Patent Application
20150292366
The present invention relates to a camshaft adjuster having a rotor and a stator, the rotor having a connecting area for rotationally fixed attachment of a camshaft and the rotor being made of a sintered material at least in sections.
The present invention also relates to a method for producing a rotor for a camshaft adjuster.
Generic camshaft adjusters are known from the prior art, e.g., from DE 100 44 423 A1, which describes a valve timing control device for internal combustion engines. An internal combustion engine having a timing chain is described there. A sprocket wheel is thereby driven synchronously with the rotation of the engine. A camshaft for actuation of the intake or exhaust valves is described. The valve timing control device includes a first rotational part, for example, a stator, on which the sprocket wheel is formed in one piece, and a second rotational part such as a rotor, which is capable of rotating relative to the first rotational part and jointly with the camshaft, a plurality of working fluid chambers bordered between two rotational parts and a feed/discharge device for working fluid to and from the working fluid chambers for inducing a relative rotation between the two rotational parts. The sprocket wheel and at least one base part of the first rotational part are formed from a porous metal part. Working fluid supplied to the working fluid chambers may penetrate through the base part into the sprocket wheel and induce adequate lubrication of an engagement section between the sprocket wheel and the timing chain. The porous metal part may be made of sintered metal.
It is basically known that sintered materials such as sintered iron may be aftertreated in particular to produce a surface-hardened workpiece. Thus, DE 41 40 148 A1, for example, describes a method for producing a workpiece made of sintered material, in particular sintered iron, this being subjected to a water vapor treatment at temperatures below 500° C., in particular at 430° C. to 480° C. and a water vapor partial pressure of 20 mbar to 80 mbar, in particular 30 mbar to 50 mbar, as well as a subsequent surface hardening after sintering to form an oxide layer on the surface. This yields workpieces, in particular hollow wheels for starters, having a wear-resistant surface and properties unchanged at the core due to the hardening.
A similar prior art, namely EP 1 400 660 A1, also describes an integrated annular gear and a housing for use in a variable valve control mechanism. The integrated annular gear and the housing include an annular gear component, which is designed essentially with a circular shape and has teeth on its outer circumference. Furthermore, it includes a housing component, which is integrally shaped with the annular gear component as a sintered body produced from a ferrous powdered material, so that it is formed inside the annular gear component, which has receptacles extending from an inner circumference of the housing component. The complete surfaces of the annular gear component and of the housing component are covered with a vapor-oxide layer formed by a vaporization treatment and are also covered with a nitrite layer formed by a gas-soft-nitriding treatment following the vaporization treatment.
Rotors, which are part of a camshaft adjuster, are usually rotationally fixedly attached to the camshaft in a force-locking manner with the aid of a screw. Such rotors are often produced from sintered material, Sint D11 being used as a standard.
A head screw or a hollow screw having a valve insert is generally used as the means for fastening the camshaft to the rotor.
Sintered steels containing carbon and copper and mixed with MoS2 are used in most cases, and sintered material Sint D11 is particularly popular. However, this material does not have optimal properties for all applications and a low cost level at the same time. Improvements are to be achieved in particular with regard to strength, dimensional stability, processability and friction in the future contact zone, while the cost level is to be reduced at the same time.
The screw used for connecting the camshaft to the rotor is also always subject to constant function and weight optimization.
Due to the constant increase in the alternating torques to be transferred during camshaft operation, the interface between the camshaft and the camshaft adjuster should be adapted. In particular the area on the rotor should be improved in this regard. The load capacity of the fastening means and of the braced parts is to be taken into account in this adaption.
It is an object of the present invention to provide a camshaft adjuster due to the fact that the rotor has an oxide layer, which is created by water vapor application during production.
The alternating torque is transferred to the contact zones of the screw connection via the applied screw pretension and as a function of the coefficient of friction. With a steady increase in the alternating torques, this means that the pretension and/or the coefficient of friction also increase(s) for the screw connection.
The screw connection is understood here to refer to the connection of the camshaft to the rotor with the aid of a screw.
The pretension may only be increased to the extent that the tolerable stresses of the braced parts are reached. It is possible to transfer an increased amount of stress and force due to the water vapor application of the rotor.
On the one hand, weight-reducing measures necessitate a reduction in the pretension, but this may be counteracted by the water vapor application of a camshaft adjuster according to the present invention. This utilizes the effective design option of increasing the coefficient of friction while the total strength of the rotor is increased at the same time.
It is possible to omit measures known previously, such as the use of diamond disks or diamond coatings or stamping of a laser-structured surface in the contact zone since these are very cost-intensive.
The water vapor application of the rotor and the use of pairings of materials between the rotor and the camshaft are more effective and more economical. Thus not only is the coefficient of friction increased by the water vapor application but also the basic strength of the sintered material is increased. Therefore, even a powder of a lower strength may be used, which is less expensive and easier to shape.
Advantageous specific embodiments are derived from the subclaims and explained in greater detail below.
It is advantageous if the sintered material is Sint D10 or Sint D11. It is therefore possible to resort to particularly tried and tested, inexpensive and/or durable materials.
It is also advantageous if the rotor has been treated with water vapor in the area of the insertion grooves for vanes, which greatly increases the strength in this area.
Furthermore, it is advantageous if the rotor is inserted into a cover screw connection of the camshaft adjuster.
An advantageous exemplary embodiment is also characterized in that the friction-increasing oxide layer is present on the surface of the connecting area and preferably remains there. It is possible in this way to omit a form-fitting connection. It is naturally possible that, in addition to the improved frictional connection, a form-fitting connection and/or an integral connection between the camshaft and the rotor may also be used.
It is also advantageous in particular if the oxide layer is formed on a section of a front face of the rotor facing the camshaft. Assembly may be thereby simplified and the production of the rotor may be carried out less expensively. The camshaft adjuster with the screw connection integrated therein is then optimized with regard to its function, its weight and its installation space.
If the section having the oxide layer is a surface of the bottom of a central recess in the rotor running transversely, preferably orthogonally, to an axis of rotation of the rotor, then the camshaft may be held centered in the recess and the coefficient of friction between the contact partners, namely the rotor and the camshaft, may be increased.
In order to allow the assembly to be carried out more reliably, it is advantageous if the bottom forms a stop for the camshaft, acting in the longitudinal direction of the rotor.
In order for this friction-increasing oxide layer to be simple to produce, it is advantageous if the rotor is strengthened in a water vapor-induced process in at least some areas or as a whole. As a pleasant side effect, then the total strength of the rotor is also improved, at least in the areas treated with water vapor, but preferably the entire component is strengthened as a whole, i.e., “through and through.”
It is also advantageous for the total strength of the individual parts of the camshaft adjuster if the stator has a friction-increasing oxide layer on at least one or both front faces due to the water vapor application. It is then possible to achieve a greater transfer of force in the installed state and the attachment of covers with the aid of screw connections.
The present invention also relates to a method for producing a rotor for a camshaft adjuster, which is improved by the fact that the rotor is constructed of sintered material at least in some sections, and at least one area of application of the sintered material, which is provided for use of a camshaft, is treated with water vapor.
In such a process sequence, the oxide layer created on the surface of the rotor may be left in place and may be used as an active unit which prevents twisting of the camshaft relative to the rotor.
It is also advantageous if the oxide layer formed by the action of water vapor is left on the surface of the rotor, so that this oxide layer preferably interacts with the camshaft in a force-transferring manner in the installed state of the rotor inside a stator.
It is quite possible for the rotor to be produced only partially or completely of metallic sintered material.
The present invention is explained in greater detail below with the aid of a drawing illustrating an exemplary embodiment in
This
Stator 3 has an integral sprocket wheel section 4 on which teeth 5 are formed, to come into force-transferring contact with a traction mechanism; the traction mechanism, such as a chain or a belt, may be and/or has been brought into a force-transferring operative contact with a crankshaft in the internal combustion engine. The traction mechanism and the crankshaft are not shown here.
Rotor 2 may rotate about an axis of rotation 6 inside stator 3 and within a fixed angular range. Axis of rotation 6 also predefines the longitudinal direction of rotor 2 and of stator 3.
Rotor 2 has a connecting area 7, which is provided for accommodating a camshaft. The connecting area 7 is formed by a front-side recess 8, in such a way that a bottom 9 forms a stop 10 for the camshaft, in such a way that a movement of the camshaft in its longitudinal direction toward rotor 2 is limited by stop 10. At least in this area, rotor 2, which is made of sintered material, preferably a sintered material composed of metallic powders, is treated with water vapor, so that an oxide layer 11 is formed.
Whereas oxide layer 11 is present on rotor 2 only inside of recess 8, in particular on the front face of rotor 2 in the area of bottom 9, such an oxide layer 11 is also formed on both front faces 12 and 13 of stator 3. A cover is screwed onto this oxide layer 11, which is present on front faces 12 and 13 of stator 3. Joints are present in a cover screw connection, the cover screw connection including at least one or two covers and at least two fastening means 16, such as screws 17, as well as stator 3. At least one cover is screwed onto stator 3 via at least two screws 17.
Rotor 2 may also have grooves for insertion of vanes (not shown), and these grooves may also be treated with water vapor.
Ultimately it is possible for both rotor 2 and stator 3 to be treated completely with water vapor and for oxide layer 11 to be formed and/or left on only one or both front faces 12 and 13 of stator 3 and on bottom 9 of rotor 2 in recess 8 due to water vapor application of the metallic sintered material.
1 camshaft adjuster
2 rotor
3 stator
4 sprocket wheel section
5 tooth
6 axis of rotation
7 connecting area
8 recess
9 bottom
10 stop
11 oxide layer
12 first front face of the stator
13 second front face of the stator
14 first cover
15 second cover
16 fastening means
17 screw
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 219 949.7 | Oct 2012 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2013/200073 | 7/24/2013 | WO | 00 |
