Fasteningelementforawiperarm,andmethodofm……

1、Fastening element for a wiper arm, and method of manufacturing the same            BACKGROUND OF THE INVENTIONThe invention is based on a fastening element for a wiper arm, and on a method for producing it.Fastening elements for windshield

2、wipers, particularly for the wiper arm, often comprise zinc or a zinc alloy and are made by pressure casting a pressure casting mold. The zinc can be processed very well, is gentle to the pressure casting tool, and makes very good surface qualities possible. However, it has been found that zinc chan

3、ges its microstructure in stressed regions over the course of time. The material becomes brittle, which increases the risk of breakage. This occurs to an increased extent in relatively long fastening elements because of the greater bending stresses and particularly at the connection points to adjoin

4、ing components, such as in the region of a conical hub of the fastening element, which is pressed by means of a nut onto a knurled conical drive shaft of a windshield wiper drive mechanism. This creates tensile strains which are superimposed on the bending stresses, thus increasing the risk of break

5、age still further.From European Patent Disclosure EP 0 584 018 A1, a fastening element with a sheet-metal part coated with plastic is known. The sheet-metal part has a conical hub on one end and a bearing point for a shaft on the other. In the region of the bearing point, the sheet-metal part protru

6、des with a curved portion out of the plastic, and in this portion there is a hole for suspending a tension spring. On its outer circumference in the region of the conical hub, the sheet-metal part has recesses or notches, so that a favorable form lock with be achieved between the plastic sheathing a

7、nd the sheet-metal part.In assembly, the fastening element is pressed directly with the conical hub of the sheet-metal part onto the drive shaft, which can damage the knurled structure of the drive shaft, so that the force transmission when a replacement part has to be installed may no longer suffic

8、e.From German Patent Disclosure DE 44 44 328 A1, a fastening element of zinc, a zinc alloy, or aluminum or an aluminum alloy is known in which a reinforcing element is integrally cast at least in the region of a conical hub and surrounds the hub and extends in corelike fashion at least partway insid

9、e the body of the fastening element.The reinforcing element has extensions that extend at least as far as the surface of the body of the fastening element. As a result, during production, the reinforcing element can be fixed exactly in its position, so that close tolerances can be adhered to in the

10、critical hub region. DE 44 44 328 A1 also proposes that the reinforcing element extend over the entire length in the body of the fastening element, which makes economies of material and thus slender fastening elements possible.The material bond between the casting material and the reinforcing elemen

11、t is reinforced by creating a form-locking bond with openings, holes or slits in the reinforcing element.In order not to destroy the knurled structure on the drive shaft during assembly, it is proposed that the reinforcing element also be surrounded toward a center axis of the hub by cast material,

12、preferably with a wall thickness of approximately 1.5 mm. As a result, the knurled structure can dig into the soft casting material so that strong forces can be transmitted with form- and force-locking. Because of the thin wall thickness, the bending stresses and tensile strains are absorbed virtual

13、ly solely by the reinforcing element.It is also known, particularly with relatively long fastening elements, to use aluminum or an aluminum or an aluminum alloy instead of zinc, to attain better long-term strength and to prevent breakage from brittleness. However, aluminum attacks the pressure casti

14、ng tool, with attendant higher post machining costs and shorter service lives of the tool. The material costs for aluminum are also higher than for zinc.The fastening elements described above from the prior art are cast or coated with a casting mold. If fastening elements of different lengths or dif

15、ferent shapes are to be made, then a separate casting mold is required for each variant.ADVANTAGES OF THE INVENTIONAccording to the invention, the fastening element comprises a middle, longitudinally extending, prefabricated carrier part, which is made from aluminum or preferably steel or a steel al

16、loy in a bending and stamping operation on the ends of the prefabricated carrier part, fastening regions that are separated from one another later are cast in the form of heads, one of which has a conical hub and the other of which has a bearing point for the wiper arm. Zinc, a zinc alloy, aluminum,

17、 an aluminum alloy, magnesium, a magnesium alloy, or in certain embodiments plastic are particularly suitable as casting material for the heads.In different variants of the fastening elements, often only the lengths and the shapes are different, while the fastening regions can be identical. With the

18、 fastening element of the invention, standard heads can be cast onto variously embodied carrier parts, thus creating different variants economically without requiring different casting molds. The number of tools required and thus tool costs are reduced. Another factor contributing to low tool costs

19、is that the casting molds are smaller, since they do not surround the entire fastening element but instead only its ends, thus economizing on casting material. Production is also facilitated because the carrier part can be fixed precisely without needing extensions. The casting tools and a fixing de

20、vice can be functionally and spatially separate and can thus be made economically.With a flexurally rigid carrier part, for instance of steel, or a steel alloy and with a hollow or U- or T-shaped profile, and so forth, especially lightweight and slender fastening elements that present only little su

21、rface area to the wind can be created.Further advantageous embodiments of the fastening element are possible with the characteristics recited in the dependent claims.In the region of the hub, the fastening element is at especially high risk of breakage and twisting, because it is in this region that

22、 the greatest bending stresses occur, because the lever arms are longest. The bending stresses also have tensile strains superimposed on them that originate in the mounting of the conical hub on a conical drive shaft. It is proposed that in this region an inlay part that surrounds the head and is ma

23、de of material with tensile strength be integrally cast with the head and in this region absorb the tensile and bending stresses and relieve the casting material. Steel, a steel alloy, aluminum, an aluminum alloy, or some other strong material familiar to one skilled in the art can be used as materi

24、al for the inlay part. By this means, different demands of the casting material can be taken better into account, such as good processability, high surface quality, and so forth.To attain a favorable flow of force from the head and especially the inlay part to the carrier part, in one feature of the

25、 invention the inlay part and the carrier part are joined together in form- and/or force-locking fashion. Peak stresses at the transitions from the carrier part to the cast-on head are avoided, and as a result the entire head can be made slender, lightweight, and with little casting material. Partic

26、ularly in this feature, casting materials with low strength can be used, such as various plastics. To that end, the inlay part and the carrier part can be joined together with familiar plug- and clamp-type connections.If the inlay part, in the region of the conical hub, comes into direct contact wit

27、h the conically embodied drive shaft, the surface of the drive shaft can be damaged, especially if it has a knurled structure. To prevent this, the drive shaft can be hardened. In one feature of the invention, however, it is proposed that the inlay part be coated toward a center axis of the hub with

28、 casting material having a wall thickness of approximately 1.5 mm. The knurled structure on the drive shaft can dig into the soft material and can transmit high rotational forces by form locking without destroying the knurled structure. Mechanical stresses, such as pressure and bending stress, howev

29、er, are absorbed virtually solely by the inlay part, because of the slight wall thickness.The casting material toward the center axis of the hub can be injected through a second channel in the casting tool. However, it is advantageous if only one channel is required for both the inner and the outer

30、casting material. According to the invention, this is attained with a region on a top and/or bottom face end of the hub by way of which the inner and outer casting material are joined to one another. In the production of the head, this casting material can flow from the outer part of the hub to the

31、inner part of the hub, or vice versa, via this region. It is also proposed that recesses be made in the hub or that hubs with recesses be used, by way of which again the casting material flows, as a result of which the casting material can be distributed quickly and uniformly.The fastening element i

32、s pressed by means of a nut with its conical hub from above onto a conical drive shaft. As a result, especially high assembly strains or pressures per unit of surface area and tensile stresses, which threaten the cross section, arise in the upper, narrower region of the hub, and especially on the su

33、rface of the head on which the nut is supported. In one embodiment of the invention, it is proposed that the inlay part have a collar toward the narrower region of the hub. Preferably, the collar extends to the surface of the head, and as a result the nut can be supported on the inlay part, while in

34、 the uppermost, narrowest region of the hub, the pressures per unit of surface area and tensile strains can be absorbed entirely by the collar.A bearing point for the wiper arm is disposed in the second head of the fastening element. As a rule, the wiper arm is connected to the fastening element via

35、 a shaft which is guided in a bearing bush in the fastening element. A retaining clip is suspended from a pin in the fastening element by a tension spring which is connected to the wiper arm and braces the two components together and presses the windshield wiper against the windshield. Preferably, t

36、he fastening region is cast integrally into the head, which saves one assembly step later, but the shaft can also be supported directly in the casting material, if this material has adequate sliding properties, or if the shaft does not execute any, or only a few, relative motions in it.The pin for t

37、he tension spring can also be cast integrally into the head, again saving a further assembly step. This effect is also attained with a carrier part which protrudes in the head region out of the casting material and has a hole or an undercut from which the tension spring can be suspended. The pins fo

38、r the fastening elements are then omitted.To reinforce the material bond between the casting material and the carrier part, it is proposed that the carrier part be form-lockingly joined to one or both heads by a shaping, for instance by means of apertures such as holes, slits, advantageously with co

39、llars or leadthroughs, by means of undercuts, notches, recesses and so forth. This is important especially with zinc or zinc alloys, which do not enter into any metal-to-metal bond with the carrier part in the pressure casting.A method for producing the fastening elements is advantageously distingui

40、shed by the fact that with one pressure casting apparatus and two pressure casting molds, standard heads can be cast onto different carrier parts, by adjusting the pressure casting molds successively or simultaneously to one another or to a respective end of the carrier part in accordance with the v

41、ariant to be made. The pressure casting molds can be small and can be made without fixing devices for the carrier part and thus can be made economically. Preferably in the method an adapter piece is disposed between the pressure casting molds; with it, the carrier part is fixed and the pressure cast

42、ing molds are adjusted to one another. The adapter piece can be replaced quickly and easily for different variants, and furthermore the pressure casting molds can be fixed quickly relative to one another or to the carrier part.BRIEF DESCRIPTION OF THE DRAWINGShown are:FIG. 1, a fastening element see

43、n from below;FIG. 2, an enlarged fragmentary section taken along the line IIII of FIG. 1;FIG. 3, a variant of the feature in FIG. 2;FIG. 4, a variant of the feature in FIG. 2;FIG. 5, a side view of the fastening element;FIG. 6, a section taken along the line VIVI of FIG. 5;FIG. 7, a section taken al

44、ong the line VIIVII of FIG. 6;FIG. 8, a variant of the feature in FIG. 7; andFIG. 9, a fastening element, fixed in an adapter piece, and two pressure casting molds.DESCRIPTION OF THE PREFERRED EMBODIMENTSIn FIG. 1, a fastening element for a wiper arm or for a windshield wiper is shown, which is secu

45、red to a conical drive shaft, not shown. The fastening element has a first fastening region 12 on one end, with a conical hub 14, and a second fastening region 18, with a bearing point 20 for the wiper arm, on the other. According to the invention, the fastening element has a middle, longitudinally

46、extending, prefabricated carrier part 22, on whose ends 10, 16 the fastening regions 12, 18 are embodied in the form of two heads 24, 26 separately cast on. Materials with high tensile strength, such as steel in particular or a steel alloy, are suitable as material for the carrier part 22. Preferabl

47、y, this part is made in a bending and stamping operation. For the material of the heads 24, 26, materials that can be readily pressure-cast are suitable, such as zinc, aluminum, magnesium, and so forth, and alloys thereof; with zinc, surfaces of especially high quality are possible, and furthermore

48、pressure casting tools used for it attain long service lives since zinc does not attack them.The ends 10, 16 of the carrier part 22 have a shaping, such as holes 44, 46, recesses 48, 50, etc., so that the material bond between the cast-on ends 24, 26 and the carrier part 22 is reinforced by form-loc

49、king.The region of the hub 14 is at especially high risk of breakage and twisting from tensile stresses on the conical drive shaft during assembly and high bending stresses as a consequence of long lever arms (FIG. 2). To reduce the risk of breakage and twisting, an inlay part 28 surrounding the hub

50、 14 is cast integrally into the head 24. The bending stresses and tensile strains are absorbed virtually entirely by the inlay part 28. The hub 14 is pressed from above onto a drive shaft via a nut, resulting in especially high stresses in the upper, narrower region 74 of the hub 14. In a variant sh

51、own in FIG. 4, the inlay part 72 has a collar 76 toward the narrower region 74 of the hub 14. The collar 76 extends as far as the surface of the head 74. As a result, the nut can be supported on the collar 76 of the inlay part 72, and thus pressures per unit of surface area and tensile stresses in t

52、he upper region 74 of the hub 14 can be absorbed virtually completely by the collar 76, and the remainder of the casting material can be relieved. The nut is preferably surrounded by a guide rib 86, which makes assembly easier and protects the nut. Materials with tensile and bending strength, such a

53、s steel, a steel alloy, aluminum, an aluminum alloy, etc., are especially suitable as materials for the inlay part 28.If the inlay part 28 comes into direct contact with the conical drive shaft, then the surface of the drive shaft can be damaged during assembly, especially if it has a knurled struct

54、ure and is not surface-hardened. It is proposed that the inlay part 28 be coated by casting in such a way that it has a cast layer 52 toward a center axis 30 of the hub 14. The cast layer 52 is located between the inlay part 28 and the drive shaft and is preferably 1.5 mm thick. Thus the knurled str

55、ucture of the drive shaft can dig into the soft casting material during assembly without being destroyed, and furthermore, because of the slight wall thickness, the bending stresses and tensile strains are absorbed virtually completely by the inlay part 28. The inner cast layer 52 can be injected th

56、rough a second channel in the casting tool.In the version of the invention shown in FIG. 4, however, the head 24 and inner cast layer 52 can be injected with only a single channel, because the inner cast layer 52 is joined to the remainder of the head 24 via a region 78 on one face end 80 of the inl

57、ay part 72. Next to the region 78, the casting material can be distributed from the outer to the inner region of the inlay part 72, or vice versa, via recesses 84, which promote uniform and also rapid distribution. The region 78 and the recesses 84 can be utilized either jointly or individually. It

58、is also possible for the cast layer 52 to be joined to the remainder of the head on the face end 82 of the inlay part via a region not shown.In an embodiment of the invention shown in FIG. 3, an inlay part 54 is connected in form- and/or force-locking fashion to the carrier part 22 via a plug connection 56, in order to achieve a favorable flow of force from the carrier part 22 to the inlay part 54 without the incidence of peak stresses at transitions. Particularly in this kind of embodiment, heads 24, 26 of plastic are also conceivable.In the head 26, a wiper arm, not shown, is p