Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
1999-10-01
2001-02-27
Rosenbaum, I Cuda (Department: 3726)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
Reexamination Certificate
active
06192582
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to assembled hollow shafts, comprising an inner shaft tube with external functional elements, joined by means of radial expansion in given sections in the axial direction, whereby the inner shaft tube is deformed plastically in the expansion sections and the functional elements are only deformed resiliently in the expansion sections and the expansion sections lie between the functional elements, whereby the functional elements are combined in part into multiple functional elements. The invention also relates to processes for producing shafts of this type and for producing multiple functional elements to be used in manufacturing assembled hollow shafts.
2. Description of the Prior Art
Given the growing importance of multiple valve technology in the field of drive and control shafts (especially cam shafts) for internal combustion engines, the problem of constructing shafts that have many closely adjacent elements, such as cams and other functional parts as well as slide bearings and axial stops, arises ever more frequently. This problem poses increasing difficulties when conventional methods are used. Another problem, especially in large-diameter shafts, is that of weight, which increases quadratically.
Interesting approaches to this set of problems have been made, particularly in the field of assembled hollow cam shafts. Although the problem of cam spacing with decreasing weight can be overcome, other difficulties then arise with respect to decreasing torsional stiffness. Furthermore, the number of functional elements that must be applied to and positioned precisely on each shaft becomes very large. In the case of truck shafts, especially for diesel engines, this problem is accompanied by another difficulty, namely, the necessity of keeping the wall of the hollow shaft relatively thick, even in the single-layered areas between functional elements, for the sake of the required torsional stiffness. The advantage of reduced weight can therefore not be achieved to the desired extent.
Finally, lengthy preparation time is required prior to assembly, especially in the case of long shafts, due to the slow introduction of high-pressure probes into the hollow shaft, for example. This lengthy preparation time reduces the productivity of expensive capital resources.
A reduction in at least some of the aforementioned problems in the production of assembled hollow shafts can be attained by using multiple functional elements, e.g., multiple cams. For example, it has been proposed to produce multiple cams from tube profiles by means of twisting, or from sheet metal blanks, which are suitably shaped, formed into annular bodies and welded.
The first of these proposals, however, is limited to uniform cam profiles. Furthermore, the cams do not possess great stiffness against external pressure, e.g., follower pressure. Moreover, both proposals have very sharp limitations with respect to the spreading or the varied angular pitch of cam tips around the circumference. This limitation can be overcome in the second proposal only by using an expensive process variant.
Generic hollow shafts are known from EP-A-292 795. Double cam elements are described therein, in which an expansion section is arranged between the two external cam sections. The reason for this structure is that the cam sections of the one-piece double cam are subsequently hardened and, due to embrittlement, are not resiliently deformable to the desired extent, so that only the non-hardened middle sections are expanded. These double cams have the disadvantage, however, that the cam sections must be clearly spaced from one another, as a result of which the design of shafts with many closely adjacent functional elements is made more difficult or prevented. Moreover, the combination is limited to two elements with the same function or load.
SUMMARY OF THE INVENTION
The invention is based on the technical problem of proposing novel designs for assembled hollow shafts with external functional elements that avoid the aforementioned problems and are advantageous and inexpensive to produce. A further object is to produce processes to produce such shafts and to produce multiple functional elements in highly productive, highly accurate and inexpensive manner.
The invention solves this problem by embodying generic assembled hollow shafts in such a way that the multiple functional elements comprise a plurality of individual parts, which are combined in the axial direction, whereby non-round individual parts have, in the axial direction, annular projections concentric to the basic circle, the internal diameter of which is slightly larger than the external diameter of the inner shaft tube, whereby the projections have, on their sides that are adjacent to non-round elements, an annular piece of approximately half wall thickness that complements the adjacent non-round individual part in such a way as to achieve full wall thickness, and round individual parts have an internal diameter that fits exactly onto the external diameter of the annular projections. The invention also provides a process to produce assembled hollow shafts, whereby the sectional expansion is carried out by means of hydraulic internal high pressure and the hydraulic fluid is introduced into the hollow shaft by a probe, whereby the external diameter of the probe is only slightly smaller than the internal diameter of the shaft and the probe is sealed against the hollow shaft at the two axial ends of the expansion sections by sealing elements, characterized by the fact that the probes, which have a detachable high-pressure rapid connection, are inserted into and placed in the shaft before the connection to the high-pressure generator and that several finally-combined multiple shafts equipped with probes are connected simultaneously to the high-pressure generator and joined by means of expansion. The invention also provides a process to produce multiple functional elements, especially multiple cams, for use in the production of assembled hollow shafts with external functional elements, especially cam shafts, in which the individual functional elements are produced from tubes with a profile (i.e., profile tubes) corresponding to the functional elements and are combined into multiple cams, whereby the non-round functional elements, in the axial direction, have annular projections concentric to the base circle, the internal diameter of which is slightly larger than the external diameter of the shaft tube, and which have on their lateral edges an annular region of approximately half wall thickness that complements the adjacent non-round functional element
2
in such a way as to achieve full wall thickness, and whereby the annular projects are produced by re-formation of the profile tube.
An entire series of advantages can be attained by using the multiple cams according to the invention. The examples shown in
FIG. 13
, below, in which the inlet cam, the outlet cam, the diesel-injection cam and a slide bearing are combined into a module, allow the number of individual parts needed for a six-cylinder diesel engine to be reduced from 26 to 9, for example, compared with the individual functional parts assembled according to the prior art. The examples shown have been selected with any eye to the usual functions of modern truck engines. The technology according to the invention permits the optimal implementation of designs that have a plurality of cams per cylinder; for example, for the purpose of using injection features or valve-shutoff and closing angle spreading.
This comparison, which contrasts cam shafts manufactured by conventional assembly methods with cam shafts of the same size and function manufactured according to the invention, illustrates the differences among various embodiments with respect to weight and torsional stiffness (expressed as the polar inertial moment J
P
in the dimension cm
4
). The advantages of the shafts according to the invention result largely from the fact that while the weight increas
Cohen & Pontani, Lieberman & Pavane
Cuda Rosenbaum I
Emitec Gesellschaft fur Emissionstechnologie mbH
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