Abstract:
An encoder device for use in a magnetic sensor arrangement, comprising: a metallic ring having a set of clearances in a ferromagnetic material, wherein said clearances are arranged around a circumference of the metallic ring, wherein the metallic ring is configured to generate an oscillating magnetic induction in a nearby magnetic sensor upon rotation of the metallic ring, wherein the metallic ring is made of at least one flat and strip-like sheet metal material, two ends of which are joined to form a loop.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to encoder devices comprising magnetic or ferromagnetic phonic wheels or impulse wheels formed as a metallic ring configured to generate an oscillating signal in a magnetic sensor. The frequency of the sensor is proportional to the speed of rotation of the ring. Encoder devices of this type are used as rotary speed sensors in many fields of application, such as automotive technology and rail vehicles. 
       BACKGROUND OF THE INVENTION 
       [0002]    Rotary speed sensors for rail vehicles such as a locomotive or a multiple unit are used to reliably and precisely determine the rotary speed of the wheels of an axle. This applies in particular to traction control, but also to wheel-slip protection. Rotary sensors are further used in registration, train control, door control, etc. Multiple rotary speed sensors may be found in various parts of the vehicle. In particular the rotary speed sensors used for traction control are used in extremely harsh operating conditions encountered by rail vehicles. 
         [0003]    It has turned out that the principle of scanning a ferromagnetic measurement scale with a magnetic sensor is extremely robust and often does not fail even if a seal has failed and the pulse generator is covered with a layer of brake dust or other dirt. 
         [0004]    Phonic wheels used as encoder devices of this type are usually machined from stainless steel with a DIN-867 teeth design and are, therefore, fairly expensive. Some cost-saving potentials have been achieved by integrating the phonic wheel with an end cap as used for clamping the inner ring of a railway bearing onto the axle, e.g., in the SKF Axletronic odometer for axle box front covers described under http://evolution.skf.com/zino.aspx?articleID=15221. A further bearing assembly with a metallic tooth ring is disclosed e.g., in U.S. Pat. No. 4,069,435. 
         [0005]    The invention addresses the problems of simplifying the manufacture, maintenance and exchange of the encoder impulse wheel in a sensor arrangement, reducing the costs thereof and simplifying its adaptation to different sensor designs. 
       SUMMARY OF THE INVENTION 
       [0006]    This object is achieved with a bearing unit having an encoder and an axle box including such an encoder device. A further aspect of the invention relates to a method for manufacturing the encoder device. 
         [0007]    According to an essential aspect of the invention, the encoder device for the use in a magnetic sensor arrangement comprises a metallic ring with a set of clearances in a ferromagnetic material. The clearances are preferably homogeneously distributed around the circumference of the metallic ring and the clearances together with ferromagnetic parts of the metallic ring arranged between pairs of adjacent clearances generate an oscillating magnetic induction in a nearby magnetic sensor upon rotation of the metallic ring. It is proposed that the metallic ring is made of a flat and strip-like sheet metal material, the ends of which are joined to form a loop. Instead of machining the encoder wheel from a solid piece of metal, the required shape can simply be stamped out of the sheet metal, which is then bent and closed to a loop so as to form a ring or a wheel. This does not only save costs, but also simplifies the replacement and maintenance of the metallic ring, and the pattern and the spacing of the clearances may be adapted in a simple way to the sensor design. 
         [0008]    In a preferable embodiment, a prefabricated metal tape with clearances may be used to form the metallic ring for the encoder device. 
         [0009]    In an advantageous embodiment of the invention, the encoder device further comprises means for connecting the end portions of the strip-like sheet-metal material in a connecting portion of the metallic ring. The means may, e.g., be bolts or clamping means such as slits, or other connecting means such as welding points or the like. 
         [0010]    The end portions of the strip-like sheet metal material may either be overlapping in the connecting portion and simultaneously fixed to a support ring around which the sheet metal strip is wound, or may alternatively be bent radially inwardly and clamped by a clamping slit in the connecting portion of the metallic ring. 
         [0011]    Further, it is possible that the length of the strip is substantially identical to the circumference of the support ring such that the ends of the strip abut upon each other and/or face each other with a minute slit which is small enough not to essentially disturb the homogeneous distribution of the clearances around the circumferences of the metallic ring. In this connection it is to be noted that the distribution of the clearances around the circumference of the metallic ring is preferably homogeneous. However, other types of distributions enabling an absolute detection of the rotary position would be possible in principle. 
         [0012]    Further, a reliable mounting of the metallic ring on a support ring may be achieved when the metallic ring comprises holes for bolting the metallic ring onto the support ring. 
         [0013]    A further aspect of the invention relates to an encoder device comprising a support ring with a substantially cylindrical outer surface, wherein the strip-like metal material forming the metal ring is wound around the outer surface of the support ring and fixed thereon. Due to the supporting ring, a thin sheet metal material may be used for the encoder/phonic/impulse wheel, the ring-shape of which will be stabilized by the support ring. 
         [0014]    A cost-saving production of the strip or tape of sheet metal material can be achieved when the clearances are stamped out of this strip. 
         [0015]    In particular for heavy duty applications, it is preferable when the clearances have a substantially rectangular shape and are surrounded by the ferromagnetic material. The metallic borders of the clearances protect the latter from wear and stabilize the metallic parts arranged between the clearances in particular as compared to an alternative embodiment where the clearances are open on one side and defined between two tabs protruding from a lateral belt of the strip such that a comb-like structure is formed. 
         [0016]    A further aspect of the invention relates to a bearing unit with an inner ring and an outer ring rotating relative to one another, and a magnetic sensor disposed nearby the portion of the metallic ring being provided with the clearances in order to measure the oscillating magnetic induction caused by the rotation of the latter. The metallic ring is connected to a first one of the rings and the magnetic sensor is connected to a second one of the rings, wherein the second ring is preferably the non-rotating ring of the application, which simplifies the readout. 
         [0017]    Further, it is preferable that an end plate of the bearing unit used for clamping a first one of the metallic rings is used as a support ring as mentioned above having an essentially cylindrical outer surface on which the strip-like metal material forming the metal ring is wound and fixed. Since the metal ring is already ferromagnetic, the end plate may be manufactured from non-magnetic materials. 
         [0018]    Further, it is proposed to provide an axlebox for railway vehicles including a bearing unit as described above, and an end cover, wherein the magnetic sensor is mounted in the end cover. 
         [0019]    A further aspect of the invention relates to a method for manufacturing an encoder device for use in a magnetic sensor arrangement, comprising a metallic ring as described above. It is proposed that the metallic ring is made of at least one flat and strip-like sheet metal material, two ends of which are joined to form a loop. 
         [0020]    Preferably, the flat and strip-like sheet metal material is cut from a prefabricated roll of metal tape with the clearances preformed therein at equal distances, preferably by stamping. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0021]    Further advantages and features of the invention will be described in the following description of the specific embodiments of the invention, which should by no means be construed as limiting its scope, but rather to enable this application in a specific field and give the skilled reader incentives to adapt it to other fields of application envisaged. 
           [0022]      FIG. 1  shows a cross-sectional view of a railway axlebox with a bearing unit equipped with an encoder device according to the invention. 
           [0023]      FIG. 2  is an end cap of the encoder device of  FIG. 1  with a metallic ring formed of a strip-like sheet metal material wound around the end plate. 
           [0024]      FIG. 3A and 3B  are schematic illustrations of the manufacturing method of the end plate according to  FIG. 2 . 
           [0025]      FIGS. 4A-4F  illustrate different alternative possibilities of the fixing the strip-like metal material tape on the radially outer surface of a support ring. 
           [0026]      FIG. 5  illustrates an alternative embodiment wherein the clearances in the metal tape are open on one side, and a corresponding method for manufacturing an encoder device for an axially oriented magnetic sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]      FIG. 1  is a schematic view of a bearing  10  with an end plate  12  serving as a support plate for a phonic wheel/impulse wheel for a magnetic anti-skidding sensor arrangement for detecting the speed of rotation of an axle (not shown), on which an inner ring (not shown) of the bearing is mounted. The end plate  12  is bolted on the end of the axle and clamps the bearing  10 , which is formed as a double-row angular contact roller bearing with cylindrical rollers arranged between the inner ring and an outer ring of the bearing  10 . 
         [0028]    An end cover  20  is connected with the outer ring via an axlebox housing  22 . A magnetic sensor  24  is mounted in the end cover  20 , so as to be oriented radially inward such that its sensing surface is oriented parallel and in proximity to the radially outer surface of a metallic ring  26  arranged on the radially outer surface of the end plate  12  with a small air gap  28  between the sensor  24  and the ring  26 . The ring  26  is the encoder ring or phonic wheel of the magnetic anti-skidding sensor arrangement which generates an oscillating inductance which can be measured by the magnetic sensor  24  and the frequency of which is proportional to the speed of rotation of the axle  14 . The sensor  24  is read out via a signalling connection  30  by a control unit (not shown). 
         [0029]      FIG. 2  illustrates the end plate  12  with the metallic ring  26  detached from the bearing unit. The metallic ring  26  is provided with many basically rectangular clearances  32  distributed at equal distances around the circumference of the ring  26 . As will be explained later, the metallic ring  26  is actually made of a band-like strip of sheet metal from which the clearances are punched out. 
         [0030]    The clearances  32  have a longitudinal direction oriented in the axial direction of the end plate  12  and are surrounded by metallic ligaments or bridges with the overall shape of a ladder. 
         [0031]      FIG. 3A and 3  B show schematically how the metallic ring  26  is manufactured. First, a piece with a length slightly longer than the circumference of the radially outer surface of the end plate  12  is cut off from a prefabricated roll of metal tape with the clearances  32  punched out, resulting in a strip-like member as shown in  FIG. 3A . The typical diameter of the end plate  12  for railway applications is around 200 mm, the length of the metal strip is around 650 mm. The strip is then closed to a loop and wound around the end plate  12  by joining its ends together and is then fixed on the radially outer surface of the end plate  12  by any of the means illustrated in  FIGS. 4A to 4E  below. 
         [0032]    The width of the strip is around 20 mm, and the width of the clearances  32  (in the circumferential direction) is around 5-8 mm. 
         [0033]      FIG. 4A  shows a first possibility for closing the metal strip illustrated in  FIG. 3  by connecting its end portions in a connecting portion  37  so as to form the metallic ring  26 . In the embodiment of  FIG. 4A , the end plate  12  has a radially outer surface which is not perfectly cylindrical but is rather provided with a slight recess, where the radially outer surface is recessed with respect to the perfectly cylindrical shape by an amount corresponding to the thickness of the metal sheet. The end portions of the strip are arranged so as to be overlapping, and are welded together by a welding point. The thickness of the sheet metal used to fabricate the strip and the depth of the recess in the end plate  12  is preferably around 0.8-1 mm. The two end portions of the strip may be fixed to the end plate  12 , which serves as the support ring, by two lateral welding points or by bolts  34  as illustrated in  FIG. 4B and 4C . 
         [0034]    In the embodiment of  FIG. 4B , the strip is cut on both of its ends within a clearance, preferably such that the major part of the lateral metallic portions delimiting the clearances  32  in which the strip is cut remain connected to the strip. These lateral portions are overlapping to an extent that it is possible to bolt them together onto the end plate  12 , as illustrated in  FIG. 4B . 
         [0035]      FIG. 4C  shows an alternative embodiment, wherein the bolts  34  are arranged on the lateral belts of the punched metal strip in a portion between two neighbouring clearances  32 , i.e. on a centre line of one of the ligaments separating the clearances. 
         [0036]    The circumference of the end plate  12  or, more precisely, the circumference of the metallic ring  26 , which corresponds to the circumference of a circle with a radius corresponding to the radius of the end plate  12  plus the thickness of the sheet metal, is a multiple of the pitch distance of the clearances  32  punched in the strip, such that the clearances  32  in the metallic ring  26  as mounted on the end plate  12  are homogenously distributed around the circumference of the metallic ring  26  without any discontinuities at the connecting portion of the metallic ring, where the end parts of the strip are overlapping. 
         [0037]      FIG. 4D  shows and alternative possibility for mounting the metallic ring  26  onto the end plate  12  to form a phonic wheel. The end portions of the strip are bent radially inward in a bending point  33  and fitted into the clamping notch  36  provided in the radially outer surface of the end plate  12 . The connection of the strip with the end plate  12  may be enhanced within the notch  36  and/or on the outer surface of the end plate by means of adhesive bonds, resin or the like, wherein it is even possible to fill the clearances  32  with non-ferromagnetic materials such as polymers. 
         [0038]      FIG. 4E  shows two possibilities for the choice of the bending points  33  for the fixation according to  FIG. 4D , and/or for the choice of the centre of the overlapping portion in the alternative of  FIG. 4B . It is preferred that these points are either in the centre of the one of the clearances  32  (dotted line, reference number  33   b ), or between two adjacent clearances (dashed line, reference number  33   a ) for symmetry reasons. 
         [0039]    It is further possible to have the ends of the strip abutting to one another without any overlapping portion, and to fix the strip on the end plate  12  by other means, e. g. adhesive bonds. 
         [0040]    Further alternative or complementing possibility for fixing the strip on the end plate  12  is to provide tabs or ears  38  with through holes on one or both sides of the strip through which the strip could then be bolted onto the radially outer cylindrical surface of the end plate  12  or of another support plate. This is illustrated in  FIG. 4F . 
         [0041]      FIG. 5  shows a further alternative embodiment of the invention with a metallic ring  26  configured to generate signals for a magnetic sensor with an axial orientation/sensing direction. The strip is provided with equidistantly spaced tabs  40  defining clearances  32  between them which are surrounded by the ferromagnetic metal material of the sheet metal strip on three sides and open on one side. For manufacturing the ring  26 , the tabs are bent by 90° and then the belt  42  connecting the tabs  40  is wound around a support plate with a cylindrical outer surface and fixed thereon by any of the means illustrated in  FIGS. 4A to 4F .