EMBODIMENTS OF THE INVENTION

[0033] In FIG. 1 , under a), 1 designates a cam according to the invention which is fastened on a hollow-cylindrical shaft 2 . The cam 1 has a first portion 1 . 1 , along which it is in bearing contact on the shaft 2 and partially surrounds the latter, and a second portion 1 . 2 which projects from the shaft and surrounds a cavity 3 . The cavity 3 has the advantage that it makes the cam 1 lighter and reduces its moment of inertia. The weight of the entire camshaft and its rotational resistance are thereby also reduced.

[0034] The cam 1 is produced from a profile strip by its ends being bent together. Such a profile strip 4 is shown in FIG. 1 under b), the profile strip 4 still being straight and unbent here. The bending direction of the profile strip 4 is indicated by arrows.

[0035] Preferably, the profile strip 4 is bent in such a way that, after bending, its ends form a butt joint 5 and its end faces butt against one another over their area. For this purpose, it may be advantageous to bevel the ends before bending, as is also illustrated in FIG. 1 b ).

[0036] Preferably, the profile strip 4 is cut to length from a continuous material. The thickness of the profile strip 4 is preferably between 5 and 15 mm. It could have a uniform, but also a variable thickness over its length, so that, for example, the portion 1 . 1 of the cam 1 is thicker than its portion 1 . 2 , or vice versa.

[0037] FIG. 2 shows a cam 1 in a bending tool 6 , such as can be used advantageously for producing it. The profile strip 4 is in this case bent into its desired final shape by extrusion in a plurality of steps via a bending core 7 by means of a plurality of bending fingers 8 . 1 - 8 . 4 . In this case, the still unbent profile strip 4 is first fixed on the bending core 7 at the top by means of the first bending finger 8 . 1 . The second bending fingers 8 . 2 then bend the profile strip 4 into an approximately V-shaped preform. By means of the third bending fingers 8 . 3 , the profile strip 4 is bent around the bending core 7 at the bottom, and, finally, the ends of the profile strip 4 are closed by means of the fourth bending finger 8 . 4 to form said butt joint.

[0038] In a further work step, the two ends butting against one another may then also be welded to one another, in particular using the resistance, laser or electron-beam welding technique.

[0039] The cam 1 thus produced is preferably also fastened on the shaft by welding, in particular, again, using the laser or electron-beam welding technique, but particularly advantageously by resistance welding.

[0040] FIG. 3 shows a resistance welding arrangement 9 , in which a cam 1 pushed onto a shaft 2 is retained in its desired position and rotary setting by means of three welding tongs/electrodes 10 . Two rings 11 clamped onto the shaft 2 form the counterelectrodes. In the current path between the electrodes, the contact faces between the cam 1 and the shaft 2 form the regions with the highest ohmic resistance. By means of a high current pulse, a high stray power can be deposited for a short time in these zones and leads to the desired welding of said contact faces to one another.

[0041] If appropriate, in this welding method, it is also possible to weld directly to one another the two ends of the profile strip 4 which butt against one another, with the result that a prior welding of these ends would advantageously be dispensed with.

[0042] Since, in this welding method, the cam is clamped between the welding tongs 10 , there is also advantageously no need for a possibly complicated prefixing of the cam on the shaft.

[0043] In a preferred refinement of the invention, the cam 1 is provided, as illustrated in FIG. 4 a ), with inwardly projecting, for example axially running ribs 12 on its first portion 1 . 1 . The ribs 12 may even be formed on the still unbent profile strip 4 , for example by rolling, as illustrated in FIG. 4 b ). They could alternatively also be produced only during bending on the bending core 7 , in which case part of the bending core would have to be provided with a corresponding surface structure. The two possibilities could also be used in combination with one another. The ribs should have, for example, a height of 0.15-0.16 mm and a spacing of 1.5-2 mm.

[0044] The presence of the ribs 12 results in defined sharp contact lines between the cam and the shaft, this being advantageous for current conduction during resistance welding, in that welding takes place along these lines. When a welding device according to FIG. 3 is used, pressure may also, to further advantage, be exerted on the cam during welding by means of the welding tongs 10 , in such a way that the ribs 12 are squeezed and the cam 1 comes to bear over its area against the shaft 4 . This gives rise to a structure with weld seams 13 of lenticular cross section, as shown in an enlargement of a detail in FIG. 4 under c).

[0045] Alternatively, instead of ribs in the axial direction, ribs in the longitudinal direction of the profile strip 4 or in the circumferential direction of the finished cam may also be used. So that, in this case, the bending core 7 can be removed again in a simple way after the bending of the profile strip 4 , it is advantageous to design the ribs, on the one hand, and the outer structure on the bending core, on the other hand, in the manner of a thread, in order to make it possible for the bending core to be unscrewed from the cam. For this purpose, as indicated in FIG. 2 , the bending core 7 would additionally have to be produced in two parts with a rotatable part 7 . 1 .

[0046] FIG. 5 illustrates a cam 1 on a shaft 2 , the cam 1 especially advantageously being designed for fastening by welding by means of a laser or electron beam. For this purpose, the cam 1 has, at least on one side, a foot strip 16 which is formed by a groove 15 on its corresponding side face. The cam can be welded, preferably over its circumference, to the shaft 2 along this foot strip 16 and through the latter in a fully orbital manner obliquely from above by means of a laser or electron beam 14 . The presence of the foot strip 16 results in a weld seam (welding cone) with a virtually optimum welding cross section, the width of which corresponds approximately to the width of the foot strip 16 and consequently ensures an extremely good, highly load-bearing and permanent connection between the cam 1 and the shaft 2 . An identical weld is, of course, also provided, and preferred, along the foot strip 17 on the other side of the cam 1 .

[0047] The foot strips 16 and 17 may advantageously be produced by forming on the still unbent profile strip 4 , on which they are simply straight grooves.

[0048] FIG. 6 shows an arrangement, such as can be used advantageously for the laser or electron-beam welding of cams 1 to a shaft 2 . However, FIG. 6 illustrates merely diagrammatically a shaft 2 with a plurality of pushed-on cams 1 and, for each cam 1 , two welding heads 18 which may be laser or electron-beam welding heads. The welding heads 18 are oriented in such a way that their welding beams 14 impinge onto the foot strips 16 or 17 of the cams 1 . FIG. 6 is to be understood such that the shaft 2 is clamped axially by means, not illustrated, and is rotated about its axis 19 while the welding heads 18 are simultaneously put into operation. It is thereby possible, in an operation lasting for only a few seconds, to fasten all the cams 1 simultaneously on the shaft 2 by welding.

[0049] Before the weld seams are applied by means of the device according to FIG. 6 , it may be necessary, if appropriate, to prefix the cams 1 on the shaft 2 in their desired position and rotary setting. This may take place, for example, by tacking by welding, but also by means of one or more of the initially explained connection methods according to the prior art, such as a shrink fit, a form-locking connection or internal high pressure. Since the preconnection does not have to be particularly firm and even not at all permanent, the initially outlined disadvantages of the known fastening methods can in this case be avoided.

[0050] Due to the welding, the shaft 4 and the cams 1 are subjected to comparatively little stress and therefore advantageously maintain their shape. The heat introduced locally into the shaft 2 and the cams 1 as a result of welding can, in the case of a tubular shaft, additionally even be discharged, for example, by a cooling medium being conveyed through the shaft, thus further reducing the possible impairment of the parts.

[0051] FIG. 7 shows, under a)-c), three further exemplary embodiments of cams 1 according to the invention, together with their not yet bent profile strips 4 associated with them in each case. In all three examples, an inwardly projecting shoulder 20 more closely surrounding the shaft 2 is formed in the transitional region between the portions 1 . 1 and 1 . 2 .

[0052] In the embodiment shown under a), there is additionally provided in the joint region 5 a weld-seam recess 21 which can receive within it the welding bead possibly occurring during the welding of the profile strip ends. This affords the advantage that, after welding, a smooth cam surface structure is obtained relative to the outside and therefore there is no need for subsequent grinding of the surface after welding.

[0053] The cam illustrated under b) has, in the length portion 1 . 2 projecting from the shaft 2 , a greater wall thickness than in the length portion 1 . 1 , thus giving the length portion 1 . 1 greater stability.

[0054] The cam illustrated under c) has, conversely, a smaller wall thickness in the length portion 1 . 2 than in the length portion 1 . 1 . In addition, here, the joint region 5 of the two profile strip ends is shifted upward into the region of the length portion 1 . 2 , this merely being a further possibility for placing said joint region on the circumference of the cams.

[0055] In the embodiment of a cam 1 , as illustrated in FIG. 8 , the two profile strip ends are designed, with a view to a further variant, so as to overlap, specifically so as to overlap in the axial direction, although an overlap in the radial direction would also be possible. An overlap in the axial direction has the advantage, however, that, on the one hand, the two ends can be brought into mutual, if appropriate elastically slightly prestressed axial bearing contact on one another even when the profile strip is being bent together and consequently are reliably in alignment with one another. On the other hand, the joint 5 is then not overrun even once during the rolling of the cam, so that a groove which may possibly be present in the joint region and, if appropriate, may even be necessary for tolerance reasons on the outside of the cam does not have an adverse effect.

[0056] In the cam of FIG. 8 , inwardly projecting ribs are also formed in its portion 1 . 1 coming to bear on the shaft, such as are likewise already described as advantageous in connection with resistance welding and are illustrated in FIG. 4 under a) and b). These ribs can advantageously also be used for producing mechanical intermeshing between the cam and the shaft. For this purpose, the cam is applied in the still open state, that is to say with the ends not yet welded to one another, onto the shaft and is acted upon there, in position, by pressure from outside in such a way that the ribs are pressed into the shaft and said intermeshing occurs at the same time. So that this is possible, the ribs must, if appropriate, be prehardened. When the ribs are oriented in the axial direction, this advantageously results in a rotational fixing of the cam on the shaft. The cam can subsequently be welded to the shaft in one of the ways described above.

[0057] Owing to the intermeshing, a welding of the cam to the shaft is, if appropriate, even superfluous, and it is sufficient solely to close the cam by the welding of its two ends. If these are in this case fused under pressure, for example by laser, the cam, to further advantage, also additionally contracts during the resolidification of the fused material and firmly closes around the shaft, because the density of liquid metal is lower than the density of solid metal.

[0058] FIG. 9 also shows, under a)-c), the steps for producing a cam 1 according to the invention composed of two bent profile strips 30 , 35 . FIG. 9 a ) illustrates in this case a profile strip 30 already finish-bent into an upper cam half comprising the cam elevation or cam tip, in a bending tool 31 which comprises an upper forming die 32 , a lower forming die 33 and a precision stop 34 . Correspondingly, FIG. 9 b ) shows a profile strip 35 complementary to the profile strip 31 and likewise already finish-bent into a lower cam half, in a bending tool 36 , of which the upper forming die is designated by 37 and the lower forming die by 38 and of which the precision stop is designated by 39 . In FIG. 9 c ), the two semicircular or halfshell-shaped cam halves are assembled between two welding electrodes 41 and 42 into a closed ring and are connected to one another by means of these electrodes by resistance welding also at their mutual contact faces.

[0059] In terms of their cross-sectional shape, the cam of FIG. 9 c ) corresponds approximately to that of FIG. 7 a ), that is to say it has in each case a shoulder 20 in the transitional region between its length portion 1 . 1 , with which it comes to bear on the shaft, and its length portion 1 . 2 , in which it projects from the shaft. The embossing of these shoulders 20 may take place before bending on the still straight profile strip 30 , but advantageously also only in the bending tool 31 during bending. All other above-described cam shapes and cam designs can, of course, likewise be produced from a plurality of profile strip pieces, and the cams do not necessarily have to be composed of an upper and lower half. In particular, they could also be composed of two identical left and right halves, with the result that even a bending tool would then be dispensed with. Further, it would be possible to use solid cams, that is to say those cams which surround the shaft on all sides and have no cavity 3 ( FIG. 1 ). A construction of the cams from more than two parts would, in principle, likewise be conceivable.

[0060] The method described has the advantage, as compared with those described above, that the two profile strips 31 and 35 do not have to be bent to such an extent separately in each case and, therefore, the material is exposed to a lower load during cam production. Also, at least the bending tools become simpler in terms of their design.

[0061] List of Designations

[0062] 1 Cam

[0063] 1 . 1 First length portion

[0064] 1 . 2 Second length portion

[0065] 2 Shaft

[0066] 3 Cavity

[0067] 4 Profile strip

[0068] 5 Joint

[0069] 6 Bending tool

[0070] 7 Bending core

[0071] 7 . 1 Rotatable part of the bending core

[0072] 8 . 1 First bending finger

[0073] 8 . 2 Second bending finger

[0074] 8 . 3 Third bending finger

[0075] 8 . 4 Fourth bending finger

[0076] 9 Resistance welding arrangement

[0077] 10 Welding electrodes

[0078] 11 Counterelectrodes

[0079] 12 Ribs

[0080] 13 Weld seams

[0081] 14 Laser or electron welding beam

[0082] 15 Grooves

[0083] 16 Foot strip

[0084] 17 Foot strip

[0085] 18 Welding heads

[0086] 19 Axis

[0087] 20 Shoulder

[0088] 21 Weld-seam recess

[0089] 30 Profile strip

[0090] 31 Bending tool

[0091] 32 Upper forming die

[0092] 33 Lower forming die

[0093] 34 Precision stop

[0094] 35 Profile strip

[0095] 36 Bending tool

[0096] 37 Upper forming die

[0097] 38 Lower forming die

[0098] 39 Precision stop

[0099] 41 Welding electrode

[0100] 42 Welding electrode