Abstract:
A fixing device for fixing an electrical connection terminal to a support having a first side, a second side opposite to the first side, and defining a through hole of a first diameter. The fixing device comprises: a ring including a receiving portion partially defining an axial recess and insertable in the through hole; a dowel including an insert portion axially insertable into the recess of the ring and a locking portion axially spaced from the insert portion, the dowel partially defining an axial bore including an internal thread, and in the locking portion the internal thread of the bore is a distorted locking thread; and a fixing screw including a threaded shank engagable with the dowel. Tightening of the fixing screw draws the insert portion of the dowel axially into the recess of the ring, thereby radially expanding the ring into press-fit engagement with the through hole.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT Application No. PCT/EP2013/072829, filed on Oct. 31, 2013 which claims priority from French Patent Application No. 1260706, filed on Nov. 12, 2012, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a device for fixing an electrical connection terminal to a support. 
         [0003]    In aircraft, some of the equipment has to be earthed. For this purpose, each item of equipment is electrically connected to the frame of the aeroplane, for example by means of metal braids or earthing wires. The ends of the metal braids or wires are received in terminals which are fixed to specific supports, the supports being mounted on the frame of the aeroplane. 
         [0004]    In this field, fixing a terminal to a support is generally carried out by means of a screw and a nut, the terminal being held tightly between the head of the screw and a surface of the support. 
         [0005]    In order to ensure good electrical contact between the terminal and the support, the surface of the support has to be stripped before the assembly of the screw and the nut. Once the assembly has been carried out, the stripped region of the support has to be protected against corrosion. 
         [0006]    In addition, in order to ensure that the assembly has good resistance to vibrations, the nut is generally fixed to the support by means of rivets. 
         [0007]    For the assembly of the screw and the nut, and for the placement of the rivets, access is required to the two sides of the support during assembly. 
         [0008]    In addition, EP 1 376 766 in the name of the applicant discloses a device for fixing an electrical connection terminal to a support, the support being formed for example by the core of a railway rail. The device comprises a ring which is provided to be introduced into a cylindrical hole which is made in the support, a socket which is provided to be threaded in the ring and has a thread, and a threaded screw, the thread of which fits with the thread of the socket. When assembling the device, the ring is firstly positioned in the cylindrical hole in the support, and then a tensile force is exerted on the socket using a tool so as to introduce the socket into the ring with force, thereby causing radial expansion of the ring and locking of the ring in the hole. The screw is then screwed into the socket, the terminal being held tightly between the head of the screw and the ring, thus making it possible to fix the terminal to the support and to establish electrical contact between the terminal and the support. 
         [0009]    An advantage of this fixing device is that it does not require the surface of the support to be stripped beforehand in order to ensure good electrical contact between the terminal and the support. This is because the electrical contact is produced between the ring and the inner surface of the cylindrical hole which is made in the support. 
         [0010]    In addition, the fixing device has a reduced size. 
         [0011]    Furthermore, in the case of the fixing device, access is not required to the two sides of the support during assembly. 
         [0012]    However, a fixing device of this type is not traditionally used in applications which require resistance to vibrations, such as for earthing equipment on board an aircraft. This is because the vibrations to which the equipment is subjected can cause loosening of the screw which holds the terminal. 
         [0013]    In order to prevent loosening of the screw, it would be possible to add a lock washer between the screw head and the support. 
         [0014]    In any case, adding such a washer would result in an increase in the number of pieces forming the fixing device and in an increase in the weight of the fixing device which is unacceptable for the intended applications, said device being multiplied a large number of times in an aircraft. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    One object of the invention is to propose a device for fixing an electrical connection terminal to a support, which device is light and resistant to vibrations. 
         [0016]    This object is achieved in the context of the present invention by means of a device for fixing an electrical connection terminal to a support, comprising a ring which is suitable for being received in a hole which is made in the support and a dowel which is suitable for being inserted with force in the ring in order to cause deformation of the ring so as to mount the ring in the hole, the dowel having a threaded bore which is suitable for receiving a fixing screw for fixing the terminal to the ring, the threaded bore having an internal thread with which an external thread of the screw engages, characterised in that the dowel comprises a locking portion in which the internal thread of the bore is distorted such that the engagement of the external thread of the screw with the internal thread of the bore in the locking portion causes locking of the screw in the dowel. 
         [0017]    The term “distorted” describes a thread which initially has a circular, helical shape with a given pitch at the time of the production thereof by threading, but which has subsequently been permanently deformed such that it has for example a non-circular, helical shape or a modified pitch or a discontinuity. A permanent deformation of this type can be obtained by subjecting the dowel to compression in the locking portion. This step of compression is carried out at the factory during the production of the device. 
         [0018]    When the fixing screw penetrates the locking portion, the engagement of the external thread of the screw with the internal thread of the bore tends to restore the initial shape of the thread, and therefore to deform the locking portion. The deformation of the locking portion produces a brake force on the external thread of the screw. 
         [0019]    The locking portion thus makes it possible to prevent accidental loosening of the screw under the effect of vibrations which are imparted to the support or rotation of the terminal relative to the support. 
         [0020]    The fixing device can also have the following features: 
         [0021]    the locking portion has been subjected to compression in a radial direction relative to an axis of the bore, 
         [0022]    in the locking portion, the internal thread of the bore has a multilobal, non-circular, helical shape, 
         [0023]    the locking portion has been subjected to compression in two diametrically opposite regions, 
         [0024]    the locking portion has been subjected to compression in three regions which are angularly distributed at 120° to one another around an axis of the bore, 
         [0025]    the locking portion has been subjected to compression in four regions which are arranged in pairs symmetrically on either side of a plane of symmetry which passes through the axis of the bore, 
         [0026]    the locking portion has been subjected to compression in an axial direction of the bore, 
         [0027]    the locking portion has one or more transverse slots that promoted the compression of the second portion in the axial direction of the bore, 
         [0028]    the ring has a receiving portion, and the dowel comprises an insertion portion which is suitable for being inserted with force in the receiving portion of the ring in order to cause the deformation of the ring, 
         [0029]    the insertion portion of the dowel has an outer surface which has a substantially conical shape, 
         [0030]    the receiving portion of the ring has an inner surface which has a substantially conical or cylindrical shape, 
         [0031]    once the dowel has been inserted with force in the receiving portion of the ring, the locking portion of the dowel projects outside the receiving portion, 
         [0032]    the dowel has a wall surrounding the bore, the wall having, in the locking portion, a thickness which is less than a thickness of the wall in the insertion portion, 
         [0033]    the ring is made of a first material and the dowel is made of a second material, the first material having a hardness which is less than the hardness of the second material, 
         [0034]    the ring is made of aluminium alloy or copper, and the dowel is made of aluminium alloy, titanium or steel, 
         [0035]    the dowel has a shoulder which is suitable for abutting against the ring in order to limit the insertion of the dowel into the ring, 
         [0036]    the ring has a shoulder which is suitable for being supported against a surface of the support on a first side of the support, whereas the locking portion of the dowel extends from a second side of the support, which is opposite the first side, 
         [0037]    the dowel is formed from a single piece of material. 
         [0038]    The invention also relates to a method for producing a fixing device of the type defined above, comprising a step of producing the dowel which consists in permanently deforming a portion of the dowel by applying a deformation force to the dowel, the deformed portion of the dowel forming the locking portion of the dowel. 
         [0039]    The deformation force can be applied by compressing the portion to be deformed of the dowel, for example by means of a clamping tool or a press or even by means of one or more balls which are supported against an outer surface of the dowel in the portion to be deformed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    Other features and advantages will become apparent from the following description, which is given purely by way of illustrative and non-limiting example and is to be read in relation to the accompanying drawings, in which: 
           [0041]      FIG. 1  is a schematic, longitudinal sectional view of a fixing device according to the invention, when mounted on a support, 
           [0042]      FIGS. 2A and 2B  are schematic views of a ring and dowel assembly before mounting on the support, said views being a longitudinal section and a cross-sectional view respectively, according to a first embodiment of the invention, 
           [0043]      FIGS. 3 to 6  are schematic views of the steps of a method for assembling the fixing device, 
           [0044]      FIGS. 7A and 7B  are schematic views of a ring and dowel assembly before mounting on the support, said views being a longitudinal section and a cross-sectional view respectively, according to a second embodiment of the invention, 
           [0045]      FIGS. 8A and 8B  are schematic views of a ring and dowel assembly before mounting on the support, said views being a longitudinal section and a cross-sectional view respectively, according to a third embodiment of the invention, 
           [0046]      FIGS. 9A and 9B  are schematic views of a ring and dowel assembly before mounting on the support, said views being a partial longitudinal section and a cross section respectively, according to a fourth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    In  FIG. 1 , the fixing device  1  is shown when mounted on a support  2 . The support  2  in this case is a thin metal wall, such as a wall of a frame of an aircraft. The wall  2  is for example made of aluminium alloy. The wall  2  has a generally planar shape with a first side  3  and a second side  4 , which is opposite the first side  3 . The wall  2  is provided with a through-hole  5  which is intended to receive the fixing device  1  in order to fix an electrical connection terminal  6  to the wall  2 . 
         [0048]    The fixing device  1  comprises a ring  7 , a dowel  8 , a screw  9  and a washer  10 . 
         [0049]    The screw  9  comprises a head  23  and a threaded shank  24 . 
         [0050]    The terminal  6  is held tightly between the washer  10  and the ring  7 , the head  23  of the screw  9  pressing the terminal against the ring  7  via the washer  10 . 
         [0051]      FIGS. 2A and 2B  are schematic views of a ring  7  and dowel  8  assembly according to a first embodiment of the invention, the assembly being shown before mounting on the support  2 . 
         [0052]    The ring  7  is made of metal, preferably of aluminium alloy or copper. The ring  7  has a first portion  11  (or collar) which is suitable for being placed in electrical contact with the terminal  6 , and a second portion  12  which is suitable for being inserted in the hole  5  through the wall  2 . The ring  7  comprises a shoulder  13  connecting the first portion  11  and the second portion  12 , the shoulder  13  being suitable for being supported against a surface of the wall  2 , on the first side  3  of the wall  2  when the ring  7  is positioned in the hole  5 . 
         [0053]    The first portion  11  of the ring  7  has a hole  17  which makes it possible to insert the screw  9  through the ring  7 , from the first side  3  of the wall  2  when the ring  7  is positioned in the hole  5 . 
         [0054]    The second portion  12  has an outer surface  14  which is suitable for being in contact with the inner surface of the hole  5  when the ring  7  is positioned in the hole  5 . The outer surface  14  of the second portion  12  has a generally cylindrical shape of revolution. The second portion  12  further has a recess  15  which opens into a side of the ring  7  which is opposite the first portion  11 . The recess  15  has an inner surface  16  which has a generally conical shape having an internal diameter which decreases as it nears the first portion  11 . Alternatively, the inner surface  16  could have a generally cylindrical shape. 
         [0055]    The dowel  8  is made of metal, preferably of aluminium alloy, titanium or steel. The metal forming the dowel  8  has a hardness which is greater than that of the material forming the ring  7 . 
         [0056]    The dowel  8  comprises a first portion  18  (or insertion portion) which is suitable for being inserted in the recess  15  in the ring  7  and a second portion  19  (or locking portion) which is suitable for projecting outside the recess  15  once the dowel  8  is inserted in the ring  7 . 
         [0057]    The first portion  18  has an outer surface  20  which has a generally conical shape and an external diameter which decreases as it moves away from the second portion  19 . The outer surface  20  of the first portion  18  of the dowel  8  and the inner surface  16  of the recess  15  of the ring  7  thus have complementary shapes. The complementary nature of the shapes makes it possible to obtain homogenous (uniform) contact between the outer surface  20  and the inner surface  16  during the insertion of the dowel  8  in the recess  25 , and therefore to obtain homogenous deformation of the second portion  12  of the ring  7  (the second portion  12  of the ring  7  retains a cylindrical shape during the deformation). 
         [0058]    The first portion  19  also comprises a locking ring  34  which projects from the outer surface  20  and forms a shoulder  35  connecting the outer surface  20  to the ring  34 . The locking ring  34  is positioned at the connection between the first portion  18  and the second portion  19 . 
         [0059]    The first portion  18  of the dowel  8  is suitable for being inserted with force in the recess  15 , the insertion having the effect of causing deformation of the ring  7  so as to mount the ring  7  in the hole  5  in the wall  2 . Since the material forming the dowel  8  is harder than the material forming the ring  7 , only the ring  7  is deformed. 
         [0060]    The shoulder  35  is suitable for abutting against the ring  7  so as to limit the insertion of the first portion  18  of the dowel  8  into the recess  15 . 
         [0061]    The second portion  19  of the dowel  8  extends in the extension of the first portion  18 , but has a thinner dimension than the first portion  18 . More specifically, the second portion  19  of the dowel  8  has an outer surface  22  which has a radial dimension which is less than an external diameter of the first portion  18 . 
         [0062]    The dowel  8  also has a threaded bore  21  having a longitudinal axis X, the bore  21  being suitable for receiving the screw  9  in order to fix the terminal  6  to the ring  7  and to hold the dowel  8  in position in the ring  7 . The bore  21  extends through the dowel  8  in a longitudinal direction of the dowel  8 , over the entire length of the dowel. In particular, the bore  21  extends continuously through the first portion  18  and through the second portion  19  of the dowel  8 . 
         [0063]    In addition, the dowel  8  has a wall  36  which surrounds the bore  21 , the wall  36  having, in the first portion  18 , a first thickness (T 1 ) which is greater than a second thickness (T 2 ) of the wall  36  in the second portion  19 . This feature has the effect of promoting deformation of the wall of the dowel in the second portion  19 , whilst protecting the second portion  19  against deformation during the insertion of the screw  9  in the bore  21 . 
         [0064]    In addition to the stop function thereof, the ring  34  also makes it possible to rigidify the second portion  19  to protect the second portion against deformation. In particular, the ring  34  forms a region having a greater thickness which prevents propagation of the deformation imposed on the second portion  19  towards the first portion  18 . 
         [0065]    The bore  21  of the dowel  8  has an internal thread  25  which can cooperate with an external thread  26  of the shank  24  of the screw  9 . The internal thread  25  extends continuously in the first portion  18  and in the second portion  19  of the dowel  8 . 
         [0066]    In any case, as is shown in  FIG. 2B , the second portion  19  of the dowel  8  is distorted. The second portion  19  has a non-circular cross section because it has been permanently radially deformed. As a result, in the second portion  19 , the bore  21  also has a non-circular cross section. 
         [0067]    More specifically, the second portion  19  has been radially deformed in three regions  26 ,  27 ,  28  which are angularly distributed at 120° to one another around the axis X of the bore  21 , such that the dowel  8  has a generally trilobal cross section in the locking portion  19 . 
         [0068]    In addition, as a result of this permanent deformation, in the second portion  19 , the internal thread  25  of the bore  21  has distortions (in this case, the thread  25  has a non-circular, helical shape), whereas in the first portion  18 , the internal thread  25  of the bore  21  has no distortion (that is to say that the thread  25  has a circular, helical shape). Due to this distortion, the thread  25  is suitable for generating, in the regions  26 ,  27 ,  28 , a frictional force on the external thread  26  of the screw  9  when the screw  9  is screwed into the dowel  8 . 
         [0069]    The radial deformation of the second portion  19  can be obtained by compressing the second portion  19 , for example by means of a hydraulic clamping tool. The compression of the second portion  19  causes permanent radial deformation of the second portion  19  of the dowel  8 . 
         [0070]    Alternatively, the radial deformation of the second portion  19  can be obtained by introducing with force the second portion  19  of the dowel  8  into a specific tool, the tool having a bore for guiding the dowel, and a plurality of balls which are held in a cage, the balls projecting into the bore of the tool. 
         [0071]    The application of the balls against the outer surface  22  of the dowel  8  causes permanent radial deformation of the second portion  19  of the dowel  8 . 
         [0072]      FIGS. 3 to 6  are schematic views of the steps of a method for mounting the fixing device  1  on a wall  2 . 
         [0073]    According to a preliminary step which is shown in  FIG. 3 , the ring  7  and the dowel  8  are preassembled. The first portion  18  of the dowel  8  is inserted in the second portion  12  of the ring  7 , so as to rigidly interconnect the ring  7  and the dowel  8 . This step of preassembly is carried out at the factory during the production of the device. 
         [0074]    According to a first step which is shown in  FIG. 4 , the preassembled ring  7  and dowel  8  assembly is screwed onto a mounting tool  29 . As can be seen in  FIG. 5 , the tool  29  comprises a cylinder  30  and a piston  31  which is slidably mounted inside the cylinder  30 . The piston  31  has a threaded rod  32  which is inserted through the hole  17  in the ring  7  and screwed inside the threaded bore  21  of the dowel  8 . 
         [0075]    The threaded rod  32  is only screwed into the first portion  18  of the dowel  8 , in which the internal thread  25  of the bore  21  is not distorted. 
         [0076]    According to a second step shown in  FIG. 5 , the preassembled ring  7  and dowel  8  assembly is positioned in the hole  5  in the support  2 , the shoulder  13  of the ring  8  being supported against the surface of the first side  3  of the wall  2 . It should be noted that the greatest transverse dimension of the dowel  8  is less than or equal to a transverse dimension of the second portion  12  of the ring  7 , so as to allow the ring  7  and dowel  8  assembly to be inserted in the hole  5  from the first side  3  of the support  2 . 
         [0077]    In this position, the dowel  8  is located on the second side  4  of the wall  2 . The tool  29  is operated so as to cause a movement of the piston  31  inside the cylinder  30 . The movement of the piston  31  inside the cylinder  30  has the effect that the piston  31  exerts a tensile force on the dowel  8  in a direction which is parallel to the axis X, which pulls the dowel  8  further inside the ring  7  (that is to say pulling dowel  8  towards collar  11 ). Due to the conical shapes of the surfaces  16  and  20 , the penetration of the dowel  8  inside the ring  7  causes radial expansion of the ring  7 . The ring  7  is thus press-fit mounted in the hole  5  in the wall  2 . 
         [0078]    In any case, the insertion of the dowel  8  into the ring  7  is limited by the shoulder  35  which abuts against the ring  7 . 
         [0079]    According to a third step which is shown in  FIG. 6 , the mounting tool  29  is unscrewed from the ring  7  and dowel  8  assembly. The shank  24  of the screw  9  is then inserted through the hole  17  in the ring  7  and screwed into the threaded bore  21  of the dowel  8 , in order to fix the terminal  6  and the washer  10  to the ring  7  and dowel  8  assembly. During the screwing, the external thread  26  of the shank  24  of the screw  9  engages with the internal thread  25  of the bore  21  in the first portion  18  and in the second portion  19  successively. 
         [0080]    Since the internal thread  25  is distorted in the second portion  19 , the engagement of the external thread  26  in the internal thread  25  causes radial elastic deformation of the second portion  19  (or locking portion). In other words, the second portion  19  of the dowel  8  is elastically deformed under the effect of the external thread  26  of the screw  9 . This has the effect of generating a frictional force on the external thread  26  of the screw  9 , thereby preventing subsequent loosening of the screw  9  due to the vibrations of the wall  2  or rotation of the terminal  6  relative to the wall  2 . The screw  9  is thus locked in the dowel  8 . 
         [0081]    It should be noted that the fixing device  1  which has just been described can be mounted on a support, without access being required to the two sides  3  and  4  of the support. This makes it possible for example to fix the terminal  6  directly to a wall  2  of the frame of an aircraft, without needing to use an additional specific support which is fixed to the wall  2 . 
         [0082]    In addition, since it is not necessary to access the two sides of the support, the device  1  can be mounted in a blind fixing hole. 
         [0083]      FIGS. 7A and 7B  are schematic views of a ring  7  and dowel  8  assembly according to a second embodiment of the invention. 
         [0084]    This second embodiment is the same as the first embodiment except for the fact that the second portion  19  of the dowel  8  has been radially deformed in two diametrically opposite regions  37 ,  38 . In this case, the dowel  8  has an oblong-shaped or bilobal cross section in the locking portion  19 . 
         [0085]    Due to this distortion, the internal thread  25  is suitable for generating, in the regions  37 ,  38 , a frictional force on the external thread  26  of the screw  9  when the screw  9  is screwed into the dowel  8 . 
         [0086]      FIGS. 8A and 8B  are schematic views of a ring  7  and dowel  8  assembly according to a third embodiment of the invention. 
         [0087]    This third embodiment is the same as the first embodiment except for the fact that the second portion  19  of the dowel  8  has been radially deformed in four regions  39  to  42  which are arranged in pairs symmetrically on either side of a plane of symmetry Z which passes through the axis X of the bore. In this case, the dowel  8  has a quadrilobal cross section in the locking portion  19 . 
         [0088]    Due to this distortion, the internal thread  25  is suitable for generating, in the regions  39  to  42 , a frictional force on the external thread  26  of the screw  9  when the screw  9  is screwed into the dowel  8 . 
         [0089]      FIGS. 9A and 9B  are schematic views of a ring  7  and dowel  8  assembly according to a fourth embodiment of the invention. 
         [0090]    In this fourth embodiment, the second portion  19  comprises two transverse slots  43  and  44  which are made through the wall  36  of the dowel  8 . Each slot  43 ,  44  extends in parallel with a plane which is orthogonal to the axis X of the bore. In addition, the slots  43  and  44  extend from two opposite sides of the wall  36 , on either side of the axis X. Each slot  43 ,  44  extends over more than half of a cross section of the second portion  19 . 
         [0091]    After the second portion  19  has been split along the two slots  43  and  44 , the second portion  19  of the dowel  8  is permanently deformed by compressing the second portion  19  in parallel with the axis X of the bore. 
         [0092]    The axial deformation of the second portion  19  can be obtained by compressing the second portion  19 , for example by means of a hydraulic press. The compression of the second portion  19  causes permanent axial deformation of the second portion  19  of the dowel  8 . 
         [0093]    The slots  43  and  44  form regions of low resistance promoting axial deformation of the second portion  19  under the effect of the compressive force which is applied to the dowel  8  in parallel with the direction X. 
         [0094]    Under the effect of this compressive force, the slots  43  and  44  are closed slightly, and the parts of material of the second portion  19  which are located on either side of the slots  43  and  44  are brought closer together. 
         [0095]    Closing the slots  43  and  44  and bringing together the parts of material which are located on either side of the slots  43  and  44  leads to a local reduction in the pitch of the internal thread  25  of the bore  21  in the second portion  19 . 
         [0096]    The engagement of the external thread  26  of the screw  9  in the distorted internal thread  25  causes axial elastic deformation of the locking portion  19 . In other words, the locking portion  19  of the dowel  8  is elastically deformed under the effect of the external thread  26  of the screw  9 . As a result, a frictional force is generating on the external thread  26  of the screw  9 , thereby preventing subsequent loosening of the screw  9  due to vibrations of the wall  2  or rotation of the terminal  6  relative to the wall  2 . The screw is thus locked in the dowel  8 . 
         [0097]    It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.