Abstract:
The invention provides a method for manufacturing a friction damped disc brake rotor, including the steps of: (A) positioning at least one insert into a mold, wherein the insert has a body with tabs extending therefrom to hold the insert in a desired position within the mold; and (B) casting a rotor cheek of the disc brake rotor in the mold around the insert such that a portion of each tab is bonded with the rotor cheek and the body is substantially non-bonded with the rotor cheek so that the body provides a proper interfacial boundary with the cheek for damping while the bonding of the tabs with the rotor cheek prevents corrosion-causing exterior elements from reaching the interfacial boundary.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/717,310, filed Sep. 15, 2005. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to a bi-metal disc brake rotor and a method of manufacturing bi-metal brake disc rotors in which an insert is cast into the brake rotor in a manner to provide improved noise damping without subjecting the rotor to corrosion.  
       BACKGROUND OF THE INVENTION  
       [0003]     Motor vehicle disc brake systems utilize a disc brake rotor at each respective wheel, wherein the disc brake rotor typically includes a rotor hat for connecting to an axle hub of a rotatable axle of the motor vehicle, and at least one annular rotor cheek connected to the rotor hat, wherein the at least one rotor cheek has a pair of mutually opposed braking surfaces onto which brake pads are selectively applied when braking is desired. Typically, the rotor cheek configuration may be solid, in which case a single rotor cheek has opposing braking surfaces thereon, or may be vented, in which case a pair of rotor cheeks are mutually separated by a web of ventilation vanes and each rotor cheek provides a respective braking surface so that, in combination, two mutually opposed braking surfaces are provided.  
         [0004]     The disc brake system further typically includes a caliper which supports a mutually opposed pair of brake pads, one brake pad disposed overlying a respective rotor cheek braking surface, wherein the caliper, the brake pads, and other associated brake components collectively form a “brake corner”. Normally, the caliper keeps the brake pads separated from the braking surfaces of the one or more rotor cheeks. Braking of the motor vehicle occurs at the brake corner by the caliper pressing the brake pads upon the braking surfaces of the one or more rotor cheeks. Frictional interaction between the one or more rotating rotor cheeks and non-rotating brake pads causes braking of the motor vehicle to transpire, the rate of braking depending upon the pressure of the brake pads against the braking surfaces.  
         [0005]     Brake squeal can be undesirably generated at the brake corner when braking occurs. This brake squeal is the result of modal excitations of the disc brake rotor (composed usually of cast iron) by the frictional material of the brake pads. It is known in the prior art that brake squeal can be addressed by reducing modal excitation on the disc brake rotor by the friction material of the brake pads (i.e., lowering the frictional coefficient), by modifying the modal excitation response of the brake corner via changing the modal properties of the rotor cheeks (i.e., in terms of resonant frequencies, mode shapes, and structural damping through higher carbon content of the one or more rotor cheeks and/or increasing the disc brake rotor mass, or using exotic, expensive materials), and by introducing additional damping for example via a shim disposed at a backing plate of the brake pads.  
         [0006]     The aforementioned brake squeal countermeasures are relatively effective for most brake corner designs, but they require a significant amount of testing and analytical resources in order to be effective. And unfortunately, brake corners for performance motor vehicles, or those motor vehicles with high friction lining materials, are resistant to the prior art brake squeal countermeasures, due to the high amount of modal excitation from the friction material of the brake pads.  
         [0007]     U.S. patent application Ser. No. 10/961,813, filed Oct. 8, 2004, commonly assigned with the present application, teaches Coulomb friction damped disc brake rotor configurations having an insert within the rotor to provide improved damping.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention provides a method for manufacturing a friction damped disc brake rotor, including the steps of: (A) positioning at least one insert into a mold, wherein the insert has a body with tabs extending therefrom to hold the insert in a desired position within the mold; and (B) casting a rotor cheek of the disc brake rotor in the mold around the insert such that a portion of each tab is bonded with the rotor cheek and the body is substantially non-bonded with the rotor cheek so that the body provides a proper interfacial boundary with the cheek for damping while the bonding of the tabs with the rotor cheek prevents corrosion-causing exterior elements from reaching the interfacial boundary.  
         [0009]     Preferably, the insert is provided with a coating that prevents wetting of the insert during the casting process, and the coating is washed off of the tabs prior to casting to achieve the bonding of the tabs with the rotor cheek. Alternatively, the insert may be differentially coated in such a manner so that the tabs are uncoated while the rest of the insert is coated. Alternatively, the tabs may be coated with graphite to improve the bonding of the tabs with the rotor cheek.  
         [0010]     The tabs may be internal to the body, external to the body, or both internal and external to the body.  
         [0011]     The insert is preferably between approximately 1.5 and 2.0 mm thick.  
         [0012]     The invention also provides a friction damped disc brake rotor, having at least one rotor cheek with an insert positioned therein. The insert has a generally annular body with a plurality of tabs extending from the body. A portion of each tab is bonded with the rotor cheek and the body is substantially non-bonded with the rotor cheek so that the body provides a proper interfacial boundary with the cheek for damping while the bonding of the tabs with the rotor cheek prevents corrosion-causing exterior elements from reaching the interfacial boundary.  
         [0013]     It is further believed that a Coulomb friction damped disc brake rotor according to the present invention has the following attributes: 1) the greater the surface area of the interfacial boundaries, the greater will be the damping; 2) the greater the number of interfacial boundaries, the greater will be the damping; 3) pre-tensioning and/or pre-loading is not required so long as the interfacial boundary provides Coulomb friction damping; and finally, 4) the thickness of the insert may be optimized based upon experimentation (i.e., a smallest possible thickness while still providing at least one interfacial boundary), and it is thought to be optimal if the thickness of the insert is small relative to the thickness of the rotor cheek.  
         [0014]     This and additional features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1   a  is a schematic side sectional view of an insert positioned within a casting mold in accordance with the present invention;  
         [0016]      FIG. 1   b  is an enlarged view taken from detail  1   b  of  FIG. 1   a;    
         [0017]      FIG. 1   c  is a schematic side sectional view of the mold and insert of  FIG. 1   a , with the mold closed and molten iron introduced into the mold to form a friction damped disc brake rotor in accordance with the invention;  
         [0018]      FIG. 1   d  is a schematic side sectional view of the mold of  FIG. 1   a , with the mold opened and a friction damped disc brake rotor ejected from the mold in accordance with the invention;  
         [0019]      FIG. 2  is a plan view of the insert shown in  FIG. 1   a - d  with alternative configurations shown in phantom;  
         [0020]      FIG. 3  is a plan view of an insert in accordance with an alternative embodiment of the invention;  
         [0021]      FIG. 3   a  is a schematic partial cross-sectional view of an insert having an alternative stiffening bump;  
         [0022]      FIG. 3   b  is a schematic partial cross-sectional view of an insert having an alternative stiffening downturned flange; and  
         [0023]      FIG. 4  is a schematic side sectional view of an insert positioned within a mold for casting a friction damped disc brake rotor having a vented rotor cheek. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Referring to  FIG. 1   a , a mold  10  is accordance with the invention having upper and lower mold halves  12 ,  14  which form a cavity  16  therebetween for casting a friction damped disk brake rotor in accordance with the invention.  FIG. 1   b  shows an insert  18  which is pre-positioned within the mold  10  and having tabs  20  which rest on cutout portions  22 ,  24  of the lower mold half  14 . As shown in  FIG. 1   c , when the upper and lower mold halves  12 ,  14  are closed together, the tabs  20  are supported between the cutout portions  22 ,  24  of the lower mold half  14  and the lands  26 ,  28 , respectively of the upper mold half  12 .  
         [0025]     Referring to  FIG. 2 , the insert  18  is shown in plan view. As shown, the insert  18  has a generally annular body  30  with tabs  20  extending therefrom. Each tab includes a distal portion  32  and a proximal portion  34 . The distal portion  32  is trapped between the cutout portions  22 ,  24  and the lands  26 ,  28 , respectively, while the proximal portion  34  of each tab  20  is exposed to molten metal within the mold cavity  16 .  
         [0026]     The mold  10  is preferably a sand mold, and the insert  18  is a pre-manufactured steel component having a coating on opposing surfaces  36 ,  38  (shown in  FIG. 1   b ) around the entire body  30 . These coated surfaces  36 ,  38  do not bond with the cast metal in the casting operation. The lack of “wetting” or affinity along these coated surfaces  36 ,  38  produces the desired interfacial boundary for damping. However, the tabs  20 , particularly the proximal portion  34  of each tab  20 , is configured in a manner to bond with the cast metal of the rotor cheek. Since the coated surfaces  36 ,  38  of the insert  18  do not bond with the cast metal of the rotor cheek, a proper interfacial boundary is formed with the cheek for damping. However, the bonding of the tabs, particularly the proximal portions  34  thereof, with the cast metal of the rotor cheek prevents corrosion causing exterior elements from reaching the interfacial boundary between the coated surfaces  36 ,  38  and the cast metal rotor cheek. This bonding may be achieved by first coating the tabs  20  with the same material which forms the coated surfaces  36 ,  38  of the body  30  and then cleaning the coating off the tabs  20  to locally remove the coating to allow the tabs to be micro-welded to the cast iron to effectively seal the rest of the insert/iron interface from intrusion by water or other elements from the exterior of the casting. Alternatively, a graphite coating may be applied to the tabs  20  to enhance bonding with the cast metal. So called “wetting” of the tab edges can also be accomplished by masking the tab prior to application of the coating. The insert may comprise any material having a melting point higher than that of cast iron that would not be dissolved during the casting process.  
         [0027]     Referring to  FIG. 1   d , mold  10  is shown in the open position with the final friction damped disk brake rotor  40  removed from the mold cavity. As shown, the friction damped disk brake rotor  40  has a hat portion  42  with a rotor cheek  44  extending about the periphery thereof, and the insert  18  positioned within the cheek  44 . The distal end  32  of the tabs  20  of the insert  18  would be machined off after the friction damped disk brake rotor  40  is removed from the mold  10 .  
         [0028]     The locating tabs can be used on the ID, OD or both positions to stabilize the insert during the metal casting operation. For example, the insert  18  shown in  FIG. 2  has optional internal tabs  56  shown in phantom. The number and placement of tabs depends on the specific rotor geometry and its dimensions, and on the thickness of the steel insert. The tabs  56  and  20  may be used together or separately.  
         [0029]     The steel inserts are preferably 1.5 to 2 mm in thickness, but other thicknesses may be used. The thicknesses are chosen to prevent bending of the insert while not being so thick as to “chill” the surrounding casting to the point that objectionable carbides are produced.  
         [0030]     By preventing the steel insert from reacting with the iron during casting, the interfaces are maintained for desired sound damping. By enhancing the bond between the tabs and the cast steel, the gap at the tab areas is eliminated in order to isolate the interfaces from the casting exterior environment to eliminate corrosion issues in service. Also, more than one insert may be cast in place in the rotor.  
         [0031]      FIG. 2  also shows in phantom optional through holes  45 , which facilitate mold filling while minimizing action of molten metal to move the insert  18 . In other words, the holes  45  prevent molten material from lifting up the insert, as the mold is filled from below through the gate channel  47  shown in  FIG. 1   d . By gating below the part and using a horizontal pouring process, metal is not directed onto or splashed onto the insert prematurely. Also, quiescent mold filling prevents splashing of metal droplets on to the insert prior to general contact with molten metal during mold filling to avoid premature solidification of small droplets of iron.  
         [0032]     Also, the molten material is preferably filtered at the gate channel  47 , shown in  FIG. 1   d , with a ceramic filter to reduce slag related defects.  
         [0033]     Turning to  FIG. 3 , an alternative insert  18 A is shown, including annular stiffening rib  41  and radial stiffening ribs  43 , which are coextensive with the tabs  20 . These optional ribs  41 ,  43  help maintain the position and shape of the insert  18 A during mold filling (i.e. prevents “potato-chipping”). The ribs are preferably 0.040 inch thick with a 0.060 inch (1.5 mm) thick insert.  
         [0034]     Alternatively, the stiffening rib  41  may be a stiffening ridge  41 A as shown in the schematic partial cross-sectional view of insert  18 B in  FIG. 3   a . Referring to  FIG. 3   b , in a further alternative embodiment, the inside diameter  49  of the annular body of the insert  18 A, shown in  FIG. 3 , may include a turned down flange  41 B as shown schematically in the partial cross-sectional view of the insert  18 C of  FIG. 3   b . These various stiffening ribs help maintain the position and shape of the insert  18 ,  18 A,  18 B or  18 C during mold filling.  
         [0035]      FIG. 3  also illustrates relief areas  71 , shown in phantom to represent clearance provided in the mold cavity formed in the area of cutout portions and lands  22 ,  26 ,  24  and  28  in  FIG. 1   c . These relief areas  71  in the mold  10  allow the insert to expand without deformation as the molten metal heats it.  
         [0036]     The present invention provides reduced disk brake noise and squeal, and limits corrosion of an exposed insert after machining.  
         [0037]     It is to be understood that the procedure outlined above can also be used with vented rotor cheek configurations, with a note that an insert or inserts are provided at both or selective one of the rotor cheeks. For example,  FIG. 4  shows a mold  60  having upper and lower mold halves  62 ,  64  forming a mold cavity  66  therebetween for forming a friction damping disc brake rotor with a vented cheek configuration. A pre-manufactured core with a web pattern  68  and insert  70  are supported within the mold cavity  66  and cast over. The core with web pattern  68  forms the venting configuration of the cheek. The insert  70  has tabs  72  supported between cutouts  74  and lands  76 . As in the embodiment described with reference to  FIG. 1   a - d , the tabs  72  are configured to bond to the cast metal, while the body of the insert is coated and does not bond to the cast metal in order to form a proper interfacial boundary for damping. The bonding of the tabs prevents corrosion.  
         [0038]     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.