Method for linking elements to hollow shafts, preferably for producing camshafts, and resulting camshaft

Abstract

A method for the linking of components to hollow shafts, preferably for producing camshafts, is disclosed where the components, especially cam rings, are manufactured so as to generate their function-related contour, that either a hardenable material is used for this purpose which, aside from its elastic deformability, after hardening still has a permissible plastic deformability of minor extent; or that subsequently the surface of the components, particularly the contact face of the cams, is subjected to a surface-hardening process. These components together with the hollow shaft to be deformed are placed into an IHPF tool in a manner to suit the respective function, and that in a second process step through the application of the IHPF process and due to the internal pressure exerted the components are joined to the hollow shaft in a force- and form-closing manner.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application is a divisional patent application Ser. No. 10 / 492,866 which was filed Oct. 18, 2004 and claimed the benefit of PCT / DE02 / 03745, filed Oct. 4, 2002 which claimed priority of German Application No. 101 50 093.9 filed Oct. 11, 2001.FIELD OF THE INVENTION [0002] The invention relates to a method for joining components, in particular individual cam rings, with a hollow shaft to form a camshaft produced in conformity with the internal high-pressure forming process (IHPF) process). Furthermore, the invention relates to a hollow shaft on which components, preferably cam rings, are mounted in a force- and form-closing manner. A preferred field of application is the manufacture of camshafts, especially for use in motor-vehicle engines. BACKGROUND OF THE INVENTION [0003] It is known to produce camshafts according to the IHPF process by placing the hollow shaft and mounted thereon components such as cam rings and drive elements acco...

AI Technical Summary

Benefits of technology

[0006] It is, therefore, the object of the invention to provide a method by means of which components, especially cams, are joined according to the known IHPF process on a hollow shaft in a force- and form-closing manner such that the cam rings have an admissible residual expansion of >=0.5% as is required to bridge the expansion of the cam ring and the manufacturing tolerances in the cam ring and / or tool due to the internal pressure. It shall thus be avoided that breakage or incipient damage occurs that may impair a future use, in particular during continuous or long-term operation. The new method shall comprise a combination of processes known per se which are economical and require little expenditure in terms of equipment. A further objective of the invention relates to the provision of a camshaft that is cost-effective, features a high degree of reliability and is suited for use in automotive engines. It shall be made of material of customary quality. Camshafts shall be produced that will cause hardly any consequential damage to the engine.

[0016] Surprisingly, it has been found that the shortcomings in the state of the art could be eliminated by the cam rings, manufactured and / or treated according to the invention, having characteristics to the effect that the stresses building up in the cam ring as a result of the maximum internal pressure exerted in the course of the IHPF process are lower than those experienced in the known through-hardened cam rings or rings consisting of a material that possesses this hardness throughout.

[0018] Significant to all embodiments of the method according to the invention is that the cam ring across its material thickness area has different material characteristics. The top layer which is mechanically strained during operation must be hard and elastically deformable whereas the layer below it has to be deformable both plastically and elastically. This will ensure that even in the event damage occurs no continuous or straight-through cracks can develop but in exceptional cases local damage only. Such spall-off will never result in a sudden destruction of an engine.

[0020] In a second embodiment the surface of the cam ring has been subjected to a surface hardening treatment applied to a defined thickness. This will render the top layer to be elastically deformable while the layer underneath will be plastically deformable. Both embodiments as they relate to the manufacture of the cam ring may also be combined so as to offer advantages in terms of improved usage properties.

Problems solved by technology

However, caused by the internal pressure also the component to be mounted, for example the cam ring, will undergo an elastic deformation.

This method of adapting the properties of the cam ring only to its subsequent function is associated with the drawback that the permissible deformation of the cam ring may be exceeded and through the formation of an incipient crack breakage or initial damage may be encountered which during subsequent operation will result in a camshaft failure.

Consequently, it is to be feared that the damage will only occur after the camshaft has been in use in the engine for a longer period of time.

It has also been determined that a higher risk of breakage exists particularly at the cam ring locations where said ring has suffered maximum stresses during the IHPF process, which is the area ahead of and after the cam tip, especially in the radii transitions and at the cam tip.

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