Abstract:
A speed sensing seal with a first support member, a second support member, a magnetic elastomer member, a sensor member and an elastomeric seal member is disclosed. The magnetic elastomeric member with alternating adjacent poles is formed on the first support member and the sensor member is attached to an aperture in the second support member and overmolded with a layer of elastomer. The first and second support members are formed in the unitized body to form an internal cavity which contains the sensor, magnetic member, and the elastomeric seal. The first support member has a low wear surface to reduce initial seal failures and to enhance seal life.

Description:
BACKGROUND OF THE INVENTION 
     A speed sensing device for producing a signal corresponding to the relative angular rotation between two structural members is well known in the prior art. With the increase in electronic controls for vehicle systems, a need has been found for numerous speed sensing devices in vehicles with increasingly stringent angular motion discrimination. Contributing to this growing interest in speed sensing devices in motor vehicles is the popularity of anti-lock braking systems (ABS), the advancement of controls for automatic transmissions, and traction control. These developments have led to the incorporation of speed sensing devices into sealing packages. Such configurations incorporate a speed sensor into a radial shaft seal or into a bearing seal to keep out dirt and retain lubrication in the device. 
     The speed sensor reacts to a stimulus or a signal with a corresponding electrical signal. In a speed sensor device, the component which produces a stimulus corresponding to the rotating shaft speed is called a target wheel or target and the other component which reacts to this stimulus with an electrical signal is called a sensor. 
     The target may be either active or passive. Active targets, otherwise known as encoders, are those that produce alternating magnetic fields which are sensed and related to shaft speed, and incorporate permanent magnetization. Passive targets, known as tone wheels, are not magnetized components, but instead are usually metal rings with teeth or notches, and may be integrated within seals as well. Sensors can also be classified as active or passive, depending on whether they produce a field internally or are supplied with external power to do so. Either type of encoder can be integrated with either type of sensor. However, the combination of an active encoder with an active sensor provides advantages in size and performance. Active encoders normally require the magnetization of an elastomeric ring. This requires that the elastomer be vulcanized with ferrite powder/filaments, thus making it unsuitable for sealing. Therefore, the active encoder and seal can only be molded as one component using two-material molding techniques. Active encoders have numerous advantages, including reduction in the size of the target wheel and sensor, weight reduction, reduction in the number of parts, and integration of the components into a small seal package. The active property of the encoder allows use of Hall-effect or magneto-resistive sensors, which are smaller than other sensors used with a passive tone wheel. 
     The performance of speed measurement systems is constantly increasing. The use of active encoders with active sensors allows wider band widths of the sensing systems, measuring speeds from zero rpm. However, the system&#39;s sensitivity to the air-gap, that is, the distance between the encoder and sensor, is a major consideration. This distance must be controlled by precise manufacturing and assembly, to minimize variations. 
     Various means exist for packaging the seal and encoder. For example, the encoder may be integrated by bonding it to the metal case of a seal, or pressing it against clamps. The sensor, due to its relative size, is usually mounted externally of the seal. It is preferable that any sensor seal design incorporate the full capability of sealing and sensing within a seal package. To accomplish this, the sealing element, encoder and sensor are all encapsulated in a metal case, with just the electric leads of the sensor protruding. Such a design would enable efficient assembly, parts reduction, and improved performance due to small air-gaps and reduced error in assembly. 
     As previously mentioned, manufacturing the sealing element and the encoder as one is difficult because of the unsuitable sealing properties of magnetizable elastomer. However, some efforts have been made to produce the encoder and seal simultaneously in one process (as in two-point injection molding), to bond the two to the housing after manufacture or to attach them mechanically. 
     Isolation of both the sensor and the encoder from their surroundings is also of high importance. Active encoders, as the source of a magnetic field, can attract contaminants and ferrite particles if subjected to internal lubrication of a bearing or a shaft. These particles originate from additives in lubricants and/or from wear particles generated due to the contact surfaces of the bearing during normal operation and can ultimately interfere with the magnetic signal by creating couplings between poles. On the other hand, in certain ABS applications, the bearing/axle may be subjected to external contaminants such as water and mud, and to other environmental disturbances such as extreme temperatures, which may affect the exposed encoder or sensor. 
     Some prior art designs emphasize the need for isolation of the encoder internally, while other designs identify the need to isolate the sensor and the encoder from their external environment. The need for a seal package that encloses and protects the encoder and sensor from the bearing surfaces and the surroundings is desirable. 
     The packaging of sensor seals creates manufacturing and assembly process challenges. The fragility of magnetic plastoferrite encoder rings is a complicating factor in manufacture and assembly, since the necessary accurate positioning and rigid clamping may increase the chances of breakage. One prior art device utilizes retaining clamps in the seal case to hold the encoder in three axes. Another prior art device relies on bonding the magnetic elastomer to the metal case prior to assembly. Inaccurate assembly might also greatly affect performance due to the above mentioned air-gap sensitivity. Aspects such as repeatability and ease of assembly have been solved by using various clamping methods or with the use of a coupling ring. 
     Vibration isolation has been achieved by rigid means of assembly of the encoder or by bonding the encoder to an elastomeric layer on the seal case to isolate vibration. External noise that may disturb the sensor signal is minimized by the encapsulation of the sensor within a metal case that acts as a magnetic shield, isolating the sensor from the environment and preserving magnetic energy from the active encoder. 
     However, these prior art devices are expensive to make and require complicated assembly procedures. Thus there remains a need for a sensor seal that is compact, inexpensive to manufacture, accurate and that does not require complicated assembly procedures. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to solve these problems. The sensor seal includes a first support member having a radially extending portion and an axially extending portion and a magnetic elastomeric member on the radially extending portion. The magnetic member forms alternating, adjacent magnetic poles on the radially extending portion. A second support member is adjacent to the first support member. The second support member has a radially extending portion and an axially extending portion. A sensor member is attached to the radially extending portion of the second support member and senses the alternating, adjacent magnetic poles. An elastomeric seal member on the radially extending portion of the second support member, has a radially extending seal portion and an elastomeric body portion. The first and second support members form an internal cavity and a unitized body. The unitized body has an internal cavity that contains the sensor, the magnetic members and the elastomeric seal member. The radially inwardly extending seal portion of the seal member is contiguous with the axially extending portion of the first support member. The axially extending portion of the first support member has a low wear surface to reduce initial seal failure incidents and to enhance the life of the seal. 
     It is an object of the present invention to provide an encoder device that forms a unitized body with an internal cavity that contains the sensor, the magnetic member and the elastomeric seal and has a low wear surface to enhance initial seal wear-in and seal life. 
     It is another object of the present invention to provide a method of forming an encoder device with a magnetic member on one support member and a seal member on the other support member with one support member being folded over during the manufacturing process. 
     It is still another object of the present invention to provide an encoder device that is inexpensive to make, easy to install, rugged and that will seal out harmful contaminates. 
    
    
     These and other features of the present invention will become apparent from the description of the embodiments and the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various advantages of the present invention will become apparent to one skilled in the art upon reading the following specification and by reference to the drawings which include: 
     FIG. 1 is a cross sectional view of the speed sensor in a wheel bearing according to the present invention; 
     FIG. 2 is a cross sectional view of the first support member and multipole ring member prior to forming the cylindrical axial extending portion; and 
     FIG. 3 is a cross sectional view of an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The speed sensing device according to the present invention is shown in FIGS. 1 and 2 and is designated by the numeral  100 . The speed sensing device  100  is disposed in a radial direction between an inner race element  2  and an outer race element  4 . The speed sensing device  100  is shown as a component of a motor vehicle wheel bearing assembly (not shown). Each component of the bearing assembly is rotatably mounted relative to one another by a rotating element distributed in the circumferential direction. The invention is suitable for use with bearings having a wide range of designs, including ball bearings, roller bearings, tapered roller bearings and needle bearings. Either thrust or radial bearing configurations may be utilized and can include tapered bearings. Anti-friction bearings having rolling elements, with or without a cage, retainer or separator are included, as well as plain bearings having no rolling elements. Alternatively, the speed sensor device  100  can be adapted for use with a rotary shaft or any other similar rotary application to measure rotation. 
     The speed sensing device  100  includes a first support member  10  and a second support member  20  and, disposed in an opening  3  between the inner race  2  and outer race  4 , are a rotation sensing device  30 , a multipole ring member  40  and a seal member  50 . The outer race  4  is attached to the motor vehicle frame assembly whereas the inner race  2  is attached to the wheel so as to rotate with the motor vehicle wheel. Those skilled in the art will recognize that the speed device  100  may also be adapted for use where the outer race is attached to the wheel and the inner race is attached to the frame assembly. 
     The rotation sensing device  30  is disposed in an aperture  22  in the radial portion  24  of the second support member  20 . The multipole ring member  40  is attached to the radial portion  14  of the first support member  10  in the internal cavity  12 . The multipole ring member  40  faces the rotation sensing device  30 . 
     In the preferred embodiment, the first support member  10  also includes a notch  15  which is adjacent to the multipole ring  40 . The second support member  20  also includes an axial portion  28  which is adjacent to the outer race  4 . The first support member  10  and second support member  20  are preferably made of stainless steel for corrosion resistance but, alternatively, they may be made of a polymeric material with magnetizable material. The polymeric material may be a thermoplastic or thermoset plastic or the support member  20  may also be made of a ferrous material such as steel which is treated for corrosion resistance. 
     The multipole ring member  40  is preferably made of a magnetizable material in an elastomeric material such as nitrile (NBR), hydrogenated nitrile (HNBR), polyacrylate (ACM), ethylene acrylate, fluorocarbon (FKM), a thermoplastic elastomer (TPE), a fluoropolymer, a thermoplastic vulcanizate (TPV) or any other similar material suitable for the application. The magnetizable material is a ferrite powder or ferrite filaments. The magnetizable elastomeric material has north and south poles alternating in the circumferential direction and extending in the radial direction which, as the wheel rotates, move alternatively past the rotating sensing device  30 . The rotation device  30  may be a Hall-effect device or a magneto-resistance device. 
     The seal member  50  is molded to the radial portion  24  of the second support member  20  so that the seal body.  52  covers the projecting portion end of the rotating sensing device  30  facing the multipole ring member  40 . 
     The seal member  50  has a radial lip primary seal  55 , extending generally in the radial direction from the seal body  52 . The radial lip primary seal  55  includes a first radially extending sealing member  54 , which has a garter spring  58  located in an annular groove  57  on the first radially extending seal member  54 . The first radially extending seal member  54  is in fluid tight sealing contact with a smooth wear surface  18  on the axial portion  19  of the first support member  10 . The smooth wear surface  18  is disposed radially inwardly of the primary radial lip seal member  55 . The present invention applies equally to seals wherein these elements are reversed, that is, the sealing element is urged radially outwardly against a seal wear flange that is disposed radially outwardly of the principal seal element. It will also be understood that the invention applies equally to seals with unitizing elements wherein the wear sleeve element is located on a rotary shaft or the like and is disposed radially inwardly of the primary radial lip seal member  55  or wherein the elements are reversed, that is, with the seal band of the primary radial lip seal member  55  urged radially outwardly against a seal companion flange or the unitizing element is disposed radially outwardly of it. 
     The seal member  50  is preferably made of a polymeric material such as NBR, HNBR, ACM, FKM, Fluoropolymer, Ethylene Acrylate, TPE, TPV or any other similar material suitable for the application. In practicing the invention, the seal member  50  and the multipole ring member  40  need not be made of the same elastomeric material since optionally, the seal member  50  and the multipole ring member  40  may be formed separately using different processes for forming each member. 
     The first radially extending sealing member  54  portion of the radial lip primary seal  55  preferably has a pair of fiasto-conical sealing surfaces  56 , with an edge  53  therebetween, and the annular groove  57  with the garter spring  58 . The seal member  50  also includes at least two excluder seals  60 . The radial lip primary seal  55  includes a first excluder seal member  62 , of the excluder seals  60 , adjacent to the first radially extending sealing member  54 . The other of the excluder seals  60  is a second excluder seal member  64 , extending from the seal body  52  to engage a wear surface  11  of the radial portion  14 . 
     The multipole ring member  40  is formed on the radial surface  14  of the first support member  10  when the support member is in the form of a flat disk member, as best shown in FIG.  2 . During the process of forming the multipole ring member  40 , the first support member  10  is clamped between a pair of mold tools. Normally, one of the mold tools is stationary and the other of the mold tools moves toward the stationary tool to close off a cavity in a rubber molding machine (not shown). As this occurs, the rubber or elastomer material is injected into the closed off cavity, or rubber preforms are placed in the cavity before closing the mold halves and are compressed to form the multipole ring member  40  on the radial surface  14 . The tool has an externally extending member which bears on the support member  10  so as to form a notch  15  adjacent to the inner radial edge of the multipole ring member  40 . When one of the mold tools opens, the first support member  10  and the multipole ring member  40 , are removed from the mold in the molding machine (not shown). The radial portion  16  of the first support member  10  below the inner radial edge of the multipole ring member  40  is then bent at the notch  15  so as to form a cylindrical axial portion  19 . The axial portion  19  is ground to form a smooth wear surface  18  by a surface smoothing technique which uses an abrasive impregnated rubber wheel or a similar surface-smoothing device. The seals  54  and  62  will be in surface contact with and seal along the wear surface.  18 , as can be seen best in FIG.  1 . 
     The first support member  10  with the radial portion  14 , the notch  15 , the axial portion  19  with the smooth wear surface  18 , and the multipole ring member  40 , are then assembled to the second support member  20  so that the multipole ring member  40  faces the rotation sensing device  30 . The seal  55  presses against the first wear surface  18  and the second excluder seal  64  presses against the wear surface  11 , thus forming the cavity  12 . The edge  53  of the first radially extending seal member  54 , and the first excluder sealing member  62 , sealingly engage the smooth wear surface  18 . The first exclude sealing member  62  prevents dust from migrating along the axial portion  19  toward the sealing member  54 . The sealing member  54  prevents lubricating fluid that may be used to lubricate the rotating elements from migrating out of the cavity  12 . 
     The second excluder seal member  64  sealingly engages the second seal wear surface  11 , adjacent to the multipole ring member  40 , in order to prevent the migration of dust or metal particles into the internal cavity  12 . 
     Since the primary seal member  55  interfaces with the smooth wear surface  18 , which minimizes any surface imperfections in the axial portion  19 , the speed sensor device  100  of the present invention is more reliable. The cost of fabricating the speed sensing device  100  is less expensive since the seal member  50  is formed in the second support member  20  separately from the formation of the multipole ring member  40  on the first support member  10 . Furthermore, protection of the sensor  30  is achieved using the same elastomer used for the seal  50 , generally, in a combined molding process, without the additional molding of an external sensor. Finally, the speed sensing device  100  is compact sine the rotation sensing device  30  can be located optimally to improve responsiveness of the rotation sensing device  30  to the multipole ring member  40  rotational movement. 
     The radially outward edge of the multipole ring member  40  extends a distance d from the radially inner periphery of the axially extending portion  19 . Preferably, the distance d is at least 4 mm, and more preferably between 5 mm to 7.5 mm, for the rotation sensing device  30  to detect the alternating magnetic poles  42 . The detection end  34  of the sensing device  30  faces the alternating magnetic poles  42  in order to detect the relative rotary motion of the multipole ring member  40 . The detection end  34  may be optimally covered with the seal body  52  in order to prevent the accumulation of debris or moisture and to reduce any vibration which can affect the performance of the rotation sensing device  30 . The width W of the speed sensing device  100  is at least 3 mm and, more preferably, between 4 mm and 6 mm. The width W extends from the end of the axial portion  28  to the exterior of the radial portion  24 . The ratio of the distance d divided by the width W (d/W) is in the range of 0.6 to 2.5 and preferably the range is from 0.7 to 1.4. 
     The multipole ring member  40  is molded onto the first support member  10  and the elastomeric material with magnetizing particles is vulcanized or at least partially cross-linked in a molding machine (not shown). The vulcanized or post cured elastomeric material which forms the multipole ring member  40  is then magnetized to form the alternating magnetic poles  42  as is well known in the art. 
     Additionally, since the rotation sensing device  30  is encapsulated in the seal body  52 , the rotation sensing device  30  is accurately oriented relative to the first support member  10  which also enhances reliability of the speed sensor seal. Only the leads  32  extend out of the seal body member  52 . Thus there is no need for any additional protection to the sensing device  30  and the manufacturing process is simplified since the encapsulation step and the seal molding process occur at the same time. 
     In operation, as the wheel rotates, the first support member  11  and the multipole ring member  40  rotate with the inner race element  2 , which is rotationally fixed to the wheel. The second support member  20 , with the rotation sensing device  30 , is rotationally fixed to the outer race element  4 , which is attached to a motor vehicle frame. Thus, there will be relative rotation between the rotation sensing device  30  and the multipole ring member  40 . The sensing device  30  detects the alternating north and south poles of the multipole ring member  40 , and thus the rotation of the wheel. Because the rotation sensing device  30  is encapsulated in the seal body member  52 , the axial spacing of the device  30  to the multipole ring member  40  is defined by the axial spacing of the first support member  10  relative to the second support member  20 . The fist sealing members  54 ,  62  and  64  will provide the sealing, as noted above, even as the first support member  10  and the second support member  20  rotate relative to one another. 
     An alternative embodiment of the speed sensing device, shown in FIG. 3, is designated by the numeral  200 . Where the elements are the same as in the first embodiment, the numerals will remain the same. The speed sensing device  200  combines the first support member  10  and a second support member  120  into a single or “unitized” assembly which is held together for cooperative sealing. By pre-assembling these elements together, proper dimensional installation is achieved, protection against nicking or other damage to the sealing elements and multipole ring  40  during handling is avoided, prelubrication of the seal, if desired, may be insured, and correct dimensional tolerances may be controlled at the point where the seal is manufactured as opposed to the point at which the other parts are manufactured and assembled together. 
     The speed sensing device  200  has two major parts that rotate relative to each other, the same as in the first embodiment. The device  200  can be installed in place between the inner shaft (e.g. inner race) element and the outer bore (e.g. outer race) element in the opening, the same as in the first embodiment. The specific details of the construction of the unitized seal will now be discussed. 
     The speed sensing device  200  includes the fist support member  10 , a second support member  120 , the rotation sensing device  30 , the multipole ring member  40  and a seal member  150 . The seal member  150  has the first radially extending sealing member  54  extending from a seal body  152  in the form of the pair of frusto-conical sealing surfaces  56  with the edge  53  in between. The sealing member  54  also includes the annular groove  57  with the garter spring  58 . As in the first embodiment, the pair of frusto-conical sealing surfaces  56  forms the primary seal wear surface which rubs against the smooth wear surface  18  of the axial portion  19 . Optionally, the sealing member  54  may be a radial lip with an end or tip. The second support member  120  has a radially extending internal portion  128  which extends axially beyond the edges of the radially extending portion  14  of the first support member  10 . The radially extending internal portion  128  also extends radially inwardly of the radial portion  14  to axially lock the first support member  10  and the second support member  120  together to form a unitized assembly. Optionally, the second excluder seal  164  is molded to the axially extending portion  126  of the second support member  120 . The seal  164  extends from the seal body member  152 . A tip  165  of the seal  164  rubs against the second seal wear surface  11  of the first support member  10 . In all other aspects, the operation of the speed sensing device  200  is the same as the speed sensing device  100  of the first embodiment. 
     While the invention has been described in connection with a preferred and an alternative embodiment, it will be understood that it is not intended to limit the invention to that embodiments only. On the contrary, it is intended to cover all alternative modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims.