Aircraft taxi system including drive chain

An aircraft taxi drive system includes a motor that is configured to transfer power to an aircraft wheel via a drive chain, such that the motor rotates the aircraft wheel via the drive chain. In some examples, the drive chain is movable between first and second positions. In the first position, the drive chain, such as an exterior surface of the drive chain, is engaged with a driven sprocket that is mechanically connected to an aircraft wheel. In the second position, the drive chain is disengaged from the driven sprocket.

TECHNICAL FIELD

This disclosure relates to aircraft, and, more particularly, aircraft taxi systems.

BACKGROUND

Aircraft may perform taxiing maneuvers on the ground, e.g., travelling from a terminal to the runway or vice versa. In some systems, propulsion for the aircraft while taxiing is provided by thrust from the main engines or a tow cart.

SUMMARY

In general, this disclosure relates to devices, systems, and techniques for taxiing an aircraft or otherwise moving the aircraft on the ground without reliance on the thrust of the main engines of the aircraft (e.g., engines used to provide thrust during flight or takeoff) to propel the aircraft. An aircraft taxi drive system that is separate from the main engines provides the energy that is used to move the aircraft on the ground. In some examples, the aircraft taxi drive system includes a motor that is configured to transfer power to an aircraft wheel via a drive chain, such that the motor rotates the aircraft wheel via the drive chain, which may result in movement of the aircraft on the ground. In some examples, the drive chain (e.g., an exterior surface of the drive chain) is configured to be disengaged from the aircraft wheel, e.g., during aircraft takeoff, landing, and other times taxiing of the aircraft is not necessary or desired, and reengaged when taxiing is desirable (e.g., after landing). In some examples, the motor and drive chain may be sized to fit on an existing land gear assembly of an aircraft, and may allow the taxi drive system to be retrofitted onto existing aircraft.

In one example, the disclosure is directed to a system comprising a motor configured to generate a mechanical output, a drive sprocket configured to be driven by the motor, a drive chain mechanically connected to the drive sprocket, an aircraft wheel and a driven sprocket mechanically connected to the aircraft wheel. The drive sprocket is configured to transfer the mechanical output from the motor to the drive chain. An exterior surface of the drive chain is configured to engage with the driven sprocket to transfer the mechanical output of the motor to the driven sprocket and the aircraft wheel. Rotation of the driven sprocket is configured to rotate the aircraft wheel.

In another example, the disclosure is directed to a system comprising means for providing a mechanical output, an aircraft wheel, means for transferring the mechanical output to the aircraft wheel, and means for moving the motor and the transferring means relative to the aircraft wheel to bring the transferring means into and out of engagement with the aircraft wheel.

In another example, the disclosure is directed to a method comprising engaging an exterior surface of a drive chain with a driven sprocket that is mechanically connected to an aircraft wheel, rotating the aircraft wheel by transferring a mechanical output of a motor to the driven sprocket and aircraft wheel via the drive chain, and disengaging the drive chain from the driven sprocket.

DETAILED DESCRIPTION

The present disclosure describes example aircraft taxi drive systems that can be used to propel an aircraft on the ground, e.g., to taxi the aircraft on the ground from one point to another. The example aircraft taxi drive system is carried by the aircraft and includes a motor that is separate from the main engines (e.g., jet engines) of the aircraft, such that the propulsion of the aircraft during taxiing is independent of the main engines used during flight. The main engines provide the thrust required during take-off of the aircraft and during flight, whereas the motor of the taxi drive system is configured to provide an output that drives an drive chain, which, when engaged with an aircraft wheel, rotates the wheel during taxiing.

In some existing aircraft taxi systems, the output of the main engines propels the aircraft during the taxiing of the aircraft. Reversing capability may be provided by thrust reversers on the one or more turbine engines of the aircraft or by reversing the pitch of the propellers on a prop plane. The low power settings for jet engines required during taxi maneuvers can be inefficient, and may result in the waste of hundreds of gallons of fuel for each modern commercial airliner every day. Further, the use of the main jet engines near the terminal and other locations may be restricted. In such situations, a tow cart may be required to maneuver the jet aircraft on the ground. The use of the tow cart to move the aircraft on the ground may consume additional manpower and require special equipment.

The example aircraft taxi drive systems described herein allows an aircraft to taxi without reliance on the aircraft main engine(s) to provide thrust or without reliance on an external device, such as a tow cart. Because the example taxi drive system has a separate motor, the aircraft may be taxied while the main engines are shutdown or at idle. With the main engines idled or shutdown, the taxi drive system allows the aircraft to maneuver under its own power, e.g., near terminal buildings at an airport. In some examples, multiple taxi drive systems may be fitted onto the aircraft, allowing directional control, e.g., through the use of differential thrust from the taxi drive system. In other configurations, the taxi drive system may be mounted on a steerable landing gear assembly.

As discussed in further detail below, the example aircraft taxi drive systems described herein are configured such that they may each be relatively easy to retrofit an existing aircraft to include such a taxi drive system, e.g., the retrofitting may not require extensive modification to the aircraft. Retrofitting existing aircraft to include a taxi drive system separate from the main engines may include various considerations. For example, retrofitting taxi drive systems onto existing aircraft without extensive modification may be limited by the dimensions of the landing gear and the landing gear bays. The taxi drive systems described herein are relatively compact, which may increase the number of types of landing gear the taxi drive system may be retrofit onto.

Compounding the design challenges faced by a taxi system is the environment the taxi system operates in. During takeoff and landing, the rotation rate of the aircraft wheels is extremely high. Thus, permanent attachment of a taxi drive system to the aircraft wheels may require mass intensive transmission or clutch systems in order to protect the taxi drive system from damage due to the torque generated by the speeds involved. The example taxi drive systems described herein is configured to engage and disengage with the aircraft wheels, e.g., by rotation or translation of the taxi drive system between a first position, in which the taxi drive system is engaged with the aircraft wheel, and a second position, in which the taxi drive system is disengaged from the aircraft wheel. In some examples, a taxi drive system includes a looped drive chain configured such that an exterior of the looped drive chain transfers torque to the aircraft wheels when the system is in the first position. By using the exterior of the drive chain loop, the drive chain loop can be relatively easily engaged or disengaged from the aircraft wheel (e.g., moved to the second position) without a complex clutch system that may be required if the interior of the loop of the drive chain was used as the engagement site.

Extra mass taken up by such a taxi drive system that includes a transmission or clutch system may decrease fuel efficiency of the aircraft and, in some cases, may reduce the passenger or cargo capability of the aircraft due to the extra space required to accommodate the taxi drive system. The example taxi drive systems described herein is able to engage or disengage as unit, allowing the use of a pivot or a translating linkage or assembly, potentially simplifying the structure and saving mass.

Also, the landing gear assembly of the aircraft may be exposed to environmental contaminants, such as dirt, melted rubber, and other contaminants. Consequently, some existing taxi drive systems that are positioned near the landing gear may be sealed from the presence of contaminants, potentially leading to a heavier taxi drive system. In contrast, the example taxi drive systems described herein may be capable of functioning robustly despite the presence of contaminants, such that enclosures for the taxi drive systems described can be, but need not be, used.

FIG. 1is a perspective diagram illustrating an example aircraft landing gear assembly10equipped with an example taxi drive system24. An aircraft may be equipped with one or more landing gear assemblies10, which can include respective one or more taxi drive systems20(e.g., one taxi drive system per landing gear assembly or per wheel of a landing gear assembly). In other examples, only a subset of the landing gear assemblies of an aircraft may be equipped with a respective taxi drive system24. In the example shown inFIG. 1, landing gear assembly10comprises aircraft tires12, cylinder14, piston16, torque arm18, and hub20. In addition, in the example shown inFIG. 1, taxi drive system24comprises plate26, motor28, drive chain30, drive sprocket32, spacers34, actuator mount36, and armature mount38.

Taxi drive system24may be located on one or more landing gear assemblies10. In the example shown inFIG. 1, taxi drive system24is installed between aircraft tires12opposite torque arm18. In some examples, taxi drive system24may be mechanically coupled to landing gear assembly10via an armature, e.g., armature assembly30(FIG. 3), and axle housing22(FIG. 3). In other examples, taxi drive system24may be connected to other points on landing gear assembly10. In addition, other mechanisms can be used to mechanically connect taxi drive system24to landing gear assembly10. As discussed in further detail below, actuator mount36may provide a connection point allowing taxi drive system24to be moved between a first position, in which drive chain30is engaged with aircraft wheel10, and a second position, in which drive chain30is disengaged from aircraft wheel10, via armature system44.

Two aircraft tires12are depicted in the example configuration of landing gear assembly10depicted inFIG. 1, but landing gear assembly10may be equipped with one or more aircraft tires12in other examples. Hub20is configured to support aircraft tires12on an axle (not shown) connected through axle housing22to piston16. An independent braking system (not shown), e.g., a brake disc stack and brake actuator, may be co-located with taxi drive system24on (e.g., directly or indirectly mechanically connected to) landing gear assembly10at or near aircraft tires12. In other examples, taxi drive system24may be located on one or more landing gear assemblies10while an independent braking system may be equipped on other landing gear assemblies of the aircraft. In some examples, one or more of landing gear assemblies10may be steerable to provide directional control over the taxiing aircraft. In addition, or instead, steering for the taxiing aircraft may be controlled by using differential braking or differential thrust from multiple landing gear assemblies10equipped with respective taxi drive systems20.

Cylinder14and piston16may be configured to provide shock absorption for landing gear assembly10. Cylinder14may, for example, comprise a hydraulic cylinder in some examples. In these examples, upon impact with the ground during landing, aircraft tires12may drive piston16into cylinder14, increasing the hydraulic pressure within the landing gear system. The motion of hydraulic fluid through cylinder14, caused by the pressure of landing, may absorb at least some of the impact of the landing and slow the movement of piston16into cylinder14. In the example shown inFIG. 1, torque arm18is a jointed arm connected to cylinder14and a point at the base of piston16, e.g., at axle housing22for the axle supporting aircraft tires12. Torque arm18is jointed, which allows piston16to extend and retract relative to cylinder14with the takeoff and landing of the aircraft, while also helping to prevent piston16from rotating in cylinder14, thereby maintaining the alignment of the aircraft tires12with the direction of travel of the aircraft.

Motor28is configured to provide motive force to taxi drive system24by rotating drive sprocket32. Drive sprocket32may be engaged with drive chain30, which may form a loop that is configured to surround drive sprocket32. As drive sprocket32rotates, the loop formed by drive chain30also moves. When taxi drive system24is in a first position, driven sprocket42, which is mechanically connected to hub20, is engaged with the exterior of the loop formed by drive chain30. Driven sprocket42is mechanically connected to hub20such that as driven sprocket42rotates, hub20rotates (e.g., driven sprocket42can be in a fixed position relative to hub20). Thus, as the loop formed by drive chain30moves, the motion is transferred to driven sprocket42(FIG. 2) and aircraft tires12, causing the aircraft to taxi. Because drive chain30is only engaged with a part of driven sprocket42and does not loop around driven sprocket42, the concern that drive chain30may come loose from sprocket42is minimized; as discussed below, an actuation system or the like holds drive chain30in engagement with driven sprocket42, and may also hold taxi drive system24in a fixed position relative to driven sprocket42in both the first and second positions.

In situations when taxi drive system24may be exposed to relatively high torques or rotation rates from aircraft tires12, taxi drive system24may be configured to move to a second position, e.g., rotated or pivoted out of engagement with driven sprocket42, such that drive chain30does not engage with driven sprocket42. Taxi drive system24may be reengaged with driven sprocket42to taxi the aircraft by moving taxi drive system24to the first position in which drive chain30is engaged with driven sprocket42.

Motor28is configured to generate torque that can be used to propel the aircraft when the aircraft is on the ground, e.g., to taxi the aircraft. Motor28can be powered using any suitable source. In some examples, motor28may comprise or consist of an electric motor. Power for an electric motor may be drawn from any suitable source, such as directly from the electrical system of the aircraft, e.g., the auxiliary power unit (APU) of the aircraft, and routed along landing gear assembly10, or from a battery or other power source of taxi drive system10and separate from the main electrical system of the aircraft. An APU may be configured to provide energy for functions other than propulsion of the aircraft, such as to start the main engines or to power lights on the aircraft. In other examples, motor28may be powered by a fuel, such as, for example the aviation fuel used to power the main engine (s) of the aircraft during flight. In some examples, a fuel line supplying motor28may be routed along landing gear assembly10, e.g., the fuel line may traverse from the aircraft fuselage to motor28along landing gear assembly10. In addition or instead, motor28may be a hydraulic motor powered by, for example, the hydraulic system of the aircraft. In other configurations taxi drive system24may have an independent electricity, hydraulic fluid, or fuel source located on landing gear assembly10or the fuselage of the aircraft.

In some, but not all, examples, motor28may include a transmission or gear box, which may help increase the torque outputted by motor28to drive sprocket32. The gear ratio in the gearbox or transmission may be fixed or selectable, e.g., via crew member input. In some examples, the rotation rate of motor28, and, therefore, the rate at which wheel12is rotated by motor28, may be controlled by crew member input. For example, if motor28comprises an electric motor, a crew member of the aircraft may control the rotation rate of motor28, and speed of the taxiing aircraft, by varying the voltage or current supplied to motor28. Motor28may be used to taxi in reverse by reversing the polarity of the voltage or current supplied to motor28.

Motor28can be mechanically connected to drive sprocket32using any suitable configuration. In the example shown inFIG. 1, plate26supports motor28, drive sprocket32, and spacers34, e.g., motor28, drive sprocket32, and spacers34may be directly or indirectly mechanically connected to a surface of plate26. Accordingly, in the example shown inFIG. 1, motor28is mechanically connected to drive sprocket32via plate26in the example shown inFIG. 1. In some examples, plate26may hold motor28, drive sprocket32, and idler sprockets40(FIG. 2) in fixed positions relative to each other. In other configurations, plate26may be configured to allow one or more of drive sprocket32or idler sprockets40to translate relative to each other, allowing the tension in drive chain30to be adjusted or engaged/disengaged with driven sprocket42. Plate26may be configured to withstand the forces generated by the interaction of drive chain30, idler sprockets40, and the landing gear assembly10of the aircraft. Plate26may be constructed of any suitable material, such as, but not limited to, an alloy of aluminum or steel.

As discussed in further detail below, plate26provides a relatively simple and lightweight mechanism by which taxi drive system24can be moved between a first position and a second position because, in some examples, movement of plate26causes movement of drive chain30away from driven sprocket42.

In some examples, plate26may be paired with a second plate that is positioned on the other side of drive chain30from plate26, such that the opposing plates enclose drive chain30and help prevent drive chain30from slipping off of idler sprockets40and drive sprocket32by limiting the potential movement of drive chain30relative to drive sprocket32and idler sprockets40. In addition, in some examples, plate26may help prevent the passage of environmental contaminants to drive chain30and drive sprocket32by at least partially covering chain30and sprocket32. In some examples, additional plating may be added to form a container around drive chain30, and one side may be left exposed provide room for drive chain30to engage with driven sprocket42of landing gear assembly10.

Drive chain30may be mechanically connected to drive sprocket32, e.g., looped around drive sprocket32such that at least some of the teeth of drive sprocket32engage with drive chain30. For example, teeth of drive sprocket32may be positioned within gaps defined by drive chain30(e.g., holes in the links of a chain). In some examples, taxi drive system24includes spacers34, which are configured to help prevent drive chain30from loosening or sliding out of engagement with drive sprocket32. Spacers34may also support a second plate26(not shown) that, together with plate26, sandwiches drive sprocket32and drive chain30, which may further help prevent drive chain30from slipping loose from drive sprocket32. Spacers34may comprise any suitable material, for example, an alloy of steel, aluminum, or titanium.

Drive chain30may be made of any suitable material, for example an alloy of steel or titanium. Drive chain30may form a loop, encompassing drive sprocket32and idler sprocket40(FIG. 2). Drive chain30may comprise engagement sites located on both the interior and exterior surfaces of the loop formed by drive chain30, surface30A and30B (FIG. 2) respectively. An interior surface of the loop may face drive sprocket32while an exterior surface may face away from drive sprocket32. Engagement sites on the interior of the loop formed by drive chain30may allow drive sprocket32to engage with, and transfer power through, drive chain30by pulling and/or rotating drive chain30. Engagement sites on the exterior of the loop formed by drive chain30may allow driven sprocket42(FIG. 2) to engage with, and be driven by, drive chain30. The engagement sites of drive chain30may, for example, be formed by the links of drive chain30. Other types of drive chains are contemplated. For example, in some examples, drive chain30may comprise a flexible belt and engagement sites may be provided by raised teeth on both sides of the belt.

As discussed above, motor28is configured to rotate drive sprocket32. In some examples, drive sprocket32may be mechanically connected to motor28, and an incorporated transmission or gearbox, if present, via a drive shaft that penetrates through plate26. The drive shaft may be configured to transfer the rotational output of motor28, and any incorporated gear box/transmission, to drive sprocket32. Drive sprocket32may have one or more sets of teeth that are configured to engage with drive chain30. Drive chain30and sprocket32may be configured to remain engaged with each other during operation of taxi drive system24, and, in some examples, when taxi drive system24is in both the first and second positions. For example, in some examples, drive chain30may be prevented from slipping off drive sprocket32by tension in the loop formed drive chain30around drive sprocket32and idler sprockets40(FIG. 2). In some examples, a second plate positioned on the other side of drive chain30from plate26may also prevent drive chain30from slipping out of engagement with drive sprocket32by sandwiching drive sprocket32, and drive chain30, between plate26and the second plate.

Spacers34may provide support and spacing to allow drive sprocket32and idler sprockets40to rotate between two plates26. In the example shown inFIG. 1, spacers34guide drive chain30around drive sprocket32and idler sprockets40by pinching the sides of the loop formed by drive chain30inwards, forcing drive chain30to engage a larger portion of the circumference of drive sprocket32than would be engaged with a taut loop stretched from drive sprocket32to idler sprockets40. Increasing the portion of drive sprocket32engaged with drive chain30may reduce the amount of wear on drive sprocket32and drive chain30as well as decrease the incidence of slippage between drive sprocket32and drive chain30.

Drive chain30may be brought into and removed from engagement with driven sprocket42, i.e., moved between first and second positions. In the disengaged position (also referred to herein as the second position for ease of description), the teeth of driven sprocket42may not contact the engagement sites on the exterior of the loop formed by drive chain30. Drive chain30may move into the disengaged position by rotating or translating taxi drive system24as a unit by an actuation system. Similarly, drive chain30may be brought into engagement with driven sprocket42(moved to the first position) by translating or rotating taxi drive system24as unit until the teeth of driven sprocket42meshes with the exterior of the loop formed by drive chain30.

Actuator mount36provides a connection point for an actuation system, e.g., a hydraulic ram, electric ballscrew, or acme lead screw drive, that mechanically connects to taxi drive system24. Aircraft tires12may rotate at relatively high speeds during takeoff and landing of the aircraft, e.g., based on movement of the aircraft primarily or solely attributable to the main engines of the aircraft. Thus, at some points during operation of the aircraft, aircraft tires12may be driven by forces not generated by taxi drive system24. Transmission of the high rotating speeds to taxi drive system24may affect the integrity of the taxi drive system24, such as by causing drive chain30and drive sprocket32to rotate at relatively high speeds. To help reduce or even prevent transmission of high rotating speeds of aircraft tires12, e.g., during takeoff and landing of the aircraft, to taxi drive system24, taxi drive system24may be selectively engaged and removed from engagement (i.e., disengaged) with driven sprocket42and aircraft tires12.

In some examples, taxi drive system24is movable between a first position, in which drive chain30is engaged with driven sprocket42, and a second position, in which drive chain30is disengaged from driven sprocket42, by an actuator connected to actuator mount36. When drive chain30is disengaged from driven sprocket42, rotation of drive chain30by drive sprocket32is not translated to driven sprocket42, such that driven sprocket42does not rotate with drive chain30. In some examples, motor28, drive sprocket32, drive chain30, plate26, and idler sprockets40may be moved between the first and second positions as a single unit. For example, motor28, drive sprocket32, drive chain30, plate26, and idler sprockets40may have fixed positions relative to each other and may be movable relative to driven sprocket42. In other examples, only a part of taxi drive system24may be moved between the first and second positions, e.g., only plate26(and, therefore, drive chain30and drive sprocket32).

In some examples, taxi drive system24may pivot into and out of engagement with driven sprocket42. In the example shown inFIG. 1, force applied, for example by a hydraulic ram or other actuator (e.g., hydraulic ram48(FIG. 3) or an electric screw drive), at actuator mount36may cause taxi drive system24to rotate about a pivot, e.g., armature mount38, and engage or disengage with driven sprocket42. In some examples, actuator mount36may be located on the casing of motor28. In other examples, actuator mount36may be located on plate26. In other examples, taxi drive system24may be translated radially or linearly into and out of engagement with driven sprocket42. Instead, or in addition, taxi drive system24may be translated radially, e.g., translated along a radius of driven sprocket42, into or out of engagement.

Armature mount38provides a connection point for a support linking taxi drive system24to landing gear assembly10. Armature mount38may be configured to provide a pivot point about which taxi drive system24may be rotated between a first position, in which drive chain30is engaged with driven sprocket42, and a second position, in which drive chain30is disengaged from driven sprocket42, by an actuator connected to actuator mount36. In other examples, armature mount38may provide a connection between taxi drive system24and a linear bearing system, or other translation means, allowing taxi drive system24to be maneuvered into and out of engagement with driven sprocket42. In some examples, armature mount38may be located on the casing of motor28. In other examples, armature mount38may be located on plate26.

Landing gear assembly10may have other configurations in other examples. For example, landing gear assembly10can include other types of tire and hub arrangements, other axle arrangements, and the like. Taxi drive system24can be used with any suitable aircraft landing gear assembly10.

FIG. 2is a perspective diagram illustrating aircraft landing gear assembly10, with an aircraft tire12removed, and taxi drive system24. As shown inFIG. 2and described above with respect toFIG. 1, hub20supports aircraft tire12. Hub20may be mechanically connected to driven sprocket42, which is depicted inFIG. 2as being engaged with drive chain30(e.g., taxi drive system24is in the first position), causing hub20and aircraft tire12to rotate with driven sprocket42. Hub20may also be connected to an axle linking the pair of aircraft tires12and hubs20, e.g., through axle housing22(FIG. 3) at the base of piston16. Driven sprocket42may be mechanically connected to hub20using any suitable technique. In some examples, hub20and driven sprocket42are formed from a single, continuous material such that they are an integral piece of material. As an example, driven sprocket42may be machined as part of hub20. In other examples, driven sprocket42may be physically separate from hub20and mechanically connected to hub20, e.g., bolted or riveted to hub20, or connected to hub20via the axle supporting hub20and aircraft tires12. Other configurations are also contemplated.

Also shown inFIG. 2are idler sprockets40, which are mounted on plate26. Taxi drive system24can include one or more idler sprockets40. As discussed above with respect toFIG. 1, idler sprockets40are configured to engage with drive chain30to help maintain tension of drive chain30to allow driven sprocket42to engage drive chain30. In addition, idler sprockets40can help shape the loop formed by chain30and expand or shrink the loop of drive chain30to change the length of drive chain30that is configured to engage with driven sprocket42. In some cases, it may be desirable to maximize a length of drive chain30that engages with driven sprocket42may increase the life span of drive chain30and driven sprocket42, as well as reduce the possibility of drive chain30slipping out of engagement with driven sprocket42. In other cases, it may be desirable to reduce the length of drive chain30that engages with driven sprocket42in order to reduce the total size of taxi drive system24and may ease the engagement/disengagement of drive chain30with driven sprocket42. Idler sprockets40may rotate under the influence of drive sprocket32and drive chain30.

In the example depicted inFIG. 2, idler sprockets40are depicted positioned in a triangular arrangement with drive sprocket32at an apex and the base of the triangle oriented towards driven sprocket42. This arrangement may prevent drive chain30from impinging on itself as drive chain30flexes towards drive sprocket32when chain30is brought into engagement with driven sprocket42. In other examples, idler sprockets40may also be located at the position of spacers34, which may help shape the path the loop of drive chain30follows and increase the proportion of drive sprocket32engaged with drive chain30. In other examples, a single idler sprocket may be used to expand drive chain30to allow the exterior of drive chain30to be brought into engagement with driven sprocket42.

Idler sprockets40may be configured to translate to maintain tension in drive chain30, for example idler sprockets40may be mounted on a spring tensioned pivot arm (not shown). A minimum tension on drive chain30to prevent drive chain30from coming loose from idler sprockets40or drive sprocket32may be maintained. Other techniques can be used in addition to or instead of idler sprockets40in order to maintain contact between idler sprockets40and drive chain30. For example, a tooth size of idler sprockets40may be selected to enable idler sprockets40to maintain contact with drive chain30. In addition, or instead, a second plate26may sandwich drive chain30between a first plate26and help prevent disengagement with idler sprockets40and drive sprocket32.

Driven sprocket42is configured to transfer the mechanical output of motor28, transmitted via drive chain30, to aircraft tire12. In the example shown inFIG. 2, driven sprocket42is larger than drive sprocket32, which may increase the torque outputted to aircraft tires12. The size of driven sprocket42and driven sprocket42may be specific to the type of aircraft taxi drive system24is used with, and can be influenced by factors such as gear ratio, sprocket tooth stress, velocity limits for drive chain30, and access restrictions around existing equipment in landing gear assembly10. Driven sprocket42is depicted as equipped with a double row of teeth inFIG. 2. In other configurations, driven sprocket42may have one or more rows of teeth sized to engage with drive chain30. Drive chain30may flex during engagement with driven sprocket42to partially follow the curvature of driven sprocket42. By flexing to follow the curve of driven sprocket42, drive chain30may reduce the individual stress on the teeth of driven sprocket42, thereby helping to increase the life of driven sprocket42and reducing chances of slippage between driven sprocket42and drive chain30.

A taxi drive system24equipped with drive chain30that is configured to engage with driven sprocket42may be advantageous over some geared drive systems in which two sprockets engage with each other to transfer mechanical output from a motor to aircraft tire12. For example, the gear drive systems may require tighter tolerances in spacing of the teeth between gears than a drive chain-sprocket mesh requires, which may require the control of the gear drive system to be more precise (e.g., thereby increasing the cost of the taxi drive system). Further, the gear drive systems may require more extensive lubrication and contaminant protections than system24including drive chain30. In addition, because drive chain30is relatively flexible relative to driven sprocket42, the amount of wear to drive chain30and driven sprocket42due to relative motion between drive chain30and driven sprocket42during operation of the taxi drive system may be reduced relative to the amount of wear between two sprockets that more directly engage with each other (e.g., by meshing teeth).

FIG. 3is a cutaway diagram illustrating an aircraft landing gear assembly10equipped with a taxi drive system24. Taxi drive system24is equipped with an armature system44, which supports taxi drive system24and allows taxi drive system24to be moved between the first and second positions. In the example shown inFIG. 3, armature system44comprises armature46, hydraulic ram48, piston mount50, axle mount52, and front support54. Taxi drive system24is depicted as being connected to armature system44via armature mount38as a pivot. In other examples, taxi drive system24may be slidably connected to armature system44such that taxi drive system24can be linearly moved between the first and second position, or armature system44may radially translate taxi drive system24towards and away from driven sprocket42. The pivot and radial translation may require less room for movement of taxi drive system24than the linear system.

Landing gear assembly10may comprise an axle housing22located at the base of piston16. Axle housing22may support an axle (not shown) connecting aircraft tires12via respective hubs20. Torque arm18, depicted partially cutaway inFIG. 3, may connect cylinder14(FIG. 1) to the base of piston16and axle housing22, preventing the rotation of piston16in cylinder14while allowing piston16to retract into cylinder14during landing. The joint between the upper and lower sections (18A and18B respectively) of torque arm18is visible inFIG. 3. The lower section of torque arm18is depicted inFIG. 3as pivotably connected to axle housing22. In other embodiments, torque arm18may be connected to other locations on piston16.

Taxi drive system24is in the first position inFIG. 3, in which drive chain30is engaged with driven sprocket42inFIG. 3. Armature46may comprise one or more rigid members extending below axle housing22and piston16to provide support for taxi drive system24. Taxi drive system24and armature46may be pivotably connected via armature mount38. In other examples, armature46may comprise a linkage allowing armature46to extend and retract, translating taxi drive system24radially into and out of engagement with driven sprocket42. In further examples, taxi drive system24may be slidably connected to armature46, allowing taxi drive system24to be translated radially or linearly into and out of engagement with driven sprocket42(e.g., between the first and second positions).

Armature46may be rigidly coupled to landing gear assembly10. As depicted inFIG. 3, armature46may be connected to piston16via piston mount50and axle mount52. By coupling armature46to landing gear assembly10, armature46and taxi drive system24may be retrofitted onto existing aircraft landing gear10without requiring modification to the size and other components of aircraft landing gear10.

In examples in which taxi drive system24pivots between the first and second positions, hydraulic ram48may provide the force that causes taxi drive system24to pivot between the first and second positions, into and out of engagement with driven sprocket42. Hydraulic ram48may comprise actuator cylinder48A and actuator piston48B. Hydraulic ram48may be pivotably connected to armature46and actuator mount36. In other configurations hydraulic ram48may be pivotably connected to front support54. In some examples, hydraulic ram48may comprise a double acting hydraulic actuator. Hydraulic fluid may be routed through feed lines located on, for example, landing gear assembly10and connected to the hydraulic system of the aircraft. In other examples, another suitable mechanism in addition to or instead of hydraulic ram48can be used to pivot taxi drive system24between the first and second positions. For example, a pneumatic piston or an electric drive actuator, such as an electric ballscrew or acme lead screw drive, can be used to pivot taxi drive system24between the first and second positions.

Piston mount50is configured to couple armature assembly30to landing gear assembly10so that taxi drive system24is supported. Piston mount50may comprise a collar bolted around or otherwise attached to piston16above axle housing22. Piston mount50may comprise two sections bolted or welded together, allowing piston mount50to be retrofitted onto existing landing gear assemblies. Piston mount50may connect to armature46via front support54, providing support for armature46under the weight of taxi drive system24and torque loads resulting from rotating driven sprocket42and aircraft tires12.

Axle mount52is configured to provide additional support to armature assembly30and taxi drive system24, mechanically coupling armature assembly30to landing gear assembly10and helping to prevent or control motion of armature assembly30. Axle mount52may be mechanically coupled to axle housing22and extend a rigid member radially away from axle housing22to connect to armature46. In some examples, axle mount52may be rigidly connected to landing gear assembly10. In other examples, axle mount52may be pivotably coupled to both armature46and axle housing22. Pivotably coupling axle mount52to axle housing22may allow axle mount52to rotate and move armature46, resulting in taxi drive system24being translated into and out of engagement with driven sprocket42.

Front support54is configured to support armature46by linking armature46to piston mount50. Front support54may comprise a rigid member connecting piston mount50and armature46. Front support54may be rigidly connected to piston mount50and armature46, providing support to armature46and taxi drive system24. In some examples, front support54may be manufactured as part of armature46. In addition, in some examples, front support54may be pivotably connected to armature46and piston mount50, allowing armature46to translate taxi drive system24into and out of engagement with driven sprocket42. Front support54may provide a mounting point for hydraulic ram48.

FIG. 4is a perspective diagram illustrating aircraft landing gear assembly10and taxi drive system24. One aircraft tire12of landing gear assembly10is not shown inFIG. 4, exposing taxi drive system24and armature system44. In the example shown inFIG. 4, taxi drive system24is in the first position, such that drive chain30is engaged with driven sprocket42.

As depicted inFIG. 4, some examples of armature system44may comprise one or more frames and bracings to increase the strength and stability of armature system44while minimizing weight. Armature system44may comprise armature46, hydraulic ram48, and axle mount52. Piston mount50(FIG. 3) and front support54(FIG. 3) are not visible inFIG. 4. As shown inFIG. 4, armature46may comprise one or more rigid members46A connected to axle mount52and armature mount38. Armature46may further comprise bracing members46B which form a frame with rigid members46A, and may prevent armature46from flexing under the weight and torque of taxi drive system24. The frames formed by one or more rigid members46A and46B may be connected together. Armature46may mechanically connect to, or be manufactured including, front support54. Front support54may mechanically connect armature46to piston mount50. Piston mount50may be bolted or otherwise mechanically connected to piston16or axle housing22, linking armature46to landing gear assembly10. Axle mount52may be coupled to axle housing22and provide further support for armature46. Hydraulic ram48, or another actuator type, may be mechanically coupled to piston mount16, armature46, or front support54, and may be configured to apply a force at actuator mount36that causes taxi drive system24to move between the first and second positions.

FIGS. 5A and 5Bare cutaway diagrams illustrating taxi drive system24in the first position, in which drive chain30is engaged with driven sprocket42that is mechanically connected to hub20.FIG. 5Adepicts taxi drive system24and armature system44, with landing gear assembly10removed, as viewed from the interior of the landing gear. Taxi drive system24is engaged with driven sprocket42and may transfer torque to aircraft wheel12to allow an aircraft to taxi.

InFIG. 5A, taxi drive system24is shown in the first (engaged) position. In the first position of taxi drive system24, the teeth of driven sprocket42mesh with drive chain30and drive chain30pulls against the teeth of driven sprocket42. To move system24into the first position by bringing drive chain30into engagement with driven sprocket42, hydraulic ram48may retract and pull taxi drive system24from the second (disengaged) position to the first position.

FIG. 5Bdepicts taxi drive system24in the first position, in which drive chain30is engaged position with driven sprocket42. An aircraft tire12is removed to better show the workings of taxi drive system24. The perspective of the diagram is from the exterior of the landing gear system and in a direction substantially parallel to the axis of rotation of wheel12.

In some examples, taxi drive system24may be rotated into engagement with driven sprocket42. For example, taxi drive system24may pivot about armature mount38as force from hydraulic ram48is applied. In other configurations, taxi drive system24may be translated into and out of the first and second positions. In some examples, armature system44may comprise a linear bearing or bale that, when actuated, retracts, pulling drive system24into contact with driven sprocket42, such that drive chain30meshes with driven sprocket42. In addition, or alternatively, axle mount52may be pivotably coupled to armature46and axle housing22. As axle mount52rotates away from taxi drive system24, armature46is pulled towards landing gear assembly10and brings taxi drive system24towards driven sprocket42. Front support54may be pivotably coupled armature46and piston mount50, supporting armature46while allowing armature46to translate under influence of axle mount52. Taxi drive system24may be rigidly coupled to armature46, as the motion of armature46may be sufficient to bring taxi drive system24into engagement. A brace extending, for example, between actuator mount36and armature46or front support54may further support taxi drive system24.

As discussed in further detail below, in some examples, prior to being moved into the first position, taxi drive system24may be activated to rotate drive chain30, such that drive chain30is rotating when it is brought into engagement with driven sprocket42. This may help reduce wear on drive chain30during engagement.

In some examples, idler sprockets40or spacers34may be movable to maintain a constant tension in drive chain30. By using movable spacers34or idler sprockets40drive chain30may be installed in taxi drive system24with some slack. In the first (engaged) position, the slack in the loop formed by drive chain30is taken up by driven sprocket42impinging on the loop. By allowing drive chain30to conform to a portion of the curve of driven sprocket42, the contact area and number of teeth of driven sprocket42engaged with drive chain30may increase, which may help reduce wear on drive chain30and driven sprocket42. As taxi drive system24is disengaged, the slack in drive chain30may be taken up by movable idler sprockets40or spacers34.

FIGS. 6A and 6Bare cutaway diagrams illustrating a taxi drive system24in the second position.FIG. 6Adepicts taxi drive system24in the second position. The perspective ofFIG. 6Bis substantially similar to that ofFIG. 5B. An aircraft tire12is removed fromFIGS. 6A and 6Bto better show the workings of taxi drive system24.

In the disengaged position, as shown inFIG. 6A, driven sprocket42and aircraft tires12rotate without influence from the influence of taxi drive system24. The teeth of driven sprocket42do not mesh with drive chain30. To move system24from the first position and into the second, hydraulic ram48may extend and push taxi drive system24into the second (disengaged) position from the first position. This may help limit or even eliminate the transfer of high rotational speeds of aircraft tires12(e.g., during takeoff and landing) to taxi drive system24.

In other examples, taxi drive system24may be translated out of engagement with driven sprocket42. For example, axle mount52may be pivotably coupled to axle housing22and armature46. As axle mount52rotates towards taxi drive system24, armature46may be forced to translate away from landing gear assembly10and move taxi drive system24out of engagement with driven sprocket42. In other examples, armature46may comprise one or more linear bearings or bales that may extend and remove taxi drive system24from engagement with driven sprocket42.

Because a force is no longer applied against drive chain30by driven sprocket42when taxi drive system24is in the second (disengaged) position, the loop formed by drive chain30may straighten at the site of the former engagement with driven sprocket42, as shown inFIG. 6B. Tension in drive chain30may be maintained by idler sprockets40or spacers34. For example, spacers34or idler sprockets40may shift to maintain tension. As an example, spacers34may be mounted on a pivot arm such that spacers34shift inwards, pinching drive chain30around drive sprocket32, extending the path drive chain30travels around drive sprocket32and idler sprockets40. In addition or instead, idler sprockets40may translate outwards, extending the distance between idler sprockets40and drive sprocket32. In the disengaged position, driven sprocket42and aircraft tires12are free to rotate without interference from taxi drive system24.

FIG. 7is a schematic functional block diagram illustrating an example taxi drive controller56, which is configured to control the operation of taxi drive system24. Taxi drive controller can be located on an aircraft that includes taxi drive system24, and may, for example, be implemented as part of the flight control hardware, software, firmware, firmware or stand-alone cockpit interface/controller hardware, firmware, hardware, or any combination thereof. In the example shown inFIG. 7, taxi drive controller56comprises processor62, actuator controller64, and motor controller66. As shown inFIG. 7, taxi drive controller56can be configured to receive user input via user interface58and signals from speed sensor60and output commands to hydraulic ram48(or other actuator) and motor28to control ram48and motor28.

Taxi drive controller56comprises any suitable arrangement of hardware, alone or in combination with software and/or firmware, to perform the techniques attributed to taxi drive controller56and taxi drive system24. In various examples, taxi drive controller56can include any one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. Although not shown inFIG. 7, taxi drive system24may also include a memory, which include any volatile or non-volatile media, such as a random access memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. The memory may store instructions for execution by taxi drive controller56that cause taxi drive controller56to perform the techniques attributed to taxi drive controller56herein. Although processor62, actuator controller64, and motor controller66are described and illustrated as separate modules of taxi drive controller56, in some examples, processor62, actuator controller64, and motor controller66can be functionally integrated. In some examples, processor62, actuator controller64, and motor controller66correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units.

Taxi drive controller56is configured to receive user input via user interface58via wired or wireless communication. User interface58, may be, for example, onboard the aircraft (e.g., in a cockpit of the aircraft) or remotely located. User interface64may include, for example, input buttons and/or a keypad and a display (e.g., a cathode ray tube (CRT) display, a liquid crystal display (LCD) or light emitting diode (LED) display). The keypad may take the form of an alphanumeric keypad or a reduced set of keys associated with particular functions. User interface58can additionally or alternatively include a peripheral pointing device, such as a mouse, via which a user may interact with user interface58. Other examples of user input mechanism of user interface58include, but are not limited to, a joystick, a switch, a throttle, or a steering wheel/yoke inputs. In some examples, a display of user interface58may include a touch screen display, and a user may interact with controller56via the display.

User interface58is configured to receive input from a user, such as a pilot or crew of the aircraft, indicating various inputs for controlling taxi drive system24. User interface58may provide the input to processor62of taxi drive controller56as, for example, electrical or optical signals. The user input can indicate, for example, a desired rotational speed of aircraft tires12, allowing the user to control the speed of the taxiing aircraft via taxi drive system24, or directional input, allowing the user to control the direction of the taxiing aircraft via taxi drive system24, e.g., via differential steering using multiple taxi drive systems24.

The user input received by processor62of controller56via user interface58may also comprise input indicating whether taxi drive system24should be moved to the first or second positions (e.g., input indicating whether taxiing of the aircraft is desirable). Thus, as shown inFIG. 7, in some examples, processor62can control actuator controller64to control hydraulic ram48(or another mechanism in other examples) to move taxi drive system24between the first and second positions, depending on the received user input.

Taxi drive controller56is also configured to receive input from speed sensor60, which may be configured to generate a signal indicative of the rotation rate of driven sprocket42. Speed sensor60may, for example, directly measure the rotation rate of driven sprocket42or may measure the rotation rate of a component connected to driven sprocket42, such as hub20, aircraft tire12, or the axle supporting hub20. In other examples, speed sensor60may measure the velocity of the aircraft. Speed sensor60may be included in taxi drive system24or the output from an existing wheel speed sensor in landing gear assembly10of the aircraft may be used. Processor62may receive the signal from speed sensor60and determine the rotation rate of driven sprocket42and the rotation rate of motor28that enables drive chain30to match the cross-radial velocity of driven sprocket42.

Processor62of taxi drive controller56is configured to control motor28via motor controller66. Motor28can be controlled, for example, to control the speed of taxiing of the aircraft. Thus, processor62can control motor controller66in some examples in response to user input received via user interface58, where the user input may request an increase or decrease in speed of the taxiing aircraft. In some examples, processor62may determine the appropriate rotation rate of motor28based on the user input and control motor controller66to control motor28via the voltage supplied to motor28, or by actuating a throttle or selecting a gear ratio of motor28or a transmission/gearbox incorporated into motor28. In order to determine the appropriate rotation rate of motor28, processor62may, for example, reference a look-up table or another data structure that associates a plurality of aircraft taxiing speeds with respective rotation rates of motor28.

In some examples, processor62is configured to move taxi drive system24between the first and second positions in response to user input received via user interface58. In other examples, processor62is configured to automatically move taxi drive system24between the first and second positions in response to a detected condition. For example, processor62can control actuator controller64to move aircraft taxi system24from the first position to the second position in response to detecting an aircraft speed greater than or equal to a stored threshold. The aircraft speed can be determined, for example, based on the signal generated by speed sensor60. As another example, processor62can control actuator controller64to move aircraft taxi system24from the second position to the first position in response to detecting an aircraft speed less than or equal to a stored threshold.

Taxi drive controller56can be configured to control multiple taxi drive systems24of an aircraft, which can be installed on multiple landing gear assemblies, e.g., on the main landing gear of an aircraft. For example, processor62can independently control the rotation rates of the motors28of each of the taxi drive systems, thereby allowing the aircraft to be steered using the differential in rotation rates. In some examples, processor62can control into rotation rates for multiple taxi drive systems in order to steer the aircraft and taxi the aircraft at the speed, e.g., indicated by the user input based on user input received via user interface58. Processor62can control the rotation rate of motor28(or multiple motors of respective taxi drive systems24), and, therefore, the speed of the aircraft during taxiing, thereby allowing the speed of the aircraft during taxi to be controlled without reliance on aircraft friction brake systems, although the friction brake system could also be used.

FIG. 8is a flow diagram illustrating an example method of operation of taxi drive system24. The method shown inFIG. 8includes rotating drive chain30, e.g., to a speed that is based on a rotation of aircraft tire12(80), engaging taxi drive system24(82), taxiing aircraft (84), and disengaging taxi drive system24(86). Engaging or disengaging taxi drive system24(82,86, respectively) may comprise pivoting taxi drive system24or translating taxi drive system24.

In the example shown inFIG. 8, drive chain30can be rotated prior to engaging drive chain30with driven sprocket42(80). As discussed above, this may help reduce wear of drive chain30and/or driven sprocket42attributable to the friction between drive chain30and driven sprocket42as they are brought into engagement with each other. Processor62of taxi drive controller56can, for example, control motor controller66to rotate drive chain30to a speed that is based on a speed of aircraft tire12, and, in some examples, is substantially equal to or equal to the speed of the aircraft tire12. An example taxi drive system24may match the rotation rate of aircraft tire12within 10 revolutions per minute (rpm) or approximately 10 rpm. The disengaged drive chain30may be rotated at a slightly greater speed than driven sprocket42if aircraft tire12is rotating during engagement. The speed of the aircraft wheel can be determined using any suitable technique. In some examples, speed sensor60(FIG. 7) may be positioned to measure the rotation rate of aircraft tire12, hub20, or driven sprocket42, while in other examples, existing wheel speed sensors aboard the aircraft may be used to monitor the rotation rate of aircraft tire12, hub20, or driven sprocket42. Taxi drive controller56(FIG. 7) may receive the output of speed sensor60to determine the cross-radial velocity of the teeth of driven sprocket42based on the radius and the angular velocity/rotational frequency of driven sprocket42. Taxi drive controller56may then control motor28and drive chain30based on the determined speed, e.g., to substantially match or match the cross-radial velocity of the teeth of driven sprocket42.

One method of determining the rotation rate of drive sprocket32that may produce the velocity of drive chain30that matches the cross-radial velocity of driven sprocket42is to use the ratio of radius of driven sprocket42to drive sprocket32multiplied by the rotational frequency of driven sprocket42. These calculations may be performed automatically by taxi drive controller56(e.g., processor62or another component) of taxi drive system24or the avionics of the aircraft. Upon determining a rotational rate for taxi drive system24, the determined rotational rate may be used by taxi drive controller56to control motor controller66to accelerate motor28to the selected rotational rate before bringing taxi drive system24into engagement with driven sprocket42.

In some examples, engaging taxi drive system24(82), i.e., moving taxi drive system to the first position, may comprise pivoting taxi drive system24into engagement with driven sprocket42. Processor62of taxi drive controller56may, for example, control actuator controller64(FIG. 7) to control hydraulic ram48(FIGS. 3 and 7) to pivot taxi drive system24to the first position. Hydraulic ram78may be pivotably coupled to actuator mount36and armature46or front support54. By retracting hydraulic ram48, taxi drive system24may be pulled about armature mount38and into engagement with driven sprocket42. Actuators that can be used instead of, or in addition to, hydraulic ram48include, but are not limited to, pneumatic pistons and electric drives, such as a ballscrew or acme lead screw drive. Pneumatic pistons may operate in a similar manner to hydraulic ram48, using a double action cylinder to retract a piston and pull taxi drive system24into engagement. Electric screw drives may comprise a threaded rod and a threaded engagement device (e.g., a nut). Either the threaded rod or the threaded engagement device may be connected to taxi drive system24. A motor may rotate the threaded rod or threaded engagement device. As the threaded rod or threaded engagement device rotates, the interaction of the threading produces a force that may pull taxi drive system24into the first position, such that drive chain30is engaged with driven sprocket42.

In other examples, taxi drive controller56can engage taxi drive system24(82) by at least translating taxi drive system24into engagement with driven sprocket42. For example, armature46(FIG. 3) may support or comprise a linear bearing system or other device configured to pull taxi drive system radially from a disengaged position into engagement with driven sprocket42, and processor62of taxi drive controller56can control actuator controller64to move armature46in order to engage drive chain30with driven sprocket42. In other examples, armature46may be pivotably connected to front support54(FIG. 3) and axle mount52(FIG. 3). Front support54may be pivotably connected to piston mount50(FIG. 3). A hydraulic actuator or motor may rotate axle mount52causing armature46to be pulled back, bring taxi drive system24into engagement with driven sprocket42.

After engagement with driven sprocket42, taxi drive system24may be used to taxi the aircraft (84). Under the control of processor62, motor controller66can control motor28(FIG. 2) to rotate drive sprocket32, driving drive chain30and rotating driven sprocket42. Driven sprocket42may be connected to hub20(FIG. 1), causing aircraft tire12to rotate with driven sprocket42. Motor controller66of taxi drive controller56(FIG. 7) may control motor28to generate a rotational rate determined, e.g., based on user input received via user interface58from a user (e.g., a pilot) regarding the desired speed of taxiing of the aircraft. Motor28may be equipped with a transmission or gear box. A transmission system may allow the gear ratio between drive sprocket32and motor28to be adjusted, which can adjust the rotational rate of motor28.

In preparation for takeoff, landing, or when idle, taxi drive controller56can control taxi drive system24to be disengaged (86), i.e., moved to the second position. Disengagement may be controlled by actuator controller64of taxi drive controller56(FIG. 7) and may occur automatically or in response to user input58. In some examples, processor62may control actuator controller64to disengage taxi drive system24by at least pivoting taxi drive system24out of engagement with driven sprocket42. In one example, hydraulic ram48may extend, pushing taxi drive system24around armature mount38and clear of the teeth of driven sprocket42. In the disengaged position aircraft tires12may rotate free of interaction with taxi drive system24. Other configurations may use a pneumatic piston or electric screw drive in place of hydraulic ram48.

In other examples, processor62may control actuator controller64to disengage taxi drive system24(86) by at least translating taxi drive system24out of engagement with driven sprocket42. Armature46may support one or more hydraulic pistons, pneumatic rams, linear bearings, or similar devices configured to push taxi drive system24radially out of engagement with driven sprocket42. Other examples may comprise rotating axle mount52to drive armature46towards taxi drive system24. As armature46may be pivotably coupled to axle mount52and front support54(and piston mount50via front support54), the motion of axle mount52may cause armature46to swing taxi drive system24out of engagement with driven sprocket42.

FIG. 9is a flow diagram illustrating an example method for using taxi drive system24. The method shown inFIG. 9may comprise engaging taxi drive system24(82), spinning-up aircraft tire12(90), disengaging taxi drive system24(86), braking aircraft to safe speed (92), rotating drive chain30prior to engaging drive chain30with driven sprocket42(80), engaging taxi drive system24(82), taxiing aircraft (84), and disengaging taxi drive system24(86).

Taxi drive system24is configured to be disengaged prior to take off and landing. In some examples, taxi drive controller56(FIG. 7), as directed by user input receive via user interface58(FIG. 7), may control taxi drive system24to temporarily bring drive chain30into engagement with driven sprocket42prior to landing (82). For example, taxi drive system24may be used to “spin-up” aircraft tire12prior to touch down (90). Spinning up aircraft tire12prior to touch down comprises causing aircraft tire12to rotate at a relatively high speed, e.g., at or near the rate that aircraft tire12will rotate after impact with the runway. This may, for example, reduce the wear on the aircraft tires12by reducing the amount of skid on the runway resulting from a near stationary aircraft tire12being forced to suddenly rotate at speed. Taxi drive system24may be configured to rotate aircraft tire12at a higher rate for spin-up than for because the inertia of the aircraft may not encumber the ability of motor28to provide the desired output as much during spin-up compared to during taxiing. After obtaining the desired rotational rate during spin up, taxi drive controller56may cause taxi drive system24to be disengaged from driven sprocket42, protecting drive chain30from being inadvertently rotated by contact with driven sprocket42during landing (86).

Upon landing, the aircraft may use thrust reversers and friction brakes to slow the aircraft (92). Once the aircraft has reached a desired speed threshold, e.g., approximately 25 knots, taxi drive controller56may control taxi drive system24to be moved to the first position, in which drive chain30is engaged with driven sprocket42(82). As discussed above with respect toFIG. 8, motor28may rotate drive chain30may be rotated to a speed that is based on a rotation rate of aircraft tires12or the current ground speed of the aircraft (80). By rotating drive chain30prior to engaging drive chain30with driven sprocket42, wear and impact on taxi drive system24and driven sprocket42during engagement may be reduced. The wear and impact on taxi drive system24from being brought into engagement with driven sprocket42may be particularly low when drive chain30is rotated to a speed that substantially matches or matches the rotation rate of aircraft tires12or the current ground speed of the aircraft prior to engaging drive chain30with driven sprocket42.

After matching rotation rates, taxi drive system24may be brought into engagement with driven sprocket42(82), e.g., under the control of taxi drive controller56of taxi drive system24or the avionics of the aircraft, and the aircraft may then begin taxiing under power from taxi drive system24(84). The speed at which the aircraft taxis may be controlled by the rotation rate of motor28, and, in some examples, the selection of a gear ratio within the gear box or transmission of motor28. The aircraft may be slowed by decreasing the rotation rate of motor28and/or using a braking mechanism, such as a brake disc stack. Directional control may be provided by installing taxi drive system24on multiple landing gear and rotating aircraft tires12at different rates on different landing gear, e.g., differential steering. In other examples, taxi drive system24may be installed on steerable landing gear assembly, for example the nose wheel of an aircraft. The steerable landing gear may be turned in the desired direction and taxi drive system24will apply force in the direction the steerable landing gear is oriented, causing the aircraft to turn. The rotational rate of taxi drive system24may be controlled by commands from the pilot or other crew member in the aircraft. These commands may be routed into the avionics of the aircraft or to taxi drive controller56of taxi drive system24which controls the rotation rate of motor28.

Taxi drive system24may be disengaged from driven sprocket42, i.e., moved to the second position (86), e.g., for maintenance, when aircraft is idling, or in preparation for takeoff. Maintenance may be facilitated by removing drive chain30from engagement with driven sprocket42, removing the interference of driven sprocket42with the inspection or removal of drive chain30. Prior to takeoff taxi drive system24may be disengaged to prevent affecting the integrity of system24from the relatively high rotational rates aircraft tires12may experience during the takeoff run. In some examples, taxi drive controller56can disengage taxi drive system24from driven sprocket42in response to a command from the pilot or a crew member of the aircraft. The command may be transmitted to the avionics of the aircraft or a processing component of taxi drive system24via user interface58. In some examples, controller56can automatically cause taxi drive system24to be disengaged based on the rotation rate of aircraft tires12or driven sprocket42or based on exceeding a ground speed threshold (e.g., 25 knots or another predetermined operating speed) or increasing the throttle past a threshold indicating impending takeoff.

Various examples of the invention have been described. These and other examples are within the scope of the following claims.