Improved switched reluctance speed sensor

Abstract: A bearing assembly for a vehicle including a fixed element (14), a rotating element (18) rotating relative to the fixed element (14) about an axis (22), and an annular sensor (10) connected to one of the fixed element and the rotating element. The sensor includes a pick-up coil (30) and an annular magnet (86) connected to the pick-up coil (30). The magnet (86) has a plurality of magnetic regions (94) which alternate in polarity around the magnet (86). The magnet generates a magnetic flux path magnetically coupling the magnet (86) to the coil (30) and resulting in the generation of an electrical signal in the coil. The rotating bearing element (18) includes a plurality of gear teeth (110). The gear teeth (110) generate a change in the reluctance of the magnetic flux path to vary the electrical signal in response to the angular speed of the fixed element (14) relative to the rotating element (18).

Description: BACKGROUND OF THE INVENTION The invention relates to a speed sensor for detecting the angular velocity of a rotating element and particularly to switched reluctance speed sensors. It is known in the art to provide a speed sensor to detect the angular velocity of rotating elements in the bearing assembly or transmission of a vehicle such as a truck or an automobile. In the case of a wheel speed sensor, the sensor is mounted in each bearing assembly of the vehicle. Referring specifically to a wheel speed sensor, the bearing assemblies typically include an inner bearing race and an outer bearing race. The bearing races rotate relative to one another and the speed sensor is mounted within the bearing assembly to measure the angular or rotational speed of the rotating element of the bearing assembly relative to the fixed element. Various types of wheel speed sensors are known in the art. In one form, the sensor includes a coil and a magnet mounted on one of the bearing races and a tone wheel mounted on the other of the bearing races. The magnet generates a flux path between the bearing races and the movement of the tone wheel relative to the coil and magnet assembly varies the reluctance of the generated flux path. The variation in reluctance causes a variation in the electrical signal generated at the coil output. In this manner, an electrical signal is created at the output of the coil which is indicative of the angular or rotational speed of the one bearing element relative to the other bearing element. This type of sensor is called a variable reluctance sensor and the vector of the magnetic flux produced by the sensor is always the same. In another form of sensor however, a magnet having alternating regions of magnetic poles is provided to change the direction of the vector of the flux path. This type of sensor is called a switched reluctance sensor. In known switched reluctance sensors, the magnet is positioned on one of the bearing races and the coil is positioned on the other of the bearing races so that the coil and the magnet rotate relative to one another. The amplitude of the electrical signal generated at the output of the coil is directly related to the distance between the coil and the magnet as well as to the flux strength of the magnet. As shown in U.S. Pat. No. 5,004,358, it is known to position the coil within a ring having a plurality of teeth extending toward the magnet to magnetically couple the magnet to the coil by creating a flux path around the coil. However, this construction necessarily consumes space within the bearing assembly, requires the use of a strong and expensive magnet and requires expensive tooling to produce the ring and teeth. Therefore, it is an advantage to provide a switched reluctance wheel speed sensor in which the magnet is mounted with the coil on the same bearing race to reduce the amount of space required by the sensor, to reduce the need for an expensive high strength magnet and to reduce the overall cost and complexity of the sensor. Accordingly, the invention provides a bearing assembly for a vehicle such as a truck or an automobile of the type recited in the preamble of claim 1, which is known from EP-A-557931. The bearing assembly includes a fixed element having an outer bearing race and a rotating element having a inner bearing race. The rotating element rotates relative to the fixed element about an axis. The bearing includes a sensor for detecting the angular speed of the rotating element relative to the fixed element. The sensor is mounted in the bearing assembly and is connected to the fixed element. The sensor includes an annular ferromagnetic ring or can having a generally U-shaped cross-section. The ferromagnetic ring defines a first annular recess in the ring and a pick-up coil is mounted in the first annular recess. An annular magnet is mounted on the ferromagnetic ring concentric with and radially inward relative to the pick-up coil. The magnet includes a plurality of magnetic regions alternating in polarity around the magnet and these regions generate a plurality of magnetic flux paths extending around the coil. Means are provided for generating a change in the reluctance of the magnetic flux path. The means provided include a plurality of ferromagnetic teeth connected to the rotating element. The teeth are mounted on the rotating element adjacent to the annular magnet. As the rotating element rotates relative to the fixed element, the ferromagnetic teeth move relative to the magnetic regions on the annular magnet so that each tooth is first aligned with the magnetic regions on the magnet having a first polarity, and then, as the rotating element rotates relative to the fixed element, each tooth is next aligned with the magnetic regions on the magnet having an opposite polarity and so on. By providing a magnet that has twice the number of magnetic regions alternating in polarity about the magnet as there are teeth on the rotating element, a sensor is provided in which all of the teeth on the rotating element are alignable (at a given moment in time) with magnetic regions on the magnet having the same polarity. A principal feature of the invention is the provision of a switched reluctance wheel speed sensor for a bearing assembly, which sensor is designed to fit within a relatively small envelope of space within the bearing assembly. Another feature of the invention is the provision of a switched reluctance wheel speed sensor wherein the coil and magnet are fixed relative to one another on the same bearing race. Another feature of the invention is the provision of a sensor that operates effectively with a lower cost, lower strength magnet. Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. DESCRIPTION OF THE DRAWINGS FIGURE 1 is an exploded perspective view of the switched reluctance speed sensor of the invention. FIGURE 2 is a cross-sectional view of the sensor showing the rotating wheel bearing races. FIGURE 3 is a partial view with portions cut-away taken along line 3-3 of FIGURE 2. FIGURE 4 is a partial view taken along line 4-4 of FIGURE 2. FIGURE 5 is an elevational view of the magnet of the sensor showing the alternating regions of magnetic polarity in the magnet. Before one embodiment of the invention is explained in detail, it is understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. DESCRIPTION OF THE PREFERRED EMBODIMENTS Shown in FIGURE 2 of the drawings is a switched reluctance wheel speed sensor 10 embodying the invention. The sensor 10 is typically mounted within the wheel end housing or bearing assembly of an automobile. The wheel end housing or bearing assembly includes a fixed bearing race 14 and a rotating bearing race 18 mounted for rotation relative to the fixed bearing race 14 about an axis 22 (FIGURE 1). As shown in FIGURE 2, the speed sensor 10 includes a sensor portion 26 mounted on the fixed bearing race 14. Referring generally to FIGURES 1 and 2, the sensor portion 26 includes an inductor or pick-up coil 30 wound onto a generally plastic bobbin 34. As is known in the art, the pick-up coil 30 is an insulated wire conductor of a selected gauge that is wound around the bobbin 34 a precise number of times to form an inductor having the desired characteristics of the sensor 10. The gauge of the wire and the number of windings may vary depending upon the particular application. The winding is terminated at each end (not shown) with a terminal 38 (FIGURE 1). The terminals 38 are housed within a connector 42 (FIGURE 1) mounted on the bobbin 34. The sensor 10 also includes an annular plastic housing 46. The annular housing 46 includes a radial inner wall 50 having inner and outer surfaces 54 and 58, a radial outer wall 62 having inner and outer surfaces 66 and 70, and a connecting wall 74 extending between the radial inner wall 50 and the radial outer wall 62. The connecting wall 74, inner wall 50 and outer wall 62 together form an annular recess 78 having a U-shaped cross-section. As shown in the drawings, the bobbin 34 and coil 30, are mounted in the recess 78. Still referring to FIGURE 2, the inner surface 54 of radial inner wall 50 defines a central opening 82 (FIGURE 1). The sensor 10 also includes an annular magnet 86 having a plurality of magnetic regions 94 (FIGURES 1, 3, and 5). As shown in FIGURE 2, the magnetic regions 94 on magnet 86 have axially aligned poles ("N" and "S"). The magnetic regions 94 alternate in polarity around the magnet 86 (FIGURES 2 and 3). Still referring to FIGURE 2, the magnet 86 includes a radial outer surface 90 and is mounted in the central opening 82 of housing 46 so that the radial outer surface 90 of the magnet 86 engages the inner surface 54 of the radial inner wall 50 of the housing 46. The magnet 86 is at least partially secured within the central opening 82 by frictional engagement between the inner surface 54 and the outer surface 90 of the magnet 86. As shown in FIGURES 1 and 2, the sensor 10 also includes an annular plate or ring 98 mounted on the housing 46 to enclose the recess 78. The annular ring 98 includes a connector housing 102 mounted on the ring 98. The connector housing 102 surrounds and encloses the connector 42 to protect the connector 42 and terminals 38 from corrosive elements such as brake dust, road dust, bearing lubricant, moisture, etc. The sensor 10 also includes an annular ring 106 of ferromagnetic material. The annular ring 106 secures the ring 98 to the annular housing 46 and fixes the axial position of the magnet 86 with respect to the race 14. The ferromagnetic ring 106 also provides a low reluctance flux path from one pole of a given magnetic region of the magnet 86 around the coil 30 to the opposite pole of the given magnetic region of the magnet 86. Illustrated in FIGURES 2 and 4 of the drawings, the rotating race 18 of the bearing assembly or wheel end housing includes a plurality of gear teeth or flinger teeth 110 arranged to rotate relative to the speed sensor 10 and to face the alternating regions 94 of magnetic polarity of the magnet 86. In the embodiment illustrated in FIGURES 2 and 4, the flinger teeth 110 are axially offset from the alternating regions 94 of magnetic polarity on the magnet 86. Thus, the embodiment illustrated in FIGURES 2 through 4 is called an "axial read" sensor. There are exactly half as many flinger teeth 110 as there are alternating regions 94 of magnetic polarity. Thus, at any given moment, all of the flinger teeth 110 will be in the process of aligning with or will be aligned with magnetic regions 94 having the same polarity. In operation, as the flinger teeth 110 on the rotating bearing race 18 rotate past the alternating regions 94 of magnetic polarity, the passage of each tooth over a given magnetic region generates a change in the reluctance of the magnetic flux path specific to that magnetic region so as to vary the electrical signal generated on the coil 30. The frequency of the variation in the electrical signal is directly related to the angular speed of the rotating bearing element relative to the fixed bearing element.

Claims: A bearing assembly for a vehicle, said bearing assembly comprising : a fixed element (14) ; a rotating element (18) rotating relative to said fixed element (14) about an axis (22) ; a plurality of ferromagnetic teeth (110,220) mounted on one of said fixed element (14) and said rotating element (18) ; and a sensor (10) mounted on the other of said fixed element (14) and said rotating element (18), said sensor (10) detecting the angular speed of said rotating element (18) relative to said fixed element (14), said sensor (10) including an annular ferromagnetic ring (106) having an annular recess (78), a pick-up coil (30) mounted in said annular recess (78), and an annular magnet (86) mounted on said ferromagnetic ring (106) adjacent said pick-up coil (30), said magnet (86) including a plurality of magnetic regions (94) alternating in polarity around said magnet (86) and said magnet (86) being oriented relative to said other of said fixed element (14) and said rotating element (18) such that at least one of said magnetic regions faces a respective one of said teeth (110), characterized in that the annular magnet (86) is mounted concentric with and radially inward relative to said pick-up coil (30). A bearing assembly as set forth in claim 1, wherein said ferromagnetic ring (106) has a first, genrally disk-shaped portion having a radially inner edge relative to the axis, a radially outer edge relative to the axis and a supporting surface between said innner edge and said outer edge. A bearing assembly as set forth in claim 2, wherein said magnet (86) is connected to said ferromagnetic ring (106) adjacent said supporting surface. A bearing assembly as set forth in claim 1, wherein said magnet (86) has twice as many magnetic regions (94) as said rotating element (18) has teeth (110). A bearing assembly as set forth in claim 1 and further comprising connecting means (90) for connecting said magnet (86) to said ferromagnetic ring (106). A bearing assembly as set forth in claim 1, wherein every other of said magnetic regions (94) is alignable with a respective one of the teeth (110) on the rotating element (18). A bearing assembly as set forth in claim 1, wherein said magnetic regions have axially aligned poles. A bearing assembly as set forth in claim 1, wherein said magnetic regions have radially aligned poles. A bearing assembly as set forth in claim 1, wherein said rotating element (18) defines an inner bearing race and said fixed element defines an outer bearing race and wherein said sensor is mounted on said outer bearing race.

Inventors: AUSAVICH TIMOTHY C, BLOOM JEFFREY J, SEEFELDT JAMES D, AUSAVICH, TIMOTHY C., BLOOM, JEFFREY J., SEEFELDT, JAMES D.
Applicants: SSI TECHNOLOGIES INC, SSI TECHNOLOGIES, INC.
Application year: 1995
Main classification: G01P3
IPC codes: G01D5, G01P3