Abstract:
A wheel assembly for a non-driven wheel includes a rotating wheel hub with a shaft portion supporting a bearing inner race. A magnetic encoder is mounted for rotation with the shaft portion. A non-rotating component radially surrounds the shaft portion and has a bearing outer race. A cap is secured to the non-rotating component and covers the outer and inner races, the shaft portion and the magnetic encoder inboard of the races to seal an inboard side of the outer and inner races. A sensor is mounted to a non-rotating vehicle steering member externally to, not covered by, and not extending through the cap. The sensor is configured to deflect to be biased into continuous contact with an outer surface of the cap to read the magnetic encoder through the cap without extending through the cap.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/298,002, filed Jan. 25, 2010, and which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The invention relates to a speed sensor for a vehicle wheel. 
     BACKGROUND 
     Speed sensor assemblies for vehicle wheels are used to monitor the speed of the wheels for various purposes such as for implementing an automatic braking system (ABS), and/or as input to an engine or transmission controller. Typical speed sensor assemblies have included those used with capped wheel bearing assemblies, and those used with wheel bearing assemblies that use an inboard seal, but no bearing cap. Sensor assemblies integrated within a capped wheel bearing assembly typically have a magnetic encoder, often referred to as a tone ring, which rotates with the rotating part of the wheel assembly, and a stationary sensor spaced from the tone ring. Both of these components are sealed from the external environment by the bearing cap and one or more seals. Protecting the bearing, the tone ring and the sensor from the environment can be advantageous. However, servicing sensors integrated within a capped wheel assembly may require disassembly of the entire wheel assembly, and thus can require replacement of the entire wheel assembly even if only the sensor component may actually need replacement. 
     Speed sensors that are not sealed and capped within the bearing assembly have the advantage of easy removal for servicing. However, these designs typically have an exposed inboard seal and tone ring. This presents design challenges, as exposure to the environment can make it difficult to maintain a gap of a specified dimensional range between the sensor and the tone ring. Placing just the tone ring within a capped wheel assembly and positioning the sensor externally to the bearing cap to read the tone ring through the cap has the advantage of easy access to the sensor. However, such a design requires either that the sensor extend through the cap, thus diminishing the sealing effectiveness of the cap, or requires the use of a less precise tone ring. The latter is due to the increased distance between the sensor and the tone ring due to the bearing cap in between. The increased distance requires the use of a tone ring with fewer magnetic pole pairs in order for the pole pairs to be of a size that creates a sufficient magnetic field to be read by the sensor through the cap. 
     SUMMARY 
     A wheel assembly is provided with a robust sensor that provides highly accurate speed monitoring with a capped bearing design, without the disadvantages of an integrated sensor assembly. Specifically, a wheel assembly for a non-driven wheel includes a rotating wheel hub with a shaft portion supporting a bearing inner race. A magnetic encoder, also referred to as a tone ring, is mounted for rotation with the shaft portion. A non-rotating component radially surrounds the shaft portion and has a bearing outer race. The bearing inner race, outer race, and rolling elements in between comprise an inboard bearing. A cap is secured to the non-rotating component and covers the outer and inner races, the shaft portion, and the magnetic encoder inboard of the races. A sensor is mounted to a non-rotating vehicle steering member, such as a steering knuckle, so that the sensor is external to, not covered by, and does not extend through the cap. The sensor is configured to deflect to be biased into continuous contact with an outer surface of the cap to read the magnetic encoder through the cap without extending through the cap. 
     In at least one embodiment, the sensor has a distal portion and a narrowed midportion spaced from the distal portion. The sensor is configured to flex at the narrowed midportion when installed in and secured to the steering member with the distal portion deflected from an initial position to remain biased against the cap. 
     Thus, the sensor is mounted to the vehicle steering member externally to, not covered by, and not extending through the cap. The sensor is configured to deflect to be biased into continuous contact with an outer surface of the cap to read the magnetic encoder through the cap. Elimination of any gap between the sensor and the cap allows a highly accurate magnetic encoder to be used, such as one with forty-eight pole pairs. Because the cap needs no access hole for the sensor, debris is prevented from reaching the bearing, and bearing drag and its associated negative affect on fuel economy are reduced. Because the sensor does not extend through the cap, sealing of components covered by the cap is not compromised. Furthermore, because the sensor is external to the capped bearing, it is easy to remove and repair without disassembling or replacing the remaining components of the wheel assembly. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective illustration of a first embodiment of a wheel assembly with a capped inboard bearing and an external wheel speed sensor; 
         FIG. 2  is a schematic side view illustration of the wheel speed sensor of  FIG. 1 ; 
         FIG. 3  is a schematic perspective illustration of the wheel speed sensor of  FIGS. 1 and 2 ; 
         FIG. 4A  is a schematic cross-sectional illustration in partial fragmentary view of the wheel assembly of  FIG. 10  taken at lines  4 A- 4 A with a cover removed and with an alternate wheel speed sensor in contact with the bearing cap and deflected a first amount; 
         FIG. 4B  is a schematic cross-sectional illustration in partial fragmentary view of a wheel assembly of  FIG. 10  taken at the lines  4 B- 4 B but with a different dimensional stack up so that the wheel speed sensor in contact with the bearing cap is deflected a second amount; 
         FIG. 5  is a schematic side view illustration of the wheel speed sensor of  FIG. 1  showing a distal portion of the sensor in both a flexed position (in phantom) and an unflexed position with an integrated circuit embedded therein; 
         FIG. 6  is a schematic fragmentary side view illustration of the distal portion of the wheel speed sensor of  FIG. 2  with an integrated circuit shown in phantom; 
         FIG. 7  is a schematic fragmentary illustration of the distal portion of the sensor of  FIG. 6  shown in phantom with an integrated circuit, a capacitor, and a nonlinear wire connection there between; 
         FIG. 8  is a schematic fragmentary illustration of the distal portion of the sensor of  FIG. 6  shown in phantom with another arrangement of the integrated circuit, capacitor and a nonlinear wire connection there between; 
         FIG. 9  is a schematic fragmentary illustration of a distal portion of the sensor of  FIG. 6  with still another arrangement of the integrated circuit, capacitor and nonlinear wire connection; 
         FIG. 10  is a schematic perspective illustration in partial fragmentary view of the wheel assembly with the sensor of  FIGS. 4A and 4B , with the cap removed to show the magnetic encoder; 
         FIG. 11  is a schematic cross-sectional illustration in partial fragmentary view of the wheel assembly of  FIG. 1  taken at lines  11 - 11  showing a shape of the distal portion of the sensor easing installation of the sensor to an installed position, shown in phantom, despite initial interference with the cap; 
         FIG. 12  is a schematic perspective illustration in partial fragmentary view of the wheel assembly with speed sensor of  FIGS. 4A and 4B  installed and secured to a steering knuckle; 
         FIG. 13  is a schematic fragmentary illustration of an alternate embodiment of the distal portion of  FIG. 6 ; and 
         FIG. 14  is a schematic fragmentary illustration of another alternate embodiment of the distal portion of  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,  FIG. 1  shows a vehicle wheel assembly  10 . A wheel hub  12  shown in partial fragmentary view is fastened to a wheel (not shown) with fasteners  14  through a radially-extending flange  16  of the wheel hub  12 , and the wheel and hub  12  rotate about and define an axis of rotation A. A non-rotating component, referred to herein as a bearing outer race  18 , is fastened to a steering knuckle  20  using fasteners (not shown) that extend through openings  22  in a flange portion  19  of the outer race  18  (two of three openings  22  shown) and through openings  24  (shown in  FIG. 12 ) in the steering knuckle  20 . 
     The hub  12  has a shaft portion  23  radially surrounded by the outer race  18  as shown in  FIGS. 4A ,  4 B,  10  and  12 . The shaft portion  23  defines or supports an inner race  25  as shown in  FIG. 4A , similar to inner race  25 A of wheel assembly  10 A of  FIG. 11 , which interfaces with rolling elements  26  that also contact an inner surface of the outer race  18 , as also illustrated with hub  12 A and outer race  18 A of  FIG. 11 . 
     A magnetic encoder  30 , shown in  FIGS. 4A ,  4 B,  10 ,  11  and  12 , is fit to the wheel hub shaft portion  23  and/or adhered to a metal stamping  32  that is press-fit to and rotates with the wheel hub shaft portion  23  so that the encoder  30  rotates with the wheel hub  12 . The magnetic encoder  30  is an annular polymer ring with embedded ferritic particles establishing forty-eight pairs of alternating north and south magnetic poles around the circumference of the encoder  30 , facing inboard. Only one pair of magnetic poles is illustrated in phantom on  FIG. 10  as north pole N and south pole S, but  47  other like pairs are evenly distributed about the circumference of the encoder  30 . The north pole N has a north pole near a radially-outward end and a south pole near a radially-inward end, while the adjacent south pole S has a south pole near a radially-outward end and a north pole near a radially-inward end. Magnetic encoders  30  with different numbers of pole pairs could also be used. For example, fewer than forth-eight pole pairs could also be used, such as forty-seven or forty-two pairs. Fewer pole pairs around the circumference of the encoder  30  can be sized to create a larger magnetic field, allowing a sensor to be spaced from the cap  34  by a gap. However, the precision of the speed sensor would be lessened. 
     Referring to  FIGS. 1 and 4B , a stainless steel cap  34  is fit over an outer surface of the outer race  18  to cover the shaft portion  23  of wheel hub  12 , the magnetic encoder  30 , the bearing races  18 ,  25  and rolling elements  26 . Alternatively, the cap  34  could fit to an inner surface of the outer race  18 . Because the wheel assembly  10  is for a non-driven wheel, a wheel spindle from the wheel (not shown) fit to splines  38  of the hub  12  (see  FIG. 12 ) does not extend axially inward past the cap  34 , permitting the cap  34  to cover and protect the aforementioned components from an inboard side of the wheel assembly  10 . The wheel spindle may be webbed or plugged to prevent contamination from reaching the bearing assembly (outer race  18 , rolling elements  26  and inner race  25 ) from the outboard side of the vehicle. As used herein, “inboard” means laterally closer to or towards a longitudinal centerline of a vehicle, and “outboard” means laterally further from or away from a longitudinal centerline of the vehicle. 
     Still referring to  FIGS. 1 and 12 , a speed sensor  40  is installed through an aperture  42  in the steering knuckle  20  and secured to the steering knuckle  20  with a fastener  44  fit through a reinforced opening  45  in a mounting flange portion  43  of the sensor  40  (see  FIG. 1 ), as best shown in  FIG. 12 . The thickness of the mounting flange portion  43  is designed to prevent movement of the flange portion  43  at maximum stress due to bending of the sensor  40 , as discussed below. When fully installed and secured to the steering knuckle  20 , a distal portion  46  of the sensor  40  is flexed to remain in contact with an outer surface  47  of the cap  34 , and may be referred to as a “zero gap” sensor, as there is no gap between the sensor  40  and the bearing cap  34 . The sensor  40  is operable to sense the changing magnetic field of the forty-eight pole pairs N, S of the magnetic encoder  30  as the pole pairs rotate past the sensor  40  with the rotating hub  12  as a vehicle with wheel assembly  10  is driven. A secondary cover  48  is installed over the cap  34  and the distal portion  46  through an aperture  49  (shown in  FIG. 12 ) in the steering knuckle  20  and secured to the steering knuckle  20 . The secondary cover  48  protects the outer surface  47  of the bearing cap  34  from road debris, maintaining constant contact between the sensor  40  and the cap  34  over a full range of expected interference due to dimensional tolerance stack up of the wheel assembly  10  components, and with typical forces distributed over the wheel assembly  10  as the vehicle travels over the road. 
     Referring to  FIGS. 2 and 3 , the sensor  40  is shown in greater detail. The sensor  40  has a narrowed midportion  50  spaced from the distal portion  46 . As is apparent in  FIG. 2 , the distal portion  46  angles downward slightly by angle D relative to the midportion  50  such that distal portion  46  and midportion  50  do not have a common center axis. Midportion  50  has a center axis C 1  and distal portion  46  has a center axis C 2  angled relative to one another by angle D. That is, distal portion  46  and midportion  50  are not collinear. A contact surface  52  of the distal portion  46  is also angled downward, parallel to center axis C 2 . When the sensor  40  is installed through the aperture  42  of  FIG. 1  and secured to steering knuckle  20 , the midportion  50  must flex to overcome interference between the cap  34  and the distal portion  46  as illustrated with respect to the wheel assembly  10 A of  FIG. 11 . The aperture  42  is designed to be adequately sized to allow the midportion  50  of the sensor  40  shown in  FIG. 2  to flex over the full expected range, and the distal portion  46  to be deflected over a full expected range. When flexed and fully installed, the contact surface  52  is configured to be in full contact with the outer surface  47  (see  FIG. 1 ) of the cap  34 . 
     Because the midportion  50  is narrowed, flexing occurs in and stress is concentrated in the midportion  50  rather than in the distal portion  46 . The midportion  50  is designed so that strain and stress due to flexing will not exceed predetermined amounts based on a range of expected interferences between the distal portion  46  and the bearing cap  34 , due to stack up of dimensional tolerances of the wheel hub  12 , outer race  18 , bearing cap  34 , steering knuckle  20  and sensor  40 . Furthermore, the material of the sensor  40  is selected to ensure the required flexibility and strain below the strain limit over a wide temperature range, such as from −40 degrees Celsius to 125 degrees Celsius, and over an expected life of the sensor  40 . For example, if the sensor  40  is made from a combination of nylon and glass, the relative amounts of each will be controlled to ensure flexibility. Those skilled in the art would be able to select an appropriate material to meet designed maximum bending stress and strain over a predetermined range of flexing. 
       FIGS. 4A and 4B  show an embodiment using a sensor  40 A with a slightly alternate design and with a designed gap G 1  of 0.8 mm between the outer inboard-facing surface of the magnetic encoder  30  and the inner outboard-facing surface of the bearing cap  34 , and with a maximum gap G 2  of 1.6 mm permitted due to dimensional tolerances of the assembled components. Flexing of the sensor  40 A will be such that the center axis C 2  of the distal portion  46 A is angled upward with respect to the center axis C 1  of the midportion  50  by an angle up to 4.25 degrees, assuming the maximum 1.6 mm gap G 2  as shown in  FIG. 4A . If the assembled components resulted in an expected gap G 1  of 0.8 mm, as designed, then the center axis C 2  would be angled upward by only 0.4 degrees relative to the center axis C 1 , as illustrated in  FIG. 4B . Flexing of the sensor  40 A within this range will ensure that the contact force of the distal portion  46 A against the cap surface  47  will not be so large that electronic components within the distal portion (discussed below) are damaged, and yet will ensure that there is a positive contact force keeping the surface  52  of the sensor  40 A in contact with the cap  34 . The sensor  40  of  FIGS. 1 ,  2 ,  3  and  5  has the distal portion  46  angled downward relative to the midportion  50  in the unflexed state, as described above. The sensor  40  may be designed to be flexed so that the angle D of the center axis C 2  of distal portion  46  to the center axis C 1  of midportion  50  is 0.7 degrees when the gap G 1  (as shown with respect to sensor  40 A in  FIG. 4B ) is as designed (0.8 mm) and 4.0 degrees when the gap is at a maximum G 2  (as shown with respect to sensor  40 A in  FIG. 4A ) due to stack up of dimensional tolerances within design specifications. 
     Referring to  FIG. 5 , the sensor  40  is shown unflexed in solid, with surface  52  in a first position, and flexed to an installed position by interference with the cap  34  of  FIG. 1  (not shown in  FIG. 5 ), with the flexed position shown in phantom. An integrated circuit IC and a capacitor CA are embedded within the distal portion  46  of the sensor  40 . The integrated circuit IC has crystals that define a flat surface  60 . The integrated circuit IC is embedded such that, when installed and in the flexed position (assuming a predetermined interference with the bearing cap  34  of  FIG. 1  resulting from a designed gap G 1  (see  FIG. 4B ) of, for example 0.7 mm, and therefore a predetermined amount of flexing to an installed position), the flat surface  60  is parallel with the outer surface  47  of the cap  34  in order to optimize the ability of the integrated circuit IC to read the magnetic field variation of the encoder  30 . In another embodiment of a sensor  40 B, alike in all other aspects to sensors  40  and  40 A, the surface of a distal portion  46 B configured to be in contact with the cap  34  of  FIG. 1  may be convex, with the portion directly aligned with the integrated circuit IC not in contact with the cap  34 , as shown in  FIG. 13 . Alternatively, in another embodiment of a sensor  40 C, alike in all other aspects to sensors  40  and  40 A, the surface of a distal portion  46 C configured to be in contact with the cap  34  of  FIG. 1  may have raised ribs  74  in areas not directly aligned with the integrated circuit IC as shown in  FIG. 14 , similar to ribs  70  and  72  on the sensor  40 , to alleviate any direct pressure on the integrated circuit IC. 
     In order to allow the midportion  50  to be narrowed and to flex as designed, the integrated circuit IC and a capacitor CAP and other embedded electronic components of the sensor  40  are embedded within the distal portion  46 , as shown in  FIG. 7 . Wiring  62  connecting the integrated circuit IC and the capacitor CAP is preferably positioned within the sensor  40  in a non-linear manner in order to prevent any tension in the wiring  62  due to the flexing. Additional wiring (not shown) runs from the electronic components to a rear portion  63  (see  FIG. 2 ) of the sensor  40  and out of the sensor  40  to an electronic controller. The installed shape of the wiring  62  may be varied, as shown by wiring  62 A of  FIG. 8  and wiring  62 B of  FIG. 9 , but in all cases is preferably nonlinear. 
     Referring to  FIG. 6 , the distal portion  46  is shown with a shaped exterior at a portion that initially interferes with the bearing cap  34  during installation. Specifically, the portion of the distal portion  46  leading into the contact surface  52  has a chamfered corner  64 . The chamfered corner  64  has rounded edges to further ease installation of the sensor  40 . As shown in  FIG. 11 , the chamfered corner  64  makes initial contact with a rounded corner  66  of the bearing cap  34  when the sensor  40  is at an initial contact position indicated as I during installation. The radii of the chamfered corner  64  and the rounded corner  66  are selected so that the sensor  40  and bearing cap  34  will have initial interference along the radii of chamfered corner  64  and rounded corner  66  over the entire range of interferences due to dimensional tolerance stack up, aiding in low force insertion with no sharp rises in the insertion force as the sensor  40  is inserted to a final installed position shown partially in phantom and indicated as F. Similarly, the distal portion  46 A of the sensor  40 A of  FIGS. 4A and 4B  has a rounded or chamfered edge  64 A at a lead-in corner. The chamfered edges  64 ,  64 A and rounded corner  66  of the cap  34  ensure that forces on the sensor  40  or  40 A and strains and stresses due to bending of the sensor  40  or  40 A do not exceed predetermined maximum levels to prevent damage to the sensor  40  or  40 A and its internal electronic components (e.g., the integrated circuit IC and the capacitor CAP). 
     The sensors  40  and  40 A are both designed with optional raised ribs  70  (see  FIGS. 2 and 5 ) on an outer surface that are positioned to center the sensors  40 ,  40 A so that the contact surface  52  will be parallel with the cap surface  47  when fully installed. The length of the ribs  70  is selected to keep a base portion  73  of the sensor  40  centered. The base portion  73  is the portion that is configured to remain in contact with the steering knuckle  20  throughout the range of bending, as illustrated with respect to sensor  40 A in  FIGS. 4A and 4B . Additionally, secondary ribs  72  extend from at least selected ones of the ribs  70 , e.g., an uppermost and a lowermost rib  70  as viewed in  FIGS. 2 and 5 , as these ribs are likely to absorb forces due to flexing of the sensors  40 ,  40 A. The secondary ribs  72  may be referred to as crush ribs, and are configured to deform under sufficient force during installation to absorb the installation forces, protecting the sensitive electronic components (integrated circuit IC and capacitor CAP). 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.