Abstract:
For fastening a flow rectifier and a grid in an air flow rate meter, until now two elements have been used, one for the sake of cushioning and the other for the sake of securing. The novel fastening element combines both functions in one element. The fastening element is embodied in undulating fashion and can be deformed in its radial dimension.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00/01852 filed on Jun. 7, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is directed to an improved fastening element and more particularly to such fastening elements for fastening components in an opening, and on a method, of fastening element in an opening. 
     2. Description of the Prior Art 
     It is already known (German Patent Disclosure DE 196 47 086 A1), in an opening of an air flow rate meter that is used to measure the mass or flow rate of a flowing medium, to secure components, that is, a flow rectifier and a grid, axially in an opening with detent hooks and to achieve an axial compensation with spring elements. The spring elements are embodied integrally on the grid and are joined to the grid via a narrow connection region provided on an outer edge of the grid. The spring elements rest on a stop in the opening of the air flow rate meter. For permanent fastening and securing of the components in the opening, the flow rectifier has arrow-shaped detent hooks, which protrude radially outward somewhat past its outer face, and which can snap into an encompassing groove provided in the inner wall of the opening. Upon introduction of the flow rectifier into the opening, the spring elements are deformed elastically and exert a spring force on the flow rectifier. When the flow rectifier reaches its installation position, the detent hooks snap into the groove and permanently hold the flow rectifier in the opening with the aid of the spring force of the spring elements. The disadvantages arise that the spring elements have to be produced and mounted individually, and that elements second, namely the detent hooks, are necessary in order to fasten the components permanently. 
     U.S. Pat. No. 5,738,059 discloses an open form of a ring embodied in undulating form for use in a coupling element. However, in that case only the spring action of the ring is exploited. It is widely known for components to be fastened in an opening with a spring ring or spring disk and a snap ring on an opposed face end of the component. 
     SUMMARY OF THE INVENTION 
     The fastening element of the invention and the method, has the advantage over the prior art that in an especially simple way, at least one component can be fastened in an opening. A further advantage is considered to be that the use of a single element for the fastening, that is, for the axial securing, which at the same time accomplishes an axial compensation, for the at least one component accommodated and resting completely in an opening of an air flow rate meter, reduces the number of elements from two to one. This lowers the production costs. Furthermore, the need to check for the presence and operability of one further element is dispensed with. The compact construction of the fastening element makes easy installation possible and thus enables a high degree of automation. This leads to a further reduction in installation times and production costs. The tools required to mount the fastening element are in part already present or are very simple and therefore inexpensive. 
     It is advantageous to use the fastening element with a closed ringlike form, because this makes for easy manipulation upon installation. It is also advantageous to use the fastening element with an open ringlike form and a certain outer edge length, as a result of which very secure fastening can be achieved even under very high shaking stresses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will be apparent from the detailed description contained below, taken with the drawings, in which: 
     FIGS. 1 a-c  are fragmentary sectional views showing a plurality of arrangements of an opening with a stop for a component, with a stop edge for the fastening element, and with a component located on the inside along with a fastening element; 
     FIG. 2 is an elevation view of an air flow rate meter with portions broken away and embodying two components and one fastening element according to the invention; 
     FIGS. 3 a-c  show a first exemplary embodiment of the fastening element in a plan view, a side view, and a three-dimensional view, respectively; 
     FIG. 4 shows a schematic arrangement of a tool on a fastening element; 
     FIG. 5 is an enlarged detail of FIG. 2; 
     FIGS. 6 a-c  show a plan view, side view and three-dimensional view of a second exemplary embodiment of the fastening element; and 
     FIG. 7 shows a schematic arrangement of a tool on a fastening element for the second exemplary embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings in detail FIG. 1 a  shows how a component  24 , for instance, rests on a stop  15  in an opening  10  that has a wall  16  and is fastened in the opening  10  by means of a fastening element  1 , which rests in a groove  18  and on the component  24 . The groove  18  and the stop  15 , in this example, are both a component of a single tube  28 . The stop  15  can be embodied not only in the form of a shoulder; it can also be a face that fills the opening  10 . For installation, the component  24  is introduced into the opening  10  to the stop  15 , and then the fastening element  1  is introduced. The installation will be explained in more detail and precision in conjunction with FIG.  4 . 
     FIG. 1 b  shows that the stop  15  can also be a component of a second tube  29 , which is joined to the first tube  28 , for instance by a thread  38 . 
     FIG. 1 c  shows that the fastening element  1  can rest not only in a groove but also against a stop edge  20  that protrudes into the opening  10 . For installation, the component  24  is introduced into the opening  10  of the tube  28  on the opposed side of the stop edge  20 . The tube  28  is then joined to the tube  29 , so that the fastening element  1  can then be introduced. 
     FIG. 2 shows an air flow rate meter  30  in partial cross section. The air flow rate meter  30  has a measurement part  31 , which is introduced for instance into an insertion opening made in a wall  16  of a measurement stub  32 . The construction of such a measurement part  31  with a measuring element  35  is adequately well known to one skilled in the art, for instance from German Published, Nonexamined Patent Application DE-OS 44 07 209, whose disclosure is hereby incorporated into the present patent application by reference. The wall  16  defines a flow cross section, which for example has a circular cross section, in the middle. of which a center axis  34  extends in the direction  33  of the flowing medium, parallel to the wall  16 . The direction of the flowing medium is indicated by corresponding arrows  33  and extends there from left to right. 
     A measuring element  35  is introduced with the measurement part  31  into the flowing medium. In the measurement part  31  of the device  30  a measurement channel  36  is formed, in which the measuring element  35  is accommodated for measuring the medium that flows in the measurement stub  32 . Upstream of the measuring element  35 , a flow rectifier  11  with a grid  13  is provided. Downstream of the flow rectifier  11 , a carrier ring  14  is provided, which supports the grid  13 . 
     For installing the grid  13 , the grid is introduced together with the carrier ring  14  into an opening  10 , for instance a circular opening, provided on the upstream end of the measurement stub  32 , until the carrier ring  14  contacts a stop  15 . Next, the flow rectifier  11  can be inserted into the opening  10 , until it contacts the carrier ring  14 . For permanently fastening the flow rectifier  11  to the grid  13 , a fastening element  1  embodied according to the invention is used. The fastening element  1  rests in a groove  18  and on the stop edge  20  thereof (FIG. 5) as well as on the flow rectifier  11 . 
     A first exemplary embodiment of the fastening element  1  embodied according to the invention is shown in FIGS. 3 a - 3   c.  The outer contour of the annular fastening element  1  has a circular shape in this example (FIG. 3 a ). A line  2  normal  2  to the area defined by the contour line emerges at a right angle from the plane of the drawing, or in other words extends parallel to the center line of the fastening element  1 . The thickness of the fastening element  1  is 0.25 mm, for example. The outside diameter of the fastening element  1  is approximately equal to the outside diameter of the flow rectifier  11  and at maximum is equal to the inside diameter of the opening  10  in FIG. 5 at the level of an edge  19  that is opposite the stop edge  20  (FIG.  5 ). The inside diameter of the fastening element  1  is not limited. A larger inside diameter of the fastening element  1  in the installed state, compared to the inside diameter of the fastening ring  37  of the flow rectifier  11  (FIG. 2) is advantageous. 
     In the side view (FIG. 3 b ), it can be seen clearly that the fastening element  1  is embodied in undulating form in the direction of the normal  2 . The difference in height between the crest  3  and trough  8  of the undulation is 5 mm, for example. Four crests  3 , each offset by 90°, can be seen in FIG. 3 c.  The embodiment of such a fastening element is not limited to this number of undulation crests and troughs or to their uniform distribution. The fastening element  1  is expediently made from plastic or metal. 
     FIG. 4 shows schematically how, with a tool  25 , for instance, a force F is exerted on the spring ring in the direction of the arrows  22  and how this spring ring is radially deformed in the direction of the arrows  26  when a suitable underlay, such as the components resting on the stop  15 , is present. The tool  25  here is a tube, for instance. The contacts of the tool  25  with the fastening element  1  and therefore the engagement points for the force are the undulation crests  3 . The outside diameter of the tube  25  is at most as large as that of the fastening ring  37 , and the thickness of the tube does not need to be any wider than the width of the fastening element  1 , although it can also be thicker. 
     The fastening element  1  is deformed elastically by the tool  25  primarily in such a way that it enters the groove  18 . Because the outside diameter has become greater as a result, it now projects permanently far enough into the groove  18  and engages the stop edge  20  (FIG. 5) and the flow rectifier  11 . The fastening element  1  thus acts as a securing ring. As a result of the deformation, the difference between the undulation crest  3  and the undulation trough  8  has lessened or even vanished. The original difference, however, is dimensioned such that after deformation of the fastening element  1 , this difference, plus the thickness of the fastening element  1 , is approximately equal to the spacing between the stop edge  20  and the face end  21  (FIG. 5) of the component, in this case the flow rectifier  11 . The undulating embodiment of the fastening element achieves a spring action in the direction  33  of the fluid flow and as a result acts as an axial compensation element. 
     A fastening element  1 , of the kind described in the first exemplary embodiment, can also be open or in other words can have a gap. In return, however, the width of this gap must be dimensioned such that as a result of the deformation upon installation, the two ends abut one another, with an ensuing increase in the outside diameter. 
     A second exemplary embodiment of a fastening element  4  embodied according to the invention is shown in FIGS. 6 a - 6   c.  The outer contour of the annular fastening element  4  has an open circular shape in this example (FIG. 6 a ). A normal  2  to the area defined by the contour line emerges at a right angle from the plane of the drawing, or in other words extends parallel to the center line of the fastening element  4 . The outer edge  9  extends along the fastening element  4  from a point  9   a  located at the gap to one opposed point  9   b,  and the length of the outer edge, in proportion to the diameter of the opening  10  at the level  23  (FIG. 5) of the stop edge  20  of the flow rectifier  11 , is greater than 1:2. 
     The cutting edges through the points  9   a  and  9   b  at the ends  6  of the, fastening element  4  are parallel to one another here. However, this is not absolutely compulsory. The spacing between these cutting edges is 25 mm, for instance. In the vicinity of the ends, for instance centrally, two holes with engagement faces  42  and with a diameter of 1.5 mm, for instance, are drilled into the fastening element  4 . The thickness of the fastening element  4  is 0.8 mm, for instance. The greatest and least radial length defined by the open ring will hereinafter be called the outside diameter  40  and inside diameter  41 , respectively, of the fastening element  4 . The outside diameter  40  of the fastening element  4  is greater than the outside diameter of the flow rectifier  11  and thus also greater than the inside diameter of the opening  10  in FIG. 5 at the level of the edge  19 , which is opposite the stop edge  20 . The inside diameter  41  of the fastening element  4  is not limited. It is advantageous if the inside diameter  41  of the fastening element  4  in the installed state is greater than the inside diameter of the fastening ring  37  of the flow rectifier  11 . 
     In the side view (FIG. 6 b ), it can be seen clearly that the fastening element  4  is embodied in undulating fashion in the direction of the normal  2 . The difference between the crest  3  and trough  8  of the undulation is 2.3 mm, for instance. In FIG. 6 c,  four troughs  8  of the undulation can be seen, offset by 90° from each other. The embodiment of the fastening element  4  is not limited to this number or to a uniform distribution of the undulation crests and troughs. The cutout for producing the gap for the open ring can be made in any region of the fastening element  4 . In this example, one undulation crest has been removed. The fastening element  4  is expediently made from plastic or metal. 
     The disposition of the fastening element  4  in the air flow rate meter  30  is equivalent to the arrangement described for the first exemplary embodiment. 
     FIG. 7 schematically shows how, for instance with a suitable gripping tool  43 , a force F is exerted in the direction of the arrows  27  on the fastening element  4 , and how the fastening element is deformed in the direction of the arrows  27 . For introducing the fastening element  4  into the air flow rate meter  30 , the fastening element  4  is deformed, by means of the gripping tool, which protrudes into the holes  5  and engages the engagement faces  42 , by an expenditure of force in such a way that the two ends  6  of the fastening element  4  are made to approach one another in the direction of the arrows  27 . As a result, the fastening element  4  is deformed in such a way that its outside diameter becomes enough smaller that it can be introduced into the opening  10  at the level of the stop edge  20  so that it rests horizontally on the flow rectifier  11 . The force on the gripping tool  43  and thus on fastening element  4  is then reduced, and as a result the fastening element  4  presses against the wall  16 . With a pressing tool, in a manner similar to the description of the first exemplary embodiment, the fastening element  4  is pressed flat in such a way that the difference between the trough and crest of the undulation is equal to or less than the difference between the face end  21  of the component and the stop edge  20  in the opening. As a result, the fastening element snaps into the groove  18 , and because of this the outside diameter  40  of the fastening element  4  increases again. After the pressing tool has been removed, the fastening element  4  now permanently protrudes far enough into the groove  18  and engages both the stop edge  20  and the flow rectifier  11  and thus acts as a securing ring. 
     As a result of the deformation, the difference between the undulation crest  3  and the undulation trough  8  has lessened or even vanished. The original difference, however, is dimensioned such that after deformation of the fastening element  4 , this difference, plus the thickness of the fastening element  4 , is approximately equal to the spacing between the stop edge  20  of the groove  18  and the face end  21  (FIG. 5) of the component, in this case the flow rectifier  11 . The undulating embodiment of the fastening element achieves a it spring action in the direction of the flow direction  33  and as a result acts as an axial compensation element. 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.