The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Most aircraft ground taxi by using thrust produced by their main engine(s). As a result of the ground taxi speeds being relatively low the engines must be run at low power. This means there is relatively high fuel consumption as a result of the poor propulsion efficiency at this low forward velocity. This leads to an increased level of both atmospheric and noise pollution locally around airports. Even when the engines are run at low power it is generally necessary to apply the wheel brakes to prevent excessive ground taxi speeds, which leads to a high degree of brake wear particularly as the brakes tend to be cold prior to take-off. It is also to be noted that reversing a civil aircraft by using its main engines is not permitted.
"Several autonomous taxi systems have been proposed in recent years for driving the wheels whilst the aircraft is on the ground. Any benefits from an autonomous taxi system must consider the fuel cost to the operator of aircraft flying with the extra mass of the ground taxi system. This means that the only practical solution is one that absolutely minimises the installed system mass. Most recent interest in autonomous ground taxi systems has focused on installing drive motors on the landing gear wheel axle. These proposed systems have several potential drawbacks.
"Since brakes are installed within the wheels of aircraft main landing gear, this region is very congested and so it is difficult to install drive motors on the wheel axle of main landing gear. Therefore, development of these proposed systems has generally been limited to the nose landing gear. Nose landing gear support low vertical load (approximately 5% of the aircraft weight) during ground taxi operations, which could lead to traction problems when the wheels are driven. This is particularly the case when the aircraft centre of gravity is towards its aft limit and when the ground surface is slippery, e.g. when wet or icy.
"Most landing gear have a shock-absorbing main leg with a sprung part attached to the aircraft and an un-sprung part which carries the wheel(s). Any drive system which is mounted on the wheel axle (i.e. on the un-sprung part of the landing gear) will increase the un-sprung mass of the landing gear. An increase to the un-sprung mass of the landing gear is undesirable from a dynamic response perspective where this could result in high loads being induced into the landing gear and aircraft structure. Significant strengthening of the landing gear and/or aircraft structure may be required to support these load increases. Furthermore the un-sprung landing gear components experience significantly higher vibration and acceleration loads than the sprung parts. For example, the accelerations on the sprung parts may be around 3.5 g to 5 g, whereas the accelerations on the un-sprung parts may be around 50 g to 60 g. Therefore, any drive system which is fixedly mounted on the un-sprung parts will need to be very robust. This is unlikely to lead to a mass optimised solution.
"Furthermore, any drive system which is installed coaxial with the wheel axle cannot easily be removed. Not only is this an important consideration for maintenance purposes but studies have indicated that the benefits of even lightweight autonomous taxi systems may only be observed for the shorter range operations where an aircraft spends a higher proportion of its time taxiing. It would therefore be desirable to be able to quickly install and remove the majority of the autonomous taxi system equipment from the aircraft so as to optimise the aircraft economics in the event of longer range operations. This is generally not possible with an integrated drive system installed coaxial with the wheel axle.
"U.S. Pat. No. 3,762,670 describes a landing gear wheel drive system including a pair of drum members arranged to move into friction driving engagement with the periphery of the tyres of the landing gear wheels for driving the wheels whilst the aircraft is on the ground. The drum members are mounted on a rotating shaft and a motor is connected to the shaft via a gearing mechanism. Most of the weight of these parts is supported by the sprung part of the landing gear main leg. Whilst this document addresses some of the short-comings of the prior art axle mounted wheel drive systems, the roller pressures on the tyre necessary to move the aircraft are considered to be so high as to lead to unacceptable damage to the tyre surface. In addition, the shaft carrying the drum members is highly loaded in bending and therefore will need to be massive or it will suffer fatigue. Therefore, this design is also unlikely to lead to a mass optimised solution, necessary for practical application."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "A first aspect of the invention provides an aircraft landing gear comprising: a shock-absorbing main leg having a sprung part for attachment to an aircraft and an un-sprung part including a slider and an axle carrying at least one wheel, the wheel having a toothed ring gear; a drive transmission mounted externally on the sprung part, or on the un-sprung part, of the main leg, the drive transmission having at least one motor and a drive pinion for meshing with the toothed ring of the wheel; and an actuator for lifting the drive transmission into and out of driving engagement with the toothed ring and for maintaining the driving engagement as the landing gear deflects during a ground taxiing operation.
"A further aspect of the invention provides a method of operating the aircraft landing gear according to the first aspect, the method comprising driving the wheel in rotation by supplying power to the motor and engaging the drive transmission with the wheel via the toothed ring as the landing gear deflects during a ground taxiing operation.
"The invention is advantageous in that it provides the potential for a mass optimised solution which has a low impact on the aircraft and landing gear baseline structure (i.e. an aircraft with a conventional landing gear without a driven wheel). The landing gear is changed little from a conventional landing gear, since the drive transmission is mounted externally. By using a drive pinion in meshing engagement with a toothed ring on the wheel, secure driving engagement is ensured without damage to the tyre on the wheel, and driving torque load paths are optimised. Given the very high acceleration experienced by the wheel during touch down, it is necessary to provide for disengagement of the drive transmission from the wheel using the actuator. There will be some deflection in the landing gear in response to grounds loads, and so it is important that the actuator can maintain the driving engagement during this movement.
"Preferably, the drive transmission is detachably mounted on the main leg. The drive transmission can therefore be removed for maintenance and/or when the aircraft is to be used for long range operations where it may not be economic to use the drive transmission due to its weight penalty in cruise.
"The landing gear may further comprise an articulating mechanism pivotally mounted on the sprung part, or on the un-sprung part, of the main leg, wherein the articulating mechanism is connected to the actuator and supports the drive transmission.
"The articulating mechanism pivot axis may be configured to tilt relative to the main leg. This may be achieved using spherical or flexible bearings, for example, at the mounting point(s) on the main leg which support the drive transmission. This ensures that the driving engagement can be maintained as the wheel axis of rotation rolls relative to the vertical due to deflections in the tyre, or uneven ground.
"The toothed ring and the drive pinion may have associated matching follower surfaces. The follower surfaces come together when the actuator presses the drive pinion into meshing engagement with the toothed ring, and act to control the orientation of the two gears relative to one another. This too helps to ensure that the driving engagement can be maintained.
"The drive pinion may include a constant-velocity joint. This too helps to ensure that the driving engagement can be maintained.
"The drive pinion and toothed ring may be in a sealed environment. This protects against contamination from environmental debris, which may affect the endurance life of the gears. For example, a brush type seal, or a flexible, possibly PTFE, type running seal may be used.
"The landing gear may have at least two of the driveable wheels. In this case, the wheels may each have a toothed ring gear, and the drive transmission may include two drive pinions each for meshing with a respective one of the toothed rings. The drive transmission may include two motors, each for driving a respective one of the drive pinions. Alternatively, the drive transmission may include a differential drive connected between the motor(s) and the drive pinions.
"The toothed ring may be disposed on the outer diameter of the wheel hub. The toothed ring may be integrally formed with the hub, or mounted thereto.
"The motor may be electric. Alternatively, it may be hydraulic and may be, for example, of a radial piston type.
"The drive transmission may include a toothed drive belt. This may be used to provide a lightweight, compact gearing solution.
"The toothed ring preferably has a larger diameter than the drive pinion to develop a significant torque magnifying gear ratio. By making use of the large hub diameter in this way, a mass optimised solution can be achieved.
"The drive transmission may be mounted externally on the sprung part of the main leg, and the actuator may be adapted to maintain the driving engagement between the drive pinion and the toothed ring as the sprung and un-sprung parts of the main leg move relative to one another during the ground taxiing operation. This may be of particular benefit as the un-sprung mass of the landing gear may be almost unchanged from the baseline landing gear.
"Alternatively, the drive transmission may be mounted on the un-sprung part of the main leg. For example, the drive transmission may be mounted on the slider and/or on the axle. For a bogie landing gear, the drive transmission may additionally or alternatively be mounted on the bogie. Although the un-sprung mass of the landing gear will be increased by attachment of the drive transmission, the drive transmission may be partially isolated from the high vibration and acceleration experienced by the un-sprung part of the landing gear, e.g. by the provision of a compliant mounting.
"When incorporated on an aircraft, the landing gear may be used with a power and control system for supplying power to, and controlling operation of, the drive transmission.
BRIEF DESCRIPTION OF THE DRAWINGS
"Embodiments of the invention will now be described with reference to the accompanying drawings, in which:
"FIG. 1 illustrates a landing gear in accordance with a first embodiment;
"FIG. 2 illustrates the drive transmission;
"FIG. 3 illustrates an exploded view of the drive transmission of FIG. 2;
"FIG. 4 illustrates a partially exploded view of the drive transmission installed on the landing gear (with one tyre removed for clarity);
"FIG. 5 illustrates a drive transmission in accordance with a second embodiment;
"FIG. 6 illustrates a drive transmission in accordance with a third embodiment installed on the landing gear (with one tyre removed for clarity);
"FIG. 7 illustrates an exploded view of the drive transmission of FIG. 6;
"FIGS. 8 a) and b) illustrate drive transmissions in accordance with fourth and fifth embodiments respectively;
"FIGS. 9 illustrates schematically a landing gear in accordance with a sixth embodiment, in which a) shows a rear view, b) shows a side view with the drive transmission engaged, and c) shows a side view with the drive transmission disengaged; and
"FIG. 10 illustrates a modified sixth embodiment in which the ring gears have radially inwardly facing teeth."
For additional information on this patent application, see: WILSON,
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