Abstract:
A disc brake assembly includes a rotor with an ABS tone ring insert assembly that functions as a rotation indicator in an anti-lock braking system. The insert is positioned in the hat of a rotor disc in a spaced relationship and is mounted to the mounting flange of the rotor disc. Forming the ring insert separately from the rotor disc also allows different coating materials to be used on the tone ring that may be more heat resistant. The ring insert assembly can be made of powder metal or made as a cast iron cylinder with a toothed cap made of powder metal having a corrosion resistant coating. Cost savings can be realized along with high performance when only a portion of the assembly if made of powder metal and coated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to brake assemblies, especially vehicular brakes including brake rotors attached to wheel hubs. This invention particularly relates to brake rotor disc assemblies equipped with anti-lock brake devices. 
     2. Description of Related Art 
     Typically, vehicles are equipped with a brake system to provide controlled slowing or stopping of the wheels to halt movement of the vehicle. A common type of brake system is a disc brake assembly associated with the wheels that is actuated by hydraulic or pneumatic pressure generated by an operator of the vehicle depressing a foot pedal. As is known, a disc brake assembly generally includes a rotor secured to the wheel of the vehicle for rotation therewith. The rotor has a pair of opposed friction plates that are selectively engaged by brake shoes supported on opposite sides of the rotor for sliding movement relative thereto. 
     In operation, the brake pads, which are operatively connected to hydraulically actuated pistons, move between a non-braking position in which they are spaced apart from the opposed friction plates of the rotor and a braking position in which they are moved into frictional engagement with the opposed friction plates of the rotor. In response to actuation by an operator, typically by depressing a brake pedal, the piston urges the brake pads from the non-braking position to the braking position. By this, the brake pads frictionally engage the friction plates of the rotor and slow or stop the rotation of the associated wheel of the vehicle. 
     To improve braking control and vehicle safety, anti-lock brake systems have been developed. In accordance with these systems, rotation of the wheel is sensed, and the braking response is automatically controlled to avoid skidding situations in which the vehicle wheels lose traction and slide over the pavement rather than engaging the surface at a slower rotational speed. 
     In a typical anti-lock brake assembly  200  seen in  FIGS. 8-11 , the rotor  210  is provided with a ring of teeth  212 , which are cast with the rotor, commonly referred to as an ABS (Anti-lock Braking System) tone ring. As the rotor  210  rotates, the rotating teeth  212  are read by an anti-lock brake sensor (not shown) that generates a signal for the anti-lock brake control system representative of the rotation of the wheel associated with the rotor  210 . The sensor reads the peaks of the teeth and the valleys between adjacent teeth, best seen in  FIGS. 10 and 11 , and uses an algorithm to determine whether the associated wheel is slipping. If it is determined that the wheel is slipping, braking pressure is released. Obviously, the arrangement and geometry of the teeth influence the signal generated by the sensor. To ensure proper operation of the anti-lock brake system, the teeth must be regularly spaced, sized, and maintained to preserve the profile of the teeth. Many sensors use magnetic pulse generation, which is created as the teeth pass by the sensor. The strength and accuracy of the signal is determined by the magnetic properties of the tone ring and the ring&#39;s geometric accuracy. Inadequate magnetic signal strength or incorrect geometric shape may cause signal failure, which can be further influenced by rotating velocity. 
     Problems have arisen with anti-lock brake systems in terms of poor performance due to irregularities and corrosion of the teeth. In known rotor assemblies in which the teeth are cast with the rotor, the teeth are also subjected to machining and coating treatments that are applied to the rotor. The disc is typically coated with an anticorrosive material, such as Geomet or Magni type coatings, that has a friction property and a corrosion resistance property. The coating is intended to lengthen the shelf life of the rotor and impede corrosion. However, since the coating is present when the rotor is put in use and then wears away from the braking surface, the coating must have adequate friction properties so that the rotor functions properly during braking at the outset before the coating is worn off. These dual property constraints limit the possible types of coatings suitable for this application. 
     Another consideration regarding the coating relates to the teeth. As noted above, the teeth are cast with the rotor, and the coating is applied to the entire piece. However, the teeth involve different design considerations. As the teeth do not function as a friction surface, the friction property of the coating is irrelevant. Further, it is desirable to maintain the anti-corrosive coating on the teeth for the functional life of the assembly. However, coatings suitable for rotor application degrade at high temperatures. This does not pose a problem with respect to the braking surface, but the teeth are exposed to high temperatures during the braking process. Since they are formed integrally with the rotor, which is normally cast iron, they heat to high temperatures, such as 800-900° F., as the rotor heats up due to the heat generated during braking. When the coating breaks down, the teeth can corrode. Corrosion alters the geometry of the teeth and causes inaccurate readings from the anti-lock braking sensor. This significantly shortens the useful life of the brake rotor assembly. When the sensor generates inaccurate readings, the assembly requires repair or replacement. 
     A problem also exists due to the state of the art casting methods and tolerances, which exist in casting of the teeth. Cast teeth will not be sufficiently accurate for most applications, and the inaccuracy in geometry will cause signal failure at higher velocities. To further machine the teeth for accuracy adds significant additional cost. 
     Another problem with cast iron tone rings relates to the magnetic properties of cast iron and how the properties change with temperature. Since cast iron has a high carbon content, its magnetism is reduced when heated to high temperatures experienced during braking. 
     There is a need, therefore, to provide a brake rotor assembly for use with anti-lock brake systems that provides an accurate and durable sensor system. There is also a need for a sensor system that can be retrofit in existing assemblies that no longer provide accurate readings. 
     SUMMARY OF THE INVENTION 
     An aspect of the invention provides a brake assembly having a rotor with an ABS tone ring for use with an anti-lock brake assembly that provides accurate and reliable readings. 
     Another aspect of the invention provides a brake assembly having a rotor with an ABS tone ring for use with an anti-lock brake assembly that has a relatively long service life. 
     An additional aspect of the invention provides a brake assembly having a rotor with an ABS tone ring for use with an anti-lock brake assembly that accommodates more versatile and durable coatings suitable for high temperature environments at a reasonable cost. 
     A further aspect of embodiments of the invention provides a tone ring assembly that can be retrofit in existing brake rotor systems. 
     The invention is directed to a brake rotor disc assembly comprising a rotor disc having a braking surface and a hat portion for mounting to a wheel hub, wherein the hat portion includes a cylindrical body and a radial mounting flange, and a tone ring insert for use with an anti-lock braking system. The tone ring insert includes a cylindrical portion and a sensor flange having a radial surface with a plurality of spaced sensing formations disposed thereon. The cylindrical portion is mounted to the radial mounting flange such that the tone ring insert is positioned within and spaced from the cylindrical body. 
     The invention is also directed to a brake rotor disc assembly comprising a rotor disc, which has a braking surface and a hat portion for mounting to a wheel hub, and a tone ring insert assembly. The hat portion includes a cylindrical body and a mounting flange. The tone ring insert assembly is designed for use with an anti-lock braking system and includes a cylindrical spacer positioned in the hat portion and mounted to the mounting flange and a cap coupled to the cylindrical spacer and having a toothed flange. 
     The invention includes the brake rotor disc assembly in combination with an anti-lock braking system including a sensor that generates signals based on rotation of the tone ring insert assembly and in combination with a vehicle. 
     The invention further relates to a tone ring assembly for use in an anti-lock braking system comprising a cylindrical spacer having a first end and a second end, wherein the first end has a plurality of axial openings formed therein, and a cap having an axial engaging portion and a radial flange extending from the axial engaging portion, wherein the radial flange has a ring of spaced teeth formed in a surface thereof. The axial engaging portion is fixed to the second end of the cylindrical spacer. 
     In the tone ring assembly, the cylindrical spacer can be made of cast iron, while the cap is made of powder metal in a high precision process and has a corrosion resistant coating thereon. 
     These and other aspects of the invention will become apparent in view of the detailed description and drawings herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
         FIG. 1  is a top perspective view of the rotor disc assembly in accordance with this invention; 
         FIG. 2  is a bottom view of the rotor disc assembly of  FIG. 1 ; 
         FIG. 3  is a top view of the rotor disc assembly of  FIG. 1 ; 
         FIG. 4  is a side view of rotor disc assembly of  FIG. 1 ; 
         FIG. 5  is an exploded side view in partial section taken along line A-A of  FIG. 3 ; 
         FIG. 6  is an enlarged partial side view of in section taken along line A-A of  FIG. 3 ; 
         FIG. 7  is an exploded bottom perspective view of the assembly of  FIG. 1 ; 
         FIG. 8  is a bottom perspective view of a prior art rotor disc assembly; 
         FIG. 9  is a bottom view of the rotor disc assembly of  FIG. 8 ; 
         FIG. 10  is a sectional side view taken along line B-B of  FIG. 9 ; and 
         FIG. 11  is an enlarged view of section C of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The disc brake rotor assembly described herein is preferred for use on vehicles, including automobiles, racing vehicles, trucks, heavy duty trucks, motorcycles and the like. The vehicles particularly suitable for use with this invention can include those vehicles having a gross vehicle weight of about 10,000 pounds and above, especially delivery trucks and buses. However, the inventive concepts discussed herein can be used in any type of application that uses rotary brakes, including automotive, other types of motorized vehicles, or railcars. The invention is especially applicable for retrofitting in existing vehicles. 
       FIG. 1  shows a brake rotor disc assembly  10  in accordance with the invention. The brake rotor disc assembly  10  includes a rotor disc  12  having a pair of opposed braking plates  14 ,  16  with friction material on the surface of each plate and a hat portion  18  for connection to a wheel hub (not shown) as is known. The hat portion  18  is defined by a cylindrical body  19  and a mounting flange  20 . The mounting flange  20  has a series of openings  21  to receive fasteners for connection to the wheel hub. Another series of openings  22 , best seen in  FIG. 3 , are provided on the outer edge of the mounting flange  20 . Preferably, the openings  22  are formed as counterbores. The rotor disc  12  shown in  FIG. 1  is a ventilated disc with vanes  24  formed between the braking plates  14 ,  16 ; however, this invention can be employed in single plate discs as well, as would be readily recognized by those of ordinary skill in the art. The rotor disc  12  is preferably made of cast iron. However, any conventionally known material may be used, including a composite. 
     In accordance with this invention, an independent toothed ring insert assembly or ABS tone ring insert is coupled to the rotor disc  12 . The toothed ring insert can be formed as a single piece in which the ring has teeth formed on a radial flange. With a single piece, any suitable material could be used. For example, the insert could be made entirely of powder metal with a corrosion resistant coating formed thereon. Alternatively, the insert could be made by molding a steel stamping into a high temperature resistant plastic or rubber. To reduce costs and offer additional material alternatives, the insert could be formed in two pieces. This configuration is illustrated in the drawings, but it will be recognized to those of ordinary skill in the art that the design of a one-piece insert would be similar except that the two pieces would be a unitary piece. 
     Referring to  FIGS. 1-7 , a toothed ring insert  26  is shown coupled to the rotor disc  12 . The insert  26  is formed in two pieces. The first piece is a cylindrical portion or spacer  28  having an annular side wall with a series of axial counterbore threaded openings  30  formed in one end. The other end has an interior annular groove  32  formed therein. Preferably the cylindrical spacer  28  is formed of cast iron, which is durable and relatively low cost. The second piece is a cap  34  that is formed as a toothed ring. The cap  34  is formed as a radial flange  36  including a ring of spaced teeth  38  and an axial engaging portion  40 . The cap  34  is made with highly accurate geometry to form well defined teeth that interact with the ABS sensor. The teeth  38  can be any type of sensing formations, such as serrations, alternating peaks and valleys, or openings. Preferably, the cap  34  is made by stamping, molding with powder metal or by machining. For cost purposes, a powder metal part or stamped part is preferred. 
     This assembly takes advantage of the lower cost of the cast iron cylindrical spacer  28  and high geometric accuracy and heat resistant magnetic properties of the powder metal cap  34  by connecting the two pieces together to act as the tone ring insert assembly  26 . The coupling can be achieved by a press fit, bolt, screw, pin, snap ring, thread or tongue and groove. One method of connection would be to use a protruding lip on the cap that is press fit within the spacer  28  to engage the annular groove  32 . Alternatively, the annular groove in the spacer  28  could be formed as an exterior annular groove with the same connecting effect. As best seen in  FIGS. 5 and 6 , a preferred method of connection is to knurl or serrate the axial engaging portion  40  and press fit the portion  40  into the groove  32  of the spacer  28 . Of course, any type of known connecting method can be used to achieve an integral component formed of two separate pieces. For example, connection can be made by a bolt, a pin, a snap ring, threads, or tongue and groove. 
     Another advantage of using two pieces for the tone ring insert  26  is that only the cap  34  needs corrosion resistant coating to protect the geometry of the teeth  38  and prevent corrosion build up to ensure accurate readings from the ring. This reduces costs as the cast iron spacer  28  does not need a coating. A preferred coating is an electroless plating process, as is known in the art. For example, electroless nickel can be used for corrosion resistance. Of course, any suitable coating can be used, including any electro-plating, electroless-plating or metallurgical plating. In the case of a one piece insert, the entire piece could be coated if desired. 
     The ring insert  26  is assembled with the rotor disc  12  by inserting the ring insert  26  into the hat portion  18 , as seen in  FIGS. 6-7 . A plurality of fasteners is used to connect the ring insert  26  to the mounting flange  20  by extending through openings  22  into threaded openings  30 . By this, the ring insert  26  is fastened to the rotor disc  12  at the wheel mounting face, which is the farthest point from the heat generating friction faces  14 ,  16  and is least susceptible to thermal deformation. As seen in  FIG. 6 , the ring insert  26  is independent of and spaced from the cylindrical body  19 , which provides some thermal insulation to the ring insert  26 , especially as compared to conventional integral toothed rotors in anti-lock brake assemblies. Also, since the ring insert  26  is fastened to the mounting flange  20  and sits within the hat portion  18 , radially inwardly from the braking plates  14 ,  16 , any twisting or bending experienced by braking plates  14 ,  16  due to thermal stresses induced during braking would not be translated to the ring insert  26 . Additionally, by forming the ring insert  26  separately from the rotor disc  12 , the choice of coating materials for the cap  34  is expanded as the coating material for the teeth does not need the friction quality required by the braking plates  14 ,  16 . 
     The assembly  10  can be originally manufactured or retrofit on vehicles into existing brake rotor systems to replace ABS systems that no longer provide accurate readings due to incorrect geometries and/or corrosion. First, the cap  34  is fixed to the spacer  28  to assemble the tone ring insert assembly  26 . The assembly  26  is then secured to the mounting flange  20  of a brake rotor disc  12  with the fasteners as described above. The entire assembly  10  is then installed in place of a conventional brake rotor. Of course, if a one-piece insert is used, the entire insert is simply installed to the mounting flange of the brake rotor disc. Since the toothed cap  34  is formed with a high precision process such as stamping, molded from powder metal, or machined, the geometry is highly accurate. The corrosion resistant coating on the toothed cap  34  ensures that corrosion will not occur and compromise the geometry of the teeth or interfere with sensor readings. Accordingly, a highly reliable brake rotor disc assembly  10  can be retrofit into an existing vehicle at a relatively low cost. 
     It can be appreciated that the ring insert  26  functions in the same manner as known toothed rings associated with brake rotor discs with anti-locking braking systems. The rotation of the teeth  38  is sensed by an anti-locking sensor to assess whether the wheel is slipping. The braking action is adjusting accordingly. Using this invention, however, will provide a more accurate and reliable reading since corrosion of the teeth is minimized and the teeth can be formed with high precision. This invention will also provide a longer service life for brake assemblies, especially in large vehicles, such as delivery trucks and buses and allow degraded tone rings to be easily replaced. 
     The invention is not limited to those embodiments described herein and may encompass various changes and modifications. It will be understood that the various modifications shown herein can be used in any combination. It is also possible to eliminate various components of the assembly and still have an effective connection. Further, different materials may be used to obtain similar results.