Patent Abstract:
A snap-in coupling for releasably connecting a first structural member and a second structural member. The snap-in coupling comprises a female coupling member comprising a plastic support member and a metallic spring clamp, said support member being insertable into a socket provided at said first structural member such that the female coupling member is retained therein, and a male coupling member comprising a mounting portion for being fixed to said second structural member, and a head portion. Said spring clamp and said head portion are arranged to snappingly engage each other when said female coupling member and said male coupling member are inserted into each other.

Full Description:
FIELD AND BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a snap-in coupling for releasably connecting a first structural member and a second structural member.  
         [0002]     DE 198 36 108 A1 discloses a snap-in coupling comprising an elastically deformable female coupling member and a male coupling member. The female coupling member is adapted to be inserted into a socket provided at said first structural member so as to be positively retained therein. It comprises a spherical female portion, an annular intermediate wall integral therewith and serving as an insertion portion, and a tubular outer wall integral with said intermediate wall, which outer wall engages a peripheral wall of the socket when the female coupling portion is inserted into the socket. The male coupling member comprises a head portion and a mounting portion adapted to be fixed to the second structural member.  
         [0003]     In this prior snap-in coupling the intermediate wall of the female coupling member is of conical shape and is stiffened by webs which extend between the tubular outer wall of the female coupling member and which are connected to the outside of the spherical female portion by radial ribs. The female coupling member is made of thermoplastic elastomeric material or rubber. This snap-in coupling has vibration dampening characteristics due to its geometry and the used material so that it provides for vibration decoupling between the first and second structural members.  
         [0004]     German Utility Model 202 16 836 discloses a snap-in coupling wherein the annular intermediate wall of the female coupling member is not of conical shape but of an undulated or corrugated profile. This provides for resiliency not only in axial directions but also in radial directions. Therefore the female coupling member may perform vibration decoupling compensation movements both in axial and radial directions and, accordingly, in all directions therebetween, i.e. three-dimensional compensation movements in space.  
         [0005]     This allows to make the female coupling member of relatively hard plastic material, for example an elastomeric material on the basis of chemically and thermally deformation resistant polyester. For example polybutylenetherephthalate (PBT) and polyethylenetherephthalate (PET) may be used.  
         [0006]     These materials are of temperature dependent hardness. For example, when they are subject to extremely low temperatures down to −40° C. to be encountered in cold climatic zones they will become so hard that the snap-in coupling cannot be released by acceptable forces. Apart from the fact that the mounting and releasing forces are dependent on temperature it is relatively difficult to precisely set the absolute values of the mounting and, respectively, releasing forces for normal environmental conditions because the characteristics of the used plastic material as well as the geometry of the plastic female coupling member cannot be readily controlled.  
       SUMMARY OF THE INVENTION  
       [0007]     It is an object of the present invention to provide a snap-in coupling wherein the forces for closing and opening of the snap-in coupling are substantially not dependent on temperature in a temperature range from about −40° to 150° C. and furthermore may be precisely controlled as to their absolute values. Furthermore, the snap-in coupling is to have vibration decoupling characteristics similar to those of the snap-in couplings in the prior art.  
         [0008]     A snap-in coupling in accordance with the present invention has been defined in claim  1 .  
         [0009]     In the snap-in coupling of the present invention the female coupling member comprises a plastic support member and a metallic spring clamp. The spring clamp of the female coupling member and the head portion of the male coupling member are formed such that they provide for a snap-in connection frictionally joining the two coupling members when they are inserted into each other.  
         [0010]     Use of a spring clamp which is preferably made from spring steel provides for the advantage that the mounting and dismounting forces of the snap-in coupling are substantially independent of temperature within the above mentioned temperature range. This results from the fact that the characteristics of the material and in particular the spring rate of the metallic spring clamp are substantially constant within said temperature range.  
         [0011]     A further advantage of the present invention is that the absolute values of the mounting and dismounting forces of the snap-in coupling may be very precisely controlled and set by spring clamp characteristics such as material thickness, type of material, geometry, etc. The forces for closing and opening a certain snap-in coupling, therefore, are substantially less responsive to variations of the characteristics of the used plastic material than in the prior art.  
         [0012]     Since the female coupling member consists not only of the metallic spring clamp but additionally of a plastic support member, the support member may be designed such that the snap-in coupling of the present invention will show substantially the same vibration decoupling characteristics as the above mentioned conventional snap-in couplings. Therefore the snap-in coupling of the present invention combines the advantageous properties of a metallic spring clamp and the vibration decoupling characteristics of a plastic coupling member.  
         [0013]     While the spring clamp could be connected to the support member of the female coupling member so as to be releasable, preferably they are fixedly connected to each other by having a base plate of the spring clamp embedded in plastic material of the support member by injection moulding.  
         [0014]     Preferably the spring clamp has a plurality of circumferentially spaced spring arms which snappingly engage the head portion of the male coupling member to provide said snap-in connection. The ends of the spring arms each comprise a holding portion and an insertion portion which are angled with respect to each other in V-shaped relationship. The head portion of the male coupling member has an annular groove matingly shaped with respect to the ends of the spring arms. As a result the insertion portion and the holding portion of the spring arms of the spring clamp may be shaped differently such that a smaller force is required to close the snap-in connection than to open the snap-in connection.  
         [0015]     Preferably the support member of the female coupling member is made of a thermoplastic elastomeric material of optimal chemical and thermal deformation resistance while the spring clamp, as mentioned above, may be made of spring steel.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:  
         [0017]      FIG. 1  is a longitudinal section through a snap-in coupling of the present invention in its mounted and closed condition;  
         [0018]      FIG. 2  is a longitudinal section through the female coupling member of the snap-in coupling in its disassembled condition;  
         [0019]      FIG. 3  is a top view of the female coupling member in  FIG. 2 ;  
         [0020]      FIG. 4  is a perspective view of the female coupling member in  FIGS. 2 and 3  from below;  
         [0021]      FIG. 5  is a side elevation of the male coupling member of the snap-in coupling in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     The snap-in coupling as shown in  FIG. 1  is intended to releasably join a structural member  2  and a structural member  4  which may be for example structural members of an automotive vehicle to be releasably connected to each other. The snap-in coupling consists of a female coupling member  6  and a male coupling member  8 ; the female coupling member  6  may be inserted into a socket  10  of the structural member  2 , and the male coupling member  8  may be fixed to the structural member  4 .  
         [0023]     In the embodiment as shown, the socket  10  is formed by a recess of the structural member  2  which is of part annular or horseshoe-shape so that the female coupling member  6  may be laterally inserted into the socket  10 . In any case the socket  10  may be of a design as shown in the above-mentioned DE 198 36 108 A1 or DE-GM 202 16 836 the disclosure of which is incorporated herein by reference.  
         [0024]     As shown in  FIGS. 1 and 2 , the female coupling member  6  comprises a support member  12  and a spring clamp  14 . In the embodiment as shown the support member  12  and the spring clamp  14  are fixedly connected to each other as will be explained in more detail below. As an alternative the spring clamp  14  may be connected to the support member  12  so as to be releasable therefrom, for example by snap-in or clip connection means or by thermal embedding.  
         [0025]     As already mentioned above the support member  12  is made of plastic material, preferably of a thermoplastic elastomeric material, in particular on a polyester base such as polybutylenetherephthalate (PBT) or polyethylenetherephthalate (PET). While these materials are resiliently deformable, they are of a relatively high shore hardness, and excellent thermal deformation resistance (150° C. and more). Furthermore, they are of excellent chemical resistance, in particular diesel oil resistance. The spring clamp  14  is made of a metallic material, in particular spring steel.  
         [0026]     The support member  12  comprises a tubular outer wall  24  adapted to be inserted into the socket  10 , and a central portion  26  which are connected to each other by circumferentially spaced webs  28 , see also  FIGS. 3 and 4 . Since the tubular outer wall  24  is of an axial length substantially exceeding that of the central portion  26 , the webs  28  have inclined lower ends (in  FIGS. 1, 2 ) and rectilinear upper ends (in  FIGS. 1, 2 ).  
         [0027]     As shown in  FIG. 3  the webs  28  extend substantially tangentially with respect to a peripheral wall  29  of the central portion  26 . The webs  28  are arranged in pairs such that the webs of any pair are directed in opposite circumferential directions. Due to this structure the webs  28  allow for relative movements between the tubular outer wall  24  and the central portion  26  in radial directions so as to provide for vibration decoupling of the snap-in coupling when in operation.  
         [0028]     In the embodiment as shown the tubular outer wall  24  and the central portion  26  are connected to each other only by the substantially straight webs  28  so as to provide for minimal space requirements of the female coupling member  6 . When more space is available, the outer wall  24  and the central portion  26  could be connected to each other by an annular intermediate wall of undulated or corrugated profile in longitudinal sections as shown and described in the above mentioned DE-GM 206 16 836. Since the shape and arrangement of such an intermediate wall with associated webs have been disclosed in the above German Utility Model in great detail, no further description thereof is required herein.  
         [0029]     The central portion  26  of the support member  12  has on its bottom side (in  FIGS. 1, 2 ) a central lens-shaped projection  30  the purpose of which will be explained further below.  
         [0030]     The spring clamp  14  comprises a base plate  34  having a central hole  36  and a plurality of spring arms  38  (four spring arms in the embodiment as shown). The spring arms  38  are integral with the base plate  34  and bent therefrom for more than 90° when they are in a relaxed condition so that they provide for a square periphery in the bottom view of  FIG. 3  for uniformly engaging the male coupling member  8  as will explained in more detail below.  
         [0031]     The spring clamp  14  is fixedly connected to the support member  12  by the base plate  34  and a small adjacent part of the spring arms  38  being embedded in the material of the support member  12  as shown in  FIGS. 1 and 2 . This is accomplished during manufacture of the support member  12  by injection moulding. A core within the injection-moulding tool holds the spring clamp  14 , and plastic material is injected about the spring clamp. Since plastic material flows also into the central hole  36  of the base plate  34  and since a small part of the spring arms  14  is enclosed by plastic material of an annular projection  32  of the central portion  26 , positive interlocking between the support member  12  and the spring clamp  14  will result.  
         [0032]     As an alternative these members could be connected to each other by releasable connection means such as snap-in or clip means, thermal embedding, or the like.  
         [0033]     Each of the spring arms  38  has a terminal end  40  bent radially inwards to snappingly engage the male coupling member  8 . Each terminal end  40  comprises a holding portion  42  and an insertion portion  44  which are inclined with respect to each other in V-shaped relationship. As shown in  FIG. 2 , the insertion portion  44  is inclined with respect to the central axis of the snap-in coupling by an angle α which is smaller than a respective angle β of the holding portion  42 . As shown the angle α is in the order of 25°, and the angle β is in the order of 45°. It should be noted, however, that other angles may be appropriate in other applications. Due to the difference between the angles α and β closing of the snap-in coupling requires a smaller force than opening the snap-in coupling as will explained in more detail below.  
         [0034]     As shown in  FIGS. 1 and 5  the male coupling member  8  comprises a head portion  46 , a mounting portion  48 , and a drive portion  50  disposed therebetween.  
         [0035]     Head portion  46  is provided with a radiused end surface  52  which is followed by a conical surface  54 . The conical surface  54  is followed by a substantially cylindrical surface  56 . The head portion  46  is provided with an annular groove  58  adjacent to said cylindrical surface  56 .  
         [0036]     The annular groove  58  of the head portion  46  and the radially inwards bent terminal ends  40  of the spring arms  38  of the spring clamp  14  are of substantially mating shapes. More particularly the annular groove  58  of the head portion  56  comprises a pair of inclined conical surfaces  60  and  62 . The cone angle of the surface  62  is similar to angle α of the insertion portions  44  of the spring arms  38 , and the cone angle of the surface  60  is similar to the angle β of the holding portions  42  of the spring arms  38 . The cone angle of the conical surface  54  is also similar to the angle α of the insertion portions  44  of the spring arms  38  so that the conical surface  54  can perform a centering action upon the male coupling member  8  when the coupling is being closed as will be explained in more detail below.  
         [0037]     The mounting portion  48  of the male coupling member  8  is formed as a threaded portion, and the drive portion  50  is of hexagonal shape for being engaged by a respective tool. As a result the male coupling member  8  may be threaded into a respective bore of the structural member  4 ; it is to be noted that the threads of the mounting portion  48  could be formed as self-cutting threads. It should be noted that the mounting portion  48  could be of any other structure and may be even an integral portion of the structural member  4 .  
         [0038]     Operation of the snap-in coupling as described is as follows: 
        When the coupling members  6  and  8  have been fixedly connected to its associated structural members  2  and  4 , closing of the snap-in coupling merely requires to insert the coupling members  6 ,  8  into each other by relative movement of the structural member  2  and  4  along the central axis whereby the spring clamp  14  of the female coupling member  6  and the head section  46  of the male coupling member  8  snappingly engage each other automatically.        
 
         [0040]     As indicated in  FIG. 2  any two diametrically opposite spring arms  38  when in a relaxed condition are spaced from each other by a predetermined minimal distance A. This distance is smaller than the minimal diameter of the annular groove  56  of the head portion  46  for a predetermined amount in order to have the spring arms  38  engage the head portion  46  under a predetermined biassing force when the snap-in coupling has been closed.  
         [0041]     While the coupling members  6  and  8  are being inserted into each other, the insertion portions  44  of the spring arms  38  initially slide along the conical surface  54  of the head portion  46  whereby the spring arms  38  are resiliently deflected in an outward direction so as to perform a centering action between the head portion  46  and the spring clamp  14 . As soon as the insertion portions  44  of the spring arms  38  have been moved beyond the cylindrical surface  56  of the head portion  46 , the spring arms  38  “snap” radially inwards so that the radially inwards bent terminal ends  40  snappingly engage into the annular groove  58  of the head portion  46 . The terminal ends  40  which are arranged so as to form a square (see  FIGS. 3 and 4 ) now uniformly contact the annular head portion  46 . In particular the holding portions  42  of the terminal ends  40  engage the conical surface  60  of the head portion  46 , and the insertion portions  44  of the terminal ends  40  engage the conical surface  62  of the head portion  46 . Due to the linear shape of the terminal ends  40  and the circular shape of the head portion  46 , line contact between these surfaces will result.  
         [0042]     Relative insertion movements of the coupling members  6  and  8  are limited by having the arcuate end surface  52  of the head portion  46  engage the lens-shaped projection  30  of the support member  12 . A point-contact between the support member  12  of resiliently deformable plastic material and the head portion  46  allows for compensation of manufacture tolerances of the involved members. Furthermore abutment between the lens-shaped projection  30  of the support member  12  and the spherical end surface  52  of the head portion  46  provides for playless engagement between the spring clamp  14  and the head portion  46 .  
         [0043]     Opening the snap-in coupling merely requires to move the structural members  2  and  4  away from each other in an axial direction so as to release the snap-in connection between the spring clamp  14  and the head portion  46 . Since the angle α of the insertion portions  44  of the spring arms  38  (and of the conical surface  44  of the head portion  46 ) is smaller than the angle β of the holding portions  42  (and of the conical surface  60  of the head portion  46 ), the dismounting force for opening the snap-in coupling substantially exceeds the mounting force necessary for closing the snap-in coupling. This allows to secure the snap-in coupling from being opened inadvertently without resulting in excessive mounting forces.  
         [0044]     The resilient properties of the spring clamp  14  made of spring steel are substantially invariable within a temperature range of e.g. from −40° to 150° C. The mounting and dismounting forces of the snap-in coupling are, therefore, independent of temperature, apart from a certain temperature dependent behaviour of the plastic support member  12 . Furthermore, the values of the mounting and dismounting forces of the snap-in coupling may be precisely controlled and set by the characteristics of the used materials and the structure (geometry, material thickness, number of spring arms, etc.) of the spring clamp  14 , while the mounting and dismounting forces may be selected to differ from each other in the desired manner by respective selection of the angles α and β. Due to the support member  12  with its webs  28  being made of plastic material and due to a possibly present intermediate wall of undulated profile, the snap-in coupling has excellent vibration decoupling properties which are similar to those of the snap-in couplings in the above mentioned publications.

Technology Classification (CPC): 5