Patent Publication Number: US-2022219813-A1

Title: Shaft driven self-powered landing gear with hubcap mounted gear reduction

Description:
BACKGROUND 
     Autonomous taxiing systems provide drive capabilities to one or more wheels of an aircraft. By utilizing electric or hydraulic motors (or other power sources) to drive the wheels, operators can push back from gates and taxi without having to use their jet engines or tow tractors. As a result, fuel costs, wear and maintenance on the jet engines, and noise are all reduced. 
     When implementing an autonomous taxiing system, it is desirable to provide a clutch that isolates the driven wheel from the driving mechanism. Ideally, this clutch is arranged such that the autonomous taxi equipment does not introduce any additional rotating failure modes compared to a landing gear without the autonomous taxi equipment. For instance, with the clutch disengaged, there should be no additional rotating bearings, shafts, or other components that could fail and introduce a retarding torque during aircraft acceleration for takeoff. 
     U.S. Pat. No. 9,540,097, issued to Schmidt et al., (“Schmidt”) and currently assigned to Safran Landing Systems, the disclosure of which is expressly incorporated herein, teaches the use of drive shafts housed within the landing gear axle to drive the aircraft wheels. Schmidt generally explains that the drive shafts may be provided with couplers for selectively coupling or uncoupling the drive shafts from the wheels. When the couplers are uncoupled, untimely powering of the motors does not rotate the wheels and does not cause a reaction torque to be applied to the undercarriage if the brakes are engaged. 
     Autonomous taxiing systems require high torque output to the driven wheels in order to taxi the aircraft. Motors designed to deliver such torques are typically undesirable as being too large and too heavy for use on aircraft. Compact, lightweight motors suitable for use on aircraft tend to have high-speed/low-torque outputs that lack the power needed to drive the aircraft wheels. 
     SUMMARY 
     In accordance with an embodiment of the present disclosure, a landing gear system is provided. The landing gear system includes an axle having an internal cavity and a wheel rotatably coupled to the axle. A drive shaft is mounted within the cavity to be rotatable about an axis. The landing gear system further includes a planetary gear assembly having a sun gear operably coupled to the drive shaft and a planet gear operably engaging the sun gear. A ring gear surrounds and is operably coupled to the planet gear such that rotation of the drive shaft rotates the ring gear. A clutch assembly is selectively moveable between an engaged state and a disengaged state. The clutch assembly transfers rotation of the ring gear to the wheel when the clutch assembly is in the engaged state, and the clutch assembly does not transfer rotation of the wheel to the ring gear when the clutch assembly is in the disengaged state. 
     In any embodiment, the planetary gear assembly further comprises a carrier fixedly positioned relative to the axle, wherein the sun gear and the planet gear are rotatably coupled to the carrier. 
     In any embodiment, the clutch assembly comprises a first clutch portion associated with the ring gear and a second clutch portion associated with the wheel. 
     In any embodiment, the first clutch portion is integrally formed with the ring gear. 
     In any embodiment, the second clutch portion is fixed in rotation relative to wheel. 
     In any embodiment, the second clutch portion is mounted for translation relative to the first clutch portion. 
     In any embodiment, the landing gear assembly further includes a plurality of slider assemblies fixedly positioned relative to the wheel, wherein the second clutch portion is slidably mounted to the plurality of slider assemblies. 
     In any embodiment, each slider assembly comprises a bolt extending through a corresponding hole in the second clutch portion. 
     In any embodiment, each slider assembly further comprises a spring engaging the second clutch assembly to urge the clutch assembly toward the disengaged state. 
     In any embodiment, the second clutch portion is fixedly coupled to the wheel. 
     In any embodiment, the second clutch portion is mounted for translational movement relative to the ring gear. 
     In any embodiment, the landing gear assembly further includes a plurality of slider assemblies fixedly positioned relative to the ring gear, wherein the second clutch portion is slidably mounted to the plurality of slider assemblies. 
     In any embodiment, each slider assembly comprises a bolt extending through a corresponding hole in the second clutch. 
     In any embodiment, each slider assembly further comprises a spring engaging the second clutch assembly to urge the clutch assembly toward the disengaged state. 
     In accordance with an embodiment of the present disclosure, a landing gear system is provided. The landing gear system includes a drive shaft disposed within an axle housing and rotatable about a first axis. A wheel is rotatably mounted to the axle for rotation about the first axis. The landing gear system further includes a planetary gear assembly, comprising a carrier fixedly coupled to the axle housing; a sun gear coupled to the carrier for rotation about the first axis and engaging the drive shaft, wherein rotation of the drive shaft rotates the sun gear about the first axis; a plurality of planet gears operably engaging the sun gear, each planet gear being mounted to the carrier for rotation about a corresponding planet gear axis parallel to the first axis; and a ring gear coupled to the carrier for rotation about the first axis, the ring gear surrounding and engaging each of the plurality of planet gears, rotation of the drive shaft rotating the ring gear. A clutch assembly selectively engages the ring gear with the wheel. 
     In any embodiment, the clutch assembly includes a first clutch portion associated with the ring gear and second clutch portion associated with the wheel. 
     In any embodiment, the first clutch portion is integrally formed with the ring gear, and the second clutch portion is slidingly associated with the wheel, the landing gear assembly further comprising an actuator configured to selectively move the second clutch portion to engage the first clutch portion. 
     In any embodiment, the first clutch portion is slidably associated with the ring gear, and the second clutch portion is fixedly positioned relative to the wheel, the landing gear assembly further comprising an actuator configured to selectively move the first clutch portion to engage the second clutch portion. 
     In any embodiment, the landing gear system further includes a first alignment fitting fixedly positioned relative to the first clutch portion and a second alignment fitting fixedly positioned relative to the axle housing, wherein the first alignment fitting engages the second alignment fitting when the clutch assembly moves from a disengaged state to an engaged state. 
     In any embodiment, the first alignment fitting comprises a first frustoconical surface, and the second alignment fitting comprises a second frustoconical surface, the first frustoconical surface engaging the second frustoconical surface when the clutch assembly is in the engaged state. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of disclosed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows a rear view of a landing gear system according to a first representative embodiment of the present disclosure; 
         FIG. 2  shows a partial top plan view thereof; 
         FIG. 3  shows a partial cross-sectional view of the landing gear system of  FIG. 1 , as indicated in  FIG. 2 ; 
         FIG. 4  shows a partial cross-sectional view of the landing gear system of  FIG. 1 , as indicated in  FIG. 2 ; 
         FIG. 5  shows a partial isometric view of a drive assembly of the landing gear system  FIG. 1 ; 
         FIG. 6  shows a partial left side elevational view of the landing gear system of  FIG. 1 ; 
         FIG. 7  shows a partial cross-sectional view of the drive assembly of the landing gear system of  FIG. 1 , as indicated in  FIG. 6 ; 
         FIG. 8  shows a partial cross-sectional view of the drive assembly of the landing gear system of  FIG. 1 , as indicated in  FIG. 6 , wherein a clutch assembly is in a disengaged position; 
         FIG. 9  shows a partial cross-sectional view of the drive assembly shown in  FIG. 8 , wherein a clutch assembly is in an engaged position; 
         FIG. 10  shows a partial isometric view of a curvic clutch of the clutch assembly shown in  FIG. 8 ; 
         FIG. 11  shows a partial isometric cutaway view of a landing gear system according to a second representative embodiment of the present disclosure; 
         FIG. 12  shows a partial cross-sectional view of a drive assembly of the landing gear system of  FIG. 11 ; 
         FIG. 13  shows a partial cross-sectional view of the drive assembly of the landing gear system of  FIG. 11 , wherein a clutch assembly is in a disengaged position; and 
         FIG. 14  shows a partial cross-sectional view of the drive assembly shown in  FIG. 13 , wherein the clutch assembly is in an engaged position. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings, where like numerals reference like elements, is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the claimed subject matter to the precise forms disclosed. 
     Examples of an autonomous taxiing system for an aircraft are set forth below according to technologies and methodologies of the present disclosure. In an embodiment, a drive shaft located within the axle is rotated by a motor mounted to the landing gear. The drive axle rotates to drive a planetary gear assembly having a ring gear that drives the wheel to taxi the aircraft. A clutch assembly selectively engages and disengages the ring gear from the wheel so that the planetary gear assembly is isolated from the wheels when the clutch assembly is in a disengaged state. 
     Referring to  FIGS. 1-10 , a first representative embodiment of a landing gear system  20  according to the present disclosure is shown. As best shown in  FIGS. 1 and 2 , the landing gear system  20  includes a strut  30  and an axle assembly  70 . One end of the strut  30  is coupled to the aircraft (not shown) and the other end of the strut is coupled to the axle assembly  70  at a strut interface  104  formed in an axle housing  72 , as shown in  FIG. 2 . In the illustrated embodiment, the axle assembly  70  extends laterally outward from the strut  30  and has a wheel  40  rotatably mounted to each end. A motor  50  is mounted to a rear side of the axle housing  72 . As explained in further detail, the motor  50  provides the driving force to rotate one or more of the wheels  40  to taxi the aircraft. 
     Each wheel  40  includes a tire  42  mounted to a rim  44  (shown in  FIGS. 8 and 9 ). At least one of the wheels  40  includes a hub  46  that is selectively rotated by the motor  50  to drive the wheel  40 . A torque link lug  76  is formed on a forward end of the axle assembly  70  to provide attachment for the lower torque link of a torque link assembly (not shown), which is commonly used in known landing gear configurations. 
     The illustrated landing gear system  20  is a configuration similar to known main landing gear assemblies used on commercial aircraft. It will be appreciated, however, that the present disclosure is not limited to the illustrated landing gear system. In this regard, embodiments of the disclosed autonomous taxiing system can be utilized with various landing gear systems for different aircraft. In one embodiment the taxiing system is utilized with main landing gear assemblies mounted to the aircraft body or wings. In other contemplated embodiments, the taxiing system drives one or more wheels of a multi-wheel, e.g., four, six, eight, etc., landing gear assembly with a bogie beam. In yet another embodiment the taxiing system is used in conjunction with a single-wheel landing gear assembly. Embodiments are also contemplated in which the motor  50  is positioned forward of the axle assembly  70  or in another suitable location, and/or the torque link assembly is positioned aft of the axle assembly. 
     Referring now to  FIG. 3 , which is a cross-sectional view of the system  20  taken along line  3 - 3  in  FIG. 2 , the motor  50  includes a housing  52  coupled to an aft side of the axle housing  72  by mechanical fasteners or other suitable means. The motor  50 , which may be electric, hydraulic, or any other suitable type of motor, includes an output shaft  54  that selectively rotates about an axis  302 . A bevel gear  56  is mounted to the output shaft  54  and engages teeth a face  60  of an intermediate gear  58 . The intermediate gear  50  is mounted for rotation about an axis  304  and engages a drive shaft gear  62 . The drive shaft gear  62  rotatably mounted within the axle housing  72  and engages a drive shaft  80  so that the rotation of the output shaft  54  of the motor  50  rotates the drive shaft gear  62  and the drive shaft  80  about a common axis  300 . 
     In the illustrated embodiment, the portion of the drive shaft  80  that engages the drive shaft gear  62  has three lobes and nests within a similarly-shaped aperture in the drive shaft gear. In other contemplated embodiments, the drive shaft  80  may be mechanically fastened to or integrally formed with the drive shaft gear  62 . Additional configurations may use different numbers and sizes of gears or other transmission elements to transform the output of the motor  50  into rotation of the drive shaft  80  about the axis  300 . 
       FIG. 4  is a partial cross-sectional rear view taken along line  4 - 4  of  FIG. 2 , the landing gear system  20  is shown with portions of the wheels  40  removed for clarity. The axle housing  72  includes an elongate internal cavity  78 . The drive shaft  80  is mounted within the cavity  78  via a plurality of bearings  82  to be rotatable about axis  300 . In the illustrated embodiment, the cavity  108  is sealed at one end by a plug  88  mounted within the axle housing  72 . The cavity  78  is fluid tight and filled with a fluid  86 . In the illustrated embodiment, the fluid  86  is a lubricating oil that lubricates the internal components of the axle assembly  70 . 
     A drive assembly  100  is positioned at one end of the axle assembly  70 . A first end of the drive shaft  80  is operably connected to the motor  50  to receive rotational input, and a second end of the drive shaft  80  is operably connected to the drive assembly  100 . The drive shaft  80  is configured to transfer rotational movement from the motor  50  to the drive assembly  100 . More specifically, the drive shaft  80  transfers rotational movement to a planetary gear assembly  110 , which selectively outputs the rotational movement to the wheel  40  through the hub  46  to provide motive force to the landing gear system  20 . 
     As shown in  FIGS. 5 and 6 , the drive shaft  80  rotates about axis  300  to drive a planetary gear assembly  110  that converts the high-speed/low-torque input from the drive shaft  80  into a low-speed/high-torque output that drives at least one wheel  40  of the landing gear assembly  20 . As will be described in further detail, the planetary gear assembly  110  includes a sun gear  112 , a plurality of planet gears  116 , and a ring gear  122 . The sun gear  112  receive rotational input from the drive shaft  80 , and the ring gear  122  outputs rotational movement to the wheel  40 . Rotational output of the ring gear  122  is selectively transferred to the wheel by engaging and disengaging a clutch assembly  130 . The clutch assembly  130  includes an outboard clutch plate  132  that reciprocates along a plurality of slider assemblies  160  to engage and disengage an inner clutch plate  138 . 
     Referring now to  FIGS. 5-7 , an embodiment of the planetary gear assembly  110  will be described. The planetary gear assembly  110  includes a carrier  120  mounted to the axle housing  72  so that the carrier is fixedly positioned relative to the axle assembly. The planetary gear assembly  110  also includes a spider plate  128  mounted to and offset from the carrier  120 . The spider plate  128  is fixedly positioned relative to the carrier  120 . Thus, the carrier  120  and the spider plate  128  cooperate to provide a frame in which the moving elements of the planetary gear assembly  110  are mounted. 
     The sun gear  112  is mounted between the carrier  120  and the spider plate  128  by bearings  114 . The sun gear  112 , which is rotatably about axis  300  has splines formed on the inner diameter of the gear. The splines of the sun gear  112  engage splines  84  formed on the end of the drive shaft  80  so that rotation of the drive shaft imparted by the motor  50  rotates the sun gear about axis  300 . 
     A plurality of planet gears  116  are positioned circumferentially around the sun gear  112 . Each planet gear  116  is rotatably mounted to the carrier  120  and the spider plate  128  by one or more bushings  118 . The external teeth of each planet gear  116  are in meshed engagement with external teeth of the sun gear  112  so that rotation of the sun gear about axis  300  rotates each planet gear about its respective axis of rotation  306 . The axis  306  of each planet gear  116  is parallel to the axis  300  of the sun gear  112  and is fixedly positioned relative to the carrier  120  and the spider plate  128 . 
     A ring gear  122  has a generally cylindrical shape and extends around the planet gears  116 . The ring gear is mounted to the carrier  120  and the spider plate  128  for rotation about axis  300 . In the illustrated embodiment, the ring gear  122  is mounted to the carrier  120  and the spider plate  128  by thrust bearings  124 . Internal teeth are formed on the ring gear  122  and are in meshed engagement with each of the planet gears  116 . Because the rotational axes  106  of the planet gears  116  are fixed relative to the carrier  120  and the spider plate  128 , and therefore the axle housing  72 , rotation of the planet gears rotates the ring gear about axis  300 . The fixed position of the planet gear axes  106  also provide a static pathway through the planetary gear assembly  110  for electrical wiring, tubing, or other systems components. 
     The illustrated planetary gear assembly  110  is configured to have a gear ratio that converts the high-speed/low torque rotation of the drive shaft  80  about axis  300  into low-speed/high-torque rotation of the ring gear  122  about axis  300 . It will be appreciated that the illustrated embodiment is exemplary only, and other configurations are possible. In some embodiments, the number and/or location of the planet gears  116  vary. In some embodiments, the planetary gear assembly  110  includes a single planet gear  116 . In some embodiments, the carrier  120  and the spider plate  128  are integrally formed or include multiple components. These and other variations of known planetary gear assemblies  110  are contemplated and should be considered within the scope of the present disclosure. 
     Referring now to  FIGS. 8 and 9 , the drive assembly  100  includes a clutch assembly  130  that selectively engages and disengages the drive shaft  80  to one or more of the wheels  40 . More specifically, the clutch assembly  130  of the illustrated embodiment is a curvic clutch that includes a first portion  132  associated drive shaft  80  and a second portion  136  associated the wheel  40 . When the clutch assembly  130  is disengaged ( FIG. 8 ), the wheel  40  turns independent of the drive shaft  80 , and when the clutch assembly is engaged ( FIG. 9 ) rotation of the drive shaft drives the wheel. 
     In the illustrated embodiment, the first clutch portion  132  is integrally formed with the planetary gear assembly  110 . More specifically, a plurality of teeth  134  are formed with the outboard edge of the ring gear  122  so that the ring gear acts as the first clutch portion  132  of the clutch assembly  130 . As such, the rotational output of the planetary gear assembly  110  derived from the rotary input of the drive shaft  80  is also the rotation of the first clutch portion  132 . In some embodiments, the first clutch portion  132  is distinct from the ring gear  122  of the planetary gear assembly  110  and is coupled to or otherwise associated with the ring gear such that rotation of the ring gear rotates the first clutch portion. 
     The second clutch portion  136  is slidably mounted to the wheel hub  46  by a plurality of slider assemblies  160  that are configured to allow reciprocating translation of the second clutch portion in the inboard and outboard directions. As shown in  FIG. 6 , the illustrated embodiment, includes six slider assemblies  160  arranged circumferentially around the axis  300  of the wheel  40 . In some embodiments, the number and position of the slider assemblies  160  have any suitable configuration. 
     The hub  46  is itself a component of the wheel  40  (see  FIG. 2 ) and rotates with the wheel. More specifically, the illustrated hub  46  is a hubcap that is reinforced to be able to transfer torque loads from the second clutch portion  136  (through the slider assemblies  160 ) to the wheel  40 . In another embodiment, the second clutch portion  136  is indirectly coupled to the wheel  40  by a known transmission, gearbox, or other suitable configuration that transfers rotation of the second clutch portion to the wheel  40 . 
     Referring to  FIGS. 8 and 9 , Each slider assembly  160  includes a slider bolt  162  extending in the inboard direction through the hub  46 . A cylindrical bushing  168  surrounds the bolt  162  on the inboard side of the hub  46 , and a nut  170  engages the inboard end of the bushing  168  to clamp the bushing against an inboard surface of the hub, thereby fixedly positioning the bolt relative to the hub. The bolt  162  and the bushing  168  extend through a compression spring  164  that engages the second clutch portion  136  at one end and a spring stop  166  at the other end. In the illustrated embodiment, the spring stop  166  is a washer disposed between the bushing  168  and the nut  170 . In some embodiments, the nut  170  acts as a spring stop. 
     An actuator  180  engages the second clutch portion  136  to selectively move the second clutch portion  136  toward the engaged position of  FIG. 9  when the actuator is energized. When the actuator  180  is not energized, the spring  164  exerts a biasing force against the second clutch portion  136  that returns the second clutch portion to the disengaged position of  FIG. 8 . In the illustrated embodiment, the actuator  180  includes one or more magnetic actuators. In some embodiments, the actuator may include one or more solenoids, magnetic actuators, hydraulic actuators, or any other suitable actuators or combinations thereof that are utilized to move the clutch assembly  130  between the engaged and disengaged positions, and such configurations should be considered within the scope of the present disclosure. 
     Due to the large deflections of aircraft landing gear axles, there will sometimes be some misalignment of the first and second clutch portions  132  and  136 . This misalignment can be angular as well radial.  FIG. 8  shows an embodiment of a clutch assembly  130  with alignment features that align the first and second clutch portions  132  and  136  as the clutch assembly  130  moves from the disengaged position to the engaged position. 
     As shown in  FIG. 8 , a first alignment fitting  150  is coupled to the first clutch portion  132 . The first alignment fitting  150  includes a base mounted to or integrally formed with the first clutch portion  132  and frustoconical recess extending in the inboard direction, i.e., away from the base and the second clutch portion  136 . 
     A second alignment fitting  152  is coupled to the second clutch portion  136 . The second alignment fitting includes a frustoconical protrusion corresponding to the frustoconical recess of the first alignment fitting  150 . 
     As the clutch assembly  130  moves from a disengaged position to the engaged position, i.e., when the second clutch portion  136  moves toward the first clutch portion  132 , the frustoconical portion of the second alignment fitting  152  is received by the frustoconical recess in the first alignment fitting  150 , even in the presence of angular and/or radial misalignment. As the second clutch portion  136  continues to move toward the first clutch portion  132 , the frustoconical portion of the second alignment fitting  152  engages the frustoconical recess in the first alignment fitting  150  to align the first and second clutch portions  132  and  136  as the clutch assembly  130  moves toward the engaged state. 
     Because of the sliding contact between the of the first alignment fitting  150  with the second alignment fitting  152  as the clutch assembly  130  engages and disengages, some embodiments will utilize dissimilar materials for the first and second alignment fittings. In an embodiment, one of the alignment fittings is formed from or coated with nitrided steel, and the other alignment fitting is formed from or coated with a copper alloy such as aluminum nickel bronze or spinoidally cast aluminum nickel tin. Other embodiments using other known materials suitable for interacting bearing surfaces are contemplated and should be considered within the scope of the present disclosure. 
     It will be appreciated that the illustrated alignment features are representative only and should not be considered limiting. In an embodiment, the positions of the first and second alignment fittings  150  and  152  are reversed, so that the alignment associated with the second clutch portion  136  receives the alignment fitting associated with the first clutch portion. In an embodiment, the recess formed in the first alignment fitting is conical, frustoconical, or any other suitable shape. These and other variations of fittings that align the first and second clutch portions  132  and  136  are contemplated and should be considered within the scope of the present disclosure. 
     In the illustrated embodiment, the clutch  140  is a curvic clutch of the type disclosed in U.S. Pat. No. 2,384,582, issued to Wildhaber on Sep. 11, 1945, and U.S. Pat. No. 6,672,966, issued to Muju et al. on Jan. 6, 2004, the disclosures of which are incorporated herein by reference. As best shown in  FIG. 10 , the first clutch portion  132  includes a plurality of teeth  136  formed so that the sides of the teeth are concave. The second clutch portion  136  has a corresponding plurality of teeth  140  formed so that the sides of the teeth are convex. When the first and second clutch portions  132  and  138  are engaged, each concave tooth surface on the first clutch portion mates with a corresponding convex tooth surface on the second clutch portion. The inclusion of mating concave and convex surfaces advantageously provides a self-centering coupling with larger contact surfaces between the clutch portions. 
     In the illustrated embodiment, the teeth  134  and  140  of the first and second clutch portions  132  and  138 , respectively, have a tooth angle θ, which is the angle measured between the side of the tooth and a plane normal to the face the clutch (see  FIG. 10 ). For embodiments with a straight cut set of teeth, i.e. teeth with a 0° tooth angle θ, if the clutch disengages under load, the actuator  180  must be sized to overcome the tooth friction load resulting from the tooth coefficient of friction and the normal force on the teeth (which is directly proportional to the applied shaft torque). With straight cut teeth there is no axial force applied to the mobile clutch as a result of shaft torque. 
     It will be appreciated that the teeth  134  and  140  of the clutch assembly  130  can be machined at any suitable angles.  FIG. 10  shows another embodiment of a clutch  130  assembly with tooth angles greater than 0°. As tooth angles greater than 0° are utilized, a ‘throw out’ axial force is produced as a function of the torque applied by the drive shaft  80 . This axial force acts to disengage the clutch assembly  130 , which allows for the use of a smaller actuator  180 . In one embodiment, the tooth angle is 7°. In another embodiment, the tooth angle is in the range of 5° to 15°. 
     In some embodiments, other types of clutches may be utilized and should be considered within the scope of the present disclosure. As one nonlimiting example, some embodiments may utilize a clutch that is a dog clutch. 
     To utilize the autonomous taxiing capabilities of the disclosed landing gear system  20 , the actuator  180  drives the second clutch portion  136  inboard to engage the first clutch portion  132 . With the clutch assembly  130  engaged, the motor  50  is selectively powered to drive one or more wheels  40  of the landing gear system  20 . By using the motor  50  to drive the wheels  40  forward or backward, a pilot can taxi the aircraft without a tow tractor and without using the aircraft engines. When the taxiing is completed, the actuator  180  is de-energized, and the spring  164  moves the second clutch portion  136  outboard to disengage the second clutch portion from the first clutch portion  132 . With the clutch assembly  130  disengaged, the wheels  40  of the aircraft are effectively isolated from motor  50  and other landing gear system components related to autonomous taxiing functionality. 
     Referring now to  FIGS. 11-14 , another representative embodiment of landing gear system  20  according to the present disclosure is shown. The landing gear system  20  is similar to the previously described landing gear system shown in  FIGS. 1-10 . In this regard, the landing gear system includes an axle assembly  70  with a motor  50  that rotates a drive shaft  80  to power a drive assembly  200 . The drive assembly includes a planetary gear assembly  210  configured to convert high-speed/low-torque rotational input from the drive shaft  80  into low-speed/high-torque output to drive the one or more wheels  40  of the landing gear system  20 . A clutch assembly  230  selectively engages and disengages to selectively connect the planetary gear assembly  210  to one or more wheels  40 . 
     For the sake of brevity, the embodiment of  FIGS. 11-14  will be described with the understanding that the landing gear  20  components are similar to those of the previously described landing gear  20  unless otherwise noted. Further, components identified with a reference number 2XX correspond to components of the previously described embodiment identified with reference number 1XX unless otherwise noted. For example, planetary gear assembly  210  corresponds to planetary gear  110  except as otherwise described. 
     Referring to  FIG. 11 , the clutch assembly  230  is positioned inboard of the planetary gear assembly  210 . This configuration provides a more compact arrangement than the embodiment of  FIGS. 1-10 . 
     As shown in  FIGS. 12-14 , the clutch assembly  230  includes a first clutch portion  232  fixedly coupled the rim  44  of the wheel. In some embodiments, the first clutch portion  232  is directly or indirectly coupled to the rim  44  by mechanical fasteners or other suitable configurations. In some embodiments, the first clutch portion  232  is integrally formed with the rim  44 . 
     A second clutch portion  236  is slidably mounted to the ring gear  222  of the planetary gear assembly  210  by a plurality of slider assemblies  260 . When the actuator  280  is de-energized, the clutch assembly  230  is in the disengaged position of  FIG. 13 , the springs  264  of the slider assemblies  260  maintain the second clutch portion  236  in an outboard position. When an actuator  280  is energized, the actuator drives the second clutch portion  236  in the inboard direction to engage the first clutch portion  232 , as shown in  FIG. 14 . With the clutch assembly  230  so engaged, rotation of the ring gear  222  is transferred to the rim  44  to drive the wheel  44 . When the actuator  280  is de-energized, the springs  264  urge the second clutch portion  236  outboard to disengaged position. 
     The present application may reference quantities and numbers. Unless specifically stated, such quantities and numbers are not to be considered restrictive, but exemplary of the possible quantities or numbers associated with the present application. Also, in this regard, the present application may use the term “plurality” to reference a quantity or number. In this regard, the term “plurality” is meant to be any number that is more than one, for example, two, three, four, five, etc. The terms “about,” “approximately,” “near,” etc., mean plus or minus 5% of the stated value. For the purposes of the present disclosure, the phrase “at least one of A, B, and C,” for example, means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), including all further possible permutations when greater than three elements are listed. 
     The principles, representative embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, aspects of the present disclosure which are intended to be protected are not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. It will be appreciated that variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, it is expressly intended that all such variations, changes, and equivalents fall within the spirit and scope of the present disclosure, as claimed.