Patent Application
20140187370
The present invention relates to engine-off taxiing of an aircraft. In particular, the invention relates to a wheel drive system for taxiing an aircraft.
Aircraft commonly employ the use of their primary propulsion method to taxi the aircraft during pre-flight and post-flight activities. Using the primary propulsion method of the aircraft to taxi burns additional fuel which creates both a negative environmental and economic impact. It is desirable to incorporate a means of taxiing an aircraft without burning fuel to engage the primary propulsion source of the aircraft. This is known as engine-off taxi.
Proposals have been made to attach a motor to the wheel of an aircraft by connecting a gear of a motor to a gear of the aircraft wheel. Directly connecting the gears of a motor and aircraft wheel can cause problems as the amount of torque applied to the gears of this arrangement may lead to the need to use an exotic design material for the gears or pinions. A gear-to-gear drive arrangement also is difficult to shield or lubricate and the gears wear out quickly. An example of such a proposal is set forth in US Pat. Pub. 2011/0156472A1.
Additional proposals for driving the wheel of an aircraft have suggested the driving motor be in permanent engagement with the aircraft wheel. Such an arrangement experiences problems during takeoff and landing where the increased rates of acceleration and speed cause issues of wear in the drive mechanism and safety concerns of failures at high speed. Other means to drive the aircraft wheel, such as grabbing the tire or the wheel, present performance and durability challenges.
An embodiment of the present invention is a wheel drive apparatus for driving a wheel having a ring gear. The wheel drive apparatus includes a drive loop carrier assembly, a drive loop, and a displacement system. The drive loop carrier assembly includes a plurality of toothed pulleys. The drive loop extends around the toothed pulleys to form a continuous loop. The displacement system is connected to the drive loop carrier assembly to selectively engage with the ring gear.
Another embodiment is a landing gear wheel drive system including a landing gear strut, a wheel, a drive loop carrier assembly, a drive loop, and a displacement system. The wheel is rotatably attached to the landing gear strut and includes a ring gear mounted to the wheel. The drive loop carrier assembly includes a plurality of toothed pulleys. The drive loop extends around the toothed pulleys to form a continuous loop. The displacement system is connected to the drive loop carrier assembly to selectively engage with the ring gear.
Embodiments of the present invention provide a landing gear wheel drive apparatus for an aircraft that does not involve the use of the primary propulsion method of the aircraft. The wheel drive apparatus solves the problems noted above by employing a displacement system to engage and disengage a drive loop carrier assembly and drive loop to selectively drive a wheel through a ring gear. Disengaging the drive loop carrier assembly allows an aircraft to takeoff or land without engaging the wheel drive apparatus. This is desirable because a permanently attached wheel drive mechanism may suffer premature failure due to the high rates of acceleration and speed during aircraft takeoff or landing. High acceleration rates cause permanently engaged wheel drive assemblies to wear and break down quickly during the life-span of a wheel drive mechanism and present a safety hazard if failure of the drive system were to cause a locked wheel condition. The capability to disengage the wheel drive apparatus prevents undue wear during aircraft takeoff or landing.
Importantly, the use of the drive loop to engage the ring gear allows for an increased surface area of torque applied to the wheel. A traditional gear-to-gear arrangement includes a small point of contact from the gear of the wheel drive mechanism to the gear of the wheel. In embodiments of the present invention, force applied to the ring gear is applied over a greater surface area of the ring gear, thus decreasing the amount of mechanical stress experienced by components of the wheel drive apparatus and the ring gear. The decrease in mechanical stress helps to decrease the amount of wear on the wheel drive apparatus and the ring gear. The wheel drive apparatus is also less susceptible to damage from contaminants and shock loads than a direct gear-to-gear drive assembly would be. The wheel drive apparatus eliminates the complexity of a clutching mechanism required for a conventional drive that is in constant engagement with an aircraft wheel.
Pivot 38 is mounted within and extends outward from strut extensions 40 on an axis parallel to wheel axle 16. Drive arm 32 includes first end 50, and second end 52 opposite first end 50. Drive arm 32 is pivotally mounted onto pivot 38 at first end 50. Ball nut 48 connects actuator 36 to drive arm 32. Ball nut 48 pivotally connects actuator 36 to drive arm 32 away from first end 50, near second end 52. The nearer ball nut 48 connects to second end 52, the greater the mechanical advantage available in pivoting drive arm 32. Displacement motor 44 is pivotally connected to strut extension 42, which also extends from landing gear strut 14. Ball screw 46 is connected to displacement motor 44 and is engaged with ball nut 48 such that as displacement motor 44 rotates connected ball screw 46, ball screw 46 rotates within ball nut 48, and causes ball nut 48, and attached drive arm 32, to move.
Two toothed pulleys 30 are mounted along drive arm 32. Each of toothed pulleys 30 is rotatable on a pulley axis that is parallel to, and spaced apart from, wheel axis 16 and from the other of toothed pulleys 30. Drive loop 28 extends around toothed pulleys 30 to form a continuous loop between toothed pulleys 30, as shown in
In some embodiments, drive loop carrier assembly 24 also includes a loop tensioning mechanism to maintain consistent tension on drive loop 28. In the embodiment of
Disengaging drive loop 28 follows the opposite sequence. If drive loop 28 is to be disengaged when wheel 12 is stopped, motor 33 is stopped, so that is it no longer impelling toothed pulley 30 stopping movement of drive loop 28. Next, displacement motor 44 is powered to rotate in a second direction, opposite the first direction direction, rotating ball screw 46, which rotates within ball nut 48, causing ball nut 48 and attached drive arm 32 to pivot away from wheel axis 16 and disengage drive loop 28 from ring gear 20. If drive loop 28 is to be disengaged when wheel 12 is still rotating, drive loop 28 is disengaged before motor 33 is stopped.
In the embodiment describe above in reference to
Thus, drive loop carrier assembly 24 is mounted such that it can be moved as a unit to bring drive loop 28 in and out of contact with ring gear 20 of wheel 12 by displacement system 26. In this way, displacement system 26 selectively engages and disengages wheel drive apparatus 22. Drive loop carrier assembly 24 includes loop tensioning mechanism 34 to ensure that proper tension of drive loop 28 is maintained whether drive loop carrier assembly 24 is engaged with ring gear 20 or not. In some embodiments, displacement system 26 is designed such that actuator 36 must be powered, or actuated, to engage drive loop carrier assembly 24 with ring gear 20. In such embodiments, a loss of power results in displacement system 26 disengaging drive loop 28 from ring gear 20.
The disengaged position of drive loop carrier assembly 24 shown in
The engaged position of drive loop carrier assembly 24 shown in
Embodiments of the present invention allow for a wheel drive apparatus for an aircraft that does not involve the use of the primary propulsion method of the aircraft. Burning engine fuel for taxiing the aircraft causes environmental issues as well as economic issues of using expensive engine fuel to taxi the aircraft. The use of drive loop carrier assembly 24 and drive loop 28 to drive wheel 12 through ring gear 20 is also less susceptible to damage from contaminants and shock loads than a direct gear-to-gear drive assembly would be. Wheel drive apparatus 22 also eliminates the complexity of a clutching mechanism required for a conventional loop drive that is in constant engagement with an aircraft wheel.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
The following are non-exclusive descriptions of possible embodiments of the present invention.
A wheel drive apparatus for driving a wheel having a ring gear includes a drive loop carrier assembly, a drive loop, and a displacement system. The drive loop carrier assembly includes a plurality of toothed pulleys. The drive loop extends around the toothed pulleys to form a continuous loop. The displacement system connects to the drive loop carrier assembly to selectively engage the drive loop with the ring gear.
The wheel drive apparatus of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
the drive loop carrier assembly further includes a drive motor connected to at least one of the toothed pulleys to drive rotation of the connected toothed pulley; and each toothed pulley is rotatable on a pulley axis parallel to, and spaced apart from, a wheel axis and another pulley axis; and the displacement system selectively engages the drive loop with the ring gear by moving the drive loop carrier assembly toward the wheel axis to engage the drive loop with the ring gear, and moving the drive loop carrier assembly away from the wheel axis to disengage the drive loop from the ring gear;
the toothed pulleys are connected to a drive motor to drive rotation of the connected toothed pulleys;
the displacement system includes a pivot connected to a first end of the drive loop carrier assembly; and an actuator connected to the drive loop carrier to rotate the drive loop carrier assembly about the pivot and move the drive loop carrier assembly relative to the wheel axis;
the displacement system disengages the drive loop from the ring gear when the actuator loses power;
the drive loop carrier assembly further includes a loop tensioning mechanism to maintain a consistent tension on the drive loop whether engaged or disengaged with the ring gear;
the drive loop is a drive belt, the drive belt including an inner surface having a series of inner teeth shaped for meshing with the toothed pulleys; and an outer surface having a series of outer teeth shaped for meshing with the ring gear; and
the drive loop is a drive chain, the drive chain including a series of links shaped for meshing with the toothed pulleys and the ring gear.
A landing gear wheel drive system includes a landing gear strut, a wheel; a drive loop carrier assembly, a drive loop, and a displacement system. The wheel is rotatably attached to the landing gear strut and includes a ring gear mounted to the wheel. The drive loop carrier assembly is connected to the landing gear strut and includes a plurality of toothed pulleys. The drive loop extends around the toothed pulleys to form a continuous loop. The displacement system is connected to the landing gear strut and to the drive loop carrier assembly to selectively engage the drive loop with the ring gear.
The landing gear wheel drive system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
the drive loop carrier assembly further includes a drive motor connected to at least one of the toothed pulleys to drive rotation of the connected toothed pulley; and each toothed pulley is rotatable on a pulley axis parallel to, and spaced apart from, a wheel axis and another pulley axis; and the displacement system selectively engages the drive loop with the ring gear to drive the wheel by moving the drive loop carrier assembly toward the wheel axis, and moving the drive loop carrier assembly away from the wheel axis to disengage the drive loop from the ring gear to cease driving the wheel;
the toothed pulleys are connected to a drive motor to drive rotation of the connected toothed pulleys;
the wheel is at least one of a main wheel and a nose wheel mounted to a landing gear strut of an aircraft; and the displacement system selectively engages the drive loop with the ring gear during taxiing of the aircraft, and disengages the drive loop from the ring gear when the aircraft is not taxiing;
the displacement system includes a pivot connecting a first end of the drive loop carrier assembly to the landing gear strut; and an actuator connected to the landing gear strut and to the drive loop carrier to rotate the drive loop carrier assembly about the pivot, and move the drive loop carrier assembly relative to the wheel axis;
the actuator includes a ball nut connected the drive loop carrier assembly closer to a second end of the drive loop carrier than to the first end, the second end opposite from the first end; a ball screw in threaded engagement with the ball nut, and a displacement motor connected to the landing gear strut and to the ball screw to rotate the ball screw, and move the engaged ball nut to rotate the drive loop carrier assembly about the pivot;
the displacement system disengages the drive loop from the ring gear when the actuator loses power;
the drive loop carrier assembly further includes a loop tensioning mechanism to maintain a consistent loop tension whether engaged or disengaged with the ring gear;
the drive loop is a drive belt, the drive belt including an inner surface having a series of inner teeth shaped for meshing with the toothed pulleys; and an outer surface having a series of outer teeth shaped for meshing with the ring gear;
the drive loop is a drive chain, the drive chain including a series of links shaped for meshing with the toothed pulleys and the ring gear;
the ring gear is mounted near an outer diameter of the wheel; and
the wheel is at least one of a main wheel and a nose wheel of an aircraft.
