of bearing elements  82  that may be disposed between an inner race  84  and an outer race  86 . The inner race  84  may extend around and may be disposed on the shaft portion  72 . The outer race  86  may extend around the bearing elements  82  and may be disposed on the housing assembly  20  or may be fixedly positioned with respect to at least a portion of the housing assembly  20 . 
     Referring to  FIG.  2   , the electric motor module  24  may provide torque to the differential assembly  30  via the drive pinion  22  and the gear reduction module  28 . In at least one configuration, the electric motor module  24  may be mounted to the differential carrier  42  and may be axially positioned between the axle housing  40  and the gear reduction module  28 . The electric motor module  24  may include a stator  90  and a rotor  92 . 
     The stator  90  may be fixedly positioned with respect to the housing assembly  20 . For example, the stator  90  may extend around the first axis  60  and may not rotate about the first axis  60 . The stator  90  may include windings that may be electrically connected to an electrical power source, such as a battery, capacitor, or the like. An inverter may electrically connect the electric motor module  24  and the electrical power source. 
     The rotor  92  may be rotatable about the first axis  60  with respect to the differential carrier  42  and the stator  90 . For example, the rotor  92  may be spaced apart from the stator  90  but may be disposed close to the stator  90 . The rotor  92  may include magnets or ferromagnetic material that may facilitate the generation of electrical current. The rotor  92  may extend continuously around the drive pinion  22 . The drive pinion  22  may extend through the rotor  92 . 
     One or more rotor bearing assemblies  26  may rotatably support the rotor  92  on the drive pinion  22 . In the configuration shown, the rotor  92  is illustrated as being rotatably supported by a pair of rotor bearing assemblies  26 . For convenience in reference, the rotor bearing assembly located closest to the gear portion  70  of the drive pinion  22  may be referred to as a first rotor bearing assembly while the drive pinion bearing located furthest from the gear portion  70  may be referred to as a second rotor bearing assembly; however, it is contemplated that these designations may be reversed. 
     The rotor bearing assemblies  26  may be received inside the rotor  92  and may extend between the drive pinion  22  and the rotor  92 . The rotor bearing assemblies  26  may have any suitable configuration. For example, a rotor bearing assembly  26  may be configured as a roller bearing assembly that may include a plurality of bearing elements  100  that may be disposed between an inner race  102  and an outer race  104 . In at least one configuration, the bearing elements  100  may extend from the inner race  102  to the outer race  104 . The inner race  102  may extend around and may be disposed on the drive pinion  22 . For instance, the inner race  102  may extend around and may contact the shaft portion  72  of the drive pinion  22 . The outer race  104  may extend around the bearing elements  100  and the inner race  102 . The outer race  104  may be disposed on the rotor  92  or may be fixedly positioned with respect to the rotor  92 . For example, the outer race  104  may engage the rotor  92  or may contact the rotor  92 . It is also contemplated that the outer race  104  may be disposed on or may contact a rotor coupling as will be discussed in more detail below. The rotor bearing assemblies  26  may be spaced apart from the differential carrier  42 . For instance, the rotor bearing assemblies  26  may not receive, contact, or engage the differential carrier  42  or a bearing support wall that may extend from the differential carrier  42 . 
     In a configuration having first and second rotor bearing assemblies  26 ,  26 , a spacer  108  may be provided. The spacer  108  may be received inside the rotor coupling  110  and may help separate and inhibit axial movement of the first and second rotor bearing assemblies  26 ,  26 . For instance, one or more spacers  108  may extend from the inner race  102  of the first rotor bearing assembly  26  to the inner race  102  of the second rotor bearing assembly  26 , may extend from the outer race  104  of the first rotor bearing assembly  26  to the outer race  104  of the second rotor bearing assembly  26 , or both. 
     A rotor coupling  110  may operatively connect the rotor  92  to the gear reduction module  28 . For example, the rotor coupling  110  may extend from the rotor  92  or may be operatively connected to the rotor  92  such that the rotor  92  and the rotor coupling  110  may be rotatable together about the first axis  60 . The rotor coupling  110  may be fixedly coupled to the rotor  92  at or proximate a first end of the rotor coupling  110  and may be coupled to the gear reduction module  28  proximate a second end. In at least one configuration, the rotor coupling  110  may be configured as a hollow tube that may extend around the first axis  60  and may receive the shaft portion  72  of the drive pinion  22 . The first end of the rotor coupling may engage the outer race  104  of the second rotor bearing assembly  26  to inhibit axial movement of the second rotor bearing assembly  26  toward the gear reduction module  28 . The rotor coupling  110  may be fixedly coupled to the rotor  92  and may be fixedly coupled to a first gear of the gear reduction module  28  as will be discussed in more detail below. For instance, the rotor coupling  110  may extend from the rotor  92  to the first gear. The rotor coupling  110  may be spaced apart from the differential carrier  42 . For instance, the rotor coupling  110  may not receive, contact, or engage the differential carrier  42  or a bearing support wall that may extend from the differential carrier  42 . 
     Referring to  FIG.  2   , the gear reduction module  28  may transmit torque between the electric motor module  24  and the drive pinion  22 . 
     The gear reduction module  28  may be provided in various configurations, such as a planetary gear set configuration or a non-planetary gear set configuration. In  FIG.  2   , the gear reduction module  28  has a planetary gear set  120 . In such a configuration, the gear reduction module  28  may include a first gear  130 , at least one planet gear  132 , a planetary ring gear  134 , and a planet gear carrier  136 . 
     The first gear  130 , which may also be referred to as a sun gear, may be disposed proximate the center of the planetary gear set  120  and may be rotatable about the first axis  60 . In addition, the first gear  130  may be operatively connected to the rotor  92  as will be discussed in more detail below. In at least one configuration, the first gear  130  may be configured as a hollow tubular body that may include a first gear hole  140  and a gear portion. 
     The first gear hole  140  may be a through hole that may extend through the first gear  130 . The first gear hole  140  may extend along and may be centered about the first axis  60 . The drive pinion  22  may extend through the first gear hole  140  and may be spaced apart from the first gear  130 . 
     The gear portion may be disposed opposite the first gear hole  140  and may have teeth that may extend away from the first gear hole  140 . The teeth of the gear portion may mate or mesh with teeth of the planet gears  132 . 
     Optionally, a bearing  144  may be received in the first gear hole  140  that may rotatably support the first gear  130  on the shaft portion  72  of the drive pinion  22 . If provided, the bearing  144  may receive the shaft portion  72  and may extend from the shaft portion  72  to the first gear  130 . 
     One or more planet gears  132  may be rotatably disposed between the first gear  130  and the planetary ring gear  134 . Each planet gear  132  may have a hole and a set of teeth. The hole may extend at least partially through the planet gear  132 . The set of teeth may be disposed opposite the hole. The set of teeth may mesh with teeth of the gear portion of the first gear  130  and teeth on the planetary ring gear  134 . The teeth may have any suitable configuration. For instance, the teeth may have a helical configuration, but it is contemplated that other tooth configurations may be provided. Each planet gear  132  may be configured to rotate about a different planet gear axis of rotation  150 . A planet gear axis of rotation  150  may extend substantially parallel to the first axis  60 . 
     The planetary ring gear  134  may extend around the first axis  60  and may receive the planet gears  132 . The planetary ring gear  134  may include a set of planetary ring gear teeth that may extend toward the first axis  60  and may mesh with teeth on the planet gears  132 . The planetary ring gear  134  may be stationary with respect to the first axis  60 . For example, the planetary ring gear  134  may be received in and may be fixedly disposed on the housing assembly  20 . 
     The planet gear carrier  136  may be rotatable about the first axis  60  and may rotatably support the planet gears  132 . For instance, each planet gear  132  may be rotatably disposed on a corresponding pin, shaft, or linkage that may extend from the planet gear carrier  136 . In addition, the planet gear carrier  136  may be fixedly coupled to the drive pinion  22 . In at least one configuration, the planet gear carrier  136  may include a planet gear carrier hole  160  and a planet gear carrier coupling portion  162 . 
     The planet gear carrier hole  160  may be a through hole that may extend through planet gear carrier  136 . The planet gear carrier hole  160  may extend along and may be centered about the first axis  60 . The shaft portion  72  of the drive pinion  22  may be received in and may extend completely through the planet gear carrier hole  160 . 
     The planet gear carrier coupling portion  162  may facilitate coupling of the planet gear carrier  136  to the drive pinion  22  such that the drive pinion  22  and the planet gear carrier  136  are rotatable together about the first axis  60  and such that the drive pinion  22  and the planet gear carrier  136  may not be rotatable about the first axis  60  with respect to each other. The planet gear carrier coupling portion  162  may have any suitable configuration. For instance, the planet gear carrier coupling portion  162  may be configured as a spline, gear, or set of teeth that may mesh with a corresponding spline, gear or set of teeth on the drive pinion  22  to inhibit relative rotational movement of the drive pinion  22  and the planet gear carrier  136 . In such a configuration, the planet gear carrier coupling portion  162  may be completely or partially received in the planet gear carrier hole  160  and may have one or more teeth that may extend toward the first axis  60 . Alternatively, the planet gear carrier coupling portion  162  may be configured as a weld, fastener, or the like that may couple the drive pinion  22  to the planet gear carrier  136 . 
     As previously mentioned, the drive pinion bearing located closest to the gear portion  70  may be referred to as a first drive pinion bearing  80  while the drive pinion bearing located furthest from the gear portion  70  may be referred to as a second drive pinion bearing  80 . The rotor  92  and the planetary gear set  120  may be axially positioned between the first drive pinion bearing  80  and the second drive pinion bearing  80 . In  FIG.  2   , the planetary gear set  120  may be axially positioned between the rotor  92  and the second drive pinion bearing  80 . 
     Referring to  FIG.  2   , the differential assembly  30  may be at least partially received in the center portion  50  of the housing assembly  20 . The differential assembly  30  may transmit torque to the wheels and permit the wheels to rotate at different velocities. The differential assembly  30  may be operatively connected to the axle shafts  32  and may permit the axle shafts  32  to rotate at different rotational speeds in a manner known by those skilled in the art. The differential assembly  30  may have a ring gear  170  that may have teeth the mate or mesh with the teeth of the gear portion  70  of the drive pinion  22 . Accordingly, the differential assembly  30  may receive torque from the drive pinion  22  via the ring gear  170  and transmit torque to the axle shafts  32 . 
     Referring to  FIGS.  1  and  2   , the axle shafts  32  may transmit torque from the differential assembly  30  to corresponding wheel hubs and wheels. Two axle shafts  32  may be provided such that each axle shaft  32  extends through a different arm portion  52  of axle housing  40 . The axle shafts  32  may extend along and may be rotatable about a second axis  180 . Each axle shaft  32  may have a first end and a second end. The first end may be operatively connected to the differential assembly  30 . The second end may be disposed opposite the first end and may be operatively connected to a wheel. Optionally, gear reduction may be provided between an axle shaft  32  and a wheel. 
     Referring to  FIG.  3   , another example of an axle assembly is shown. The axle assembly in  FIG.  3    is similar to the axle assembly shown in  FIG.  2   , but the gear reduction module  28 ′ is configured as a countershaft transmission. More specifically, the gear reduction module  28 ′ may include a set of drive pinion gears  200 , a first countershaft subassembly  202 , and a second countershaft subassembly  202 ′. 
     The set of drive pinion gears  200  may include a plurality of gears that may be selectively coupled to the drive pinion  22 . In the configuration shown, the set of drive pinion gears  200  includes a first gear  210 , a second gear  212 , and a third gear  214 ; however, it is to be understood that a greater or lesser number of gears may be provided. A member of the set of drive pinion gears  200  may be rotatable about the first axis  60  with the drive pinion  22  when that gear is coupled to the drive pinion  22 . Conversely, the drive pinion  22  may be rotatable about the first axis  60  with respect to a member of the set of drive pinion gears  200  that is decoupled from or not coupled to the drive pinion  22 . A member of the set of drive pinion gears  200  may be selectively coupled to the drive pinion  22  in any suitable manner, such as with a clutch as will be discussed in more detail below. In at least one configuration, no more than one gear of the set of drive pinion gears  200  may be coupled to the drive pinion  22  at the same time when the drive pinion  22  rotates about the first axis  60 . 
     The first gear  210  may receive the shaft portion  72  of the drive pinion  22 . For example, the first gear  210  may have a through hole through which the shaft portion  72  may extend. The first gear  210  may extend around the first axis  60  and the shaft portion  72  and may have a plurality of teeth that may be arranged around and may face away from the first axis  60 . The teeth of the first gear  210  may contact and may mate or mesh with teeth of a first countershaft gear that may be provided with the first countershaft subassembly  202  and the second countershaft subassembly  202 ′ as will be discussed in more detail below. The first gear  210  may be operatively connected to the rotor  92  of the electric motor module  24  such that the rotor  92  and the first gear  210  are rotatable together about the first axis  60 . For example, the first gear  210  may be fixedly positioned with respect to the rotor  92  or fixedly coupled to the rotor  92  such that the first gear  210  does not rotate about the first axis  60  with respect to the rotor  92 . In at least one configuration, the first gear  210  may be axially positioned along the first axis  60  between the second gear  212  and the electric motor module  24 . 
     The second gear  212  may receive the shaft portion  72  of the drive pinion  22 . For example, the second gear  212  may have a through hole through which the shaft portion  72  may extend. The second gear  212  may extend around the first axis  60  and the shaft portion  72  and may have a plurality of teeth that may be arranged around and may face away from the first axis  60 . The teeth of the second gear  212  may contact and may mate or mesh with teeth of a second countershaft gear that may be provided with the first countershaft subassembly  202  and the second countershaft subassembly  202 ′ as will be discussed in more detail below. The second gear  212  may have a different diameter than the first gear  210  and the third gear  214 . For example, the second gear  212  may have a larger diameter than the first gear  210  and a smaller diameter than the third gear  214 . In at least one configuration, the second gear  212  may be axially positioned along the first axis  60  between the first gear  210  and the third gear  214 . 
     The third gear  214  may receive the shaft portion  72  of the drive pinion  22 . For example, the third gear  214  may have a through hole through which the shaft portion  72  may extend. The third gear  214  may extend around the first axis  60  and the shaft portion  72  and may have a plurality of teeth that may be arranged around and may face away from the first axis  60 . The teeth of the third gear  214  may contact and may mate or mesh with teeth of a third countershaft gear that may be provided with the first countershaft subassembly  202  and the second 
     shaft subassembly  202 ′ as will be discussed in more detail below. The third gear  214  may have a different diameter than the first gear  210  and the second gear  212 . For example, the third gear  214  may have a larger diameter than the first gear  210  and the second gear  212 . In at least one configuration, the third gear  214  be axially positioned along the first axis  60  further from the electric motor module  24  than the first gear  210  and the second gear  212 . 
     Optionally, a bearing  144  such as a roller bearing may receive the shaft portion  72  and may rotatably support a corresponding gear. For instance, a first bearing may be received between the first gear  210  and the shaft portion  72 , a second bearing may be received between the second gear  212  and the shaft portion  72 , and so on to facilitate rotation of the drive pinion  22  with respect to a gear when the gear is not coupled to the drive pinion  22 . 
     The first countershaft subassembly  202  may be at least partially received in the housing assembly  20 . The first countershaft subassembly  202  may be rotatable about a first countershaft axis  220 . The first countershaft axis  220  may be disposed parallel or substantially parallel to the first axis  60  in one or more embodiments. The first countershaft subassembly  202  may be spaced apart from the differential assembly  30  such that the electric motor module  24  may be positioned along the first axis  60  between the first countershaft subassembly  202  and the differential assembly  30 . The first countershaft subassembly  202  may include a first countershaft  230  and a plurality of gears. In the configuration shown, the plurality of gears of the first countershaft subassembly  202  include a first countershaft gear  240 , a second countershaft gear  242 , and a third countershaft gear  244 ; however, it is contemplated that a greater number of gears or a lesser number of gears may be provided. 
     The first countershaft  230  may be rotatable about the first countershaft axis  220 . For instance, the first countershaft  230  may be rotatably supported on the housing assembly  20  by one or more roller bearing assemblies. As an example, a roller bearing assembly may be located near opposing first and second ends the first countershaft  230 . The roller bearing assembly may have any suitable configuration. For instance, the roller bearing assembly may include a plurality of rolling elements that may be disposed between an inner race and an outer race. The inner race may be mounted to the first countershaft  230  and may extend around and may receive the first countershaft  230 . The outer race may extend around the inner race and may be mounted to the housing assembly  20 . The first countershaft  230  may support the first countershaft gear  240 , the second countershaft gear  242 , and the third countershaft gear  244 . 
     The first countershaft gear  240  may be fixedly disposed on the first countershaft  230  or fixedly mounted to the first countershaft  230 . As such, the first countershaft gear  240  may rotate about the first countershaft axis  220  with the first countershaft  230 . For example, the first countershaft gear  240  may have a hole that may receive the first countershaft  230  and may be fixedly coupled to the first countershaft  230 . The first countershaft gear  240  may extend around the first countershaft axis  220  and may have a plurality of teeth that may be arranged around and may face away from the first countershaft axis  220 . The teeth of the first countershaft gear  240  may contact and may mate or mesh with the teeth of the first gear  210 . In at least one configuration, the first countershaft gear  240  may be axially positioned along the first countershaft axis  220  between the second countershaft gear  242  of the first countershaft subassembly  202  and the electric motor module  24 . 
     The second countershaft gear  242  may be fixedly disposed on the first countershaft  230  or fixedly mounted to the first countershaft  230 . As such, the second countershaft gear  242  may rotate about the first countershaft axis  220  with the first countershaft  230 . For example, the second countershaft gear  242  may have a hole that may receive the first countershaft  230  and may be fixedly coupled to the first countershaft  230 . The second countershaft gear  242  may extend around the first countershaft axis  220  and may have a plurality of teeth that may be arranged around and may face away from the first countershaft axis  220 . The teeth of the second countershaft gear  242  may contact and may mate or mesh with the teeth of the second gear  212 . The second countershaft gear  242  may have a different diameter than the second countershaft gear  242  and the third countershaft gear  244 . In at least one configuration, the second countershaft gear  242  may be axially positioned along the first countershaft axis  220  between the first countershaft gear  240  of the first countershaft subassembly  202  and the third countershaft gear  244  of the first countershaft subassembly  202 . 
     The third countershaft gear  244  may be fixedly disposed on the first countershaft  230  or fixedly mounted to the first countershaft  230 . As such, the third countershaft gear  244  may rotate about the first countershaft axis  220  with the first countershaft  230 . For example, the third countershaft gear  244  may have a hole that may receive the first countershaft  230  and may be fixedly coupled to the first countershaft  230 . The third countershaft gear  244  may extend around the first countershaft axis  220  and may have a plurality of teeth that may be arranged around and may face away from the first countershaft axis  220 . The teeth of the third countershaft gear  244  may contact and may mate or mesh with the teeth of the third gear  214 . The third countershaft gear  244  may have a different diameter than the first countershaft gear  240  and the second countershaft gear  242 . In at least one configuration, the third countershaft gear  244  may be axially positioned along the first countershaft axis  220  further from the electric motor module  24  than the first countershaft gear  240  and the second countershaft gear  242  of the first countershaft subassembly  202 . 
     The second countershaft subassembly  202 ′ may be at least partially received in the housing assembly  20  and may be rotatable about a second countershaft axis  220 ′. The second countershaft axis  220 ′ may be disposed parallel or substantially parallel to the first countershaft axis  220  in one or more embodiments. The second countershaft subassembly  202 ′ may be spaced apart from the differential assembly  30  such that the electric motor module  24  may be positioned along the first axis  60  between the second countershaft subassembly  202 ′ and the differential assembly  30 . The second countershaft subassembly  202 ′ may generally be disposed on an opposite side of the first axis  60  from the first countershaft subassembly  202  or may be disposed directly opposite the first countershaft subassembly  202 . Moreover, the second countershaft subassembly  202 ′ may have substantially the same configuration as the first countershaft subassembly  202 . For example, the second countershaft subassembly  202 ′ may include a second countershaft  230 ′ that may be analogous to or may have the same structure as the first countershaft  230 . In addition, the second countershaft subassembly  202 ′ may include a plurality of gears. In the configuration shown, the plurality of gears of the second countershaft subassembly  202 ′ include a first countershaft gear  240 ′, a second countershaft gear  242 ′, and a third countershaft gear  244 ′; however, it is contemplated that a greater number of gears or a lesser number of gears may be provided. The first countershaft gear  240 ′, a second countershaft gear  242 ′, and a third countershaft gear  244 ′ of the second countershaft subassembly  202 ′ may be analogous to or may have the same structure as the first countershaft gear  240 , a second countershaft gear  242 , and a third countershaft gear  244 , respectively, of the first countershaft subassembly  202 , may be arranged along second countershaft axis  220 ′ rather than the first countershaft axis  220 , and may be fixed to the second countershaft  230 ′ rather than the first countershaft  230 . 
     The first gear  210  and the first countershaft gears  240 ,  240 ′ may provide a different gear ratio than the second gear  212  and the second countershaft gears  242 ,  242 ′ and may provide a different gear ratio than the third gear  214  and the third countershaft gears  244 ,  244 ′. As a non-limiting example, the first gear  210  and the first countershaft gears  240 ,  240 ′ may provide a gear ratio of more than 2:1, the second gear  212  and the second countershaft gears  242 ,  242 ′ may provide a gear ratio from 1:1 to 2:1, and the third gear  214  and the third countershaft gears  244 ,  244 ′ may provide a gear ratio of 1:1 or less. For instance, the first countershaft gears  240 ,  240 ′ may have a larger diameter than the first gear  210 , the second countershaft gears  242 ,  242 ′, and the third countershaft gears  244 ,  244 ′. The second countershaft gears  242 ,  242 ′ may have a larger diameter than the second gear  212  and the third countershaft gears  244 ,  244 ′. The third gear  214  may have the same diameter as the third countershaft gears  244 ,  244 ′. 
     It is also contemplated that other gear configurations may be provided. As one example, the first gear  210  may have a larger diameter than the second gear  212  and the third gear  214 . As another example, gears or gear pairings may be arranged in different sequences along their respective axes. As another example, multiple meshing gear pairings or no gear pairings may provide “overdrive” gear ratios of less than 1:1. As another example, multiple meshing gear pairings may provide gear ratios of greater than 1:1. As such, gear ratios may be provided that are greater than 1:1, less than 1:1, equal (i.e., 1:1), or combinations thereof. 
     The teeth of the countershaft transmission gears may be of any suitable type. As a non-limiting example, the meshing teeth of the members of the set of drive pinion gears  200  and the gears of the first countershaft subassembly  202  and the second countershaft subassembly  202 ′ may have a helical configuration. 
     A control system may control operation of the axle assembly. The control system may include one or more electronic controllers, such as a microprocessor-based controller, that may monitor and/or control operation of various components of the axle assembly. In addition, the control system may control coupling and decoupling of the gears of the set of drive pinion gears  200  to and from the drive pinion  22 . For instance, the control system may control operation of one or more clutches that may couple/decouple at least one member of the set of drive pinion gears  200  to/from the drive pinion  22 . 
     A clutch may have any suitable configuration. The clutch may be configured as a disc clutch that may include friction discs that may be selectively engaged to couple a gear to a corresponding shaft. Alternatively, the clutch may be configured as a dog clutch or clutch collar that may receive, rotate with, and slide along a corresponding shaft to selectively couple and decouple one or more members of the set of drive pinion gears  200  to the drive pinion  22 . For example, a clutch that is configured as a dog clutch or a clutch collar may have a through hole that may receive the shaft portion  72  of the drive pinion  22  and may rotate about the first axis  60  with the shaft portion  72 . For instance, the clutch and shaft portion  72  may have mating splines that inhibit rotation of the clutch with respect to the shaft portion  72  while allowing the clutch to slide in an axial direction along the first axis  60  with respect to the shaft portion  72  to engage or disengage a member of the set of drive pinion gears  200 . Such a clutch may have a tooth or teeth that may be configured to selectively mate or mesh with corresponding teeth on a member of the set of drive pinion gears  200  to couple the gear to the shaft portion  72  such that the gear rotates about the first axis  60  with the drive pinion  22 . The tooth or teeth of the clutch may be configured as a face gear that may be disposed along a lateral side of the clutch or may be configured like a spline and may be received inside a hole of a member of the set of drive pinion gears  200 . Clutches will primarily be described below as having a dog clutch or clutch collar configuration; however, it is to be understood that a clutch may have a different configuration and may not be configured as a dog clutch or a clutch collar, that a different number of clutches may be provided, and that clutches may be associated with a single member of the set of drive pinion gears  200  rather than multiple drive pinion gears or vice versa. 
     In at least one configuration, a first clutch  250  and a second clutch  252  may be provided. The first clutch  250  may be axially positioned along the first axis  60  between the first gear  210  and the second gear  212  while the second clutch  252  may be axially positioned between the second gear  212  and the third gear  214 . The first clutch  250  and the second clutch  252  may be configured to selectively couple a single gear or multiple gears to the drive pinion  22 . For instance, the first clutch  250  may selectively couple the first gear  210  to the drive pinion  22  or may selectively couple the first gear  210  or the second gear  212  to the drive pinion  22 . The second clutch  252  may selectively couple the third gear  214  to the drive pinion  22  or may selectively couple the third gear  214  or the second gear  212  to the drive pinion  22 . It is contemplated that a single actuator may be provided to actuate multiple clutches, like the first clutch  250  and the second clutch  252  or that different actuators may actuate different clutches. 
     The first clutch  250  may be operatively connected to a first actuator  260  that may be configured to move the first clutch  250  along the first axis  60 . For example, a linkage, such as a shift fork, may operatively connect the first clutch  250  to the first actuator  260 . The first actuator  260  may be of any suitable type. For example, the first actuator  260  may be an electrical, electromechanical, pneumatic, or hydraulic actuator. In at least one configuration, such as when the first clutch  250  is a clutch collar or dog clutch, the first actuator  260  may move the first clutch  250  along the first axis  60  and may execute a shift when the rotational speed of the first clutch  250  and a corresponding member of the set of drive pinion gears  200  are sufficiently synchronized to complete a shift so that the teeth of the first clutch  250  may mesh with teeth on a drive pinion gear or so that the teeth of the first clutch  250  gear may disengage from teeth on a drive pinion gear. The control system may monitor and/or control operation of the first actuator  260 . 
     The second clutch  252  may be operatively connected to a second actuator  262  that may be configured to move the second clutch  252  along the first axis  60 . It is also contemplated that a single actuator may be provided to actuate multiple clutches, like the first clutch  250  and the second clutch  252 . For example, a linkage, such as a shift fork, may operatively connect the second clutch  252  to the second actuator  262 . The second actuator  262  may be of any suitable type. For example, the second actuator  262  may be an electrical, electromechanical, pneumatic, or hydraulic actuator. In at least one configuration, such as when the second clutch  252  is a clutch collar or dog clutch, the second actuator  262  may move the second clutch  252  along the first axis  60  and may execute a shift when the rotational speed of the second clutch  252  and a corresponding member of the set of drive pinion gears  200  are sufficiently synchronized to complete a shift so that the teeth of the second clutch  252  may mesh with teeth on a drive pinion gear or so that the teeth of the second clutch  252  gear may disengage from teeth on a drive pinion gear. The control system may monitor and/or control operation of the second actuator  262 . 
     Sufficient synchronization to permit shifting or movement of a clutch, like the first clutch  250  or the second clutch  252 , may be attained using a gear synchronizer, by controlling the rotational speed of the rotor  92 , or combinations thereof. Such synchronization components or control actions may be omitted with different clutch configurations, such as a clutch that is a disc clutch. 
     Referring to  FIG.  4   , another example of an axle assembly is shown. The axle assembly in  FIG.  4    is similar to the axle assembly shown in  FIG.  2    except for the configuration of the rotor coupling. 
     The rotor coupling  110 ′ in  FIG.  4    may share some characteristics with the rotor coupling  110  shown in  FIG.  2   . For example, the rotor coupling  110 ′ may operatively connect the rotor  92  to the gear reduction module  28  or  28 ′ such that the rotor  92  and the rotor coupling  110 ′ may be rotatable together about the first axis  60 . The rotor coupling  110 ′ may engage the rotor  92  and may be fixedly positioned with respect to the rotor  92 , such as by being fixedly coupled to the rotor  92  proximate a first end and may be coupled to the gear reduction module  28  proximate a second end. The rotor coupling  110 ′ may be fixedly coupled to a first gear  130 ,  210  of the gear reduction module  28 . In addition, the rotor coupling  110 ′ may be configured as a hollow tube that may extend around the first axis  60  and may receive the shaft portion  72  of the drive pinion  22 . The rotor coupling  110 ′ may be spaced apart from the differential carrier  42 . For instance, the rotor coupling  110 ′ may not receive, contact, or engage the differential carrier  42  or a bearing support wall that may extend from the differential carrier  42 . 
     Unlike the configuration shown in  FIG.  2   , the rotor coupling  110 ′ in  FIG.  4    may be received inside the rotor  92 . For example, the rotor coupling  110 ′ may have a greater axial length and may extend into a hole defined by the rotor  92 . The rotor coupling  110 ′ may be radially positioned between the rotor  92  and one or more rotor bearing assemblies  26 . For instance, the rotor coupling  110 ′ may be received inside and may contact an interior side of the rotor  92  that may face toward the first axis  60  while first and second rotor bearing assemblies  26 ,  26  may be received inside the rotor coupling  110 ′ and may engage or contact an interior side of the rotor coupling  110 ′ that may be disposed opposite and may face away from the rotor  92 . The rotor bearing assemblies  26 ,  26  may extend from the drive pinion  22  to the rotor coupling  110 ′. It is to be understood that the rotor coupling  110 ′ shown in  FIG.  4    may be used with the axle assembly configuration shown in  FIG.  3   . 
     Referring to  FIGS.  5 - 7   , multiple examples of how the rotor coupling  110 ,  110 ′ may be connected to the first gear  130 ,  210  are shown. The configurations shown in  FIGS.  5 - 7    may be employed with any of the axle assembly configurations previously discussed, such as the axle configuration shown in  FIGS.  2 - 4   . 
     Referring to  FIG.  5   , an example of a connection interface is shown in which the rotor coupling  110 ,  110 ′ is partially received inside the first gear  130 ,  210 . In such a configuration, the first gear  130 ,  210  may have a mounting ring  300 . 
     The mounting ring  300  may extend around the drive pinion  22  and may extend in an axial direction toward the rotor  92 , or to the left from the perspective shown. The mounting ring  300  may have a mounting ring spline  302 . The mounting ring spline  302  may extend toward the drive pinion  22  and may extend from a first side  304  of the first gear  130 ,  210 . 
     The rotor coupling  110 ,  110 ′ may be received inside the mounting ring  300 . The rotor coupling  110 ,  110 ′ may have a rotor coupling spline  310 . The rotor coupling spline  310  may face away from the drive pinion  22  and may mesh with the mounting ring spline  302  to inhibit rotation of the rotor coupling  110 ,  110 ′ with respect to the first gear  130 ,  210 . 
     Referring to  FIG.  6   , an example of a connection interface is shown in which the rotor coupling  110 ,  110 ′ may receive a portion of the first gear  130 ,  210 . In such a configuration, the first gear  130 ,  210  may have a mounting ring  300 . 
     The mounting ring  300  that may extend around the drive pinion  22  and may extend in an axial direction toward the rotor  92 . The mounting ring  300  may be received inside the rotor coupling  110 ,  110 ′. The mounting ring  300  may have a mounting ring spline  302 ′. The mounting ring spline  302 ′ may face away from the drive pinion  22  and may extend from a first side  304  of the first gear  130 ,  210 . 
     The rotor coupling  110 ,  110 ′ may receive the mounting ring  300 . The rotor coupling  110 ,  110 ′ may have a rotor coupling spline  310 . The rotor coupling spline  310  may face toward and may extend toward the drive pinion  22 . The rotor coupling spline  310  may mesh with the mounting ring spline  302  to inhibit rotation of the rotor coupling  110 ,  110 ′ with respect to the first gear  130 ,  210 . 
     Referring to  FIG.  7   , an example of a connection interface is shown in which the rotor coupling  110 ,  110 ′ may be integrally formed with the first gear  130 ,  210 . 
     The axle assembly configurations described above may allow a rotor to be packaged closer to a drive pinion without an intervening fixed component such as a differential carrier or bearing support wall that extends from the differential carrier being radially positioned between the rotor and drive pinion. As a result, smaller diameter bearing assemblies may be used to support the rotor that can better handle the high rotational speeds of the rotor and the relative rotational speed of the rotor bearings may be reduced. The use of smaller diameter bearings may help reduce associated bearing temperatures and lubrication requirements, which may help improve durability. The use of smaller bearings may also allow electric motors having higher rotational speeds to be used. Elimination of an intervening fixed component such as a differential carrier or bearing support wall may also allow a smaller diameter motor to be used, which may reduce cost and weight. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.