Abstract:
This method of tightening a threaded fastener ( 6 ) to a predetermined torque comprises steps in which: axial and rotational coupling is begun, by surface shrinking to a tight fit, of the threaded fastener ( 6 ) to a tightening member ( 2 ) capable of turning the threaded fastener ( 6 ) and thereby tightening it, the tightening member ( 2 ) and the threaded fastener ( 6 ) being able, from an initial coupled configuration between the tightening member and the threaded fastener, to remain rotationally coupled at a rotary drive torque, transmitted by the tightening member to the threaded fastener, that is less than the predetermined tightening torque, and to be rotationally decoupled from each other at a rotary drive torque, transmitted by the tightening member to the threaded fastener, that is equal to the predetermined tightening torque; and from this initial coupled configuration, a rotary movement is applied to the tightening member ( 2 ) up to a rotary drive torque, transmitted by the tightening member ( 2 ) to the threaded fastener ( 6 ), that causes rotational decoupling of the tightening member ( 2 ) from the threaded fastener ( 6 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and to a member for tightening one or more screw-fastener elements, and also to a fastener and tightening device enabling the method to be performed. 
     2. Brief Description of the Related Art 
     Controlling the tightening of a screw-fastener element, such as a nut, a bolt, or a stud, conventionally relies on determining the tightening torque to be applied to the screw-fastener element. In the usual approach, applying this tightening torque requires a calibrated tightening member to be used, and also requires the tightening torque for application to be determined. This determination may be performed on the basis of the coefficient of friction between the threads, which is data provided by the screw-fastener manufacturer. Such tightening to torque therefore requires action to be performed by a qualified operator. 
     It is also known to make use of standardized tightening means for transmitting a predetermined tightening toque to a screw-fastener element, said means being designed to transmit destructive forces to the screw-fastener element when the predetermined torque is reached. In such devices, once the screw-fastener element has been tightened, it is damaged and cannot be tightened again in the event of variations in the tightening, as might result for example from vibration or creep of the material on which the screw-fastener element is mounted, when the material is concrete or wood. 
     U.S. Pat. No. 3,425,314 discloses a fastener and tightening device that comprises a nut and a ring for turning said nut. The ring is constituted by a succession of tubular portions that are separated in pairs by slits. When the tightening torque between the ring and the nut reaches a maximum value, the above-mentioned portions flex outwards under the action of a ratchet defined externally by the nut. Thus, the operation of that device relies solely on the capacity of portions of its ring to flex, thus preventing the delivery of a high level of tightening force and preventing an accurate transmission of force to the vertices of the ratchet, which are entirely unsuitable for implementing tight-fit interference. 
     U.S. Pat. No. 4,176,582 and FR-A-2 791 404 disclose fastener and tightening devices including a member for turning a screw-fastener element. That member is designed to transmit limited torque because its material is capable of deforming easily. Similarly, U.S. Pat. No. 6,364,585 discloses a tightening member described as being a resin endpiece, that is suitable for deforming elastically in its material so as to transmit a torque of limited magnitude to a screw-fastener element. Thus, the devices proposed in those documents are structurally incapable of delivering a high level of tightening or of transmitting an accurate force. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to propose a method and a member for tightening that guarantee reliable tightening of a screw-fastener element with a predetermined tightening torque, and that make it possible to perform subsequent tightening operations on the screw-fastener element after a first tightening operation, with performance of the method and use of the member not requiring action on the part of qualified personnel. 
     To this end, the invention provides a method and a member for tightening a screw-fastener element with a predetermined tightening torque, as defined respectively in claims  1  and  5 . 
     Thus, in the invention, co-operation by interference between two parts designates co-operation between surfaces in a tight-fit between those two parts, with one of them engaged, at least in part, in the other. The tolerances, adjustments, and stresses that are involved during such tight-fit surface interference are essential to the invention in that, by complying with these tolerances, adjustments, and stresses, the invention presents the remarkable advantage of enabling tightening to be provided that is sufficiently powerful and of enabling an accurate force to be transmitted. 
     In addition, in the meaning of the invention, two parts are constrained to turn together when turning one of the parts causes the other part to turn in the same direction, with or without relative slip between the parts. In particular, two parts that are constrained to turn together may have speeds of rotation that are different as a result of one of the parts slipping relative to the other. Furthermore, two parts that are initially constrained to turn together are subsequently released to turn relative to each other in the meaning of the invention from the moment when, for any additional turning applied to one of the parts, the other part remains stationary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The characteristics and advantages of the invention appear from the following description of four embodiments of a method and a device of the invention for fastening and tightening, given purely by way of example, and made with reference to the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view of a fastener and tightening device in accordance with a first embodiment of the invention, prior to tightening a screw-fastener element by means of a tightening member; 
         FIG. 2  is a longitudinal section of the  FIG. 1  fastener and tightening device in use for assembling together two parts; 
         FIG. 3  is a view on a larger scale of a detail III of  FIG. 2 ; 
         FIG. 4  is a cross-section view of the screw-fastener element and the tightening member of  FIGS. 1 and 2 , during a first step of tightening the screw-fastener element; 
         FIG. 5  is a section analogous to  FIG. 4 , during a second step of tightening the screw-fastener element; 
         FIG. 6  is a section analogous to  FIG. 4 , during a third step of tightening the screw-fastener element; 
         FIG. 7  is a section analogous to  FIG. 4 , during a fourth step of tightening the screw-fastener element; 
         FIG. 8  is a section analogous to  FIG. 4 , during a fifth step of tightening the screw-fastener element; 
         FIG. 9  is a section analogous to  FIG. 4 , showing the screw-fastener element in the tightened configuration; 
         FIG. 10  is a section analogous to  FIG. 2 , during a step of checking the tightening force transmitted by the tightening member of the screw-fastener element at the end of tightening; 
         FIG. 11  is a section analogous to  FIG. 2 , during another step of checking the tightening force transmitted by the tightening member of the screw-fastener element at the end of tightening; 
         FIG. 12  is a section on a larger scale of a variant of the screw-fastener element of the  FIG. 1  fastener and tightening device, the variant element being shown co-operating with a tightening member; 
         FIG. 13  is a section analogous to  FIG. 2  for a fastener and tightening device in accordance with a second embodiment of the invention; 
         FIG. 14  is a longitudinal section of a fastener and tightening device in accordance with a third embodiment of the invention prior to tightening a screw-fastener element by means of a tightening member; 
         FIG. 15  is a section on XV-XV of  FIG. 14  while tightening the screw-fastener element; 
         FIG. 16  is a longitudinal section of a fastener and tightening device in accordance with a fourth embodiment of the invention, prior to tightening a screw-fastener element by means of the tightening member; 
         FIG. 17  is a section on line XVII-XVII of  FIG. 16  while tightening the screw-fastener element; 
         FIG. 18  is a longitudinal section of a fastener and tightening device in accordance with a fifth embodiment of the invention, prior to simultaneous tightening of two screw-fastener elements by means of a tightening member; 
         FIG. 19  is a section analogous to  FIG. 18  for a fastener and tightening device in accordance with a sixth embodiment of the invention prior to simultaneous tightening of two screw-fastener elements by means of a tightening member; 
         FIG. 20  is a plan view of the screw-fastener elements of  FIG. 19 ; 
         FIG. 21  is a view on a larger scale showing detail XXI of  FIG. 19 ; 
         FIG. 22  is a section analogous to  FIG. 19 , in the tightened configuration of the screw-fastener elements; and 
         FIG. 23  is a section analogous to  FIG. 18  for a fastener and tightening device in accordance with a seventh embodiment of the invention, prior to simultaneous tightening of two screw-fastener elements by means of a tightening member. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  shows two parts  7  and  9  that are to be assembled together by means of a fastener and tightening device  1  in accordance with the invention. As shown in  FIG. 1 , the device  1  comprises a nut-and-bolt type connection  5  comprising a nut  6  and a bolt  4 , together with a ring or hoop  2  for tightening the connection  5 . The tightening ring  2  is suitable for being engaged around the nut  6  and it presents an inside peripheral surface S 2  that is substantially complementary to an outside peripheral surface S 6  of the nut  6 . The ring  2  and the nut  6  are rigid parts capable of withstanding locally and overall the interference produced by the tight fit obtained between them when implementing the tightening means. As explained in detail below, this co-operation by interference corresponds to co-operation over a tight-fit surface area that can be compared with the behavior of H7p6 or H6p5 type fits. 
     The tightening ring  2  includes internal peripheral splines  22  complementary to external peripheral splines  62  of the nut  6 . The elements  2  and  6  are thus suitable for being engaged one in the other by putting their respective splines into correspondence, with the central axes X 2  and X 6  to the elements  2  and  6  then coinciding. In the meaning of the invention, a configuration in which the splines  22  of the tightening ring  2  are in correspondence with the splines  62  of the nut  6  is a configuration in which the surface portions S 21  projecting from the splined inside surface S 2  of the tightening ring  2  are placed in register with setback surface portions S 63  in the splined outside surface S 6  of the ring  6 , while the setback surfaces S 23  of the surface S 2  of the tightening ring  2  are placed in register with surface portions S 62  projecting from the surface S 6  of the nut  6 . Such a configuration of the splines  22  and  62  in correspondence enables the tightening ring  2  and the nut  6  to be both mutually engaged and separated. 
     Starting from a configuration in which the tightening ring  2  is engaged relative to the nut  6 , as shown in  FIG. 4 , the tightening ring  2  is suitable for being turned about its central axis X 2 , as represented by arrows R 0 , R 1 , and R 2  in  FIGS. 4 to 8 , so as to induce tightening on the nut  6 , i.e. on the screw-fastened connection  5 . By a first turning movement R 0  through an angle α 0 , axial and rotary holding is initiated by interference between the tightening ring  2  and the nut  6 . The turning movement R 0  brings each surface portion S 21  projecting from the tightening ring  2  into contact with a surface portion S 61  projecting from the nut  6 , as shown in  FIGS. 5 and 6 . Each surface S 21  is adapted to co-operate by interference with a surface S 61 , such that starting from the initial configuration where the tightening ring  2  is held in rotation relative to the nut  6 , the tightening ring  2  is suitable, by making a turning movement R 1 , for entraining the nut  6  to turn about its central axis X 6 . More precisely, moving the tightening ring  2  through a turn R 1  causes the nut  6  to turn in the same direction, with the speeds of rotation of the tightening ring  2  and the nut  6  being different because of relative slip between them as a function of the force transmitted by the nut  6  and bolt  4  system to the parts  7  and  9 . In particular, the tightening ring  2  is suitable for exerting on the nut  6  both a radial force and an axial force enabling it to be tightened without possibility of release during this tightening. Advantageously, the surface portions S 21  and S 61  correspond to surfaces in tangential or quasi-tangential contact in order to eliminate edges that could lead to seizing. 
     Starting from the initial configuration in which the tightening ring  2  is held relative to the nut  6 , as shown in  FIG. 6 , the friction force between the surfaces S 21  and S 61  is designed to increase until it reaches a maximum friction force, beyond which there is no longer any entrainment by friction between the surfaces S 21  and S 61 . This maximum friction force is adapted to be equal to the force exerted by the surfaces S 21  on the surfaces S 61  when the turning torque C transmitted by the tightening ring  2  to the nut  6  starting from the initial held-together configuration of  FIG. 6  is equal to a predetermined tightening torque C 0  for applying to the nut  6 . In this way, starting from their initial held-together configuration, the tightening ring  2  of the nut  6  are suitable for remaining constrained together in rotation for a turning torque C that is less than the tightening torque C 0  and for being released relative to each other in rotation for a turning torque C that is equal to the tightening force C 0 . In order to control the friction force exerted at the interface between the surfaces S 21  and S 61 , these surfaces are advantageously provided with a surface coating, such as a friction lining, so that the coefficient of friction between these surfaces is well determined. In particularly advantageous manner, this surface coating is adapted to change in appearance while the nut  6  is being tightened by means of the tightening ring  2 . This surface coating may also perform other known advantageous functions, e.g. an anti-corrosion function. 
     As can be seen more particularly in  FIG. 3 , the nut  6  includes circular ribs  65  centered on the axis X 6  on its face  64  that is to be brought to bear against one of the parts for assembly. By way of example, the ribs  65  may be in the form of a screw thread with its thread tightening towards the axis X 6  in the tightening direction. These ribs  65  seek to limit radial deformation of the nut  6  when subjected to radial and axial reactions from the threads of the bolts  4  and of the bearing part  9  during tightening. The threads in contact between the nut  6  and the bolt  4  are thus stressed more uniformly during tightening. In addition, control over the radial deformation of the nut  6  is necessary in order to control the interference contact between the surfaces S 21  and S 61 , thereby enabling the nut  6  to be accurately tightened with the predetermined tightening torque C 0 . The ribs  65  also contribute to maintaining the tightening of the nut  6  at the torque C 0 , by an anti-loosening effect. 
     A method of tightening the nut  6  by means of the tightening ring  2  comprises steps such as those described below. 
     Initially, the tightening ring  2  is engaged relative to the nut  6  for tightening, and as represented by arrow F in  FIG. 2 , by putting the splines  22  of the tightening ring  2  into correspondence with the splines  62  of the nut  6 . The elements  2  and  6  are then in the engaged configuration as shown in  FIG. 4 . 
     Starting from this engaged configuration, a turning movement R 0  is imparted to the tightening ring  2  about its axis X 2 . The tightening ring  2  is thus caused to pivot relative to the nut  6  until it reaches an initial configuration in which it is held both axially and in rotation relative to the nut  6 , as shown in  FIG. 6 , in which configuration each surface portion S 21  projecting from the tightening ring  2  co-operates with interference with each surface portion S 61  projecting from the nut  6 . The tightening ring  2  is then suitable, on being turned, for transmitting a rotary drive torque C to the nut in order to tighten it. 
     The polygonal outside surface, here a hexagonal surface, of the tightening ring  2  enables it to co-operate with a wrench of the kind as conventionally used with polygonal nuts. In a variant, any known means for transmitting tightening torque may be used for turning the tightening ring  2 . 
     Rotary drive of the tightening ring  2  is then continued by turning through R 1 , in the same direction as the turning movement R 0 , so as to reach a rotary drive torque C that is transmitted by friction from the tightening ring  2  to the nut  6 , thereby enabling the tightening ring  2  to be released in rotation relative to the nut  6 . This release of the tightening ring  2  in rotation relative to the nut  6  is made manifest by the fact that the nut  6  stops moving while the tightening ring  2  continues to be driven in rotation. The tightening ring  2  then makes available a tightening torque C that is greater than C 0 . The tightening ring  2  becoming released in rotation relative to the nut  6  indicates that the tightening operation has finished and that the predetermined tightening torque C 0  has indeed been transmitted to the nut  6 . 
     From this configuration in which the tightening ring  2  is free to turn, the tightening ring  2  is caused to perform a turning movement R 2  about its axis X 2  while the nut  6  remains stationary in rotation. The turning movement R 2  is continued until the elements  2  and  6  are once more in a mutually-engaged configuration. More precisely, this new mutually-engaged configuration, as shown in  FIG. 9 , corresponds to a configuration of the elements  2  and  6  in which the splines  22  and  62  correspond once more, with the tightening ring  2  having pivoted relative to the nut  6  so as to put each of its splines  22  into engagement with the following splines  62  of the nut  6  relative to the starting mutually-engaged configuration. 
     Given the relative characteristics of the tightening ring  2  and of the nut  6 , this arrival in a new mutually-engaged configuration indicates that the predetermined tightening torque C 0  has been applied by the tightening ring  2  to the nut  6 . Advantageously, an operator observing that the tightening ring  2  has turned by this amount relative to the nut  6 , i.e. by an amount enabling the elements  2  and  6  to return to a mutually-engaged configuration, constitutes a step of monitoring and confirming the tightening in the context of the method of tightening the nut  6  by means of the tightening ring  2 . 
     The tightening ring  2  is then caused to slide axially relative to the nut  6  so as to separate the two elements  2  and  6 . In particularly advantageous manner, this relative axial sliding of the elements  2  and  6  is possible only in the mutually-engaged configuration of  FIG. 9 , such that the tightening cannot be interrupted until the tightening torque C 0  has been achieved. The screw-fastened connection  5  is then tightened and the parts  7  and  9  are assembled together. 
     As can be seen from the above-described steps of the tightening method, the contact area between the tightening ring  2  and the nut  6  varies during tightening. This contact area is zero or at a minimum in the initial mutually-engaged configuration of the ring  2  and the nut  6 , and then increases during the turning movements R 0  and R 1  of the tightening ring  2 , and finally decreases during the turning movement R 2  of the tightening ring  2 , so as to become once more zero or at a minimum so as to enable the tightening ring  2  to be separated from the nut  6 . 
     As shown in  FIGS. 10 and 11 , the fastener and tightening device  1  in accordance with this first embodiment of the invention may also include means for checking the tightening force delivered at the end of tightening by the nut  6  and bolt  4  system to the assembled-together parts  7  and  9 . In particular, as shown in  FIG. 10 , the device  1  includes a calibrated checking ring  8  of radial dimensions that are adapted to correspond to the radial dimensions of the nut  6  when it delivers a desired predetermined tightening force to the parts  7  and  9 . In a variant, the device  1  may include a checking ring  10 , as shown in  FIG. 11 , that is premounted around the nut  6  before it is tightened and that is adapted to break under the effect of the nut  6  being deformed radially by an amount that corresponds to the nut  6  delivering a desired predetermined tightening force to the parts  7  and  9 . Other means for checking the tightening force delivered by the nut  6 , e.g. involving evaluating the radial deformation of the nut  6 , may also be used. As non-limiting examples, such as checking means may comprise a checking ring premounted around the nut  6  before it is tightened and that is adapted to be prevented from moving under the effect of the nut  6  being radially deformed by an amount that corresponds to the nut  6  delivering a desired predetermined tightening force on the parts  7  and  9 , or else of a tightening ring that is suitable for breaking under the effect of radial deformation of the nut  6  that corresponds to the parts  7  and  9  being subjected to a desired predetermined tightening force. 
     Advantageously, as shown in  FIG. 12 , the outside peripheral surface S 6  of the nut  6  of a fastener and tightening device  1  in accordance with the invention may also include two superposed zones Z 1  and Z 2  that serve respectively to drive the nut  6  in rotation by means of the tightening ring  2 , and to drive the nut  6  in rotation by means of some other drive member, such as a conventional wrench for tightening polygonal nuts. Such a structure for the nut  6  serves to facilitate prior connection of and removal thereof in the event of disassembly as compared with acting via the tightening ring  2 . 
     In the second embodiment shown in  FIG. 13 , elements that are analogous to those of the first embodiment are given references that are identical, plus  100 . The device  101  in this second embodiment comprises, in analogous manner to the first embodiment, a nut-and-bolt type connection  105  comprising a nut  106  and a bolt  104 , together with a ring or hoop  102  for tightening the connection  105 . The device  101  differs from the device  1  of the first embodiment solely in that the bearing face  164  of the nut  106  presents a conical chamfer  167  for co-operating with a washer  103 . The conical chamfer  167  of the bearing face  164  acts in a manner analogous to the ribs  65  of the first embodiment to limit radial deformation of the nut  106  while it is being tightened by means of the ring  102 . Thus, the contacting threads between the nut  106  and the screw  104  are stressed more uniformly during tightening, and the interference contact between the surfaces of the tightening ring  102  and of the nut  106  is well controlled, thereby guaranteeing that the nut  106  is tightened with the predetermined tightening torque C 0 . In addition, a measurement of the deformation of the washer  103  as occurs during tightening provides advantageous means for verifying the force that has been applied at the end of tightening. 
     In the third embodiment shown in  FIGS. 14 and 15 , elements analogous to those of the first embodiment are given identical references plus  200 . The device  201  in accordance with this third embodiment comprises a tightening member  202  and a bolt  204  having a head  242  that defines a face  264  that is to come to bear against a part. In its head  242 , the bolt  204  includes a housing  241  suitable for receiving a male portion  221  of the tightening member  202 . As shown in  FIG. 14 , the outside peripheral surface S 221  of the male portion  221  is frustoconical. This surface S 221  is designed to co-operate by interference with the inside peripheral surface S 241  of the housing  241 , which is likewise frustoconical. More precisely, the male portion  221  is suitable for being engaged as a force-fit in the housing  241  so as to occupy the clearance J that is visible in  FIG. 14 , with the central axes X 202  and X 204  of the tightening member  202  and of the bolt  204  then coinciding. When the male portion  221  is engaged as a force-fit in the housing  241 , as shown in  FIG. 15 , the tightening member  202  and the bolt  204  are held together both axially and in rotation by co-operation by interference between the surfaces S 221  and S 241 . Thus, the force-fit of the male portion  221  in the housing  241  initiates axial and rotary holding together of the tightening member  202  and of the bolt  204  by interference. From this initial held-together configuration, the tightening member  202  is suitable by a turning movement R 1  for driving the screw  204  in rotation about its central axis X 204 . More precisely, the turning movement R 1  of the tightening member  202  causes the screw  204  to turn in the same direction, without relative slip between them. In particular, the tightening member  202  is suitable for exerting a force on the bolt  204  that is both radial and axial, thereby enabling it being tightened. 
     The maximum friction force between the surfaces S 221  and S 241 , i.e. the force beyond which there is no longer any friction drive between the surfaces S 221  and S 241 , is adapted to be equal to the force exerted by the surface S 221  on the surface S 241  when the rotary drive torque C transmitted by the tightening member  202  of the bolt  204  from their initial held-together configuration is equal to a predetermined tightening torque C 0  that is to be applied to the bolt  204 . Thus, the tightening member  202  and the bolt  204  are suitable, starting from their initial held-together configuration, for remaining constrained to turn together when subjected to a turning drive force C that is less than the tightening torque C 0  and to slip relative to each other, i.e. to be released in turning relative to each other, for a turning drive torque C that is equal to the tightening torque C 0 . As in the above-described embodiments, the surfaces S 221  and S 241  are advantageously provided with a surface coating, such as a friction lining, so as to obtain a coefficient of friction and a friction force at the interface between these surfaces that are well determined. 
     A method of tightening the bolt  204  by means of the tightening member  202  comprises steps as described below. 
     To begin with, the tightening member  202  is caused to be held both axially and in rotation relative to the bolt  204  by engaging the male portion  221  of the tightening member  202  as a force-fit in the housing  241  of the bolt  204 , i.e. by occupying the clearance J as represented by arrow F in  FIG. 14 . 
     From this initial held-together configuration, a turning movement R 1  is imparted to the tightening member  202  so as to reach a turning drive torque that is transmitted by the tightening member  202  to the bolt  204  that enables them to slip relative to each other, i.e. that enables the tightening member  202  to be released in rotation relative to the bolt  204 . 
     Because of the relative characteristics of the tightening member  202  and of the bolt  204 , the possibility of slip between the tightening member  202  and the bolt  204  is a sign that the predetermined tightening torque C 0  has been applied by the tightening member  202  to the bolt  204 . An operator observing this possibility for the tightening member  202  to slip relative to the screw  204  constitutes a step of checking and confirming the tightening in the context of the method of tightening the bolt  204  by means of the tightening member  202 . The male portion  221  is then caused to slide away from the housing  241  so as to separate the tightening member  202  from the bolt  204 . As in the above embodiment, this sliding of the male portion  221  relative to the housing  241  from a configuration in which the clearance J has been occupied is possible only when the tightening torque C 0  has been applied to the bolt  204 , in other words the tightening of the bolt  204  cannot be interrupted until the predetermined tightening torque C 0  has been obtained. 
     In the fourth embodiment shown in  FIGS. 16 and 17 , elements analogous to those of the first embodiment carry identical references plus  300 . The device  301  in accordance with the fourth embodiment comprises a stud  304  and a tightening member  302 . The tightening member  302  has a female housing  321  suitable for receiving a male end  341  of the stud  304 . As shown in  FIG. 16 , the inside peripheral surface S 321  of the female housing  321  is frustoconical, as is the outside peripheral surface S 341  of the end  341 . The surfaces S 321  and S 341  are designed to co-operate by interference. More precisely, in a manner analogous to the third embodiment, the male end  341  of the stud  304  is suitable for being engaged as a force-fit in the housing  321  so as to occupy the clearance J shown in  FIG. 16 , the central axes X 302  and X 304  of the tightening member  302  and of the stud  304  then coinciding. When the male end  341  is engaged as a force-fit in the housing  321 , as shown in  FIG. 17 , the tightening member  302  and the stud  304  are held together both axially and in rotation by the co-operation by interference between the surfaces S 321  and S 341 . As a result of this force-fit of the male end  341  in the housing  321 , the tightening member  302  and the stud  304  are held together both axially and in rotation by interference. 
     Starting from this held-together configuration, the tightening member  302  is suitable, by a turning movement R 1 , for driving the stud  304  in rotation about its central axis X 304 . More precisely, the turning movement R 1  of the tightening member  302  causes the stud  304  to turn in the same direction without relative sliding between them. Furthermore, in accordance with the invention, the maximum friction force between the surfaces S 321  and S 341 , i.e. the force beyond which there is no longer friction drive between the surfaces S 321  and S 341 , is adapted to be equal to the force exerted by the surface S 321  on the surface S 341  when the rotary drive force C transmitted by the tightening member  302  to the stud  304  from their initial held-together configuration is equal to a predetermined tightening force C 0  for application to the stud  304 . The tightening member  302  and the stud  304  are thus suitable, starting from their initial held-together configuration, for remaining constrained together in rotation for a rotary drive torque that is less than the tightening torque C 0  and for being movable in slip relative to each other, i.e. for being released in rotation, by a rotary drive torque C that is equal to the tightening torque C 0 . In particular, in the context of a method of tightening the stud  304  by means of the tightening member  302 , which method is performed in manner analogous to the method described for the third embodiment, the tightening member  302  can be separated from the stud  304  from a configuration in which the clearance J is occupied, only once the tightening torque C 0  has been applied to the stud  304 , and as a result the tightening of the stud  304  cannot be interrupted until the predetermined tightening torque C 0  has been obtained. 
     In the fifth embodiment shown in  FIG. 18 , in the sixth embodiment shown in  FIGS. 19 to 22 , and in the seventh embodiment shown in  FIG. 23 , elements that are analogous to those of the first embodiment are given identical references plus  400 . The device  401  in accordance with these three embodiments comprises a bolt  404 , a first nut  406 , and a second nut  408  provided as a lock nut. The nuts  406  and  408  are designed to co-operate with the bolt  404  in order to assemble together two parts  407  and  409 . These nuts  406  and  408  are two distinct nuts that are substantially identical to each other. In particular, the nuts  406  and  408  have respective external peripheral splines  462  or  482  with the splines  462  of the nut  406  being substantially identical to the splines  482  of the nut  408 . As shown in the figures, each of the nuts  406  and  408  is a hexagonal nut. 
     In a manner analogous to the first embodiment, the device  401  further includes a ring or hoop  402  for tightening the nuts  406  and  408  relative to the bolt  404  in order to assemble together the parts  407  and  409 . The tightening ring  402  is suitable for being engaged around the superposed nuts  406  and  408  in order to tighten both of these nuts simultaneously. For this purpose, as in the first embodiment, the tightening ring  402  has internal peripheral splines  422  that are complementary to the external peripheral splines  462  of the nut  406  and  482  of the nut  408 . The tightening ring  402  is thus suitable for being engaged on the superposed nuts  406  and  408  by putting the splines  422  of the ring into correspondence with the splines  462  and  482  in alignment of the nuts  406  and  408 , the central axes X 402  of the ring  402  and X 406 , X 408  of the nuts  406  and  408  then coinciding. 
     In order to guarantee freedom of the tightening ring  402  engaged relative to the nuts  406  and  408  to move in translation along the direction of the coinciding axes X 402 , X 406 , and X 408 , both before and after tightening, the nuts  406  and  408  are fabricated in such a manner that the splines  462  and  482  are always substantially in angular alignment with one another about the axes X 406  and X 408 , both before tightening and at the end of tightening. For this purpose, various techniques can be envisaged. Three of them correspond respectively to the fifth, sixth, and seventh embodiments, it being observed that the person skilled in the art is capable of combining and/or modifying the implementation of these three embodiments as a function of the fabrication method used in order to comply with dimensional tolerances and as a function of the assembly method used with the nuts  406  and  408 . Before describing the tightening ring  402  in greater detail and how it co-operates mechanically with the nuts  406  and  408 , there follows a description of the specific features of the fifth, sixth, and seventh embodiments. 
     In the embodiment of  FIG. 18 , the nuts  406  and  408  are fabricated identically or to correspond, e.g. from two blanks that are mounted with prestress on a threaded rod, and then by machining the splines  462  and  482  on each of these blanks, and in alignment with one another. Thus, by way of example, for nuts  406  and  408  of the M12 type, functional dimensional tolerances are typically less than 0.05 millimeters (mm), such that the splines  462  and  482  are in alignment providing they are angularly offset by no more than 10° after the nuts have been tightened by means of the ring  402 . 
     In the embodiment of  FIGS. 19 to 22 , and in the embodiment of  FIG. 23 , the nuts  406  and  408  are not mounted in contact with each other as in the embodiment of  FIG. 18 , but rather at a spacing referenced e in  FIGS. 19 to 22  and e′ in  FIG. 23 . This spacing e or e′ is made up of a tolerance, plus positive or negative functional clearance, typically less than 0.05 mm for hexagonal M12 type nuts, possibly plus a distance that is equal to, or is a multiple of, the pitch divided by the number of faces of the nuts. 
     In the embodiment of  FIGS. 19 to 22 , the spacing e is occupied by a film or a washer  410  that establishes a bridge between the nuts  406  and  408  that are fabricated to be identical or to correspond, the film or washer  410  being made of a plastics material or of a ductile material, preferably forming an adhesive interface with the nuts. The assembly constituted by the nuts  406  and  408 , when assembled together by the film or the washer  410 , can then be handled as a single part, thereby making the method of tightening the nuts  406  and  408  easier. Advantageously, the value of the spacing e, corresponding to the thickness of the film or of the washer  410 , is determined so that the nut  406  is tightened before the lock nut  408 , with this applying even in the circumstances shown in  FIGS. 20 and 21  where the angular offset between the nut  406  and the lock nut  408 , corresponding to the angle referenced β, has the effect of positioning the lock nut  408  upstream from the nut  406  in the conventional screw-fastening direction, with this being because the flexibility of the film or washer  410  maintaining priority for screwing the nut relative to screwing the lock nut. It should be observed that for better visibility the values for the spacing e and for the angle β are exaggerated in the figures. 
     In the embodiment of  FIG. 23 , the spacing e′ results from material being removed when cutting through an initial single nut in order to fabricate the nut  406  and the lock nut  408 . This cutting of a single nut to obtain the two nuts  406  and  408  may be performed by any suitable technique, in particular by means of a cutter tool, a wire, or a beam. Furthermore, the cutting of the initial nut from which the nuts  406  and  408  are fabricated may be performed in full or in part only. If the initial nut is cut in part only, then the nuts  406  and  408  remain assembled together via at least one bridge of material, which bridge is sheared during tightening of the nuts  406  and  408  when they are driven in rotation by interference by means of the tightening ring  402 . Thus, fabricating the nut  406  and the lock nut  408  by partially cutting apart a single initial nut enables the nuts  406  and  408  to be handled as a single part, with the nuts  406  and  408  continuing to be connected together by at least one bridge formed by the material of the initial nut and acting for the purpose of connecting the nuts  406  and  408  together in a manner analogous to the film or the washer  410  of the sixth embodiment. 
     In all of these ways of making the nuts  406  and  408  so that their splines  462  and  482  are in angular alignment about the axes X 406  and X 408  before and after tightening, the tightening ring  402  is suitable, from a mutually-engaged configuration of said ring relative to the superposed nuts  406  and  408 , for being driven in rotation about its central axis X 402  so as to tighten the nut  406  simultaneously with or slightly in advance of the tightening of the lock nut  408 . An initial turning movement of the tightening ring  402  serves to cause the ring  402  to be held by interference relative to each of the nuts  406  and  408  both axially and in rotation. Starting from this initial held-together configuration, the friction force between the projecting portions S 421  of the inside peripheral surface S 402  of the ring and the projecting portions S 461  of the outside peripheral surface S 406  of the nut  406  is designed to increase up to a maximum friction force, beyond which there is no longer any friction drive between the projecting surface portions S 421  and S 461 . The maximum friction force between the projecting portions S 421  and S 461  corresponds to a rotary drive torque C transmitted by the tightening ring  402  to the nut  406  starting from the initial held-together configuration that is equal to a predetermined tightening torque C 0  for application to the nut  406 . Likewise, starting from the initial held-together configuration of the ring  402  and the lock nut  408 , the friction force between the projecting portions S 421  of the inside peripheral surface S 402  of the ring and the projecting portions S 481  of the outside peripheral surface S 408  of the nut  408  is designed to increase up to a maximum friction force, beyond which there is no longer any friction drive between the projecting surface portions S 421  and S 481 . The maximum friction force between the projecting portions S 421  and S 481  corresponds to a rotary drive torque C transmitted by the tightening ring  402  to the nut  408  starting from the initial held-together configuration that is equal to a predetermined tightening torque C 0 ′ for application to the nut  408 . Thus, the tightening ring  402  is suitable, starting from the initial held-together configuration, for remaining constrained to turn with the nut  406  or with the nut  408  for a rotary drive torque C that is respectively less than the tightening torque C 0  or the tightening torque C 0 ′, and to be released in rotation relative to the nut  406  or the nut  408  for a rotary drive torque C that is respectively equal to the tightening torque C 0  or the tightening torque C 0 ′, respectively. 
     As in the first embodiment, the nut  406  advantageously includes circular ribs (not shown) on its face  464  that is to bear against one of the parts for assembling together, which ribs are centered on the axis X 406  and seek to limit radial deformation of the nut  406  that is subjected to the radial and axial reactions from the threads of the bolt  404  and from the bearing part  409  during tightening. In order to limit radial deformation of the lock nut  408  during tightening, the nut  408  may also include circular ribs (not shown), on its face  484  that is to bear against the nut  406 , which circular ribs are centered on the axis X 408 . 
     A method of simultaneously tightening the nuts  406  and  408  by means of the tightening ring  402  comprises steps as described below. 
     Initially, the tightening ring  402  is engaged relative to the superposed nuts  406  and  408  so that the splines  462  and  482  are in angular alignment about the coinciding axes X 406  and X 408  by putting the splines  422  into correspondence with the splines  462  and  482 . The elements  402 ,  406 , and  408  are then in a mutually-engaged configuration. 
     From this engaged configuration, turning movement is imparted to the tightening ring  402  about its axis X 402  in order to reach an initial configuration in which the ring  402  is held both axially and in rotation relative to the nut  406  and the nut  408 . The tightening ring  402  is then suitable, on being turned, for transmitting a turning drive torque C to the nuts  406  and  408  in order to tighten them. Turning drive continues to be applied to the tightening ring  402  until reaching a turning drive torque as transmitted by friction between the tightening ring  402  and each of the nuts  406  and  408  that enables the tightening ring  402  to be released to turn relative to each of the nuts  406  and  408 . This release of the tightening ring  402  to turn relative to the nuts  406  and  408  is made manifest by the fact that the nuts  406  and  408  become stationary while the tightening ring  402  continues to be turned. The release of the tightening ring  402  allowing it to turn relative to the nut  406  indicates that the predetermined tightening torque C 0  has been transmitted to the nut  406 , whereas the release of the tightening ring  402  leaving it free to turn relative to the lock nut  408  indicates that the predetermined tightening torque C 0 ′ has been transmitted to the nut  408 . Furthermore, specifically for the embodiment of  FIGS. 19 to 22 , the tightening of the nuts  406  and  408  also serves to shear and flatten the film or washer  410  between the nuts so as to cause the material of the film or the washer to be expelled from the outside peripheral surfaces S 406  and S 408  of the two nuts, thereby making it possible visually to verify that the nuts are indeed tightened. Furthermore, during tightening, the film or the washer  410  will also be expelled towards the threads of the nuts  406  and  408  at the interface between the bolt  404  and the nut. Such an injection of material at that interface contributes to preserving the properties of the materials constituting the elements  404 ,  406 , and  408  and to maintaining tightening of the nuts  406  and  408  at their respective torques C 0  and C 0 ′, thereby obtaining an anti-loosening effect. 
     From this configuration where the tightening ring  402  is released to turn, additional turning movement is imparted thereto about its axis X 402  while the nuts  406  and  408  remain stationary in rotation, until a new mutually-engaged configuration of the ring  402  relative to the nuts  406  and  408  is reached, with the splines  422  once more coinciding with the splines  462  and  482 . The tightening ring  402  has then been pivoted relative to the nuts  406  and  408  in such a manner as to put each of its splines  422  into correspondence with the following splines  462  of the nut  406  and  482  of the nut  408  relative to the initial mutually-engaged configuration. In particular, each spline  462  of the nut  406  may, at the end of tightening, be in alignment with a spline  482  of the nut  408  that is different from the spline with which it was in alignment in the engaged configuration of the tightening ring relative to the nuts  406  and  408  prior to tightening. 
     The tightening ring  402  is then caused to slide axially along the direction of the coinciding axes X 402 , X 406 , and X 408  relative to the superposed nuts  406  and  408  so as to separate the ring  402  from the nuts. Each of the nuts  406  and  408  is then tightened at its respective predetermined torque C 0  or C 0 ′, and the parts  407  and  409  are assembled together. 
     As can be seen from the above-described examples, the tightening device and method in accordance with the invention serve to guarantee that at least one screw-fastener element  6 ,  106 ,  204 ,  304 ,  406 ,  408  is tightened with a predetermined tightening torque C 0 , C 0 ′. According to the principle of the invention, this tightening torque is transmitted by the tightening member to the or each screw-fastener element by means of co-operation by interference between the peripheral surfaces of these two elements. This co-operation by interference between the peripheral surfaces of the two elements is initiated either by relative turning between the two elements or by relative engagement as a force-fit between corresponding portions of these two elements. 
     In particularly advantageous manner, the tightening member and the or each screw-fastener element of a device in accordance with the invention are suitable for being released to turn relative to one another, and thus optionally to be separated axially, only when the appropriate tightening torque C 0 , C 0 ′ has been applied to the screw-fastener element by the tightening member. Any partial stressing of the or each screw-fastener element is thus made impossible, thereby making tightening reliable. 
     In addition, since the tightening torque C 0 , C 0 ′ for application to the or each screw-fastener element is imposed mechanically as a result of the characteristics relating to the contacting surfaces of the screw-fastener element and of the tightening member, performance of the tightening method in accordance with the invention does not require action to be taken by a qualified operator. The imposed tightening torque C 0 , C 0 ′ also makes it possible to avoid any overdimensioning of the screw-fastener element, since the maximum torque that can be applied to the screw-fastener element is the predetermined tightening torque C 0 , C 0 ′. This predetermined tightening torque is easily adjusted by adapting the coefficient of friction at the interface between the contacting surfaces of the screw-fastener element and of the tightening member, in particular by applying a surface coating, or indeed by varying the profiles of the contacting surfaces, e.g. by providing splines of greater or lesser width. 
     Furthermore, a tightening device and method in accordance with the invention make it possible to preserve the integrity of the or each screw-fastener element during tightening, such that it is possible to proceed with successive tightening operations on the screw-fastener element. In particular, it is possible to retighten a screw-fastener element for which the tightening force has varied, e.g. as a result of vibration or damage to the material in which it is secured. Furthermore, as can be seen from the above-described examples, the tightening member of a device of the invention may equally well comprise a male tightening portion or a female tightening portion, thereby making it possible to tighten all types of screw-fastener element. In addition, the interference that generates the tightening may act via a conical contact surface, thereby maximizing contact areas, even when tightening screw-fastener elements of small dimensions. Finally, the tightening member in accordance with the invention is of limited manufacturing cost and is easily machined from conventional parts. 
     The invention is not limited to the examples described and shown. In particular, the tightening member of a device of the invention may have a variety of shapes, in particular shapes that are different from those described above. By way of example, the tightening rings  2 ,  102 , and  402  may be replaced by a bushing presenting inside machining analogous to that of the rings  2  and  102 . In addition, each of the tightening members described above is designed to be turned by an external tool independently of the tightening member. In a variant, a tightening member in accordance with the invention may form part of a tool, i.e. it may constitute a portion thereof, e.g. the socket of a wrench. 
     As shown in  FIGS. 1 to 9 ,  12  and  18  to  23 , it is also emphasized at this point that the rings or hoops  2 ,  102 , and  402  that include peripheral splines and the corresponding screw-fastener elements  6 ,  106 ,  406 , and  408  are in contact via six suitable surfaces. In practice, the necessary and sufficient number of contact surfaces between the male or female driver parts and the female or male driven parts is advantageously selected application by application. 
     Furthermore, providing splines at the interference interface between the tightening member and the screw-fastener element for tightening is not reserved to a tightening member of the female type, and may be transposed to the third and fourth embodiments. In addition, means for checking the tightening force delivered by the screw-fastener element after it has been tightened by means of a device of the invention, and as described in the first embodiment, may also be provided in any device in accordance with the invention that makes use of a contact surface  64 ,  164 ,  264 , or  464  between the screw-fastener element and a part for tightening by means of the screw-fastener element. 
     Furthermore, a tightening device and method of the invention may be used for tightening any type of screw-fastener element, e.g. for tightening a wood screw, a sheet metal screw, nuts, etc. A tightening device and method of the invention may also be used for tightening a screw-fastener element that is held stationary relative to an intermediate part, it then being possible for the tightening member to be designed to co-operate by interference with said intermediate part, which should be considered as forming a single piece with the screw-fastener element. The provision of such an intermediate part that is prevented from moving relative to the screw-fastener element makes it easy to implement a tightening device and method of the invention with a standard screw-fastener element. 
     Finally, the above-described examples of simultaneously tightening two nuts by interference by means of one tightening ring may be transposed to tightening some arbitrary number of nuts greater than two. In addition, when simultaneously tightening a nut and lock nut, the two nuts may present dimensions that are different from each other. In particular, in order to enhance tightening of one nut relative to the other nut, provision may be made for the nuts to have heights along the direction of the central axes of the nuts that differ from one nut to the other. The nut and the lock nut may also present diameters that are different, the inside profile of the tightening ring then being adapted to enable both nuts to be driven simultaneously for tightening purposes. This variant has the advantage of making it possible, at will, to perform simultaneous tightening and checking or else to perform tightening and checking that are different for the nut and for the lock nut.