Abstract:
A device for fixing an electrical connection terminal to a support provided with an opening, the device comprising: a generally tubular bush for location within the opening of the support and provided with opposed front and rear ends between which extends a bore; a dowel configured for forced insertion into the bore so as to cause outward deformation of the bush, the dowel being provided with connection means engageable with a connector for fastening the terminal to the support and to facilitate the forced insertion; wherein there is further provided a weak region interconnecting the bush and the dowel.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from European Patent Application No. 15306262.5, filed on Aug. 4, 2015, 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]    Electrical equipment used in many different industries must be earthed (grounded), including for example, communications equipment on aircraft or signaling equipment on railways. This typically requires each item of equipment to be electrically connected by means of metal braids or earthing wires to a substrate such as the frame of the aircraft or a rail of railway. The ends of the metal braids or wires are received in terminals which are fixed to the substrate. 
         [0004]    Fixing a terminal to a support may typically be 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 substrate. In order to ensure good electrical contact between the terminal and the substrate, the surface of the substrate must be stripped of paint or other coating before the assembly of the screw and the nut. Once the assembly has been carried out, the stripped region of the support must be protected against corrosion. For the assembly of the screw and the nut, access is required to the two sides of the substrate during assembly. 
         [0005]    EP 1 376 766 in the name of the applicant discloses a device for fixing an electrical connection terminal to a substrate comprising, for example, a railway rail. The device comprises a ring which is to be introduced into a cylindrical hole formed in the substrate, a socket for insertion into the ring and a screw for engagement with a threaded opening provided in the socket. When assembling the device, the ring is firstly positioned in the cylindrical hole in the substrate, 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 threaded opening in 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 substrate and to establish electrical contact between the terminal and the substrate. 
         [0006]    An advantage of this fixing device is that it does not necessarily require the surface of the substrate to be stripped beforehand in order to ensure good electrical contact between the terminal and the substrate. This is because the electrical contact is produced between the ring and the inner surface of the cylindrical hole which is made in the substrate. A further advantage with this fixing device is that it may be assembled without requiring both sides of the substrate to be accessible. 
         [0007]    However a disadvantage of the fixing device lies in the pre-assembly process. This process requires the socket to be inserted into the ring very slightly so as to form a unitary item ready for eventual location in the hole of the substrate. However, the extent of insertion is critical as over insertion will result in too much deformation of the ring and under insertion will result in the socket and the ring detaching. The extent of insertion depends on many factors, including the material hardness, the outer diameter of the socket, the inner diameter of the ring, surface finish and the amount of forced applied to those parts. Therefore, an effective pre-assembly process requires close control of those variables. 
         [0008]    Upon completion of the pre-assembly process, the pre-assembled fixing devices must be carefully packaged to ensure the ring and socket of each fixing device do not detach and thus become mixed up with other rings and sockets in the package during delivery. 
         [0009]    Therefore, an object of the present invention is to overcome the disadvantages associated with the prior art by providing a fixing device which is less time consuming and expensive to produce. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one aspect of the invention, there is provided a device for fixing an electrical connection terminal to a support provided with an opening, the device comprising: 
         [0011]    a generally tubular bush for location within the opening of the support and provided with opposed front and rear ends between which extends a bore; 
         [0012]    a dowel configured for forced insertion into the bore so as to cause outward deformation of the bush, the dowel being provided with connection means engageable with a connector for fastening the terminal to the support and to facilitate the forced insertion; and 
         [0013]    a weak region interconnecting the bush and the dowel. 
         [0014]    An advantage with this fixing device is that the dowel and the bush may be manufactured as a single unit thus obviating the need for such an onerous pre-assembly process. In addition, the dowel and the bush form a single unit that are less likely to become inadvertently separated and therefore less care may be taken when packaging the fixing devices to avoid separation of those parts. 
         [0015]    In a preferred embodiment, the weak region may be configured to break upon forced insertion of the dowel into the bush. For instance, a force may be applied to the dowel to facilitate insertion into the bore and the weak region may break upon initiation of that force, depending on the magnitude of the force and the strength of the weak region. Advantageously, the dowel may be rearward of the bush and urged forward for insertion into the bore. It may therefore be preferable for the weak region to interconnect the rear end of the bush and the front end of the dowel. 
         [0016]    The shape and size of the weak region may be selected according to the capabilities of the manufacturing process and the desired strength of the weak region. The weak region must be sufficiently weak to break under the desired load and sufficiently strong to withstand the manufacturing process, delivery and subsequent handling prior to installation. For instance, the weak region may comprise one or more tabs spaced regularly or irregularly around the periphery of the fixing device. In a preferred arrangement, the weak region comprises an annular flange extending substantially around the periphery of the fixing device. The annular flange may taper rearwardly so as to extend between the rear end of the bush, which may have a larger cross-section, and the front end of the dowel, which may have a smaller cross-section. 
         [0017]    The fixing device may be made from a range of electrically conductive materials, such as aluminium, copper, titanium, stainless steel or brass. It may also be advantageous to harden at least part of the device, such as the dowel, for instance. 
         [0018]    Furthermore, it may be preferable to coat the fixing device with a material which resists corrosion, has a low electrical resistance and is sufficiently ductile to allow deformation. A coating of that nature may be particularly preferable for fixing devices made from some of the more corrosive materials, such as aluminium, copper and titanium. Even if the fixing device is sufficiently well coated during manufacture, uncoated portions of the dowels and the bush are likely to result from the broken weak region. The uncoated portion of the dowel is likely to move within the bore upon full insertion of the dowel into the bush and thus be concealed from the elements. The uncoated portion of the bush may be concealed by a rib, which is provided on the dowel and configured to engage the uncoated portion of the bush upon full insertion. The rib may also serve as an abutment which limits the amount by which the dowel may be inserted into the bush. 
         [0019]    The connection means may comprise an opening into a threaded hole extending at least partway through the dowel. The threaded hole may be sized to receive a connector such as a screw for securing the terminal to the substrate. In an alternative arrangement, the connection means may comprise a threaded spigot extending forward of the front end and configured to engage a connector such as a nut. In yet a further alternative arrangement, the connection means may comprise a bayonet fitting, for example. 
         [0020]    The degree of deformation of the bush upon forced insertion of the dowel may depend on the size and shape of the dowel and the bore. Preferably at least part of the dowel forms an interference fit with the bore so as to cause deformation of the bush. In particular, the cross section of the dowel is larger than the cross-section of the bore at least at some corresponding points along their lengths so as to cause deformation of the bush upon forced insertion of the dowel. The dowel may be cylindrical or it may narrow towards the front end and the bore may be cylindrical or it may narrow towards the front end of the bush. The cross-sections of the dowel and the bore may be selected to cause deformation of the bush behind the substrate such that a portion of the bush engages a rear face of the substrate. This restricts forward movement of the fixing device to prevent removal from the hole. Rearward movement of the fixing device is prevented by a flange extending radially from the front end of the bush for engagement with the front face of the substrate. 
         [0021]    According to a further aspect of the invention, there is provided a method of installing a fixing device on a substrate provided with an opening, the method comprising the steps of: 
         [0022]    (a) providing a fixing device comprising: a bush with a bore, a dowel and a weak region interconnecting the bush and the dowel; 
         [0023]    (b) mounting the fixing device to the substrate such that the bush locates in the opening in said substrate; 
         [0024]    (c) applying a force to the dowel in a direction towards the bush so as to cause the weak region to break; and 
         [0025]    (d) continuing to apply the force to the dowel so as to cause forced insertion of the dowel into the bore and cause outward deformation of the bush. 
         [0026]    Advantageously, the method described above may also include the steps of (a) furnishing the dowel with a rib and (b) continuing to apply the force to the dowel to cause the rib to abut the bush. The abutment of the rib and the bush may conceal a portion of the bush exposed following the breaking of the weak region and thus protect that portion from the elements. This is particularly advantageous when a protective coating was applied to the device during manufacture and the portion of the bush exposed following the breaking of the weak region is uncoated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    By way of example only, one specific embodiment of the present invention will now be described in detail, with reference being made to the accompanying drawings, in which: 
           [0028]      FIG. 1  is a rear perspective view of the fixing device according to the invention; 
           [0029]      FIG. 2  is a cross-sectional view from the fixing device shown in  FIG. 1 ; 
           [0030]      FIG. 3  is an exploded cross-sectional view of the weak region of the fixing device shown in  FIG. 2 . 
           [0031]      FIGS. 4 a  to 4 c    show three stages of the process of installing the fixing device of  FIGS. 1 to 3  into a substrate; 
           [0032]      FIG. 5  shows the fixing device fitted to the substrate; and 
           [0033]      FIG. 6  shows the electrical terminal secured to the fixing device by a screw. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    Referring initially to  FIGS. 1 to 3 , there is provided a fixing device, generally indicated  10 , suitable for securing an electrical terminal  100  ( FIGS. 5 and 6 ) to a substrate  110  ( FIGS. 5 and 6 ) provided on an aircraft, a railway line and so on. The fixing device comprises a bush  20 , a dowel  50  and a weak region  70  interconnecting the bush  20  and the dowel  50 . The fixing device may be cast, machined or cold formed as a unitary item from aluminum, copper, stainless steel or titanium and finally machine finished to a high standard before possibly being provided with a coating. 
         [0035]    The bush  20  has a cylindrical body  22  defining front and rear ends  24 , 26  and a bore  28  extending axially therethrough. The cylindrical body  22  is intended for location in an opening  112  in the substrate  110  and is sized to engage closely the portion of the substrate inside the opening  112 , such that electrical energy may be conducted between the bush  20  and the substrate  110 . 
         [0036]    The bush  20  also includes a plate  30  provided on the front end  24  of the cylindrical body  22  and is sized to extend radially someway therebeyond. The plate  30  has a generally planar rear face  36  and a generally planar front face  38  to which the terminal  100  can be secured. An aperture  40  is formed in the centre of the plate  30  for allowing the passage of a screw  114 , bolt or other mechanical fastener to be discussed below in connection with  FIGS. 5 and 6 . The plate  30  may include a lip  32  extending rearwardly from its periphery to define a rearward facing annular contact face  34 . 
         [0037]    The dowel  50  includes a generally cylindrical front portion  52 , a generally cylindrical rear portion  54  and a circumferential abutment  56  therebetween. The dowel  50  has a generally circular front face  58  defined by the front portion  52 , a generally circular rear face  60  defined by the rear portion  54  and a hole  62  extending between those front and rear faces  58 , 60 . The hole  62  is slightly diametrically smaller than the aperture  40  and is threaded to engage the screw  114 . The front portion  52  has a length substantially equal to the length of the bore  28  and a diameter generally greater than the diameter of the bore  28 , except for a narrow portion  64  adjacent the front face  58  which tapers inwardly. The abutment  56  is diametrically larger than the front portion  52  and defines a forward facing inclined face  66 . 
         [0038]    As best shown in  FIG. 3 , the weak region  70  is a thin band of material interconnecting the bush  20  and the dowel  50 . The weak region  70  is defined by an internal radius  72  between the front face  58  of the dowel  50  and the bore  28  of the bush  20 . In addition, the weak region  70  is defined by the vertex  74  between the narrow band  64  and the end face of the cylindrical body  22  which are arranged at an acute angle. 
         [0039]    Installation of the fixing device  10  is illustrated in  FIGS. 4 a  to 4 c   .  FIG. 4 a    shows the fixing device located in the opening  112  formed in the substrate  110  and achieves two points of contact between the fixing device and the substrate. The first point of contact and possibly the most reliable is between the cylindrical body  22  of the bush  20  and the portion of the substrate  110  inside the opening  112 . The second point of contact and possibly the least reliable (at least with a coated substrate) is between the annular contact face  34  of the bush  20  and the front face  116  of the substrate  110 . 
         [0040]    A setting tool  130  is employed to install the fixing device on the substrate  110 . The setting tool  130  has a cylinder  132  which bears against the front face  38  of the plate  30  to urge the bush  20  towards the substrate  110 . The setting tool  130  also has a rotatable piston  134  provided with a threaded shank  136  adapted to extend through the aperture  40  and threadingly to engage the hole  62 . 
         [0041]    Turning now to  FIG. 4 b   , the piston has been partially retracted within the cylinder so as to apply a tensile force to the dowel  50  in a forward direction while restricting movement of the bush  20 . This tensile force causes the weak region to break as the front portion  52  of the dowel  50  begins to move into the bore  28 . Movement of the dowel  50  into the bore  28  is assisted initially by the narrow portion  64  adjacent the front face  58  which tapers inwardly. The narrow portion may indeed act as a cam surface to cause outward deformation of the cylindrical body  22 . The outwardly deformed portion  68  of the cylindrical body  22  bears against the rear face  118  of the substrate  110  and thus restricts forward movement of the fixing device  10  relative to the substrate  110 . 
         [0042]      FIG. 4 c    shows the final step of the installation process in which the piston  134  is further retracted in the cylinder  130  so as to cause the front portion  52  of the dowel  50  to locate fully within the bore  28  of the cylindrical body  22 . In this position, further deformation of the cylindrical body  22  has occurred so as to achieve greater contact with the rear face  118  of the substrate  110 . Upon breaking the weak region  70 , uncoated portions of the dowel  50  and the bush  20  appear in the area of the break. The uncoated portion of the dowel  50  locates in the bore  28  and is thus protected adequately from the elements to minimize the chance of corrosion. The uncoated portion of the cylindrical body is shielded by the inclined face  66  of the abutment  56 , which abuts the cylindrical body  22  once the dowel  50  fully locates inside the bore  28 . In fact, the inter-engagement of the abutment  56  and the cylindrical body  22  may serve as an indication that full insertion of the dowel  50  within the bore  28  has been achieved. 
         [0043]      FIG. 5  shows the fixing device  10  secured to the substrate  110 , which is trapped tightly between the lip  32  of the plate  30  and the deformed portion  68  of the cylindrical body  22 . In preparation for installation, the terminal  100 , the washer  106  and the screw  114  are presented to the fixing device  10 . The terminal  100  and the washer  106  each have respective openings  104 ,  108  corresponding to opening  112  for allowing the passage of the screw  114 . 
         [0044]      FIG. 6  shows the terminal  100  secured to the substrate  110  via the screw  114 , washer  106  and the fixing device  10 . The inter-engagement of those parts facilitates effective electrical conductivity between the terminal and the substrate. 
         [0045]    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.