Abstract:
A brake disc arrangement has a mounting portion formed of a metal, with a plurality of radial protuberances extending radially outward therefrom. The radial protuberances each have a radially distal tip portion, and a ceramic coating is applied to the radially distal tip portion of the radial protuberances. The brake plate portion is cast so as to surround the radially distal tip portions. However, it is isolated therefrom by the ceramic coating. At least some of the radially distal tip portions are formed of metal having a microstructure created by electrical discharge machining to increase dampening. A sand core within a core box holds the mounting portion in a predetermined fixed orientation. The molten metal is poured into the core box mold, and the metal brake plate portion is prevented by the ceramic coating from welding to any of the plurality of radial protuberances.

Description:
RELATIONSHIP TO OTHER APPLICATION 
     This application is a US national stage filing under 35 U.S.C. §371 of International Application No. PCT/US2009/002880 filed on May 8, 2009 and claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 61/127,272 filed on May 8, 2008. The disclosure of this provisional patent application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to brake discs for motor vehicles, and more particularly, to a composite brake disc arrangement formed of two cast portions, a mounting portion and a brake band portion, the two portions forming a frictional interface. 
     2. Description of the Related Art 
     Brake discs that conventionally are formed of a combination of a mounting portion and a brake plate portion employ, in some known arrangements, a continuous skirt extending radially outward of the mounting portion, the continuous skirt engaging a brake plate portion (i.e., brake band). The mounting portion is sometimes referred to as a “rotor hat,” due to its raised central portion and a substantially cylindrical portion extending axially therefrom. This combination, particularly with a continuous skirt extending radially from the cylindrical portion and disposed axially distal from the central portion gives the general appearance of a hat. It is also known as the “mounting bell.” 
     In the known art, the engagement between the continuous skirt and the brake plate portion is achieved in a plurality of ways. One engagement method involves direct communication between the mounting portion and the brake plate portion, thereby forming a continuous product. In other known connection arrangements, fingers radiate radially inward from the brake plate portion and at connected by fasteners to the continuous skirt. The radially inwardly extending fingers can be formed integrally with the brake plate portion. In these known arrangements, the mounting portion and the brake plate portion are so firmly attached to one another that the operate as a single element. 
     It has been recognized that heating of the brake plate portion during manufacture and use in a motor vehicle will cause various forms of warpage and deformation, particularly including radial deformation. On known approach to alleviating this problem is to employ radially inwardly directed fingers, which are formed integrally with the brake plate portion, and communicate with the mounting portion. The fingers, however, are able to be displaced radially, thereby arguably enabling radial dilation of the brake plate portion so as to accommodate the radial deformation. There is no mechanism in the known arrangement that will reduce vibration during braking, notwithstanding that the mounting portion and the brake plate portion have a small measure of separation between them. 
     There is a need, therefore, for a brake disc arrangement that is characterized with increased dampening over conventional brake disc arrangements. 
     There is a further need for a brake disc arrangement that exhibits reduced deformation in response to thermal and mechanical loading during service in a motor vehicle, and during the manufacturing process. 
     There is additionally a need for a brake disc arrangement that is characterized with an overall reduced mass. 
     SUMMARY OF THE INVENTION 
     The foregoing and other needs and objects of the invention are satisfied and achieved by this invention, which provides, in accordance with a first apparatus aspect, a brake disc arrangement of the type having a mounting portion and a brake plate portion. In accordance with the invention, there is provided a radial protuberance extending radially outward from the mounting portion. The radial protuberance has a radially distal tip portion. A coating is arranged to surround the radially distal tip portion, such that when the brake plate portion is cast to surround the radially distal tip portion, the coating functions to prevent the brake plate portion from welding to the radially distal tip portion. 
     In accordance with one embodiment of the invention, there are provided a plurality of the radial protuberances. The plurality of radial protuberances are arranged to be substantially coplanar with respect to each other. In a further embodiment, the plurality of radial protuberances are integrally formed with the mounting portion. 
     The radial protuberance is, in one embodiment, formed of metal. Moreover, the radially distal tip portion is subjected to an electrical discharge machining (EDM) process that increases a dampening characteristic of the metal in the region of the radially distal tip portion. 
     A sand core facilitates the casting of the brake plate portion to surround the radially distal tip portion. In one embodiment, the sand core is provided with a plurality of apertures therethrough for forming corresponding pillars between two halves of the brake plate portion during casting. 
     The coating must be able to withstand the temperature of the molten metal during the casting of the brake plate portion. In one embodiment, the coating is formed of a ceramic material. 
     In accordance with a further apparatus aspect of the invention, there is provided a brake disc arrangement having a mounting portion formed of a metal, the mounting portion having a plurality of radial protuberances extending radially outward therefrom. At least some of the radial protuberances each have a radially distal tip portion. A ceramic coating is applied to the radially distal tip portion of at least some of the radial protuberances. The brake plate portion is cast so as to surround the radially distal tip portions. However, it is isolated therefrom by the ceramic coating. 
     In one embodiment of this further apparatus aspect of the invention, at least some of the radially distal tip portions are formed of metal having a microstructure created by EDM. Additionally, the radial protuberances that have radially distal tip portions have a microstructure that has been created by EDM. Such radial protuberances are substantially equally distributed around the mounting portion. 
     In accordance with a method aspect of the invention, there are provided the steps of: 
     forming a mounting portion having a plurality of integrally formed radial protuberances; 
     applying a ceramic coating to the radial protuberances; and 
     casting a metal brake plate portion so as to surround the radial protuberances with molten metal. 
     In one embodiment of this method aspect of the invention, prior to performing the step of applying a ceramic coating there is provided the step of machining the radial protuberances. In a further embodiment, prior to performing the step of applying a ceramic coating there is provided the step of subjecting at least some of the radial protuberances to electrical discharge machining (EDM). There is additionally provided the step of distributing the at least some of the radial protuberances to EDM substantially equally around the mounting portion. 
     In a further method embodiment, the step of casting a metal brake plate portion includes the further step of forming a sand core that holds the mounting portion in a predetermined fixed orientation. The step of casting the metal brake plate portion includes, in a further embodiment, the step of pouring the molten metal onto the sand core. Such pouring includes in still further embodiments the step of pouring the molten metal onto the sand core and the formation of pillars within an interior portion of the brake plate portion. 
     In yet a further embodiment of the invention, prior to performing the step of pouring the molten metal onto the sand core, there is provided the further step of forming a core box mold. In this embodiment, the step of pouring the molten metal onto the sand core includes the step of pouring the molten metal into the core box mold. It is important in the practice of the invention to ensure that the metal brake plate portion does not weld to any of the plurality of integrally formed radial protuberances. 
     The unique two-part design of the brake disc of the present invention enables design considerations, such as thinner wall sections, to be achieved, while simultaneously reducing mass. The specialized fabrication of the mounting portion creates localized areas of high dampening, thereby significantly reducing the propensity for vibration of the entire part. Finally, the independent, yet constrained, interaction between the mounting section and plate section allows each segment to react to external stimulus without affecting the other, thus reducing the overall deformation of the part under mechanical and thermal loading. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Comprehension of the invention is facilitated by reading the following detailed description in conjunction with the annexed drawings, in which: 
         FIG. 1  is a simplified schematic perspective representation of a cast mounting portion for use in a brake disc arrangement in accordance with the invention; 
         FIG. 2(   a ) is a partially cross-sectional side view representation of the cast mounting portion of  FIG. 1 ;  FIG. 2(   b ) is an enlarged cross-sectional representation showing in greater detail a mounting section of the cast mounting portion; and  FIG. 2(   c ) is an enlarged representation of the mounting section of  FIG. 2(   b ) of the cast mounting portion; 
         FIG. 3  is a simplified schematic perspective representation of a cast brake disc showing the cast mounting portion combined with a cast brake band portion; 
         FIG. 4  is a plan representation of the cast brake disc of  FIG. 3 ; 
         FIG. 5(   a ) is a partially cross-sectional representation of the cast brake disc of  FIG. 3 ;  FIG. 5(   b ) is an enlarged partially cross-sectional representation of the interconnection between the cast mounting portion and the cast brake band portion; 
         FIG. 6(   a ) is a plan representation of the interior of the cast brake disc of  FIG. 3  during manufacture, showing a sand core; and  FIG. 6(   b ) is and enlargement of a portion of the plan representation of  FIG. 6(   a ) showing additional detail of the interconnection between the cast mounting portion and the sand core prior to casting of the brake band portion; 
         FIG. 7  is a simplified schematic perspective representation of a cast brake disc showing the cast mounting portion combined with a cast brake band portion, and further showing the cast mounting portion with apertures therethrough for mounting onto the axle of a motor vehicle; and 
         FIG. 8  is a partially cross-sectional side representation of the completed cast brake disc of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     The brake disc arrangement of the present invention is formed of essentially two parts. These are, as will be described in detail herein, a mounting portion and a brake plate portion. The manufacture of the mounting and brake plate portions will result in a brake disc wherein the mounting portion is physically constrained by the brake plate portion. Nevertheless, both such portions respond to external stimulus independently of each other. The result is a brake disc that is advantageously characterized by increased dampening, reduced deformation during service and manufacturing, and reduced mass. 
       FIG. 1  is a simplified schematic perspective representation of a cast mounting portion  100  for use in a brake disc arrangement (not shown in this figure) in accordance with the invention. As will be described hereinbelow, mounting portion  100  supports and constrains the brake plate portion (not shown in this figure) through several radial protuberances  122  that are distributed substantially equally around an outer circumference  117  of mounting portion  100 . The use of radial protuberances  122 , as opposed to a conventional circumferentially continuous section (not shown), contributes significantly to the attainment of mass reduction over conventional one-piece designs. As will be described below, radial protuberances  122  are configured to be accommodated the brake plate portion, and serve as the interaction point between the mounting portion and the brake plate portion. 
     In the practice of the invention, mounting portion  100  is produced first, separate from the brake plate portion. This manufacturing sequence wherein the mounting portion is cast separately from the brake plate portion facilitates the achievement of the advantage of permitting the use of significantly thinner wall-section thicknesses, compared to a conventional one-piece design. In this specific illustrative embodiment of the invention, this reduction in thickness, along with the use of radial protuberances  122 , constitute the primary features through which the advantageous reduction in the mass of the brake disc (not shown in this figure) is achieved. 
     Mounting portion  100  has an integrally formed mounting surface  110 . In this specific illustrative embodiment of the invention, mounting surface  110  has an aperture  115  therethrough that, upon completion of the manufacture of the brake disc, will facilitate its installation on the axle (not shown) of a motor vehicle (not shown). 
     In the manufacture of mounting portion  100  of this specific illustrative embodiment of the invention, a conventional sand molded casting process is employed. The mounting portion can be made of gray iron, aluminum, nodular iron, or other suitable metals. However, after completion of the casting of mounting portion  100 , several additional processing steps are required in preparation for the joining thereto of the brake plate portion. 
       FIG. 2(   a ) is a partially cross-sectional side view representation of mounting portion  100 , as described previously in relation to  FIG. 1 .  FIG. 2(   b ) is an enlarged cross-sectional representation showing in greater detail a radial protuberance  122  of mounting portion  100 . Additionally,  FIG. 2(   c ) is an enlarged representation of radial protuberances  122  of mounting portion  100 . Elements of structure that have previously been discussed are similarly designated. 
     As shown in these figures, radial protuberances  122  extends radially outward from outer circumference  117 . Each of radial protuberances  122  has integrally formed therewith a tip portion  120 . Each tip portion  120  has an external surface  125 . In order to achieve the design goals of increasing dampening and reducing deformation during service and manufacturing, external surface  125  is machined in a conventional manner. Such machining enables greater control over the surfaces, which is advantageous during further processing. 
     Following traditional machining, it is necessary to subject external surface  125  of tip portion  120  of several radial protuberances  122  to electrical discharge machining (EDM). Generally, the principal purpose of the EDM process is to remove material. A secondary result of this process, however, is a change within the microstructure of the metal. This change in the microstructure provides the advantage of increasing greatly the dampening properties of the metal in the area subjected to EDM, a very useful secondary effect. In the practice of the invention, the EDM process is applied to several, not necessarily all, of radial protuberances  122  to create areas with high dampening characteristic. This dampening is achieved by dissipating common modes of vibration with the brake plate portion. 
     In the practice of this embodiment of the invention, the results desired from the application of the EDM process are best achieved when some, not all, of the radial protuberances  122  are subjected to the EDM process. It is preferable that the radial protuberances  122  that are processed using EDM are substantially equally spaced around the circumference of mounting portion  100 . This is done so that there will be distinct areas distributed around the entire brake plate portion of very high dampening, available to keep vibration from increasing and propagating around the brake plate portion. 
     Following the EDM process, a ceramic coating (not shown) is applied to all of radial protuberances  122 . The ceramic coating is of a thickness that will preclude welding between the tip portions of the radial protuberances and the brake plate portion. During the formation of the brake plate portion, as will be discussed below, molten metal will be poured around the radial protuberances  122  of mounting portion  100 . If the brake plate portion and the mounting portion  100  weld together during this step, the benefits achieved by the present invention will in large measure be lost because the mounting portion and the brake plate portion will not be able to behave as two separate bodies. Upon completion of the application of the ceramic coating, mounting portion  100  is ready to be combined with the brake plate portion, as follows. 
       FIG. 3  is a simplified schematic perspective representation of a cast brake disc (not specifically designated) showing the cast mounting portion  100  with a cast brake plate portion  130 .  FIG. 4  is a plan representation of the cast brake disc of  FIG. 3 . Elements of structure that have previously been discussed are similarly designated. The brake plate portion of a brake disc is also known in the art as a brake band. 
     It is seen in these figures that brake plate portion  130  is installed to surround circumferentially mounting portion  100 . Although portions of radial protuberances  122  are visible in these figures, tip portions  120  are contained within the inner circumference of brake plate portion  130  and therefore cannot be seen in these figures. 
       FIG. 5(   a ) is a partially cross-sectional representation of the cast brake disc of  FIGS. 3 and 4 .  FIG. 5(   b ) is an enlarged partially cross-sectional representation of the interconnection between cast mounting portion  100  and cast brake plate portion  130 . Elements of structure that have previously been discussed are similarly designated. 
     It is seen in  FIGS. 5(   a ) and  5 ( b ) that tip portions  120  of radial protuberances  122  are surrounded within the inner circumference (not specifically designated) of brake plate portion  130 . The combining of mounting portion  100  and brake plate portion  130  is actually the addition of one part to the other. More specifically, the brake plate portion  130  is, in this embodiment of the invention, cast around radial protuberances  122  of mounting portion  100 . However, it is critical that mounting portion  100  be maintained in correct and precise orientation while the metal for cast brake plate portion  130  is being poured and cooled. In the practice of a specific illustrative embodiment of the invention, this problem is solved by using a sand core. 
       FIG. 6(   a ) is a plan representation of the interior of the cast brake disc of  FIG. 3  during manufacture, showing a sand core  140 .  FIG. 6(   b ) is and enlargement of a designated portion of the plan representation of  FIG. 6(   a ), and shows greater detail of the interconnection between mounting portion  100  and sand core  140  prior to casting of the brake band portion (not shown in this figure). 
     In a conventional one-piece design of a brake disc, the brake plate portion is formed using a combination of two sand molds (not shown) with a sand core, such as sand core  140  sandwiched between. The sand-core enables the production of a detailed geometry, and is held in place by the two sand molds on either side of the sand core. In the practice of this embodiment of the invention, mounting portion  100  is combined with sand core  140  to ensure that proper orientation is maintained throughout the process of casting the brake plate portion. In this embodiment, sand core  140  is produced by blowing sand (not specifically designated) into a mold, typically called a “core box.” By inserting mounting portion  100  into the core box, and then blowing the sand around it to produce the sand core, the result is a combination sand core/mounting portion article. 
     The combination sand core/mounting portion article is then inserted between the two sand mold sections as if it were a typical sand core. The sand-molds hold the combination sand core/mounting portion article in proper alignment, ensuring that the cast brake plate portion solidifies correctly around the radial protuberances  122  of mounting portion  100 . Since the ceramic coating precludes welding between the brake plate portion and the mounting portion during casting of the brake plate portion, there is thereby produced a system of two parts that are constrained together, but which react independently to stimulus. Because of the independent relationship, the deflection/deformation of the brake plate portion during both machining and application as a vehicle brake will greatly be reduced. 
     It is additionally seen in  FIGS. 6(   a ) and  6 ( b ) that sand core  140  has apertures therethrough. In this regard, see apertures  142 ,  144 , and  146  in  FIG. 6(   b ). As will be seen in relation to  FIG. 7 , below, these apertures enable the creations of pillars between the two halves of brake plate portion  130 . More specifically, some of the molten metal (not shown) that is poured during the process of casting brake plate portion  130  is accommodated within the apertures to form the pillars. 
       FIG. 7  is a simplified schematic perspective representation of a cast brake disc showing mounting portion  100  combined with brake plate portion  130 , and further showing mounting apertures  160  therethrough for enabling mounting of the brake disc onto the axle of a motor vehicle (not shown). Elements of structure that have previously been discussed are similarly designated. 
     It is seen in this figure that there are provided pillars, such as pillars  152 ,  154 , and  156  interposed between the two halves of the brake plate portion. In this specific illustrative embodiment of the invention, pillar  152  is the result of molten metal entering aperture  142  ( FIGS. 6(   a ) and  6 ( b )); pillar  154  is formed as a result of the presence of aperture  144 ; and pillar  156  is the result of aperture  146 . It is to be understood that the apertures in sand core  140  and the resulting pillars in brake plate portion  130  are replicated about the circumference of brake plate portion  130 . In addition, the apertures and resulting pillars are not limited to the configuration shown in the present figures. Persons of skill in the art can produce additional and different aperture and corresponding pillar configurations without departing from the claimed invention. 
     Following the casting of the brake plate portion around the mounting portion, there remains the process of final machining of the complete brake disc part. In the practice of this specific illustrative embodiment of the invention, machining is effected in the same way as a conventional one-piece design. However, the present invention affords less deformation, which results in increased processing control and significantly increasing the likelihood that lower tolerance machining geometric and dimensional specifications can be achieved. 
       FIG. 8  is a partially cross-sectional side representation of the completed cast brake disc of  FIG. 7 . Elements of structure that have previously been discussed are similarly designated.  FIG. 8  shows the cast brake disc after machining. 
     Although the invention has been described in terms of specific embodiments and applications, persons skilled in the art can, in light of this teaching, generate additional embodiments without exceeding the scope or departing from the spirit of the claimed invention. Accordingly, it is to be understood that the drawing and description in this disclosure are proffered to facilitate comprehension of the invention, and should not be construed to limit the scope thereof.