Process for fastening components on a hallow shaft

The invention relates to a process for fastening components on a hollow shaft (1), during which process the components (21, 22, 23), exhibiting an opening, are put into specified positions on the hollow shaft (1) and for the purpose of fastening components (21, 22, 23) the hollow shaft (1) is expanded by introducing a pressure medium. Support matrices (3) are arranged only between the components (21, 22, 23) for the purpose of bracing the regions of the hollow shaft (1) between the components (21, 22, 23) during the expansion operation.

BACKGROUND OF THE INVENTION
 Field of the Invention
 The present invention relates to a process for fastening components on a
 hollow shaft, in particular to manufacture a constructed cam shaft,
 according to a process for fastening cam components on a hollow shaft in
 which the cam components are put into specified positions on the hollow
 shaft and the hollow shaft is expanded by introducing a pressure medium in
 order to fasten the cam components onto the shaft.
 The EP C257175 B1 discloses a process for the manufacture of a constructed
 cam shaft, where the components are fastened on the outer periphery of a
 pipe by introducing an expanding mandrel into the pipe. The shell of said
 expanding mandrel has at least two pairs of sealing rings, whereby the
 distance between the two sealing rings of each pair of sealing rings is
 equivalent to the axial stretch of the respective fastening place for a
 component. The pairs of sealing rings are spaced apart on the expanding
 mandrel in accordance with the spacing of the components on the pipe. Each
 pair of sealing rings forms an expanding space between its two sealing
 rings, said expanding space being connected to a central pressure channel
 of the expanding mandrel by means of a connecting channel. When the
 pressure medium is introduced into the central pressure channel, the
 result is a targeted expansion of the pipe between the sealing rings of a
 pair of sealing rings in order to fasten the components. The problem with
 this process is that first of all the expanding mandrel is complicated in
 its construction and secondly also comparatively difficult to handle,
 because it has to be accurately oriented relative to the fastening sites.
 The EP 0257175 B1 also describes a process, wherein the use of an expanding
 mandrel can be avoided, according to FIG. 1, by laying the pipe into the
 central cavity of a matrix, which comprises two halves of a matrix that
 can be clamped together. Prior to laying the pipe into the matrix, the
 components are arranged on it. To receive these components, the matrix has
 suitable recesses. The components are heated and/or the pipe is cooled so
 that a temperature differential is produced.
 Through the temperature differential a further shrink fitting of the
 components on the pipe takes place, when fastening the components through
 expansion of the entire pipe. It is easy to see that such a process is
 relatively time consuming and, therefore, cost intensive, because, on the
 one hand, the matrix is complicated on account of the need to provide
 recesses to receive the components; and, on the other hand, producing
 different temperatures at the pipe or the components is also complicated
 and expensive. The fastening procedure requires such an interaction
 between the expansion operation of the pipe and the shrink fitting of the
 heated components on the deformed pipe areas that in the area of the
 components the components rest against the inner surfaces of the same.
 SUMMARY OF THE INVENTION
 The object of the present invention is to provide a process for the purpose
 of fastening components on a hollow shaft, wherein, on the one hand, the
 components shall be fastened reliably and, on the other hand, the process
 shall be comparatively simple and economical.
 This problem is solved by a process which the support matrices are arranged
 between the components for the purpose of bracing the regions of the
 hollow shaft between the components during expansion of the shaft.
 The important advantage of the present invention lies in the fact that
 components can be fastened relatively simply and inexpensively on a hollow
 shaft without the need for expensive matrices and additional cost
 intensive shrink fitting operations, which require the heating of the
 components and/or cooling of the hollow shaft.
 One important advantage of a special embodiment of the process of the
 invention lies in the fact that with a special development of the support
 matrices simultaneously with the fastening of the components on the hollow
 shaft a bearing between two adjacent components can be produced outside
 the shell of the hollow shaft. This has the advantage of avoiding the
 drawbacks with respect to the stability of the hollow shaft; said
 shortcomings occur during the manufacture of such a bearing directly on
 the shell of the hollow shaft due to machining or grinding operations.
 Further scope of applicability of the present invention will become
 apparent from the detailed description given hereinafter. However, it
 should be understood that the detailed description and specific examples,
 while indicating preferred embodiments of the invention, are given by way
 of illustration only, since various changes and modifications within the
 spirit and scope of the invention will become apparent to those skilled in
 the art from this detailed description.
 The invention and its embodiments shall be explained in detail with
 reference to the figures in the following.

DETAILED DESCRIPTION OF THE INVENTION
 The invention was the result of the following considerations. The
 prevailing manufacture of a constructed cam shaft, where the entire,
 preassembled cam shaft is arranged in a specially designed matrix and is
 subsequently expanded with the use of hydraulic pressure in the area of
 the preassembled components, during which process the components are
 simultaneously heated and/or the hollow shaft is cooled in order to obtain
 with the temperature equalization an additional holding force by shrink
 fitting the components on the hollow shaft for the purpose of fastening by
 expanding the hollow shaft in the region of the components, is problematic
 because the manufacture of the necessary special matrix, which must
 receive the entire preassembled cam shaft, is very expensive, because the
 preassembled cams are offset with respect to each other in the
 circumferential direction on the hollow shaft. Therefore, such a
 displacement is also necessary in the matrix for the recesses, to be
 provided for the components to be received. The heating of the components
 and/or the cooling of the hollow shaft is associated with other cost
 intensive and expensive operations. In connection with the present
 invention it was now recognized for the first time that during the
 hydraulic expansion of the entire hollows shaft it is enough to provide
 support matrices only in the areas between two adjacent components. This
 has the advantage that the support matrix can be constructed quite simply,
 since it does not have to exhibit any recesses to receive components. In
 addition to the support matrix, there is only a need for holding devices
 that lock the individual components in specific positions in the
 circumferential direction. In realizing this process it turned out that it
 is not necessary to intensify the shrink fitting by heating and/or
 cooling.
 In FIG. 1 a hollow shaft is marked with the reference numeral 1. On this
 hollow shaft there are components 21, 22, 23, spaced apart in the
 longitudinal direction of the hollow shaft 1. The hollow shaft 1 is in
 particular a cam shaft and the components 21, 22, 23 are cams, which are
 offset from each other by a specific angle in the circumferential
 direction. The actual cam faces of the components 21, 22 and 23 are marked
 with the reference numerals 21', 22', 23'.
 The procedure for fastening the components 21, 22, 23 on the hollow shaft 1
 is as follows. First, the components 21, 22 and 23 are slid on the hollow
 shaft 1 and put into specific axial positions on the hollow shaft 1. Then
 matrices 3, which brace the shell of the hollow shaft 1 in the regions
 between the components, are inserted in the spaces between the components
 21, 22 or 22, 23. For example each support matrix 3 of FIG. 2 comprises
 two matrix sections 31, 32, which enclose a circular opening 33 when they
 are put together; the diameter of the opening 33 is dimensioned in such a
 manner that the inner wall of the opening 33 rests against the outer
 surface of the hollow shaft 1. For specific applications it can also be
 expedient to have a specific amount of clearance between the inner wall
 and the outer surface. The length of the support matrix 3 is preferably
 dimensioned in such a manner that it supports in essence the bulk of the
 space. It is also conceivable to construct the matrix 3 out of several
 matrix sections, instead of two halves 31, 32, in order to form the
 opening 33.
 After the components 21, 22, 23 have been put into the specified positions
 in the circumferential direction and held in these positions, both ends of
 the hollow shaft 1 are sealed. At one end the shaft is sealed with a plug,
 as indicated by the reference numeral 5 in the schematic. To the other end
 is attached, for example, a connecting piece 6, through whose channel 61 a
 pressure medium is brought into the hollow shaft 1, as indicated by the
 reference numeral 4. The consequence is that the hollow shaft 1 is
 expanded in the region of the components 21, 22, 23, thus producing a
 permanent connection between the components 21, 22, 23 and the hollow
 shaft 1. The support matrices 3 provide that the hollow shaft 1 does not
 remain in the expanded state in the area between the components 21, 22, 23
 or that this expansion is limited to some specified degree. In this manner
 the undesired deformations of the hollow shaft are avoided.
 Preferably support matrices 3 are also arranged between the respective
 outsides of the outer components 21, 23 and the ends of the hollow shaft
 1.
 FIG. 3 shows an embodiment, in which a bearing in the region between two
 components 21, 22 or 22, 23 is produced in an especially advantageous
 manner through a special design of the matrices 3 simultaneously with the
 fastening of the components 21, 22, 23 on the hollow shaft 1. To this end
 the interior surfaces of the openings 33 of the support matrices 3 exhibit
 circumferential depressions 34, which render it possible during the
 expansion process to expand the hollow shaft 1 in the region of these
 circumferential depressions 34 of the matrices 3, so that this region of
 the hollow shaft 1 exhibits a raised bearing shoulder 11, which can be
 machined in such an extremely simple manner following fastening of the
 components 21, 22, 23 on the hollow shaft 1 and the removal of the same
 from the matrices 3 during the machining or grinding operation that the
 result is a smooth concentric bearing surface for arranging the bearing
 rings for supporting the hollow shaft 1. The manufacture of the bearings
 in this manner has the advantage that during the manufacture of the same
 with grinding technology there is no need to penetrate with a tool, such
 as a turning tool or an abrasive compound, directly into the shell of the
 hollow shaft, in order to produce there a concentric bearing. The use of a
 tool directly on the surface of the hollow shaft would produce notches,
 which would have harmful effects on the stability and also, for example,
 on the bending property of the hollow shaft.
 The aforementioned holding devices, which adjust the components 21, 22, 23
 in the circumferential direction, can be formed preferably by adjusting
 and locating pins 7, which are inserted into the appropriate axial
 boreholes 8 of the sides of the support matrices 3 facing the components,
 in such a manner that one eccentric region 21', 22' or 23' of the
 components 21, 22, 23 is held between at least two pins 7.
 It is also conceivable according to FIG. 1 that the holding devices are
 adjusting and locating devices 7', which can be introduced independently
 of the support matrices 3 and from the outside into the spaces of two
 adjacent support matrices 3, in order to adjust and lock in position the
 eccentric regions 21', 22' or 23' of the components 21, 22 or 23 in the
 circumferential direction. For example, such adjusting and locating
 devices 7' can be fork-shaped parts, which envelop the eccentric regions
 21', 22', 23' from the outside, when they are in the specified positions.
 The invention being thus described, it will be obvious that the same may be
 varied in many ways. Such variations are not to be regarded as a departure
 from the spirit and scope of the invention, and all such modifications as
 would be recognized by one skilled in the art are intended to be included
 within the scope of the following claims.