Abstract:
The invention relates to an aircraft undercarriage including a steerable bottom portion and a steering member suitable for turning the steerable bottom portion in response to a steering order. According to the invention, the steering member comprises a plurality of electromechanical steering actuators each comprising at least one main electric motor, and the actuators are disposed on the undercarriage so as to enable all of them to co-operate simultaneously with the steerable bottom portion in order to steer it, each of the electro-mechanical steering actuators including controllable coupling means for selectively placing the actuator:
       either in a coupled state in which it is coupled with the steerable bottom portion, in which the main electric motor of the actuator is suitable for causing the steerable bottom portion to turn; or   else in an uncoupled state in which it is uncoupled from the steerable bottom portion and in which the main electric motor of the actuator is isolated from the steerable bottom portion.

Description:
[0001]    The invention relates to an aircraft undercarriage including a plurality of electromechanical steering actuators. 
       BACKGROUND OF THE INVENTION 
       [0002]    Aircraft undercarriages are known that include a bottom portion that is steerable and a steering member adapted to turn the steerable bottom portion in response to a steering order. 
         [0003]    The steering member often includes one or more actuators which act on the steerable bottom portion. Other types of steering member are known, e.g. using a rack. 
         [0004]    In the field of carrier-borne aircraft, it is known to use steering members that include an actuator with a hydraulic motor co-operating with a toothed ring secured to the steerable bottom portion of the undercarriage. 
         [0005]    In the field of light aircraft, it is known to use a steering member including an actuator with an electric motor co-operating with a toothed ring secured to the steerable bottom portion of the undercarriage. 
         [0006]    Nevertheless, if the actuator member fails, command over steering is lost completely, and it is no longer possible to direct the aircraft under its own control other than by differential braking or by asymmetrical thrust from its engines. 
       OBJECT OF THE INVENTION 
       [0007]    The invention seeks to improve steering control and to provide new possibilities for use. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    In order to achieve this object, the invention provides an aircraft undercarriage including a steerable bottom portion and a steering member suitable for turning the steerable bottom portion in response to a steering order, in which, in accordance with the invention, the steering member comprises a plurality of electro-mechanical steering actuators each comprising at least one main electric motor, and the actuators are disposed on the undercarriage so as to enable all of them to co-operate simultaneously with the steerable bottom portion in order to steer it, each of the electromechanical steering actuators including controllable coupling means for selectively placing the actuator: 
         [0009]    either in a coupled state in which it is coupled with the steerable bottom portion, in which the main electric motor of the actuator is suitable for causing the steerable bottom portion to turn; or 
         [0010]    else in an uncoupled state in which it is uncoupled from the steerable bottom portion and in which the main electric motor of the actuator is isolated from the steerable bottom portion. 
         [0011]    Thus, if one of the actuators breaks down, it is decoupled and steering can still be provided by the working actuator. 
         [0012]    The aircraft can then be allowed to take off from an airport even if a spare actuator is not available at that airport, thus contributing to making the aircraft easier to operate. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention can be better understood in the light of the following description with reference to the figures of the accompanying drawings, in which: 
           [0014]      FIG. 1  is a diagrammatic view of the bottom of an undercarriage fitted with electromechanical steering actuators of the invention; 
           [0015]      FIG. 2  is a plan view of the  FIG. 1  undercarriage; 
           [0016]      FIG. 3  is a section view through an electro-mechanical steering actuator on line III-III of  FIG. 2 , the shock absorber being removed, the coupling member being shown in its coupled position; 
           [0017]      FIG. 4  is a fragmentary section view on line IV-IV of  FIG. 3 ; 
           [0018]      FIG. 5  is a section view on line V-V of  FIG. 3  showing a portion of the coupling member in the coupled state; 
           [0019]      FIG. 6  is a section view on line VI-VI of  FIG. 7 ; 
           [0020]      FIG. 7  is a section view analogous to that of  FIG. 3  showing the coupling member in the uncoupled state; and 
           [0021]      FIG. 8  is a section view analogous to  FIG. 3  showing a variant embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    With reference to  FIGS. 1 and 2 , and in accordance with a particular embodiment of the invention, the under-carriage shown comprises a main fitting  1 , also called cylinder, in which a turnable tube  2  is mounted to turn about a longitudinal axis Z 1 . A telescopic shock absorber  3  extends inside the turnable tube  2 . The bottom portion of the shock absorber projects from the tube  2  and carries an axle  4  that receives wheels  5 . A scissors linkage  6  extends between the tube  2  and the shock absorber  3  to constrain the tube  2  to turn with the shock absorber  3  while allowing the shock absorber to shorten freely into the main fitting  1  along the axis Z 1 . 
         [0023]    At its bottom end, the tube  2  carries a toothed ring  7  (shown in  FIG. 3 ) which is received in a housing  8  in the strut  1  and which is constrained to turn with the turnable tube  2  by fluting  9 . 
         [0024]    In the invention, the undercarriage is fitted with two modular electromechanical steering actuators  10  adapted to co-operate with the toothed ring  7  to turn the tube  2  and thus turn the wheels  5  via the scissors linkage  6 . The electromechanical steering actuators  10  in this example form individual modules and they are fitted to corresponding housings  8  in the main fitting  1  so as to be easily removed without that requiring the other electromechanical steering actuator or any other structural portion of the undercarriage to be removed as well. 
         [0025]    With reference to  FIG. 3 , the toothed ring  7  is engaged by an outlet pinion  11  from the electromechanical steering actuator that is mounted to turn relative to the electromechanical steering actuator about an axis Z 2  that is parallel to the axis Z 1  of the undercarriage. The pinion  11  is connected to a driver  12  via a controllable coupling member  100  that is described in detail below. The driver  12  is secured to the outlet member  13  of a gearbox  14  of the type shown in U.S. Pat. No. 2,906,143, i.e. having a deformable circular wall  18  carrying on its outside face teeth that co-operate with facing teeth of a ring  17 , provided in slightly greater number. The cooperation between the teeth of the output member  13  and of the ring  17  is ensured by deforming the circular wall  18  under thrust from the input member  15  of the gearbox, forcing the teeth to co-operate in two diametrically opposite portions. It should be observed that the ring  17  in this example forms a portion of the housing of the electromechanical steering actuator. The remainder of the gearbox is conventional and does not form part of the subject matter of the invention as such. 
         [0026]    The input member  15  of the gearbox  14  is turned by a main electric motor  16 . Thus, assuming that the coupling member establishes mechanical coupling between the main electric motor  16  and the outlet pinion  11 , then controlled rotation of the main electric motor  16  causes the pinion  11  to be turned via the gearbox  14 , and thus serves to turn the toothed ring  7 . 
         [0027]    The coupling member  10  is described below in detail. 
         [0028]    The outlet pinion  11  is mounted to rotate freely on the driver  12 . The coupling member  100  includes a claw clutch  21  which is movable axially relative to the driver  12  between an engaged position (shown here) in which the clutch  21  extends between the outlet pinion  11  and the driver  12  so as to constrain them to rotate together, and a release position (visible in  FIG. 7 ) in which the clutch releases the outlet pinion  11  so that it is free to turn relative to the driver  12 . 
         [0029]    Thus, when the clutch  21  is in the engaged position, the main electric motor  16  is mechanically connected to the outlet pinion  11  such that the electromechanical steering actuator is coupled to the toothed ring  7  and can steer the wheels of the undercarriage, whereas when the clutch  21  is in the release position, the main electric motor  16  is no longer mechanically connected with the outlet pinion  11 , such that the electromechanical steering actuator is no longer coupled to the toothed ring  7  and can thus no longer steer the wheels of the undercarriage. 
         [0030]    As can be seen in  FIG. 4 , the clutch  21  and the outlet pinion  11  present complementary fluting  23  such that when the clutch  21  is in the engaged position, the clutch  21  is constrained to rotate with the outlet pinion  11 . Furthermore, the clutch  21  is constrained to rotate with the driver  12  by means of fingers  24  secured to the clutch  21  and extending through oblong slots  25  formed in the wall of the driver  12  to open out into a central cavity thereof, as can be seen more particularly in  FIG. 5 . 
         [0031]    As can be seen in  FIG. 5 , the ends of the fingers  24  are received in a groove  26  formed in the end of a control rod  20  of the coupling member  100  that extends in the central orifice of the driver  12  along the axis Z 2 . Sliding washers  27  are placed on the flanks of the groove  26 . Axial displacement of the control rod  20  causes the clutch  21  to move axially in corresponding manner. 
         [0032]    The control rod  20  is moved axially by an auxiliary electric motor  28  that is arranged to apply drive in one direction or the other to a control wheel  29  mounted to rotate on the electromechanical steering actuator about the axis Z 2  and having a threaded end  30  that co-operates with complementary tapping in the control rod  20 . The helical connection as organized in this way between the control wheel  29  and the control rod  20  allows rotation of the auxiliary electric motor  28  to cause the control rod  20  to move up or down, thereby moving the clutch  21  up or down. The control rod  20  is prevented from turning by fluting  31  co-operating with complementary fluting in the body of the actuator. 
         [0033]    As can be seen in  FIG. 6 , when the clutch  21  is in the release position, the oblong slots no longer match the width of the fingers  24  but they are slightly wider so that the fingers  24  and thus the clutch  21  have a small amount of freedom to turn relative to the driver  12 , thus facilitating engagement of the fluting  23  when the clutch  21  returns towards the engaged position. 
         [0034]    In order to determine the state of the coupling member  100 , an indicator needle  40  is secured to the end of the control rod  20  and forms the core of an inductive position sensor  41  of the linear variable differential transformer (LVDT) type from which the output signal varies depending on the axial position of the needle  40  and thus of the clutch  21 , thus making it possible to detect whether the clutch  21  is in the engaged or the release position. 
         [0035]    It should be observed that when the clutch  21  is in the release position, deliberate or accidental rotation of the main electric motor  16  cannot lead to untimely engagement, so the released state is a stable state. Similarly, when the clutch  21  is in the engaged position, intentional or accidental rotation of the electric motor  16  cannot lead to untimely release, such that the engaged state is also a stable state. 
         [0036]    A difficulty arises during engagement, if the ends of the fluting on the clutch  21  extend in register with the ends of the fluting on the outlet pinion  11 . In order to avoid damaging the fluting, it is appropriate to stop the motor  28  quickly in order to avoid applying excessive pressure on the facing ends of the fluting. 
         [0037]    The motor  28  is then reversed so as to separate the clutch  21  from the outlet pinion  11 , and the outlet pinion  11  is caused to turn using the other electromechanical steering actuator which, by turning the toothed ring  7  causes the outlet pinion  11  of the released actuator to turn. Thus, the fluting of the clutch  21  can be brought out of register with the fluting in the outlet pinion  11  thus enabling the clutch  21  to penetrate easily into the outlet pinion  11 . 
         [0038]    In a variant shown in  FIG. 8 , the control rod  20  is no longer axially connected to the clutch  21  in direct manner. The rod  20  is subdivided into two elements  20 A and  20 B that are movable axially relative to each other so that the rod  20  can be shortened. For this purpose, the element  20 B includes a pin  20 C which is engaged in slots in the element  20 A, a spring  20 D keeping the elements  20 A and  20 B in a spaced-apart position. 
         [0039]    In this example, the actuator is shown with the clutch  21  in the release position. 
         [0040]    During engagement, rotation of the motor  28  causes the control wheel to turn, and thus causes the rod  20  and the clutch  21  to move axially. If the fluting of the clutch  21  is in register with the fluting of the outlet pinion  11 , then the clutch  21  cannot engage in the outlet pinion  11 . The clutch  21  and the element  20 B are prevented from moving axially, which is easily identifiable by means of the sensor  41 , with the element  20 A continuing to move axially under drive from the rotating motor  28 . 
         [0041]    The spring  20 D serves to absorb this difference in axial movement between the elements  20 A and  20 B, and avoids imparting a large pressure force on the ends of the fluting which could hammer their ends or even damage them. 
         [0042]    In this situation, it suffices to cause the motor  28  to turn in the other direction so as to separate the clutch  21  from the outlet pinion  11 , and then cause the outlet pinion to turn slightly by using the other electromechanical steering actuator which, by turning the toothed ring  7  causes the outlet pinion  11  of the released actuator to turn. Thus, the ends of the fluting on the clutch  21  and on the outlet pinion  11  are no longer in register and the clutch  21  can penetrate easily into the outlet pinion  11 . 
         [0043]    The use of such electromechanical steering actuators presents several advantages: 
         [0044]    in normal operation, both electromechanical steering actuators operate in parallel, thereby giving appreciable speed of response to the steering command; 
         [0045]    if one of the electromechanical steering actuators  10  breaks down, it can be decoupled, thus making it possible to avoid locking the position of the tube  2  in the event of the failed electromechanical steering actuator itself being prevented from rotating. Under such circumstances, and providing each of the electromechanical steering actuators is sufficiently powerful on its own to control steering, steering can continue to be provided using the healthy electromechanical steering actuator, even if that is at the cost of poorer steering performance; 
         [0046]    the ability to decouple makes it possible to test the electromechanical steering actuators after the undercarriage has been extended but prior to landing. In order to test the motor of each of the electromechanical steering actuators, it suffices to begin by causing decoupling to take place and then to turn the corresponding main motor. The motor must turn easily while being fed with low current, given that it is no longer connected to the toothed ring  7 . Then in order to test the coupling member, it suffices to initiate coupling and verify that the motor needs much higher current in order to make it turn, corresponding to the resistance that is to be expected from the motor being coupled; 
         [0047]    the ability to uncouple makes it possible to use large stepdown ratios, which presents the advantage of enabling smaller motors to be used, but makes the actuators irreversible. Any drawback normally associated with irreversibility, which runs the risk of the entire steering control system becoming blocked in the event of one of the actuators failing, is overcome in this configuration because of the possibility to achieve uncoupling. It is then advantageous to provide for it to be possible for personnel on the ground to be able to achieve uncoupling so that this can be done while the aircraft is being towed and without damaging the electromechanical steering actuators; 
         [0048]    the disposition of the electromechanical steering actuators of the invention makes it possible to implement maintenance of the line replaceable unit (LRU) type, which consists in identifying which electromechanical steering actuator is faulty, and then replacing the faulty electromechanical steering actuator and only that actuator with a new electromechanical steering actuator. In this configuration, it suffices to unplug various electric cables, to undo the screws fastening the electromechanical steering actuator, and to move the electromechanical steering actuator radially away from the undercarriage, without it being necessary to dismantle the other electromechanical steering actuator or any other structural portion of the undercarriage; and 
         [0049]    the electromechanical steering actuators make it possible in this configuration, given the way they co-operate with the toothed ring  7 , to steer the bottom portion through 360° without any limit on its angular stroke. 
         [0050]    In a particular aspect of the invention that can be seen in  FIG. 3 , the housing  8  at the bottom of the main fitting  1  is closed by a cover  50  that also forms a bearing for the turnable tube  2 . This disposition makes it possible to clear access to the toothed ring  7  completely and enables the toothed ring  7  to be separated from the turnable tube  2 , and thus allow it to be replaced. This disposition makes it possible to limit the diameter of the turnable tube in register with the bearing to a value that is slightly greater than the outside diameter of the fluting  9 , thus enabling the turnable tube to be simple in shape. 
         [0051]    The invention is not limited to the description above, but on the contrary covers any variant coming within the ambit defined by the claims. 
         [0052]    In particular, although an undercarriage is shown that is fitted with two electromechanical steering actuators, it is possible to fit the undercarriage with a larger number of modular electromechanical steering actuators. It can thus be made possible for the modular electromechanical steering actuator to be dimensioned so that using two of them suffices for the needs of an aircraft of the A320 type, while for larger aircraft, e.g. of the A340 or A380 type, it is possible to continue using the same type of electromechanical steering actuator but in larger numbers so as to be capable of delivering higher levels of steering torque. 
         [0053]    Finally, although the preferred arrangement of the electromechanical steering actuators of the invention is actuators that are in modular form and that are fitted releasably on the undercarriage, the invention also covers an undercarriage having electromechanical steering actuators of the invention that are integrated in the undercarriage.