Abstract:
The assembly comprises a first and a second nut intended to cooperate with a screw in particular provided in an adjustable tailplane actuator for an aircraft, and a mechanical connection between the first and the second nut comprising means for fusible driving of the second nut by the first nut, in which the mechanical connection also comprises adjustable spacing means forming a wedge between the first and second nuts.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to French Application No. 0755040, filed May 11, 2007, which is incorporated by reference herein. 
       BACKGROUND AND SUMMARY 
       [0002]    The invention relates to a mechanical connection between a primary nut and a so-called “failsafe” secondary nut, as well as the assembly thus formed. 
         [0003]    The invention is intended in particular for use in the case of a THSA actuator (Trimmable Horizontal Stabilizer Actuator) provided on aircrafts. These actuators comprise two mechanical means, one primary, the other secondary, with the latter being intended to take up the stress when a failure occurs in the primary means. Each of the primary and secondary means is associated with a primary and secondary nut, respectively. In normal operation on the primary means, the forces pass through the primary nut to a ball or roller screw, from a variable tailplane of an aircraft, and vice versa. The secondary nut is mechanically connected to the primary nut in order to follow the latter in its translation movements along the ball or roller screw, without being subjected to any stresses. For this, the secondary nut has a treading complementary to the threading of the ball or roller screw, but having a play therewith, and is connected to the primary nut by means of a radially mounted fusible pin perpendicular to the axis of the screw. The pin, while ensuring that the primary nut is followed by the secondary nut, makes it possible to preserve the play between the threadings of the secondary nut of the screw so that there is no contact between them in normal operation. 
         [0004]    In the event of a failure of the primary means, in particular at the level of the primary nut, the forces first pass from the variable tailplane of the aircraft through the primary nut to the secondary nut via the pin. The play between the threadings of the secondary nut and the screw is recovered, causing the transmission of the previous forces from the secondary nut to the screw. However, when the forces that pass are greater than the value of a predetermined load, the pin then acts as a fuse and breaks, thus releasing the secondary nut from the primary nut. Then, the forces pass from the variable tailplane to the screw via the secondary nut, implementing the secondary means of the actuator. 
         [0005]    The following disadvantage arises from the fusible pin technology. When assembling the two nuts on the screw, it is necessary to use a complex instrumentation in order to hold the two nuts in a relative position with respect to one another so that the precise play between the threading of the secondary nut and the threading of the screw is present. Thus, the housing of the pin is back-drilled via the two nuts and the pin is put in place. This operation is time-consuming and costly. 
         [0006]    An objective of the invention is to propose an assembly formed by the primary nut and the secondary nut, with a simplified and faster assembly, while ensuring optimal reliability in the event of an operation failure of the primary nut. To this end, the invention proposes an assembly comprising a first and a second nut, intended to cooperate with a screw, in particular provided in an adjustable tailplane actuator for an aircraft, and a mechanical connection between the first and the second nut comprising means for fusible driving of the second nut by the first nut, in which the mechanical connection also comprises adjustable spacing means forming a wedge between the first and second nuts. Thus, the use in the mechanical connection of adjustable spacing means forming a wedge between the first and second nuts enables the quick, simple and secure positioning while maintaining the precise play desired, without requiring equipment that is heavy and expensive, both in terms of cost and time, in order to produce the mechanical connection between the two nuts. 
         [0007]    Advantageously, but optionally, the assembly comprises at least one of the following features: 
         [0008]    the adjustable spacing means are constituted by a wedge capable of being adjusted in thickness; 
         [0009]    the adjustable spacing means are constituted by a pealable or separable wedge; 
         [0010]    the fusible driving means comprise a fusible link anchored in the first nut and extending into the second nut; 
         [0011]    the link is substantially parallel to an axis of the second nut; 
         [0012]    the link is screwed into the first nut; 
         [0013]    the link comprises a portion with cross-section sized so as to break under a predetermined load; 
         [0014]    the link comprises a portion with a cross-section sized so as to break with a predetermined extension. 
         [0000]    According to the invention, an adjustable tailplane actuator for an aircraft comprising an assembly with at least one of the aforementioned features is also proposed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Other features and advantages of the invention will become clear from the following description, provided for purely illustrative and non-limiting purposes, to be read in view of the appended drawings, in which: 
           [0016]      FIG. 1  is a three-dimensional drawing of an assembly according to the invention, of a primary nut and a secondary nut according to the first embodiment; 
           [0017]      FIG. 2  is a longitudinal cross-section view according to II-II of the assembly according to the first embodiment; 
           [0018]      FIG. 3  is a top view of the first embodiment of the assembly according to the invention; and 
           [0019]      FIG. 4  is a partial three-dimensional view of an assembly according to a second embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    In reference to  FIGS. 1 to 3 , we will now describe a first embodiment of the invention. An assembly according to the invention comprises two nuts  3  and  5 . Nut  3  is called the primary nut, while nut  5  is called the secondary nut. The assembly  1  has a longitudinal axis X. It is capable of being mounted on a screw not shown and extending according to the X-axis. 
         [0021]    The primary nut  3  has, on an external surface, means  31  for connection with an adjustable tailplane according to primary means, neither of which are shown, in the context of a THSA actuator for an aircraft. At one of its ends, the primary nut  3  has a collar  93 . This collar  93  comprises orifices  33  capable of receiving a pin  9 , which will be described below. The primary nut  3  can be a ball or roller nut intended to be mounted on a so-called ball or roller screw, respectively. 
         [0022]    The secondary nut  5  has, on an external surface, means for connection  59  with the adjustable tailplane via so-called secondary means, neither of which are shown, in the context of a THSA actuator for an aircraft. In an internal bore passing through along the X-axis, the secondary nut  5  has a threading  51 . This threading is complementary in its shape to the threading of the screw on which it is intended to be mounted, assembled to the primary nut  3 . This threading  51 , although complementary to the threading of the screw on which it is intended to be mounted, is of a size so that once it has been mounted, the threading  51  of the nut has a play with the threading of the screw on which it is mounted. At one of its ends, the secondary nut  5  has a collar  54  capable of being received by the collar  93  of the primary nut  3 , as shown in  FIG. 2 . The collar  54  has openings  55  capable of receiving, when the secondary nut  5  is mounted on the primary nut  3 , the aforementioned pin  9 . Angularly, in line with said openings  55 , the secondary nut  5  comprises protuberances  53  extending radially outwardly, projecting from the external surface and in which a through-hole is provided, substantially parallel to the X-axis of the secondary nut  5 . The through-hole is capable of receiving a link  7 , which will be described below. It should be noted that the orifices  33  of the collar  93  of the primary nut  3 , the openings  55  of the collar  54  of the secondary nut  5 , as well as the protuberances  53 , are in this case, as shown, in pairs located diametrally opposed with respect to the X-axis of the assembly  1 . 
         [0023]    The assembly  1  also comprises a wedge  11  inserted between the primary nut  3  and the secondary nut  5 . The role of this wedge  11  is to ensure the precise relative positioning between the primary nut  3  and the secondary nut  5 . The thickness of the wedge  11  is calculated so that, once the two nuts have been mounted on the screw not shown, a play appears between the threading  51  of the secondary nut  5  and the threading of the screw on which the assembly  1  is mounted. This play makes it possible, in normal, effective operation of the assembly  1  mounted on the screw, for there to be no contact between the threading  51  of the secondary nut  5  and the threading of the screw. The wedge  11  can be obtained directly by calculation or adjusted, for example, by machining, by pealable means or by grading, or any other means enabling the required play to be obtained. 
         [0024]    The wedge  11  is, as shown in  FIG. 2 , located between an end surface of the collar  54  and a base of the bore delimited by the collar  93  of the primary nut  3 . Alternatively, the nut  11  is located between an end surface of the collar  93  and an edge substantially perpendicular to the X-axis of the secondary nut  5  located at the foot of the collar  54 . 
         [0025]    In addition, the assembly  1  according to the invention comprises a pin  9  associated with a link  7 . The pin  9  includes a tail  91  as well as a threaded opening perpendicular to the tail  91  of the pin  9 . The pin  9  is mounted radially with respect to the X-axis in the orifice  33  of the collar  93  of the primary nut  3 , through which it passes, and into the opening  55  formed in the collar  54  of the secondary nut  5 , which is then mounted on the primary nut  3 , so that the openings  55  and the orifices  33  are opposite one another. With the pin  9  thus mounted, the threaded orifice perpendicular to the tail  91  of the pin  9  is located opposite the through-hole of the protuberance  53 . Then, a link  7  is inserted into said orifice, as shown in  FIG. 2 . The link  7  has a general rotating form and successively comprises a head  7  of which the diameter is greater than a diameter of the through-hole of the protuberance  53  in which it is received, then a smooth cylindrical rotating portion  73  of which the diameter is slightly smaller than the diameter of the through-hole in which the link  7  is received, then a portion  71  having a reduced diameter, and finally, a threaded portion  75  capable of being screwed into the threaded orifice of the pin  9 . The portion  71  of the link  7  has a cross-section sized so that, when a predetermined pulling force is exerted between the threaded portion  75  and the head  7 , the portion  71  breaks. This breakage occurs after a predetermined extension according to the cross-section of the portion  71  subjected to said predetermined pulling force. 
         [0026]    The mounting of the assembly  1  includes the primary nut  3 , the wedge  11  and the secondary nut  5 , which are stacked one on top of another. The orifices  33  are placed opposite openings  55  in order to enable pins  9  to be mounted. Finally, the links  7  are inserted into the through-hole of the protuberances  53  and are screwed into the threaded orifice of the pins  9  so as to hold the stack of the primary nut  3 , the wedge  11  and the secondary nut  5  during normal operation. However, the pulling force caused by the tightening of the links  7  in order to hold the stack should be negligible with respect to the predetermined pulling force for breaking the portion  71  of the links  7 . 
         [0027]    We will now, in reference to  FIG. 4 , describe a second embodiment of an assembly according to the invention. We will simply describe the differences between this second embodiment and the first embodiment of the invention described above. The main difference lies in the collar  90  of the primary nut  3 , which is differentiated from the collar  93  of the primary nut  3  of the preceding embodiment. The collar  90  has protuberances  95  projecting outwardly and radially with respect to the X-axis. These protuberances  95  make it possible to eliminate, in this embodiment, the pins  9  of the first embodiment described above. These protuberances  95  therefore have a threaded orifice capable of receiving, by screwing, the threaded portion  75  of the link  7 . The wedge  11  is mounted between the secondary nut  5  and the primary nut  3  according to the alternative mounting described in the first embodiment: between an end surface of the collar  95  and an edge of the nut  5  extending radially outwardly and perpendicularly to the X-axis at the foot of the collar  54 . 
         [0028]    In addition, the assembly  10  comprises retaining means  53 . These retaining means  53  make it possible to hold the head  7  and the portion  73  of the link  7  in place when the portion  71  of the link  7  is broken under the effect of a predetermined pulling force. This prevents, in the event of a breakage, said portion of the link  7  from damaging, by breaking away, other components of the aircraft on which the assembly  10  is installed. 
         [0029]    In the two embodiments, when there is a failure of the primary nut  3  leading to a loss in connection between the primary nut  3  and the screw, there is a change in the flow of forces originating in the adjustable tailplane. First, according to the loss in connection between the primary nut/screw, the forces originating from the adjustable tailplane always pass through the primary means to the primary nut  3 , then via the links  7  to the secondary nut  5 . The play between the threadings of the secondary nut and the screw is then taken up, and the threadings come into mutual contact. And the forces are transmitted to the screw by the secondary nut  5 . Second, once the forces originating from the adjustable tailplane reach a value greater than the pulling effect causing a breakage of the portion  71  of the links  7 , the latter break, detaching the secondary nut  5  from the primary nut  3 . Then, the forces originating from the adjustable tailplane pass directly via the secondary means to the secondary nut  5 , and from there to the screw.