Abstract:
A blind attachment that includes a body ( 36 ) with—at a first end—a visible surface ( 38 ), through which a bore ( 40 ) passes that accommodates a rod ( 42 ) of which a first end ( 44 ) projects relative to the visible surface ( 38 ) and of which the other end includes a head ( 46 ) that can deform a deformation zone ( 48 ) when the rod ( 42 ) moves translationally, with the visible surface including holding elements for coupling the body ( 36 ) to a tool that is used for driving the rod ( 42 ) in rotation, whereby the holding elements include at least one lug ( 52 ) that is connected at the visible surface ( 38 ) and that projects relative to the latter, characterized in that the at least one lug ( 52 ) is connected to the body ( 36 ) by a junction zone ( 54 ) that can break when the lug undergoes a force that exceeds a given threshold.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a blind attachment equipped with a self-breaking holding system. 
     2. Description of the Related Art 
     A blind attachment makes it possible to assemble parts while having access only to a single side of the assembly. 
     As illustrated in  FIG. 2 , a blind attachment comprises a body  10  that comprises a bore  12  in which a rod  14  is housed with a head  16  at a first end and whose other end  18  projects relative to the body  10  in such a way as to be able to be gripped by a tool. A sleeve  20  that is also called a bulb is arranged between the head  16  and the body  10 . 
     To ensure the translational motion of the rod  14 , one approach consists in providing a threaded rod  14  that is screwed into a threaded bore  12  of the body  10 . The end  18  of the rod  14  comprises at least one flat surface for making it possible for a tool  22  to drive the rod  14  in rotation. 
     As illustrated in  FIG. 2 , the surface  24  of the body oriented toward the tool  22  comprises slots  26  (hollow shape) that make it possible to immobilize the body  10  in rotation so that the rotation of the rod  14  creates a relative translational motion between the rod  14  and the body  10 . 
     According to one embodiment, a nut  28  can be interposed between the tool  22  and the surface  24  of the body. 
     According to an operating method, in a first step, the blind attachment is put into a bore  30  made in the parts  32  to be assembled, as illustrated in  FIG. 1A . When the tool  22  drives the rod  14  in rotation, this tends to deform the sleeve  20  gradually, as illustrated in  FIGS. 1B and 1C , which, after creep, flattens itself against the surface that is inaccessible after the assembly. When the sleeve  20  is completely deformed, the force in the threaded rod  14  becomes too great so that the latter breaks as illustrated in  FIG. 1D . 
     Subsequently, it is advisable to plane down the threaded rod so that the latter is flush with the surface  24  of the body. 
     After the installation of the blind attachment and the application of paint, the slots  26  remain visible. Consequently, this type of attachment is not entirely satisfactory in terms of esthetics. 
     According to another point, when these slots  26  are arranged at the surface of the fuselage, they form rough spots that create disturbances on the aerodynamic plane. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is to eliminate these drawbacks. 
     For this purpose, the object of this invention relates to a blind attachment that comprises a body with a visible surface at a first end, through which a bore that accommodates a rod passes and whose first end projects relative to the visible surface and whose other end comprises a head that can deform a deformation zone when the rod moves translationally, with the visible surface comprising holding means for coupling the body to a tool that is used to drive the rod in rotation, whereby said holding means comprise at least one lug that is connected to the visible surface and that projects relative to the latter, characterized in that said at least one lug is connected to the body by a junction zone that can break when the lug is subject to a force that exceeds a given threshold. After the installation of the attachment, this approach makes it possible to obtain a visible surface without recessed rough spots. Advantageously, at the junction zone, each lug comprises at least one notch that makes it possible to obtain a small cross-section and to track the rupture of the lug. According to one embodiment, for each lug, the notch is made at the base of the lug. 
     In addition, the invention proposes a tool for installing a blind attachment according to the invention, characterized in that it comprises a front surface, able to rest against the visible surface of the blind attachment, with at least one slot for housing a lug. 
     Advantageously, the tool has two directions of rotation, a first direction for causing the deformation of the blind attachment and the rupture of the rod, and a direction that is opposite to the first for causing the rupture of the lug(s). 
     According to one embodiment, at each slot, the tool comprises a wedge shape that can penetrate a notch of a corresponding lug. 
     As a variant, each slot comprises a surface that rests at a distance from the bottom of a notch that is made at the corresponding lug so as to create a moment that facilitates the rupture of the lug(s). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Other characteristics and advantages will emerge from the following description of the invention, a description that is provided only by way of example, relative to the accompanying drawings in which: 
         FIGS. 1A to 1D  are views that illustrate the installation of an attachment according to the prior art, 
         FIG. 2  is a perspective view of a blind attachment according to the prior art, 
         FIG. 3  is a perspective cutaway of a blind attachment according to the invention, 
         FIG. 4  is a perspective view of the upper part of a blind attachment according to the invention during its deformation, with the part of the tool being illustrated in transparency, 
         FIG. 5  is a perspective view of the upper part of a blind attachment according to the invention after the rupture of the rod, 
         FIG. 6  is a perspective view of the upper part of a blind attachment according to the invention during the rupture of the holding means, with the part of the tool being illustrated in transparency, 
         FIG. 7  is a perspective view of the upper part of a blind attachment according to the invention at the end of the installation process, 
         FIGS. 8A to 8D  are cutaways that illustrate different variants of lugs, 
         FIGS. 9A and 9B  are cutaways that illustrate the action of a tool on a blind attachment according to the invention respectively during the two installation phases for a first form of lugs, and 
         FIGS. 10A and 10B  are cutaways that illustrate the action of a tool on a blind attachment according to the invention respectively during the two installation phases for a second form of lugs. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As illustrated in  FIG. 3 , a blind attachment  34  comprises a body  36  of cylindrical shape with a tapered shape at a first end and a surface called a visible surface  38  below. This body  36  comprises a bore  40  that accommodates a rod  42  of which a first end  44  projects relative to the visible surface  38  and of which the other end comprises a head  46 . 
     The blind attachment comprises a deformation zone  48  that can deform because of compressive forces exerted by the head  46  when the rod  42  moves translationally upward. 
     According to one variant, the deformation zone  48  is a sleeve  49  that is interposed between the head  46  and the body  36 . 
     According to another variant, the deformation zone  48  is provided at the end of the body  36  that is oriented toward the head. 
     According to one variant, to ensure the relative translational movement between the rod  42  and the body  36 , the rod  42  is threaded and screwed into the bore  40  that is tapped. In particular, a tool can impress a movement of rotation on the threaded rod  42 . To do this, the end  44  of the threaded rod comprises a flat surface for making it possible to couple the threaded rod  42  to a rotary tool. 
     According to another variant, a tool can pull on the end  44  of the threaded rod so that the latter moves translationally. 
     The rod  42  comprises a rupture initiator that makes it possible to cut it into sections in a plane that is flush with the visible surface  38  when the deformation zone is deformed in a suitable manner. According to one embodiment, the rod  42  comprises a notch at the rupture plane  50  that is visible in  FIG. 5 . 
     According to the different variants, the visible surface  38  comprises holding means for coupling the body  36  to a tool, provided either for immobilizing the blind attachment in rotation, in particular when the threaded rod  42  is put into rotation for deforming the deformation zone  48 , or for subjecting a torque to the blind attachment, in particular after the rod  42  is broken to verify the good tightening of the attachment. 
     According to the invention, the holding means comprise at least one lug  52  that is connected at the visible surface  38  and that projects relative to the latter. The lug  52  is connected to the body  36  by a junction zone  54  that can break when the lug undergoes a force that exceeds a given threshold, called a lug rupture threshold, which is less than the mechanical strength of the blind attachment so as not to damage it. 
     In addition, as illustrated in  FIG. 4 , a tool  56  (of which only one part is illustrated) is provided for putting the rod  42  in rotation along its longitudinal axis  58  and comprises a frontal surface  60 , able to rest against the visible surface  38  with an opening  62  for making it possible for the rod  42  to pass, and at least one slot  64  for housing the lug  52 . 
     Advantageously, the blind attachment comprises several lugs  52  for distributing the forces and for ensuring that the body is held during the deformation of the zone  48  and the cross-section of the rod  42 . 
     In addition, the tool  56  comprises a number of slots  64  that is at least equal to that of the lugs  52 , with the slots  64  being arranged at the frontal surface  60  in a manner that is suitable for housing the lugs  52 . 
     For each lug, the junction  54  between the lug  52  and the body  36  is sized in such a way as to break when the force exerted by the tool reaches the lug rupture threshold. 
     Thus, as illustrated in  FIG. 6 , when the tool  56  pivots around the longitudinal axis  58  and it exerts a force that reaches the lug rupture threshold, it causes the rupture of the lugs  52  that are cut into sections at the junction zone  54 . 
     Advantageously, the lugs  52  are cut into sections at the plane of the visible surface  38 . Thus, after its installation, the blind attachment does not need to be planed down and has a flat surface as illustrated in  FIG. 7 . 
     For this purpose, each lug  52  comprises—at the junction zone  54 —at least one notch  66  that makes it possible to obtain a small cross-section and to track the rupture of the lug at the plane of the visible surface  38 . 
     For each lug, the notch  66  is made at the base of the lug, from the side where the force of the tool is applied to cut the lug into sections. 
     The notch  66  can have different shapes as illustrated in  FIGS. 8A to 8D . 
     According to one embodiment, for at least one lug, the notch  66  is delimited by two parallel surfaces  68 ,  68 ′, one of the two surfaces  68  being arranged in the plane of the visible surface  38 , as illustrated in  FIGS. 8A and 8B . According to a variant that is illustrated in  FIG. 8A , the bottom of the notch  66  has a rounded shape. According to another variant that is illustrated in  FIG. 8B , the bottom of the notch  66  has a quarter round shape. 
     According to an embodiment that is illustrated in  FIGS. 8C and 8D  for at least one lug, the notch  66  has a triangular cross-section with a surface  70  that is arranged in the plane of the visible surface  38  and another surface  70 ′ that makes an angle that is less than or equal to 60°. According to a variant that is illustrated in  FIG. 8C , the surface  70 ′ makes an angle on the order of 45° with the surface  70 . According to another variant that is illustrated in  FIG. 8D , the surface  70 ′ makes an angle on the order of 30° with the surface  70 . The intersection between the two surfaces  70 ,  70 ′ can be rounded as illustrated in  FIG. 8C  or not rounded as illustrated in  FIG. 8D . 
     According to a first operating mode, the relative rotational movement between the visible surface  38  of the body and the frontal surface  60  of the tool  56  that is necessary for breaking the lugs  52  has the same direction as the one that is necessary for causing the deformation of the blind attachment and the rupture of the threaded rod  42 . 
     In this case, the lug rupture threshold is greater than the force that is necessary for cutting the rod  42  into sections, which is itself greater than the one that is necessary for deforming the deformation zone  48  completely. 
     According to another operating mode, the tool has two directions of rotation. Thus, the relative rotational movement between the visible surface  38  of the body and the frontal surface  60  of the tool  56  that is necessary for breaking the lugs  52  has a direction that is opposite to the one that is necessary for causing the deformation of the blind attachment and the rupture of the rod  42 . 
     Each lug  52  has two surfaces  72 ,  72 ′ that are arranged in two essentially radial planes, one of them  72 ′ having a notch  66  at its base. In parallel, each slot  64  of the tool  56  comprises two surfaces  74 ,  74 ′ that are arranged in two essentially radial planes, with a first surface  74  being able to rest against the surface  72  of the lug for immobilizing the body  36  in rotation during its rotating of the rod  42 , as illustrated in  FIG. 9A , with the other surface  74 ′ being able to rest against the surface  72 ′ of the lug for breaking it, as illustrated in  FIG. 9B . 
     This reversal of direction makes it possible to create an operation that is clearer for the operator, who can distinguish between the two installation phases, namely the deformation phase of the deformation zone to the rupture of the rod  42  and then the rupture phase of the lugs. This reversal of direction also makes it possible to verify the good mechanical hold of the deformation zone and that the blind attachment is prestressed well. 
     Advantageously, in the first direction of rotation, the tool is in contact with the base of each lug, as illustrated in  FIG. 9A . This makes it possible not to create heavy stresses. In the opposite direction, force is applied at a distance from the bottom of the notch  66 , which tends to create a moment  76  that facilitates the rupture of the lug as illustrated in  FIG. 9B . 
     According to another variant that is illustrated in  FIGS. 10A and 10B , the tool  56  comprises—at each slot  64 —a wedge shape  78  that can penetrate the notch  66  of the corresponding lug  52 . As illustrated in  FIG. 10B , this arrangement makes it possible to create a vertical force  80  on the lug that tends to facilitate the rupture of the lug  52 .