This application claims the priority of European Patent Application, Serial No. EP 12 15 1603, filed Jan. 18, 2012, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein.
The present invention relates to a coated cogwheel and to a method for producing a coated cogwheel.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Case hardening is a process used for hardening drive components and cogwheels to achieve a high degree of edge hardness and compressive stresses that counteract the wear and the failure modes due to Hertzian stress. Special coatings can further be applied to regions that are under pressure on cogwheels to further reduce wear. Practice has shown, however, that uneven loading of coated cogwheels can cause a coating of such kind to flake off, as a result of which the cogwheels' life span is very limited.
It would be desirable and advantageous to provide an improved coated cogwheel to obviate prior art shortcomings.
According to one aspect of the present invention, a coated cogwheel includes a cogwheel body made from a basis material having a hardness, a layer arranged at least on a part of the cogwheel body and having a hardness which is greater than the hardness of the basis material, said layer being subdivided by seams into in a multiplicity of segments in spaced-apart relationship.
According to another aspect of the present invention, a method for producing a coated cogwheel includes the steps of arranging a layer of a first hardness on at least a part of a cogwheel body made from a basis material of a second hardness, with the first hardness being greater than the second hardness, and subdividing the layer by seams into a multiplicity of segments in spaced-apart relationship
A load in real applications is virtually never distributed evenly over a cogwheel's region under load, in particular a tooth flank, owing to shaft tilting, for instance, or compliance exhibited by a housing. Nor can such inhomogeneities always be suppressed by corrections because corrections are always optimal only for a specific load. The region under load, for example the tooth flank, therefore has to additionally adjust to and balance out the uneven loading by way either of elastic deformation or of running-in wear. As both mechanisms are difficult to implement in the case of layers protecting against wear that are conventionally embodied as being totally closed, the result has frequently been that the layers protecting against wear flake off. That disadvantage is avoided thanks to the inventive segmenting of the layer protecting against wear.
The invention is based on the knowledge that segmenting a relatively hard layer applied in the case of a cogwheel to a cogwheel body made from a softer basis material to provide protection from wear enables the two advantageous properties “rigidity” and “flexibility” to be distributed over different surface levels of the cogwheel. The terms “layer”, “coating” and “layer protecting against wear” are employed synonymously below.
The segmented layer offers protection against wear due to its hardness while the seams between the segments enable them to individually align themselves while under a load. Uneven loading of the coated cogwheel can in that way be balanced out better than if there were no segmenting so that the coating is prevented from flaking. The overall result is an improved property profile with reference to cogwheel loading because on the one hand protection against wear is provided owing to the hard surface layer and on the other hand a measure of flexibility and compliance is provided owing to the layer's being subdivided into separate segments. The cogwheel is hence in its coated regions able to combine two properties otherwise regarded more as being contrary.
Compared with continuous, i.e. closed coatings that often prove inflexible under a load, more even load distributing across a cogwheel's surface, in particular the surface of a tooth flank, is made possible by the present invention. That improves the protection against wear.
According to another advantageous feature of the present invention, the layer can form a surface of the coated cogwheel. The layer that serves as a protection against wear and is harder and usually also less flexible than the basis material from which the cogwheel body is made can therefore form an outer surface of the cogwheel. The layer can consequently function optimally as a layer protecting against wear.
According to another advantageous feature of the present invention, the layer can be arranged on at least one tooth flank of the cogwheel body. A tooth flank is normally the region on a cogwheel that is especially subject to loading and hence to wear. It is even possible for the segmented layer to be arranged exclusively on the cogwheel body's tooth flanks. For example the necessary elasticity in the region of the tooth base is in that way not adversely affected.
To increase the load capacity of tooth systems they are furnished with a coating that is not formed as being continuous or, as the case may be, closed but is segmented. Formed between adjoining segments are seams that are not furnished with a coating. According to another advantageous feature of the present invention, the layer is completely cut through by the seams. The layer's individual segments are in that way totally separate from each other and hence able to align themselves mutually totally independently. Stresses in the coating are largely obviated thereby and the layer hence prevented from flaking.
According to another advantageous feature of the present invention, the seams can be sized to extend into the cogwheel body. That means that advantageously also the basis material to which the coating is applied is cut into in the region of the seams. In that way a cogwheel surface, for example a tooth flank, is created having a plurality of plateaus exhibiting different hardness.
The effect of segmenting can thus be intensified by “cutting into” not only the layer but also a region of the basis material close to the surface. The result is thus a loading region of the cogwheel, for example a tooth flank, which region has plateaus exhibiting different hardness and suitably also different elasticity. The top region of the plateaus is strengthened by the hard layer and the plateaus are mutually separated by seams or grooves. The depth of the seams is to be selected such that the plateaus can align themselves flexibly in keeping with the load situation on a counter flank. The basis material's being cut into intensifies the advantageous combination of the properties “rigidity” and “flexibility” because the seams provide room for the lateral expansion occurring under a compressive stress and hence the compliance of the layer protecting against wear is being reduced.
According to another advantageous feature of the present invention, the seams can have a width sufficient to leave room for a lateral expansion occurring when the coated cogwheel is subjected to a pressure load. Seams having a sufficient width intensify the advantageous combination of the properties “rigidity” and “flexibility” because the seams provides room for the lateral expansion occurring under a compressive stress and hence the compliance of the layer protecting against wear is reduced. The shape of coated regions and the size of non-coated regions can be best suited to other boundary conditions. Any shape is basically possible. The type of layer is also freely selectable because the method is basically suitable for all layer types.
The segments can be formed by cutting into an originally closed coating or by covering the subsequent seams with a mask then applying the coating and finally removing the mask.
According to another advantageous feature of the present invention, the layer can be arranged on at least a part of the cogwheel body by covering the seam regions with a mask; applying the layer to non-covered regions of the cogwheel body; and removing the mask. The layer can be applied directly segmented by, for example, masking the intermediate regions with a structure so that the basis material remains uncoated there.
As an alternative, the layer can be arranged on at least a part of the cogwheel body by applying a closed layer to the cogwheel body; and segmenting the closed layer by forming the seams. The layer is thus first applied closed and then divided into the individual segments.
According to another advantageous feature of the present invention, the seams can be formed using a laser beam. Other methods, for example mechanical, chemical, or electric removal, are, of course, also possible.
Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:
Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.
Turning now to the drawing, and in particular to
In a second step, shown in
The mask 11 applied to the tooth flanks 4 is removed in a third step, shown in
In a second step, shown in
While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein:
Number | Date | Country | Kind |
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12151603.3 | Jan 2012 | EP | regional |