Patent Description:
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.

<CIT>, ("Schmidt") and currently assigned to Safran Landing Systems, 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 transfer from the drive shaft(s) to the driven wheels in order to taxi the aircraft. Accordingly, a dog clutch, i.e., a clutch that couples rotating components by interference rather than friction, is generally preferable. However, the high operational loads generated during taxiing cause deflections in the axle and drive shaft. These deflections cause angular misalignment as well as radial offsets between the mating parts of the clutch. As a result, a typical dog clutch known in the art will not properly engage and disengage without large gaps between the teeth of the mating parts.

<CIT> discloses a wheel rotating mechanism.

In accordance with an embodiment of the present invention, a landing gear system is provided. The 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 rod slidably mounted within the drive shaft and a clutch. The clutch has a first portion that is coupled to the rod and rotates with the drive shaft. A second portion of the clutch is fixedly coupled to the wheel. The rod selectively reciprocates along the axis between a first position and a second position to engage and disengage the clutch.

In an embodiment, the clutch is a curvic clutch.

In an embodiment, the landing gear system further includes a motor operably coupled to the drive shaft to rotate the drive shaft about the axis.

In an embodiment, the landing gear system further includes an actuation system coupled to the rod to reciprocate the rod between the first and second positions.

In an embodiment, the actuation system comprises a piston slidably mounted within the drive shaft and coupled to the rod, wherein the cavity is configured to be selectively pressurized to move the piston to drive the rod from the first position to the second position.

In an embodiment, the landing gear system further includes a first alignment fitting associated with the first clutch portion and a second alignment fitting associated with the second clutch portion. The first alignment fitting engages the second alignment fitting to align the first clutch portion with the second clutch portion as the rod moves from the first position to the second position.

In an embodiment, the landing gear system further includes a lockout assembly with a first lockout fitting associated with first clutch portion and a second lockout fitting associated with the second clutch portion. At least one of the first and second lockout fittings is selectively movable between a locked position and an unlocked position. Engagement of the first and second lockout fittings prevents engagement of the first and second clutch portions when the at least one of the first and second lockout fittings is in the locked position.

In accordance with an embodiment, a piston is at least partially disposed within the drive shaft and coupled to the rod.

In an embodiment, the landing gear system further includes a motor coupled to the drive shaft to rotate the drive shaft about the axis.

In an embodiment, the cavity is configured to be selectively pressurized to move the piston from the first position to the second position and depressurized to move the piston from the second position to the first position.

In an embodiment, the cavity is selectively pressurized by at least one of oil, air, and nitrogen.

In an embodiment, the landing gear system further includes a spring disposed within the axle to bias the piston toward the first position.

In an embodiment, the landing gear system further includes a first alignment fitting associated with the first clutch portion and a second alignment fitting associated with the second clutch portion. The first alignment fitting engages the second alignment fitting to align the first clutch portion with the second clutch portion as the piston moves from the first position to the second position.

In an embodiment, the landing gear system further includes a lockout assembly with first and second lockout fittings. The first lockout fitting is associated with first clutch portion and the second lockout fitting is associated with the second clutch portion. At least one of the first and second lockout fittings is selectively movable between a locked position and an unlocked position. Engagement of the first and second lockout fittings prevents engagement of the first and second clutch portions when the at least one of the first and second lockout fittings is in the locked position.

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:.

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 selectively engages and disengages with the wheel through a curvic clutch to drive the wheel to taxi the aircraft. In some embodiments, a piston is slidingly disposed within the drive shaft to reciprocate a portion of the curvic clutch between an engaged position and a disengaged position. The piston is driven toward the engaged position by a pressurized fluid within the axle. A spring provides a return force to bias the piston toward the disengaged position.

Referring now to <FIG>, a first representative embodiment of a landing gear system <NUM> according to the present disclosure is shown. As best shown in <FIG> and <FIG>, the landing gear system <NUM> includes a strut <NUM> and an axle assembly <NUM>. One end of the strut <NUM> is coupled to the aircraft (not shown) and the other end of the strut is coupled to the axle assembly <NUM> at a strut interface <NUM> formed in an axle housing <NUM>, as shown in <FIG>. In the illustrated embodiment, the axle assembly <NUM> extends laterally outward from the strut <NUM> and has a wheel <NUM> rotatably mounted to each end.

As best shown in <FIG>, a motor <NUM> is mounted to a rear side of the axle housing <NUM>. As explained in further detail, the motor <NUM> provides the driving force to rotate one or more of the wheels <NUM> to taxi the aircraft. As will be described in further detail, at least one of the wheels <NUM> includes a hub <NUM> that engages the axle assembly <NUM>. A torque link lug <NUM> is formed on a forward end of the axle assembly <NUM> 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 <NUM> 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 <NUM> is positioned forward of the axle assembly <NUM> or in another suitable location, and/or the torque link assembly is positioned aft of the axle assembly.

Referring now to <FIG>, which is a cross-sectional view of the system <NUM> taken along line <NUM>-<NUM> in <FIG>, the motor <NUM> includes a housing <NUM> coupled to an aft side of the axle housing <NUM> by mechanical fasteners or other suitable means. The motor <NUM>, which may be electric, hydraulic, or any other suitable type of motor, selectively rotates an output gear <NUM>. The output gear <NUM> is operably coupled to a drive shaft gear <NUM> rotatably mounted within the axle housing <NUM> through an intermediate gear <NUM>. The drive shaft gear <NUM> engages a drive shaft <NUM> so that the rotation of the drive shaft gear <NUM> rotates the drive shaft <NUM> about a common axis <NUM>.

In the illustrated embodiment, the portion of the drive shaft <NUM> that engages the drive shaft gear <NUM> has three lobes and nests within a similarly-shaped aperture in the drive shaft gear. In other contemplated embodiments, the drive shaft <NUM> may be mechanically fastened to or integrally formed with the drive shaft gear <NUM>. Additional configurations may use different numbers and sizes of gears or other transmission elements to transform the output of the motor <NUM> into rotation of the drive shaft <NUM> about the axis <NUM>.

Referring now to <FIG>, which is a partial cross-sectional rear view taken along line <NUM>-<NUM> of <FIG>, the landing gear system <NUM> is shown with portions of the wheels <NUM> removed for clarity. The axle housing <NUM> includes an elongate internal cavity <NUM>. The drive shaft <NUM> is mounted within the cavity <NUM> via a plurality of bearings <NUM> to be rotatable about axis <NUM>.

An elongate cavity <NUM> is formed in the drive shaft <NUM> and extends along the axis <NUM> of the drive shaft. A first end of the cavity <NUM> is in fluid communication with the cavity <NUM> of the axle housing <NUM>. Slidingly disposed in a second end of the cavity <NUM> is a piston assembly <NUM>. The piston assembly <NUM> includes a piston <NUM> in sliding contact with the wall of the drive shaft cavity <NUM> and a rod <NUM> extending from the piston and slidingly supported by a bearing <NUM> mounted within the drive shaft cavity. A return spring <NUM> is positioned between the bearing <NUM> and the piston <NUM> to provide a biasing force that urges the piston assembly <NUM> in an inboard direction. As the piston <NUM> moves in an outboard direction, the spring <NUM> is compressed between the bearing <NUM> and the piston <NUM>, and the biasing force provide by the spring increases.

As previously described, the drive shaft cavity <NUM> is in fluid communication with the cavity <NUM> of the axle housing <NUM>. In the illustrated embodiment, the cavity <NUM> is sealed at one end by a plug <NUM> mounted within the axle housing <NUM>. The cavity <NUM> is fluid tight and filled with a fluid <NUM>.

In the illustrated embodiment, the fluid <NUM> is a lubricating oil that lubricates the internal components of the axle assembly <NUM>. The fluid <NUM> also provides an actuating force to drive the piston assembly <NUM> from a first (inboard) position to a second (outboard) position. The actuating force is generated by pressurizing the cavity <NUM> with fluid <NUM> to drive the piston assembly <NUM>. As the pressure of the fluid <NUM> increases, the force exerted on the piston <NUM> increases until the force overcomes the biasing force of the spring <NUM>, at which point the piston moves in an outboard direction. As the pressure of the fluid <NUM> decreases, the actuating force decreases, and the spring <NUM> returns the piston assembly <NUM> to the first position. As will be described in further detail, the reciprocating movement of the piston assembly <NUM> between the first and second positions engages and disengages a curvic clutch <NUM> that connects the drive shaft to <NUM> to a hub <NUM> of one of the wheels <NUM>. It will be appreciated that while embodiments are disclosed that utilize a curvic clutch <NUM>, other types of clutches may be utilized and should be considered within the scope of the present disclosure. As one nonlimiting example, one alternate embodiment utilizes a clutch that is a dog clutch.

As described, the illustrated embodiment, utilizes pressurized lubricating oil (or another suitable lubricant) both to lubricate the internal components of the axle assembly <NUM> and to provide an actuating force that drives the piston assembly <NUM> from the first position to the second position. In another contemplated embodiment, the cavity <NUM> of the axle assembly <NUM> includes an amount of lubricating fluid suitable to lubricate the internal components of the axle assembly <NUM>, and the remainder of the cavity is filled with dry air, nitrogen, or another suitable gas. The cavity <NUM> is pressurized with the gas to pneumatically actuate the piston <NUM> to engage the curvic clutch <NUM> and is vented to disengage the curvic clutch <NUM>.

It will be appreciated that the illustrated configuration to engage and disengage the curvic clutch is exemplary only. In this regard, other configurations are contemplated in which solenoids, magnetic actuators, hydraulic actuators, or any other suitable actuators are utilized to move the curvic clutch between the engaged and disengaged positions, and such configurations should be considered within the scope of the present disclosure.

Referring now to <FIG>, a curvic clutch <NUM> selectively engages and disengages the drive shaft <NUM> to one of the wheels <NUM>. More specifically, the curvic clutch <NUM> includes a first portion <NUM> associated with the drive shaft <NUM> and a second portion <NUM> associated with the hub <NUM>, such that the wheel turns independent of the drive shaft when the curvic clutch is disengaged (<FIG>), and rotation of the drive shaft drives the wheel when the curvic clutch is engaged (<FIG>).

The first clutch portion <NUM> is slidably mounted to the drive shaft <NUM> by a splined connection. More specifically, the drive shaft <NUM> extends partially through a central opening formed in the first clutch portion <NUM> so that splines <NUM> formed in the first clutch portion engage corresponding splines <NUM> formed on an exterior surface of the drive shaft <NUM>. The engagement of the splines <NUM> and <NUM> causes the first clutch portion <NUM> to rotate about axis <NUM> with the drive shaft, while also allowing the first clutch portion to translate relative to the drive shaft in the direction of the axis <NUM>. The first clutch portion <NUM> is also coupled to the rod <NUM> of the piston assembly <NUM> so that when the piston assembly reciprocates between the first and second positions, the first clutch portion reciprocates between the disengaged and engaged positions, respectively.

The second clutch portion <NUM> is fixedly coupled to a hub <NUM> that is itself a component of the wheel <NUM> (see <FIG>) and rotates with the wheel. The illustrated hub <NUM> is a hubcap that is reinforced to be able to transfer torque loads from the drive shaft <NUM> to the wheel <NUM>. In another embodiment, the second clutch portion <NUM> is coupled directly to the rim of the wheel <NUM>. In another embodiment, the second clutch <NUM> portion is indirectly coupled to the wheel <NUM> by a known transmission, gearbox, or other suitable configuration that transfers rotation of the second clutch portion to the wheel <NUM>.

In the illustrated embodiment, the clutch <NUM> is a curvic clutch of the type disclosed in <CIT>, and <CIT>. As best shown in <FIG>, the first clutch portion <NUM> includes a plurality of teeth <NUM> formed so that the sides of the teeth are concave. The second clutch portion <NUM> has a corresponding plurality of teeth <NUM> formed so that the sides of the teeth are convex. When the first and second clutch portions <NUM> and <NUM> 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.

The teeth <NUM> and <NUM> of the first and second clutch portions <NUM> and <NUM>, 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, as shown in <FIG>. The teeth <NUM> and <NUM> of the curvic clutch <NUM> can be machined at a variety of angles. <FIG> show a first embodiment with a straight cut set of teeth, i.e. teeth with a <NUM>° tooth angle θ. However, if the clutch disengages under load, the return spring <NUM> 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. <FIG> shows another embodiment of a a clutch <NUM> with tooth angles greater than <NUM>°. As tooth angles greater than <NUM>° are utilized, a 'throw out' axial force is produced as a function of the torque applied by the drive shaft <NUM>. This axial force acts to disengage the clutch <NUM>, which allows for the use of a smaller return spring <NUM>. In one embodiment, the tooth angle is <NUM> °. In another embodiment, the tooth angle is in the range of <NUM> ° to <NUM> °.

To utilize the autonomous taxiing capabilities of the disclosed landing gear system <NUM>, the cavity <NUM> of the axle housing <NUM> is pressurized to engage the curvic clutch <NUM>. With the curvic clutch <NUM> engaged, the motor <NUM> is selectively powered to drive one or more wheels <NUM> of the landing gear system <NUM>. By using the motor <NUM> to drive the wheels <NUM> 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 axle housing <NUM> is depressurized, and the curvic clutch <NUM> returns to the disengaged position. With the curvic clutch disengaged, the wheels <NUM> of the aircraft are effectively isolated from motor <NUM> and other landing gear system components related to autonomous taxiing functionality.

Due to the large deflections of aircraft landing gear axles, there will sometimes be some misalignment of the first and second clutch portions <NUM> and <NUM>. This misalignment can be angular as well radial. <FIG> shows an embodiment of a curvic clutch <NUM> with alignment features that align the first and second clutch portions <NUM> and <NUM> as the curvic clutch <NUM> moves from the disengaged position to the engaged position.

As shown in <FIG>, a first alignment fitting <NUM> is coupled to the first clutch portion <NUM>. The first alignment fitting <NUM> includes a base mounted to or integrally formed with the first clutch portion. A generally cylindrical portion of the first alignment fitting <NUM> extends axially from the base toward the second clutch portion <NUM>. An external chamfer formed on the end of the cylindrical portion defines a frustoconical first alignment surface <NUM>.

A second alignment fitting <NUM> is coupled to the hub <NUM> or the second clutch portion <NUM>. The second alignment fitting includes a cylindrical recess defining an inner surface <NUM>. The inboard end of the recess includes a chamfer that defines a second alignment surface <NUM>.

As the curvic clutch <NUM> moves from a disengaged position to the engaged position, i.e., when the first clutch portion <NUM> moves toward the second clutch portion <NUM>, the first alignment surface <NUM> of the first alignment fitting <NUM> contacts the second alignment surface <NUM> of the second alignment fitting <NUM>, even in the presence of angular and/or radial misalignment. As the first clutch portion <NUM> continues to move toward the second clutch portion <NUM>, the first alignment surface <NUM> slides along the second alignment surface <NUM> and then the inner surface <NUM> of the second alignment fitting. Engagement of the first alignment fitting <NUM> with the second alignment fitting <NUM> in this manner aligns the first and second clutch portions <NUM> and <NUM> as the curvic clutch <NUM> moves toward the engaged position.

Because of the sliding contact between the of the first alignment fitting <NUM> with the second alignment fitting <NUM> as the curvic clutch <NUM> 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 aluminium 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 <NUM> and <NUM> are reversed, so that the alignment fitting coupled to the drive shaft receives the alignment fitting coupled to the wheel. In an embodiment, the recess formed in the second alignment fitting is conical, frusto-conical, or any other suitable shape. These and other variations of fittings that alight the first and second clutch portions <NUM> and <NUM> are contemplated and should be considered within the scope of the present disclosure.

Referring now to <FIG>, an illustrated embodiment includes a mechanical lockout that prevents engagement of the clutch <NUM>. The lockout system includes a first lockout fitting <NUM> coupled to the first clutch portion <NUM>. In the illustrated embodiment, the first lockout fitting <NUM> is a cylindrical fitting that has a first surface <NUM> on the end closest to the second clutch portion. A second lockout fitting <NUM> is positioned on the hub <NUM> and has a second surface <NUM> on the end closest to the first lockout fitting <NUM>. The second lockout fitting <NUM> is extendable between a disabled (retracted) position, shown in <FIG>, and an enabled (extended) position, shown in <FIG>. In the disabled position, i.e., when the lockout feature is disabled, the clearance between the first and second lockout fittings <NUM> and <NUM> is such that the lockout fittings do not contact each other as the curvic clutch <NUM> moves from the disengaged position to the engaged position.

To enable the lockout, the second lockout fitting <NUM> is moved to the extended position. With the second lockout fitting <NUM> in the extended position, the first surface <NUM> engages the second surface <NUM> as the curvic clutch <NUM> moves toward the engaged position. This engagement occurs before the first clutch portion <NUM> engages the second clutch portion <NUM> and prevents further movement of the clutch <NUM> toward the engaged position. As a result, engagement of the curvic clutch <NUM> is prevented.

The illustrated second lockout fitting <NUM> is a cam or screw driven mechanism that extends and retracts through rotation of a cap. In other contemplated embodiments, the second lockout fitting is a translating cylinder configured to be pinned in the enabled position from the outside, a device that is pushed inwards and rotated to lock into detents, or a threaded fitting adjustably mounted to the hub. These and other lockout configurations that selectively prevent engagement of the curvic clutch <NUM> are contemplated and should be considered within the scope of the present disclosure.

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 <NUM>% 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.

Claim 1:
A landing gear system (<NUM>), comprising:
an axle (<NUM>) comprising an internal cavity (<NUM>); and
a wheel (<NUM>) rotatably coupled to the axle (<NUM>);
a drive shaft (<NUM>) disposed within the cavity (<NUM>), the drive shaft (<NUM>) being rotatable about an axis (<NUM>),
wherein the landing gear system (<NUM>) comprises:
a rod (<NUM>) slidably mounted within the drive shaft (<NUM>); and
a clutch (<NUM>), comprising:
a first clutch portion (<NUM>), and
a second clutch portion (<NUM>) fixedly coupled to the wheel (<NUM>),
wherein the rod (<NUM>) selectively reciprocates along the axis (<NUM>) between a first position and a second position, the first clutch portion (<NUM>) being disengaged from the second clutch portion (<NUM>) when the rod (<NUM>) is in the first position, the first clutch portion (<NUM>) engaging the second clutch portion (<NUM>) when the rod (<NUM>) is in the second position; characterised in that the first clutch portion (<NUM>) is fixedly coupled to the rod (<NUM>) and configured to rotate with the drive shaft (<NUM>).