Patent Publication Number: US-2007114099-A1

Title: Exciter ring for a brake rotor

Description:
RELATED APPLICATIONS  
      The present application is a continuation of U.S. patent application Ser. No. 10/977,020, filed Oct. 29, 2004, the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to braking systems for vehicles and, more particularly, to exciter rings for brake rotors.  
     BACKGROUND OF THE INVENTION  
      Anti-lock braking systems (“ABS”) are used to increase traction and control of a vehicle under difficult braking conditions. On slippery surfaces, braking can cause the wheel to “lock up” and stop rotating. As a result, the portion of the wheel in contact with the road simply slides relative to the surface, which severely reduces traction and the ability to steer the vehicle. The loss (reduction) of traction causes the truck or tractor-trailer to become unstable and directional control becomes difficult. This problem is of particular concern for heavy commercial vehicles, such as tractor-trailers, where the loss of control can cause the vehicle to jack-knife.  
      ABS systems prevent wheel lock up by rapidly releasing and reapplying pressure to the brakes, to permit the skidding wheel to regain traction and steering. ABS systems typically comprise a speed sensor positioned adjacent to four or more wheels of the vehicle. Each speed sensor is connected to a controller that monitors the acceleration/deceleration of the wheels. When wheel lock up occurs, the controller detects the abnormally abrupt deceleration of the wheel and operates a valve in the corresponding brake line to release pressure on the brake until the wheel begins to accelerate again. Once the controller senses the wheel accelerate, the controller reverses the valve to allow brake pressure to increase once more. The controller repeats this cycle of acceleration/deceleration many times per second, such that braking is kept near, but does not exceed, the point at which the wheel locks up.  
      Speed sensors typically operate by detecting the rate of rotation of the wheel hub, brake drum or brake rotor. In the case of an ABS brake rotor, evenly spaced teeth are integrally cast on the surface of the brake rotor in the shape of a ring. The ring of teeth is commonly referred to as a tone ring or exciter ring, and the teeth are referred to as pulse teeth or exciter teeth. A typical exciter ring has about 80 to 120 teeth, depending on the size of the tire. The sensor typically comprises a magnetic pickup that is positioned adjacent to the exciter ring and measures the speed of the rotor by detecting the change in magnetic flux caused by the movement of the exciter teeth.  
      A variety of methods are used to detect changes in magnetic flux, including variable reluctance, Hall effect and magnetic resistance, as are well known in the art. In each case, the strength of the signal received by the speed sensor decreases with distance from the exciter ring. Accordingly, some skill and care must be used to ensure that the speed sensor is positioned as close as possible to the exciter ring without actually contacting the exciter teeth.  
      ABS brake rotors also require additional steps of machining and inspection to ensure that the exciter teeth are uniform and that the exciter ring is not damaged. Brake rotors are typically cast in rough form and then machined to their finished dimensions. However, the numerous teeth of the exciter ring are difficult to cast and frequently have casting defects and imperfections which require the rotor to be scrapped. In addition, the exciter teeth are susceptible to damage caused by mishandling following the casting step of the manufacturing process, which increases the scrap rate. Furthermore, the exciter teeth must have uniform depth and clean surfaces for the speed sensors to function properly. Thus, the exciter ring requires an additional machining step to remove any imperfections that would interfere with the operation of the speed sensor. Further yet, the exciter ring is integral with the brake rotor and unrepairable damage to the exciter ring results in discarding of the entire brake rotor. Replacing entire brake rotors due to damaged exciter rings can become very expensive. In addition, dirt and other debris accumulates on the exciter ring, which increases the rate of corrosion. As a result, the exciter ring is frequently the limiting factor in the life of a brake rotor.  
      Thus, it would be desirable to provide an exciter ring that is formed separately from an ABS brake rotor and is removably connectable to the brake rotor to facilitate relatively easy replacement of the exciter ring when the exciter ring becomes damaged. In addition, it would be desirable to provide a simple, inexpensive, and quick process of refurbishing a wheel assembly when the exciter ring or exciter teeth are damaged.  
     SUMMARY OF THE INVENTION  
      In some aspects, the invention provides a wheel assembly having a brake rotor including a barrel section having an interior surface defining a barrel cavity, a brake disc extending radially outwardly from the barrel section and defining a disc cavity in communication with the barrel cavity, and a projection extending from the interior surface of the barrel section into the barrel cavity, and an exciter ring formed separately from the brake rotor and being engagable with the projection within the barrel cavity to removably connect the exciter ring to the brake rotor.  
      In some aspects, the invention provides an exciter ring formed separately from and removably connectable to a brake rotor, the exciter ring including a substantially cylindrical body portion having an inner surface and an outer surface, the inner surface defining a ring cavity, the body portion including a detent protruding outwardly from the outer surface and extending at least partially around the outer surface of the body portion, and a flange extending radially outwardly from the body portion and having a plurality of apertures therein.  
      In some aspects, the invention provides a wheel assembly including a brake rotor having a projection, and an exciter ring formed separately from and removably connectable to the brake rotor, the exciter ring including a body portion and a flange extending radially outwardly from the body portion, the body portion having an inner surface and an outer surface, the inner surface defining a ring cavity, the body portion including a detent protruding outwardly from the outer surface and extending at least partially around the outer surface of the body portion, the flange having a plurality of apertures therein, wherein the detent is engagable with the projection to removably connect the exciter ring to the brake rotor.  
      In some aspects, the invention provides a method of assembling a wheel assembly, the method including providing a brake rotor including a barrel section and a brake disc extending radially outwardly from the barrel section, the barrel section having an interior surface defining a barrel cavity and including a projection extending from the interior surface of the barrel section into the barrel cavity, the brake disc having a disc cavity, providing an exciter ring formed separately from the brake rotor, inserting the exciter ring through the disc cavity and into the barrel cavity, and engaging the exciter ring with the projection in the barrel section after inserting to removably connect the exciter ring to the brake rotor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a wheel assembly including an exciter ring embodying aspects of the invention.  
       FIG. 2  is a front view of a wheel hub, a brake router and the exciter ring of the wheel assembly shown in  FIG. 1 .  
       FIG. 3  is a rear perspective view of the exciter ring shown in  FIGS. 1 and 2 .  
       FIG. 4  is a partial cross sectional view of the brake rotor and the exciter ring, taken along line  4 - 4  in  FIG. 2 . 
    
    
      The invention is not limited in its application to the details of the construction and arrangements of the components set forth in the following description or illustrated in the drawings. The invention includes other embodiments and can be practiced or carried out in various different ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and variations thereof herein are used broadly and encompass direct and indirect connections and couplings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings.  
     DETAILED DESCRIPTION  
       FIG. 1  illustrates a wheel assembly  20  including a brake rotor  24 , a wheel hub  28 , a tire or wheel  32 , and an exciter ring  36 . A brake pad (not shown) or other braking mechanism is engagable with the brake rotor  24  to control the rotation of the wheel  32 . The wheel hub  28  is connected to the brake rotor  24  with a plurality of fasteners  40  and rotates with the brake rotor  24 . The brake rotor  24  defines a rotor cavity  44  and the wheel hub  28  defines a hub cavity (not shown) therethrough that are aligned when the brake rotor  24  and wheel hub  28  are connected. The wheel hub  28  includes a plurality of fasteners  48 , such as, for example a combination of lug nuts and lug bolts, for connecting the wheel  32  to the wheel hub  28  and facilitating rotation of the wheel  32  with the wheel hub  28  and the brake rotor  24 . A wheel axle (not shown) has an end thereof inserted through the aligned cavities of the brake rotor  24  and wheel hub  28  and connected to the wheel hub  28 . The wheel axle is connectable to a wheel assembly  20  at each end of the axle.  
      With reference to  FIGS. 1 and 4 , the brake rotor  24  defines a central longitudinal axis  52  through a center thereof about which the brake rotor  24  and the exciter ring  36  are symmetrically oriented. The brake rotor  24  includes a brake disc  56  having an inboard portion  60  and an outboard portion  64  that are separated by a series of vent holes  68 , defined by spaced dividers  69 , for cooling the rotor  24 . An inboard brake surface  72  is formed on the inboard side of the inboard portion  60 . Similarly, an outboard brake surface  76  is formed on the outboard side of the outboard portion  64 . As used herein, the term “outboard” means facing away from or distal to the vehicle, and the term “inboard” means facing toward or proximal to the vehicle. The brake disc  56  has a disc cavity  78  that is defined in the brake disc  56  between the inboard brake surface  72  and an interior surface  100  (described in more detail below). The brake rotor  24  also includes a cylindrical barrel section  80  extending in the outboard direction from the brake disc  56 . The barrel section  80  is provided with a radial flange  84  extending radially inwardly that has a series of apertures for receiving the fasteners  40  for attaching the brake rotor  24  to the wheel hub  28 . The barrel section  80  also includes an interior barrel surface  88  that defines a barrel cavity  92  through the barrel section  80 . A barrel projection  96  extends inwardly from the interior barrel surface  88  toward a center of the barrel section  80  to provide a reduced diameter mouth to the barrel cavity  92 . In the illustrated construction, the barrel projection  96  extends into the barrel cavity  92  substantially perpendicular to the longitudinal axis  52 . In some constructions, the barrel projection  96  is at least partially aligned with the outboard portion  64  of the brake disc  56  and is not between the inboard and outboard portions  60 ,  64  of the brake disc  56 . The outboard portion  64  of the brake disc  56  forms an interior surface  100  adjacent the barrel section  80 , and a recess  104  is formed in the interior surface  100  near the barrel section  80 .  
      With reference to  FIGS. 1-4 , the exciter ring  36  includes a body portion  108  substantially cylindrical in shape and a ring flange  112  extending radially outward from the body portion  108 . In the illustrated construction, the exciter ring  36  is formed by stamping, while in other constructions the exciter ring  36  is formed by molding. No matter what the manner used to form the exciter ring  36 , the exciter ring  36  is formed separately from the brake rotor  24 .  
      In the illustrated construction, the ring flange  112  extends substantially perpendicular from the body portion  108 . The body portion  108  has an interior body surface  116  and an exterior body surface  120  and includes a detent  124  that extends outwardly from and completely around the exterior body surface  120  of the body portion  108 . In some constructions, the detent  124  does not extend completely around the exterior body surface  120  of the body portion  108 . In other constructions, a plurality of detents are spaced from one another around the exterior body surface  120  of the body portion  108 . A plurality of evenly spaced apertures  128  are defined in the ring flange  112  to define a plurality of exciter teeth  132 . The number of apertures  128  and exciter teeth  132  can vary depending on the size of the wheel  32  and/or the braking system being used with the wheel  32  and exciter ring  36 .  
      With particular reference to  FIG. 4 , assembly of the exciter ring  36  and the brake rotor  24  will be described. The exciter ring  36  is positioned for assembly with the body portion  108  oriented toward the brake rotor  24  and aiming in the outboard direction and the ring flange  112  oriented generally parallel to the brake disc  56 . The body portion  108  is aligned with the barrel cavity  92  such that the longitudinal axis  52  substantially extends through a center of the body portion  108 . The body portion  108  of the exciter ring  36  is sized slightly larger than the reduced diameter portion of the barrel cavity  92  defined by the barrel projection  96 . The exciter ring  36  is inserted along the longitudinal axis  52  in the outboard direction and is forced into the barrel cavity  92 , which slightly deflects the body portion  108  inwardly to allow the detent  124  to pass by the barrel projection  96 . Once the detent  124  passes by the projection  96 , the body portion  108  flexes outwardly to position the detent  124  on the outboard side of the barrel projection  96  and position the ring flange  112  in the recess  104  defined in the interior surface  100  of the brake disc  56 . The exciter ring  36  is connected to the brake rotor  24  when the detent  124  is positioned on the outboard side of and in some constructions, engaged with the barrel projection  96  and when the outboard surface of the ring flange  112  engages the interior surface  100  of the brake disc  56  within the recess  104 . The exciter ring  36  and reduced diameter portion of the barrel cavity  92  defined by the barrel projection  96  are appropriately sized to secure the exciter ring  36  to the brake rotor  24  by a friction or interference connection. In some constructions, the body portion  108  is sized so that the distance between the detent  124  and ring flange  112  is only slightly larger than the width of the barrel projection  96 , so that the exciter ring fits snugly against the interior barrel surface  88  and the interior surface  100  within the recess  104  of the brake disc  56 . An adequate amount of force must be applied to the exciter ring  36  in an outboard direction to connect the exciter ring  36  to the brake rotor  24  and an adequate amount of force must be applied to the exciter ring  36  in an inboard direction to disconnect the exciter ring  36  from the brake rotor  24 . The exciter ring  36  and brake rotor  24  are configured such that the adequate amount of force required to disconnect the exciter ring  36  from the brake rotor  24  is larger than any force that may be applied to the exciter ring  36  in the inboard direction during normal operating conditions of the wheel assembly  20 .  
      Upon assembly of the exciter ring  36  and the brake rotor  24  and operation of the wheel assembly  20 , a sensor (not shown) of the ABS brake rotor  24  is positioned adjacent to the exciter ring  36  and measures the speed of the rotor  24  by detecting the change in magnetic flux caused by the movement of the exciter teeth  132  separated by the apertures  128  in the exciter ring  36 .  
      In case of wear, damage, uncleanliness, etc. to the exciter ring  36 , the exciter ring  36  can be simply removed and replaced with another exciter ring  36 , rather than machining or cleaning of the exciter ring  36  or even disposal of the entire brake rotor which was necessary in previous brake rotors. The current exciter ring  36  eliminates the need for lengthy repair or cleaning services necessary to return the brake rotor and exciter ring to operating condition and does so in a relatively inexpensive manner.  
      Although particular constructions of the present invention have been shown and described, other alternative constructions will be apparent to those skilled in the art and are within the intended scope of the present invention. Thus, the present invention is to be limited only by the claims.