Abstract:
The present invention provides a landing gear assembly for an aircraft landing gear, the assembly comprising a steering mechanism for steering at least one wheel of the landing gear, a deployment mechanism for moving a leg of the landing gear between a stowed position and a deployed position, and an actuator arranged to actuate both the steering mechanism and the deployment mechanism. The invention also provides an aircraft landing gear, an aircraft and methods of operating an aircraft landing gear.

Description:
RELATED APPLICATIONS 
     The present application claims priority from Great Brittain Application Number 1414986.8, filed Aug. 22, 2014, the disclosure if which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns a landing gear assembly for an aircraft landing gear. More particularly, but not exclusively, the present invention concerns a landing gear assembly comprising a steering mechanism for steering at least one wheel of the landing gear and a deployment mechanism for moving a leg of the landing gear between a stowed position and a deployed position. The invention also concerns an aircraft landing gear, an aircraft and methods of operating an aircraft landing gear. 
     A typical prior art aircraft nose landing gear comprises a steering mechanism for steering at least one wheel of the landing gear and a deployment mechanism for moving a leg of the landing gear between a stowed position and a deployed position. Each of the mechanisms has an actuator associated with it to actuate the mechanism. The steering actuator actuates the steering mechanism to steer the at least one wheel. The deployment actuator actuates the deployment mechanism, including a foldable drag stay, to deploy or stow the landing gear. The deployment mechanism also typically comprises an uplock link for preventing the drag stay from folding when the landing gear leg is in the deployed position. The uplock link functions as a two-part linkage with an over-centre hinge, to lock it in place. There is also typically an uplock actuator that moves the uplock out of a locking position when the leg is to be moved to the stowed position. A typical prior art aircraft nose landing gear also comprises a centreing cam arrangement. This centreing cam arrangement ensures that a wheel of the landing gear is centred—i.e. orientated in a straight direction (in an orientation so that the aircraft would not be steered left or right, off its course—i.e. when the wheel is substantially parallel to the aircraft centre line) when in a “weight off wheel” situation. This means that when the landing gear is deployed and the aircraft then lands, the aircraft is not accidentally steered off course. 
     There is a desire to make landing gears as light as possible to reduce fuel burn, whilst still providing the required functionality and safety. The prior art landing gears may be considered to be heavier than desired. 
     The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved landing gear assembly for an aircraft landing gear. 
     SUMMARY OF THE INVENTION 
     The present invention provides, according to a first aspect, a landing gear assembly for an aircraft landing gear, the assembly comprising a steering mechanism for steering at least one wheel of the landing gear, a deployment mechanism for moving a leg of the landing gear between a stowed position and a deployed position, and an actuator arranged to actuate both the steering mechanism and the deployment mechanism. 
     The inventor has realised that the same actuator could be used for actuating both the steering mechanism and the deployment mechanism. In particular, it is noted that, when the aircraft is to be steered by the landing gear (when it is in a “weight on wheel” situation), the landing gear is always deployed, and when the landing gear is stowed, or being moved to be stowed, (when it is in a “weight off wheel” situation) the aircraft does not need to be steered by the landing gear. Having one actuator (and associated systems and pipework) instead of two, reduces the weight of the landing gear assembly, and thus decreases fuel burn of the aircraft. It also reduces the maintenance burden and reduces the drag and noise generated by the landing gear assembly, when the landing gear leg is deployed. 
     The present invention provides a landing gear assembly for an aircraft landing gear, the assembly comprising a steering mechanism for steering at least one wheel of the landing gear, a deployment mechanism for moving a leg of the landing gear between a stowed position and a deployed position, and a single actuator arranged to actuate both the steering mechanism and the deployment mechanism. 
     The landing gear assembly is preferably for an aircraft nose landing gear. 
     Preferably, the landing gear assembly further comprises a coupling mechanism for coupling the actuator to the steering mechanism and the deployment mechanism, wherein the coupling mechanism is arranged to couple the actuator to only one of the steering mechanism and the deployment mechanism at any one time. This ensures that the actuator can be coupled to only the appropriate mechanism in each appropriate situation. 
     The coupling mechanism is arranged to couple the actuator to each respective mechanism such that the respective mechanism is able to be actuated by the actuator. The coupling mechanism may do this by connecting the respective mechanism to the actuator. However, preferably, the coupling mechanism does this by preventing the other mechanism from being actuated by the actuator. 
     Preferably, the coupling mechanism is arranged to automatically couple the actuator to only one of the steering mechanism and the deployment mechanism at any one time. The automatic coupling is preferably achieved by mechanical action of the coupling mechanism. 
     Preferably, the landing gear assembly further comprises a coupling mechanism for coupling the actuator to the steering mechanism and the deployment mechanism, wherein the coupling mechanism is arranged to automatically couple (preferably by a mechanical action of the coupling mechanism) the actuator to only one of the steering mechanism and the deployment mechanism at any one time. 
     More preferably, the coupling mechanism is arranged to couple the actuator to the steering mechanism when the wheel is in a “weight on wheel” situation and to couple the actuator to the deployment mechanism when the wheel is in a “weight off wheel” situation. This ensures that the steering mechanism can be actuated when it is needed and the deployment mechanism can be actuated when it is needed. 
     More preferably, the coupling mechanism is arranged to automatically couple the actuator to the steering mechanism when the wheel is in a “weight on wheel” situation and to automatically couple the actuator to the deployment mechanism when the wheel is in a “weight off wheel” situation. The automatic coupling is preferably achieved by mechanical action of the coupling mechanism. 
     A “weight on wheel” situation is one in which the at least one wheel would be touching the ground and supporting at least a first amount of the weight of the aircraft. A “weight off wheel” situation is one in which the at least one wheel would be supporting less than the first amount of weight of the aircraft and the wheel is often not touching the ground. The first amount may be very small and may be zero or close to zero. 
     The automatic coupling of the coupling mechanism is preferably achieved by a mechanical action of the coupling mechanism as a result of a change between a “weight on wheel” and a “weight off wheel” situation. 
     Even more preferably, the coupling mechanism comprises a locking mechanism, comprising a locking element moveable between a steering locked position, in which the steering mechanism is prevented from steering the wheel, and a steering unlocked position, in which the steering mechanism is able to steer the wheel, wherein when the wheel is in a “weight on wheel” situation the locking element is (automatically) moved to the steering unlocked position and when the wheel is in a “weight off wheel” situation, the locking element is (automatically) moved to the steering locked position. This allows the “switch” between the mechanisms by the coupling mechanism to be provided by the locking mechanism. 
     Even more preferably, the locking element (automatically) moves from the steering locked position to the steering unlocked position under the action of the wheel being moved from a dropped position to a raised position relative to the locking element when the wheel changes from a “weight off wheel” to a “weight on wheel” situation and (automatically) moves from the steering unlocked position to the steering locked position under the action of the wheel being moved from the raised position to the dropped position relative to the locking element when the wheel changes from a “weight on wheel” to a “weight off wheel” situation. This allows the “switch” between the mechanisms by the coupling mechanism to be “automatic”, without user/pilot input being required. 
     The coupling mechanism may be arranged to convert linear motion of the actuator to rotational motion, in order to rotate a part of the steering mechanism. 
     Even more preferably, the coupling mechanism comprises a crank arm rotatable between first and second rotation positions by the actuator when the locking element is in the steering unlocked position, and prevented from rotating when the locking element is in the steering locked position. The crank arm being prevented from rotating provides that steering of the at least one wheel can be prevented. 
     Even more preferably, the crank arm is connected to the steering mechanism such that when the crank arm is in the first rotation position, the steering mechanism steers the wheel in a first direction and when the crank arm is in the second rotation position, the steering mechanism steers the wheel in a second different direction. This allows the rotation of the crank arm to enable steering of the at least one wheel. 
     Even more preferably, the crank arm is connected to the steering mechanism by a bevel gear arrangement such that rotational movement of the crank arm is converted to rotational movement of the steering mechanism. 
     Preferably, when in the steering locked position, the locking element acts on the bevel gear arrangement to prevent its rotation. 
     Additionally or alternatively, when in the steering locked position, the locking element acts on the steering mechanism to prevent its rotation. 
     The locking mechanism may comprise two or more locking elements; a first locking element may act on the bevel gear arrangement to prevent its rotation, and a second locking element may act on the steering mechanism to prevent its rotation. 
     Preferably, the locking element is part of a centring arrangement for centring the steering mechanism, such that the wheel is steered in a central direction (i.e. when the at least one wheel is centred—i.e. orientated in a straight direction (in an orientation so that the aircraft would not be steered left or right, off its course) when the wheel is in a “weight off wheel” situation. This means that when the landing gear is deployed and the aircraft then lands, the aircraft is not accidentally steered off course. 
     Preferably, the coupling mechanism comprises a lever arm connected at its first end to the actuator and moveable by the actuator between extended and retracted positions. 
     Even more preferably, the lever arm is rotatably connected at its second end to the crank arm such that when the lever arm is caused to extend and retract by the actuator, the crank arm is caused to rotate by the lever arm. 
     Even more preferably, when the crank arm is prevented from rotating by the locking element in the steering locked position, movement by the actuator of the lever arm between extended and retracted positions instead causes the landing gear leg to move between the deployed and stowed positions. 
     Preferably, the steering mechanism comprises a steering collar connected to the actuator and one or more torque links connected to the wheel. 
     Preferably, the deployment mechanism comprises a number of moveable links, including a lock link, connected between the actuator and the landing gear leg. 
     More preferably, the deployment mechanism further comprises a lock link actuator for moving the lock link. 
     According to a second aspect of the invention there is also provided an aircraft landing gear comprising the landing gear arrangement of the first aspect of the invention. The aircraft landing gear is preferably an aircraft nose landing gear. 
     According to a third aspect of the invention there is also provided an aircraft comprising the aircraft landing gear of the second aspect of the invention or the landing gear arrangement of the first aspect of the invention. 
     According to a fourth aspect of the invention there is also provided a method of operating an aircraft landing gear comprising the step of providing a landing gear arrangement, aircraft landing gear or aircraft of the first, second or third aspect of the invention. 
     According to a fifth aspect of the invention there is also provided a method of operating an aircraft landing gear comprising the steps of, in a first time period, placing a wheel of the landing gear on the ground such that the wheel is in a “weight on wheel” situation, thereby moving a steering locking element of the landing gear to a steering unlocked position (in which the steering mechanism is able to steer the wheel), and then using an actuator of the landing gear to steer the wheel, and, in a second time period, removing the wheel of the landing gear from the ground such that the wheel is in a “weight off wheel” situation, thereby moving the steering locking element to a steering locked position (in which the steering mechanism is prevented from steering the wheel), and then using the actuator to stow and/or deploy the landing gear. 
     According to a fifth aspect of the invention there is also provided a method of operating an aircraft landing gear comprising the steps of, in a first time period, placing a wheel of the landing gear on the ground such that the wheel is in a “weight on wheel” situation, thereby moving a steering locking element of the landing gear to a steering unlocked position (in which the steering mechanism is able to steer the wheel), and then using an actuator of the landing gear to steer the wheel, and, in a second time period, removing the wheel of the landing gear from the ground such that the wheel is in a “weight off wheel” situation, thereby moving the steering locking element to a steering locked position (in which the steering mechanism is prevented from steering the wheel), and then using the same actuator to stow and/or deploy the landing gear. 
     Preferably, the aircraft landing gear is an aircraft nose landing gear. 
     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 
       Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: 
         FIG. 1  shows a side view of an aircraft nose landing gear according to a first embodiment of the invention, in a deployed “weight on wheel” situation; 
         FIG. 2  shows a side view of the aircraft nose landing gear, in a deployed “weight off wheel” situation; 
         FIG. 3  shows a side view of the aircraft nose landing gear being moved into a stowed position; 
         FIG. 4 a    shows a side view of part of the aircraft nose landing gear in a deployed “weight on wheel” situation, whilst the wheel is being steered left; 
         FIG. 4 b    shows a side view of part of the aircraft nose landing gear in a deployed “weight on wheel” situation, whilst the wheel is being steered centrally; 
         FIG. 4 c    shows a side view of part of the aircraft nose landing gear in a deployed “weight on wheel” situation, whilst the wheel is being steered right; 
         FIG. 5  shows a perspective view of a centreing cam arrangement of the aircraft nose landing gear in a “weight on wheel” situation; 
         FIG. 6 a    shows a side view of part of an aircraft nose landing gear according to a second embodiment of the invention in a “weight off wheel” situation; 
         FIG. 6 b    shows a side view of part of the aircraft nose landing gear of  FIG. 6 a    in a “weight on wheel” situation; and 
         FIG. 7  shows a front view of an aircraft, including the aircraft nose landing gear of either the first or second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a side view of an aircraft nose landing gear  500  according to a first embodiment of the invention, in a deployed “weight on wheel” situation and  FIG. 2  shows a side view of the aircraft nose landing gear  500 , in a deployed “weight off wheel” situation. The forwards direction  701  is shown. In addition, the ground surface  700  is also shown. 
     The landing gear  500  comprises a landing gear leg  501 , which is suspended from a fuselage  100  of an aircraft by a pivot point  506 . 
     In addition, an actuator  530  is also suspended from the fuselage  100  by a pivot point  531  behind the leg pivot point  506 . The actuator  530  itself will be explained in more detail in relation to  FIGS. 4 a  to 4 c   . The actuator  530  is attached to the landing gear leg  501 , by a lever arm  532  (acting as an actuator rod), pivotally connected at pivot point  534  to a crank arm  533 . The crank arm  533  is pivotally connected to a bevel gear  515  located in the upper portion  505  of the landing gear leg  501 . 
     In the “weight on wheel” situation of  FIG. 1 , the bevel gear  515  is located adjacent a steering disc  513  of a steering mechanism  510 . The steering disc  513  connected to a steering column  514 . The steering column  514  is rotatably housed in the landing gear leg  501 . Hence, pivotal movement of the crank arm  533  causes rotation of the bevel gear  515  which causes rotation of the steering disc  513  and steering column  514 . The steering column  514  is connected to a first torque link  512  at a lower portion  504  of the landing gear leg  501 . The first torque link  512  is pivotally connected to a second torque link  511  and that second torque link  511  is connected to a wheel  502  of the landing gear leg  501  at an axle  503 . Hence, rotation of the steering column  514  causes, through the torque links  511 ,  512 , steering of the wheel  502 . 
     The wheel  502  is supported by a wheel strut  541  which extends upwards through the landing gear leg  501  and is slidably mounted in the steering column  514 . When in the “weight on wheel” situation of  FIG. 1 , the wheel  502  and wheel strut  541  slide upwards in relation to the landing gear leg  501  and steering column  514 . When in the “weight off wheel” situation of  FIG. 2 , the wheel  502  and wheel strut  514  slide downwards in relation to the landing gear leg  501  and steering column  514 . 
     The wheel strut  541  and steering column  514  are linked by a centreing cam arrangement (schematically shown as  542 ), which will be described in more detail in relation to  FIG. 5 . 
     The landing gear  500  also comprises a deployment mechanism  520  comprising a two-part drag strut, comprising an upper part  521  pivotally connected at pivot point  525   b  to a lower part  522 . The upper end of the upper drag strut  521  is suspended from the fuselage  100  at a pivot point  525   a  behind the actuator pivot point  531 . The lower end of the lower drag strut  522  is pivotally connected to an upper portion  505  of the landing gear leg  501  by pivot point  525   c.  The deployment mechanism  520  also comprises a two-part uplock, comprising a back part  524  and a front part  523 . The front end of the front part  523  is pivotally connected to the drag strut near (or at the same point) as the pivot point  525   b,  at pivot point  526   a.  The back  524  and front  523  parts are pivotally connected to each other at pivot point  526   b  and the back end of back part  524  is pivotally attached to the upper portion  505  of the landing gear leg  501  by pivot point  526   c,  above pivot point  525   c.    
     The “over-centre” uplock  523 ,  524  is used to lock the drag strut  521 ,  522  in the deployed position shown in  FIGS. 1 and 2 . A second actuator  527  is used to move the uplock past the “over-centre” point to allow the drag strut  521 ,  522  to move to stow the landing gear leg  501 . The stowing of the landing gear leg  501  will be described in more detail, in relation to  FIG. 3 . 
       FIG. 4 a    shows a side view of part of the aircraft nose landing gear  500  in a deployed “weight on wheel” situation, whilst the wheel  502  is being steered left. Here, the actuator  530  can be seen more clearly. It comprises an actuator block  537  fixed on an actuator rod (the lever arm  532 ). The block  537  is contained within an actuator chamber  538  of the actuator  530 . Hence, actuation of the actuator  530  moves the block  537  along the length of the actuator chamber  538  and thus effectively increases and decreases the length of the lever arm  532  extending from the actuator  530 . In  FIG. 4 a   , the actuator block  537  is located at the upper end of the actuator chamber  538  and hence a relatively large length of the lever arm  532  has been pulled within the actuator  530 . This means that the effective (protruding) length of the lever arm  532  is small. This causes the lever arm  523  to pull on the crank arm  533  and, by pivot point  534 , rotate the crank arm  533  in an anti-clockwise direction (as shown in  FIG. 4 a   ). This causes the bevel gear  515  to also rotate anti-clockwise. This then causes the steering disc  513  to rotate from left to right (as shown in  FIG. 4 a   —i.e. anti-clockwise if viewed from the top of  FIG. 4 a   ) and cause the steering column  514  to also rotate in that direction. This then causes the torque links  511 ,  512  to rotate the wheel  502  so that it is steered in a left direction. 
       FIG. 4 b    shows a side view of part of the aircraft nose landing gear in a deployed “weight on wheel” situation, whilst the wheel is being steered centrally. Here, the actuator block  537  is located substantially centrally in the actuator chamber  538 . The lever arm  532  has been effectively lengthened from  FIG. 4 a   , and therefore crank arm  533  and bevel gear  515  have been pivoted clockwise. This rotates the steering disc  513  and steering column  514  to rotate towards the right and also causes the torque links  511 ,  512  to change the direction of the wheel  502  so that it is being steered in a central direction. 
       FIG. 4 c    shows a side view of part of the aircraft nose landing gear in a deployed “weight on wheel” situation, whilst the wheel is being steered right. Here, the actuator block  537  has been moved further down the actuator chamber  538  to a lower end of it. The lever arm  532  has been effectively lengthened further from  FIG. 4 b   , and therefore crank arm  533  and bevel gear  515  have been pivoted further clockwise. This rotates the steering disc  513  and steering column  514  to rotate further to the right and also causes the torque links  511 ,  512  to change the direction of the wheel  502  so that it is being steered in a right direction. 
     Hence, the steering direction of the wheel  502  can be controlled by the actuator  530  when in the “weight on wheel” situation. 
       FIG. 5  shows a perspective view of the centreing cam arrangement  542  of the aircraft nose landing gear  500  in a “weight on wheel” situation. The centreing cam arrangement is designed to do two things. Firstly, when there is a “weight off wheel” situation, the arrangement  542  ensures that the wheel  502  is orientated in a central orientation. This means that when the aircraft lands so that the wheel  502  controls the direction of the aircraft, the aircraft will not be steered off course by a wheel that is being orientated significantly left or right. This is achieved by the wheel strut  541  sliding downwards in relation to the steering column  514  when in a “weight off wheel” situation. This causes an internal downwardly facing notch  544  in the wheel strut  541  to fall into a corresponding internal upwardly facing groove  543  of the steering column  514 . It is also noted that each of the notch and groove  544 ,  543  have corresponding tapered sides  546 ,  545  to effect rotation of the steering column  514  (and therefore wheel  502 ) as the notch  544  and groove  543  line up. 
     Secondly, also when there is a “weight off wheel” situation, the arrangement  542  (and in particular, the notch  544  in groove  543 ) rotationally fixes the steering column  514  in relation to the wheel strut  541  so that the steering column  514  cannot rotate. This means that the steering disc  513 , bevel gear  515  and crank arm  533  also cannot rotate. Hence, when in a “weight off wheel” situation, lengthening and shortening of the lever arm  532  does not cause rotation of the crank arm  533 , but instead causes the landing gear leg  501  to be pulled on by the lever arm  532  (via crank arm  533 ) so that it pivots about pivot point  506  to pivot the leg  501  in a stowing direction  702 , as shown in  FIG. 3 . 
     In order for this to happen, the uplock actuator has to also be actuated to move the uplock “over-centre” so that the two parts  523 ,  524  of the uplock can collapse and allow the two parts of the drag strut  521 ,  522  to also collapse, as shown in  FIG. 3 . 
       FIGS. 6 a  and 6 b    show side views of part of an aircraft nose landing gear  600  according to a second embodiment of the invention. Here, corresponding similar elements to the first embodiment (which are not described again for efficiency) are labelled with a preceding “ 6 ” instead of a “ 5 ”. In this second embodiment, the wheel strut  641  is provided at an upper end with a downwardly pointing triangular member  680 . When in the “weight on wheel” situation of  FIG. 6 a   , the wheel strut  641  has been slid upwards in relation to the steering column  614  and hence triangular member  680  is above the bevel gear  615  and does not affect its ability to rotate. However, when in the “weight off wheel” situation of  FIG. 6 b   , the wheel strut  641  has been slid downwards in relation to the steering column  614  and hence triangular member  680  is adjacent to the bevel gear  615 . In fact, the point of the triangle lodges in between two projections (not shown) on the edge of the bevel gear  615  and prevent its rotation. Hence, the triangular member  680  is used to lock the bevel gear  615 , steering disc  613  and steering column  614  and prevent their rotation when in the “weight off wheel” situation. This ensures that actuation of the actuator  630  would cause deployment/stowage of the landing gear  60 , rather than steering of the wheel  602 , in a similar way to the centreing cam arrangement  542  of the first embodiment. 
       FIG. 7  shows a front view of an aircraft  1000 . The aircraft  1000  comprises a fuselage  100 , two wings  210 ,  202  (each with one underwing engine) and a tailplane  300 . Each of the wings  201 ,  202  is also provided with a main landing gear  401 ,  402 . Finally, the aircraft  1000  is fitted with a nose landing gear according to either the first  500  or the second  600  embodiment. 
     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. By way of example only, certain possible variations will now be described. 
     The landing gear may be provided with two ways of rotationally fixing the steering column  514 ,  615 ; one way using a notch  544  of the centreing cam arrangement  542  of  FIG. 5  and another way of using a triangular member  680  as shown in  FIGS. 6 a    and  6   b.    
     The aircraft landing gear  500 ,  600  may comprise more than one wheel  502 ,  602 . 
     The aircraft landing gear  500 ,  600  may be a nose landing gear or any other landing gear. 
     Any aircraft may be used with this invention, and not just (a particularly sized) commercial passenger airliner, as shown in  FIG. 7 . 
     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.