Abstract:
The invention relates to connecting elements for mechanically connecting constructive elements ( 2, 3 ). It is proposed to use an elastically deformable tensioning element ( 10 ), comprising a spring material consisting of a superelastic shape memory alloy, in particular a nickel-titanium alloy, elastically expanded in the tensioning element ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The invention relates to a connecting element for mechanically connecting constructive elements. It comprises an elastically deformable tensioning element which applies a holding force in its elastically deformed state, onto at least one constructive element connected by the connecting element, thus generating a nonpositive connection of at least one constructive element with the tensioning element or with another constructive element. In particular, the invention relates to the linking of longitudinal, wire-shaped constructive elements as e.g. profiles and tubes, also with small diameters in the range of a few millimeters or less. A connection is to be understood as the joint of a tensioning element to a constructive element to be connected, or the connection of two or more constructive elements to each other. In particular, the invention relates to the mechanical-connection of constructive elements consisting of a material which is difficult to weld or to solder, e.g. a nickel-titanium alloy. 
   2) Description of the Related Art 
   In many ranges of technology, there is the requirement to connect constructive elements mechanically, however, connections which allow detachment if necessary, are desired, too. A usual method is to use an elastically deformable tensioning element which applies a holding force in its elastically deformed state, onto one constructive element to be connected, thus generating a nonpositive connection of at least one constructive element with the tensioning element or with another constructive element. Principally, there are two ways of deforming the tensioning element elastically. 
   The first variant is to bring the tensioning element from a relaxed initial position into a pre-tensioned position by means of an elastic deformation, where it is deformed and elastically expanded. In the pre-tensioned position, the constructive element to be connected (at least one) can be inserted into the tensioning element (or, if necessary, vice versa, the tensioning element into the constructive element). After that, the tensioning element is allowed to return to a less tensioned position, where it applies a holding force, caused by the elastic deformation, onto the connected constructive element. This holding force generates the nonpositive connection. 
   The second possibility is to bring the tensioning element from its relaxed initial position into a tensioned position, where the mechanical tension generated by the expansion causes the holding force. The tensioning element can be pre-tensioned in an opposite direction before the insertion of the constructive element to be connected, if necessary. 
   Thus, as to the state of the art, it is known to fit coil springs made of steel to the ends of Allan keys; these coil springs are wound around the tip of the key in a way that the coil spring fixes the key in a non-positive way due to the spring load. With this, the key can be fixed to a bunch of keys by means of the coil spring. According to the first described variant, the coil spring is expanded for inserting the Allen key, and generates the holding force in a partially relaxed position. On the other hand, the coil spring can also be applied to the key by the second described variant, being contracted and decreasing the diameter, which presents similarities with crimping; this, too, generates a holding force by the winding around the key end. 
   Another known example from the state of the art are shrinking joint sleeves for the butt joining of tubes, e.g. according to the literature reference Engineering Aspects of Shape Memory Alloys, Duerig, Melton, Stöckel, Wayman, Verlag Butterworh-Heinemann Ltd., 1990 or according to DE 4026644 C1. Here, a shape memory alloy in form of a sleeve, with a suppressed shape memory effect, is located around the joint and shrunk. The entire usable shrinking effect amounts to approximately three to four percent after subtracting the installation tolerance, the substrate tolerance, the substrate deformation during shrinking and the suppressed shape memory effect; this makes it necessary to comply exactly with the tolerances in order to generate a reliable joint. These shrunk joints are based on a one-way effect, this means that the joints cannot be detached any more. The effect applied for joining during the shrinking process is based on a phase transformation, during which the metallographic structure of the shrinking sleeve changes. 
   SUMMARY OF THE INVENTION 
   Taking into account this state of the art, the invention relates to the creation of a connecting element for mechanically connecting constructive elements, which allows bigger tolerances and dimensional deviations for the tensioning element and/or the constructive elements, but at the same time creates a high holding force. The strength of the connection and the generated holding force must be high. Furthermore, it is desirable to detach the realized connection if necessary. 
   The solution according to the invention, for a connecting element for mechanically connecting constructive elements, comprising an elastically deformable tensioning element adapted to apply a holding force in its elastically expanded state, onto at least one constructive element connected by the connecting element, thus generating a nonpositive (frictional) connection of at least one constructive element with the tensioning element or with another constructive element, consists of the fact that the tensioning element comprises a spring material made of a superelastic shape memory alloy, in particular a nickel-titanium alloy, which is expanded elastically (purely elastically, superelastically) in the tensioning element. 
   For alloys containing a similar amount of titanium and nickel atoms, particular effects can be observed. Due to these effects, such alloys are also designated shape memory alloys. These effects are based on thermoelastic martensitic phase transformation, i.e. a temperature-dependent modification of the crystalline structure: at high temperatures, the alloy is austenitic, at low temperature, however, it is martensitic. According to T. W. Duerig and H. R. Pelton, (“TI-NI Shape Memory Alloys”, in: Materials Properties Handbook: Titanium Alloys, 1994, pages 1035-1048, ASM International 1994), two characteristics have to be distinguished for shape memory alloys. Alloys with a titanium content between 49.7 to 50.7 atom % show a thermal shape memory, also designated shape memory; whereas alloys with a titanium content of 49.0 to 49.4 atom % show a mechanical shape memory, also designated superelasticity. Not only binary nickel-titanium alloys can have the stated properties. A shape memory alloy can contain ternary ingredients (e.g. iron, chrome or aluminum). The relation of nickel and titanium, as well as the existence of ternary ingredients, has a big influence on the intensity of the thermal and mechanical shape memory. 
   In order to use the thermical shape memory for constructive elements as e.g. the shrinking sleeves described above, an alloy with adequate composition is converted diffusionlessly from the austenitic crystalline structure to the martensitic crystalline structure by cooling down. A subsequent deformation of a constructive element made of this alloy can be reversed by a thermal treatment of that constructive element (heating to a temperature above a certain conversion temperature). This recovers the initial austenitic crystalline structure and the constructive element returns to its original shape. The conversion temperature is generally understood as the temperature at which the martensite has completely converted to austenite. The conversion temperature strongly depends on the composition of the alloy and on the internal tensions of the constructive element. Constructive elements which have a thermal shape memory can perform movements and/or apply forces. 
   For a constructive element with austenitic crystalline structure, the mechanical shape memory effect appears when the constructive element is deformed in a certain temperature range. For this, it is energetically more favorable for the austenitic crystalline structure, to convert to martensite in a tension-induced way, whereby elastic expansions of up to 10% can be obtained. When unloaded, the crystalline structure returns to the austenitic phase. Therefore, constructive elements made of such alloys are used for the storage of deformation energy. 
   Alloys showing the characteristics described above are known by the designations of Nickel-Titanium, Titanium-Nickel, Tee-nee, Memorite R , Nitinol, Tinel R , Flexon R , Euroflex R  and Shape Memory Alloys. These terms do not refer to a single alloy with a certain composition, but to a family of alloys showing the described characteristics. 
   Due to the particular properties of nickel-titanium alloys, there is a high interest in many fields of technology, e.g. medical engineering and precision mechanics, in the application of constructive elements made of shape memory alloys, also in form of tubes, in particular with small outer diameter. In mechanics, they can e.g. be used for switching elements, setting elements or valves. In medical engineering, too, shape memory alloys are increasingly applied, as constructive elements made of such alloys are bio-compatible and fatigue-resistant, and because they show high buckling resistance in case of superelastic alloys. Examples for the application of nickel-titanium alloys in medical engineering are guidance wires for catheters, vessel supports (stents), as well as endoscopic and laparoscopic instruments for the minimal invasive diagnosis and therapy. 
   The special characteristic of superelastic shape memory alloys, consisting in achieving elastic expansions of up to ten percent, thus significantly higher than for spring materials made of steel or bronze, is applied in the scope of the invention, in order to use tensioning elements which are elastically expanded, made of such spring material. As the elastic expansion range is ten times higher as compared to a spring steel, the tolerances of invention-related tensioning elements can be bigger dimensioned. 
   The usable effect of the invention-related tensioning element is increased by the factor of three approximately, as compared to a shrinking sleeve made of a shape memory alloy as described above. During installation, such a shrinking sleeve is in martensitic state and converts to austenitic state when heated. The shrinking sleeve tries to restore the initial, smaller shape, thus generating the holding force. 
   The tensioning element according to the invention is in austenitic state already at the start of the installation and converts to the tension-induced, martensitic state during the elastic tensioning or expanding, respectively. Due to the geometric shape of the tensioning element, the usable effect can be increased by the factor three approximately, as compared to the known shrinking sleeve. In general, for an invention-related tensioning element, no elongation effects, i.e. shrinking effects, occur for the generation of the cohesive force, but merely bending forces or shear forces. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following embodiments of the invention show further advantageous features and specialties; these are further described and explained with the schematic representation in the drawings, as follows. 
       FIG. 1  shows a tensioning element according to the invention in form of a compression spring. 
       FIG. 2  shows a compression spring during assembly. 
       FIG. 3  shows a connecting element according to the invention with a compression spring. 
       FIG. 4  shows a tensioning element according to the invention in form of a tension spring. 
       FIG. 5  shows a tension spring during assembly. 
       FIG. 6  shows a connecting element according to the invention with a tension spring. 
       FIG. 7  shows a connecting element according to the invention with a spring and a joint element. 
       FIG. 8  shows a tensioning element according to the invention in form of a leg spring. 
       FIG. 9  shows a leg spring during assembly. 
       FIG. 10  shows a first connecting element according to the invention with a leg spring. 
       FIG. 11  shows a second connecting element according to the invention with a leg spring. 
       FIG. 12  shows a first connecting element according to the invention in form of a clamping sleeve. 
       FIG. 13  shows a pre-tensioned clamping sleeve as to FIG.  12 . 
       FIG. 14  shows a cross section of a first connecting element according to the invention with a clamping sleeve. 
       FIG. 15  shows a longitudinal section as to FIG.  14 . 
       FIG. 16  shows a first invention-related connecting element with leg spring and clamping sleeve. 
       FIG. 17  shows a second connecting element according to the invention with leg spring and clamping sleeve. 
       FIG. 18  shows a second connecting element according to the invention in form of a clamping sleeve. 
       FIG. 19  shows a pre-tensioned clamping sleeve as to FIG.  18 . 
       FIG. 20  shows a cross section of a second connecting element according to the invention element with a clamping sleeve. 
       FIG. 21  shows a longitudinal section as to FIG.  20 . 
       FIG. 22  shows a third connecting element according to the invention in form of a clamping sleeve, 
       FIG. 23  shows a pre-tensioned clamping sleeve as to FIG.  22 . 
       FIG. 24  shows a cross section of a third connecting element according to the invention with a clamping sleeve, 
       FIG. 25  shows a longitudinal section as to FIG.  24 . 
       FIG. 26  shows a fourth connecting element according to the invention in form of a clamping sleeve. 
       FIG. 27  shows a pre-tensioned clamping sleeve as to FIG.  26 . 
       FIG. 28  shows a cross section of a fourth connecting element according to the invention with a clamping sleeve. 
       FIG. 29  shows a longitudinal section as to FIG.  28 . 
       FIG. 30  shows a fifth connecting element according to the invention in form of a clamping sleeve. 
       FIG. 31  shows a pre-tensioned clamping sleeve as to FIG.  30 . 
       FIG. 32  shows a cross section of a fifth connecting element according to the invention with a clamping sleeve. 
       FIG. 33  shows a longitudinal section as to FIG.  32 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1-6  show lateral views of connecting elements according to the invention, the tensioning element of which comprises a helicoidal spring  1 ,  4 ,  7 , into which is inserted, in axial direction, at least one constructive element  2  to be connected. For this, the spring can be elastically deformed and pre-tensioned for inserting at least one constructive element into it, being partially relaxed for realizing the connection, or the spring will be tensioned in order to realize the connection. Furthermore it may be necessary to turn open the coil of the spring for increasing the diameter of the coil when inserting the mentioned at least one constructive element. 
   In  FIGS. 1-3 , the tensioning element is a compression spring  1 . In  FIG. 1 , it is illustrated in relaxed state. It consists of a shape memory alloy with superelastic characteristics. In order to connect two or more wire-shaped constructive elements  2 ,  3  at their face ends, the compression spring  1  will be compressed in axial direction and pre-tensioned when inserting the constructive elements  2 ,  3 . This increases the diameter of the spring, so the parts to be connected can be inserted as shown in FIG.  2 . The constructive elements  2 ,  3  are pressed together at their face ends; this is not illustrated in the figures for reasons of clearness. 
   After that, the compression spring is partially relaxed as illustrated in  FIG. 3 , whereby it expands again in longitudinal direction, trying to reach its initial, smaller diameter. This is inhibited, as the diameter of the constructive elements  2 ,  3  to be connected is bigger than the initial internal diameter of the spring which it now aims to restore. This partial relaxation causes a contact pressure of the compression spring  1  onto the constructive elements  2 ,  3 , with the compression spring now in tight contact to the constructive elements  2 ,  3  to be connected, generating the desired holding forces of the joint connection. The constructive elements  2 ,  3  to be connected at their front ends, are drawn with a gap in  FIG. 3 , for better presentability. For detaching the connection, the pressure spring  1  can once again be pressed into a shape according to  FIG. 2 , thus enabling to pull out the constructive elements  2 ,  3 . 
     FIGS. 4-6  show a connection of two constructive elements  2 ,  3 , realized by a tension spring  4 , shown in  FIG. 4  in relaxed state, made of a superelastic shape memory material. The tension spring is preferably wound to a block, i.e. winding next to winding. For inserting the two or more constructive elements  2 ,  3 , the windings are opened a little, so that the diameter of the windings becomes a little bigger, and stretched in axial direction at the same time. The constructive elements  2 ,  3  will be pushed together with their face ends, not shown in  FIG. 5  for a better presentability, and the tension spring  4  will be partially relaxed. Then, it adapts a state according to  FIG. 6 , where its diameter as well as its length are increased as compared to the initial state illustrated in  FIG. 4 , and decreased as compared with the state according to FIG.  5 . This generates a contact pressure onto the inserted constructive elements  2 ,  3 , causing the desired holding forces of the joint connection. 
     FIG. 7  illustrates a cross section through a connecting element according to the invention with a spring, which can be a compression spring  1 , a tension spring  4 , or a leg spring  7 , described further below. Two or more constructive elements  2 ,  3  are inserted into the spring, with their face ends joined, being connected to each other by the spring. The two constructive elements  2 ,  3  contact each other with their face ends in the range of the spring  1 ,  4 ,  7 , or are oriented to each other with their face ends. The constructive elements  2 ,  3  are preferably rod-shaped or tube-shaped and preferably have a circular cross section. However, other cross sections, e.g. rectangular or square cross sections, are possible, too. 
   Alternatively, it is possible that the spring  1 ,  4 ,  7  is not wound around two constructive elements  2 ,  3  joined together, but around a core consisting of one piece, so that only one constructive element to be connected is inserted into the spring. The inserted constructive element can then be connected to another element by means of the spring, e.g. with one leg of the spring. 
   Another advantageous feature shown in  FIG. 7  can consist in the fact that the two or more constructive elements  2 ,  3  are surrounded, in the range of their contact point, by a joint element, e.g. a joint tube  5  with thin walls or various joint shells, transferring the holding force of the spring to the constructive elements  2 ,  3  to be connected. 
   If the surfaces of the constructive elements  2 ,  3  to be connected, or those of a single-piece core, respectively, are very smooth, it can be advantageous to increase the holding forces by increasing the friction of a section  6  of at least one constructive element to be connected and inserted into the spring, being engaged with the tensioning element, i.e., the spring, by e.g. raising, structuring or coating. In special designs, it may occur that two or more constructive elements  2 ,  3  to be connected, are arranged parallel to each other within a section  6  of the spring. 
     FIGS. 8-11  show embodiments of connecting elements according to the invention, the tensioning element of which being a leg spring  7  shown relaxed in  FIG. 8 , with two legs  8 ,  9 , consisting of a superelastic shape memory alloy. It can be used in a way similar to the compression springs  1  and tension springs  4  described above, whereas the particularities further explained as to  FIG. 7 , e.g. one-piece cores, joint elements and friction-increasing sections are possible here, too. 
   According to a first variant illustrated in  FIGS. 9 and 10 , the legs  8 ,  9  of the leg spring  7  are bent up during the insertion of at least one of the constructive elements  2 ,  3 , in order to increase the diameter of its windings and for pre-tensioning of the leg spring  7  against the direction of winding of the leg spring  7 . The legs  8 ,  9  of the leg spring  7  then are transposed to each other by a certain transposition angle. After inserting the constructive elements  2 ,  3  to be connected into the leg spring  7 , the leg spring  7  is partially relaxed for realizing the connection; it adopts a state according to FIG.  10 . By this, the diameter of its coils decreases and the desired holding force onto the inserted constructive elements  2 ,  3  is obtained. 
   As an alternative, it is also possible, starting from the relaxed state of the leg spring  7  according to  FIG. 8 , or starting from the pre-tensioned state of the leg spring  7  according to  FIG. 9 , to bend together in winding direction of the leg spring, exceeding the relaxed state, the legs  8 ,  9  of the leg spring  7 , after the insertion of the constructive elements  2 ,  3  to be connected, for a decrease of the diameter of its windings, to obtain the connection. By this, the leg spring  7  is tensioned and decreases its pitch, which can be set forth until block formation, and decreases its diameter. 
   The diameter decrease is partially inhibited, however, by the inserted constructive elements  2 ,  3 , as soon as the inner diameter of the leg spring  7  comes in contact with the parts to be connected. This produces a contact pressure which obtains the desired holding forces of the joint connection. According as the leg spring  7  is or is not bent up in an intermediate step according to  FIG. 9 , constructive elements  2 ,  3  with a diameter bigger or smaller than the winding diameter, can be inserted into the leg spring  7 . 
   For the variant illustrated in  FIG. 11 , the constructive elements  2 ,  3 , the diameter of which is smaller than the leg spring  7 , are inserted in an initial position according to  FIG. 8 , and the legs  8 ,  9  are bent together in winding direction of the spring. Preferably, the legs  8 ,  9  are bent together until they reach a parallel orientation. This makes it easier to fix the legs  8 ,  9  with respect to each other, thus assuring the maintenance of the spring tension. 
   For this, the legs  8 ,  9  can be located, e.g. side by side, and fixed with a section of a spring tube, pushed over the leg ends  8 ,  9 , preferably consisting of a superelastic shape memory material, thus corresponding to a clamping sleeve, described hereafter. At the same time, one or more further pieces can be introduced and also joined into the other end of the sleeve, fixing the tensioned legs  8 ,  9  of the leg spring  7 . 
     FIGS. 12-15  illustrate a first connecting element according to the invention which comprises a tensioning sleeve made of a superelastic shape memory material as the connecting element.  FIG. 12  illustrates a cross section through the clamping sleeve. In its relaxed state, it preferably shows a circular cross section ( FIG. 12-10   r ); in the pre-tensioned state according to  FIG. 13  ( 10   pt ), and in the partially relaxed state according to  FIG. 14  ( 10   pr ), it presents an oval cross section. 
   For the insertion, in axial direction, of the constructive elements  2 ,  3  to be connected, into the clamping sleeve, it is necessary to bring the clamping sleeve  10   r  from the position illustrated in  FIG. 12 , to the oval to form  10   pt  according to  FIG. 13 , by compressing it. Hereby, the clamping sleeve  10   pt  is elastically deformed and pretensioned. In this state, both constructive elements  2 ,  3  to be connected are inserted, according to the cross section in  FIG. 14 ; after that, the clamping sleeve  10   pr  is relaxed. 
   The unloading partially relaxes the clamping sleeve  10   pt  as it aspires to recover its initial, round state. This, however, is partially impeded, as the inserted constructive elements  2 ,  3  together have a dimension that is bigger than the initial inner diameter of the relaxed clamping sleeve  10   r . This generates a force pressing together the constructive elements  2 ,  3  to be connected, joining them reliably. For detaching the connection, the clamping sleeve  10   pr  can once again be pressed into a shape according to  FIG. 13 , bringing it into a pre-tensioned state ( 10   pt ), enabling to pull out the constructive elements  2 ,  3 . 
   As compared to a conventional spring steel or a spring bronze, which allow a maximum elastic expansion of 0.5%, the clamping sleeve according to the invention, consisting of a superelastic shape memory, offers the advantage to allow up to 8% or more of elastic expansion. Thus, it is possible to allow bigger tolerances, whereas, e.g., half of the usable expansion range can be applied for the manufacturing tolerances and the other half can be applied for the maintenance of the elastic deformation and the generation of the holding forces. 
   Also as compared to the known shrinking sleeves consisting of shape memory alloys, used for shrinking connections, the clamping sleeves according to the invention offer essential advantages, as they allow bigger tolerances and dimensional deviations without affecting the function. For example, a pre-expanded shrinking sleeve of an inner diameter of 0.80 mm, can be shrunk to an inner diameter of 0.76 mm as a maximum. On the other hand, a round, superelastic tube section of a clamping sleeve  10  with an inner diameter of 0.80 mm can be compressed to an inner diameter of 0.47 mm without a permanent deformation of the pre-tensioned tube. The holding forces for this are generated by elastic deformations, bending forces and expansions. 
   In the embodiment according to the  FIGS. 12-14 , the outer diameter of the clamping sleeve  10   r  in its initial or relaxed state is 1.00 mm according to  FIG. 12 , and the inner diameter is 0.82 mm. In the pre-tensioned state according to  FIG. 13  ( 10   pt ), the large outer diameter is 1.62 mm, the large inner diameter is 1.44 mm, the small outer diameter is 0.64 mm and the small inner diameter is 0.46 mm. The diameter of the two constructive elements  2 ,  3  is 0.45 mm each, so that the clamping sleeve  10   pr  according to  FIG. 14 , shows the following dimensions in the partially relaxed state: large outer diameter 1.10 mm, large inner diameter 0.92 mm, small outer diameter 0.90 mm and small inner diameter 0.72 mm. 
     FIG. 15  illustrates a section A-A′ according to FIG.  14 . The section B-B′ corresponds to the representation in FIG.  14 . It can be seen that the constructive elements  2 ,  3  to be connected, are inserted into the tube-shaped clamping sleeve  10   pr ; the constructive elements are arranged parallel to each other in a section of clamping sleeve  10   pr . As an alternative, more than two constructive elements to be connected, can be inserted into the clamping sleeve. Furthermore, embodiments are possible, in which two or more constructive elements  2 ,  3  to be connected, are inserted, which contact each other with their face ends in the clamping sleeve, or which are oriented with their ends facing to each other. 
   The respective ends of the connected constructive elements  2 ,  3  can be inside of the clamping sleeve  10   pr , as shown in  FIG. 15 , or stick out of the clamping sleeve. The holding force generated by the clamping sleeve is determined by the mechanical material properties, the dimensions, the geometric conditions and the surface structure. If the clamping sleeve has a corresponding length, it can achieve a tensile strength of the connection which is higher than that of the connected constructive elements  2 ,  3 . 
     FIG. 16  illustrates a connecting element fulfilling the function of a T-junction. A leg spring  7  is wound around a constructive element  2 ; the legs  8 ,  9  of the leg spring  7  are fixed with a clamping sleeve  10   pr . This procedure generates a fixed connection of the leg spring  7  and the constructive element  2 . A further constructive element  3  is inserted in the clamping sleeve  10   pr , and fixed together with the legs  8 ,  9 . It is held, together with the legs  8 ,  9 , by the clamping sleeve  10   pr  by means of elastic deformation forces. 
   In  FIG. 17 , a leg spring  7  is wound around a constructive element  2  and connected to it, e.g., as described in  FIGS. 10 and 11 . One of the legs  8  is connected to a further constructive element  3  with a clamping sleeve  10   pr ; the other leg  9  is connected to a further constructive element  3   a  with a clamping sleeve  10   a . By this, it is possible to generate cross junctions. 
     FIGS. 18-21  correspond to the  FIGS. 12-15  and show a second connecting element according to the invention, featuring a clamping sleeve with two or more constructive elements  2 ,  3  to be connected, inserted; these constructive elements can contact each other with their face ends in the clamping sleeve, or are oriented with their ends facing to each other. In its relaxed state (FIG.  18 ), the clamping sleeve  10   r  can show a circular cross section, and in the pre-tensioned state ( FIG. 19-10   pt ), and in the partially relaxed state ( FIG. 20-10   pr ), an oval cross section. In this example, the cross section of the parts ( 2 ″,  3 ″) to be joined is oval. 
     FIGS. 22-25  correspond to the  FIGS. 12-15  and show a third connecting element according to the invention, featuring a clamping sleeve with two constructive elements  2 ,  3  inserted; these constructive elements are oriented with their ends facing to each other. In its relaxed state (FIG.  22 ), the clamping sleeve  10 ′ r  can show an oval cross section, in the pre-tensioned state (FIG.  23 - 10 ′ pt ), it can show a deformed state as compared to the relaxed state, e.g. a circular or oval cross section, and in the partially relaxed state (FIG.  24 - 10 ′ pr ), an oval cross section. In this example, the cross section of the constructive elements  2 ,  3  to be joined is circular. 
     FIGS. 26-29  correspond to the  FIGS. 12-15  and show a fourth connecting element according to the invention, featuring a clamping sleeve with two constructive elements  2 ′,  3 ′ to be connected, inserted; these constructive elements are arranged parallel to each other within a section of the clamping sleeve. In its relaxed state (FIG.  26 ), the clamping sleeve  10   r  can show a circular cross section, and in the pre-tensioned state ( FIG. 27-10   pt ), and in the partially relaxed state ( FIG. 28-10   pr ), an oval cross section. In this example, the cross section of the constructive elements  2 ′,  3 ′ to be joined is rectangular. 
     FIGS. 30-33  correspond to the  FIGS. 12-15  and show a fifth connecting element according to the invention, featuring a clamping sleeve with three constructive elements  2 ,  3 ,  3   a  to be connected, inserted; these constructive elements are arranged parallel to each other within a section of the clamping sleeve. In its relaxed state (FIG.  30 ), the clamping sleeve  10 ″ r  can show a circular or oval cross section, in the pre-tensioned state (FIG.  31 - 10 ″ pt ), it can show a cross section deformed on three sides in radial direction, or a cross section flattened on three sides, respectively, and in the partially relaxed state (FIG.  32 - 10 ″ pr ), a cross section arced on three sides. In this example, the cross section of the constructive elements  2 ,  3 ,  3   a  to be connected is circular. 
   List of Reference Signs 
   
       
         1  Compression spring 
         2  First constructive element 
         3  Second constructive element 
         3   a  Further constructive element 
         4  Tension spring 
         5  Joint tube 
         6  Section 
         7  Leg spring 
         8  First leg 
         9  Second leg 
         10  Clamping sleeve