Abstract:
A retaining cam ( 20 ) for a rotatable fastener for connecting components ( 16, 17 ) is provided. The retaining cam ( 20 ) has a housing ( 22 ) pivotally supported on a base plate ( 24 ), by which the retaining cam ( 20 ) can be fixedly connected to one ( 17 ) of the components ( 16, 17 ). A screw ( 30 ) is secured rotationally fixed in the housing ( 22 ). A fastener bolt ( 40 ) rotatably connected to another ( 16 ) of the components ( 16, 17 ) can be screwed onto the screw ( 30 ). Spring elements are associated with the screw ( 30 ) for generating an elastic pretension for securing the fastener bolt ( 40 ) against rotation. The housing ( 22 ) is pivotally supported on the base plate ( 24 ) by a spherical washer ( 50 ). An angle deviation between the center axes of the retaining cam ( 20 ) and the fastener bolt ( 40 ) can be compensated for by pivoting the retaining cam on the spherical washer ( 50 ) while maintaining full-surface contact of the retaining cam ( 20 ).

Description:
BACKGROUND 
     The invention relates to a retaining cam for a rotatable fastener to connect components, with the retaining cam comprising a housing, which is pivotally supported on a base plate, by which the retaining cam can be connected to one of the components in a fixed manner, and into which a screw is inserted in a rotationally fixed fashion, onto which a fastener bolt can be screwed, rotationally connected to one of the other components, with at least one spring element being allocated to the screw for creating an elastic pretension for rotationally securing the fastener bolt. 
     A rotatable fastener of the above-mentioned type is a standard part in aeronautics and space exploration. The retaining cam of this rotatable fastener complies with the standard prEN 6092 of AECMA (The European Association of Aerospace Industries-Standardization, Brussels, Belgium, Edition P1, draft dated Mar. 22, 2004.) The fastener bolt of the rotatable fastener complies with the standard prEN 6088 of AECMA (Edition P1, April 2006.) Such rotatable fasteners are used in aeronautics and space exploration to transfer strong forces, for example a maximum tensile stress of 6300 N and a maximum shearing force of 11,000 N. These known rotatable fasteners are used in an aircraft, for example for a detachable connection of an interior cover panel or an access panel to the fuselage frame or a cell. The retaining cam is fastened via its base plate to the fuselage frame, for example via rivets. The fastener bolt is connected to an interior cover panel or an access panel in a rotational but captive fashion. The fastener bolt has a bore with a double-threaded internal thread. The screw inserted into the retaining cam in a rotationally fixed fashion has a double-threaded external tread. A perfect connection of the fastener bolt to the retaining cam can only be created in prior art when their axes are aligned to each other, e.g., when two components to be connected to each other are parallel in reference to each other. Such alignment of the axes or the parallel positioning of the components may already be difficult due to permissible tolerances per se. During the assembly, the fastener bolt will pull the retaining cam, which is pivotal to a certain extent in reference to the base plate, against said base plate. When the axes are not aligned to each other, the retaining cam will attempt to pull itself with its circular contact area, which encompasses a facial opening of its housing facing the fastener bolt, against the base plate, with the retaining cam attempting to align said contact area to the base plate parallel in reference to the fuselage frame. If the axes fail to assume a perpendicular position in reference to the fuselage frame tensions can develop in the rotatable fastener, because the retaining cam will not contact the base plate over its entire area. This insufficient contact can even lead to the housing of the retaining cam, which is embodied relatively thinly, becoming damaged. Furthermore, there are applications in which curved interior cover panels shall be fastened at the fuselage frame. Previously, particular expenses incurred to appropriately position the fastener cams at the frame side for a screwed connection to the fastener bolt, prevent the occurrence of the above-mentioned tensions or the above-mentioned damage of the housing of the retaining cam. Additionally, particular expenses are necessary for the retaining cam to contact the base plate with its entire contact area, within permissible tolerances, when screwed to the fastener bolt. This is even further aggravated in that such rotatable fasteners are designed for frequent reusability. Commonly such a rotatable fastener should withstand  1500  screw cycles. 
     Quarter-rotation fasteners are known (for example from the catalog Alcoa Fastening Systems, 2007), in which the above-mentioned difficulties are avoided such that the retaining cam is connected via the base plate to the fuselage frame or the like in a stiff fashion and that a fastener pin is inserted, which at its frontal end comprises a Phillips pin. During fastening, the Phillips pin of the fastener pin glides over a ramp of the retaining cam and after a quarter rotation reaches a catch position, in which it is held by the elastic pretension of a spring element. Such a rotatable fastener shows a simple design and can easily be assembled; however it is only useable for considerably lower tensile stress applications. 
     SUMMARY 
     The object of the invention is to provide a retaining cam of the type mentioned at the outset that allows greater angular deviations between its axis and the axis of the fastener pin to be compensated without any problems. 
     This object is attained according to the invention in that the housing of the retaining cam is supported on the base plate in a pivotal fashion via a spherical washer. In the retaining cam according to the invention it is ensured, here, that the retaining cam always contacts an area holohedrally over its entire perimeter. This is allowed by the spherical washer, arranged between the base plate and the adjacent face of the housing of the retaining cam, on which the housing can be pivoted until the axis of the screw of the retaining cam and the axis of the fastening pin are aligned to each other. Here, although the retaining cam can take a diagonal position in reference to the base plate, however, it maintains its holohedral contact at the spherical washer, which on its opposite side has a planar area, via which it upholds a holohedral contact to the base plate. It is obvious that the angular deviation of axes, which are not aligned and can be compensated thereby, must be within a limited range, however that within said limited range always a holohedral contact of the retaining cam to the base plate remains ensured (via the spherical washer), contrary to prior art, where even a minor angular deviation may lead to canting and thus prevent a holohedral contact of the retaining cam to the base plate. A rotatable fastener equipped with the retaining cam according to the invention also allows the fastening of curved panels or the like to the fuselage frame without any problems. Due to the fact that variable angular deviations can be compensated, fewer expenses are incurred at the structure to fasten the retaining cam in the correct position. In general, the retaining cam according to the invention allows an additional way to compensate tolerances. 
     Further advantageous embodiments of the retaining cams according to the invention are described in the dependent claims. 
     When in an embodiment of the retaining cam according to the invention of a facial opening of the housing, adjacent to the base plate, is provided with supporting projections diametrically opposed each other, which engage the neighboring support openings of the base plate, the spherical washer can easily be arranged between the base plate and the housing by simply embodying the support openings of the base plate in an appropriately larger size. 
     When in another embodiment of the retaining cam according to the invention the spherical washer is provided with another diametrically opposite additional support projection, also engaging the support openings of the base plate, the assembly and fastening of the spherical washer is facilitated between the base plate and the housing. 
     In another embodiment of the retaining cam according to the invention, a contact area of the housing, extending around the face of the opening, is embodied complementary in reference to the spherical area of the spherical washer so that the holohedral surface contact of the housing is always ensured regardless of the angular position of the housing in reference to the base plate. 
     In another embodiment of the retaining cam according to the invention, the housing is pivotal by a total of 10° in reference to a central plane extending through the center of the support plate and the support openings, so that according to experience the range of angular deviations expected in practices is covered. 
     In another embodiment of the retaining cam according to the invention, the housing is pivoted by a total of 10° around an axis extending perpendicular in reference to a central plane, the retaining cam can compensate arbitrary angular deviations between the axes of the rotatable fastener parts to be screwed together. 
     In another embodiment of the retaining cam according to the invention, the ability of the housing to pivot is enabled by sufficient play of at least the supporting projections of the housing in the support openings of the base plate, and the retaining cams require only minor modifications from the standard embodiment, except for the additionally provided spherical washer, by selecting appropriately greater support openings of the base plate. 
     In another embodiment of the retaining cams according to the invention, the screw inserted in the housing comprises a high-strength material, so that higher forces can easily be transferred compared to using with conventional retaining cams. In this case, beneficially the rotatable fastener is also made from a high-strength material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, exemplary embodiments of the invention are described in greater detail using the drawings. They show: 
         FIG. 1  is an exploded perspective view of a rotatable fastener comprising a retaining cam according to the invention and two components to be connected therewith, 
         FIG. 2  is a partially longitudinal cross-sectional view of a rotatable fastener comprising a retaining cam according to the invention, namely in  FIG. 2   a  a retaining cam fastened at a fuselage frame and in  FIG. 2   b  a fastening pin fastened at an interior cover panel, 
         FIG. 3  is a detail A of the indicated area in  FIG. 2   a,    
         FIG. 4  is two side views of the rotatable fastener according to  FIG. 1 , offset by 90° in reference to each other, (omitting the components connected therewith), the maximally possible pivotal position of the exemplary embodiment of the retaining cam according to the invention shown in reference to its base plate, 
         FIG. 5  is a perspective view of the retaining cams according to the invention in a view from the bottom, 
         FIG. 6  is a side view of the retaining cams according to  FIG. 5 , 
         FIG. 7  is a cross-sectional view of the retaining cams according to the invention taken along the line VII-VII in  FIG. 6 , 
         FIG. 8  is an exploded perspective view of the retaining cam according to the invention, 
         FIG. 9  is a top view of a spherical washer of the retaining cam according to the invention showing the spherical area, 
         FIG. 10  is a cross-sectional view of the spherical washer taken along the line X-X in  FIG. 9 , 
         FIG. 11  is a perspective view of a housing of the retaining cam according to the invention, 
         FIG. 12  is a longitudinal cross-sectional view of the housing according to  FIG. 11 , 
         FIG. 13  is a detail A of the illustration in  FIG. 12 , and 
         FIG. 14  is a top view of the housing according to  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a perspective and exploded view,  FIG. 1  shows a rotatable fastener, in its entirety marked  15 , for connecting two components  16  and  17  under elastic pre-tension. The component  16  may be an interior cover panel in the cabin of an airplane, with then the component  17  symbolizing the fuselage frame. The rotatable fastener  15  comprises a retaining cam, in its entirety marked  20 , and a fastening pin  40 . According to the illustration in  FIGS. 2   a  and  2   b , which are additionally being referenced in the following, the retaining cam  20  comprises a housing  22  and a base plate  24 , on which the housing  22  is supported in a pivotal fashion. Via the base plate  24  the retaining cam  20  can be connected to the component  17  in a fixed fashion, in the exemplary embodiment shown with the help of two rivets  25 .  FIG. 2   a  shows the finished rivet connection. The fastening pin  40  is held rotational but captively in a bore in the component  16 , namely with the help of two washers  26 ,  27  and cir-clip  28 . A screw  30  ( FIG. 2   a ) is inserted in a rotationally fixed fashion into the housing  22  of the retaining cam  20 , which is explained in greater detail in the following. According to  FIG. 2   b , the fastening pin  40  comprises a bore  41  with an internal thread  42 , by which it can be screwed onto an external thread  44  of the screw  30 , shown in  FIG. 3 . According to the illustration in  FIGS. 2 and 3  the housing  22  is supported on the base plate  24  via a spherical washer  50  in a pivotal manner. It is now described in greater detail with reference to the illustrations of the other  FIGS. 5-14 . 
       FIG. 5  shows the retaining cam  20  in a perspective illustration in a view from the bottom.  FIG. 6  shows the retaining cam  20  in a side view,  FIG. 7  in a longitudinal cross-section according to the line VII-VII in  FIG. 6 , and  FIG. 8  in an exploded illustration. At a facial opening adjacent to the base plate  24  the housing  22  is provided with two diametrically opposite support projections  32 , which engage two neighboring support openings  34  of the base plate  24 . The spherical washer  50  is provided with additional support projections  52  diametrically opposite each other, which also engage the support openings  34  of the base plate  24 , as discernible in  FIGS. 4-7 . The support openings  34  of the base plate  24  are sized such that the housing  22  is pivotal by a total of 10° in reference to a central plane extending through a center  36  of the support plate  24  and the support openings  34 . Due to this construction the retaining cam  20  allows an angular compensation of up to 5° per side.  FIG. 4  shows in two side views of the rotatable fastener  15  according to  FIG. 1 , which are off-set by 90° in reference to each other, (and omitting the components  16 ,  17  that are to be connected to each other) the maximally possible pivotal positions of the exemplary embodiment of the retaining cam  20  shown in reference to its base plate  24 . In  FIGS. 4   a  and  4   b  the rotatable fastener  15  is shown pivoted by 5° to the left and by 5° to the right each, i.e. by 10° each, respectively. The ability of the housing  22  of the retaining cam  20  to pivot is allowed by sufficient play of at least the supporting projections  32  of the housing  22  in the support openings  34  of the base plate  24 . It is generally sufficient for the support projections  32  of the housing  22  to have sufficient play, because the spherical washer  50  remains compressed to the bottom of the base plate  24  when the housing  22  is pivoted in reference to the base plate  24  and thus the support projections  32  are pivoted in the support openings  34 . 
     In order to ensure the contact of the spherical washer  50  to the base plate  24  and the pivotal holohedral contact of the housing  22  to the spherical washer  50 , the spherical washer comprises, according to the illustration in  FIGS. 9 and 10 , a plane area  54  and on its side opposite the plane area a spherical area  56 , having a radius of curvature R. More precisely, the spherical area  56  represents the circular surface of a section of a sphere having the radius R. According to the illustration in  FIGS. 12-14 , a contact surface  29  of the housing  22 , extending around a facial opening  23 , adjacent to the base plate  24 , is embodied complementary to the spherical surface  56  of the spherical washer  50 , i.e. it has the same radius of curvature R. Regardless of the angular position of the housing  22  in reference to the base plate  24 , the housing  24  remains in a holohedral contact to the spherical washer  50  and thus, via the plane area  54 , also in a holohedral contact to the base plate  24  when the axis of the fastener bolt  50  and the central axis  36  of the screw  30  and thus the housing  22  are aligned to each other, however said axes are not perpendicular in reference to the base plate  24 . 
     The assembly of the retaining cam  20  according to the invention differs from the assembly of the standard retaining cam of the type mentioned at the outset primarily such that the spherical washer  50  is additionally to be inserted between the housing  22  and the base plate  24 . Prior to the assembly the housing  22  is completely cylindrical at the end opposite the support projections  32 , i.e. it is embodied as shown in  FIG. 11 , however differing from the one shown in  FIGS. 7 and 8 . Namely, during the assembly first the screw  30  is inserted into the housing  22  together with two helical compression springs  60  and  62  having small and/or large diameters and two sprockets  64  and  66 , embodied with teeth at their facing sides. At its interior the housing  22  has two diametrically opposite grooves  68 ,  70 . The screw  30  and the sprocket  64  each have two radial projections  72  and/or  74 , diametrically opposite each other, with only one of the two projections  72  being visible in  FIG. 8 . During the assembly the projections  72  and  74  are inserted into the grooves  68 ,  70  and prevent any rotation of the screw  30  and/or the sprocket  64 . When the screw  30  is inserted into the housing  22  to such an extent as shown in  FIG. 7 , the exterior circumferential perimeter of the housing  72 , initially embodied cylindrical, is compressed inwardly as shown in  FIGS. 7 and 8  in order to encompass the screw  30  in the housing  22 . Here, the sprocket  64  remains axially displaceable; the same applies to the sprocket  66 , with its teeth engaging the teeth of the sprocket  64  in a detachable, form-fitting manner. The sprocket  66  has at its lower face, shown in  FIG. 8 , two catching protrusions engaging a groove  46  in the face of the fastener bolt  40  in a form-fitting fashion, when the fastener bolt  40  is screwed onto the screw  30  of the retaining cam  20 . In order to allow rotation, at the end opposite the groove  46 , the fastener bolt  40  comprises a TORX style connection  48 . When rotated the fastener bolt  40  entrains the sprocket  66 . During the rotation of the sprocket  66  the sprocket  64  can be deflected in the axially opposite direction, due to the springs  60  and  62  such that the sprocket  66  moves like a ratchet over the sprocket  64  until the fastener pin  40  has reached its final position. The ultimately remaining, elastically pre-tensioned mutual engagement of the teeth of the sprockets  64 ,  66  ensures that the screwed connection between the fastener bolt  40  and the retaining cam  20  cannot unintentionally loosen, even under strongest stress or vibration of the rotatable fastener  15 . The elastic pre-tension necessary to prevent any rotation of the rotatable fastener  40  is applied by the springs  60 ,  62 . 
     The base plate  24  has two approximately perpendicularly bent support eyelets, in which the support eyelets  34  are embodied diametrically opposite in reference to each other. Successively, the spherical washer  50  with its support projections  52  and the housing  22 , in which the above-described components have been assembled, are also inserted in the support openings  34  with their support projections  52 ,  32 . The support projections  52  and  32  can be inserted on a side into the support opening  34 . Subsequently, pressure can be applied at the opposite side by the opposite support projections  52  and  32  onto the adjacent support eyelet, with the support eyelet elastically deflecting and allowing the support projections  52  and  32  to pass until they have been accepted by the allocated support opening  34 . The play of at least the support projections  32  in the support openings  34  is here sized such that the housing  22  can be pivoted relative to the central plane extending through the center of the support plate  24  and the support openings  34  and around an axis extending perpendicular in reference to the central plane by a total of up to 10° each. The cross-sectional line VII-VII according to  FIG. 6  is located in the above-mentioned central plane of the cross-sectional illustration in  FIG. 7 . 
     The screw  30  inserted into the housing  22  comprises a high-strength material, preferably a high-strength stainless steel, which is malleable for producing the external thread  44 . The external thread  44  produced by cold processing is subsequently hardened and additionally coated with a sliding lacquer. Suitable are, for example, the material 1.4016/DIN EN 10263-5. Preferably the fastener bolt  40  is also made from stainless steel, with here rather a steel being used that can be processed in a cutting fashion. The material 1.40301/EN 10088-3A is a suitable material for the base plate  24 . 
     LIST OF REFERENCE CHARACTERS 
     
         
         
           
               15  Rotatable fastener 
               16  Component 
               17  Component 
               20  Retaining cam 
               22  Housing 
               23  Facial opening 
               24  Base plate 
               25  Rivet 
               26  Washer 
               27  Washer 
               28  Cir-clip 
               29  Support area 
               30  Screw 
               32  Support projection 
               34  Support openings 
               36  Central axis 
               40  Fastening bolt 
               41  Bore 
               42  Internal thread 
               44  External thread 
               46  Groove 
               48  TORX-style connection 
               50  Spherical washer 
               52  Support projections 
               54  Plane area 
               56  Spherical surface 
               60  Pressure spring 
               62  Pressure spring 
               64  Sprocket 
               66  Sprocket 
               68  Groove 
               70  Groove 
               72  Radial projections 
               74  Radial projections