The invention concerns an encoder element for displaying an adjustment and/or movement of a bearing constituent, in particular a constituent of a wheel bearing. The invention also relates to a bearing with such an encoder element.
An encoder generally serves for recording one or more measured variables that are characteristic of the adjustment and/or movement of a movable bearing constituent. Understood here as measured variables that are characteristic of the adjustment of the bearing constituent are, in particular, an angle of rotation, a tilting with respect to a bearing axis or a distance from a predetermined reference point. Measured variables that are characteristic of the movement of the bearing constituent particularly comprise the rotational speed, the direction of movement or variables that characterize the vibration of the bearing constituent. Encoders are also used for recording measured variables derived from the adjustment information and/or movement information as such, particularly acting forces and torques or the temperature of the bearing.
The use of magnetic encoders for wheel bearings is known in automotive engineering. Corresponding encoders are known, for example, in WO 2006/026950 A2, DE 20 2006 017 414 U1 and EP 1 722 238 A2.
The known encoders respectively comprise an encoder element which is formed by a carrier and a magnetic layer applied thereto. In this case, the carrier is an annular sheet-metal part. The magnetic layer consists either of a thermoplastic or an elastomer, this material in each case being filled with a magnetic powder. In the case of an elastomer layer, it is usually vulcanized on the carrier. In the case of a thermoplastic layer, it is usually adhesively attached to the carrier.
For use as an encoder, the layer of the encoder element filled with the magnetic powder is provided with a magnetic coding in a downstream production step.
The production of such encoder elements is comparatively complex. Moreover, the magnetic layers of these encoder elements must be made comparatively thick for dependable processing under the conditions of the process. This means that such an encoder element requires a comparatively large installation space.
Also known, from DE 10 2004 063 462 B3, is a method for producing a scale carrier for a magnetic length or angle measurement. In the case of this method, a groove formed in a machine part is filled with a magnetic powder paste. After hardening of the magnetic powder paste, the surface formed over the groove is smoothed flush with the adjacent surface of the machine part, in particular by machining processes. However, the production of such a scale carrier is likewise comparatively complex.
The invention is based on the object of providing an easily producible and space-saving encoder element for displaying an adjustment and/or movement of a bearing constituent. The invention is also based on the object of providing a bearing with such an encoder element.
This object is achieved according to the invention with respect to the encoder element by the features of claim 1. Accordingly, the encoder element includes a carrier with a magnetic or magnetizable encoder layer applied flatly to it. The encoder layer is formed here from a matrix material which is liquid in the raw state, with added magnetic powder, and is applied directly to a carrier surface from the liquid raw state by a coating process.
Understood here as the coating process—in particular in differentiation from casting processes, adhesive bonding processes and vulcanizing processes, which require separate prefabrication of the encoder layer or the use of a mold—is a procedure in which the liquid coating material is freely applied directly to the carrier surface. Particularly suitable coating techniques comprise an operation involving application by brushing, spraying, dipping or pressing and a subsequent hardening process.
Such a coating process can, on the one hand, be easily carried out from technical aspects of production. On the other hand, an encoder layer with a particularly small thickness can be realized in this way. In a preferred configuration, the thickness of the encoder layer produced according to the invention is less than 0.8 mm, in particular between 0.3 mm and 0.7 mm.
Used with preference as the matrix material for the encoder layer is a lacquer. However, a different coating compound (paint), an adhesive or a resin may also be used as the matrix material, provided that this material in the hardened state enters into an adhesive bond with the carrier and can be applied by means of the coating process. The matrix material may also be composed of the mixture of more than one substance of the aforementioned type.
The magnetic powder is preferably a ferrite, a rare-earth metal or a mixture of such magnetizable constituents. In an advantageous configuration, at least 50% by volume of magnetic powder, measured in the liquid raw state, is added to the matrix material.
In a preferred configuration of the invention, the encoder element is developed into the finished encoder by a magnetization being impressed on the encoder layer.
In an expedient variant of the invention, the encoder layer carries an annular magnetization track with a polarity that alternates periodically in the circumferential direction, i.e. a magnetization track of which the magnetization—particularly the axially oriented magnetization—periodically changes signs in the circumferential direction. Optionally, a number of magnetization tracks arranged concentrically in relation to one another may be impressed into the encoder layer. These magnetization tracks differ in particular in that the polarity of every two magnetization tracks varies in a different way in dependence on the angle of rotation.
Such an encoder serves, in particular, for displaying a rotational adjustment, rotational speed and/or direction of rotation, etc. of the associated bearing constituent.
In an alternative configuration, a magnetization that is homogeneous in the circumferential direction is impressed in the encoder layer. The encoder implemented in such a way makes it possible, in particular, to display a tilted position of the associated bearing constituent with respect to a bearing axis.
Both coding variants may also be implemented on one and the same encoder layer, for example in that two concentric magnetization tracks, one with polarity alternating in the circumferential direction and one with homogeneous magnetization, are provided.
To protect the encoder layer better against environmental influences, in an advantageous configuration of the invention the encoder layer is coated by a non-magnetic protective layer on the side facing away from the carrier. This protective layer preferably consists of a lacquer, a thermoplastic or an elastomer, in the latter case the protective layer expediently being vulcanized on the carrier and the encoder layer. In an embodiment that is particularly insensitive to aging effects and environmental influences, this protective layer consists of the same matrix material that also forms the basic substance of the encoder layer, but, in contrast to the encoder layer, no magnetic powder is added to the protective layer. The protective layer preferably has a smaller thickness in comparison with the encoder layer. In particular, in the case of a lacquer coating, the protective layer is preferably only a few micrometers thick.
In an advantageous variant of the invention, the carrier is formed by an angled plate which is fastened or is fastenable to the bearing constituent. In another advantageous embodiment, the encoder layer is applied directly to an inner bearing race or an outer bearing race, so that this inner or outer bearing race serves as the carrier.
In the case of a bearing in which the inner bearing race or outer bearing race has two running surfaces for rolling elements at a distance axially from one another with respect to a bearing axis, in an expedient configuration of the invention the encoder layer is arranged between these two running surfaces, and consequently in the interior of the bearing. As a result, the encoding layer is protected particularly effectively from environmental influences, in particular dirt and water.
In a further variant of the invention, the encoder layer is applied directly to a hub or a bearing flange, so that in this case the hub or the bearing flange serves as the carrier for the encoder layer.
In a further variant of the invention, the carrier of the encoder layer is formed by a rolling element cage or by a rolling element. The last-mentioned configuration is used with preference in the case of a bearing with roller-shaped rolling elements. The encoder layer is in this case applied in particular to one of the end faces of the rolling element—which is largely free from loading during the operation of the bearing. The application of the encoder layer to one or more rolling elements is advantageous in particular for testing and inspection purposes, in order to technically record the circulation and/or rotation of the rolling elements during the operation of the bearing to be tested.
In a further variant of the invention, the carrier carrying the encoder layer is part of a bearing seal. In particular, here the carrier forms a sealing surface against which a sealing lip of the bearing seal lies.
In all the aforementioned variants of the invention, the carrier surface carrying the encoder layer is preferably aligned at least partially axially (i.e. perpendicularly to the bearing axis), radially (substantially concentrically to the bearing axis) or obliquely to the bearing axis in the intended installation position of the respective carrier.
The above object is achieved according to the invention with respect to the bearing by the features of claim 21. According to this claim, the bearing comprises an encoder element of the type described above.
In order to record the orientation of a movable bearing constituent with the aid of the encoder element, the bearing expediently additionally comprises a magnetic sensor. The magnetic sensor is in this case associated with the encoder element provided with a magnetization in such a way that it records the magnetic field generated by the encoder element during the operation of the bearing. The magnetic sensor derives from this a measurement signal that is characteristic of the adjustment and/or movement of the bearing constituent.
The advantages that the invention involves are, in particular, that, as a result of the particularly flat and consequently space-saving encoder layer, the application of the same can take place at virtually any location of the bearing. Depending on the requirements that a specific bearing has to meet, the encoder layer may therefore be applied at the location that is optimal for this bearing. The production of the encoder layer is also particularly uncomplex, and consequently cost-effective.
All the variants described above for applying the encoder layer to various bearing constituents may also be used in combination with one another. In particular, a number of encoder layers may be provided on a bearing at different bearing constituents.
Exemplary embodiments of the invention are explained in more detail below with reference to a drawing, in which:
Parts and variables that correspond to one another are provided with the same designations in all the figures.
Formed between the outer race 2 and the hub 4 with the inner race 7 fastened on it are two axially spaced-apart raceways 8 and 9, which concentrically surround the bearing axis 5 in an annular form and in which ball-shaped rolling elements 10 circulate. The rolling elements 10 circulating in each of the raceways 8 and 9 are rotatably enclosed in an annular (rolling element) cage 11 in each case. Outside the raceways 8 and 9, a seal 12 or 13 is respectively provided at both end faces of the bearing 1, between the outer race 2 and the hub 4 or between the outer race 2 and the inner race 7, respectively. These seals 12, 13 serve the purpose of sealing the bearing gap 14 formed between the outer race 2 and the hub 4 and between the outer race 2 and the inner race 7 from penetrating dirt and penetrating moisture. The seals 12 and 13 also prevent lubricating grease from escaping from the bearing gap 14.
The bearing 1 further comprises an encoder element 20, represented in more detail in
Arranged outside the encoder element 20 is a magnetic sensor 24 in the form of a Hall sensor or a magnetoresistive sensor. Here, the magnetic sensor 24 is fastened to the outer race 2 in a rotationally fixed manner, in particular is adhesively bonded to it. During the operation of the bearing 1, the magnetic sensor 24 measures the magnetic field generated by the encoder element 20 and fluctuating during rotation of the hub 4 at the location of the magnetic sensor 24. The magnetic sensor 24 thereby emits by way of a feed line 25 a measurement signal correlating with the intensity of the measured magnetic field, from which the rotational speed and/or the rotationally angular orientation of the hub 4 is determined by an evaluation unit that is not represented.
The embodiment of the bearing 1 represented in
In the case of the configuration according to
Opposite the encoder layer 23, a radial bore 28 is provided in the outer race 2 for receiving a magnetic sensor (not represented here).
In the case of the variant of the bearing 1 that is represented in
The variants of the bearing 1 that are represented in
Represented in
In the configuration according to
Deveating from this, according to
In the case of the exemplary embodiment according to
The configuration of the seal 13 that is represented in
The configuration of the seal 13 that is represented in
According to
According to
By contrast with this,
On the other hand,
According to
While the encoder element 20 shown in
In the embodiment according to
If this encoder layer 23 is homogeneously magnetized, the circumferential speed of the rolling elements 54 formed as the encoder element 20, i.e. the movement of the center of gravity of the rolling elements 54, can be recorded by means of a magnetic sensor fastened to the stationary bearing constituent. If a magnetization of varying polarity in the circumferential direction of the rolling element 54 is impressed on the encoder layer 23, the rolling speed of the rolling elements 54 can also be determined. Knowledge of these variables is of interest in particular for testing and inspection purposes as part of bearing development.
Finally,
In the case of all the exemplary embodiments described, the encoder layer 23 is sprayed directly onto the component respectively serving as the carrier 21. Serving here as the starting material is a liquid lacquer suitable for application to a metal surface, to which preferably about 60% by volume of a magnetic powder of ferrites is added. After the application and hardening of the lacquer with added magnetic powder, the encoder element 20 itself is complete. In a following production step, the possibly provided protective layer 35 is then optionally applied and/or a desired magnetization is impressed.
Number | Date | Country | Kind |
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10 2007 050 256.9 | Oct 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE08/01691 | 10/16/2008 | WO | 00 | 7/12/2010 |