Abstract:
An exciter ring/disc brake rotor assembly allows snap in fitting of the exciter ring onto the disc brake rotor. Either of two snap fit mechanisms limits clocking of the ring in use.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The invention relates to anti-lock brake systems for motor vehicles and more particularly to an exciter ring and disc brake rotor assembly which allows snap in fitting and retention of the exciter ring on the disc brake rotor.  
         [0003]     2. Description of the Problem  
         [0004]     Brake units for motor vehicles should provide smooth braking with reasonable service life. In some applications this need has been met with disc brakes. The cost effectiveness of disc brake systems depends in part on making the components out of easily worked, inexpensive material. Disc brake rotors have generally been made from relatively inexpensive gray iron castings. Gray iron is, however; highly susceptible to corrosive attack, particularly in the operating environment of vehicles where brake components are open to the air, subject to substantial transient heating and exposed to water and salt water spray. In regular use, the working surfaces of the discs are rubbed clean by contact with the disc pads, which are typically made of a composite material and which rub off corroded areas. However, other areas of the brake discs are not swept by the brake pads and are not regularly cleaned. Prior to anti-lock braking systems, such concerns were not paramount with brakes which were frequently in use, since the rotor is a regularly replaced part and the remaining areas subject to attack were not critical.  
         [0005]     With the advent of anti-lock braking systems (ABS) other sections of the disc brake rotor take on importance, particularly the anti-lock brake system exciter ring. The exciter ring is a cylindrical section of the rotor having a common axis of rotation with the rotor. A plurality of teeth is formed in a ring, which is flat in the plane of rotation of the rotor to pass closely by a stationary sensor. One type of sensor used is a variable reluctance sensor which generates an electrical pulse train as a function of the varying magnetic flux leakage between the sensor head and the exciter ring. In this system the frequency of the resulting electrical pulse train indicates the rotational speed ofthe wheel on which the rotor is mounted. The generation of clean pulse train is greatly aided by having teeth of uniform shape, size and spacing. Where the ring is cast as one piece with the rotor, corrosion of the rotor can compromise all of these factors, resulting in difficulty in detecting the passage of teeth and gaps and causing generation of an irregular pulse train.  
         [0006]     The problem of corrosion of exciter rings for anti-lock brake systems is not limited to disc brake systems, but is also an issue with drum brakes. In drum brakes the exciter ring has not been an integral part of the drum, but rather has been a separate part, press fitted on the end of a wheel hub. Press fitted parts can readily be made of material more corrosion resistant than gray iron, such as a mild low carbon steel. However, the press fitting of rings onto disc rotors has proven less successful than it has for hubs using drum brakes. The difficulty stems from the fact that in disc brake systems the exciter ring is in direct contact with the rotor, which is part of the active brake assembly, whereas the axle hub using drum brakes is not a brake component. On drum systems less heat is transferred from the hub which carries the exciter ring than is transferred in disc systems from the rotor to an exciter ring. Exciter rings are made of low carbon steel which has a different thermal coefficient of expansion than does iron. The difference in coefficients of expansion in the materials used for the ring and the hub or rotor causes more problems in disc brake systems than in drum systems since more heat is transferred by a rotor to a ring than by a hub to a ring and thus an exciter ring and rotor vary more in size in relation to each other than do an exciter ring and a hub. An exciter ring which loses its tight fit with a rotor can begin to clock (i.e., the ring rotates relative to the rotor). If a ring rotates on a rotor, the ring will not reflect actual wheel rotational velocity. This affects ABS operation. Such a ring could also “pop” off.  
       SUMMARY OF THE INVENTION  
       [0007]     According to the invention there is provided a snap in ABS exciter ring for fitting to a cast gray iron disc rotor. The ABS exciter ring is preferably fabricated in a stamping from low carbon steel, which exhibits substantially greater resistance to corrosion than does the disc rotor. However, the exciter ring may also be made of stainless steel or any other materials. Tangs extend from one side of the exciter ring for engaging the disc rotor. The embodiments of the invention differ in the details of the capture mechanism between the tangs and an interior surface of the rotor. In one embodiment, projecting parts of the tangs snap into indentations machined into the surface of the rotor. The attachment provides a positive lock of the ring to the rotor. The only modification required of rotors is limited machining. In a second embodiment the tangs engage beads projecting from the rotor.  
         [0008]     Exciter rings in accordance with the invention are readily fabricated in different sizes to accommodate rotors of differing sizes. No loose fasteners are required for installation.  
         [0009]     Additional effects, features and advantages will be apparent in the written description that follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a perspective view of a rotor/exciter ring assembly in accordance with the invention.  
         [0012]      FIG. 2  is a perspective view in partial cutaway illustrating mating of the exciter ring to the disc brake rotor in accordance with a first of two preferred embodiments of the invention.  
         [0013]      FIG. 3  is a perspective view of an exciter ring in accordance with the first embodiment of the invention.  
         [0014]      FIG. 4  is a side elevation of the exciter ring of  FIG. 3 .  
         [0015]      FIG. 5  is a section view of a rotor constructed in accordance with the first embodiment.  
         [0016]      FIG. 6  is a cutaway view of rotor/exciter ring assembly in accordance with a second embodiment of the invention.  
         [0017]      FIG. 7  is a cutaway view of the rotor of  FIG. 6 .  
         [0018]      FIG. 8  is a perspective view of the exciter ring for the second embodiment.  
         [0019]      FIG. 9  is a side elevation of the exciter ring of  FIG. 8 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     Referring now to the figures and in particular to  FIG. 1 , an assembly  10  of a rotor  12  and an exciter ring  14  for a disc brake is shown. Exciter ring  14  is situated in a recess  16  in rotor  12 , flat along one side of the ring against a shelf  24  (see  FIG. 2 ). Shelf  24  is formed in rotor  12  during casting. Five tangs  18  are shown extending from an inner circumference  17  (see  FIG. 3 ) of exciter ring  14 . The number of tangs may be varied. The rings are preferably set at an oblique angle of  90  to  110  degrees with respect to the plane of the ring, and engage with rotor  12 . The precise configuration of tangs  18  and the manner of attachment of ring  14  to rotor  12  also varies between the two preferred embodiments. Rotor  12  is a gray iron casting. Rotor  12  provides a wearable surface  22  which pads of the disc brake close on and wear against. Exciter ring  14 , in both embodiments, is a stamped piece of mild low carbon steel, snap fit by tangs  18  onto the rotor and retained in position by the tangs. Exciter ring  14  is set as a recess  20  in rotor  12  centered within wearable surface  22 .  
         [0021]     Referring to  FIGS. 2-5 , details of exciter ring  14  and rotor  12  relating to capture between the elements are illustrated. In  FIG. 2 , exciter ring  14  is held along one major side to a shelf  24 . One of tangs  18  is seen extending from the inner circumference  17  of exciter ring  14  into a deeper recess  20  in rotor  12 . Tang  18  abuts along one side the inner cylindrical surface  21  ofthe deeper recess  20 . Extending radially inwardly from the cylindrical surface  21  into recess  20  is a bead  26 . Tang  18  operates as a catch, its sides defining an aperture  30  parallel to the interior surface forming recess  21 . Tang  18  is captured on a bead  26  upon aligning the aperture  30  with the bead  26 , holding the exciter ring  14  in place on rotor  12 . Capture is assisted by the profile of bead  26 , which has a bevel  28  facing the direction from which tang  18  is fitted into the recess  20 . Beveled faces  57  are also applied to leading edges of the tangs  18 . Upon introduction of the ring  14  into recess  16  each tang  18  is rotated into alignment with a bead  26  in the deeper recess  21 . As ring  14  is moved axially into rotor  12  tangs  18  encounter the beveled surfaces  28  of the trapezoidally shaped beads  26  and ride up and over the beads before snapping down the far edge of the bead. A trapezoidal shape is not required. Only some sort of allowance between the ring and rotor is required. Beads  26  may be seen to not be a continuous ring, but as isolated raised points. This configuration serves to keep ring  14  from clocking.  
         [0022]     This first embodiment of the invention produces highly secure attachment between tang and rotor, but requires modification of molds in which rotors are cast to produce the beads  26 .  
         [0023]     Referring to  FIGS. 6-9 , a second embodiment of the invention is illustrated. To avoid the expense of modifying molds to provide beads  26  on rotor  12  surfaces, indentations  34  may be machined into the cylindrical interior surface  21  of rotors  12 . Exciter rings  14  are then modified to attach to the indentations  34 , as best seen in  FIG. 7 . Indentations  34  are radially distributed around the cylindrical surface  21 . As seen in  FIGS. 8 and 9 , tangs  18  are modified to incorporate radially outwardly oriented projections  19  which are sized to fit into indentations  34 . Projections  19  have a base inside tang  18  and extend outwardly toward the main body of exciter ring  18 . Projections  19  can be seen to be partially punched out of the tangs, leaving an opening into which the projections can be pushed. Since the tangs  18  lead introduction of an exciter ring  14  to a rotor  12 , the projections flatten into the openings in the tangs  18  as the ring is pushed into position on rotor  12 . The projections 19  are, in effect, torsion springs which snap out along the trailing edge into indentations  34 .  
         [0024]     The first embodiment of the invention emphasizes a secure attachment of the exciter ring  14  to a rotor  12  to minimize any prospect of clocking of the ring. The second embodiment of the invention costs less to produce than the first.  
         [0025]     While the invention is shown in only two of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.