Patent Publication Number: US-2010122880-A1

Title: Surface configurations for damping inserts

Description:
TECHNICAL FIELD 
     The technical field of this disclosure relates generally to friction damped devices and to inserts for use in the same. 
     BACKGROUND 
     A number of devices have used friction damping inserts as a mechanism to mitigate unwanted noise outputs. One such example is a brake rotor assembly, which is a common braking device used in motor vehicles. In fact, in today&#39;s automobiles, brake rotor assemblies are typically employed at each front wheel, and in many instances at all four wheels, and are even sometimes utilized in conjunction with other braking devices such as drum brake assemblies. 
     Each brake rotor assembly is generally designed to selectively stop or slow its respective vehicle wheel upon actuation from the vehicle&#39;s driver. In most instances this involves forcibly engaging a brake pad or other related braking means against a portion of the brake rotor assembly that co-rotates with the vehicle wheel. And the frictional interaction experienced as a result of this engagement inhibits or halts the continued rotation of the vehicle wheel in accordance with the driver&#39;s directive. 
     But sometimes, during normal and severe braking conditions, a noise phenomena known as brake squeal occurs when parts of a brake rotor assembly vibrate or oscillate at high frequencies. And this can be loud and annoying. As such, a variety of products and methods are being investigated that may help diminish the occurrence, intensity, and longevity of brake squeal emitted from motor vehicle braking systems. 
     SUMMARY OF EXEMPLARY EMBODIMENTS 
     One embodiment of a product includes an insert for disposition in or on a component. The insert may have at least one contact surface that can experience relative frictional movement against an adjacent interior surface of the component. The at least one contact surface of the insert may comprise a nominal plane and surface features arranged in a nonstochastic pattern. The insert may also be constructed and arranged for disposition in or on the component to dampen sound when the component is vibrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a side elevational view of a brake rotor assembly according to one embodiment of the invention. The view of brake rotor assembly shown includes a side view of a brake rotor and a cross-sectional view of a brake caliper. 
         FIG. 2  is a cross-sectional view of a brake rotor according to one embodiment of the invention. 
         FIG. 3  is a perspective and magnified fragmentary view of an insert that may be disposed in the brake rotor according to one embodiment of the invention. 
         FIG. 4  is a perspective and magnified fragmentary view of an insert that may be disposed in the brake rotor according to one embodiment of the invention. 
         FIG. 5  is a perspective and magnified fragmentary view of an insert that may be disposed in the brake rotor according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description of the embodiment(s) is merely exemplary in nature and is not intended to limit the scope of the invention, it application, or its uses. 
     A conventional brake rotor assembly  10 , as illustrated in  FIG. 1  may include a brake rotor  20  and a brake caliper  30  as its main components. The brake rotor  20  may include a centrally located rotor hat  22  that secures the brake rotor  20  to a vehicle wheel (not shown) so that the two can co-rotate in unison when the vehicle is moving. The brake rotor  20  may also include one or more annular rotor cheeks  24  that extend annularly from the rotor hat  22  and provide the brake rotor  20  with at least one, and usually two, braking surfaces  26  against which brake pads  32  may be selectively engaged when braking is desired. Suitable materials often utilized for forming the brake rotor include ferrous alloys such as iron and non-ferrous metals such as aluminum, titanium and alloys thereof. In some instances, as shown here, the rotor cheek  24  may be of the solid-type and thus provide a braking surface  26  on each of its opposed sides. And in other instances the brake rotor  24  may be of the vented-type; a configuration where a pair of thinner rotor cheeks  24  are separated by a web of ventilation vanes that aid in extracting heat away from the braking surfaces  26 . In such a configuration each rotor cheek  24  provides a single opposed braking surface  26  on its outer side so that the two cheeks  24 , in combination, provide a pair of opposed braking surfaces  26 . Nonetheless, both rotor cheek configurations are well known in the art and, as such, need not be described in further detail here. 
     The brake caliper  30  may straddle the brake rotor  20  and carry the one or more brake pads  32  in close proximity to the one or more braking surfaces  26  of the brake rotor  24 . When desired, the one or more brake pads  32  can be actuated and pressed against the rotor&#39;s  20  one or more braking surfaces  26  to generate frictional resistance therebetween. This resistance is what allows the driver to controllably stop or slow the brake rotor  20  and thus the wheel to which it is rigidly secured. In most instances the driver of the vehicle transmits the force needed to actuate the one or more brake pads  32  and achieve the desired braking outcome through a hydraulic, pneumatic, mechanic or electromechanic mechanism, such as, for example, depressing a foot pedal or pulling a hand lever. A wide variety of brake calipers  30  have been developed and thus their exact mechanical design may fluctuate from vehicle to vehicle—most notably from older vehicles to newer ones. In fact, one specific and exemplary type of brake caliper  30  commonly employed in today&#39;s automobiles is a single-piston-floating caliper. A notable trait of these types of brake calipers is their ability to self-center and self-adjust upon actuation. Still other types of brake calipers such as duel or four-piston fixed calipers can be found on many automobiles. 
     When the one or more brake pads  32  engage the one or more braking surfaces  26 , however, there is a tendency for the brake rotor  20  to oscillate at frequencies in the range of about 4,000 to about 11,000 Hz. The resulting noise from such an occurrence is oftentimes referred to as “brake squeal.” And it, in addition to being rather annoying, often fosters the perception that the vehicle braking system is damaged or of low quality. 
     Thus, in one embodiment, as shown best in  FIG. 2 , at least one insert  40  may be disposed in or on a component of a device such as the rotor cheek  24  or cheeks to friction damp the brake rotor  20  when the one or more brake pads  32  are engaged therewith. The insert  40  may be fabricated from the same or different material from that of the brake rotor  20 . For example, the insert  40  may be formed from a metal, a reinforced ceramic, or any other appropriate material. Suitable metals include, but are not limited to, a low-grade steel such as AISI 1010 or 1008, aluminum alloys, titanium alloys, and stainless steel 316. A suitable reinforced ceramic that may be used is a silicon carbide composite. One role of the insert  40  is to convert the mechanical energy contained in the rotor&#39;s  20  high frequency oscillations into thermal energy capable of being easily expelled to the surrounding environment. For example, the oscillating brake rotor  20  may cause relative movement to transpire between independent contacting surfaces—such as an exterior contact surface  42  of the insert  40  and an adjacent interior surface  28  of the rotor cheek  24 . The frictional interaction between these surfaces  42 ,  28  can thus absorb and dissipate an appreciable amount of the mechanical energy imparted to the brake rotor  20  such that any surviving oscillations or vibration propagation is diminished. 
     In one embodiment, the insert  40  may comprise a coating to prevent substantial wetting at the surface interface between the contact surface  42  and the interior surface  28  during brake rotor  20  manufacturing. For instance, such a coating may be useful if the brake rotor  20  is manufactured using a conventional casting procedure. A suitable material that may be used to form the coating may be a refractory-based or graphite-based material. The refractory-based material may include particles of alumina, iron, silica, and/or nickel dispersed in a binder material. The graphite material may be any form of graphite or graphite oxide blends mixed with an organic or inorganic binder, a clay, water, petroleum solvent, or an alcohol. These graphite-based materials may also be treated with a variety of functional groups to enhance the bonding characteristics of the graphite particulate matter. The thickness of the coating may vary considerably depending on the manufacturing process utilized to make the brake rotor  20 . For example, when the brake rotor  20  is manufactured by casting, the thickness of the coating may be such that molten metal is prevented from bonding to the contact surface  42  of the insert  40 . A typical coating thickness under conventional casting circumstances may range from about 1-650 μm, from about 10-400 μm, from about 30-300 μm, from about 30-40 μm, from about 40-100 μm, from about 100-120 μm, from about 120-200 μm, from about 200-300 μm, from about 300-600 μm, from about 300-550 μm, from about 350-450 μm, or variations of those ranges. The coating may be applied to the contact surface  42  of the insert  40  by any method known to skilled artisans such as baking or physical pressing under a compressive force. An exemplary set of baking conditions that may be appropriate for a graphite-based coating include a baking temperature from about 50° C. to about 500° C. and a baking time from about 5 to about 35 minutes. 
     The size and shape of the insert  40  may be varied for a multitude of reasons and purposes such as, for example, operational experience or product design requirements. For instance, in one embodiment, the insert  40  may be annularly disposed in the rotor cheek  24  so that immediate friction damping can occur no matter where the one or more brake pads  32  first engage the one or more braking surfaces  26 . It may also be substantially coextensive with the rotor cheek  24  in its radial dimension so as to provide an appreciable friction interface between the contact surface  42  of the insert and the interior surface  28 . Additional inserts of similar or dissimilar sizes and shapes may also be employed if desired in the rotor cheek. 
     In one exemplary embodiment, as shown in  FIG. 3 , the contact surface  42  of the insert  40  may be provided with surface features  46  arranged in a nonstochastic pattern so as to further minimize brake squeal by deadening sound transmission to inaudible levels through incoherent sound scattering. The surface features  46  may cover the entire contact surface  42  or they may cover only selective portions thereof. The term “nonstochastic” as utilized here refers to a predetermined pattern where the arrangement of the surface features  46  on the contact surface  42  in relation to one another may be controlled with a relatively high degree of precision. The size of the surface features  46  and the particular nonstochastic pattern employed can also be manipulated so as to deaden sound most effectively at certain target brake rotor  20  oscillation frequencies. Although not explicitly shown in  FIG. 3 , it should be noted that the opposite side of the insert  40  may, if desired, be similarly configured with the same or a different nonstochastic pattern of surface features. In fact, the insert  40  can be configured such that it comprises spatially correlated surface features on both of its contact surfaces; that is, each surface feature on one contact surface of the insert has a corresponding and axially aligned surface feature on the opposite contact surface. Or, on the other hand, the insert may be configured such the surface features on its contact surfaces are deliberately offset and thus not in axial alignment. As such the discussion of  FIG. 3  is meant to apply to both contact surfaces of the insert  40  even though only one surface is described for the sake of simplicity. 
     In this embodiment at least a portion of the insert  40  may comprise rounded surface features  46  raised above the nominal plane  44 —sometimes referred to as the measuring plane—of the contact surface  42 . In this configuration the surface features  46  of the contact surface  42  are in periodic contact with the interior surface  28  of the rotor cheek  24  for at least the purpose of experiencing the relative movement required for friction damping. The rounded surface features  46  may, in one embodiment, be hemispherical in shape and be defined by a radius D r  in the range of about 25 μm to about 1500 μm. The features  46  may also be arranged in a diamond pattern (as shown by the dotted diamond shape in  FIG. 3 ) to maintain staggering of the features  46  in both the circumferential and radial directions along the contact surface  42  of the insert  40 . This arrangement allows the surface features  46  to be equidistantly spaced apart from their immediately surrounding surface features  46  at center-to-center distances D c  that range from about 75 μm to about 4500 μm. The concentration of the equidistantly spaced hemispherical surface features  46  on the contact surface  42  can thus be varied from approximately 5.8×10 4  surface features/m 2  to approximately 2.1×10 8  surface features/m 2  by modifying the size and space parameters within the ranges just mentioned. And as a general guideline, brake squeal associated sound waves that are emitted from high frequency brake rotor  20  oscillations are dampened more effectively by higher concentrations of surface features  46  than lower concentrations. Similarly, lower concentrations of surface features  46  may be sufficient to effectively deaden brake squeal associated sound waves that are emitted from lower frequency brake rotor  20  oscillations. The particular and often optimized concentration of surface features  46  on the contact surface  42  of the insert  40  can be determined for a number of brake rotor  20  designs and applications through routine experimentation, trial-and-error iterative testing procedures, and/or the experiences of skilled artisans. 
     It is believed that the nonstochastic pattern of surface features  46  just described deadens sound through at least a couple mechanisms. First, the surface features  46  increase or extend the surface area of the contact surface  42  so that more sound deflection can occur. Moreover, the increased surface area provided by the surface features  42  stiffens the insert  40 . This added stiffening can help prevent the insert  40  form warping if it experiences nonhomogeneous thermal expansion during braking. Second, the nonstochastic pattern of the surface features  46  ensures that sound transmission is disrupted to produce randomly scattered sound waves that progressively weaken as they “bounce” between the precisely placed surface features  46  and interfere with one another. And third, the manufacture of the insert  40  and the brake rotor  20  may result in slightly imperfect microengagements between the interior surface  28  of the rotor cheek  24  and the contact surface  42  of the insert that can hamper vibration propagation. For example, if the brake rotor  20  is manufactured by being cast around the insert  40 , then it is possible that molten metal material that is to form the rotor cheek may solidify around the surface features  46  of the insert in a manner that results in the formation sporadic micro-air gaps therebetween. Such a phenomenon may be attributed to the surface tension properties of the molten metal and its related tendency to form a molten metal meniscus along the exposed surfaces of the surface features  46 . The presence of these micro-air gaps may provide at least two disparate sound transmission mediums—the solid insert material and air—that in combination can help diminish the overall propagation of sound waves through the rotor cheek  24 . 
     The rounded surface features  46  may be formed in a nonstochastic pattern by a variety of precision surface forming techniques. For example, in one embodiment, the surface features  46  may be formed on the contact surface  42  by a chemical etching procedure as known and understood by skilled artisans. Such a procedure generally involves selectively exposing a predetermined portion of a substrate to a chemical reagent capable of controllably dissolving the substrate material. The unexposed or protected portion of the substrate, on the other hand, generally remains unaffected by the chemical reagent. The end result of such a process is that a raised pattern forms in the surface of the substrate. 
     To form the rounded surface features  46  on the contact surface  42  of the insert  20  so that they that are hemispherically shaped and arranged in a diamond pattern, as described with reference to  FIG. 3 , an exemplary chemical etching process may first involve providing a substrate blank that may or may not be pre-formed in the shape of the insert  40 . The surface of the substrate blank that is to become the contact surface  42  may then be thoroughly cleaned and degreased to help to provide an adherent surface for a later-applied mask and to also ensure that substrate material is uniformly removed during etching. Next, a protective mask that is resistant to the particular chemical reagent that will be used during etching may be applied to the cleaned and degreased surface of the substrate blank. The mask may be designed to cover and protect the localities on the substrate blank that are to become the surface features  46  and to leave exposed those areas in between for removal. Suitable masks may include a variety of elastomers, plastics, or other materials known to skilled artisans that are capable of protecting the substrate blank, and they may be configured as tapes, a curable liquid, or a pre-formed template. 
     The masked substrate blank may now be exposed to the chemical reagent. At this juncture the chemical reagent attacks the portions of the substrate blank not protected by the mask in a manner that can be controlled by process variables such as, but not limited to, the concentration of the reagent, the exposure time, the temperature of the chemical reagent, and the rate of chemical reagent agitation. Commonly used chemical reagents include hydrochloric and nitric acids (steels), sodium hydroxide (aluminums), ferric chloride (stainless steels), and hydrofluoric acids (titaniums). Nevertheless, these and other chemical reagents and the types of materials they are able to appropriately dissolve during chemical etching are well known to skilled artisans and thus a further discussion of the chemical reagent/substrate material relationship is not necessary here. 
     The protective mask may be removed after the substrate blank is exposed to the chemical reagent by, for example, scraping, peeling, washing, or some other removal technique. The contact surface  42  with a nonstochastic pattern of surface features  46  is now provided on the substrate blank. This area may now be washed to remove any chemical reagent drag-out to ensure that additional substrate removal does not inadvertently continue. Next, the substrate blank may be formed or machined into the shape of the insert  20 , if necessary, and prepared for introduction into the brake rotor  20 . Such preparation may include additional machining such as surface polishing, and/or other insert preparation steps such as providing the graphite coating or other appropriate barrier for inhibiting wetting of the contacting surface  42  of the insert  40 . 
     A sand casting procedure may now be employed to form the brake rotor  20  such that the insert  40  is disposed in the rotor cheek  24 . At the outset of such a sand casting procedure, the insert  40  may be secured inside a brake-rotor-shaped mold cavity that is formed by a pair of sand die halves. A molten material that is to form the brake rotor  20  may then be introduced into the mold cavity around the insert  40  and allowed to solidify. The sand die halves can then be broken apart in order to remove the brake rotor  20  from the mold cavity. Additional machining or treatments, such as heat treatments, can now be performed on the brake rotor  20  to further advance it towards becoming operational in a motor vehicle. 
     While the rounded surface features  46  raised above the nominal plane  44  of this embodiment have been described as hemispherical in shape and arranged in a diamond pattern, it should be understood that other alternative designs are possible. For example, the rounded surface features  46  may be defined by a variety of cross-sections such as paraboloidal or elliptical. Also, the rounded surface features  46  may be arranged in other nonstochastic patterns such as a hexagonal pattern or one in which the surface features  46  are arranged in a plurality of concentric circles that are aligned in relation to one another in both the circumferential and radial directions along the contacting surface  42  of the insert  40 . Moreover, other precision surface forming techniques can be utilized to form the nonstochastic pattern of rounded surface features  46 . These techniques include forging, hot rolling, and knurling. 
       FIG. 4  shows an alternative exemplary embodiment that is similar in many respects to the embodiment of  FIG. 3  such that those similarities need not be repeated here. At least one difference in this embodiment is that at least a portion of the insert  140  may comprise a nonstochastic pattern of sharp-edged surface features  146  raised above the nominal plane  144  of the contact surface  142 . The sharp-edged surface features  146  may include four triangular sides that meet in an apex  150  which can assume a height of about 25 μm to about 1500 μm above the nominal plane  144 . The surface features  146  may also be arranged so that their apexes  150  define a diamond pattern similar to that of the previous embodiment; that is, the apexes  150  of the surface features  146  may be staggered in the radial and circumferential directions along the contact surface  142  and also be equidistantly spaced apart from one another at apex-to-apex distances D a  that range from about 75 μm to about 4500 μm. Possible methods for forming a nonstochastic pattern of the four-sided sharp-edged surface features  146  just described include knurling and photoetching. 
     While the sharp-edged surface features  146  raised above the nominal plane  144  of this embodiment have been described as including four sides, meeting in an apex  150 , and being arranged in a diamond pattern, it should be understood that other alternative designs are possible. For example, the sharp-edged surface features  46  may include three sides, or be truncated so that the top of the surface features  146  are flat instead of pointed. The sharp-edged surface features  146  may also be arranged in other known nonstochastic patterns including those mentioned in the previous embodiment. Other precision surface forming techniques that can be utilized to form the nonstochastic pattern of sharp-edged surface features  146  include precision laser and electron beam machining as disclosed in U.S. Pat. No. 5,789,066 to DeMare et al. 
       FIG. 5  shows an alternative exemplary embodiment that is similar in many respects to the embodiment of  FIG. 3  such that those similarities need not be repeated here. At least one difference in this embodiment is that at least a portion of the insert  240  may comprise a nonstochastic pattern of surface features  246  depressed below the nominal surface  244  of the insert  240 . The surface features  246  may be hemispherical in cross-section and defined by the same radius, spacing, concentration, and nonstochastic pattern arrangement parameters described with respect to the rounded surface features  46  of  FIG. 3 . Here, however, the depressed nature of the surface features  246  places the nominal plane  244  of the contact surface  242 —as opposed to the surface features in FIG.  3 —into contact with the interior surface  28  of the rotor cheek  24  for the purpose of experiencing the relative movement required for friction damping. 
     The surface features  246  of this embodiment may be formed in a nonstochastic pattern by a variety of precision surface forming techniques. For example, to form surface features  246  depressed below the nominal plate  244  that are hemispherical in cross-section and arranged in a diamond pattern on the contact surface  242 , a focused energy electron beam laser device may be utilized. A devise of this kind can generally emit electron beam pulses of very high energy at a substrate surface that is to become the contacting surface  242  of the insert  240 . The electron beam pulse quickly liquefies and then vaporizes the substrate at predetermined localities along the contacting surface  242 ; the result being hemispherical surface features  246  depressed into the contact surface  242  at those localities. To help arrange the surface features  246  in a nonstochastic diamond pattern, a suitable number of algorithms may be utilized to control the timing and placement of the electron beam pulses. An example of such an algorithm can be found in “ Focused Energy Beam Work Roll Surface Texturing Science and Technology ,” Journal of Materials Processing and Manufacturing Science, Volume 2, Number 1, July 1993, pp. 102-104, which relates to electron beam texturing of cylindrical tool steel surfaces that rotate beneath a pulsed electron beam. 
     While the surface features  246  depressed below the nominal plane  44  of this embodiment have been described as hemispherical in cross-section and arranged in a diamond pattern, it should be understood that other alternative designs are possible. For example, the surface features  246  may exhibit other cross-sections and be arranged in other nonstochastic patterns such as those mentioned in the embodiment of  FIG. 3 . Moreover, other precision surface forming techniques can be utilized to form the nonstochastic pattern of surface features  246  depressed below the nominal plane  244 . These techniques include an electric discharge device, a CO 2  laser, a Nd:YAG solid state laser, or mechanical techniques such as embossing. 
     The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention. Skilled artisans will understand that the subject matter of this disclosure can be used in a wide variety of devices. Such other devices include magnesium sub-systems in automobiles in which foam structures that contain plastic inserts having the nonstochastic patterned topographies described above could be used to deaden sound transmission through components formed of lightweight magnesium alloys.