Abrading – Abrading process – Cam
Reexamination Certificate
1999-02-16
2001-03-13
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
Cam
C451S049000, C451S056000, C451S058000, C451S072000, C451S195000, C451S246000
Reexamination Certificate
active
06200200
ABSTRACT:
The invention relates to a method and to an apparatus for grinding cams having concave flanks on a camshaft, and more particularly to a method and apparatus using a grinding wheel of relatively small diameter with a grinding zone arranged on the outer surface for the finish-grinding of the cam.
Cam shapes having concave flanks in the run-on and run-off region of the cam are increasingly employed, for example by car manufacturers, since their use contributes to a reduction in fuel consumption and as a result of the use of roller-lever valve-drive technology.
A method and an apparatus for producing such cam structures of known type are described, for example, in DE 44 26 452 C1. In accordance therewith, the axis of the grinding spindle is arranged parallel to the axis of rotation of the workpiece. Because of the space relationship and the small grinding-wheel diameter, this leads to the situation in which very slender, long grinding spindles have to be used, in particular when they are driven directly by a high-frequency motor, it being necessary for the grinding spindle to be designed to be longer than the camshaft. In the case of camshaft lengths of, for example, more than 500 mm, there are then problems in relation to the rigidity and the inherent vibration frequencies of the grinding spindle.
This is similarly true in the case of DE 41 37 924 C1, the subject-matter of which likewise concerns operating with a grinding spindle for the finish-grinding of the cam, the axis of the spindle running parallel to the axis of rotation of the workpiece.
According to yet another known approach, as disclosed in DE-PS 678 981, and as shown in
FIGS. 3
to
6
thereof, operations are carried out with a grinding spindle aligned perpendicular to the camshaft axis. Here, the concave sub-area of the cam is ground out using a separate grinding wheel. This results in a shape error in the transition region to the concave cam section, since the cam shape is not finish-ground over its entire circumference using a grinding wheel. The diameter of the grinding wheel is limited by the fact that the respective cam, which is arranged alongside the cam to be ground in the direction of the camshaft longitudinal axis, predefines the maximum grinding wheel diameter through the maximum diameter of rotation of the second cam. In addition, in order to obtain a flat cam shape, it is necessary to operate with a movement or oscillation of the grinding wheel in the direction of the camshaft longitudinal axis, which is time-consuming and uneconomical.
Furthermore, it is known that cams are ground using a band grinding method. In accordance with such a system, the disadvantage is that the grinding bands have to be replaced frequently, and the cam running surface can only be ground flat. The circumstance of frequent grinding-band replacement leads to the fact that this system is uneconomical by comparison with grinding using ceramically bound CBN.
In addition, in order to grind oblique cams, the entire grinding unit has to be pivoted. From the point of view of the rectilinearity of the cam outer surface in the direction of the camshaft longitudinal axis, the accuracy values as in the case of grinding cannot be achieved.
The invention is based on the object of developing a method and an apparatus of the aforementioned known general type in such a way that the above-described disadvantages are eliminated and that, in particular at high accuracy, the finished machined camshaft can be worked with a very short and correspondingly rigid grinding-spindle design.
SUMMARY OF THE INVENTION
This object is achieved, in terms of the method, by providing a grinding wheel of relatively small diameter with a grinding zone arranged on an outer surface thereof for finish-grinding of the cam. An axis of a grinding spindle is aligned at a predetermined angle, preferably ranging from about 10° to 30° to a camshaft longitudinal axis, and grinding operations are carried out by tracking the grinding spindle, together with the grinding wheel, which is dressed at the predetermined angle of the grinding spindle, in the direction of a vertical advance axis running perpendicular to an infeed axis, such that the grinding zone of the grinding wheel is maintained at the same position on a generatrix of the grinding wheel. An apparatus in accordance with the invention permits carrying out of the aforementioned method.
According to the invention, by virtue of the oblique position of the grinding spindle, it is possible to operate with a small grinding-wheel diameter and nevertheless a very short and rigid grinding spindle. The accuracy of the finished machined camshaft results from the coordination of the movements of the grinding spindle in relation to three different CNC axes. As a result of the oblique position of the grinding spindle, the situation in the machine in relation to interfering edges is very greatly simplified. As a result, it is possible, for example, even to grind concave cam shapes with a small concave radius on long camshafts. In addition, the system is significantly more flexible than would be the case in the case of a grinding spindle, for the small grinding wheel, arranged parallel to the camshaft central axis.
As in the case of the band grinding method, the resulting advantages are that very small concave radii can be realized and that, by means of appropriate dressing of the grinding wheel, even spherical and oblique cam running tracks, with or without a chamfer, can be produced.
In the case of a grinding dimension of, for example, a few tenths of a millimeter, it is possible for the cam contour to be finish-ground using a single grinding wheel.
Further embodiments of the apparatus in accordance with the invention are also described, in which grinding operations are further enhanced .
The invention is explained in more detail below with reference to exemplary embodiments illustrated schematically in the accompanying drawings, in which like reference numerals designate the same elements.
REFERENCES:
patent: 2654189 (1953-10-01), Dunn et al.
patent: 4580368 (1986-04-01), Smith
patent: 5899797 (1999-05-01), Junker
patent: 529959 (1931-07-01), None
patent: 678981 (1939-07-01), None
patent: 1477912 (1971-11-01), None
patent: 3309424 (1983-09-01), None
patent: 4137924 (1993-02-01), None
patent: 4426452 (1995-09-01), None
patent: 2208275 (1989-03-01), None
patent: 2271731 (1994-04-01), None
Eley Timothy V.
Erwin Junker Maschinenfabrik GmbH
Jordan and Hamburg LLP
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