GB2592602A - An aircraft parking brake - Google Patents

Abstract

A parking brake 20, for an aircraft landing gear with at least one wheel 11, has a first locking member 5, such as a pin or rod, mounted so it may move relative to a second locking member 18, such as a toothed ring, between a disengaged unlocked position, and a locked position in which the first locking member engages the second locking member to prevent wheel movement. The parking brake is configured so that the first locking member returns to the unlocked position, due to gravity or spring mechanism for example, if an actuator 8 ceases to hold the first locking member in the locked position, if actuator power supply fails for example. The second locking member may be in the form of a ring with apertures 18a, recesses or through holes, for receiving a part of the first locking member, spaced apart around its circumference. The locking pin preferably moves in a radial direction with respect to the locking ring and/or the wheel between the locked and unlocked positions. The actuator may be connected to the lock pin, and mounted to a wheel axle 17 or wheel hub 22, with the locking ring mounted to the other.

Description

AN AIRCRAFT PARKING BRAKE

BACKGROUND OF THE INVENTION

[0001] The present invention concerns aircraft landing gear. More particularly, but not exclusively, this invention concerns a parking brake for an aircraft landing gear, an aircraft landing gear including such a parking brake, an aircraft including such a landing gear and a method of operating such a parking brake or an aircraft including such a parking brake.

[0002] In order to prevent an aircraft moving during loading or unloading, wheel chocks may be used. The chocks comprise blocks manually placed between the ground and wheel to prevent rotation of the wheel. The chocks are placed in position by ground crew. It would be advantageous to provide a method of preventing an aircraft moving during turnaround that did not require manual intervention by ground crew.

[0003] Landing gear often include a disk brake that is used to slow the aircraft down when landing or taxiing. Typically, these brakes comprise a set of rotating discs and a set of stationary discs which are squeezed together by an actuator. The friction between the two disc sets prevents the wheel from rotating. EP2460723 discloses an example of such a brake. The friction generated during landing means that such brakes are initially very hot after touchdown. If these disk brakes are used as a parking brake the disks are squeezed together for a prolonged period of time. The surface area available for the disks to cool is reduced by several orders of magnitude, thereby increasing the time that the brakes remain hot which can lead to deterioration of the brake, for example through accelerated brake oxidation. Furthermore, it may be necessary for the temperature of the disk brakes to reduce below a threshold temperature before the aircraft can take off again but using the disk brake as a parking brake may increase the time taken to reach this temperature thereby increasing turnaround times.

[0004] The present invention seeks to mitigate the above-mentioned problems.

Alternatively or additionally, the present invention seeks to provide an improved parking brake for use in immobilising a stationary aircraft, for example during loading and/or unloading.

SUMMARY OF THE INVENTION

[0005] The present invention provides, according to a first aspect, a parking brake for an aircraft landing gear having at least one wheel. The parking brake may comprise a first lock member and a second lock member. The first lock member may be mounted for movement relative to the second lock member between an unlocked position, for example in which the first lock member is disengaged from the second lock member, and a locked position, for example in which the first lock member engages the second lock member to prevent movement of the at least one wheel. The parking brake may comprise an actuator that holds the first lock member in the locked position when the parking brake is engaged. It may be that the parking brake is configured such that the first lock member returns to the unlocked position if the actuator ceases to hold the first lock member in the locked position.

[0006] Thus, in the case that the actuator fails such that it ceases to maintain the first lock member in the locked position the parking brake is released. Parking brakes in accordance with the present invention may provide an alternative to chocks or using the disk brake of an aircraft to immobilise the aircraft, for example during loading and unloading. Additionally or alternatively, parking brakes in accordance with the present invention may fail to an unlocked configuration in the event of an actuator failure, for example a loss of power to the actuator, leaving the aircraft wheel free to rotate. This reduces the risk of parking brake failure delaying departure of an aircraft.

[0007] The parking brake may be configured such that gravity and/or a biasing force act to return the first lock member to the unlocked position. It may be that the first lock member is biased to return to the unlocked position such that in the event the actuator fails the parking brake is released so that the at least one wheel can rotate.

[0008] The actuator may be configured to hold the first lock member in the locked position. That is to say, the first lock member may be connected to the actuator such that force from the actuator acts against gravity and/or the biasing force to prevent the first lock member returning to the unlocked position. The event of the actuator failing may comprise the actuator ceasing to providing a sufficient opposing force to gravity and/or the biasing force as a result of events outside normal operation of the parking brake, for example a failure of energy (power) supply to the actuator or malfunction of the actuator mechanism, for example breaking of an actuator arm.

[0009] The second lock member may comprise a plurality of apertures, for example recesses or through-holes configured to receive at least a portion of the first lock member. The second lock member may comprise a plurality of teeth, said plurality of teeth defining, at least in part, a plurality of recesses into which at least a portion of the first lock member may be received. The apertures may be configured to receive part of the first lock member or all of the first lock member. The shape of the first lock member and the shape of the apertures of the second lock member may be complementary, such that at least a portion of the first lock member can be received in at least one of said apertures.

[0010] The first lock member may be said to be engaged with the second lock member when at least part of the first lock member is received in at least one of said apertures. The first lock member may be said to be disengaged from the second lock member when no part of the first lock member is received in said apertures.

[0011] The first lock member may be an elongate body, for example a pin or rod.

Additionally or alternatively the first lock member may be an elongate body comprising one or more protrusions, for example teeth, configured to be received in corresponding recesses, for example the recesses formed by a corresponding set of teeth, on the second lock member.

[0012] The second lock member may comprise a ring or part of a ring. The ring or part thereof may comprise a plurality of apertures that are spaced apart circumferentially around the ring. The ring may comprise a face, the normal of which is substantially parallel to the longitudinal axis of the ring and/or the axis of rotation of the wheel. The ring may comprise a curved inner surface. The normals of the curved inner surface may point towards and be perpendicular to the longitudinal axis of the ring and/or the axis of rotation of the wheel. The ring may comprise a curved outer surface. The normals of the curved outer surface may point away from and be perpendicular to the longitudinal axis of the ring. The plurality of apertures may be arranged on the face, the inner surface of the ring and/or the outer surface of the ring. The plurality of apertures may be spaced apart circumferentially around the ring. In use, the ring may be mounted on the wheel, for example on a hub of the wheel for rotation therewith. The ring may extend around a portion of, for example the majority of a circumference of the wheel, for example the outer circumference of the hub. -4 -

[0013] The parking brake may comprise an actuator connected to the first lock member so that, in use, the actuator holds (e.g. maintains) the first lock member in the locked position when the parking brake is engaged. The actuator may be configured to move the first lock member in a first direction from the unlocked position to the locked position. The actuator may be configured to move the first lock member in a second, opposite, direction to the unlocked position from the locked position. Thus, in normal operation the actuator may be configured to move the first lock member between the locked and unlocked positions.

[0014] The first lock member may be mounted for radial movement relative to the second lock member and/or the wheel. The first and/or second direction may be a radial direction. A radial direction may be defined as a direction perpendicular to the axis of rotation of the wheel. Thus, the actuator may be configured to move the first lock member in a first radial direction from the unlocked position to the locked position. The actuator may be configured to move the first lock member in a second radial direction to the unlocked position from the locked position. The first radial direction may be away towards the outer rim of the wheel (e.g. radially outwards) and/or away from the axle on which the wheel is mounted. The second radial direction may be away from the outer rim of the wheel (e.g. radially inwards) and/or towards the axle on which the wheel is mounted. Mounting the first lock member for radial movement may facilitate use of a mechanically simpler parking brake arrangement.

[0015] Alternatively, the first lock member may be mounted for axial movement.

Thus, the first and/or second direction may be an axial direction. An axial direction may be defined as a direction parallel to the axis of rotation of the wheel. Thus, the actuator may be configured to move the first lock member in a first axial direction from the unlocked position to the locked position. The actuator may be configured to move the first lock member in a second axial direction to the unlocked position from the locked position.

[0016] The actuator may require an energy supply, for example an electrical, hydraulic or other type of energy (power) supply to hold the first lock member in the locked position and/or to move the first lock member. For example, a hydraulic actuator may require that fluid pressure be maintained in order to hold the first lock member in the locked position. An electrically powered actuator may require an electrical power supply in order to hold the first lock member in the locked position. -5 -

The event of the actuator failing may comprise a loss of energy (power) supply to the actuator, for example a loss of electrical power to the actuator.

[0017] The actuator may comprise a moveable actuator member (or arm). When power is supplied to the actuator, the actuator member may move, for example extend and/or retract. The first lock member may be connected to the actuator member such that movement of the actuator causes the first lock member to move in the first and/or second direction.

[0018] The first lock member may be directly connected to the actuator or actuator member or indirectly connected to the actuator or actuator member by a linking mechanism. The linking mechanism may be configured such that force is transmitted from the actuator to the lock member to hold the first lock member in the locked position. The linking mechanism may be configured to transform movement of the actuator member into movement of the first lock member. A wide range of such mechanisms will be apparent to the skilled person.

[0019] The parking brake, for example the actuator, first lock member and/or second lock member may be arranged such that gravity acts to move the first lock member away from the second lock member. For example, the first lock member may be mounted below a portion of the second lock member with which the first lock member engages when in the locked position. The position of the first lock member in the locked position may be above, for example directly above, the position of the first lock member in the unlocked position so that the first lock member drops from the locked position to the unlocked position, for example in the event the actuator ceases to hold the first lock member up. The parking brake may be configured such that the first lock member returns to the unlocked position due to the action of gravity alone if the actuator ceases to hold it in the locked position. It may be that the parking brake does not include a biasing mechanism. The provision of a first lock member that simply falls back to the unlocked position, for example in the event the actuator ceases to hold the first lock member, may allow for a mechanically simple parking brake that fails to the unlocked position.

[0020] Additionally or alternatively, the parking brake may comprise a biasing mechanism that biases the first lock member to return to the unlocked position. The biasing mechanism may provide a biasing force that acts to return the first lock member to the unlocked position. The biasing mechanism may comprise a resilient member, for -6 -example a spring, for example a coil, torsion or leaf spring, or other elastically deformable and resilient members. The resilient member may be arranged to return the first lock member to the unlocked position. The biasing mechanism and/or resilient member may be configured to move the first lock member from the locked position to the unlocked position in the absence of a holding force from the actuator. The provision of a biasing mechanism may provide additional design flexibility in the parking brake and/or may reduce or eliminate the need to reply on gravity.

[0021] The parking brake may comprise a sleeve. The sleeve may be configured to be received on an axle of the landing gear. The actuator, the first lock member and/or the second lock member may be mounted on the axle using the sleeve.

[0022] The connection between the first lock member and actuator may be configured to fail in the event a significant external torque, for example a spin up load, is applied to the wheel. Such a connection may reduce the risk of damage to the landing gear in the event that the parking brake is not disengaged prior to manoeuvring of the aircraft.

[0023] The first lock member may be connected to the actuator for rotation about the longitudinal axis of the lock member. Having a rotatable first lock member may reduce the risk of the first and second lock members jamming as they move into engagement.

[0024] The first and/or second lock member may be compliant, for example elastically deformable. Having elastically deformable lock member(s) may improve engagement and/or reduce the risk of the first and second lock members jamming as they move into engagement.

[0025] The parking brake may comprise a torque reaction pin. The torque reaction pin may connect the actuator member and/or lock member to the actuator to prevent rotation relative to the actuator of the actuator member and/or lock member.

[0026] The parking brake may comprise an indicator system configured to provide an indication, for example a visual indication, of the status of the parking brake. For example the indicator system may be configured to provide an indication when the parking brake is engaged. The indicator system may comprise an indicator member. The indicator member may comprise a region having an distinctive appearance, for example a brightly coloured region, for example a red region, hereafter referred to as an indicator region. The indicator system may be configured to move the indicator -7 -member from an 'unlocked' position in which at least a portion, for example the whole of, the indicator region is hidden from view to a 'locked' position in which a portion of the indicator region that is hidden in the 'unlocked' position is visible. The indicator system may be configured such that the indicator member moves to the 'locked' position when the first lock member moves to the locked position. Additionally or alternatively, the indicator system may comprise a light that is illuminated when the parking brake is engaged. In use, the indicator member and/or light may be mounted on the wheel so as to be visible to ground crew. Such an indicator system may allow ground crew to confirm that the parking brake is engaged before loading and/or unloading of the aircraft commences.

[0027] In a second aspect of the invention, there is provided an aircraft landing gear comprising a parking brake in accordance with the first or any other aspect of the invention. The aircraft landing gear may comprise the wheel and an axle upon which the wheel is mounted for rotation. The wheel may comprise a hub via which the wheel is mounted to the axle. The wheel may comprise a tyre, for example mounted on the hub.

[0028] It may be that the actuator and/or first lock member is mounted on the axle and the second lock member is mounted on the hub for rotation therewith. The actuator and/or first lock member may be mounted on the axle such that the actuator and/or first lock member does not rotate about the axle. Thus, engagement between the first lock member and second lock member may prevent rotation of the wheel. Mounting the actuator and/or first lock member on the axle may facilitate the supply of energy to the actuator.

[0029] It may be that the actuator and/or first lock member is mounted on the hub for rotation therewith and the second lock member is mounted on the axle. The second lock member may be mounted on the axle such that the second lock member does not rotate about the axle. Thus, engagement between the first lock member and second lock member may prevent rotation of the wheel.

[0030] It may be that at least a portion of the second lock member, for example a portion of the second lock member with which the first lock member engages when in the locked position is mounted above the first lock member. The portion of the second lock member located above the first lock member may comprise one or more recesses into which at least a portion of the first lock member is received. Thus, the actuator -8 -may be configured to move the first lock member up into the locked position and/or to hold the first lock member up in the locked position.

[0031] The actuator may move the first lock member up and/or down into and/or out of the locked position.

[0032] The aircraft landing gear may be a nose landing gear (NLG) or a main landing gear (MILG). One or more landing gear on the aircraft may include a parking brake in accordance with any other aspect of the invention [0033] In a third aspect of the invention, there is provided an aircraft comprising an aircraft landing gear and/or parking brake in accordance with any other aspect of the invention.

[0034] The parking brake may further comprise a control system. Elements of the control system may be mounted on the landing gear and/or the rest of the aircraft. The control system may be configured to receive a signal from a user and/or an aircraft system to engage the parking brake and, in dependence on the signal so received, provide power to the actuator to engage the brake and/or maintain the brake in the locked position. The control system may be configured to receive a signal from a user and/or an aircraft system to disengage the parking brake and, in dependence on the signal so received, provide power to the actuator to disengage the brake and/or cease the supply of power to the actuator such that the brake disengages. The control system may be configured to provide an indication, for example an audible or a visual indication, of the status of the parking brake. The control system may be configured to provide such an indication to the flight crew, for example to the cockpit. The control system may provide an indication when the parking brake is engaged. Alternatively or additionally, the control system may provide an indication when parking brake is disengaged.

[0035] In addition to the parking brake, the aircraft and/or landing gear may include a disk brake for use during landing and/or taxiing. The disk brake may comprise a first set of stationary disks and a second set of rotatable discs and an actuator configured to bring the first and second set of disks into engagement so as to control the rotation of a wheel. It will be appreciated that disk brakes (or other forms of brake) may be used to control the speed of the aircraft while in motion and/or to bring the aircraft to a stop, while the parking brake of the present invention is used to immobilise a stationary aircraft. -9 -

[0036] In a fourth aspect of the invention, there is provided a method of operating a parking brake for an aircraft landing gear (or an aircraft including such a parking brake), the landing gear having at least one wheel, the parking brake having a first lock member and a second lock member, and an actuator connected to the first lock member.. The method may comprise one or more of the following steps: the actuator maintains the first lock member in engagement with the second lock member to prevent the rotation of the wheel; and in the event of an actuator failure, for example loss of power to the actuator, the first lock member disengages from the second lock member thereby releasing the parking brake so that the at least one wheel can rotate.

[0037] Thus, methods in accordance with the present aspect of the invention provide a parking brake that fails to an unlocked configuration in the event the actuator fails. This reduces the risk that a parking brake failure would delay departure of the aircraft, for example because the parking brake has failed in the locked configuration.

[0038] Gravity and/or a biasing force, for example from a biasing mechanism, may act to move the first lock member from the locked position to the unlocked position. The actuator may act against gravity and/or the biasing force. Thus, in the case that the actuator ceases to act on the first lock member, gravity and/or the biasing force return the first lock member to the unlocked position. The method may comprise the first lock member dropping from the locked position to the unlocked position when the actuator no longer holds it in the locked position.

[0039] The actuator may cease to hold the first lock member in the locked position as a result of actuator failure.

[0040] The method may comprise the step of power being supplied to the actuator to hold the first lock member in the locked position. Actuator failure may comprise a failure of the power supply. The power so supplied may be electrical power or hydraulic power or any other suitable type of power.

[0041] The method may further comprise the step of moving the first lock member between an unlocked position in which the first lock member is disengaged from the second lock member and a locked position in which the first lock member engages with the second lock member to prevent movement of the at least one wheel. The method may comprise the step of power being supplied to the actuator to move the first lock member from the unlocked to the locked positions and/or vice versa.

-10 - [0042] The method may further comprise the step of engaging the parking brake, for example in response to an input from a user or aircraft system. The method may comprise supplying energy to an actuator in response to such an input, and the actuator moving the first lock member to the locked position. The method may comprise the step of disengaging the parking brake, for example in response to an input from a user or aircraft system. The method may comprise supplying energy to an actuator in response to such an input, and the actuator moving the first lock member to the unlocked position. Alternatively, the method may comprise ceasing the supply of energy to an actuator in response to such an input, and the first lock member returning to the unlocked position. It will be appreciated that engaging and disengaging the parking brake in response to an input from a user or aircraft system constitutes normal use of the parking brake. It may be that the first member is moved to and/or from the locked position by the actuator during normal operation. In the case that the actuator fails, for example through a loss of energy (power), e.g. the failure of an electrical or hydraulic connection, then the first lock member returns to the unlocked position under the action of gravity and/or the biasing force. Thus, it may be that the first lock member only moves independently of the actuator when the actuator is in a failure state. Alternatively, it may be that the first lock member returns to the unlocked position independently of the actuator during normal operation as part of the normal disengagement of the parking brake.

[0043] The method may further comprise the steps of providing an indication that the parking brake is engaged, and/or providing an indication that the parking brake is disengaged. Such an indication may be provided by a control system and/or indicator system as discussed above. The method may comprise providing the indication to flight crew, for example in the cockpit, or ground crew, for example via an indication on the landing gear.

[0044] The method may comprise the step of operating a disk brake before, during and/or after applying the parking brake. The method may comprise bringing the aircraft to a halt, for example using a disk brake and/or reverse engine thrust and then, once the aircraft is stationary, applying the parking brake.

[0045] The method may further comprise the step of manually placing one or more wheel chocks under at least one wheel of an aircraft landing gear. The one or more chock may be applied before, during and/or after applying the parking brake. The method further comprises the step of removing the one or more chock from the aircraft landing gear. The step of removing the one or more chock may be applied before, during and/or after the parking brake is disengaged.

[0046] The method may further comprise the step of providing the actuator with power to move the first lock member between the locked and unlocked position. The method may comprise the step of maintaining a supply of power to the actuator to hold the first lock member in the locked position, for example against the action of gravity and/or a biasing mechanism as described above.

[0047] In another aspect of the invention there is provided an aircraft landing gear comprising a wheel mounted on an axle and a parking brake. The parking brake may comprise a first lock member mounted on the axle and/or a second lock member mounted on the wheel for rotation therewith. The second lock member may comprise a plurality of recesses. It may be that the first lock member is mounted for movement relative to the second lock member between a locked position in which at least part of the first lock member is received in at least one of said plurality of recesses, and an unlocked position in which the first lock member is spaced apart from the second lock member. It may be that an actuator is connected to the first lock member to hold the first lock member in the locked position when the parking brake is engaged. It may be that the first lock member is mounted below, for example directly underneath, a portion of the second lock member comprising one or more of said plurality of recesses so that in the event of an actuator failure the first lock member drops from the locked position into the unlocked position.

[0048] The second lock member may be a ring as described above in connection with other aspects. The first lock member may be mounted within the ring, for example concentrically with the ring, such that a portion of the circumference of the ring comprising one or more recesses is located above the first lock member.

[0049] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

-12 - [0050] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: [0051] Figure 1 shows an aircraft including an aircraft landing gear in accordance with embodiments of the invention; [0052] Figure 2a shows a parking brake in accordance with embodiments of the invention mounted on an aircraft landing gear with a lock member in the unlocked position; [0053] Figure 2b shows the parking brake of Figure 2a with the lock member in the locked position; [0054] Figure 3 shows a parking brake in accordance with another embodiment of the invention with a lock member in the locked position; [0055] Figure 4 shows part of a parking brake in accordance with another embodiment of the invention; and [0056] Figure 5 shows a flow chart of an example method of operating a parking brake.

DETAILED DESCRIPTION

[0057] Figure 1 shows an aircraft 1 comprising two main landing gear 3 and nose landing gear 7, each of the main landing gear 3 and nose landing gear 7 includes a parking brake in accordance with embodiments of the invention. In other embodiments the parking brake may only be provided on some of the landing gear, for example it may be that only the nose landing gear 7 includes a parking brake. In use, the parking brake is applied to immobilise the aircraft when the aircraft is stationary during turnaround, for example during loading and unloading. Thus, parking brakes in accordance with the present embodiments may avoid the need to use chocks or to engage the aircraft disk brakes to immobilise the aircraft. In addition to the parking brake, the aircraft 1 includes one or more disk brakes (not shown) for use during landing and taxiing [0058] Figures 2a and 2b show a parking brake 20 mounted to an aircraft landing gear wheel 11 in the unlocked position and the locked position respectively. The wheel 11 comprises a tyre 21 mounted to a hub 22 which is itself mounted to an axle 17. A toothed ring 18 is mounted on the hub 22, concentric to the axle 17 with the teeth 18a of the ring 18 extending radially inward towards the axle 17. An actuator 8 comprising an arm 2 connected to the actuator 8 via a shear pin 25 is mounted on a sleeve 16 at a 12 o'clock position in Figure 2a and 2b. Sleeve 16 is concentrically mounted to axle 17. The arm 2 of the actuator 8 extends radially upward away from the sleeve 16 and towards the ring 18. A pin 5, which appears circular when viewed in cross-section in Figures 2a and 2b is mounted on the distal end of the arm 2. A power supply 26, illustrated schematically in Figure 2a, supplies power to the actuator 8. In some embodiments this may be an electrical power supply, in other embodiments this may be a supply of hydraulic fluid at pressure. A control system 28, illustrated schematically in Figure 2a, provides control signals to the power supply and/or actuator.

[0059] Figure 2a shows the pin 5 in an unlocked positon, in which the pin is spaced apart from the teeth 18a. Figure 2b shows the pin 5 in a locked position in which the pin 5 is engaged in a gap 18b formed between two of the teeth 18a.

[0060] In use, when the parking brake 20 is engaged the actuator 8 moves pin 5 upwards into a gap 18b between two teeth 18a. The presence of the pin 5 in the gap 18b prevents the hub 22 (and therefore the tyre 21) rotating relative to the axle 17 thereby immobilizing the wheel 11. When Figure 2a and Figure 2b are compared it can be seen that the pin 5 has moved radially upwards from the unlocked position to the locked position. While the parking brake 20 is engaged the actuator 8 holds the pin 5 in the gap 18b thereby preventing movement of the wheel I. In normal use, when the parking brake 20 is disengaged, the pin 5 is moved downwards from the locked position shown in Figure 2b under the control of the actuator 8 to the unlocked position shown in Figure 2a and the wheel 11 is then free to rotate. The actuator 8 receives power from power supply 26 under the control of control system 28. The parking brake 20 may be engaged and disengaged via user input to control system 28 or automatically under the control of an aircraft system, for example the autopilot. In the event that the supply of power from power supply 26 to actuator 8 is lost or the arm 2 breaks, then the pin 5 drops under the action of gravity from the locked position shown in Figure 2b to the unlocked position shown in Figure 2a and the wheel 11 is then free to rotate. Thus, pin 5 is biased to return to the unlocked position in the event of an actuator failure, for example a failure of the power supply 26 to the actuator 8. Accordingly, parking brakes in accordance with the present example embodiment fail to an unlocked position therefore reducing the risk that a failure in connection with the parking brake would prevent the aircraft from taking off In the event of such a failure of the parking brake -14 -the disk brake or chocks may be used to immobilise the aircraft instead. Shear pin 25 is sized to fail in the event that a large external torque, for example a spin up load is applied to wheel 11, thereby allowing wheel rotation and reducing the risk of damage to the landing gear in the event the parking brake is not disengaged prior to spin up. The arrangement of the pin 5 in the present embodiment means that gravity acts to return the pin to the unlocked position, thereby providing a mechanically simple mechanism by which a parking brake can fail to the unlocked position and reducing the risk of malfunction as well as the cost and weight of the parking brake [0061] In the example embodiment described above, the pin 5 may be mounted to rotate about its longitudinal axis in order to reduce the risk of jamming as the pin 5 moves into engagement with the toothed ring 18. In some embodiments, the pin 5 may be compliant to improve the engagement between the pin 5 and the teeth 18a.

[0062] In the example embodiment described above, the lock members are in the form of a cylindrical pin 5 and a toothed disk 18. It will however be appreciated that other shapes of lock members may be used. Figure 3 shows an embodiment of the invention where a disk 18 has an inward facing (i.e. facing towards the axle 17) surface 18a in which a plurality of radially-extending apertures 18b are formed, the radially-extending apertures 18b being spaced apart around the inward facing surface 18a. In Figure 3 the pin 5 appears square when viewed in cross-section.

[0063] In the examples above, the pin 5 is returned to the unlocked position by the action of gravity. In the same or yet further embodiments a spring or other biasing mechanism may be used to return the lock member to the unlocked position. In some embodiments, the pin 5 may be located at a different position around the circumference of the wheel. In such embodiments a spring or other resilient member and/or mechanism may be used to return the pin to the unlocked position. Such biasing mechanisms are well known in the art.

[0064] Figure 4 shows part of a parking brake in accordance with another example embodiment. Figure 4 shows a portion of the lock member 18 which is mounted on the hub comprising triangular teeth 18a defining triangular recesses 18b between them. In the Figure 4 embodiment the lock member 5 that is connected to the actuator 8 via arm 2 is in the form of two triangular teeth 5a. The actuator 8, arm 2 and lock member 5 are mounted above the lock member 18. A spring 29 extends between the actuator 8 and the lock member 5. The parking brake is shown in the unlocked position in Figure 4. In the locked position the triangular teeth 5a are received in the recesses 18b. For simplicity teeth 18a are shown in a straight line in Figure 4 but it would be appreciated that these would be arranged along a curved line in practice. In use, actuator 8 moves lock member 5 downwards into engagement with the lock member 18, thereby stretching the spring 29. In normal operation, actuator 8 also moves lock member 5 upwards out of engagement with the lock member 18 thereby releasing the parking brake. In the event that actuator 8 fails, spring 29 acts to move lock member 5 upwards out of engagement with the lock member 18 thereby releasing the parking brake.

[0065] In the examples above, the actuator (and the moveable lock member) is mounted on the axle and the stationary lock member is mounted on the hub. In general this is preferred as it is simpler to provide power to the actuator in this configuration. However, in other embodiments it may be advantageous for the actuator (and the moveable lock member) to be mounted on the hub and the stationary lock member to be mounted on the axle.

[0066] In the examples above, the actuator 8 is arrange to move the pin 5 in a radial direction (e.g. perpendicular to the longitudinal axis of the axle 17). In other embodiments the actuator may be arranged to move the pin or other locking member in a direction parallel to the longitudinal axis of the axle 17.

[0067] Figure 5 shows a flow chart of an example method of operating of a parking brake in accordance with the present invention. Optionally, the method comprises the step of a user or control system providing 30 a control signal to engage the brake. This may be done once the aircraft is stationary. Optionally, in response to the provision 30 of the signal the actuator moves 32 a first lock member into engagement with a second lock member thereby preventing rotation of the wheel. The actuator then holds 34 the first lock member in engagement with the second lock member. Optionally, in response to a user or control system providing 36 a control signal to disengage the brake the actuator moves 38 the first lock member out of engagement with the second lock member to an unlocked position thereby releasing the wheel to rotate. In the case that power supply to the actuator fails 40, the method may comprise the first lock member automatically returning 42 to an unlocked position (i.e. disengaging from the lock member). Thus, methods in accordance with the present example may provide a parking brake that fails to an unlocked configuration in the case that the supply of power to the actuator fails.

-16 - [0068] In addition to the steps described above, the method may comprise providing an indication of the status of the parking brake to the flight crew and/or ground crew, for example a visual or audible indication that the brake is engaged or disengaged [0069] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

[0070] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments

Claims (1)

1. -17 -CLAIMS1 A parking brake for an aircraft landing gear having at least one wheel, the parking brake comprising: a first lock member and a second lock member, the first lock member being mounted for movement relative to the second lock member between an unlocked position in which the first lock member is disengaged from the second lock member and a locked position in which the first lock member engages the second lock member to prevent movement of the at least one wheel; and an actuator that holds the first lock member in the locked position when the parking brake is engaged; and wherein the parking brake is configured such that the first lock member returns to the unlocked position if the actuator ceases to hold the first lock member in the locked position 2. A parking brake as claimed in claim 1 wherein the second lock member comprises a plurality of apertures, for example recesses or through-holes configured to receive at least a portion of the first lock member.3. A parking brake as claimed in claim 1 or 2 wherein the first lock member is an elongate body, for example a pin or rod.4 A parking brake as claimed in any preceding claim wherein the second lock member is a ring and the plurality of apertures are spaced apart circumferentially around the ring A parking brake as claimed in any preceding claim wherein the first lock member is configured to move in a radial direction with respect to the second lock member and/or the wheel between the unlocked position and the locked position.6 A parking brake as claimed in any preceding claim wherein the actuator is connected to the first lock member to move the first lock member from the -18 -unlocked position to the locked position, and optionally, from the locked position to the unlocked position.7. A parking brake as claimed in any preceding claim wherein the first lock member returns to the unlocked position due to the action of gravity alone.8 A parking brake as claimed in any of claims 1 to 6 further comprising a biasing mechanism configured to act on the first lock member to return the first lock member to the unlocked position 9. An aircraft landing gear comprising a parking brake as claimed in any preceding claim 10. An aircraft landing gear as claimed in claim 9, the aircraft landing gear comprising an axle upon which the wheel is mounted, the wheel comprising a hub and a tyre.11 An aircraft landing gear as claimed in claim 9 or 10, wherein the position of the first lock member in the locked position is above the position of the first lock member in the unlocked position, so that the first lock member drops into the unlocked position if the actuator ceases to hold the first lock member in the locked position.12. An aircraft landing gear as claimed in claim 10 or 11, wherein the actuator is mounted on the axle and the second lock member is mounted on the hub for rotation therewith 13. An aircraft landing gear as claimed in claim 10 or 11, wherein the actuator is mounted on the hub for rotation therewith and the second lock member is mounted on the axle.14 An aircraft landing gear as claimed in any of claims 9 to 13, wherein the aircraft landing gear comprises a disk brake for use during landing and/or taxiing.-19 - 15. An aircraft comprising an aircraft landing gear as claimed in any of claims 9 to 14.16. A method of operating a parking brake for an aircraft landing gear having at least one wheel, the parking brake comprising a first lock member and a second lock member, and an actuator connected to the first lock member, the method comprising the following steps: - the actuator maintains the first lock member in engagement with the second lock member thereby preventing rotation of the wheel; and - in the event of actuator failure, the first lock member disengages from the second lock member thereby releasing the parking brake so that the at least one wheel can rotate.17. A method according to claim 16, wherein power is supplied to the actuator to allow the actuator to maintain the first lock member in engagement with the second lock member, and the actuator failure comprises failure of the power supply.18. A method according to claim 16 or claim 17, wherein the first lock member drops out of engagement with the second lock member in the event of actuator failure.19 An aircraft landing gear comprising a wheel mounted on an axle and a parking brake, the parking brake comprising a first lock member mounted on the axle; a second lock member mounted on the wheel for rotation therewith, and comprising a plurality of recesses, the first lock member being mounted for movement relative to the second lock member between a locked position in which at least part of the first lock member is received in at least one of said plurality of recesses, and an unlocked position in which the first lock member is spaced apart from the second lock member; -20 -an actuator connected to the first lock member to hold the first lock member in the locked position when the parking brake is engaged; and wherein the first lock member is mounted below a portion of the second lock member comprising one or more of said plurality of recesses so that in the event of an actuator failure the first lock member drops from the locked position into the unlocked position.