Method for producing a toothed wheel

The invention relates to a method for producing a toothed wheel (1) in net shape or near-net shape quality, in particular a chain wheel, for a VVT system from a powder, with the toothed wheel (1) having an at least approximately cylindrically shaped housing (2) which is delimited in axial direction by one respective end face (6, 7) and which has an outside surface (3), and at the outside surface (3), a toothing (8) having teeth (9) and tooth roots (10) between the teeth (9) is embodied at a distance to both of the end faces (6, 7), and the toothing (8) has a tooth root circle (25) having a tooth root circle diameter, and the powder is filled into a mold (28) and pressed by means of at least one punch, and protrusions (11, 20) are embodied at least in the region of the teeth (9) at the outside surface (3) of the housing (2) and projecting over the latter in radial direction.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. §119 of Austrian Application No. A 50505/2012 filed on Nov. 12, 2012, the disclosure of which is incorporated by reference.

The invention relates to a method for producing a toothed wheel in net shape or near-net shape quality, in particular a chain wheel, for a VVT system from a powder, with the toothed wheel having an at least approximately cylindrically shaped housing which is delimited in axial direction by one respective end face and which has an outside surface, and at the outside surface, a toothing having teeth and tooth roots between the teeth is embodied at a distance to both of the end faces, and the toothing has a tooth root circle having a tooth root circle diameter, and the powder is filled into a mold and pressed by means of at least one punch, as well as a toothed wheel, in particular a chain wheel, for a VVT system made of a powder, with the toothed wheel that has an at least approximately cylindrically shaped housing that is in axial direction delimited by one respective end face and that has an outside surface, and at the outside surface, a toothing having teeth and tooth roots between the teeth is embodied at a distance to both of the end faces, and the toothing has a tooth root circle having a tooth root circle diameter.

The importance of producing near-net-shape components is increasing, as thereby those components can be produced considerably more cost-efficiently. It seems that powder-metallurgy is predestinated for this purpose, as also components having a complex geometry can be manufactured by way of this technology without requiring considerable reworking. But also this technology is reaching its limits, if the geometry is getting too complex, since thin-walled component regions or components bear a higher risk of fracture and consequently an increased spoilage due to the adhesion of the components at the walls of the mold.

Regarding the manufacture of sintered components it is proposed in prior art to assemble such components from individual parts. Document DE 10 2010 034 014 A1 for example describes a method for the powder-metallurgical production of a rotational body, in which a first starting body is compacted from metal powder and a second starting body is formed from metal separately from the first starting body, the starting bodies being placed adjacent to each other in axial contact via end faces in relation to a longitudinal axis of the rotational body and being connected to be permanently fixed, with the first base body being compacted from an aluminum-based powder and the second base body formed from an aluminum material and the starting bodies being collectively sintered at their respective end faces.

The objective of the present invention is to create an above-mentioned toothed wheel in a press-technical way.

The objective is on the one hand achieved by the method previously mentioned and on the other hand by the above-mentioned toothed wheel, and it is according to the method provided that protrusions are embodied at least in the region of the teeth at the outside surface of the housing and projecting over the latter in radial direction, or it is for a toothed wheel provided that protrusions are formed at least in the region of the teeth at the outside surface of the housing and projecting over the latter in radial direction.

It is here advantageous that the wall thickness of the housing can be reduced, with the result that a corresponding reduction of weight can be achieved, but it is nevertheless possible to produce the toothed wheel by means of powder-metallurgical methods, so that it is also possible for a toothed wheel exhibiting a complex geometry to be produced cost-efficiently, as no or only slight reworking is required. It is thus easier to produce high-precision toothed wheels.

According to a variant of embodiment of the method and the toothed wheel it is provided that the protrusions are in axial view embodied in the type of a wave profile. By avoiding edges at the transition regions between the protrusions and the surface of the housing—as seen in radial view—a better demolding characteristic and a better compressibility of the powder or the toothed wheel is achieved. Furthermore, the weight of the toothed wheel is thereby reduced at at least approximately constant stability in the region of the teeth during the pressing step.

It is also possible for the protrusions to be formed from axially elongating the recesses for the tooth roots of the toothing, with the result that also the demolding characteristic and the compressibility can be achieved due to the possibility of the simpler design of the punch.

It can furthermore be provided that the protrusions are repressed. Due to this repressing, which can take place during the shaping by accordingly adjusting the at least one punch, the supporting function of the protrusions for the teeth of the toothing is improved.

The powder is preferably compressed by means of a multi-part punch and a multi-part die. Due to this multi-part design, an improvement of the powder compression is achieved. A better production of components exhibiting a complex geometry, in particular undercuts, is furthermore allowed. It is additionally also possible to simplify demolding characteristics.

It can be provided that the diameter of the tooth root is manufactured to be smaller than a maximum outside diameter of the housing. It is thus possible to reduce the powder used per component and therefore also the weight of the toothed wheel.

It is preferred if the protrusions have a height beyond the surface of the housing, which is selected from a range having a lower limit of 20% and an upper limit of 70% of a tooth height of the teeth. In the event of this height being below 20%, the protrusions achieve a supporting function though, it could however be noted that a higher number of tooth fractures occurred in the mold. Above 70%, there was the risk that the protrusions disturbed the interaction of the toothed wheel with a further tooth element meshing with the toothed wheel or the interaction of the toothed wheel with the chain links of a chain.

It is possible for the protrusions to be arranged directly adjacent to the teeth in axial direction, with the result that the supporting effect for the teeth is recognized more clearly. It is nevertheless also possible that the protrusions are arranged to be spaced apart from the teeth in axial direction. This can particularly be achieved by a subjecting the tooth wheel to a machine-cutting process, with the result that on the one hand, the supporting function can be improved while the tooth wheel is being produced, on the other hand, however, the meshing of the further tooth element or the chain with the toothing of the toothed wheel can be improved due to the spacing of the finished toothed wheel. This embodiment is particularly advantageous if the diameter of the tooth root circle is smaller than the maximum outside diameter of the housing.

It can furthermore be provided that the protrusions are arranged in the regions of both of the axial end faces of the teeth, i.e. the teeth are in each case arranged between two protrusions, with the result that a better stabilization of the teeth during the pressing can be achieved.

Firstly, it should be pointed out that the same parts described in the different embodiments are denoted by the same reference numbers and the same component names and the disclosures made throughout the description can be transposed in terms of meaning to same parts bearing the same reference numbers or same component names. Furthermore, the positions chosen for the purposes of the description, such as top, bottom, side, etc., relate to the drawing specifically being described and can be transposed in terms of meaning to a new position when another position is being described. Individual features or combinations of features from the different embodiments illustrated and described may be construed as independent inventive solutions or solutions proposed by the invention in their own right.

TheFIGS. 1 to 4show a first variant of embodiment of a toothed wheel1, in particular a chain wheel, in different views.

The toothed wheel1according to theFIGS. 1 to 4is provided for a so-called VVT system (variable valve timing system). The toothed wheel1according to theFIGS. 1 to 4is in particular embodied as a stator for a VVT system.

Such stators, as they are also described by the above-mentioned DE 10 2010 034 014 A1, are used for producing swing-wing adjusters for adjusting the rotational angular position of a valve control shaft, e.g. a camshaft, relative to a crankshaft of an internal combustion engine. Stator refers to the part of the swing-wing adjuster which is driven in a in a fixed rotational angular relationship to the crankshaft and outputs onto the valve control shaft via a rotor of the swing-wing adjuster. The rotor can be rotated back and forth about the longitudinal axis relative to the stator within a limited pivoting angle and thus the rotational angular position of the valve control shaft relative to the crankshaft can be adjusted. The stator can be mechanically coupled to the crankshaft by means of its drive disc, in particular by a chain drive or a cogged-belt drive.

According to a powder-metallurgical process, the toothed wheel1is manufactured from a sintering powder, in particular from a metal powder, preferably an iron powder. Such powder-metallurgical processes have been known from prior art and include in particular the process steps of optional mixing of powders, compressing powder to achieve a green compact, optionally machining the green compact, sintering the green compact, calibrating the sintered component, optionally reworking, such as grinding, washing, curing and suchlike. As these principle process steps and the different powder-metallurgical methods have been known from prior art, it is at this point referred to relevant literature.

The toothed wheel is furthermore manufactured to have net shape or near-net shape quality. Net shape quality in this case means that no machine-cutting is carried out after sintering. Near-net shape, in contrast, refers to a quality that allows a slight machine-cutting for forming the final contour. These terms will be used within the scope of this description in accordance with the technical language use.

The toothed wheel1has at least one approximately cylindrically shaped housing2. “At least approximately cylindrically shaped” means that it is possible for an outside surface3and/or an inside surface4of the housing2to deviate from an exact cylindrical shape depending on the intended use of the toothed wheel1.

In axial direction according to arrow5, the housing2is delimited by a first end face6and a second end face7.

A toothing8is arranged or embodied on the outside surface3, which toothing8has teeth9and tooth roots10between the teeth9.

The toothing8is designed for letting a drive chain engage. There is however also the possibility that the teeth9have an other shape, for example for a toothed wheel or a toothed bar of another toothed wheel or generally a further toothed part having a toothing to engage.

The toothing8is arranged to have a distance to both of the end faces6,7, and in the variant of the embodiment illustrated, the distance to the first end face6is smaller than the distance to the second end face7.

The toothing8is designed to be integral with the housing2, i.e. deviating from the above-cited prior art the tooth wheel is not composed of two components. Generally, the entire toothed wheel1is designed to be one piece and integral.

Several protrusions11are arranged or embodied on the outside surface3of the housing2to project beyond the latter in radial direction. The protrusions11are arranged in the region of the teeth9. The protrusions11are in particular arranged between two tooth roots10in the region of tooth end faces directing in radial direction.

The cross-section of the protrusions11—as viewed in axial direction according to arrow5—can be square, rectangular, triangular, trapezoid, polygonal, etc. In the preferred embodiment, the protrusions11are however embodied as a kind of a wave profile. It is preferred if the wave troughs13are disposed below the tooth roots10and the wave peaks14below the tooth crests15of the teeth9, as can be gathered particularly from the detail inFIG. 5. As viewed in radial direction in each case, the deepest places of the wave troughs13are particularly arranged exactly below the deepest places of the tooth roots10and/or the highest places of the wave peaks14are exactly disposed below the highest places of the tooth crests15, in each case within the frame of the manufacturing tolerances. In the case of this embodiment, any protrusions11are connected to one another to be one common wave profile. It is essentially possible to approximately reproduce the “wave shape” of the toothing8by means of the protrusions11. It is at this point expressively stated that no further toothing is formed from these wave shape of the protrusions11.

In the preferred embodiment, one protrusion11is disposed in the region of one tooth9, with the result that one protrusion11is formed in the region of each tooth9.

It should be noted that it is possible within the scope of the invention that more than one protrusion11, e.g. two, etc., in the region of one of the tooth end faces12are arranged per tooth9or in the region of individual teeth9.

In radial direction, the protrusions11can have a height16(FIG. 2) above the outside surface3of the housing2, which height is selected from a range having a lower limit of 20%, in particular 30%, and an upper limit of 70%, in particular 60%, of a tooth height17(FIG. 5) of the teeth9. This height16is in this case measured starting from that place, from where the outside surface3of the housing2stops having the cylindrical shape, as it is e.g. formed inFIG. 2in the region following the second end face7.

A width18of the protrusions11in axial direction according to arrow5can be selected from a range having a lower limit of 5%, in particular 10%, and an upper limit of 80%, in particular 70%, of a housing width19in the same direction. It is particularly possible for the protrusions11to extend from the toothing8up to the first end face6, as can be gathered fromFIGS. 1 to 4.

It is in principle possible that the protrusions11are arranged on only one side of the teeth9, as viewed in axial direction according to arrow5. TheFIGS. 1 to 4however show the preferred embodiment of the toothed wheel1, where—besides the protrusions11in the region of the tooth end face12—protrusions20are also arranged in the region of a further tooth end face21directing towards the, or in the direction of the second end face7.

It is in principle possible that those protrusions20are embodied like the protrusions11, so that it is in this context referred to the above-mentioned explanations.

In the preferred embodiment, however, these further protrusions20are designed to be ramp-shaped, having an ascending height starting at the outside surface3of the housing2up to the region of the teeth9, as can particularly be gathered fromFIGS. 3 and 4. The inclination can in this case be selected from a range having a lower limit of 0.5° and an upper limit of 5°. This being the case, it is also possible for the further protrusions20to have an inclination of 0°, in particular in the region of the teeth9.

As can be gathered from these further protrusions20inFIGS. 1 to 4, the protrusions20can also end ahead of the second end face7of the housing2, so that a region22of the cylindrically shaped housing2stays free from further protrusions. This also applies to the protrusions11. It is naturally also possible for the further protrusions20to extend to the second end face7of the housing2.

Referring to the terms “cylindrically shaped housing2” and “protrusions11,20”, it is generally noted that the protrusions11or the further protrusions20start where the housing starts deviating from the cylindrical shape. It is in this case also possible that the housing is stepped, i.e. has several cylinders following one another and exhibiting different diameters. In this case, the respective description regarding the protrusions11or20refers to the respectively corresponding cylindrically shaped outside surface3.

It is further noted that the housing2can at its inside surface4also have functional installations that are designed to be integral with the housing2, preferably integral with the housing2by way of one or several pressing steps. The wording “at least approximately cylindrically shaped” above refers to the housing2deviating from the cylindrical shape due to these installations.

FIGS. 1 to 4furthermore show that the protrusions11exhibit a geometry different from the further protrusions20. It is within the scope of the invention however possible that the geometry of protrusions11is the same as of the further protrusions20.

The further protrusions20are separated from one another by means of recesses23. In the preferred embodiment, these recesses23are formed by axial elongation of recesses24for forming the tooth roots10of the toothing8. In other words: the tooth roots10are elongated in the direction towards the second end face7of the housing2. It is in this case preferred if the diameter of the recesses23decreases as viewed in top view between the further protrusions20in the direction towards the second end face7of the housing, i.e. if they are embodied to be at least approximately tapering to a point, and the “point” is designed to be rounded.

It is also possible that the recesses23between the further protrusions20have another cross-sectional shape, e.g. rectangular or trapezoid or having rounded lateral faces, etc. The rounded lateral faces are in this case also possible for the tapering design of these recesses23.

The height16in radial direction of the protrusions11can be selected in such a way that these protrusions11reach or have their maximum height16at the height of a tooth root circle25of the tooth roots10, as can be gathered fromFIG. 5. The tooth root circle here designates the diameter of the circle that is formed by the deepest places of the tooth roots10.

There is nevertheless also the possibility that the protrusions11extend in radial direction to above the tooth root circle25or end below the latter.

According to another embodiment, it may be provided that the tooth root circle25has a smaller diameter than a maximum outside diameter of the cylindrically shaped housing2in the region adjacent to the tooth roots10, in other words: the tooth roots10are formed by negative depressions in the housing2.

In the embodiment of the toothed wheel1shown inFIGS. 1 to 4, the protrusions11and20are arranged according to arrow5in axial direction to be directly adjacent to the teeth9of the toothing8.

InFIGS. 6 and 7, another and optionally independent embodiment of the toothed wheel1is shown, with the same reference numbers or same component names as in the above Figs. being used for the same parts. In order to avoid unnecessary repetitions, reference is made to the aboveFIGS. 1 to 5.

The essential differences as compared to the above-described embodiment of the tooth wheel1is that, on the one hand, only the further protrusions20are embodied, i.e. only the region between the first end face6of the housing2and the teeth9is free from protrusions, and that, on the other hand, the further protrusions20are arranged to be spaced apart from the teeth in axial direction, i.e. a circumferential groove26between the teeth9and the further protrusions20is embodied.

This embodiment is made of a sintered and calibrated “blank” of a toothed wheel1, which is shown inFIG. 1, by way of machine-cutting. For this purpose, at first the blank has the toothing8extending in axial direction to the first end face6of the housing2. A section of this toothing8starting at the first end face6is then removed.

Further, the further protrusions20of the blank are embodied to lie against the teeth9, and then, a part of the further protrusions20is removed in the region adjacent to the teeth8by forming the groove26.

FIG. 7shows the finished toothed wheel1after these machining steps. In this embodiment, the toothed wheel1is thus produced in the near-net shaped quality.

FIG. 8shows a detail of a pressing tool27for producing the toothed wheel1.

It is noted that this pressing tool27can be used for compacting the powder for forming the green compact for the toothed wheel1and/or for calibrating the sintered toothed wheel1. The method according to the invention thus refers to the pressing step and/or the calibrating step of the powder-technological production of the toothed wheel1.

The pressing tool27has a mold28, a punch29and a die30. The punch29and/or the die30are embodied to be displaceable relative to each other in vertical direction.

It is preferred if the punch29is designed to be multi-part and has at least a first part of punch31and a second part of punch32. This being the case, the first part of punch31is disposed between the mold28and the second part of punch32. The two parts of the punch31,32are embodied to be displaceable independent from each other.

It is also preferred if the die30is embodied to be multi-part and has at least a first part of die33and a second part of die34. This being the case, the first part of die33is disposed between the mold28and the second part of die34. The two part of the die33,34are designed to be displaceable independent from each other.

FIG. 9shows a detail of the toothed wheel1, and the intersection line VIII-VIII corresponds to the section through the pressing tool27inFIG. 8. The dashed line illustrated inFIG. 8represents the tooth contour of the toothing8

Splitting the punch29into the two parts of the punch31,32and splitting the die30into the two parts of the die33,34is such selected that the part of punch31and the part of die33are provided for machining or embodying the toothing8and the part of punch32and the part of die34are provided for machining or embodying the protrusions11.

Using this pressing tool27it is possible to produce the toothed wheel1in net shape or near-net shape quality.

Optionally, at least regions of the toothing8are brushed and/or grinded after the toothed wheel1has been produced.

The multiple parts of the punch29and/or the die30allow the protrusions11,20to be repressed by way of adjusting the part of punch32and/or the part of die34.

According to the method for producing a toothed wheel1in net shape or near-net shape quality for a VVT system it is provided that the toothed wheel1having the at least approximately cylindrically shaped housing2which is in axial direction delimited by one end face6,7and which has the outside surface3, is made from a powder, and at the outside surface3, the toothing8having teeth9and tooth roots10between the teeth9is embodied at a distance from the two end faces6,7, and the toothing8has a tooth root circle25having a diameter, and the powder is filled into the mold28and compacted by means of at least one punch, and protrusions11,20are formed in the region of the teeth9at the outside surface3of the housing2, which protrusions project beyond the latter in radial direction.

This method can also be used for the production of other sintered parts, such as cogged-belt wheels or chain wheels.

The method is particularly provided for producing thin-walled sintered parts having a toothing8.

The exemplary embodiments show possible embodiment variants of the toothed wheel1and the pressing tool27.

For the sake of good order, finally, it should be pointed out that, in order to provide a clearer understanding of the structure of the toothed wheel1and the pressing tool27, they and their constituent parts are illustrated to a certain extent out of scale and/or on an enlarged scale and/or on a reduced scale.