Abstract:
A sensor ring and method for forming same is provided in which the ring has a stamped configuration bent into a final configuration. The stamped configuration has a flat, annular sensor portion extending from a cylindrical hub portion and the sensor portion has a plurality of substantially identical, circumferentially spaced window openings therein. Each window opening has an inner edge adjacent to and spaced radially outward from the hub and an outer edge spaced radially inward from the outer peripheral end of the sensor portion and leading and trailing edges extending, respectively, from the ends of the inner and outer edges to form each window as a polygon, preferably a trapezoid. In the final configuration, the sensor portion has a bight segment extending radially outward from the hub and a sensor or finger segment extending from the bight segment in the direction fo the hub to form a U-shaped cross-section. The sensor segment has an undulation between the outer edge of each window and the outer peripheral end of the sensor portion. The depth of the undulation is correlated to the window configuration to produce fingers and window openings laying in a cylindrical or frusto-conical plane.

Description:
BACKGROUND  
         [0001]    A) Field of the Invention.  
           [0002]    This invention relates generally to a rotational velocity sensor ring and method for forming the ring.  
           [0003]    The invention is particularly applicable to and will be described with reference to a rotational velocity sensor ring for use in a speed sensor package mounted on a wheel bearing spindle of a vehicle for anti-lock and like purposes. However, those skilled in the art will recognize that the invention has broader application and can be applied in any number of industrial and non-vehicular applications in which the rotational movement of an object is to be detected.  
           [0004]    B) Incorporation by Reference.  
           [0005]    The following patents are incorporated by reference herein and made a part hereof so that details related to wheel bearings, wheel bearing spindles and sensors used with sensor rings which are conventionally well known in the art need not be described in detail in the specification of this patent.  
           [0006]    1) U.S. Pat. No. 5,696,442, issued Dec. 9, 1997 to Foster, et al., entitled “ROTATIONAL VELOCITY SENSOR RING APPARATUS AND METHOD”.  
           [0007]    2) U.S. Pat. No. 5,111,138, issued May 5, 1992 to Kramer, entitled “SPEED SENSOR HAVING A CLOSED MAGNETIC FLUX PATH FOR SENSING SPEED FROM AN AXIAL FACE OF A ROTATING MEMBER”.  
           [0008]    3) U.S. Pat. No. 5,010,290, issued Apr. 23, 1991 to Foster, entitled “EASILY INSTALLED WHEEL BEARING SENSOR PACKAGE”.  
           [0009]    4) U.S. Pat. No. 4,988,220, issued Jan. 29, 1991 to Christiansen et al., entitled “SERVICABLE WHEEL SPEED SENSOR ASSEMBLY”.  
           [0010]    5) U.S. Pat. No. 4,795,278, issued Jan. 3, 1989 to Hayashi, entitled “BEARING ASSEMBLY”.  
           [0011]    The material incorporated by reference herein does not, per se, form the present invention.  
           [0012]    C) Prior Art.  
           [0013]    In a known manner of sensing rotational velocity of a rotating body, a sensor ring, also known as an encoder ring, exciter ring or tone ring, is mounted so that it rotates with the rotating body. A variable inductance or variable reluctance sensor is mounted concentrically around the sensor ring or, alternatively, proximate to one portion of the exterior of the sensor ring. The sensor is fixedly mounted and does not rotate with the sensor ring. The sensor includes circuitry configured to provide an output signal that varies with the rotational velocity of the sensor ring. Typically, as the rotational velocity of the sensor ring increases, the frequency of the output signal increases.  
           [0014]    One known type of sensor ring comprises a machined or pressed metal ring with extending teeth substantially equally spaced around the outside perimeter of the ring. The sensor is configured so that when the ring is in certain positions, each tooth lines up with one or more poles of the sensor. When the ring is then turned from that position so that the teeth are no longer directly aligned with the pole, the sensor detects a change in inductance or reluctance of the magnetic circuit including the sensor poles and the sensor ring. It is through detecting such changes in inductance or reluctance that rotational velocity sensors operate.  
           [0015]    For the most part, sensor rings have been formed from powdered metal sintered into a desired shape. Certain metals in the composites are selected for their magnetic properties. However, the prior art has recognized that plain carbon steels, (i.e., sheet metal stock or plain carbon steel with alloying elements for enhanced magnetic properties), has superior ferro-magnetic properties and does function, if properly formed, as rotational sensor rings. Plain carbon steel sensor rings have been fabricated in a variety of ways which can be generally classified or grouped in several categories.  
           [0016]    One category can be explained as forming fingers on a rotating hub such as shown in U.S. Pat. No. 5,080,500, issued Jan. 14, 1992, which are difficult to handle in mass manufacturing and tend not to be durable. Accordingly, the fingers are strengthened by being bent back onto one another and formed into a ring such as shown in my prior &#39;442 patent cited above or interlocked together to form two hubs forming “windows” such as shown, for example, in U.S. Pat. No. 4,940,937, issued Jul. 10, 1990, which is generally not desirable.  
           [0017]    Another category forms windows on a hub such as shown in the &#39;138 patent and U.S. Pat. No. 5,166,611, issued Nov. 24, 1992. In the &#39;278 patent, the windows are formed on a hub or on a hub which is formed as a cup or in one embodiment, a hub with a “V” shaped cross-section. The “windows” are formed between the ends or edges of the hub. In practice, it is difficult to form the shapes depicted from a blank without distorting the cylindrical hub and the windows.  
           [0018]    Another type of sensor ring is shown in pictorial representation in prior art FIGS. 1A and 1B. This design has proven itself to be commercially durable, extremely rigid, and produces acceptable sensor signals. It is a variation of a design illustrated in the second embodiment disclosed in the &#39;442 patent. The sensor is produced from a stamped blank in which the hub  1  is drawn and a stepped “U” shaped sensor portion  2  as shown in prior art FIG. 1B is formed radially outward of hub  1 . The outer leg  3  of the “U” is corrugated or formed with sine shaped undulations  3  as best shown in FIG. 1B. Undulations  3  have peaks  4  and valleys  5  which correspond to the “windows” discussed above. The sensor pickup head detects the changes in the magnetic flux density which is caused by the peaks and valleys and then detects the rotational velocity of the sensor ring.  
           [0019]    All of the sensor rings discussed are functional and several have been commercially implemented. Each, however, have drawbacks and can be improved. For example, finger designs are suspect of being bent or distorted not only in use but simply in the handling and storing of a large number of rings inevitably occurring in the manufacturing process of a bearing assembly. Window designs are preferred for reasons discussed below but are difficult to accurately produce from a stamped blank with minimal forming steps. Variations in the window edges cause accuracy error in the sensor signal and may require revised sensor design and/or cause mounting restrictions. Corrugated sensor rings give limits to sensor sensitivity due to lack of sharp edges which tend to provide better flux changes.  
         SUMMARY OF THE INVENTION  
         [0020]    Accordingly, it is one of the main objects of the invention to provide an improved sensor ring which can be formed from a metal blank of minimal mass while producing improved magnetic performance.  
           [0021]    This object along with other features of the invention is achieved in a method of manufacturing a rotational velocity sensor ring which includes the steps of forming a flat ring-shaped blank from a sheet of ferro-magnetic metal stock and drawing a cylindrical hub portion from the radially inner portion of the ring blank so that the blank has an L-shaped, cross-sectional configuration with an annular sensor portion extending radially outward from the hub portion. In the drawn blank, a plurality of substantially identical, circumferentially spaced windows are punched in the sensor portion with each window having an inner edge adjacent to but spaced radially outward from the hub portion and an outer edge adjacent to and spaced radially inwardly from the outside edge of the sensor portion. Importantly, the sensor portion is bent along an imaginary bend circle adjacent the windows&#39; inner edges in the direction of the hub so that the blank now has a U-shaped, cross-sectional configuration while simultaneously forming an undulation in the sensor portion of the blank between the peripheral outer end of the sensor portion and the outer edge of each window whereby a symmetrically uniform sensor portion of the sensor ring is formed into a rigid structure from a blank with less metal or mass than that of the prior art.  
           [0022]    In accordance with another important feature of the invention, the depth of the undulations formed in the bending step are precisely controlled to produce a sensor portion in the form of a substantially symmetrical cylinder or, alternatively, a substantially symmetrical frusto-conical sensor portion generally concentric with the hub portion of the ring whereby the sensor ring can be easily configured to match any number of anti-lock or like sensor mounting arrangements while maintaining a consistent air gap with the sensor during ring rotation to enhance sensor performance.  
           [0023]    In accordance with another aspect of the invention, a one piece rotational velocity sensor ring is provided which includes a longitudinally-extending cylindrical hub portion and a sensor portion extending from the hub portion. The sensor portion has an annular bight segment extending radially outward from the hub portion and a generally cylindrical (or frusto-conical), longitudinally extending sensor segment extending from the bight segment and terminating an outer peripheral end. The sensor segment has a plurality of substantially identical window openings at equally spaced, circumferential increments therein with each window having an inner edge adjacent the hub portion and located within the bight segment, an outer edge adjacent to but spaced from the outer end of the sensor segment and a trailing and a spaced leading window edge extending between the inner and outer window edges, respectively. An undulation in the sensor segment between the outer end of the sensor segment and each window outer edge in combination with the windows results in a plurality of metal lands or teeth or fingers which extend between the trailing edge of one window and the leading edge of an adjacent window. The sensor lands are rigidized at one end by the bight sensor segment and at their other end by the undulations to provide a rigid ring which is not susceptible of being bent or distorted during handling or transport in mass assembly procedures while the open space provided by the windows between adjacent lands or fingers significantly enhances the magnetic permeability of the rings.  
           [0024]    In accordance with yet another aspect of the invention, a rotational velocity sensor ring is provided which is formed from a ring having a stamped configuration bent into a final configuration. The stamped configuration of the ring has a flat annular sensor portion extending from a cylindrical hub portion to form an L-shaped cross-section with the sensor portion having a plurality of substantially identical window openings at equally spaced circumferential increments therein. Each window has an inner edge adjacent to and spaced radially outward from the hub, an outer edge adjacent to and spaced radially inward from the outer peripheral end of the sensor portion and a leading and trailing edge extending respectively from opposite ends of the inner and outer edges to form each window as a polygon, preferably a trapezoid. The sensor portion of the ring in the final configuration includes a bight sensor segment extending radially outward from the hub portion a distance beyond the inner edge and a sensor segment extending from the bight segment in the direction of the hub portion to form with the hub portion a U-shaped cross section with the sensor segment having an undulation between the outer edge of each window and the outer peripheral end whereby the leading and trailing edges of adjacent windows forming metal lands, teeth or fingers therebetween (circumferentially spaced about the ring) are substantially parallel to one another to produce consistent and clearly defined flux changes as the lands or fingers and the open spaced windows pass by the sensor head(s) when the sensor rotates.  
           [0025]    In accordance with a more subtle but important feature of the invention, the geometric configuration of the window is correlated with the depth of the undulation to produce a desired spacing between the leading and trailing edges of adjacent metal lands or fingers. While the edges are preferably parallel to give precise demarcation flux changes as the magnetic flux lines pass from an open window space to a space occupied by a metallic finger or land, other configured edge relationships producing desired flux changes are possible. In all instances, the sensor pickup head is mounted between the undulations and the bight segment of the sensor portion, so that any influence on the flux fields caused by these metallic surfaces is minimized. Still further, the minimal effects on the magnetic permeability of the sensor ring caused by the undulations and the bight sensor segment are constant because of the irregular repeating patterns in the ring and the resulting noise is constant.  
           [0026]    It is thus an object of the invention to provide a sensor ring formed with a minimal amount of metal.  
           [0027]    It is another object of the invention to provide a sensor ring which has a configuration capable of providing improved or enhanced sensor performance.  
           [0028]    In conjunction with the immediately preceding object, it is a specific object of the invention to provide a rotational sensor ring which allows for a wider air gap between sensor and ring at which the sensor can detect flux changes than conventional, metal stamped sensor rings.  
           [0029]    In conjunction with the immediately preceding object, it is yet a more specific object of the invention to provide an improved rotational sensor ring which allows a greater freedom of sensor mounting and consequently an ability to mate a large variety of sensor packages in wheel bearing assemblies.  
           [0030]    Yet another object of the invention is to provide a method for forming a rotational sensor ring which can readily produce conical as well as cylindrical sensor rings for use in a wide variety of wheel bearing assemblies.  
           [0031]    Yet another object of the invention is to provide a rotational sensor ring which is stiff, durable and not readily deformable in the harsh automotive environment.  
           [0032]    Still another specific object of the invention is to provide a formed metal rotational sensor ring which eliminates interlocking of individual parts which may otherwise occur in the ring manufacturing process or in the subsequent handling of a large number of the rings present when the rings are assembled onto wheel bearing spindles and the like.  
           [0033]    A still further object of the invention is to provide a stamped metal rotational sensor ring which exhibits improved magnetic performance and contributes to the robustness of the sensor pickup unit when compared to existing stamped or powder metal sensor rings.  
           [0034]    A general object of the invention is to provide a metal rotational sensor ring which is inexpensive and readily formed.  
           [0035]    These and other objects, features and advantages of the invention will become apparent to those skilled in the art upon reading and understanding the Detailed Description of the Invention set forth below taken in conjunction with the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]    The invention may take form in certain parts and in an arrangement of certain parts taken together and in conjunction with the attached drawings which form part of the invention and wherein:  
         [0037]    FIG  1 A is a perspective view of a prior art sensor ring over which this invention is an improvement thereof;  
         [0038]    [0038]FIG. 1B is a section view of a portion of the prior art sensor ring of FIG. 1A taken along lines  1   b - 1   b  of FIG. 1A;  
         [0039]    [0039]FIG. 2 is a plan view of the sensor ring of the present invention;  
         [0040]    [0040]FIG. 3 is a section view of the sensor ring shown in FIG. 2 taken along lines  3 - 3  of FIG. 2;  
         [0041]    [0041]FIG. 4 is a plan view of a stamped blank formed in accordance with the invention;  
         [0042]    [0042]FIG. 5A is a plan view of the formed sensor ring of the present invention similar to that shown in FIG. 2 but without details present in FIG. 2;  
         [0043]    [0043]FIG. 5B is a magnified view of a portion of the sensor ring shown in a circle of FIG. 5A;  
         [0044]    [0044]FIG. 6 is a longitudinally sectioned view of a portion of the sensor ring taken generally along lines  6 - 6  of FIG. 5A;  
         [0045]    [0045]FIG. 7 is a view similar to FIG. 6 showing a longitudinally sectioned view of a portion of a sensor ring having a conical sensor ring shape; and,  
         [0046]    [0046]FIG. 8 is a perspective view of the rotational sensor ring of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0047]    Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting the same, there is shown in FIG. 4 a metal blank  10  after blank  10  has been drawn and stamped into the shape illustrated in FIG. 4. Blank  10  is a metal with Ferro-magnetic properties, such as steel, so that when the sensor ring of the present invention is finally formed, the ring can function with variable reluctance, variable induction or inductance or active sensor technology. In the preferred embodiment, blank  10  is conventional sheet metal having gauge thickness typically associated with sheet metal stock. However, as noted in the Background, it is contemplated that blank  10  can include alloying elements which enhance the magnetic permeability of the metal although a plain carbon steel has been found satisfactory for blank  10 . The invention does not contemplate forming the ring from sintered, powder metal composites which are not believed cost effective for the applications to which the present invention is directed nor is it believed that such composite bodies can be formed as desired in the present invention. Thus, Ferro-magnetic metal stock as used herein does not include sintered metal composites.  
         [0048]    Referring still to FIG. 4, an annular, solid, thin metal blank (not shown) is initially provided (or stamped from a flat sheet) and a longitudinally extending hub portion  11  is drawn or punched in the inner portion thereof. When drawn, blank  10  has an L-shaped cross sectional configuration as best shown in FIG. 6 and includes a longitudinally extending hub portion  11  and a radially outwardly extending sensor portion  12 . A part of sensor portion  12  is shown in dash outline form in FIG. 6 which is the cross-sectioned configuration of a portion of blank  10  of FIG. 4 taken along line  6 - 6 . A plurality of openings or windows  14  are then stamped out of sensor portion  12 . It should be noted that drawing hub portion  11  will extrude or reduce slightly the thickness of blank  10  in hub portion when compared to sensor portion  12 . If windows  14  were punched before hub portion  11  was drawn, there could be a distortion in the shape of windows  14  which, as will become apparent shortly, is not desired and there is also the possibility that the flatness of sensor portion  12  could be adversely affected when drawing hub portion  11  if the windows were previously stamped out of blank  10 . Thus the preferred embodiment prefers the sequence of initially drawing the hub followed by stamping the windows. In the broader scope of the invention, it is recognized that there may be metal forming techniques which allow the window stamping to occur at or prior to the time of hub drawing which will prevent or minimize window distortion or warping of sensor portion  12  so that it is not believed strictly necessary that the sequence be followed to practice the invention in its broader scope.  
         [0049]    The size, shape and positioning of windows  14  in sensor portion  12  have a particularly important affect on the invention and the geometry of windows  14  are defined, for the preferred embodiment, to best explain the invention. Hub portion  11 , as noted, is cylindrical and concentric about a longitudinally extending axis best indicated by point  15  in FIG. 4 represent the axis as extending out of the plane of the drawing. The peripherally extending outer end  16  of sensor portion  12  is concentric with hub  11  and thus lies in a circle centered on centerline  15 . Each window  14  in the preferred embodiment has an outer arcuate edge  18  which is spaced radially inwardly from outer peripheral end  16 . All outer edges  18  of windows  14 , in the preferred embodiment, lie on the circumference of an outer window circle, only a portion of which is shown in FIG. 4 and designated by reference numeral  19 . Each window  14  also has an inner arcuate edge  20  adjacent to but spaced radially outwardly from hub portion  14 . In the preferred embodiment, inner edges  20  for all windows  14  lie on the circumference of an inner window circle  21  centered on centerline  15  and a portion of inner window circle  21  is shown in FIG. 4 and designated by reference numeral  21 . Each window  14  has a radial leading edge  23  extending from outer edge  18  to inner edge  20  and a radial trailing edge  24  also extending from outer edge  18  to inner edge  20 . As shown in FIG. 4 and in the preferred embodiment, leading and trailing edges  23 ,  24  are radial lines extending from centerline  15 . In the stamped condition of the sensor, leading and trailing edges  23 ,  24  are not parallel with one another. It should also be noted that some prior art sensor rings show a finally formed sensor configuration similar to the stamped blank configuration of FIG. 4. Such prior art sensor rings require that the sensor be mounted such that its detector head extends parallel to hub portion  11  to maintain perpendicularity with sensor portion  12  (instead of perpendicular to hub portion  11  which is conventional because of bearing space constraints). In such prior art arrangements, leading and trailing edges  23 ,  24  are not parallel and will not produce a precise, on/off flux change as the sensor rotates and the rigidity of the prior art ring is suspect. In the preferred embodiment, window configuration is trapezoidal for reasons which will be explained shortly. However, the invention in its broader sense is not limited to trapezoidal windows and can encompass any polygonal window shape.  
         [0050]    The steel in blank  10  between leading edge  23  and trailing edge  24  of adjacent windows  14  is defined as a finger or a tooth or a land  25 . For definitional purposes, land  25  encompasses steel between trailing and leading edges  24 ,  23  of adjacent windows  14  extending from inner edge  20  to peripheral outer end  16  of sensor portion  12 . Note that leading and trailing edges  23 ,  24  of any window  14  forms leading and trailing edge surfaces in adjacent fingers or lands  25 . Because the leading and trailing edges of each window forms the leading and trailing edge surfaces of adjacent lands, the same reference numerals  23 ,  24  will be used for both so that drawing clarity can be maintained. The steel in blank  11  between window outer edge  18  and peripheral outer end  16  of sensor portion  12  is defined as a deformable sensor segment  28 . Completing the description of blank  10  is an imaginary bend circle designated by reference numeral  30 . Diameter of bend circle  30  is, among other things, a function of the geometry of windows  14  and the circumferential distance of lands  25 . More particularly, the diameter of bend circle  30  cannot be less than inner window circle  21  and in theory could not approach the diameter of outer window circle  19 . Additionally, bend circle  30  is a function of the final desired shape of sensor portion  12 .  
         [0051]    The stamped and drawn blank  10  shown in FIG. 4 is bent (not drawn so that metal thickness in sensor portion  12  remains approximately the thickness of metal blank  15 ) in the direction of hub portion  11 . It is preferred that sensor portion  12  be bent in the direction of hub  11  for ring rigidity. However, in accordance with the broader scope of the invention, sensor portion  12  could be bent in a direction opposite of portion  11  (forming an “S” shaped cross-sectional configuration). It should be clear that if sensor portion  12  is bent along bend circle  30  without anything more, the diameter of peripheral outer end  16  would have to shrink to the diameter of bend circle  30  (assuming sensor portion  12  was shaped as a cylinder concentric with hub portion  11  as shown in FIG. 6). The result would be a distortion or a waviness formed in sensor portion  12 . The invention recognizes that this result would otherwise occur and while bending sensor portion  12  about imaginary circle  30 , a bend or an undulation  33 , as best shown in FIG. 5B, is formed in each deformable sensor segment  28 . Only deformable sensor segment  28  is bent into an undulation. Fingers or lands  25  are not bent into an undulation. That is, the bending operation is performed, for example, by an annular backing die or a plate (not shown) formed as a cylinder (or a cone) with a plurality of fingers matched to fingers or lands  25  extending from imaginary bend circle  30  all the way to the outer peripheral end  16  of blank  10  (annular blanking die or plate fitted onto hub portion  11 ). A press die (not shown) would then bend sensor portion  12  against the backing die into the desired configuration and has a number of V-shaped bending studs which press the center  34  of each deformable center segment  28 . Because the backing die supports land  25 , all lands remain flat and undistorted all the way to peripheral outer edge  16  while the unsupported deformable sensor segments  28  are indented by the V-shaped bending studs generally assume an undulating shape  33  which, in practice, generally takes the form of a sine wave.  
         [0052]    Referring now to FIGS. 6 and 7, sensor portion  12  can be bent about imaginary circle  30  to form lands  25  lying in a cylindrical plane concentric with a portion  11  or, as shown in FIG. 7, lying in a frusto-conical plane pitched or inclined either towards hub portion  7  as designated by reference numeral  25 A or away from hub portion  7  as designated by reference numeral  25 B. Reference numeral  25 B is the preferred embodiment of the invention and is illustrated in FIGS. 2, 3 and  8 . With metal blank  10  bent as described to form sensor ring  50 , the ring has a U-shaped cross-sectional configuration as illustrated in FIGS. 3, 6,  7  and  8 . The base or bottom leg of the U is hub shaped portion  11  and the top or sensor leg of the U comprise lands  25  while the base or bight segment  51  of the U is that radially extending segment of sensor portion  12  formed in blank  10  which is not bent. Again, it should be clear that leading and trailing edges  23 ,  24  of windows  14  form leading and trailing edge surfaces of adjacent fingers or lands  25 . In the preferred embodiment, the leading and trailing edge metal surfaces are radial as shown in FIG. 4, but the depth of undulation  33  designated by reference dimension “X” in FIG. 6 is set at a distance such that the leading and trailing edge surfaces are brought into substantially parallel relationship when the blank  10  is formed into sensor ring  50 . (The depth of undulation  33  for conical applications shown in FIG. 7 are designated X′ and X″ and are slightly different from one another and form the cylindrical application shown in FIG. 6.) More specifically, inner arcuate edge  20  of each window  14  extends a distance between leading and trailing edges  23 ,  24  which is less than the arcuate distance of outer arcuate edge  18  between leading and trailing edges  23 ,  24 . The depth “X” of undulation  33  is set to close outer arcuate edge  18  to a distance equal to that of inner arcuate edge  20 . Window  14  is thus, for the preferred embodiment, brought from a trapezoidal into a rectangular shape with the result that the leading and trailing edge segments of fingers or lands  25  are substantially parallel with one another. Preferably, this relationship is maintained by sizing trapezoidal windows  14  to account for the applications of sensor ring  50  when sensor ring  50  is formed so that fingers  25  are lying in a conical or frustoconical plane either pitched towards or away from hub portion  11  as shown in FIG. 7. While it is preferred to set undulation depth X, X′, or X″ to bring leading and trailing edges  23 ,  24  into parallel relationship for cylindrical or conical configurations of sensor ring  50 , those skilled in the art will recognize that it is important that the depth of all undulation  33  in sensor ring  50  be equal.  
         [0053]    The final configuration of sensor ring  50  is best shown in the pictorial view of FIG. 8. As noted, hub portion  11  is drawn whereas sensor portion  12  is bent so sensor portion  12  retains gauge thickness of sheet stock  10  maximizing magnetic permeability of sensor ring  50 . Importantly, fingers or lands  25  are rigidly supported at their axial ends. One end is supported by bight segment  51  which finger  25  is integral with and the opposite axial end is supported by deformable sensor segments  28  extending from leading and trailing edge surfaces  23 ,  24  of each finger  25 . Thus, fingers  25  when bent at bend circle  30  and supported as stated, lie in a cylindrical or frusto-conical plane in a surprisingly rigid, non-deformable manner. Because there are no edge openings between the fingers as in some prior art sensor rings described above, the handling, storage or transportation problems present when sensor rings  50  are applied to automotive wheel bearings on an assembly line are minimized. More importantly, sensor rings  50  are durable when applied to the harsh environment in which vehicular applications are subjected to.  
         [0054]    Importantly, the magnetic permeability of sensor ring  50  is enhanced or improved for at least two reasons. First, window  14  has no bottom. This should be contrasted with prior art ring shown in FIG. 1A in which the undulations had peaks and valleys  4 ,  5  so that the lines of flux detected by the pickup or detector heads of the sensor always passed through metal surfaces although at different distances. By providing an open window air space, a dramatic change in flux occurs as fingers  25  and window air spaces  14  pass by the sensor heads (poles). The result is that the detector head of the sensor (i.e., sensor pole(s)) can be spaced radially further from sensor ring  50  to operate at a wider air gap than in some of the prior art arrangements discussed above. The air gap is schematically illustrated in FIGS. 2 and 3 by the dimension indicated by reference letter G which is shown for a sensor having a single pickup unit or detector head (i.e., pole) schematically illustrated by dash lines indicated by reference numeral  55 . Those skilled in the art will understand that depending upon sensor design, the sensor may have only one pickup unit  55  or may, in fact, have a plurality of pickup units, even to the extent of circumscribing sensor ring  50  such as illustrated in the &#39;442 patent. The second reason for improved magnetic permeability of sensor ring  50  is the fact that, in the preferred embodiment, leading and trailing edges  23 ,  24  of adjacent fingers  25  are straight line, parallel edge surfaces. It is recognized that so long as the window  14  and finger  25  spacing is constant, for all windows and all fingers on sensor ring  50 , the trailing and leading edges do not have to be parallel. However, theoretically, there conceivably could be slight axial shaft run out when the sensor ring rotates in some applications which will cause variation in the spacing between windows and fingers or lands  25  if the trailing and leading edges are not parallel. While the sensor will still function, the sensitivity of sensor ring  50  is enhanced if leading and trailing edge surfaces  23 ,  24  are parallel as discussed for the preferred embodiment.  
         [0055]    Finally, it is noted that in theory the presence of deformable sensor segment  28  in windows  14  could affect lines of magnetic flux as sensor ring  50  transitions between finger  25  and window  14  or window  14  and finger  25 . In practice, this is not a concern because, as shown in FIG. 3, the width of the pickup head  55  is less than the length of fingers  25  so that pickup head  55  can be positioned over the unobstructed open space provided by window  14 .  
         [0056]    Use of various terminology herein such as pickup head, detector head, sensor pole, pickup unit, etc., are all basically referring to the sensor, i.e., single or multiple poles detecting magnetic flux changes and are used interchangeably herein.  
         [0057]    Stamped sensor rings have been used in wheel speed sensors in the past as low cost/low mass replacements for powdered metal parts. Each of these rings was configured to provide interruptions in a solid magnetically permeable surface which could be sensed with a common magnetic speed sensor. Configurations used were either individual fingers which were stamped and formed, where holes stamped in a flat surface to provide “windows” in the surface, or where surfaces formed by stamping which gave convoluted or wavy surfaces. Each of these designs had its faults—windows gave little flexibility in the part shape, fingers were very vulnerable to damage and bending, while convoluted rings were very robust but gave marginal sensor performance. This invention covers a stamped ring which is different from any seen today as it combines the best performance features from a stamped window type ring with the physical robustness of a convoluted ring.  
         [0058]    The ring configuration utilizes a stamping operation as well as a bending and folding operation for the formation of the sensor teeth but not drawing which might tend to thin the teeth and reduce the magnetic mass and degrade sensor output. As may be seen in the attached drawings a part for use with a radial sensor might be formed as in FIG. 4 with the bore or ring mounting surface being formed up out of the plane of the teeth or fingers while the material is a blank shape. Next the fingers or teeth of the sensor ring are actually formed by stamping keystone shaped holes in the flat surface of the ring material. The sides of the teeth are somewhat parallel to maximize the magnetic mass. The part is then formed as demonstrated in FIG. 6 from an “L” shape into a “U” shape. As this forming takes place the basis of this invention comes to light. The outer ring which was formed in the window stamping process to produce the teeth or fingers is actually reduced in circumference by a deforming of the metal into a wave form as shown in FIG. 5A or better in FIG. 5B. It is this wave form which gives the part the stiffness required to maintain tooth or finger position and actually ties the ends of the teeth together to eliminate interlocking of individual parts in the manufacturing process or subsequent handling while at the same time being away from the active surface of the teeth and therefore increasing magnetic performance.  
         [0059]    The outer surface of this ring need not be cylindrical but might also be conical for certain applications.  
         [0060]    The invention has been described with reference to a preferred embodiment. Obviously, alterations and modifications will occur to those skilled in the art upon reading and understanding the Detailed Description of the Invention as set forth herein. It is intended to include all such modifications and alterations insofar as they come within the scope of the present invention.