QUICK-FIXING ASSEMBLY FOR, E.G., A SWITCH DEVICE

Abstract: The present invention is related to a fixing assembly for use in, e.g., a switch device, said assembly comprising a female element (10) in the first piece (21) to be connected and a male element (12) in the second piece (18) to be connected. According to the invention, the male element (12) is elongated and elastic and has its end (14) provided with at least one locking surface (15), and the female element (10) comprises at least one locking shoulder (11) and a corresponding widening recess (19) of the female element passageway for the purpose of permitting the entry of a locking surface (15) of the end (14) of the male element (12) to the rear of the locking shoulder (11) into a locking position by way of a twisting/untwisting motion.

Description: Quick-fixing assembly for, e.g., a switch device The present invention is related to a fixing assembly for, e.g., a svvitch device according to the preamble of claim 1. Conventionally, pieces are fixed to each other among other methods by means of, e.g., a screw connection formed by a screw plus a compatible inner thread on the counter piece. Also used is a bolt connection in which the nut is separate or a threaded insert is cast integral with the counter piece already in the mold. Further, a self-tapping screw can be used. Quick-fixing can be implemented using, e.g., snap-action flat spring clips between which the piece to be fixed is clamped. Also known in the art are plastic clips designed to snap-lock against a mating surface with the help of backing surfaces. The above-described techniques are hampered by a plurality of drawbacks. Screw connection is not preferred in series-production because of its time-consuming char¬ acter. Moreover, accurate tolerancing is required to achieve suitable fixing tightness, since an excessively loose fixing may permit separation ofthe pieces while a too tight fixing may in turn overtorque the threads. Both the spring and plastic clip fixing methods have the disadvantage of subjecting the fixing to a continuous bending stress due to the cantilever-type of clip leg tensioning which in the long run leads to fatigue ofthe spring/elastic material. The clips will release easily when the pieces are subjected to a separating pull force. In demanding fixings, spring and plastic clips can be opened too easily. While the grip of plastic clips can be improved through the use of steep angles on the mating surfaces ofthe snap connection, such a nearly perpendicular angle results in a disadvantageous end clearance. Pieces may also be connected by ultrasonic welding, which requires substantial investments in machinery. Moreover, this method of connection necessitates maximum planarity and cleanness from the surfaces to be welded together. Due to wide quality variations, the strength ofthe welds cannot be estimated sufficiently accurately. Furthermore, the number of materials suitable for ultrasonic welding is limited. It is an object ofthe present invention to overcome the drawbacks ofthe above- described fixing techniques and to provide an entirely novel type of fixing assembly suitable for use in, e.g., switch devices. The goal ofthe invention is achieved by combining the fixing assembly from such a female element and a male element in which the male element is a flexible reed-like lug member adapted to twist about its longitudinal axis during the locking step and then returns back to its stress-free state at the completion ofthe locking step. More specifically, the fixing assembly according to the invention is characterized by what is stated in the characterizing part of claim 1. The invention offers significant benefits. When locked, the leg ofthe male element is free from a twisting/bending stress. Provided that the number of symmetrical lug hooks is two, the leg ofthe male element will be subjected to a tensile stress alone under a pulling force separating the pieces from each other. The required amount of end clearance is close to zero even in a self- locking fixing assembly. The assembly according to the invention is also especially suitable for such a demanding fixing application in which the pieces must be positively fixed to each other. The fixing assembly requires no auxiliary parts and can be implemented in tight places. Pieces provided with the present fixing assembly are easy to assemble and when required can be made difficult to open. For the purpose of aiding the release step, the space reserved for unfixing with fingers can be designed larger as desired. The pieces will stay positively fixed without using an additional locking edge on the mating surfaces. The assembly according to the invention is also suitable for fixing metallic pieces if the fixing lug hooks are made from an elastic material. Finally, secured fixing can be readily verified visually. In the following, the invention will be examined in more detail with the help of exem¬ plifying embodiments by making reference to the attached drawings, in which: Figures la - lb show a fixing embodiment according to the prior art; Figures 2a - 2b show another fixing embodiment according to the prior art; Figures 3a - 3j show a fixing embodiment according to the invention in different projections; Figure 4 shows an opening device suitable for releasing the fixing assembly according to the invention; Figure 5 shows a perspective view ofthe cover and body structures of a switch device incorporating the fixing assemblies according to the invention; Figure 6 shows in a rear view ofthe body part of a switch device provided with the female fixing elements according to the invention but without having the male fixing elements yet inserted; and Figure 7 shows the embodiment of Fig. 6 with the male fixing elements now inserted in place. Referring to Fig. 1 a, the embodiment shown therein has the conventional flat spring clips 1 still apart from the pieces 2 to be fixed. In Fig. lb the clips 1 are shown placed fixing the pieces 2. As is evident from the latter diagram, the clips 1 remain under a continuous bending stress when mounted in place. Referring to Fig. 2a, therein are correspondingly illustrated a plastic body piece 4 and a counter piece 3 forming a conventional fixing assembly based on hooked cantilever lugs 5 ofthe counter piece 3 and the preload tension 6 ofthe hooked lugs 5. The embodiment shown in Fig. 2b requires an end clearance 7. This is because the positive locking ofthe fixing assembly necessitates the use of a locking angle α greater than zero for the tips ofthe fixing lugs 5, whereby the insertion ofthe piece requires said end clearance 7. However, such an end clearance 7 degrades the rigidity ofthe fixing. Referring to Fig. 3 a, in the assembly according to the invention shown therein, the female element 10 is designed integral with the other piece to be fixed, which in the present case is a body piece 21. In the illustrated embodiment the female element 10 comprises a narrow and elongated passageway. The female element 10 has a width- to-height ratio of approx. 1:3 - 1:5 typical, advantageously approx. 1:4. To the top and bottom inner wall corners ofthe passageway forming the female element 10 shown in the diagram, at the opposite sides ofthe passageway, are made locking shoulders 11, whereby also corresponding widening recesses 19 ofthe passageway as shown in Figs. 3f and 3d are made to the sides opposing said locking shoulders. In Fig. 3d is shown a section along line A - A of Fig. 3 a. The widening recesses 19 have a width approximately equal to the basic width ofthe passageway in the female element 10. Acting as the male fixing element, the fixing lug 12 shown in Fig. 3b is inserted during the fixing step into the female fixing element 10, whereby the end 14 ofthe leg ofthe male fixing lug is twisted by the guide surfaces 20 ofthe locking shoulders 11, whereby the end 14 ofthe fixing lug is guided into the widening recesses 19 ofthe passageway in the manner shown in Fig. 3j. As the fixing lug 12 reaches its final locking position as shown in Fig. 3h, the locking surface 15 ofthe lug will be locked behind the shoulder 11 in a positive manner and the leg ofthe lug 12 can untwist back into the stress-free state as shown in Fig. 3i. The stress-free state is particularly attained in a design having two locking shoulders 11 and two locking surfaces 15. As is evident from the diagrams, the outside dimensions ofthe lug end 14 are essentially equal to the inside dimensions ofthe female element 10. It must be noted that Figs. 3i and 3j are projections taken from direction D marked in Fig. 3h. In turn, Fig. 3h is a sectional view along direction C - C marked in Fig. 3i. In Fig. 3c the female element is viewed without the insertion ofthe male element from direction E marked in Fig. 3 a. In Figs. 3b and 3j are illustrated the bevels 16 that are provided to aid the insertion ofthe end 14 ofthe fixing lug 12 through the passageway ofthe female element 10. A precondition to the function ofthe present invention is that the leg 13 ofthe fixing lug 12 is be made sufficiently elastic to provide the required twisting action. To assure the strength ofthe fixing lug 12, the stem section 17 is designed wider than the elastic leg section 13. The stem section 17 joins with one of the pieces to be fixed together which in the illustrated case is the cover 18 of a switch device. When required, the locking can be assured by forming an angle α greater than zero to locking shoulder 11 and the locking surface 15 ofthe fixing lug. However, such an angle is not mandatory for the function ofthe embodiment according to the invention. Referring to Fig. 4, an unlocking tool 22 is shown therein comprising finger surfaces 23 on which the opening force is imposed and a shaft 24 ofthe tool having unlocking tips 25 provided at the shaft end. The unlocking tool 22 is first inserted into the passageway so that the unlocking tips 25 are aligned on both sides ofthe end 14 of the fixing lug 12 and then the tool 22 is rotated and pushed, whereby the end 14 of the fixing lug 12 is guided past the locking shoulders 11 via the passageway widening recesses 19 out from the locking space. Referring to Fig. 5, the number ofthe fixing lugs 12 can be, e.g., four. In the illustrated embodiment, the fixing lugs 12 are permanently fixed to the cover 18 ofthe switch device, while the female elements 10 are correspondingly situated in the body piece 21. The ends 14 ofthe fixing lugs 12 extend inside the locking space approximately level with the rear surface ofthe body piece 21. Referring to Fig. 6, a rear view ofthe body piece 21 is shown therein. In the illustrated structure both the locking shoulders 11 and the passageway widening recesses 19 formed at the shoulders are clearly visible in the female elements 10. Respectively, in Fig. 7 the fixing lugs are shown inserted in place and the ends 14 of the fixing lugs are visible. The ends 14 ofthe fixing lugs are approximately level with the rear suiface ofthe body piece 21. Instead ofthe four fixing lugs 12 shown in the diagrams, two fixing lugs or other suitable number ofthe fixing assemblies can be used. An essential property to the function ofthe invention is the twisting and untwisting locking motion ofthe end 14 ofthe fixing lug, which permits the lug leg to assume a stress-free state in the locked position. Accordingly, also other cross-sectional shapes than a flat leg are possible for the fixing lug including a leg with a round section, too, if the material ofthe fixing lug leg is selected from the group of materials permitting a twisting motion. Hence, a leg with an annular cross section is feasible provided that the lug leg is designed to have sufficient flexibility. According to the invention, the male element 12 may alternatively be integrated with the body piece 21, whereby the female element 10 is obviously integrated with the cover piece 18. Without departing from the scope ofthe invention, the number ofthe locking shoulders 11 in each assembly can be only one, whereby also only one passageway widening recess 19 is needed. In a typical embodiment ofthe invention, the pieces fixed together will not be dismounted any more, whereby the fixing method disclosed herein is an optimal solu¬ tion. When a greater number ofthe present type of fixing assemblies are employed in a single housing construction, dismounting ofthe housing becomes complicated without the use of special tools, since each fixing assembly must be unlocked simultaneously. However, dedicated tools can be developed to accomplish this task. The assembly according to the invention is typically made from a thermoplastic polymer, but thermosetting polymers and metals may also be used as the material of the assembly.

Claims: Claims: 1. A fixing assembly for use in, e.g., a switch device, said assembly comprising - a female element (10) in the first piece (21) to be connected, and - a male element (12) in the second piece (18) to be connected, characterized in that - the male element (12) is elongated and elastic and has its end (14) provided with at least one locking surface (15), and - the female element (10) comprises at least one locking shoulder (11) and a corresponding widening recess (19) ofthe female element passageway for the purpose of permitting the entry of a locking surface (15) ofthe end (14) ofthe male element (12) to the rear ofthe locking shoulder (11) into a locking position by way of a twistinguntwisting motion. 2. A fixing assembly as defined in claim 1, characterized in that said female element (10) is a narrow and elongated slot-like passageway. 3. A fixing assembly as defined in claim 1, characterized in that the number of said locking shoulders (11) on each female element (10) is two, and correspondingly, the number of locking surfaces (15) on each male element (12) is t o. 4. A fixing assembly as defined in any foregoing claim, characterized in that each locking shoulder (11) incoφorates a guide surface (20) for the purpose of guiding the end (14) ofthe fixing lug into a twisting motion. 5. A fixing assembly as defined in any foregoing claim, characterized in that the end (14) ofthe fixing lug incorporates bevels (16) serving to aid the sliding motion ofthe fixing lug.

Inventors: VUORINEN VALTO, VUORINEN, VALTO
Applicants: ABB STROEMBERG KOJEET OY, VUORINEN VALTO, VUORINEN, VALTO
Application year: 1996
Main classification: H01H9
IPC codes: H02B1, H05K5